[Federal Register Volume 89, Number 82 (Friday, April 26, 2024)]
[Rules and Regulations]
[Pages 32532-32757]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-07773]



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Vol. 89

Friday,

No. 82

April 26, 2024

Part II





Environmental Protection Agency





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40 CFR Parts 141 and 142





PFAS National Primary Drinking Water Regulation; Final Rule

  Federal Register / Vol. 89 , No. 82 / Friday, April 26, 2024 / Rules 
and Regulations  

[[Page 32532]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 141 and 142

[EPA-HQ-OW-2022-0114; FRL 8543-02-OW]
RIN 2040-AG18


PFAS National Primary Drinking Water Regulation

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: In March 2023, the U.S. Environmental Protection Agency (EPA) 
proposed and requested comment on the National Primary Drinking Water 
Regulation (NPDWR) and health-based Maximum Contaminant Level Goals 
(MCLGs) for six per- and polyfluoroalkyl substances (PFAS): 
perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), 
perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), 
hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX 
Chemicals), and perfluorobutane sulfonic acid (PFBS). After 
consideration of public comment and consistent with the provisions set 
forth under the Safe Drinking Water Act (SDWA), the EPA is finalizing 
NPDWRs for these six PFAS. Through this action, the EPA is finalizing 
MCLGs for PFOA and PFOS at zero. Considering feasibility, the EPA is 
promulgating individual Maximum Contaminant Levels (MCLs) for PFOA and 
PFOS at 4.0 nanograms per liter (ng/L) or parts per trillion (ppt). The 
EPA is also finalizing individual MCLGs and is promulgating individual 
MCLs for PFHxS, PFNA, and HFPO-DA at 10 ng/L. In addition to the 
individual MCLs for PFHxS, PFNA, and HFPO-DA, in consideration of the 
known toxic effects, dose additive health concerns and occurrence and 
likely co-occurrence in drinking water of these three PFAS, as well as 
PFBS, the EPA is finalizing a Hazard Index (HI) of 1 (unitless) as the 
MCLG and MCL for any mixture containing two or more of PFHxS, PFNA, 
HFPO-DA, and PFBS. Once fully implemented, the EPA estimates that the 
rule will prevent thousands of deaths and reduce tens of thousands of 
serious PFAS-attributable illnesses.

DATES: This final rule is effective on June 25, 2024. The incorporation 
by reference of certain publications listed in the rule is approved by 
the Director of the Federal Register as of June 25, 2024.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OW-2022-0114. All documents in the docket are 
listed on the http://www.regulations.gov website. Although listed in 
the index, some information is not publicly available, e.g., 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Certain other material, such as 
copyrighted material, is not placed on the internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available electronically through https://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT: Alexis Lan, Office of Ground Water and 
Drinking Water, Standards and Risk Management Division (Mail Code 
4607M), Environmental Protection Agency, 1200 Pennsylvania Avenue NW, 
Washington, DC 20460; telephone number 202-564-0841; email address: 
[email protected].

SUPPLEMENTARY INFORMATION: 

Executive Summary

    The Environmental Protection Agency (EPA) is issuing an adaptive 
and flexible National Primary Drinking Water Regulation (NPDWR) under 
the Safe Drinking Water Act (SDWA) to manage risks of per- and 
polyfluoroalkyl substances (PFAS) in drinking water. The EPA is 
establishing drinking water standards for six PFAS in this NPDWR to 
provide health protection against these individual and co-occurring 
PFAS in public water systems. The EPA's final rule represents data-
driven drinking water standards that are based on the best available 
science and meet the requirements of SDWA. For the six PFAS, the EPA 
considered PFAS health effects information, evidence supporting dose-
additive health concerns from co-occurring PFAS, as well as national 
and state data for the levels of multiple PFAS in finished drinking 
water. SDWA provides a framework for the EPA to regulate emerging 
contaminants of concern in drinking water. Under the statute, the EPA 
must act based on the ``best available'' science and information. Thus, 
the statute recognizes that the EPA may act in the face of imperfect 
information. It also provides a mechanism for the EPA to update 
standards as more science becomes available. For the PFAS covered by 
this rule, the EPA concluded that the state of the science and 
information has sufficiently advanced to the point to satisfy the 
statutory requirements and fulfill SDWA's purpose to protect public 
health by addressing contaminants in the nation's public water systems.
    PFAS are a large class of thousands of organic chemicals that have 
unique physical and chemical properties. These compounds are designed 
to be stable and non-reactive because of the applications in which they 
are used: certain industrial and manufacturing processes; stain and 
water repellants in clothing, carpets, and other consumer products, as 
well as certain types of fire-fighting foams. PFAS tend to break down 
slowly and persist in the environment, and consequently, they can 
accumulate in the environment and the human body over time. Current 
scientific research and available evidence have shown the potential for 
harmful human health effects after being exposed to some PFAS. Although 
some PFAS have been phased out of use in the United States, they are 
still found in the environment and in humans based on biomonitoring 
data.
    Drinking water is one of several ways people can be exposed to 
PFAS. The EPA's examination of drinking water data shows that different 
PFAS can often be found together and in varying combinations as 
mixtures. Additionally, decades of research demonstrates that exposure 
to mixtures of different chemicals can elicit dose-additive health 
effects: even if the individual chemicals are each present at levels 
considered ``safe,'' the mixture may cause significant adverse health 
effects. The high likelihood for different PFAS to co-occur in drinking 
water; the additive health concerns when present in mixtures; the 
diversity and sheer number of PFAS; and their general presence and 
persistence in the environment and the human body are reflective of the 
environmental and public health challenges the American public faces 
with PFAS, which poses a particular threat for overburdened communities 
that experience disproportionate environmental impacts. The final NPDWR 
includes:

1. Individual Maximum Contaminant Levels (MCLs)
    a. Perfluorooctanoic acid (PFOA) MCL = 4.0 nanograms per liter or 
parts per trillion (ng/L or ppt)
    b. Perfluorooctane sulfonic acid (PFOS) MCL = 4.0 ng/L
    c. Perfluorohexane sulfonic acid (PFHxS) MCL = 10 ng/L
    d. Perfluorononanoic acid (PFNA) MCL = 10 ng/L
    e. Hexafluoropropylene oxide dimer acid (HFPO-DA) MCL = 10 ng/L
    2. A Hazard Index MCL to account for dose-additive health effects 
for mixtures that could include two or more of four

[[Page 32533]]

PFAS (PFHxS, PFNA, HFPO-DA, and perfluorobutane sulfonic acid (PFBS)). 
The Hazard Index MCL defines when the combined levels of two or more of 
these four PFAS requires action. A PFAS mixture Hazard Index less than 
or equal to 1 (unitless) indicates a level at which no known or 
anticipated adverse effects on the health of persons occur and allows 
for an adequate margin of safety with respect to health risk associated 
with a mixture of PFAS in finished drinking water. A PFAS mixture 
Hazard Index greater than 1 (unitless) indicates an exceedance of the 
health protective level. To calculate the Hazard Index, a ratio is 
developed for each PFAS by dividing the measured level of the PFAS in 
drinking water by the level (in ng/L or ppt) below which adverse health 
effects are not likely to occur (i.e., the Health Based Water 
Concentration or HBWC). The HBWCs for each PFAS in the Hazard Index 
are:

a. PFHxS = 10 ng/L or ppt
b. PFNA = 10 ng/L
c. HFPO-DA = 10 ng/L
d. PFBS = 2,000 ng/L

    The individual PFAS ratios are then summed across the mixture to 
yield the Hazard Index MCL as follows:
[GRAPHIC] [TIFF OMITTED] TR26AP24.000

    Based on the administrative record for the final PFAS NPDWR and as 
discussed above, certain PFAS (including PFHxS, PFNA, HFPO-DA, and 
PFBS) have been shown to be toxicologically similar; i.e., elicit the 
same or similar profile of adverse effects in several biological organs 
and systems (see USEPA, 2000a; USEPA, 2007; USEPA, 2024a; USEPA, USEPA, 
2024c; and section IV.B of this preamble). Studies with PFAS and other 
classes of chemicals support the health-protective conclusion that 
chemicals that have similar observed adverse effects following 
individual exposure should be assumed to act in a dose-additive manner 
when in a mixture unless data demonstrate otherwise (USEPA, 2024a). 
Additionally, the record further supports that there is a substantial 
likelihood that PFBS, PFHxS, PFNA, and HFPO-DA co-occur as mixtures in 
drinking water at levels of public health concern (see USEPA, 2024b and 
sections VI.C and D of this preamble). Though the EPA is not 
promulgating an individual MCL or Maximum Contaminant Level Goal (MCLG) 
for PFBS at this time as it is for PFHxS, PFNA, and HFPO-DA (see 
section III.A of this preamble for specific discussion), based on these 
evaluations, the agency is establishing a Hazard Index MCL that 
addresses PFBS as part of mixtures where its co-occurrence with other 
PFAS (PFHxS, HFPO-DA, and/or PFNA) can affect health endpoints when 
present in these mixtures.
    The individual and Hazard Index MCLs are independently applicable 
for compliance purposes.
    Additionally, the EPA is finalizing important public ``right to 
know'' provisions of the EPA's SDWA regulations, specifically, public 
notification (PN) and Consumer Confidence Report (CCR) requirements. 
The changes under this rule will strengthen risk communication and 
education for the public when elevated levels of these PFAS are found. 
Finally, the EPA is finalizing monitoring and reporting requirements 
that enable public water systems (PWSs) and primacy agencies to 
implement and comply with the NPDWR.
    Consistent with the timelines set out under SDWA, PWSs are required 
to conduct their initial monitoring by April 26, 2027, and to conduct 
PN and include PFAS information in the CCR. After carefully considering 
public comment, the EPA is extending the compliance deadline for all 
systems nationwide to meet the MCL to allow additional time for capital 
improvements. As such, PWSs are required to make any necessary capital 
improvements and comply with the PFAS MCLs by April 26, 2029.
    As part of its Health Risk Reduction and Cost Analysis (HRRCA), the 
EPA evaluated quantifiable and nonquantifiable health risk reduction 
benefits and costs associated with the final NPDWR. At a two percent 
discount rate, the EPA estimates the quantifiable annual benefits of 
the final rule will be $1,549.40 million per year and the quantifiable 
costs of the rule will be $1,548.64 million per year. The EPA's 
quantified benefits are based on the agency's estimates that that there 
will be 29,858 fewer illnesses and 9,614 fewer deaths in the 
communities in the decades following actions to reduce PFAS levels in 
drinking water. While the modeled quantified net benefits are nearly at 
parity, under SDWA, the EPA must consider whether the costs of the rule 
are justified by the benefits based on all statutorily prescribed costs 
and benefits, not just the quantified costs and benefits (see SDWA 
1412(b)(3)(c)(i)).
    The EPA expects that the final rule will result in additional 
nonquantifiable costs, including costs with generally greater 
uncertainty, which the EPA has examined in quantified sensitivity 
analyses in the Economic Analysis for the final rule. First, the EPA 
had insufficient nationally representative data to precisely 
characterize occurrence of HFPO-DA, PFNA, and PFBS. In an effort to 
better consider and understand the costs associated with treatment of 
these regulated compounds at systems both with and without PFOA, PFOS 
and PFHxS occurrence in exceedance of the MCLs, the EPA performed a 
quantitative sensitivity analysis of the costs associated with Hazard 
Index and/or MCL exceedances resulting from HFPO-DA, PFNA, and PFBS. 
The EPA expects that the quantified national costs, which do not 
include HFPO-DA, PFNA, and PFBS treatment costs are marginally 
underestimated (on the order of 5 percent). Second, stakeholders have 
expressed concern to the EPA that a hazardous substance designation for 
certain PFAS may limit their disposal options for drinking water 
treatment residuals (e.g., spent media, concentrated waste streams) 
and/or potentially increase costs. The EPA has conducted a sensitivity 
analysis and found that should all water systems use hazardous waste 
disposal options national costs would increase by 7 percent.
    The EPA anticipates significant additional benefits that cannot be 
quantified, will result from avoided negative developmental, 
cardiovascular, liver, immune, endocrine, metabolic, reproductive, 
musculoskeletal, and carcinogenic effects as a result of reductions in 
the levels of the regulated PFAS and other co-removed contaminants. For 
example, elevated

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concentrations of both PFOA and PFOS negatively impact the immune and 
endocrine systems, impacts which the agency is unable to quantify at 
this time. As another example, the EPA assessed the developmental 
benefits associated with PFNA exposure reductions semi-quantitively in 
sensitivity analysis, and the analysis demonstrates significant 
additional benefits associated with reductions in PFNA. There are other 
nonquantifiable benefits for other PFNA health endpoints, and numerous 
endpoints for PFHxS, HFPO-DA, PFBS, and other PFAS that are anticipated 
to be removed as a result of the final NPDWR. Additionally, as a result 
of the ability for available treatment technologies to remove co-
occurring contaminants, there are benefits not quantified for removal 
of co-occurring contaminants for this regulation (e.g., certain 
pesticides, volatile organic compounds). Considering both quantifiable 
and nonquantifiable costs and benefits of the rule, the EPA is 
reaffirming the Administrator's determination at the time of proposal, 
that the quantifiable and nonquantifiable benefits of the final rule 
justify the quantifiable and nonquantifiable costs.
    To help communities on the frontlines of PFAS contamination, the 
passage of the Infrastructure Investment and Jobs Act (IIJA), also 
referred to as the Bipartisan Infrastructure Law (BIL), invests 
billions of dollars over a 5-year period. BIL appropriates over $11.7 
billion in the Drinking Water State Revolving Fund (DWSRF) General 
Supplemental; $4 billion to the DWSRF for Emerging Contaminants; and $5 
billion in grants to the Emerging Contaminants in Small or 
Disadvantaged Communities. These funds will assist many disadvantaged 
communities, small systems, and others with the costs of installation 
of treatment when it might otherwise be cost-challenging.

Table of Contents

I. General Information
    A. What are the EPA's final rule requirements?
    B. Does this action apply to me?
II. Background
    A. What are PFAS?
    B. Human Health Effects
    C. Statutory Authority
    D. Statutory Framework and PFAS Regulatory History
    E. Bipartisan Infrastructure Law
    F. EPA PFAS Strategic Roadmap
III. Final Regulatory Determinations for Additional PFAS
    A. Agency Findings
    B. Statutory Criterion 1--Adverse Health Effects
    C. Statutory Criterion 2--Occurrence
    D. Statutory Criterion 3--Meaningful Opportunity
    E. The EPA's Final Determination Summary
IV. MCLG Derivation
    A. MCLG Derivation for PFOA and PFOS
    B. MCLG Derivation for Additional PFAS
V. Maximum Contaminant Levels
    A. PFOA and PFOS
    B. PFAS Hazard Index: PFHxS, PFNA, HFPO-DA, and PFBS
    C. Individual MCLs: PFHxS, PFNA and HFPO-DA
VI. Occurrence
    A. UCMR 3
    B. State Drinking Water Data
    C. PFAS Co-Occurrence
    D. Occurrence Relative to the Hazard Index
    E. Occurrence Model
    F. Combining State Data With Model Output To Estimate National 
Exceedance of Either MCLs or Hazard Index
    G. UCMR 5 Partial Dataset Analysis
VII. Analytical Methods
    A. Analytical Methods and Practical Quantitation Levels (PQLs) 
for Regulated PFAS
VIII. Monitoring and Compliance Requirements
    A. What are the Monitoring Requirements?
    B. How are PWS Compliance and Violations Determined?
    C. Can Systems Use Previously Collected Data To Satisfy the 
Initial Monitoring Requirement?
    D. Can systems composite samples?
    E. Can primacy agencies grant monitoring waivers?
    F. When must systems complete initial monitoring?
    G. What are the laboratory certification requirements?
    H. Laboratory Quality Assurance/Quality Control
IX. Safe Drinking Water Act (SDWA) Right To Know Requirements
    A. What are the Consumer Confidence Report requirements?
    B. What are the Public Notification (PN) requirements?
X. Treatment Technologies
    A. What are the best available technologies?
    B. PFAS Co-Removal
    C. Management of Treatment Residuals
    D. What are Small System Compliance Technologies (SSCTs)?
XI. Rule Implementation and Enforcement
    A. What are the requirements for primacy?
    B. What are the record keeping requirements?
    C. What are the reporting requirements?
    D. Exemptions and Extensions
XII. Health Risk Reduction and Cost Analysis
    A. Public Comment on the Economic Analysis for the Proposed Rule 
and EPA Response
    B. Affected Entities and Major Data Sources Used To Develop the 
Baseline Water System Characterization
    C. Overview of the Cost-Benefit Model
    D. Method for Estimating Costs
    E. Nonquantifiable Costs of the Final Rule
    F. Method for Estimating Benefits
    G. Nonquantifiable Benefits of PFOA and PFOS Exposure Reduction
    H. Nonquantifiable Benefits of Removal of PFAS Included in the 
Final Regulation and Co-Removed PFAS
    I. Benefits Resulting From Disinfection By-Product Co-Removal
    J. Comparison of Costs and Benefits
    K. Quantified Uncertainties in the Economic Analysis
XIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 14094 Modernizing Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act of 1995
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations and Executive Order 14096: Revitalizing Our Nation's 
Commitment to Environmental Justice for All
    K. Consultations With the Science Advisory Board, National 
Drinking Water Advisory Council, and the Secretary of Health and 
Human Services
    L. Congressional Review Act (CRA)
XIV. Severability
XV. Incorporation by Reference
XVI. References

I. General Information

A. What are the EPA's final rule requirements?

    The Safe Drinking Water Act (SDWA) provides a framework for the 
Environmental Protection Agency (EPA) to regulate emerging contaminants 
of concern in drinking water. Under the statute, the EPA may act based 
on the ``best available'' science and information. Thus, the statute 
recognizes that the EPA may act in the face of imperfect information 
and provides a mechanism for the EPA to update standards as more 
science becomes available. For the per- and polyfluoroalkyl substances 
(PFAS) covered by this rule, the EPA concluded that the state of the 
science and information has sufficiently advanced to the point to 
satisfy the statutory requirements and fulfill SDWA's purpose to 
protect public health by addressing contaminants in the nation's public 
water systems. In this final action, the EPA is finalizing the PFAS 
National Primary Drinking Water Regulation (NPDWR) that is based upon 
the best available peer-reviewed

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science. The final NPDWR for PFAS establishes Maximum Contaminant Level 
Goals (MCLGs) and enforceable Maximum Contaminant Levels (MCLs) for six 
PFAS compounds: perfluorooctanoic acid (PFOA), perfluorooctane sulfonic 
acid (PFOS), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic 
acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly 
known as GenX Chemicals), and perfluorobutane sulfonic acid (PFBS). The 
final rule requirements and references to where additional discussion 
can be found on these topics are summarized here:
    The EPA is finalizing MCLGs for PFOA and PFOS at zero (0) and 
enforceable MCLs for PFOA and PFOS at 4.0 ng/L (ng/L or ppt). Please 
see section IV of this preamble on the MCLG derivation for PFOA and 
PFOS. Additionally, please see section V of this preamble for 
discussion on the MCL for PFOA and PFOS.
    The EPA is finalizing individual regulatory determinations to 
regulate PFHxS, PFNA, and HFPO-DA (commonly known as ``GenX 
Chemicals''). The EPA is deferring the individual regulatory 
determination to regulate PFBS in drinking water. Concurrent with the 
final determinations, the EPA is promulgating individual MCLGs and MCLs 
for PFHxS, PFNA, and HFPO-DA at 10 ng/L each.
    Additionally, the EPA is finalizing a regulatory determination for 
mixtures of PFHxS, PFNA, HFPO-DA, and PFBS due to their substantial 
likelihood for co-occurrence and dose-additive health concerns when 
present as a mixture in drinking water. Concurrent with this final 
determination, the EPA is finalizing a Hazard Index (HI) of 1 as the 
MCLG and enforceable MCL to address mixtures of PFHxS, PFNA, HFPO-DA, 
and PFBS where they co-occur in drinking water. Please see section III 
of this preamble for discussion on the EPA's final regulatory 
determinations; section IV of this preamble for discussion on the MCLG 
derivation for these additional compounds; and section V of this 
preamble for a discussion on the final MCLs.
    This action also lists feasible technologies for public water 
systems (PWSs) that can be used to comply with the MCLs. The EPA notes 
that systems are not required to use the listed technologies to meet 
the MCL; rather, the MCL is a numeric regulatory limit systems must 
meet that is developed while considering treatment feasibility and 
cost. Please see section X for additional discussion on feasible 
treatment technologies.
    The EPA is finalizing SDWA Right-to-Know requirements for the final 
rule, including Consumer Confidence Report (CCR) and Public 
Notification (PN) requirements. Community water systems (CWSs) must 
prepare and deliver to its customers an annual CCR in accordance with 
40 CFR part 141, subpart O. Under this rule, CWSs will be required to 
report detected PFAS in their CCRs and provide health effects language 
in the case of MCL violations. Additionally, under the final rule, MCL 
violations require Tier 2 public notification, or notification provided 
as soon as practicable but no later than 30 days after a system learns 
of the violation, as per 40 CFR 141.203. Additionally, monitoring and 
testing procedure violations require Tier 3 notification, or notice no 
later than one year after the system learns of the violation. Please 
see section IX of this preamble for additional discussion on SDWA 
Right-to-Know requirements.
    Additionally, the EPA is finalizing monitoring and reporting 
requirements for PWSs to comply with the NPDWR. PWSs are required to 
sample each EP using a monitoring regime generally based on the EPA's 
Standard Monitoring Framework (SMF) for Synthetic Organic Contaminants 
(SOCs). As a part of these requirements, to establish baseline levels 
of regulated PFAS, water systems must complete initial monitoring 
within three years following rule promulgation and/or use results of 
recent, previously acquired monitoring to satisfy the initial 
monitoring requirements. Following initial monitoring, beginning three 
years following rule promulgation, to demonstrate that finished 
drinking water does not exceed the MCLs for regulated PFAS, PWSs will 
be required to conduct compliance monitoring for all regulated PFAS at 
a frequency specifically based on sample results. Compliance with the 
NPDWRs will be based on analytical results obtained at each sampling 
point. PWSs are required to report to primacy agencies the results of 
all initial and compliance monitoring to ensure compliance with the 
NPDWRs. Please see section VIII of this preamble for additional 
discussion on these requirements.
    Finally, the EPA is exercising its authority under SDWA section 
1412(b)(10) to implement a nationwide capital improvement extension to 
comply with the MCL. All systems must comply with the MCLs by April 26, 
2029. All systems must comply with all other requirements of the NPDWR, 
including initial monitoring, by April 26, 2027. For additional 
discussion on extensions and exemptions, please see section XI.

B. Does this action apply to me?

    Entities regulated by this action are CWSs and non-transient non-
community water systems (NTNCWSs). A PWS, as defined in 40 CFR 141.2, 
provides water to the public for human consumption through pipes or 
``other constructed conveyances, if such system has at least fifteen 
service connections or regularly serves an average of at least twenty-
five individuals daily at least 60 days out of the year.'' A PWS is 
either a CWS or a non-community water system (NCWS). A CWS, as defined 
in Sec.  141.2, is ``a public water system which serves at least 
fifteen service connections used by year-round residents or regularly 
serves at least twenty-five year-round residents.'' The definition in 
Sec.  141.2 for a NTNCWS is ``a public water system that is not a [CWS] 
and that regularly serves at least 25 of the same persons over 6 months 
per year.'' The following table provides examples of the regulated 
entities under this rule:

------------------------------------------------------------------------
                                      Examples of potentially affected
             Category                             entities
------------------------------------------------------------------------
Public water systems..............  CWSs; NTNCWSs.
State and Tribal agencies.........  Agencies responsible for drinking
                                     water regulatory development and
                                     enforcement.
------------------------------------------------------------------------

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be regulated by this 
action. This table includes the types of entities that the EPA is now 
aware could potentially be regulated by this action. To determine 
whether your entity is regulated by this action, this final rule should 
be carefully examined. If you have questions regarding the 
applicability of this action to a particular entity, consult the person 
listed in the FOR FURTHER INFORMATION CONTACT section.
    All new systems that begin operation after, or systems that use a 
new source of water after, April 26, 2024, must demonstrate compliance 
with the MCLs

[[Page 32536]]

within a period of time specified by the Primacy Agency. The EPA has 
defined in 40 CFR chapter I, subchapter D, part 141, Sec.  141.2, a 
wholesale system as a PWS that supplies finished PWSs and a consecutive 
system as a PWS that buys or otherwise receives some or all its 
finished water from a wholesale system. In this action, the EPA 
reiterates that all CWS and NTNCWS must comply with this regulation. 
This includes consecutive CWS and NTNCWS systems; however, the 
requirements these consecutive systems must implement to comply with 
the regulation may be, and often are, much less extensive. For finished 
water that is provided through a system interconnection, the wholesale 
systems will be responsible for conducting the monitoring requirements 
at the entry point (EP) to the distribution system. The final 
regulation does not require that any monitoring be conducted at a 
system interconnection point. Where a violation does occur, the 
wholesale system must notify any consecutive systems of this violation 
and it is the responsibility of the consecutive system to provide PN to 
their customers pursuant to Sec.  141.201(c)(1). In addition, wholesale 
systems must also provide information in Subpart O to consecutive 
systems for developing CCRs (Sec.  141.201(c)(1)). Consecutive systems 
are responsible for providing their customers with the reports (Sec.  
141.153(a)).

II. Background

A. What are PFAS?

    Per- and polyfluoroalkyl substances (PFAS) are a large class of 
thousands of synthetic chemicals that have been in use in the United 
States and around the world since the 1940s (USEPA, 2018a). The ability 
for PFAS to withstand heat and repel water and stains makes them useful 
in a wide variety of consumer, commercial, and industrial products, and 
in the manufacturing of other products and chemicals. This rule applies 
directly to six specific PFAS: perfluorooctanoic acid (PFOA), 
perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), 
hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX 
Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane 
sulfonic acid (PFBS). Due to their widespread use, physicochemical 
properties, and prolonged persistence, many PFAS co-occur in air, 
water, ice, and soil, and in organisms, such as humans and wildlife. 
Exposure to some PFAS can lead to bioaccumulation in tissues and blood 
of aquatic as well as terrestrial organisms, including humans (Domingo 
and Nadal, 2019; Fromme et al., 2009). Pregnant and lactating women, as 
well as infants and children, may be more sensitive to the harmful 
effects of certain PFAS, such as PFOA, PFOS, PFNA, and PFBS. For 
example, studies indicate that PFOA and PFOS exposure above certain 
levels may result in adverse health effects, including developmental 
effects to fetuses during pregnancy or to breast- or formula-fed 
infants, increased risk for certain cancers, and negative immunological 
effects, among others (USEPA, 2024c; USEPA, 2024d). It has been 
documented that exposure to other PFAS are associated with a range of 
adverse health effects (USEPA, 2021a; USEPA, 2021b; ATSDR, 2021; NASEM, 
2022).
    The Environmental Protection Agency (EPA) is aware that PFAS still 
enter the environment and there are viable pathways for human exposure. 
Most United States production of PFOA, PFOS, and PFNA, along with other 
long-chain PFAS, was phased out and then generally replaced by 
production of PFHxS, HFPO-DA, PFBS, and other PFAS. The EPA is also 
aware of ongoing use of PFOA, PFOS, PFNA, and other long-chain PFAS 
(USEPA, 2000b; ATSDR, 2021). Long-chain PFAS are typically defined as 
including perfluoroalkyl sulfonic acids containing >= 6 carbons, and 
perfluoroalkyl carboxylic acids with >=7 carbons. While domestic 
production and import of PFOA has been phased out in the United States 
by the companies participating in the 2010/2015 PFOA Stewardship 
Program, small quantities of PFOA may be produced, imported, and used 
by companies not participating in the PFOA Stewardship Program (USEPA, 
2021c). The EPA is also aware of ongoing use of PFAS available from 
existing stocks or newly introduced via imports (see USEPA, 2022a). 
Additionally, the environmental persistence of these chemicals and 
formation as degradation products from other compounds may contribute 
to their ongoing release in the environment (ATSDR, 2021).
    The six PFAS in this rule and their relevant Chemical Abstract 
Service registry numbers (CASRNs) are:

 PFOA (C8F15O2-; 
CASRN: 45285-51-6)
 PFOS (C8F17SO3-; 
CASRN: 45298-90-6)
 PFHxS (C6F13SO3-; 
CASRN: 108427-53-8)
 PFNA (C9F17O2-; 
CASRN: 72007-68-2)
 HFPO-DA (C6F11O3-; 
CASRN: 122499-17-6)
 PFBS (C4F9SO3-; 
CASRN: 45187-15-3)

    These PFAS may exist in multiple forms, such as isomers or 
associated salts, and each form may have a separate CAS registry number 
or no CASRN at all. Additionally, these compounds have various names 
under different classification systems. However, at environmentally 
relevant pHs, these PFAS are expected to dissociate in water to their 
anionic (negatively charged) forms. For instance, International Union 
of Pure and Applied Chemistry substance 2,3,3,3-tetrafluoro-2-
(heptafluoropropoxy) propanoate (CASRN: 122499-17-6), also known as 
HFPO-DA, is an anionic molecule which has an ammonium salt (CASRN: 
62037-80-3), a conjugate acid (CASRN: 13252-13-6), a potassium salt 
(CASRN: 67118-55-2), and an acyl fluoride precursor (CASRN: 2062-98-8), 
among other variations. At environmentally relevant pHs these all 
dissociate into the propanoate/anion form (CASRN: 122499-17-6). Each 
PFAS listed has multiple variants with differing chemical connectivity, 
but the same molecular composition (known as isomers). Commonly, the 
isomeric composition of PFAS is categorized as `linear,' consisting of 
an unbranched alkyl chain, or `branched,' encompassing a potentially 
diverse group of molecules including at least one, but potentially 
more, offshoots from the linear molecule. While broadly similar, 
isomeric molecules may have differences in chemical properties. This 
rule covers all salts, isomers and derivatives of the chemicals listed, 
including derivatives other than the anionic form which might be 
created or identified.

B. Human Health Effects

    The publicly available landscape of human epidemiological and 
experimental animal-based exposure-effect data from repeat-dose studies 
across PFAS derive primarily from carboxylic and sulfonic acid species 
such as PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and PFBS (ATSDR, 2021; USEPA, 
2021a; USEPA, 2021b; USEPA, 2024c; USEPA, 2024d). Many other PFAS have 
some human health effects data available (Mahoney et al., 2022) and 
some PFAS, such as PFBS, HFPO-DA, PFNA, and PFHxS, have sufficient data 
that has allowed Federal agencies to publish toxicity assessments 
(USEPA, 2021a; USEPA, 2021b; USEPA, 2024c; USEPA, 2024d; ATSDR, 2021) 
and derive toxicity values (e.g., a reference dose), which is an 
estimate of daily exposure to the human population

[[Page 32537]]

(including sensitive populations) that is likely to be without an 
appreciable risk of deleterious effects during a lifetime). The adverse 
health effects associated with exposure to such PFAS include (but are 
not limited to): effects on the liver (e.g., liver cell death), growth 
and development (e.g., low birth weight), hormone levels, kidney, the 
immune system (reduced response to vaccines), lipid levels (e.g., high 
cholesterol), the nervous system, and reproduction, as well as 
increased risk of certain types of cancer.
    Exposure to PFAS may have disproportionate health effects on 
children. Adverse health effects relevant to children associated with 
exposure to some PFAS include developmental effects to fetuses during 
pregnancy or to breast-fed infants, cardiovascular effects, immune 
effects, endocrine effects, and reproductive effects. Additionally, 
PFAS are known to be transmitted to the fetus via the placenta and to 
the newborn, infant, and child via breast milk (USEPA, 2021a; USEPA, 
2021b; USEPA, 2024c; USEPA, 2024d; ATSDR, 2021).
    Please see sections III.B and IV of this rule for additional 
discussion on health considerations for the six PFAS the EPA is 
regulating in this document.

C. Statutory Authority

    Section 1412(b)(1)(A) of SDWA requires the EPA to establish 
National Primary Drinking Water Regulations (NPDWRs) for a contaminant 
where the Administrator determines that the contaminant: (1) may have 
an adverse effect on the health of persons; (2) is known to occur or 
there is a substantial likelihood that the contaminant will occur in 
PWSs (public water systems) with a frequency and at levels of public 
health concern; and (3) in the sole judgment of the Administrator, 
regulation of such contaminant presents a meaningful opportunity for 
health risk reduction for persons served by PWSs.

D. Statutory Framework and PFAS Regulatory History

    Section 1412(b)(1)(B)(i) of the Safe Drinking Water Act (SDWA) 
requires the EPA to publish a Contaminant Candidate List (CCL) every 
five years. The CCL is a list of contaminants that are known or 
anticipated to occur in PWSs, are not currently subject to any proposed 
or promulgated NPDWRs and may require regulation under the drinking 
water program. In some cases, developing the CCL may be the first step 
in evaluating drinking water contaminants. The EPA uses the CCL to 
identify priority contaminants for regulatory decision-making (i.e., 
regulatory determinations), and for data collection. Publishing a CCL 
does not impose any requirements on PWSs. The EPA included PFOA and 
PFOS on the third and fourth CCLs published in 2009 (USEPA, 2009a) and 
2016 (USEPA, 2016a). The EPA then included PFAS as a chemical group in 
its most recent list, the fifth CCL (CCL 5) (USEPA, 2022b). This group 
is inclusive of the PFAS the EPA is regulating through this action; 
however, the fifth CCL did not include PFOA and PFOS as they had 
already had final positive regulatory determinations completed for them 
in March 2021 (USEPA, 2021d).
    The EPA collects data on the CCL contaminants to better understand 
their potential health effects and to determine the levels at which 
they occur in PWSs. SDWA 1412(b)(1)(B)(ii) requires that, every five 
years and after considering public comments on a ``preliminary'' 
regulatory determination, the EPA issues a determination to regulate or 
not regulate at least five contaminants on each CCL. In addition, 
section 1412(b)(1)(B)(ii)(III) authorizes the EPA to make a 
determination to regulate a contaminant not listed on the CCL at any 
time so long as the contaminant meets the three statutory criteria 
based on available public health information. SDWA 1412(b)(1)(B)(iii) 
requires that ``each document setting forth the determination for a 
contaminant under clause (ii) shall be available for public comment at 
such time as the determination is published.'' To implement these 
requirements, the EPA issues preliminary regulatory determinations 
subject to public comment and then issues a final regulatory 
determination after consideration of public comment. Section 
1412(b)(1)(E) requires that the EPA propose an NPDWR no later than 24 
months after a final determination to regulate. The statute also 
authorizes the EPA to issue a proposed rule concurrent with a 
preliminary determination to regulate. The EPA must then promulgate a 
final regulation within 18 months of the proposal (which may be 
extended by 9 additional months).
    The EPA also implements a monitoring program for unregulated 
contaminants under SDWA 1445(a)(2) that requires the EPA to issue a 
list once every five years of priority unregulated contaminants to be 
monitored by PWSs. This monitoring is implemented through the 
Unregulated Contaminant Monitoring Rule (UCMR), which collects data 
from community water systems (CWSs) and non-transient community water 
systems (NTNCWSs) to better improve the EPA's understanding of the 
frequency of unregulated contaminants of concern occurring in the 
nation's drinking water systems and at what levels. The first four 
UCMRs collected data from a census of large water systems (serving more 
than 10,000 people) and from a statistically representative sample of 
small water systems (serving 10,000 or fewer people).
    Between 2013-2015, water systems collected monitoring data for six 
PFAS (PFOA, PFOS, PFHxS, PFNA, PFBS, and perfluoroheptanoic acid 
(PFHpA)) as part of the third UCMR (UCMR 3) monitoring program. The 
fifth UCMR (UCMR 5), published December 2021, requires sample 
collection and analysis for 29 PFAS, including PFOA, PFOS, PFHxS, PFNA, 
HFPO-DA, and PFBS, to occur between January 2023 and December 2025 
using drinking water analytical methods developed by the EPA. Section 
2021 of America's Water Infrastructure Act of 2018 (AWIA) (Pub. L. 115-
270) amended SDWA and specifies that, subject to the availability of 
the EPA appropriations for such purpose and sufficient laboratory 
capacity, the EPA must require all public water systems (PWSs) serving 
between 3,300 and 10,000 people to monitor and ensure that a nationally 
representative sample of systems serving fewer than 3,300 people 
monitor for the contaminants in UCMR 5 and future UCMR cycles. All 
large water systems continue to be required to participate in the UCMR 
program. Section VI of this preamble provides additional discussion on 
PFAS occurrence. While the complete UCMR 5 dataset was not available to 
inform this rule and thus not a basis for informing the agency's 
decisions for the final rule, the EPA acknowledges that the small 
subset of data released (7 percent of the total results that the EPA 
expects to receive) as of July 2023 confirms the EPA's conclusions 
supported by the extensive amount of data utilized in its UCMR 3, state 
data, and modelling analyses. This final rule allows utilities and 
primacy agencies to use the UCMR 5 data to support implementation of 
monitoring requirements. Sections VI and VIII of this preamble further 
discusses these occurrence analyses as well as monitoring and 
compliance requirements, respectively.
    After careful consideration of public comments, the EPA issued 
final regulatory determinations for contaminants on the fourth CCL (CCL 
4) in March of 2021 (USEPA, 2021d) which included determinations to 
regulate two contaminants, PFOA and PFOS, in drinking water. The EPA 
found that PFOA and PFOS may have

[[Page 32538]]

an adverse effect on the health of persons; that these contaminants are 
known to occur, or that there is a substantial likelihood that they 
will occur, in PWSs with a frequency and at levels that present a 
public health concern; and that regulation of PFOA and PFOS presents a 
meaningful opportunity for health risk reduction for persons served by 
PWSs. As discussed in the final Regulatory Determinations 4 Notice for 
CCL 4 contaminants (USEPA, 2021d) and the EPA's PFAS Strategic Roadmap 
(USEPA, 2022c), the agency has also evaluated additional PFAS chemicals 
for regulatory consideration as supported by the best available 
science. The agency finds that additional PFAS compounds also meet SDWA 
criteria for regulation. The EPA's regulatory determination for these 
additional PFAS is discussed in section III of this preamble.
    Section 1412(b)(1)(E) provides that the Administrator ``may publish 
such proposed regulation concurrent with the determination to 
regulate.'' The EPA interprets this provision as allowing concurrent 
processing of a preliminary determination with a proposed rule, not a 
final determination (as urged by some commenters--see responses in 
section III of this preamble). Under this interpretation, section 
1412(b)(1)(E) authorizes the EPA to issue a preliminary determination 
to regulate a contaminant and a proposed NPDWR addressing that 
contaminant concurrently and request public comment at the same time. 
This represents the only interpretation that accounts for the statutory 
language in context and is the only one that fulfills Congress's 
purpose of permitting the agency to adjust its stepwise processes where 
appropriate to avoid any unnecessary delay in regulating contaminants 
that meet the statutory criteria. To the extent the statute is 
ambiguous, the EPA's interpretation is the best interpretation of this 
provision for these same reasons. As a result, this rule contains both 
a final determination to regulate four PFAS contaminants (individually 
and/or as part of a PFAS mixture), and regulations for those 
contaminants as well as the two PFAS contaminants (PFOA and PFOS) for 
which the EPA had already issued a final Regulatory Determination. The 
EPA developed an MCLG and an NPDWR for six PFAS compounds pursuant to 
the requirements under section 1412(b)(1)(B) of SDWA. The final Maximum 
Contaminant Level Goals (MCLGs) and NPDWR are discussed in more detail 
in the following section.

E. Bipartisan Infrastructure Law

    The passage of the Infrastructure Investment and Jobs Act (IIJA), 
often referred to as the Bipartisan Infrastructure Law or BIL, invests 
over $50 billion to improve drinking water, wastewater, and stormwater 
infrastructure--the single largest investment in water by the Federal 
Government. This historic investment specific to safe drinking water 
includes $11.7 billion in the Drinking Water State Revolving Fund 
(DWSRF) General Supplemental (referred to as BIL DWSRF General 
Supplemental); $4 billion to the Drinking Water SRF for Emerging 
Contaminants (referred to as BIL DWSRF EC); and $5 billion in grants 
for Emerging Contaminants in Small or Disadvantaged Communities 
(referred to as EC-SDC) from Federal fiscal years 2022 through 2026 
(USEPA, 2023a). For the BIL DWSRF General Supplemental and BIL DWSRF 
EC, states must provide 49% and 100%, respectively, as additional 
subsidization in the form of principal forgiveness and/or grants. The 
EC-SDC grant has no cost-share requirement. Together, these funds will 
assist many disadvantaged communities, small systems, and others with 
the costs of addressing emerging contaminants, like PFAS, when it might 
otherwise be cost-challenging. This financial assistance can be used to 
address emerging contaminants in drinking water through actions such as 
technical assistance, certain water quality testing, operator and 
contractor training and equipment, and treatment upgrades and 
expansion. Investments in these areas which will allow communities 
additional funding to meet their obligations under this regulation and 
help ensure protection from PFAS contamination of drinking water. The 
Drinking Water SRF can be used by water systems to reduce the public 
health concerns around PFAS in their drinking water and is already 
being successfully utilized. Additionally, to support BIL 
implementation, the EPA is offering water technical assistance 
(WaterTA) to help communities identify water challenges and solutions, 
build capacity, and develop application materials to access water 
infrastructure funding (USEPA, 2023b). The EPA collaborates with 
states, Tribes, territories, community partners, and other stakeholders 
with the goal of more communities with applications for Federal 
funding, quality water infrastructure, and reliable water services.

F. EPA PFAS Strategic Roadmap

    In October 2021, the EPA published the PFAS Strategic Roadmap (or 
Roadmap) that outlined the whole-of-agency approach to ``further the 
science and research, to restrict these dangerous chemicals from 
getting into the environment, and to immediately move to remediate the 
problem in communities across the country'' (USEPA, 2022c). The Roadmap 
offers timelines by which the EPA acts on key commitments the agency 
made toward addressing these contaminants in the environment, while 
continuing to safeguard public health. These include the EPA proposing 
to designate certain PFAS as Comprehensive Environmental Response, 
Compensation, and Liability Act (CERCLA) hazardous substances; issuing 
advance notice of proposed rulemakings on various PFAS under CERCLA; 
and issuing updated guidance on destroying and disposing of certain 
PFAS and PFAS-containing materials. Additionally, the EPA is issued a 
memorandum to states in December 2022 that provides direction on how to 
use the National Pollutant Discharge Elimination System (NPDES) program 
to protect against PFAS (USEPA, 2022d; USEPA, 2022e). The EPA also 
announced revisions to several Effluent Limitation Guidelines (ELGs) 
including, Organic Chemical, Plastic, Synthetic Fibers manufacturing, 
Metal Finishing & Electroplating, and Landfills to address PFAS 
discharge from these point source categories. These ELGs collectively 
will, if finalized, restrict and reduce PFAS discharges to waterways 
used as sources for drinking water. The EPA is taking numerous other 
actions to advance our ability to understand and effectively protect 
people from PFAS, such as the October 11, 2023, rule finalized under 
the Toxic Substances Control Act (TSCA) that will provide the EPA, its 
partners, and the public with a dataset of PFAS manufactured and used 
in the United States. The rule requires all manufacturers (including 
importers) of PFAS and PFAS-containing articles in any year since 2011 
to report information to the extent known or reasonably ascertainable: 
chemical identity, uses, volumes made and processed, byproducts, 
environmental and health effects, worker exposure, and disposal to the 
EPA. With this final NPDWR, the EPA is delivering on another key goal 
in the Roadmap to ``establish a National Primary Drinking Water 
Regulation'' for PFAS. This rule will protect the American people 
directly from everyday PFAS exposures that might otherwise occur from 
PFAS-contaminated drinking water,

[[Page 32539]]

complementing the many other actions in the Roadmap to protect public 
health and the environment from PFAS.

III. Final Regulatory Determinations for Additional PFAS

A. Agency Findings

    As noted earlier, in 2021, the EPA made a determination to regulate 
two per- and polyfluoroalkyl substances--perfluorooctanoic acid (PFOA) 
and perfluorooctane sulfonic acid (PFOS)--in drinking water under the 
Safe Drinking Water Act. This section describes the EPA's regulatory 
determination findings with respect to three additional PFAS and 
mixtures of four PFAS.
    Pursuant to sections 1412(b)(1)(A) and 1412(b)(1)(B)(ii)(II) of 
SDWA, the EPA is making a final determination to individually regulate 
as contaminants PFHxS, PFNA, and HFPO-DA and is publishing Maximum 
Contaminant Level Goals (MCLGs) and promulgating National Primary 
Drinking Water Regulations (NPDWRs) for these compounds individually. 
Under this authority, the EPA is also making a final determination to 
regulate as a contaminant a mixture of two or more of the following: 
perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid 
(HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic 
acid (PFHxS), and perfluorobutane sulfonic acid (PFBS), and is 
publishing an MCLG and promulgating an NPDWR for mixtures of these 
compounds. The agency has determined that PFHxS, PFNA, and HFPO-DA may 
have individual adverse health effects, and any mixture of these three 
PFAS and PFBS may also have dose-additive adverse effects on the health 
of persons; that there is a substantial likelihood that PFHxS, PFNA, 
and HFPO-DA occur individually with a frequency and at levels of public 
health concern and that mixtures of these three PFAS and PFBS occur and 
co-occur in public water systems (PWSs) with a frequency and at levels 
of public health concern; and that, in the sole judgment of the 
Administrator, individual regulation of PFHxS, PFNA, and HFPO-DA, and 
regulation of mixtures of these three PFAS and PFBS, presents a 
meaningful opportunity for health risk reduction for persons served by 
PWSs. The EPA refers to ``mixtures'' in its regulatory determinations 
to make clear that its determinations cover all the combinations of 
PFHxS, PFNA, HFPO-DA, and PFBS that could co-occur in a mixture but 
that each regulated mixture is itself a contaminant.
    While the final determination includes mixtures of PFBS in 
combinations with PFHxS, HFPO-DA, and PFNA, the EPA is deferring the 
final individual regulatory determination for PFBS to further evaluate 
it individually under the three SDWA regulatory determination criteria; 
consequently, the agency is not promulgating an individual MCLG or 
NPDWR for PFBS in this action. The EPA is deferring its final 
individual regulatory determination because after considering the 
public comments, the EPA has decided to further consider whether 
occurrence information supports a finding that there is a substantial 
likelihood that PFBS will individually occur in public water systems 
and at levels of health concern. However, as stated previously, when 
evaluating PFBS in mixtures combinations with PFHxS, PFNA, and/or HFPO-
DA, the EPA has determined that based on the best available information 
it does meet all three statutory criteria for regulation when a part of 
these mixtures, including that it is anticipated to have dose-additive 
adverse health effects (see sections III.B and IV.B.1), there is a 
substantial likelihood of its co-occurrence in combinations with PFHxS, 
PFNA, and/or HFPO-DA with a frequency and at levels of public health 
concern (see sections III.C, VI.C, VI.D, and USEPA 2024b), and there is 
a meaningful opportunity for health risk reduction by regulating 
mixture combinations of these four PFAS (see section III.D of this 
preamble). Hence, although the agency is deferring the individual final 
regulatory determination for PFBS, it is included in the final 
determination to regulate mixture combinations containing two or more 
of PFHxS, PFNA, HFPO-DA, and PFBS.
    This section describes the best available science and public health 
information used by the agency to support the regulatory 
determinations. The MCLGs and NPDWR, including the MCLs, are discussed 
further in sections IV and V of this preamble.
1. Proposal
    The agency proposed preliminary determinations to regulate PFHxS, 
PFNA, HFPO-DA, and PFBS individually, and to regulate mixtures of these 
four PFAS contaminants, in drinking water. In the proposal, the agency 
concluded that PFHxS, PFNA, HFPO-DA, and PFBS, and mixtures of these 
PFAS, may cause adverse effects on the health of persons; there is a 
substantial likelihood that they will occur and co-occur in PWSs with a 
frequency and at levels of public health concern, particularly when 
considering them in a mixture; and in the sole judgment of the 
Administrator, regulation of PFHxS, PFNA, HFPO-DA, PFBS, and mixtures 
of these PFAS, presents a meaningful opportunity for health risk 
reductions for people served by PWSs.
    Within the proposal, the agency described section 1412(b)(1)(E) 
which provides that the Administrator may publish a proposed drinking 
water regulation concurrent ``with the determination to regulate.'' 
This provision authorizes a more expedited process by allowing the EPA 
to make concurrent the regulatory determination and rulemaking 
processes. As a result, for the proposal, the EPA interpreted the 
relevant reference to ``determination to regulate'' in section 
1412(b)(1)(E) as referring to the regulatory process in 
1412(b)(1)(B)(ii) that begins with a preliminary determination. Under 
this interpretation, section 1412(b)(1)(E) authorizes the EPA to issue 
a preliminary determination to regulate a contaminant and a proposed 
NPDWR addressing that contaminant concurrently and request public 
comment at the same time. This allows the EPA to act expeditiously 
where appropriate to issue a final determination to regulate 
concurrently with a final NPDWR to avoid delays to address contaminants 
that meet the statutory criteria.
    Additionally, as part of the proposal, the EPA explained why 
mixtures of PFAS qualify as a ``contaminant'' for purposes of section 
1412. SDWA section 1401(6) defines the term ``contaminant'' to mean 
``any physical, chemical or biological or radiological substance or 
matter in water.'' A mixture of two or more of the regulated PFAS 
qualifies as a ``contaminant'' because the mixture itself is ``any 
physical, chemical or biological or radiological substance or matter in 
water'' (emphasis added). Therefore, pursuant to the provisions 
outlined in section 1412(b)(1)(A) and 1412(b)(1)(B) of SDWA, the agency 
made a preliminary determination to regulate PFHxS, PFNA, HFPO-DA, 
PFBS, and any mixtures of these PFAS as a contaminant in drinking 
water. In the past and in this instance, the EPA's approach to 
regulating contaminant groups or mixtures under SDWA considers several 
factors, including health effects, similarities in physical and 
chemical properties, contaminant co-occurrence, ability for treatment 
technology co-removal, or where such a regulatory structure presents a 
meaningful opportunity to improve public health protection.

[[Page 32540]]

2. Summary of Major Public Comments and EPA Responses
    The EPA requested comments on its preliminary regulatory 
determinations for PFHxS, PFNA, HFPO-DA, and PFBS, and mixtures of 
these PFAS, including the agency's evaluation of the statutory criteria 
and any additional data or studies the EPA should consider that inform 
the preliminary regulatory determinations for these contaminants and 
their mixtures. The EPA also requested comment on its preliminary 
determination that regulation of PFHxS, PFNA, HFPO-DA, PFBS, and their 
mixtures, in addition to regulation of PFOA and PFOS, will also provide 
protection from PFAS (e.g., PFDA, PFDoA, PfHpA, PFHxA, PFHpS, PFPeS) 
that will not be regulated because the treatment technologies that 
would be used to ensure compliance for these PFAS are also effective in 
reducing concentrations of other unregulated PFAS.
    Many commenters expressed support for the EPA's preliminary 
regulatory determinations, including that the EPA has appropriately 
determined that the three statutory criteria for regulation have been 
met for all four contaminants and their mixtures using the best 
available information. Many other commenters did not agree that the 
agency presented sufficient information to make a preliminary 
determination to regulate PFHxS, PFNA, HFPO-DA, PFBS, and their 
mixtures, with some commenters recommending that that the agency 
withdraw the portion of the proposed rule associated with these four 
PFAS because in their view there is insufficient health effects and/or 
occurrence data at this time to support the EPA's action. For some of 
the four contaminants and their mixtures, a few commenters stated that 
the EPA had not met the statutory criteria for regulation or that data 
suggests a determination not to regulate is more appropriate. The EPA 
disagrees with these commenters because there is information to support 
individual regulation of PFHxS, PFNA, and HFPO-DA, as well as mixtures 
of these three PFAS and PFBS, based on the three statutory criteria 
(these findings are discussed in this section).
    As discussed earlier in this section, after consideration of all 
the public comments on this issue, the agency is deferring the 
determination to individually regulate PFBS for further evaluation 
under the statutory criteria. This determination is informed by public 
comment suggesting that the three statutory criteria for individual 
regulation of PFBS, particularly related to the occurrence criterion 
have not been met. The EPA will continue to consider other available 
occurrence information, including from UCMR 5, to determine whether the 
information supports a finding that there is a substantial likelihood 
that PFBS will individually occur in PWSs and at a level of public 
health concern. The record demonstrates that exposure to a mixture with 
PFBS may cause adverse health effects; that there is a substantial 
likelihood that PFBS co-occurs in mixtures with PFHxS, PFNA, and/or 
HFPO-DA in PWSs with a frequency and at levels of public health 
concern; and that, in the sole judgment of the Administrator, 
regulation of PFBS in mixtures with PFHxS, PFNA, and/or HFPO-DA 
presents a meaningful opportunity for health risk reduction for persons 
served by PWSs.
    Furthermore, the EPA is making a final determination to regulate 
PFHxS, PFNA, and HFPO-DA individually. While the EPA recognizes there 
will be additional health, occurrence, or other relevant information 
for these PFAS and others in the future, the EPA has determined that 
there is sufficient information to make a positive regulatory 
determination and the agency concludes that these three PFAS currently 
meet all of the statutory criteria for individual regulatory 
determination. Therefore, the agency is proceeding with making final 
determinations to regulate these contaminants both individually and as 
part of mixtures with PFBS and is concurrently promulgating individual 
MCLs for PFHxS, PFNA, and HFPO-DA (see section V of this preamble). For 
detailed information on the EPA's evaluation of the three regulatory 
determination statutory criteria for PFHxS, PFNA, and HFPO-DA 
individually and mixtures of these three PFAS and PFBS, as well as more 
specific comments and the EPA responses related to each of the three 
statutory criteria, see subsections III.B, C, and D.
    Several commenters requested that the EPA evaluate additional 
occurrence data to further inform its analysis for the regulatory 
determinations. In response to public comments on the proposal, the EPA 
evaluated updated and new occurrence data and the updates are presented 
within subsection III.C. and section VI of this preamble. These 
additional occurrence data further confirm that the SDWA criteria for 
regulation have been met for PFHxS, PFNA, and HFPO-DA as individual 
contaminants and for mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS.
    A couple of commenters questioned the EPA's rationale for selecting 
PFHxS, PFNA, HFPO-DA, and PFBS for regulation. The agency's process is 
allowable under SDWA and, as described within this section of the 
preamble, there is available health, occurrence, and other meaningful 
opportunity information for three PFAS (PFHxS, PFNA, and HFPO-DA) to 
meet the SDWA statutory criteria for regulation individually and four 
PFAS (PFHxS, PFNA, HFPO-DA, and PFBS) as a mixture. The EPA disagrees 
with commenters who suggested that the agency should not develop 
national regulations that differ from state-led actions. While states 
may establish drinking water standards for systems in their 
jurisdiction prior to regulation under SDWA, once an NPDWR is in place, 
SDWA 1413(a)(1) requires that states or Tribes adopt standards that are 
no less stringent than the NPDWR to maintain primacy. Moreover, the 
agency further notes that all four PFAS the EPA is regulating 
individually or as a mixture are currently regulated by multiple states 
as shown in table 4-17 of USEPA, 2024e.
    The EPA received several comments related to the EPA's 
interpretation in the proposal that the agency may, as it did here, 
issue a preliminary regulatory determination concurrent with a proposed 
NPDWR. Many stated that the EPA is authorized under SDWA to process 
these actions concurrently and agreed with the EPA's interpretation of 
the statute, noting that the EPA has followed all requirements under 
SDWA including notice and opportunity for public comment on both the 
preliminary regulatory determination and proposed NPDWR, and that 
simultaneous public comment periods are not precluded by SDWA. Several 
other commenters expressed disagreement with the EPA's interpretation. 
These dissenting commenters contend that the statute only allows the 
EPA to ``publish such proposed regulation concurrent with the 
determination to regulate'' (i.e., in their view, the final 
determination), not the ``preliminary determination to regulate.'' 
Moreover, some of these commenters further indicated that they believe 
the EPA's final determination to regulate must precede the EPA's 
proposed regulation. The EPA disagrees with commenters who stated that 
the EPA cannot issue a preliminary determination concurrent with a 
proposed NPDWR. Section 1412(b)(1)(e) states that ``[t]he Administrator 
shall propose the maximum contaminant level goals and national primary 
drinking water regulation for a contaminant not later than 24 months

[[Page 32541]]

after the determination to regulate under subparagraph (B), and may 
publish such proposed regulation concurrent with the determination to 
regulate'' (emphasis added). The EPA maintains its interpretation that 
``determination to regulate'' in the second phrase of 1412(b)(1)(E) 
allows for concurrent processing of a preliminary determination and 
proposed rule, not a final determination and proposed rule.
    The first clause of the provision provides an enforceable 24-month 
deadline for the EPA to issue a proposed rule once it has decided to 
regulate. Contrary to the suggestion of some commenters, the statutory 
language providing that the EPA ``shall'' propose an NPDWR ``not later 
than 24 months after the determination to regulate'' states when the 24 
months to issue a proposed rule begins, i.e., the deadline is 24 months 
after making a final determination to issue a proposed regulation. The 
phrase ``after the determination to regulate'' here simply identifies 
when SDWA's deadline begins to run; there is no textual or other 
indication in the language that Congress meant it to constitute the 
beginning of an exclusive 24-month window in which the EPA is permitted 
to propose an NPDWR. Further, though the EPA's reading is clear on the 
face of the provision, it is also supported by language elsewhere in 
SDWA illustrating that when Congress intends to provide a window for 
action (as opposed to a deadline for action) it knows how to do so 
clearly. In fact, Congress did so in this very provision when it 
required the EPA to ``publish a maximum contaminant level goal and 
promulgate a national primary drinking water regulation within 18 
months after the proposal thereof.'' See also, 42 U.S.C. 1448 
(providing, among other things, that petitions for review of the EPA 
regulations under SDWA ``shall be filed within the 45-day period 
beginning on the date of the promulgation of the regulation . . .'') 
(emphasis added). In addition, the phrase ``not later than,'' expressly 
acknowledges that the EPA may issue a proposed rule concurrent with a 
final determination. And because this language only provides a deadline 
without a beginning trigger, the language in the first clause of this 
provision would also not preclude the EPA from issuing a proposed rule 
at any time prior to the expiration of the 24 months after a final 
regulatory determination, including issuing the proposed rule on the 
same day as the preliminary regulatory determination.
    The second clause, which states that the Administrator ``may 
publish such proposed regulation concurrent with the determination to 
regulate'' should not be read to limit when the EPA can issue a 
proposed rule prior to a final determination. First, Congress's use of 
the phrase ``determination to regulate'' elsewhere in SDWA is not 
consistent, requiring the agency to discern its meaning based on 
statutory context. Second, reading ``determination to regulate'' to 
refer to a final determination would, without good reason, hinder 
Congress' goal in enacting this provision, to accelerate the EPA action 
under SDWA. Finally, the EPA's interpretation to allow for concurrent 
processes is fully consistent with, and indeed enhances, the 
deliberative stepwise process provided in the statute for regulating 
new contaminants.
    Language throughout the statute demonstrates that Congress did not 
use the term ``determination to regulate'' consistently. In fact, 
``preliminary determination'' only appears once in the entire 
provision, ``final determination'' is never used, and the remainder of 
the references simply refer to ``determination.'' Specifically, section 
1412(b)(1)(B)(ii)(I) expressly requires public comment on a 
``preliminary'' regulatory determination made as part of the 
contaminant candidate listing process. The rest of section 
1412(b)(1)(B)(ii) and (iii) as well as the title of the provision only 
refer to a ``determination to regulate'' or ``determination.'' For 
example, 1412(b)(1)(B)(iii) states that ``[e]ach document setting forth 
the determination for a contaminant under clause (ii) shall be 
available for public comment at such time as the determination is 
published.'' \1\ Although this provision only refers to a 
``determination for a contaminant under clause (ii),'' this language 
clearly refers to public comment on a preliminary determination and not 
a final determination to regulate. The EPA has interpretated 
``determination'' in this paragraph to refer to ``preliminary 
determination'' because that is the best interpretation to effectuate 
Congressional intent to provide public comment prior to issuing a final 
determination. The EPA has done the same with section 1412(b)(1)(E) 
here, as only a reading that allows for, in appropriate cases, 
concurrent processing of a preliminary determination to regulate and 
proposed NPDWR allows for rulemaking acceleration by the EPA as 
Congress envisioned. To the extent there is ambiguity, the EPA's 
reading of section 1412(b)(1)(E) is the best one to effectuate these 
purposes.
---------------------------------------------------------------------------

    \1\ Even the first clause of section 1412(b)(1)(E) setting the 
24-month deadlines use ``regulatory determination'' without further 
clarifying whether it is preliminary or final. Again, it is clear 
when viewed in context that the term refers to a final 
determination, as triggering a deadline to propose regulations on a 
preliminary decision to regulate would not be reasonable, as the 
agency may change its mind after reviewing publicv comment, 
obviating the need for a proposed NPDWR.
---------------------------------------------------------------------------

    The EPA could issue a proposed rule concurrent with a final 
determination; there is nothing in the statute or the APA that requires 
the EPA to wait. The SDWA gives the EPA 24 months to act after a final 
determination but does not require the agency to wait 24 months. The 
``no later than'' language in the first clause of section 
1412(b)(1)(E), expressly acknowledges that the EPA may issue a proposed 
rule concurrent with a final determination. Therefore, construing the 
second phrase of section 1412(b)(1)(E) simply to authorize the EPA to 
issue a proposed rule concurrent with a final determination renders 
that provision of the statute authorizing the EPA to publish such 
proposed regulation concurrent with the determination to regulate a 
nullity. The well-known tools of statutory construction direct the 
agencies and courts not to construe statutes so as to render Congress's 
language mere surplusage, yet that it is what commenters' 
interpretation would do. The EPA's construction is the one which gives 
meaning to that language.
    Moreover, the EPA's interpretation of ``determination to regulate'' 
in the phrase ``may publish such proposed regulation concurrent with 
the determination to regulation'' in section 1412(b)(1)(E) to be a 
preliminary determination best effectuates Congress' goal in enacting 
this provision, to accelerate the EPA action under SDWA when the EPA 
determines such a step is necessary and the EPA has, as it does here, a 
sufficient record to proceed with both regulatory determination and 
regulation actions concurrently. In addition to authorizing concurrent 
processes, Congress' intent to expedite regulatory determinations when 
necessary is evidenced more generally by the text and structure of 
section 1412(b)(1)(B)(ii). The statute contemplates regulatory 
determinations could be made as part of the 5-year cycle for the 
contaminant candidate list under section 1412(b)(1)(B)(ii)(I) but may 
also be made at any time under section 1412(b)(1)(B)(ii)(III). The fact 
that Congress provided the EPA with express authority to make a 
regulatory determination at any time is a recognition that the EPA may 
need to act expeditiously to address public

[[Page 32542]]

health concerns between the statutory periodic 5-year cycle. The EPA's 
interpretation of the relevant language in section 1412(b)(1)(E) best 
effectuates all provisions of the statute because simultaneous public 
processes for off-cycle regulatory determinations and NPDWRs allow for 
administrative efficiency that may be needed to address pressing public 
health concerns.
    Finally, the EPA's interpretation of the statute allowing for 
concurrent processes is fully consistent with the stepwise process for 
issuing an NPDWR set out by the statute. Here, the EPA provided for 
public comment on an extensive record for both the regulatory 
determinations and the proposed regulatory levels and it is not clear 
what further benefit would be provided by two separate public comment 
periods. This is especially true given the D.C. Circuit's ruling in 
NRDC v. Regan, 67 F.4th 397 (D.C. Cir 2023), which held that the EPA 
cannot withdraw a final determination to regulate a contaminant. Thus, 
even if the EPA were to provide two separate comment periods, the 
information provided on a proposed rule cannot be used to undo a final 
regulatory determination. Indeed, although not required by the statute, 
the EPA in proposing actions concurrently provides commenters with much 
more information to evaluate the preliminary regulatory determinations. 
This is because the EPA has provided not just the information to 
support the preliminary determinations to regulate but also the full 
rulemaking record and supporting risk, cost, occurrence, and benefit 
analysis that supports the proposed Maximum Contaminant Levels (MCLs). 
Further, the EPA has a much more comprehensive record for the 
regulatory determinations to ensure that the final determination, which 
cannot be withdrawn, is based on the comprehensive record provided by 
the rulemaking and Health Risk Reduction and Cost Analysis (HRRCA) 
development processes.
    The EPA received comments on its statutory authority to regulate 
mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS, specifically the 
agency's interpretation under section 1401(6) that a mixture of two or 
more contaminants also qualifies as the definition of a contaminant 
under SDWA since a mixture itself meets the same definition. A few 
commenters disagreed and contended that a mixture does not meet the 
definition of being a single contaminant under SDWA. The EPA disagrees 
with these commenters, as the SDWA definition of a contaminant does not 
specify that a contaminant is only a singular chemical. The SDWA 
definition is very broad, specifically stating that a contaminant is 
``any physical, chemical or biological or radiological substance or 
matter'' (emphasis added), with no specific description or requirement 
for how it is formed. Matter for example, by definition, is comprised 
of either pure substances or mixtures of pure substances. A pure 
substance is either an element or compound, which would include any 
PFAS chemical. The statute encompasses ``matter'' which is a broad term 
that includes mixtures and therefore definitionally includes PFAS 
mixtures, comprised of a combination of PFAS (chemical substances), as 
itself qualifying as a ``contaminant'' under SDWA. Moreover, other 
provisions of the statute, would be restricted in a manner inconsistent 
with Congressional intent if the EPA were to adopt the cabined approach 
to ``contaminant'' suggested by some commenters. For example, section 
1431 of SDWA provides important authority to the EPA to address 
imminent and substantial endangerment to drinking water supplies posed 
by ``a contaminant'' that is present in or threatened those supplies. 
Congress clearly intended this authority to be broad and remedial, but 
it would be significantly hampered if the EPA would be restricted to 
only addressing individual chemicals and not mixtures threatening a 
water supply. For these reasons, the EPA's interpretation of the 
definition of contaminant is the only reading that is consistent with 
the statutory definition and use of the term in context and at to the 
extent the definition of contaminant is ambiguous, the EPA's 
interpretation represents the best interpretation of that term. 
Finally, even if a mixture is considered a group, as some commenters 
suggest, Congress clearly contemplated that the EPA could regulate 
contaminants as groups. See H.R. Rep. No 93-1185 (1974), reprinted in 
1974 U.S.C.C.A.N. 6454, 6463-64) (noting the tens of thousands of 
chemical compounds in use commercially, with many more added each year, 
of which many will end up in the nation's drinking water and finding 
that ``[i]t is, of course, impossible for EPA to regulate each of these 
contaminants which may be harmful to health on a contaminant-by-
contaminant basis. Therefore, the Committee anticipates that the 
Administrator will establish primary drinking water regulations for 
some groups of contaminants, such as organic and asbestos.'') Thus, the 
EPA has the authority to regulate a mixture as a contaminant under 
SDWA.
    The commenters also suggested that the EPA has not followed its 
Supplementary Guidance for Conducting Health Risk Assessment of 
Chemical Mixtures (USEPA, 2000a), specifically that the agency did not 
use a ``sufficiently similar mixture'' where ``components and 
respective portions exist in approximately the same pattern'' and 
suggested that there has to be consistent co-occurrence of the mixture 
components. The EPA disagrees with these comments. It is not possible 
or necessary to use a whole-mixture approach for PFHxS, PFNA, HFPO-DA, 
and PFBS or a ``sufficiently similar mixture.'' Instead, the EPA is 
using a longstanding component-based mixture approach called the Hazard 
Index, which was endorsed in the context of assessing potential risk 
associated with PFAS mixtures by the Science Advisory Board (SAB) 
during its 2021 review of the EPA's Draft Framework for Estimating 
Noncancer Health Risks Associated with Mixtures of Per- and 
Polyfluoroalkyl Substances (PFAS) (USEPA, 2021e) (see section IV of 
this preamble). The goal of this component-based approach is to 
approximate what the whole-mixture toxicity would be if the whole 
mixture could be tested and relies on toxicity information for each 
individual component in a mixture (USEPA, 2000a). A whole-mixture 
approach for regulating these four PFAS in drinking water is not 
possible because it would entail developing a single toxicity value 
(e.g., a reference dose (RfD)) for one specific mixture of PFHxS, PFNA, 
HFPO-DA, and PFBS with defined proportions of each PFAS. Toxicity 
studies are typically conducted with only one test substance to isolate 
that particular substance's effects on the test organism, and whole-
mixture data are exceedingly rare. There are no known whole-mixture 
studies for PFHxS, PFNA, HFPO-DA, and PFBS, and even if they were 
available, the corresponding toxicity value (i.e., a single RfD for a 
specific mixture of these four PFAS) would only be directly applicable 
to that specific mixture. Thus, a more flexible approach that takes 
into account the four component PFAS in different combinations and at 
different concentrations (i.e., the Hazard Index approach) is 
necessary. The Hazard Index indicates risk from exposure to a mixture 
and is useful in this situation to ensure a health-protective MCLG in 
cases where the mixture is spatially and/or temporally variable. For a 
more detailed discussion on whole-mixture and component-based 
approaches for PFAS health assessment, please see the EPA's Framework 
for

[[Page 32543]]

Estimating Noncancer Health Risks Associated with Mixtures of Per- and 
Polyfluoroalkyl Substances (PFAS) (USEPA, 2024a).
    Many other commenters supported the EPA's interpretation of 
regulating a mixture as a ``contaminant'' that consists of a 
combination of certain PFAS, citing the EPA's broad authority under 
SDWA to set regulatory standards for groups of related contaminants and 
the EPA precedent for doing so under other NPDWRs including 
disinfection byproducts (DBPs; for total trihalomethanes [TTHMs] and 
the sum of five haloacetic acids [HAA5] (USEPA, 1979; USEPA, 2006a)), 
as well as radionuclides (USEPA, 2000c) and polychlorinated biphenyls 
(PCBs). The EPA also noted some of these examples within the proposed 
rule. One commenter disagreed that these previous EPA grouping 
approaches are applicable to the mixture of the four PFAS, noting that 
TTHMs and HAA5 are byproducts of the disinfection process and are the 
result of naturally occurring compounds reacting with the disinfectants 
used in drinking water treatment; thus, their formation cannot be 
controlled and is dependent on the presence and amount of disinfectant. 
As a result of these factors, measuring them as a class is required; 
however, the four PFAS are not byproducts, and the presence of one PFAS 
does not change the presence of the other PFAS. Moreover, the commenter 
provided that related to radionuclides, alpha particles are identical 
regardless of their origination and using this example for PFAS is not 
supported since the four PFAS are fundamentally different. The EPA 
disagrees with this commenter. As noted above, the SDWA definition of 
contaminant is very broad (``any physical, chemical or biological or 
radiological substance or matter'' (emphasis added)) with no 
limitations, specific description or requirement for how it is formed. 
The statute therefore easily encompasses a mixture, comprised of a 
combination of PFAS (chemical substances), as itself qualifying as a 
``contaminant'' under SDWA. Moreover, as also noted above, to the 
extent the mixture is considered a ``group,'' Congress clearly 
anticipated that the EPA would regulate contaminants by group. As a 
result, even if the PFAS ``group'' is different than other SDWA 
regulatory groupings, such a regulation is clearly authorized under the 
statute. Furthermore, it makes sense to treat these mixtures as a 
``contaminant'' because the four PFAS share similar characteristics: it 
is substantially likely that they co-occur; the same treatment 
technologies can be used for their removal; they are measured 
simultaneously using the same analytical methods; they have shared 
adverse health effects; and they have similar physical and chemical 
properties resulting in their environmental persistence.
3. The EPA's Final Determination
    The EPA is making determinations to regulate PFHxS, PFNA, and HFPO-
DA individually and to regulate mixtures of PFHxS, PFNA, HFPO-DA, and/
or PFBS. A mixture of PFHxS, PFNA, HFPO-DA, and PFBS can contain any 
two or more of these PFAS. The EPA refers to ``mixtures'' in its final 
regulatory determinations to make clear that its determinations cover 
all of the combinations of PFHxS, PFNA, HFPO-DA, and PFBS that could 
co-occur in a mixture but that any combination itself qualifies as a 
contaminant.
    In this preamble, as discussed earlier, the EPA is deferring the 
final determination to regulate PFBS individually to further evaluate 
the three criteria specified under SDWA 1412(b)(1)(A), particularly 
related to its individual known or likely occurrence, but is making a 
final determination to regulate PFBS as part of a mixture with PFHxS, 
PFNA, and/or HFPO-DA.
    To support the agency's regulatory determinations, the EPA 
carefully considered the public comments and examined health effects 
information from available final peer-reviewed human health assessments 
and studies, as well as drinking water monitoring data collected as 
part of the UCMR 3 and state-led monitoring efforts. The EPA finds that 
oral exposure to PFHxS, PFNA, and HFPO-DA individually, and 
combinations of these three PFAS and PFBS in mixtures, may result in a 
variety of adverse health effects, including similar or shared adverse 
effects on several biological systems including the endocrine, 
cardiovascular, developmental, immune, and hepatic systems (USEPA, 
2024f). Based on the shared toxicity types, exposure to PFHxS, PFNA, or 
HFPO-DA individually, or combinations of these three PFAS and PFBS in a 
mixture, is anticipated to affect common target organs, tissues, or 
systems to produce dose-additive effects from co-exposures. 
Additionally, based on the agency's evaluation of the best available 
science, including a review of updated data from state-led drinking 
water monitoring efforts discussed in subsection III.C of this 
preamble, the EPA finds that PFHxS, PFNA, and HFPO-DA each have a 
substantial likelihood to occur in finished drinking water and that 
these three PFAS and PFBS are also likely to co-occur in mixtures and 
result in increased total PFAS exposure above levels of public health 
concern. Therefore, as discussed further in this section, the agency is 
determining that:
     exposure to PFHxS, PFNA, or HFPO-DA individually, and any 
mixture of these three PFAS and PFBS, may have adverse effects on the 
health of persons;
     there is a substantial likelihood that PFHxS, PFNA, and 
HFPO-DA will occur and there is a substantial likelihood that 
combinations of these three PFAS plus PFBS will co-occur in mixtures in 
PWSs with a frequency and at levels of public health concern; and
     in the sole judgment of the Administrator, individual 
regulation of PFHxS, PFNA, and HFPO-DA, and mixtures of the three PFAS 
plus PFBS, presents a meaningful opportunity for health risk reductions 
for persons served by PWSs.
    The EPA is making a final individual regulatory determination for 
PFHxS, HFPO-DA, and PFNA and promulgating individual MCLGs and NPDWRs 
for PFHxS, HFPO-DA, and PFNA. These NPDWRs ensure public health 
protection when one of these PFAS occurs in isolation above their MCLs 
and also support risk communication efforts for utilities (see section 
V of this preamble for more information). The EPA is also making a 
final mixture regulatory determination and promulgating a Hazard Index 
MCLG and NPDWR for mixtures containing two or more of PFHxS, PFNA, 
HFPO-DA, and PFBS. The Hazard Index is a risk indicator and has been 
shown to be useful in chemical mixtures decision contexts (USEPA, 
2023c).\2\ Individual NPDWRs do not address dose additive risks from 
co-occurring PFAS. However, the Hazard Index NPDWR accounts for PFAS 
co-occurring in mixtures where the individual concentrations of one or 
more PFAS may not exceed their individual levels of public health 
concern, but the combined levels of these co-occurring PFAS result in 
an overall exceedance of the health-protective level. In this way, the 
Hazard Index NPDWR protects against dose-additive effects. This 
approach also recognizes that exposure to the PFAS included in the 
Hazard Index is associated with adverse health effects at differing 
potencies (e.g., the toxicity reference value for PFHxS is lower than

[[Page 32544]]

the one for PFBS) and that, regardless of these potency differences, 
all co-occurring PFAS are included in the hazard calculation (i.e., the 
health effects and presence of lower toxicity PFAS are neither ignored 
nor are they over-represented). Furthermore, the approach accounts for 
all the different potential combinations of these PFAS that represent a 
potential public health concern that would not be addressed if the EPA 
only finalized individual NPDWRs and considered individual PFAS in 
isolation.
---------------------------------------------------------------------------

    \2\ Some describe the Hazard Index as an indicator of potential 
hazard because it does not estimate the probability of an effect; 
others characterize the Hazard Index as an indicator of potential 
risk because the measure integrates both exposure and toxicity 
(USEPA 2000c; USEPA, 2023c).
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B. Statutory Criterion 1--Adverse Health Effects

    The agency finds that exposure to PFHxS, PFNA, and HFPO-DA 
individually, and any mixture of these three PFAS and PFBS, may have an 
adverse effect on the health of persons. Following is a discussion of 
health effects information for each of these four individual PFAS and 
the levels at which those health effects may be adverse. The agency 
developed health reference levels (HRLs) for PFHxS, PFNA, HFPO-DA, and 
PFBS as part of its effort to identify the adverse effects each 
contaminant may have on the health of persons. In this instance, the 
EPA identified the HRL as the level below which adverse health effects 
over a lifetime of exposure are not expected to occur, including for 
sensitive populations and life stages, and allows for an adequate 
margin of safety. The HRLs are also used as health-based water 
concentrations (HBWCs) in the calculation of the Hazard Index MCLG (see 
section IV).
1. PFHxS
    Studies have reported adverse health effects, including on the 
liver, thyroid, and development, after oral exposure to PFHxS (ATSDR, 
2021). For a detailed discussion on adverse effects associated with 
oral exposure to PFHxS, please see ATSDR (2021) and USEPA (2024f).
    The EPA derived the individual HRL/HBWC for PFHxS using a chronic 
reference value of 0.000002 (2E-06) mg/kg/day based on adverse thyroid 
effects (follicular epithelial hypertrophy/hyperplasia), a sensitive 
noncancer effect determined to be adverse and relevant to humans, 
observed in male rats after oral PFHxS exposure during adulthood 
(ATSDR, 2021; USEPA, 2024f). The EPA applied a bodyweight-adjusted 
drinking water intake (DWI-BW) exposure factor for adults within the 
general population (0.034 L/kg/day; 90th percentile direct and indirect 
consumption of community water, consumer-only two-day average, adults 
21 years and older) and a relative source contribution (RSC) of 0.20 to 
calculate the HRL/HBWC (USEPA, 2024f). The HRL/HBWC for PFHxS is 10 ng/
L which was used to evaluate individual occurrence of PFHxS for the 
final regulatory determination as discussed in section III.C of this 
preamble.
2. PFNA
    Studies have reported adverse health effects, including on 
development, reproduction, immune function, and the liver, after oral 
exposure to PFNA (ATSDR, 2021). For a detailed discussion of adverse 
effects associated with oral exposure to PFNA, please see ATSDR (2021) 
and USEPA (2024f).
    The EPA derived the HRL/HBWC for PFNA using a chronic reference 
value of 0.000003 (3E-06) mg/kg/day based on decreased body weight gain 
and impaired development (i.e., delayed eye opening, delayed sexual 
maturation) in mice born to mothers that were orally exposed to PFNA 
during gestation (with presumed continued indirect exposure of 
offspring via lactation) (ATSDR, 2021; USEPA, 2024f). These sensitive 
noncancer effects were determined to be adverse and relevant to humans 
(ATSDR, 2021; USEPA, 2024f). The EPA applied a DWI-BW exposure factor 
for lactating women (0.0469 L/kg/day; 90th percentile direct and 
indirect consumption of community water, consumer-only two-day average) 
and an RSC of 0.20 to calculate the HRL/HBWC (USEPA, 2024f). The HRL/
HBWC for PFNA is 10 ng/L which was used to evaluate individual 
occurrence of PFNA for the final regulatory determination as discussed 
in section III.C of this preamble.
3. HFPO-DA
    Animal toxicity studies have reported adverse health effects after 
oral HFPO-DA exposure, including liver and kidney toxicity and immune, 
hematological, reproductive, and developmental effects (USEPA, 2021b). 
The EPA determined that there is Suggestive Evidence of Carcinogenic 
Potential after oral exposure to HFPO-DA in humans, but the available 
data are insufficient to derive a cancer risk concentration for oral 
exposure to HFPO-DA. For a detailed discussion of adverse effects of 
oral exposure to HFPO-DA, please see USEPA (2021b).
    The most sensitive noncancer effects observed among the available 
data were the adverse effects on liver (e.g., increased relative liver 
weight, hepatocellular hypertrophy, apoptosis, and single-cell/focal 
necrosis), which were observed in both male and female mice and rats 
across a range of exposure durations and dose levels, including the 
lowest tested dose levels and shortest exposure durations. The EPA 
derived the HRL/HBWC for HFPO-DA from a chronic oral RfD of 0.000003 
(3E-06) mg/kg/day that is based on adverse liver effects, specifically 
a constellation of liver lesions including cytoplasmic alteration, 
single-cell and focal necrosis, and apoptosis, observed in parental 
female mice following oral exposure to HFPO-DA from pre-mating through 
day 20 of lactation (USEPA, 2021b). The EPA applied a DWI-BW exposure 
factor for lactating women (0.0469 L/kg/day; 90th percentile direct and 
indirect consumption of community water, consumer-only two-day average) 
and an RSC of 0.20 to calculate the HRL/HBWC (USEPA, 2024f). The HRL/
HBWC for HFPO-DA is 10 ng/L which was used to evaluate individual 
occurrence of HFPO-DA for the final regulatory determination as 
discussed in section III.C of this preamble.
4. PFBS
    Toxicity studies of oral PFBS exposure in animals have reported 
adverse health effects on development, as well as on the thyroid and 
kidneys (USEPA, 2021a). Human and animal studies evaluated other health 
effects following PFBS exposure including effects on the immune, 
reproductive, and hepatic systems and lipid and lipoprotein 
homeostasis, but the evidence was determined to be equivocal (USEPA, 
2021a). No studies evaluating the carcinogenicity of PFBS in humans or 
animals were identified. The EPA concluded that there is Inadequate 
Information to Assess Carcinogenic Potential for PFBS and its potassium 
salt (K + PFBS) by any route of exposure based on the EPA's Guidelines 
for Carcinogen Risk Assessment (USEPA, 2005a). For a detailed 
discussion on adverse effects after oral exposure to PFBS, please see 
USEPA (2021a).
    As noted previously, the agency is deferring the final individual 
regulatory determination for PFBS. For the purposes of evaluating PFBS 
in mixture combinations with PFHxS, PFNA, and HFPO-DA (see section 
III.B.5 of this preamble), the EPA derived the HRL/HBWC for PFBS from a 
chronic RfD of 0.0003 (3E-04) mg/kg/day that is based on adverse 
thyroid effects (decreased serum total thyroxine) observed in newborn 
mice following gestational exposure to the potassium salt of PFBS 
(USEPA, 2021a). The EPA applied a DWI-BW exposure factor for women of 
child-bearing age (0.0354 L/kg/day; 90th percentile direct and indirect 
consumption of community water, consumer-only two-day average) and an

[[Page 32545]]

RSC (relative score contribution) of 0.20 to calculate the HRL/HBWC 
(USEPA, 2024f). The HRL/HBWC for PFBS is 2000 ng/L.
5. Mixtures of PFHxS, PFNA, HFPO-DA, and PFBS
    Exposure to per- and polyfluoroalkyl acids (PFAAs), a subclass of 
PFAS that includes PFHxS, PFNA, HFPO-DA, and PFBS, can disrupt 
signaling of multiple biological pathways, resulting in a shared set of 
adverse effects, including effects on thyroid hormone levels, lipid 
synthesis and metabolism, development, and immune and liver function 
(ATSDR, 2021; EFSA et al., 2018; EFSA et al., 2020; USEPA, 2021a; 
USEPA, 2021b; USEPA, 2024f; see further discussion in section III.B.6.e 
of this preamble).
    Studies with PFAS and other classes of chemicals support the 
health-protective conclusion that chemicals that have similar observed 
adverse effects following individual exposure should be assumed to act 
in a dose-additive manner when in a mixture unless data demonstrate 
otherwise (USEPA, 2024a). Dose additivity means that the combined 
effect of the component chemicals in the mixture (in this case, PFHxS, 
PFNA, HFPO-DA, and/or PFBS) is equal to the sum of their individual 
doses or concentrations scaled for potency (USEPA, 2000a). In other 
words, exposure to these PFAS, at doses that individually would not 
likely result in adverse health effects, when combined in a mixture may 
result in adverse health effects. See additional discussion of PFAS 
dose additivity in section IV of this preamble.
    The EPA used a Hazard Index (HI) HRL of 1 (unitless) to evaluate 
co-occurrence of combinations PFHxS, PFNA, HFPO-DA, and PFBS in 
mixtures for the final regulatory determination as discussed in section 
III.C of this preamble. For technical details on the Hazard Index 
approach, please see section IV of this preamble, USEPA (2024a), and 
USEPA (2024f).
6. Summary of Major Public Comments and EPA Responses
    Commenters referred to the HRLs and HBWCs interchangeably, so 
comments related to those topics are addressed in this section. (Other 
comments related to the MCLGs are addressed in section IV of this 
preamble.)
    Many commenters expressed support for the EPA's derivation of HRLs/
HBWCs and use of best available peer-reviewed science, specifically the 
use of the final, most recently published Agency for Toxic Substances 
and Disease Registry (ATSDR) minimal risk levels for PFHxS and PFNA as 
chronic reference values. Other commenters criticized the EPA for using 
ATSDR minimal risk levels and stated that they are inappropriate for 
SDWA rulemaking.
    The EPA finds that the ATSDR minimal risk levels for PFHxS and PFNA 
currently represent the best available, peer-reviewed science for these 
chemicals. SDWA specifies that agency actions must rely on ``the best 
available, peer-reviewed science and supporting studies conducted in 
accordance with sound and objective scientific practices.'' At this 
time, the 2021 ATSDR Toxicological Profile for Perfluoroalkyls, which 
covers 10 PFAS including PFHxS and PFNA, represents the best available 
peer-reviewed scientific information on the human health effects of 
PFHxS and PFNA. ATSDR minimal risk levels for PFHxS and PFNA are 
appropriate for use under SDWA because ATSDR uses scientifically 
credible approaches, its work is internally and externally peer-
reviewed and undergoes public comment, and its work represents the 
current best available science for these two chemicals. The 2021 ATSDR 
Toxicological Profile for Perfluoroalkyls underwent intra- and 
interagency review and subsequent external peer review by seven experts 
with knowledge of toxicology, chemistry, and/or health effects.
    The agency acknowledges that ATSDR minimal risk levels and EPA RfDs 
are not identical. The two agencies sometimes develop toxicity values 
for different exposure durations (e.g., intermediate, chronic) and/or 
apply different uncertainty/modifying factors to reflect data 
limitations. Additionally, ATSDR minimal risk levels and EPA RfDs are 
developed for different purposes: ATSDR minimal risk levels are 
intended to serve as screening levels and are used to identify 
contaminants and potential health effects that may be of concern at 
contaminated sites, whereas EPA RfDs are used to support regulatory and 
nonregulatory actions, limits, and recommendations in various 
environmental media. However, from a practical standpoint, an oral 
minimal risk level and an oral RfD both represent the level of daily 
oral human exposure to a hazardous substance for a specified duration 
of exposure below which adverse health effects are not anticipated to 
occur. The EPA has routinely used and continues to use ATSDR minimal 
risk levels in human health assessments when they represent the best 
available science--for example, in the context of Clean Air Act section 
112(f)(2) risk assessments in support of setting national emission 
standards for Hazardous Air Pollutants (HAPs), developing Clean Water 
Act ambient water quality criteria, evaluating contaminants for the 
CCL, and site evaluations under the Resource Conservation and Recovery 
Act (RCRA) and the Comprehensive Environmental Response, Compensation, 
and Liability Act (CERCLA).
    Some commenters questioned the EPA's external peer-review process 
for the four underlying final toxicity assessments used to calculate 
the HRLs/HBWCs. Some commenters noted that the EPA does not yet have 
completed Integrated Risk Information System (IRIS) assessments for 
PFHxS and PFNA, questioning the EPA's use of non-EPA assessments (see 
above). The EPA notes that all four toxicity assessments containing the 
toxicity values (RfD or minimal risk level) used to calculate the HRLs/
HBWCs (i.e., the EPA human health toxicity assessments for HFPO-DA and 
PFBS (USEPA, 2021a; USEPA, 2021b) and the ATSDR toxicity assessments of 
PFNA and PFHxS (ATSDR, 2021)) underwent rigorous, external peer review 
(ATSDR, 2021; USEPA, 2021a; USEPA, 2021b). The EPA is not required 
under SDWA to exclusively use EPA assessments to support an NPDWR, and 
in fact, SDWA's clear direction in section 1412(b)(3)(A)(i) is to use 
the best available, peer-reviewed science when developing NPDWRs 
(emphasis added). Final EPA assessments for PFHxS and PFNA are under 
development but are not currently available; final, peer reviewed ATSDR 
assessments are available.
    Other commenters offered critical comments on the HRLs/HBWCs for 
PFHxS, PFNA, HFPO-DA, and PFBS and raised technical and process 
concerns with the underlying human health assessments. Some commenters 
asserted that the human health toxicity values (EPA RfDs, ATSDR minimal 
risk levels) upon which the HRLs/HBWCs are based have too much 
uncertainty (e.g., inappropriately apply a composite uncertainty factor 
(UF) of 3,000) and are therefore inadequate to support a SDWA 
regulatory determination. The EPA disagrees with these comments. The 
HRLs/HBWCs are data-driven values that incorporate UFs based on the EPA 
guidance and guidelines thus, represent the levels below which adverse 
health effects are not expected to occur over a lifetime. According to 
the EPA guidelines and longstanding practices (USEPA, 2002a; USEPA, 
2022f), UFs reflect the limitations of the data across the five areas 
used in the current EPA human health risk assessment development: (1) 
human interindividual

[[Page 32546]]

variability (UFH); (2) extrapolation from animal to human 
(UFA); (3) subchronic-to-chronic duration extrapolation 
(UFS); (4) lowest-observed-adverse-effect level-to-no-
observed-adverse-effect level (LOAEL-to-NOAEL) extrapolation 
(UFL); and (5) database uncertainty (UFD). In 
minimal risk level development, ATSDR also applies uncertainty factors 
as appropriate to address areas of uncertainty, with the exception of 
subchronic-to-chronic duration extrapolation (ATSDR, 2021). For the 
ATSDR minimal risk levels on which the HRLs/HBWCs for PFNA and PFHxS 
are based, ATSDR utilized UFHs, UFAs, and what 
ATSDR calls a modifying factor to address database deficiencies 
(equivalent to the EPA's UFD) (ATSDR, 2021). The EPA 
carefully reviewed ATSDR's application of uncertainty and modifying 
factors for PFNA and PFHxS and applied additional uncertainty factors 
as warranted. Specifically, the EPA applied an additional UF 
(UFS) for PFHxS to extrapolate from subchronic to chronic 
duration per agency guidelines (USEPA, 2002a) and standard practice 
because the critical effect was not observed during a developmental 
lifestage (i.e., the effect was in parental male rats). A chronic 
toxicity value (i.e., RfD, MRL) represents the daily exposure to the 
human population (including sensitive subgroups) that is likely to be 
without an appreciable risk of deleterious effects during a lifetime; 
the EPA is using a chronic toxicity value to derive the MCLG to ensure 
that it is set at a level at or below which no known or anticipated 
adverse effects on human health occur and allowing an adequate margin 
of safety. The EPA guidelines indicate that the composite (total) UF 
may be equal to or below 3,000; composite UFs greater than that 
represent ``excessive uncertainty'' (USEPA, 2002a; USEPA, 2022f). In 
the case of this final NPDWR, a composite UF of 3,000 was appropriately 
applied to derive toxicity values used to develop HRLs/HBWCs for two of 
the four PFAS (HFPO-DA and PFHxS) following peer-reviewed agency 
guidance and longstanding practice (see USEPA (2024f) for complete 
discussion of UF application for all four PFAS). The EPA has previously 
developed an MCLG for a chemical that had a composite UF of 3,000 
applied to derive a toxicity value (e.g., thallium [USEPA, 1992]). 
Further, a composite uncertainty factor of 3,000 has been applied in 
the derivation of oral RfDs for several chemicals that have been 
evaluated within the EPA's IRIS (Integrated Risk Information System) 
program (e.g., fluorene, cis- and trans-1,2-dichloroethylene, 2,4-
dimethylphenol; please see the EPA's IRIS program website [https://www.epa.gov/iris] for further information).
    Some commenters opposed the EPA's application of a 20 percent RSC 
(relative source contribution) in the HRL/HBWC calculations and stated 
that it was a ``conservative default'' approach not supported by 
available information and that adequate exposure data exist to justify 
an RSC other than 20 percent (although commenters did not offer a 
suggested alternative RSC). The EPA disagrees with these comments. The 
EPA applies an RSC to account for potential aggregate risk from 
exposure routes and exposure pathways other than oral ingestion of 
drinking water to ensure that an individual's total exposure to a 
contaminant does not exceed the daily exposure associated with toxicity 
(i.e., threshold level or reference dose). Application of the RSC in 
this context is consistent with EPA methods (USEPA, 2000d) and long-
standing EPA practice for establishing drinking water MCLGs and NPDWRs 
(e.g., see USEPA, 1989; USEPA, 2004; USEPA, 2010). The RSC represents 
the proportion of an individual's total exposure to a contaminant that 
is attributed to drinking water ingestion (directly or indirectly in 
beverages like coffee, tea, or soup, as well as from dietary items 
prepared with drinking water) relative to other exposure pathways. The 
remainder of the exposure equal to the RfD (or minimal risk level) is 
allocated to other potential exposure sources (USEPA, 2000d). The 
purpose of the RSC is to ensure that the level of a contaminant (e.g., 
MCLG) in drinking water, when combined with other identified potential 
sources of exposure for the population of concern, will not result in 
total exposures that exceed the RfD (or minimal risk level) (USEPA, 
2000d). This ensures that the MCLG under SDWA meets the statutory 
requirement that it be a level of a contaminant in drinking water at or 
below which no known or anticipated adverse effects on human health 
occur and allowing an adequate margin of safety.
    To determine the RSCs for the four HRLs/HBWCs, the agency assessed 
the available scientific literature on potential sources of human 
exposure other than drinking water. The EPA conducted literature 
searches and reviews for each of the four HRLs/HBWCs to identify 
potential sources of exposure and physicochemical properties that may 
influence occurrence in environmental media (Deluca et al., 2022; 
USEPA, 2024f). Considering this exposure information, the EPA followed 
its longstanding, peer-reviewed Exposure Decision Tree Approach in the 
EPA's Methodology for Deriving Ambient Water Quality Criteria for the 
Protection of Human Health (USEPA, 2000d) to determine the RSC for each 
PFAS. As discussed by the EPA in the Hazard Index MCLG document (USEPA, 
2024f), the EPA carefully evaluated studies that included information 
on potential exposure to these four PFAS (PFHxS, PFNA, HFPO-DA, and 
PFBS) via sources other than drinking water, such as food, soil, 
sediment, and air. For each of the four PFAS, the findings indicated 
that there are significant known or potential uses/sources of exposure 
beyond drinking water ingestion (e.g., food, indoor dust) (Box 6 in the 
EPA Exposure Tree; USEPA, 2000d), but that data are insufficient to 
allow for quantitative characterization of the different exposure 
sources (Box 8A in USEPA, 2000d). The EPA's Exposure Decision Tree 
approach states that when there are insufficient environmental and/or 
exposure data to permit quantitative derivation of the RSC, the 
recommended RSC for the general population is 20 percent (Box 8B in 
USEPA, 2000d). This means that 20 percent of the exposure equal to the 
RfD is allocated to drinking water, and the remaining 80 percent is 
attributed to all other potential exposure sources.
    Some commenters disagreed with the bodyweight-adjusted drinking 
water intake (DWI-BWs) that the EPA used to calculate the HRLs/HBWCs 
and thought the selected DWI-BWs were too high (overly health 
protective). One commenter stated that the DWI-BW used in the 
calculation of the HRL/HBWC for HFPO-DA is inappropriate and that the 
EPA should have used a DWI-BW for general population adults instead of 
for lactating women. The EPA disagrees with this comment. To select an 
appropriate DWI-BW for use in derivation of the HRL/HBWC for HFPO-DA, 
the EPA considered the HFPO-DA exposure interval used in the oral 
reproductive/developmental toxicity study in mice that served as the 
basis for chronic RfD derivation (the critical study). In this study, 
parental female mice were dosed from pre-mating through lactation, 
corresponding to three potentially sensitive human adult life stages 
that may represent critical windows of HFPO-DA exposure: women of 
childbearing age, pregnant women, and lactating women (Table 3-63 in 
USEPA, 2019a). Of these three, the highest DWI-BW, for lactating women 
(0.0469 L/kg/day), is anticipated to be protective of the other two 
sensitive life

[[Page 32547]]

stages and was used to calculate the HRL/HBWC for HFPO-DA (USEPA, 
2024f).
    Other commenters urged the EPA to consider infants as a sensitive 
life stage for PFHxS, PFNA, and PFBS and use the DWI-BW for infants to 
calculate the HRLs/HBWCs. The EPA disagrees with this comment. The 
EPA's approach to DWI-BW selection includes a step to identify the 
sensitive population(s) or life stage(s) (i.e., those that may be more 
susceptible or sensitive to a chemical exposure) by considering the 
available data for the contaminant, including the adverse health 
effects observed in the toxicity study on which the RfD/minimal risk 
level was based (known as the critical effect within the critical or 
principal study). Although data gaps can complicate identification of 
the most sensitive population (e.g., not all windows or life stages of 
exposure and/or health outcomes may have been assessed in available 
studies), the critical effect and point of departure (POD) that form 
the basis for the RfD (or minimal risk level) can provide some 
information about sensitive populations because the critical effect is 
typically observed at the lowest tested dose among the available data. 
Evaluation of the critical study, including the exposure window, may 
identify a sensitive population or life stage (e.g., pregnant women, 
formula-fed infants, lactating women). In such cases, the EPA can 
select the corresponding DWI-BW for that sensitive population or life 
stage from the Exposure Factors Handbook (USEPA, 2019a). DWI-BWs in the 
Exposure Factors Handbook are based on information from publicly 
available, peer-reviewed studies, and were updated in 2019. In the 
absence of information indicating a sensitive population or life stage, 
the DWI-BW corresponding to the general population may be selected. 
Following this approach, the EPA selected appropriate DWI-BWs for each 
of the four PFAS included in the Hazard Index MCLG (see USEPA, 2024f). 
The EPA did consider infants as a sensitive life stage for all four 
PFAS; however, the agency did not select the infant DWI-BW because the 
exposure intervals of the critical studies supporting the chronic 
toxicity values did not correspond to infants. Instead, the exposure 
intervals were relevant to other sensitive target populations (i.e., 
lactating women or women of childbearing age) or the general 
population. (See also comments related to DWI-BW selection under PFBS 
section III.B.6.d. of this preamble).
a. PFHxS
    Some commenters noted a typographical error in the HRL/HBWC 
calculation for PFHxS which was reported as 9.0 ng/L in the proposal. 
The agency has corrected the value in this NPDWR and within the 
requirements under 40 CFR part 141, subpart Z. The correct HRL/HBWC for 
PFHxS is 10 ng/L.
    Two commenters questioned the human relevance of thyroid effects 
(i.e., changes in tissue structure (e.g., enlarged cells; increased 
numbers of cells) in the thyroids of adult male rats) observed in the 
critical study used to derive the ATSDR minimal risk level and the 
EPA's PFHxS HRL/HBWC because, as noted in the ATSDR Toxicological 
Profile for Perfluoroalkyls, this observed effect may have been 
secondary to liver toxicity and, therefore, the commenters state that 
its significance is unclear. The EPA disagrees with this comment. SDWA 
requires that the EPA use ``the best available, peer reviewed science'' 
to inform decision making on drinking water regulations. Although there 
is some uncertainty regarding the selection of thyroid alterations as 
the critical effect (as the ATSDR toxicological profile notes), at this 
time, the 2021 ATSDR toxicological profile represents the best 
available peer reviewed scientific information regarding the human 
health effects of PFHxS. As the most sensitive known effect as 
supported by the weight of the evidence, the thyroid effect was 
appropriately selected by ATSDR as the critical effect. Additionally, 
published studies in rats have shown that PFHxS exposure results in 
other thyroid effects, including decreases in thyroid hormone 
(primarily T4) levels in serum (NTP, 2018a; Ramh[oslash]j et al., 
2018). Similarly, peer-reviewed final EPA assessments of other PFAS, 
including PFBS (USEPA, 2021a) and perfluorobutanoic acid (PFBA) (USEPA, 
2022g), have concluded that these changes in rodents are adverse and 
human-relevant, and appropriate for RfD derivation. Furthermore, it is 
appropriate to use other health protective (toxicity) values developed 
by other authoritative governmental agencies, including ATSDR minimal 
risk levels, if available, as these agencies use scientifically 
credible approaches and their work is peer-reviewed (the ATSDR 
toxicological profile underwent intra- and interagency review and 
external peer review by seven experts with knowledge of toxicology, 
chemistry, and/or health effects). The ATSDR minimal risk levels 
reflect the best available, peer-reviewed science.
    Furthermore, the EPA's draft IRIS Toxicological Review of 
Perfluorohexanesulfonic Acid (PFHxS) and Related Salts (Public Comment 
and External Review Draft) (USEPA, 2023d), which is in the public 
domain, preliminarily provides confirmatory evidence that PFHxS 
significantly affects human development (emphasis added): ``Overall, 
the available evidence indicates that PFHxS exposure is likely to cause 
thyroid and developmental immune effects in humans, given sufficient 
exposure conditions. For thyroid effects, the primary supporting 
evidence for this hazard conclusion included evidence of decreased 
thyroid hormone levels, abnormal histopathology results, and changes in 
organ weight in experimental animals. For immune effects, the primary 
supporting evidence included decreased antibody responses to 
vaccination against tetanus or diphtheria in children.'' Although the 
EPA did not rely on this draft IRIS toxicological review for PFHxS in 
this rule, the draft is available to the public and offers confirmation 
that PFHxS elicits developmental effects in humans.
b. PFNA
    Some commenters questioned the human relevance of developmental 
effects observed in PFNA animal studies (i.e., decreased body weight 
gain, delayed eye opening, delayed sexual maturation) used to derive 
the ATSDR minimal risk level and the EPA's PFNA HRL/HBWC. The EPA 
disagrees with this comment. At this time, the 2021 ATSDR Toxicological 
Profile for Perfluoroalkyls represents the best available peer-reviewed 
scientific information regarding the human health effects of PFNA. In 
addition, according to the March 2023 Interagency PFAS Report to 
Congress, PFNA is documented to affect the developmental health domain 
(United States OSTP, 2023), and a recently published meta-analysis 
(Wright et al., 2023) specifically supports decreases in birth weight 
as an effect of PFNA exposure in humans. Published studies have shown 
that PFNA exposure results in statistically significant, dose-
responsive developmental effects, including reduced fetal/pup 
bodyweight, reduced fetal/pup survival, changes in fetal/pup liver gene 
expression, increased fetal/pup liver weight, and delayed onset of 
puberty. Also, the EPA's 1991 Guidelines for Developmental Toxicity 
Risk Assessment (USEPA, 1991a; pp. vii-ix and pp. 1-2) cites evidence 
that, in the absence of clear evidence to the

[[Page 32548]]

contrary, developmental effects observed in experimental animals are 
interpreted as relevant to humans.
c. HFPO-DA
    A few commenters submitted critical comments related to the adverse 
health effects associated with exposure to HFPO-DA and how these health 
effects are quantified to derive the RfD in the human health toxicity 
assessment for HFPO-DA (USEPA, 2021b). Commenters claimed that the RfD 
for HFPO-DA is not scientifically sound, and cited one or more of the 
following reasons why: (1) the selected critical effect from the study 
(constellation of liver lesions) includes different liver effects that 
were not consistently observed across male and female mice and were not 
necessarily all adverse; (2) the hepatic effects in mice (the selected 
critical effect) are mediated by a rodent specific MOA, peroxisome 
proliferator-activated receptor alpha (PPAR[alpha]), and therefore not 
relevant to humans; (3) the EPA incorporated results of a pathology 
working group which misapplied diagnostic criteria classifying 
apoptotic and necrotic lesions; and (4) the EPA misapplied uncertainty 
factors (UFs) (i.e., the subchronic to chronic UF and database UF) 
according to agency guidance resulting in the maximum possible UF of 
3,000 (USEPA, 2002a; USEPA, 2022f). Another commenter thought that the 
interspecies UF should be further increased. Also, some commenters 
stated that the EPA did not properly consider all available 
epidemiological data. These comments are addressed in this preamble.
    Overall, the EPA disagrees with the commenters and maintains that 
the final published peer-reviewed human health toxicity assessment that 
derived the RfD for HFPO-DA is appropriate and sound, reflects the best 
available peer-reviewed science, and is consistent with agency 
guidance, guidelines, and best practices for human health risk 
assessment. Notably, the EPA sought external peer review of the 
toxicity assessment twice (USEPA, 2018b; USEPA, 2021f), released the 
draft toxicity assessment for public comment and provided responses to 
public comment (USEPA, 2021g), and engaged a seven-member pathology 
working group at the National Institutes of Health--an entirely 
separate and independent organization--to re-analyze pathology slides 
from two critical studies (USEPA, 2021b, appendix D), all of which 
supported the EPA's conclusions in the toxicity assessment, including 
the RfD derivation.
    Regarding critical effect selection: the EPA's approach to critical 
effect selection for the RfD derivation considers a range of factors, 
including dose at which effects are observed, biological variability 
(which can produce differences in effects observed between sexes), and 
relevance of the effect(s) seen in animals to human health. The EPA 
maintains that selection of the constellation of liver lesions as the 
critical effect for HFPO-DA RfD derivation is appropriate and 
scientifically justified, and that the constellation of liver lesions 
represents an adverse effect. The EPA engaged a pathology working group 
within the National Toxicology Program (NTP) at the National Institutes 
of Health to perform an independent analysis of the liver tissue 
slides. The pathology working group determined that the tissue slides 
demonstrated a range of adverse effects and that the constellation of 
liver effects caused by HFPO-DA exposure, which included cytoplasmic 
alteration, apoptosis, single cell necrosis, and focal necrosis, 
constitutes an adverse liver effect in these studies (USEPA, 2021b, 
appendix D). The EPA evaluated the results of the pathology working 
group and determined that the effects were relevant to humans according 
to the best available science (e.g., Hall et al., 2012). Additionally, 
the EPA convened a second independent peer-review panel of human health 
risk assessment experts to review the EPA's work on HFPO-DA, including 
critical effect selection. The panel unanimously agreed with the 
selection of the constellation of liver lesions as the critical effect, 
the adversity of this effect and its relevance to humans (USEPA, 
2021f).
    The commenters' assertion that the hepatic effects observed in mice 
are not relevant to humans because they are PPAR[alpha]-mediated is 
unsupported. The commenter claims that one specific effect--apoptosis--
can be PPAR[alpha]-mediated in rodents (a pathway that some data 
suggest may be of limited or no relevance to humans). However, in 
supporting studies cited by commenters, a decrease in apoptosis is 
associated with a PPAR[alpha] MOA, with Corton et al. (2018) stating, 
``[t]he data indicate that a physiological function of PPAR[alpha] 
activation is to increase hepatocyte growth through an increase in 
hepatocyte proliferation or a decrease in apoptosis or a combination of 
both effects'' while HFPO-DA is associated with increased apoptosis 
(USEPA, 2021b). Therefore, the commenter's claim that apoptosis is 
associated with the known PPAR[alpha] MOA is unsupported. the critical 
study selected by the EPA, and indeed other studies as well, reported 
not only apoptosis but also other liver effects such as necrosis that 
are not associated with a PPAR[alpha] MOA and therefore are relevant 
for human health (Hall et al., 2012). Further, according to the 
available criteria, effects such as cytoplasmic alteration in the 
presence of liver cell necrosis are considered relevant to humans (Hall 
et al., 2012). Additionally, commenters asserted that a 2020 study by 
Chappell et al. reported evidence demonstrating that the rodent liver 
effects are not relevant to humans, and that the EPA failed to consider 
this study. It is important to note that while Chappell et al. (2020) 
was published after the assessment's literature search cut-off date 
(USEPA, 2021b, appendix A; USEPA, 2022h), the EPA considered this paper 
initially through the Request for Correction process (USEPA, 2022h) and 
noted that this study specifically assessed evidence for PPAR[alpha]-
driven apoptosis and did not investigate other potential modes of 
action or types of cell death, specifically necrosis. The authors state 
that they could ``not eliminate the possibility that necrotic cells 
were also present.'' The EPA again considered Chappell et al., (2020), 
in addition to other studies submitted through public comment (Heintz 
et al., 2022; Heintz et al., 2023; Thompson et al., 2023), and 
determined that these studies do not fully explore a necrotic/cytotoxic 
MOA with Thompson et al., 2023 stating that ``there are no gene sets 
for assessing necrosis in transcriptomic databases.'' Critically, the 
commenter and these cited studies fail to recognize that increased 
apoptosis is a key criterion to establish a cytotoxic MOA. As outlined 
in the toxicity assessment (USEPA, 2021b), Felter et al., (2018) 
``identified criteria for establishing a cytotoxicity MOA, which 
includes: . . . (2) clear evidence of cytotoxicity by histopathology, 
such as presence of necrosis and/or increased apoptosis.'' Overall, the 
EPA has determined that these studies support the mechanistic 
conclusions of the toxicity assessment ``that multiple MOAs could be 
involved in the liver effects observed after GenX chemical exposure'' 
including PPAR[alpha] and cytotoxicity (USEPA, 2021b).
    With respect to claims that the EPA misapplied diagnostic criteria 
classifying apoptotic and necrotic lesions: as mentioned above, the EPA 
engaged a pathology working group within the NTP at the National 
Institutes of Health to perform an independent analysis of the liver 
tissue slides. Seven pathologists--headed by Dr. Elmore, who was the 
lead author of the pathology criteria that the

[[Page 32549]]

commenter cites (Elmore et al., 2016)--concluded that exposure to HFPO-
DA caused a ``constellation of liver effects'' that included 
cytoplasmic alteration, apoptosis, single cell necrosis, and focal 
necrosis, and that this full ``constellation of lesions'' should be 
considered the adverse liver effect within these studies. The EPA then 
used the established Hall criteria (Hall et al., 2012) to determine 
that since liver cell death was observed, all effects, including 
cytoplasmic alteration, were considered adverse and relevant to humans.
    The EPA disagrees with the commenters' assertion about UF 
application. As noted above, agency guidance (USEPA, 2002a; USEPA, 
2022f) have established the appropriateness of the use of UFs to 
address uncertainty and account for data limitations. UFs reflect the 
limitations of the data across the five areas used in the current EPA 
human health risk assessment development (referenced above); all 
individual UFs that are applied are multiplied together to yield the 
composite or total UF. The EPA guidance dictates that although a 
composite UF greater than 3,000 represents ``excessive uncertainty'' 
(USEPA, 2002a; USEPA, 2022f), a composite UF can be equal to 3,000. For 
HFPO-DA, a composite UF of 3,000 was appropriately applied to account 
for uncertainties, including variability in the human population, 
database uncertainties, and possible differences in the ways in which 
humans and rodents respond to HFPO-DA that reaches their tissues. 
Furthermore, the composite UF of 3,000 and specifically the database UF 
and subchronic-to-chronic UF used for HFPO-DA was peer-reviewed by a 
panel of human health risk assessment experts, and the panel supported 
the application of the database UF of 10 and the subchronic-to-chronic 
UF of 10 (USEPA, 2021f). Additionally, a UFA of 3 was 
appropriately applied, consistent with peer-reviewed EPA methodology 
(USEPA, 2002a), to account for uncertainty in characterizing the 
toxicokinetic and toxicodynamic differences between rodents and humans. 
As noted in the toxicity assessment for HFPO-DA (USEPA, 2021b), in the 
absence of chemical-specific data to quantify residual uncertainty 
related to toxicokinetics and toxicodynamic processes, the EPA's 
guidelines recommend use of a UFA of 3.
    Finally, some commenters claimed that the EPA did not consider 
available epidemiological evidence showing no increased risk of cancers 
or liver disease attributable to exposure to HFPO-DA. The EPA disagrees 
with this comment because the agency considered all available 
scientific evidence, including epidemiological studies (USEPA, 2021b). 
The exhibit submitted by the commenter presents an observational 
analysis comparing cancer and liver disease rates in North Carolina to 
rates in other states. It does not present the results of a new 
epidemiological study that included HFPO-DA exposure measures, health 
outcome measures, or an assessment of association between exposure and 
health outcome. The exhibit submitted by the commenter consists of a 
secondary analysis of disease rate information that was collected from 
various sources and does not provide new, high-quality scientific 
information that can be used to assess the impact of exposure to 
concentrations of HFPO-DA on human health.
d. PFBS
    A few commenters suggested that the EPA lower the HRL/HBWC for PFBS 
to account for thyroid hormone disruption during early development and 
cited the Washington State Action Level for PFBS, which is 345 ng/L. 
Washington State used the same RfD (3E-04 mg/kg-d) but a higher DWI-BW 
to develop their Action Level as compared to the EPA's HRL/HBWC 
(Washington State used the 95th percentile DWI-BW of 0.174 L/kg/day for 
infants, whereas the EPA selected the 90th percentile DWI-BW of 0.0354 
L/kg/day for women of child-bearing age). The EPA disagrees that the 
infant DWI-BW is more appropriate for HRL/HBWC calculation. The EPA 
selected the thyroid hormone outcome (decreased serum total thyroxine 
in newborn mice seen in a developmental toxicity study) as the critical 
effect in its PFBS human health toxicity assessment (USEPA, 2021a). 
Notably, the RfD derived from this critical effect included application 
of a 10X UF to account for life-stage-specific susceptibility 
(UFH). To select a DWI-BW for use in deriving the HRL/HBWC 
for PFBS, the EPA followed its established approach of considering the 
PFBS exposure interval used in the developmental toxicity study in mice 
that was the basis for chronic RfD derivation. In this study, pregnant 
mice were exposed throughout gestation, which is relevant to two human 
adult life stages: women of child-bearing age who may be or become 
pregnant, and pregnant women and their developing embryos or fetuses 
(Table 3-63 in USEPA, 2019a). To be clear, the critical study exposed 
mice to PFBS only during pregnancy and not during postnatal 
development; newborn mice in early postnatal development, which would 
correspond to the human infancy life stage, were not exposed to PFBS. 
Of the two relevant adult stages, the EPA selected the 90th percentile 
DWI-BW for women of child-bearing age (0.0354 L/kg/day) to derive the 
HRL/HBWC for PFBS because it is the higher of the two, and therefore 
more health-protective. Please see additional information related to 
DWI-BW selection above.
    Other commenters stated that the EPA's human health toxicity 
assessment for PFBS is overly conservative, uncertain, and that the 
confidence in the chronic RfD is low. The EPA disagrees with these 
comments. Confidence in the critical study (Feng et al., 2017) and 
corresponding thyroid hormone critical effect in newborn mice was rated 
by the EPA as `High;' this rating was a result of systematic study 
evaluation and risk of bias analysis by a team of EPA experts. The Feng 
et al. (2017) study, the critical effect of thyroid hormone disruption 
in offspring, dose-response assessment, and corresponding RfD were 
subjected to extensive internal EPA, interagency, and public/external 
peer review. While confidence in the critical study was rated `High,' 
the `Low' confidence rating for the PFBS chronic RfD was in part a 
result of the lack of a chronic exposure duration study in any 
mammalian species; this lack of a chronic duration study was one of the 
considerations that resulted in the EPA applying a UF of 10 to account 
for database limitations (UFD). Based on the EPA's human 
health assessment practices, the lowest confidence rating across the 
areas of consideration (e.g., existent hazard/dose-response database) 
is assigned to the corresponding derived reference value (e.g., RfD). 
Thus, the EPA has high confidence in the critical study (Feng et al., 
2017) and critical effect/thyroid endpoint, but the database is 
relatively limited. Although the PFBS RfD was based on best available 
peer-reviewed science, there is uncertainty as to the hazard profile 
associated with PFBS after prolonged (e.g., lifetime) oral exposure. In 
the toxicity assessment for PFBS (USEPA, 2021a), the EPA noted data 
gaps in specific health effects domains, as is standard practice. 
Toxicity assessments for most chemicals identify data gaps; the issue 
of uncertainty due to toxicological study data gaps is not unique to 
PFBS. Data gaps are considered when selecting the UFD 
because they indicate the potential for exposure to lead to adverse 
health effects at doses lower than the POD derived from the 
assessment's critical

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study. There is a potential that effects with greater dose-response 
sensitivity (i.e., occurring at lower daily oral exposures) might be 
discovered from a chronic duration exposure study. Due to this 
uncertainty, the EPA applied a UFD of 10.
    One commenter questioned the EPA's approach to estimating the human 
equivalent dose (HED) from the animal data using toxicokinetic (TK) 
data rather than using default body-weight scaling and suggested that 
the default allometric approach is more appropriate for estimating an 
HED. The EPA disagrees with this comment. In human health risk 
assessment practice, the EPA considers a hierarchical approach to 
cross-species dosimetric scaling consistent with technical guidance to 
calculate HEDs (USEPA, 2011; see pp. X-XI of the Executive Summary in 
`Recommended Use of Body Weight3/4 as the Default Method in Derivation 
of the Oral Reference Dose'). The preferred approach is physiologically 
based toxicokinetic (PBTK) modeling; however, there are rarely 
sufficient chemical-specific data to properly parameterize such a 
model. In the absence of a PBTK model, the EPA considers an 
intermediate approach in which chemical-specific data across species, 
such as clearance or plasma half-life, are used to calculate a 
dosimetric adjustment factor (DAF) (USEPA, 2011). If chemical-specific 
TK data are not available, only then is a default approach used wherein 
allometric scaling, based on body weight raised to the \3/4\ power, is 
used to calculate a DAF. The human health toxicity assessment for PFBS 
invoked the intermediate approach, consistent with guidance, as TK data 
were available for humans and rodents.
e. Mixtures of PFHxS, PFNA, HFPO-DA, and PFBS
    Comments on the EPA's preliminary regulatory determination on the 
mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS were varied. Many 
commenters supported the EPA's proposal to regulate a mixture of these 
PFAS and agreed with the EPA's scientific conclusions about PFAS dose 
additivity. Many commenters urged the EPA to consider making a 
determination to regulate for additional PFAS (in a mixture) or all 
PFAS as a class. As described throughout section III of this preamble, 
the agency is required to demonstrate a contaminant meets the SDWA 
statutory criteria to make a regulatory determination. In this 
preamble, in addition to PFOA and PFOS which the EPA has already made a 
final determination to regulate, the agency is making final 
determinations for all PFAS with sufficiently available information to 
meet these statutory criteria either individually and/or as part of 
mixture combinations. As information becomes available, the agency will 
continue to evaluate other PFAS for potential future preliminary 
regulatory determinations.
    Many commenters opposed the EPA's conclusion about PFAS dose 
additivity and use of the Hazard Index approach to regulate co-
occurring PFAS. A few commenters agreed with the EPA's decision to 
regulate mixtures of certain PFAS and the EPA's conclusion about dose 
additivity but questioned the EPA's use of the general Hazard Index, 
and instead, suggested alternative approaches. Please see section IV of 
this preamble for a summary of comments and the EPA responses on the 
Hazard Index MCLG and related topics.
    There is substantial evidence that PFHxS, PFNA, HFPO-DA, and PFBS 
act in a dose additive manner, that these four PFAS elicit similar 
health effects, and that exposure to mixtures of these PFAS may have 
adverse health effects. Following is a discussion of dose additivity 
and similarity of adverse effects of PFHxS, PFNA, HFPO-DA, and PFBS.
    As noted in this section, the available data indicate that PFHxS, 
PFNA, HFPO-DA, and PFBS, while not necessarily toxicologically 
identical, elicit many of the same or similar adverse health effects 
across different levels of biological organization, tissues/organs, 
lifestages, and species (ATSDR, 2021; EFSA et al., 2018; EFSA et al., 
2020; USEPA, 2021d; USEPA, 2021f; USEPA, 2024f). Each of these PFAS 
disrupts signaling of multiple biological pathways, resulting in a 
shared set of adverse effects including effects on thyroid hormone 
levels, lipid synthesis and metabolism, development, and immune and 
liver function (ATSDR, 2021; EFSA et al., 2018; EFSA et al., 2020; 
USEPA, 2021d; USEPA, 2021f; USEPA, 2024f). Please also see USEPA 
(2024a) for an overview of recent studies that provide supportive 
evidence of similar effects of PFAS.
    Available health effects studies indicate that PFAS mixtures act in 
a dose-additive manner when the individual components share some health 
endpoints/outcomes. Individual PFAS, each at doses that are not 
anticipated to result in adverse health effects, when combined in a 
mixture may result in adverse health effects. Dose additivity means 
that when two or more of the component chemicals (in this case, PFHxS, 
PFNA, HFPO-DA, and/or PFBS) exist in one mixture, the risk of adverse 
health effects following exposure to the mixture is equal to the sum of 
the individual doses or concentrations scaled for potency (USEPA, 
2000a). Thus, exposure to these PFAS, at doses that individually would 
not likely result in adverse health effects, when combined in a mixture 
may pose health risks.
    Many commenters supported the EPA's scientific conclusions about 
PFAS dose additivity and agreed that considering dose-additive effects 
is a health-protective approach. Many other commenters disagreed with 
the EPA's scientific conclusions regarding PFAS dose additivity and a 
few commenters questioned the agency's external peer-review process and 
whether the agency sufficiently responded to SAB (Science Advisory 
Board) comments. For example, these commenters stated that the evidence 
base of PFAS mixture studies is too limited to support dose additivity 
for these four PFAS and recommended that the EPA re-evaluate its 
conclusion about dose additivity as new data become available. A few 
commenters stated that the EPA failed to adequately follow the SAB 
recommendation that ``discussion of studies of toxicological 
interactions in PFAS mixtures in the EPA mixtures document be expanded 
to also include studies that do not indicate dose additivity and/or a 
common MOA [mode of action] for PFAS.'' The EPA's responses to these 
comments are summarized in this section.
    The EPA continues to support its conclusion that PFAS that elicit 
similar adverse health effects following individual exposure should be 
assumed to act in a dose-additive manner when in a mixture unless data 
demonstrate otherwise. Numerous published studies across multiple 
chemical classes, biological effects, and study designs support a dose-
additive mixture assessment approach for PFAS because they demonstrate 
that experimentally observed responses to exposure to PFAS and other 
chemical mixtures are consistent with modeled predictions of dose 
additivity (see the EPA's Framework for Estimating Noncancer Health 
Risks Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS) (USEPA, 2024a)). Since the EPA's draft PFAS Mixtures Framework 
underwent SAB review in 2021, new studies from the EPA and others have 
published robust evidence of combined toxicity of PFAS in mixtures, 
corroborating and confirming earlier findings (e.g., Conley et al., 
2022a; Conley et al., 2022b; USEPA, 2023c; see USEPA, 2024a for 
additional examples). Additionally, the National Academies of

[[Page 32551]]

Sciences, Engineering, and Medicine (NASEM, 2022) recently recommended 
that clinicians apply an additive approach for evaluating patient 
levels of PFAS currently measured in the National Health and Nutrition 
Examination Survey (NHANES) in order to protect human health from 
additive effects from PFAS co-exposure.
    The EPA directly asked the SAB for feedback on PFAS dose additivity 
in the charge for the 2021 review of the EPA's draft PFAS Mixtures 
Framework. Specifically, the EPA asked the SAB to, ``[p]lease comment 
on the appropriateness of this approach for a component-based mixture 
evaluation of PFAS under an assumption of dose additivity'' (USEPA, 
2022i). The SAB strongly supported the scientific soundness of this 
approach when evaluating PFAS and concurred that it was a health 
protective conclusion. For example, the SAB said:

. . . The information included in the draft framework supports the 
conclusion that toxicological interactions of chemical mixtures are 
frequently additive or close to additive. It also supports the 
conclusion that dose additivity is a public health protective 
assumption that typically does not underestimate the toxicity of a 
mixture . . . (USEPA, 2022i)
    The SAB Panel agrees with use of the default assumption of dose 
additivity when evaluating PFAS mixtures that have similar effects 
and concludes that this assumption is health protective. (USEPA, 
2022i)

    Regarding the commenters' assertion that the agency did not 
adequately follow the SAB recommendation to expand its discussion of 
PFAS mixtures study results that did not show evidence of dose 
additivity and/or a common MOA, the EPA disagrees. The EPA reviewed all 
studies provided by the SAB and in response, included a discussion of 
relevant additional studies in its public review draft PFAS Mixtures 
Framework (see section 3 in USEPA, 2023w). Since then, the EPA has 
included additional published studies and those findings further 
confirm dose additive health concerns associated with PFAS mixtures 
(see section 3 in USEPA, 2024a). Data from in vivo studies that 
rigorously tested accuracy of Dose Additivity (DA), Integrated Addition 
(IA), and Response Additivity (RA) model predictions of mixtures with 
components that disrupted common pathways demonstrated that DA models 
provided predictions that were better than or equal to IA and RA 
predictions of the observed mixture effects (section 3.2 in USEPA, 
2024a). The National Academy of Sciences (NAS) conclusions on 
phthalates (and related chemicals) (NRC, 2008) and systematic reviews 
of the published literature (Boobis et al., 2011 and Martin et al., 
2021; see also section 3.2 in USEPA, 2024a) support DA as the default 
model for estimating mixture effects in some circumstances, even when 
the mixtures included chemicals with diverse MOAs (but common target 
organs/effects) (Boobis et al., 2011; Martin et al., 2021; USEPA, 
2024a). Recent efforts to investigate in vitro and in vivo PFAS mixture 
effects have provided robust evidence that PFAS behave in a dose-
additive manner (see section 3 in USEPA, 2024a).
    As supported by the best available science, the SAB, the agency's 
chemical mixtures guidance (USEPA, 1991b; USEPA, 2000a), and the EPA 
Risk Assessment Forum's Advances in Dose Addition for Chemical 
Mixtures: A White Paper (USEPA, 2023c), the EPA proposed a Hazard Index 
MCLG for a mixture of up to four PFAS (PFHxS, PFNA, HFPO-DA, and PFBS) 
based on dose additivity because published studies show that exposure 
to each of these individual four PFAS elicits some of the same or 
similar adverse health effects/outcomes. As noted above, many 
commenters, as well as the SAB (USEPA, 2022i), supported this 
conclusion of dose additivity based on similarity of adverse effects.
    While the SAB also noted that there remain some questions about 
PFAS interaction in mixtures (USEPA, 2022i), the available data justify 
an approach that accounts for PFAS dose additivity. Studies that have 
assessed PFAS mixture-based effects do not offer evidence for 
synergistic/antagonistic effects (USEPA, 2024a). For example, Martin et 
al. (2021), following a review of more than 1,200 mixture studies 
(selected from > 10,000 reports), concluded that there was little 
evidence for synergy or antagonism among chemicals in mixtures and that 
dose additivity should be considered as the default. Experimental data 
demonstrate that PFAS disrupt signaling in multiple biological pathways 
resulting in common adverse effects on several of the same biological 
systems and functions including thyroid hormone signaling, lipid 
synthesis and metabolism, developmental toxicity, and immune and liver 
function (USEPA 2024a). Additionally, several EPA Office of Research 
and Development (ORD) studies provide robust evidence that PFAS behave 
in a dose-additive manner (Conley et al., 2022a; Conley et al., 2022b; 
Conley et al., 2023; Gray et al., 2023).
    Several commenters opposed the conclusion of dose additivity based 
on similarity of adverse effects and stated that the EPA failed to 
establish that the four PFAS included in the Hazard Index (PFHxS, PFNA, 
HFPO-DA, and PFBS) elicit similar adverse health effects. The EPA 
disagrees with these comments because the available epidemiology and 
animal toxicology studies demonstrate that these four PFAS (PFHxS, 
PFNA, HFPO-DA, and PFBS) have multiple health endpoints and outcomes in 
common (USEPA, 2024f). Further, these four PFAS are well-studied PFAS 
for which the EPA or ATSDR have developed human health assessments and 
toxicity values (i.e., RfDs, minimal risk levels). As shown in Table 1, 
available animal toxicological data and/or epidemiological studies 
demonstrate that PFHxS, PFNA, HFPO-DA, and PFBS are documented to 
affect at least five (5) of the same health outcomes for this 
evaluation: lipids, developmental, immune, endocrine, and hematologic 
(USEPA, 2024g). Similarly, according to the 2023 Interagency PFAS 
Report to Congress (United States OSTP, 2023), available animal 
toxicological data show that PFHxS, PFNA, HFPO-DA, and PFBS are 
documented to significantly affect at least eight (8) of the same major 
health effect domains: body weight, respiratory, hepatic, renal, 
endocrine, immunological, reproductive, and developmental. In short, 
multiple evaluation efforts have clearly demonstrated that each of the 
PFAS regulated by this NPDWR impact numerous of the same or similar 
health outcomes or domains.

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    In summary, there is substantial evidence that mixtures of PFHxS, 
PFNA, HFPO-DA, and PFBS act in a dose-additive manner and elicit 
multiple similar toxicological effects. Studies by the EPA and others 
provide evidence that corroborates the dose-additive toxicity of PFAS 
mixtures, and data on different chemical classes and research also 
provide support for dose additivity. Additionally, numerous in vivo and 
in vitro studies demonstrate that these four PFAS share many common 
health effects across diverse health outcome categories (e.g., 
developmental, immunological, and endocrine effects), and that they 
induce some of the same effects at the molecular level along biological 
pathways (USEPA, 2024f).

C. Statutory Criterion 2--Occurrence

    The EPA has determined that there is a substantial likelihood that 
PFHxS, PFNA, and HFPO-DA will individually occur and combinations of 
these three PFAS and PFBS will co-occur in mixtures in PWSs with a 
frequency and at levels of public health concern based on the EPA's 
evaluation of the best available occurrence information. In this 
preamble, while the EPA is making a final determination to regulate 
PFBS in mixtures with PFHxS, PFNA, and/or HFPO-DA, the agency is 
deferring the final individual regulatory determination for PFBS so 
that the agency can continue to evaluate this contaminant relative to 
the SDWA criteria for regulation, particularly related to its 
individual known or likely occurrence. For the other three PFAS, the 
EPA is making a final determination to regulate them individually in 
this preamble (i.e., PFHxS, PFNA, and HFPO-DA). The EPA recognizes 
there will be additional occurrence or other relevant information for 
these and other PFAS in the future. The EPA has, however, determined 
that there is more than sufficient occurrence information to satisfy 
the statutory criterion to regulate PFNA, PFHxS, and HFPO-DA.
    The EPA's evaluation of the second statutory criterion for 
regulation of PFHxS, PFNA, and HFPO-DA individually and regulation of 
combinations of these PFAS and PFBS in mixtures follows a similar 
process to previous rounds of regulatory determinations including the 
written Protocol developed under Regulatory Determination 3 (USEPA, 
2014a) and also described in detail in the Preliminary Regulatory 
Determination 4 (USEPA, 2020a). Using the Protocol, and as conducted 
for the regulatory determinations in this action, the agency compares 
available occurrence data relative to the contaminant HRL, a health-
based concentration against which the agency evaluates occurrence data 
when making regulatory determinations, as a preliminary factor in 
informing the level of public health concern. For both this regulatory 
determination and previous regulatory determinations, this is the first 
screening factor in informing if there is a substantial likelihood the 
contaminant will occur at a frequency and level of public health 
concern. Consistent with the Protocol and similar to all past 
regulatory determinations, these regulatory determinations are also 
based on other factors, not just the direct comparison to the HRL. As 
described clearly in the proposal, the EPA has not been able to 
determine a simple threshold of public health concern for all 
contaminants the agency considers for regulation under SDWA; rather, it 
is a contaminant-specific decision which ``involves consideration of a 
number of factors, some of which include the level at which the 
contaminant is found in drinking water, the frequency at which the 
contaminant is found and at which it co-occurs with other contaminants, 
whether there is an sustained upward trend that these contaminant will 
occur at a frequency and at levels of public health concern, the 
geographic distribution (national, regional, or local occurrence), the 
impacted population, health effect(s), the potency of the contaminant, 
other possible sources of exposure, and potential impacts on sensitive 
populations or lifestages.'' (USEPA, 2023f). It also includes 
consideration of production and use trends and environmental fate and 
transport parameters which may indicate that the contaminant would 
persist and/or be mobile in water. Appropriately, the EPA has 
considered these relevant factors in its evaluation

[[Page 32553]]

that there is a substantial likelihood that PFHxS, PFNA, and HFPO-DA 
will individually occur and combinations of these three PFAS and PFBS 
will co-occur in mixtures in PWSs with a frequency and at levels of 
public health concern.
    The EPA's evaluation of the second statutory criterion is based on 
the best available health information, which includes UCMR 3 data and 
more recent PFAS drinking water data collected by several states. Based 
on suggestions in public comments to update state occurrence data, the 
EPA supplemented the data used to inform the rule proposal with new 
data from states included in the original proposal and additional 
states that have made monitoring data publicly available since the rule 
proposal (USEPA, 2024b). Consistent with section 1412(b)(1)(B)(II), 
this information combined represents best available occurrence data. It 
includes results from tens of thousands of samples and the assembled 
data represent one of the most robust occurrence datasets ever used to 
inform development of a drinking water regulation of a previously 
unregulated contaminant. The state data were primarily gathered after 
the UCMR 3 using improved analytical methods that could measure more 
PFAS at lower concentrations. These additional data demonstrate greater 
occurrence and co-occurrence of the PFAS monitored under UCMR 3 (PFHxS, 
PFNA, and PFBS) at significantly greater frequencies than UCMR 3 and 
the data initially included in the analysis. Furthermore, the state 
data show the co-occurrence of PFAS at levels of public health concern, 
as well as the demonstrated occurrence and co-occurrence of HFPO-DA 
which was not included within UCMR 3. As discussed subsequently, these 
data demonstrate that there is a substantial likelihood PFHxS, PFNA, 
and HFPO-DA will occur and combinations of PFHxS, PFNA, HFPO-DA, and 
PFBS will co-occur in mixtures with a frequency and at levels of public 
health concern. When determining that there is a substantial likelihood 
PFHxS, PFNA, and HFPO-DA will occur and PFHxS, PFNA, HFPO-DA, and/or 
PFBS will co-occur at levels of public health concern, the EPA 
considered both the occurrence concentration levels for PFHxS, PFNA, 
and HFPO-DA individually, as well as their collective co-occurrence and 
corresponding dose additive health concerns from co-exposures with PFBS 
for purposes of considering a regulatory determination for mixtures of 
these four PFAS. The EPA also considered other factors in evaluating 
the second criterion and informing level of public health concern for 
PFHxS, PFNA, and HFPO-DA individually and combinations of these three 
PFAS and PFBS in mixtures, including the frequency at which the 
contaminant is found, the geographic representation of the 
contaminant's occurrence, and the environmental fate and transport 
characteristics of the contaminant. As the EPA noted previously, while 
the agency is not making an individual regulatory determination for 
PFBS at this time, PFBS is an important component in mixtures with 
PFHxS, PFNA, and HFPO-DA and the EPA presents occurrence information 
for PFBS as part of section III.C.5 and its co-occurrence analyses in 
sections VI.C and D of this preamble.
    The EPA focused the evaluation of the state data on the non-
targeted or non-site specific (i.e., monitoring not conducted 
specifically in areas of known or potential contamination) monitoring 
efforts from 19 states. Non-targeted or non-site-specific monitoring is 
likely to be more representative of general occurrence because its 
framework and monitoring results will be less likely to potentially 
over-represent concentrations at locations of known or suspected 
contamination. Sixteen (16) of 19 states reported detections of at 
least three of PFHxS, PFNA, HFPO-DA, or PFBS.
    The EPA considered the targeted state monitoring data separately 
since a higher rate of detections may occur as a result of specifically 
looking in areas of suspected or known contamination. For the targeted 
state data nearly all these states also reported detections at systems 
serving millions of additional people, as well as at levels of public 
health concern, both individually for PFHxS, PFNA, and HFPO-DA, and as 
mixtures of these three PFAS and PFBS. State data detection frequency 
and concentration results vary for PFHxS, PFNA, HFPO-DA, and PFBS, both 
between these four different PFAS and across different states, with 
some states showing much higher reported detections and concentrations 
of these PFAS than others. The overall results demonstrate the 
substantial likelihood that individually PFHxS, PFNA, and HFPO-DA and 
mixtures of these three PFAS with PFBS will occur and co-occur at 
frequencies and levels of public health concern. Tables 2 and 3 show 
the percent of samples with state reported detections of PFHxS, PFNA, 
HFPO-DA, and PFBS, and the percentage of monitored systems with 
detections of PFHxS, PFNA, HFPO-DA, and PFBS, respectively, across the 
non-targeted state finished water monitoring data. The EPA notes that 
Alabama is not included in Tables 2 and 3 as only detections were 
reported and there was no information on the total number of samples 
collected to determine percent detection.
BILLING CODE 6560-50-P

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[[Page 32555]]


[GRAPHIC] [TIFF OMITTED] TR26AP24.003

BILLING CODE 6560-50-C
    As shown in Tables 2 and 3, all states except three report sample 
and system detections for at least three of the four PFAS. For those 
states that reported detections, the percentage of samples and systems 
where these PFAS were found ranged from 1 to 39.8 percent and 0.1 to 
38.1 percent, respectively. While these percentages show occurrence 
variability across states, several of these states demonstrate that a 
significant number of samples (e.g., detections of PFHxS in 26.2 
percent of New Jersey samples) and systems (e.g., detections of HFPO-DA 
in 12.2 percent of monitored systems in Kentucky) contain some or all 
four PFAS. This occurrence information, as well as the specific 
discussion related to individual occurrence for PFHxS, PFNA, and HFPO-
DA and co-occurrence of these three PFAS and PFBS, supports the 
agency's determination that there is a substantial likelihood that 
PFHxS, PFNA, HFPO-DA occur and PFHxS, PFNA, HFPO-DA, and PFBS co-occur 
in combinations of mixtures with a frequency of public health concern. 
Additionally, the agency emphasizes that occurrence and co-occurrence 
of these PFAS is not only at a regional or local level, rather it 
covers many states throughout the country; therefore, a national level 
regulation is necessary to ensure all Americans served by PWSs are 
equally protected.
1. PFHxS
    The occurrence data presented above, throughout section VI of this 
preamble and discussed in the USEPA (2024b) support the agency's final 
determination that there is a substantial likelihood PFHxS occurs with 
a frequency and at levels of public health concern in drinking water 
systems across the United States. PFHxS was found under UCMR 3 in 
approximately 1.1 percent of systems, serving 5.7 million people across 
25 states, Tribes, and U.S. territories. However, under UCMR 3, the 
minimum reporting level for PFHxS was 30 ng/L. As this reporting level 
is three times greater than the health-based HRL for PFHxS (10 ng/L), 
it is extremely likely there is significantly greater occurrence and 
associated population exposed in the range between the HRL of 10 ng/L 
and the UCMR 3 minimum reporting level of 30 ng/L (as demonstrated by 
both the more recent state data and the EPA's occurrence model 
discussed in this section and in section VI of this preamble showing 
many results in this concentration range). Through analysis of 
available state data, which consisted of approximately 48,000 samples 
within 12,600 systems, 18 out of the 19 states that conducted non-
targeted monitoring had reported detections of PFHxS in 1.3 to 32.9 
percent of their systems (Tables 2 and 3). These same systems reported 
concentrations ranging from 0.2 to 856

[[Page 32556]]

ng/L with median sample concentrations ranging from 1.17 to 12.1 ng/L, 
demonstrating concentrations above the HRL of 10 ng/L.
    Targeted state monitoring data of PFHxS show similar results. For 
example, in its targeted monitoring efforts, California reported 38.5 
percent of monitored systems found PFHxS, where concentrations ranged 
from 1.1 to 160 ng/L, also demonstrating concentrations above the HRL. 
In total, considering both the non-targeted and targeted state data, 
PFHxS was found above the HRL in at least 184 PWSs in 21 states serving 
a population of approximately 4.3 million people.
    The EPA also evaluated PFHxS in a national occurrence model that 
has been developed and utilized to estimate national-scale PFAS 
occurrence for four PFAS that were included in UCMR 3 (Cadwallader et 
al., 2022). The model has been peer reviewed and is described 
extensively in Cadwallader et al. (2022). The model and results are 
described in section VI.E of this preamble; briefly, both the UCMR 3 
and some state data were incorporated into a Bayesian hierarchical 
model which supported exposure estimates for select PFAS at lower 
levels than were measured under UCMR 3. Hundreds of systems serving 
millions of people were estimated to have mean concentrations exceeding 
the PFHxS HRL (10 ng/L). Therefore, the UCMR 3 results, the national 
occurrence model results, and the substantial state data demonstrate 
the substantial likelihood PFHxS occurs at a frequency and level of 
public health concern. Finally, UCMR 5 data are being reported to the 
EPA while this final rule is being prepared. See section VI of this 
preamble for more information on the preliminary results. While these 
UCMR 5 PFHxS data are too preliminary to provide the basis for the 
regulatory determination, these preliminary UCMR 5 results appear to 
confirm state data and model results.
    Further supporting this final determination, PFHxS is very stable 
and persistent in the environment. While PFHxS was phased out in the 
U.S. in the early 2000's there are still detections as previously 
demonstrated. In addition, legacy stocks may also still be used, 
production continues in other countries, and products containing PFHxS 
may be imported into the U.S. (USEPA, 2000b). Since PFHxS is 
environmentally persistent and products containing PFHxS are still in 
use and may be imported into the United States, the EPA anticipates 
environmental contamination to sources of drinking water will continue. 
To illustrate this point further, PFOA and PFOS, two of the most 
extensively sampled PFAS, are also very environmentally persistent and 
have similarly been phased out in the U.S. for many years, though these 
two contaminants continue to often be found at levels of public health 
concern as discussed in section VI of this preamble. Currently, this 
also appears to be a similar trend for PFHxS occurrence, where the 
drinking water sample data demonstrates it continues to occur at levels 
of public health concern. Therefore, in consideration of factors 
relating to the environmental persistence of PFHxS, its presence in 
consumer products and possible continued use, and the observed 
occurrence trend of PFOA and PFOS, the EPA finds that there is a 
substantial likelihood PFHxS occurs or will occur at a frequency and 
level of public health concern.
2. PFNA
    The occurrence data presented above, throughout section VI of this 
preamble, and discussed in USEPA (2024b) support the agency's final 
determination that there is a substantial likelihood PFNA occurs with a 
frequency and at levels of public health concern in drinking water 
systems across the U.S.
    PFNA was found under UCMR 3 in approximately 0.28 percent of 
systems, serving 526,000 people in 7 states, Tribes, and U.S. 
territories, using a minimum reporting level of 20 ng/L. As this 
reporting level is two times greater than the health-based HRL of 10 
ng/L, the EPA expects there is even greater occurrence and exposed 
population in the range between 10 and 20 ng/L. Additionally, through 
analysis of the extensive amount of available state data, which 
consisted of approximately 57,000 samples within approximately 12,400 
systems, 16 of 19 non-targeted monitoring states reported detections of 
PFNA within 0.3 to 16.5 percent of their systems (Tables 2 and 3). 
These same states reported sample results ranging from 0.23 to 330 ng/
L, demonstrating levels above the HRL of 10 ng/L, with median sample 
results ranging from 0.35 to 7.5 ng/L.
    Targeted state monitoring data of PFNA are also consistent with 
non-targeted state data; for example, Pennsylvania reported 5.8 percent 
of monitored systems found PFNA, where concentrations ranged from 1.8 
to 18.1 ng/L, also showing concentrations above the HRL. When 
considering all available state data, there are at least 480 systems in 
19 states serving more than 8.4 million people that reported any 
concentration of PFNA, and at least 52 systems in 12 states within 
different geographic regions serving a population of 177,000 people 
with reported concentrations above the HRL of 10 ng/L. Furthermore, 
when evaluating only a subset of the available state data representing 
non-targeted monitoring, PFNA was reported in approximately 3.6 percent 
of monitored systems; if these results were extrapolated to the nation 
and those system subject to the final rule requirements, the agency 
estimates that PFNA would be detectable in over 2,300 PWSs serving 24.9 
million people. If those results were further compared to the HRL for 
PFNA (10 ng/L), PFNA would be detected above the HRL in 228 systems 
with 830,000 people exposed. Thus, in addition to the UCMR 3 results, 
these extensive state data also reflect there is a substantial 
likelihood PFNA occurs at a frequency and level of public health 
concern because it is observed or likely to be observed within numerous 
water systems above levels of public health concern across a range of 
geographic locations. Finally, UCMR 5 data are being reported to the 
EPA while this final rule is being prepared. See section VI of this 
preamble for more information on the preliminary results. While these 
PFNA UCMR 5 data are too preliminary to provide the basis for the 
regulatory determination, these preliminary UCMR 5 results appear to 
confirm state data discussed above.
    Further supporting this final determination, PFNA is very stable 
and persistent in the environment. While it has generally been phased 
out in the U.S. there are still detections as demonstrated previously. 
Additionally, legacy stocks may still be used and products containing 
PFNA may still be produced internationally and imported to the U.S. 
(ATSDR, 2021). Since PFNA is environmentally persistent and products 
containing PFNA are still in use and may be imported into the U.S., 
there is a substantial likelihood that environmental contamination of 
sources of drinking water will continue. To illustrate this point 
further, PFOA and PFOS, two of the most extensively sampled PFAS, are 
also very environmentally persistent and have similarly been phased out 
in the U.S. for many years, though these two contaminants continue to 
often be found at levels of public health concern as discussed in 
section VI of this preamble. Currently, this also appears to be a 
similar trend for PFNA occurrence, where the drinking water sample data 
demonstrates it continues to occur at levels of public health concern. 
Therefore, in consideration of factors relating to the environmental 
persistence of PFNA, its presence in

[[Page 32557]]

consumer products and possible continued use, and the observed 
occurrence trend of PFOA and PFOS, the EPA finds that there is a 
substantial likelihood PFNA occurs or will co-occur at a frequency and 
level of public health concern.
3. HFPO-DA
    The occurrence data presented above, throughout section VI of this 
preamble, and discussed in the USEPA (2024b) support the agency's final 
determination that there is a substantial likelihood HFPO-DA occur with 
a frequency and at levels of public health concern in drinking water 
systems across the U.S. HFPO-DA was not included as a part of the UCMR 
3; however, through analysis of available state data, which consisted 
of approximately 36,000 samples within approximately 10,100 systems, 10 
of the 16 states that conducted non-targeted monitoring had state 
reported detections of HFPO-DA within 0.1 to 12.2 percent of their 
systems (Tables 2 and 3). These same states reported sample results 
ranging from 0.7 to 100 ng/L and median sample results ranging from 1.7 
to 29.6 ng/L, demonstrating concentrations above the HRL of 10 ng/L.
    Additionally, targeted state monitoring in North Carolina included 
sampling across six finished drinking water sites and 438 samples with 
HFPO-DA. Concentrations ranged from 9.52 to 1100 ng/L, a median 
concentration of 40 ng/L, and 433 (99 percent) samples exceeding the 
HRL (10 ng/L). When considering all available state data, there are at 
least 75 systems in 13 states serving more than 2.5 million people that 
reported any concentration of HFPO-DA, and at least 13 systems in 5 
states within different geographic regions of the country serving a 
population of 227,000 people with reported concentrations above the HRL 
of 10 ng/L. Additionally, when evaluating only a subset of the 
available state data representing non-targeted monitoring to ensure 
that the data were not potentially over-represented by sampling 
completed in areas of known or suspected contamination, HFPO-DA was 
reported in approximately 0.48 percent of monitored systems; if these 
results were extrapolated to the nation and those system subject to the 
final rule requirements, the agency estimates that HFPO-DA would be 
detectable in over 320 PWSs serving 9.9 million people. If those 
results were further compared to the HRL for HFPO-DA (10 ng/L), HFPO-DA 
would be detected above the HRL in 42 systems with at least 495,000 
people exposed. Finally, UCMR 5 data are being reported to the EPA 
while this final rule is being prepared. See section VI of this 
preamble for more information on the preliminary results. While these 
HFPO-DA UCMR 5 data are too preliminary to provide the basis for the 
regulatory determination, these preliminary UCMR 5 results appear to 
confirm the state data discussed above.
    Further supporting this final determination, HFPO-DA is very stable 
and persistent in the environment. Additionally, unlike PFOA, PFOS, 
PFHxS, and PFNA which have been phased out in the U.S, HFPO-DA 
continues to be actively produced and used within the country and is 
generally considered to have replaced the production of PFOA. Since 
HFPO-DA is environmentally persistent and products containing HFPO-DA 
are still being actively produced and used, the EPA anticipates that 
contamination will continue, if not increase, due to disposal and 
breakdown in the environment. To illustrate this point further, PFOA 
and PFOS, two of the most extensively sampled PFAS, are also very 
environmentally persistent and have been phased out in the United 
States for many years, though these two PFAS continue to often be found 
at levels of public health concern as discussed in section VI of this 
preamble. Therefore, in consideration of factors relating to the 
environmental persistence of HFPO-DA, its continued and possibly 
increasing presence in consumer products and use, and the observed 
occurrence trend of PFOA and PFOS, the EPA anticipates that occurrence 
levels of HFPO-DA will similarly continue to be found at least to the 
levels described in this preamble demonstrating that there is a 
substantial likelihood HFPO-DA will occur at a frequency and level of 
public health concern.
    As discussed, HFPO-DA continues to be actively produced and used 
throughout the U.S., it currently occurs at levels above its HRL, and 
it occurs within geographically diverse areas of the country 
demonstrating it is not a local or regional issue only. While the 
current individual occurrence profile of HFPO-DA is not as pervasive 
and is found at somewhat lower frequency as the currently observed 
levels of PFOA, PFOS, or PFHxS, based upon the available substantial 
amount of state occurrence data and given factors previously described, 
the EPA has determined that there is a substantial likelihood HFPO-DA 
occurs or will occur at a frequency and level of public health concern.
4. PFBS
    The agency is deferring the final individual regulatory 
determination for PFBS to further consider whether occurrence 
information supports a finding that there is substantial likelihood 
that PFBS will individually occur in PWSs and at a level of public 
health concern. While current information demonstrates that PFBS 
frequently occurs, it has not been observed to exceed its HRL of 2,000 
ng/L in isolation. However, when considered in mixture combinations 
with other PFAS, including PFHxS, PFNA, and HFPO-DA, PFBS is 
anticipated to have dose-additive adverse health effects (based on 
available data on PFAS and dose additivity) and there is a substantial 
likelihood of its co-occurrence in combinations of mixtures with PFHxS, 
PFNA, and HFPO-DA with a frequency and at levels of public health 
concern. This is described further in sections III.C.5 and VI.C. and 
VI.D of this preamble.
5. Mixtures of PFHxS, PFNA, HFPO-DA, and PFBS
    Through the information presented within this section and in USEPA 
(2024b), along with the co-occurrence information presented in sections 
VI.C and VI.D of this preamble, the EPA's evaluation of all available 
UCMR 3 and state occurrence data demonstrates that there is a 
substantial likelihood that combinations of PFHxS, PFNA, HFPO-DA, and 
PFBS (collectively referred to as ``Hazard Index PFAS'') co-occur or 
will co-occur in mixtures at a frequency and level of public health 
concern.
    As discussed throughout section III.C of this preamble, the EPA has 
determined that PFHxS, PFNA, and HFPO-DA each meet the second statutory 
criterion for individual regulation. Additionally, as demonstrated in 
sections VI.C. and D. of this preamble, the EPA has determined that 
these three PFAS also meet the second statutory criterion when present 
in mixture combinations. PFBS has not been observed to exceed its HRL 
of 2,000 ng/L in isolation; therefore, the EPA is deferring the 
individual regulatory determination for this PFAS to further consider 
future occurrence information. However, the agency has determined that 
PFBS frequently occurs (as shown in Table 2 and Table 3), and that when 
considering dose additivity there is a substantial likelihood of its 
co-occurrence in mixtures of PFHxS, PFNA, and/or HFPO-DA with a 
frequency and at a level of public health concern. Therefore, the 
agency has

[[Page 32558]]

determined that PFBS also meets the criterion when present in mixture 
combinations with PFHxS, PFNA, and/or HFPO-DA.
    In sections VI.C and D of this preamble, the EPA has presented its 
evaluation and findings related to the likelihood and frequency of co-
occurrence of the four Hazard Index PFAS, including both through 
groupwise and pairwise analyses for the Hazard Index PFAS, in non-
targeted state monitoring datasets. The groupwise co-occurrence 
analysis established the broad occurrence frequency of Hazard Index 
PFAS through a linkage to the presence of PFOA and PFOS. Because not as 
many states have monitored for the Hazard Index PFAS as compared to 
PFOA and PFOS, their occurrence information is less extensive than the 
occurrence information for PFOA and PFOS. Therefore, though the agency 
has previously made a final regulatory determination for PFOA and PFOS, 
establishing co-occurrence of Hazard Index PFAS with PFOA and PFOS is 
important to better understand the likelihood of Hazard Index PFAS 
occurrence. In this analysis, the six PFAS were separated into two 
groups--one consisted of PFOS and PFOA and the other group included the 
four Hazard Index PFAS. The analysis broke down the systems and samples 
according to whether chemicals from the two respective groups were 
detected. Given that the groupwise co-occurrence analysis established 
that there is a substantial likelihood that the Hazard Index PFAS 
frequently occur, particularly alongside PFOA or PFOS, the pairwise co-
occurrence was relevant for understanding how the Hazard Index PFAS co-
occur with each other instead of occurring independently. Pairwise co-
occurrence analysis explored the odds ratios for each unique pair of 
PFAS included in the regulation. For every pair of PFAS chemicals 
included in the final regulation, the odds ratio, a statistic that, in 
this context, quantifies the strength of association between two PFAS 
being present, was found to be statistically significantly greater than 
1. This means there was a statistically significant increase in the 
odds of reporting a chemical as present after knowing that the other 
chemical was detected. In most instances the odds appeared to increase 
in excess of a factor of ten. Thus, based on the large amount of 
available data, the chemicals are clearly demonstrated to frequently 
co-occur rather than occur independently of one another, supporting the 
agency's determination for mixtures of the four PFAS.
    For the groupwise analysis, results generally indicated that when 
PFOA and PFOS were found, Hazard Index PFAS were considerably more 
likely to also be present. Additionally, for systems that only measured 
PFOA and/or PFOS and did not measure the Hazard Index PFAS, it can be 
assumed that the Hazard Index PFAS are more likely to be present in 
those systems, and that Hazard Index occurrence may be underestimated. 
Moreover, while PFOA and PFOS are not included within the Hazard Index 
PFAS or the determination to regulate mixtures of these PFAS, the 
pervasive occurrence of PFOA and PFOS shown in section VI of this 
preamble is a strong indicator that these other Hazard Index PFAS are 
also more likely to be found than what has been reported in state 
monitoring data to date. In this analysis, comparisons were also made 
between the number of Hazard Index PFAS analyzed and the number of 
Hazard Index PFAS reported present. As more Hazard Index PFAS were 
analyzed, more Hazard Index PFAS were reported present. Systems and 
samples where Hazard Index PFAS were found were more likely to find 
multiple Hazard Index PFAS than a single Hazard Index PFAS (when 
monitoring for three or four Hazard Index PFAS), demonstrating an 
increased likelihood of their co-occurrence. Additionally, for both 
system-level and sample-level analyses where PFOA and/or PFOS were 
reported present and all four Hazard Index PFAS were monitored, two or 
more Hazard Index PFAS were reported present more than half of the 
time, exhibiting they are more likely to occur together than in 
isolation. Furthermore, the EPA notes that when evaluating only a 
subset of the available state data representing non-targeted monitoring 
where either three or four Hazard Index PFAS were monitored, regardless 
of whether PFOA or PFOS were reported present, two or more of the 
Hazard Index PFAS were reported in approximately 12.1 percent of 
monitored systems; if these results were extrapolated to the nation, 
two or more of these four PFAS would co-occur in about 8,000 PWSs (see 
section VI.C.1 of this preamble for additional information).
    The EPA uses a Hazard Index of 1 as the HRL to further evaluate the 
substantial likelihood of the Hazard Index PFAS co-occurring at a 
frequency and level of public health concern. As discussed in greater 
detail in section VI.D, of this preamble based on available state data 
the EPA finds that across 21 states there are at least 211 PWSs serving 
approximately 4.7 million people with results above a Hazard Index of 1 
for mixtures including two or more of the Hazard Index PFAS. 
Specifically evaluating the presence of PFBS, in these same 211 systems 
where the Hazard Index was found to be greater than 1, PFBS was 
observed at or above its PQL in mixtures with one or more of the other 
three Hazard Index PFAS in at least 72 percent (152) of these systems 
serving approximately 4.5 million people. Additionally, as described 
previously in sections III.C.1-3, PFHxS, PFNA, HFPO-DA, and PFBS are 
all very stable and persistent in the environment. All are either still 
being actively used or legacy stocks may be used and imported into the 
U.S. Consequently, there is a substantial likelihood that environmental 
contamination of sources of drinking water from these PFAS will 
continue to co-occur to at least the levels described in this preamble.
    Therefore, in consideration of the environmental persistence of 
these PFAS, their presence in consumer products and continued use, the 
findings of both the pairwise and groupwise co-occurrence analyses, and 
demonstration of combinations of Hazard Index PFAS mixtures exceeding 
the Hazard Index of 1, the EPA has determined there is sufficient 
occurrence information available to support the second criterion that 
there is a substantial likelihood that combinations of the four Hazard 
Index PFAS in mixtures co-occur at frequencies and levels of public 
health concern.
6. Summary of Major Public Comments and EPA Responses
    The EPA requested comment on its preliminary regulatory 
determination for all four PFAS and their mixtures and its evaluation 
of the statutory criteria that supports the finding. The EPA also 
requested comment on additional occurrence data the agency should 
consider regarding its decision that PFHxS, PFNA, HFPO-DA, and PFBS and 
their mixtures occur or are substantially likely to occur in PWSs with 
a frequency and at levels of public health concern. The EPA received 
many comments on the agency's evaluation of the second statutory 
criterion under section 1412(b)(1)(A) of SDWA. Many commenters 
supported the EPA's preliminary determination that PFHxS, PFNA, HFPO-
DA, and PFBS and mixtures of these four contaminants meet the second 
statutory occurrence criterion under SDWA.

[[Page 32559]]

    A couple of commenters claimed that the EPA does not have a robust 
understanding of available occurrence data that supports any of the 
regulatory determinations for the four PFAS in this rule. Additionally, 
some commenters suggested that the preliminary determinations were 
``rushed'' and ``non-scientific,'' and that the agency should wait 
until some or all of the UCMR 5 data is available and considered. The 
EPA disagrees. Sufficient occurrence data are available to establish a 
substantial likelihood of occurrence at frequencies and levels of 
health concern. Per the intent of the statute, the agency used the best 
available data in an expeditious manner, which, as the agency described 
earlier, was also a very large dataset consisting of tens of thousands 
of samples and representing one of the most robust occurrence datasets 
ever used to inform development of a drinking water regulation of a 
previously unregulated contaminant. The agency also disagrees that the 
occurrence analyses undertaken and available in the preamble as well as 
the technical support document for occurrence were non-scientific. 
Based on publicly available information within the state data, the EPA 
verified that the very large majority of samples (at least 97 percent) 
were collected using EPA-approved methods; the slight percentage the 
agency was unable to verify would not result in different agency 
conclusions. Additionally, the EPA notes that the aggregated data were 
assessed using precedented statistical metrics and analyses. In 
addition, the Cadwallader et al. (2022) model uses a robust, widely 
accepted Bayesian statistical approach for modeling contaminant 
occurrence. Based on these analyses, the EPA has a clear understanding 
of the occurrence of the modeled contaminants. As discussed in section 
III.C of this preamble and USEPA, 2024b, the EPA also has sufficient 
state data which consist of a greater number of total systems and 
samples than that included within the monitoring under UCMR 3, to 
confidently establish that there is a substantial likelihood of 
occurrence at frequencies and levels of public health concern.
    As discussed above, the agency believes that the best currently 
available occurrence data demonstrate substantial likelihood of 
occurrence for the chemicals included in the final rule as they are 
demonstrated at frequencies and levels of public health concern. UCMR 5 
data are being reported to the EPA while this final rule is being 
prepared. See section VI of this preamble for more information on the 
EPA's evaluation of the preliminary results. While these data are too 
preliminary to provide the basis for a regulatory determination, these 
preliminary UCMR 5 results appear to support the data discussed 
previously.
    Several commenters disagreed that the available occurrence 
information supports a preliminary determination for HFPO-DA, with a 
few citing a lack of nationally representative data and suggesting a 
delay until UCMR 5 data is collected. The EPA disagrees with these 
comments, as the state monitoring data for the proposed rule 
demonstrates HFPO-DA occurrence in 13 geographically diverse states, 
including at 75 systems serving at least 2.5 million people. Moreover, 
non-national datasets may serve to demonstrate occurrence of a 
contaminant to warrant a positive determination and subsequent 
development of an NPDWR. For example, the best available HFPO-DA state 
data consists of approximately 36,000 samples within 10,000 systems and 
is representative of multiple geographic locations.
    One commenter stated that a regulatory determination for PFNA was 
unnecessary as they do not believe it occurred with frequency under 
UCMR 3 monitoring, and a couple of other commenters suggested that a 
negative determination was appropriate for PFNA citing occurrence 
levels. The EPA disagrees that a negative determination is appropriate 
for PFNA as it has been demonstrated to occur at levels of public 
health concern in at least 52 water systems across 12 states. 
Furthermore, as described previously, when evaluating only a subset of 
the available state data representing non-targeted monitoring, PFNA was 
reported in approximately 3.6 percent of monitored systems and if those 
results were extrapolated across the country, PFNA would be detectable 
at any concentration in over 2,300 PWSs serving 21.2 million people and 
detectable above 10 ng/L in 227 systems serving 711,000 people. 
Additionally, PFNA frequently co-occurs with other PFAS, and as 
previously discussed in this section, presents dose additive health 
concerns with other PFAS demonstrating it is also an important 
component of the determination to regulate it in mixtures with PFHxS, 
HFPO-DA, and/or PFBS.
    Commenters both agreed and disagreed with the EPA's individual 
preliminary determination for PFBS. With respect to commenters who 
suggested that the EPA has not met the occurrence criterion, while PFBS 
occurs at significant frequency, the agency is deferring the individual 
determination to regulate PFBS when it occurs individually until it 
conducts further evaluation under the statutory criteria. The EPA 
further finds that PFBS exposure may cause dose additive adverse health 
effects in mixtures with PFHxS, PFNA, and/or HFPO-DA; that there is a 
substantial likelihood that PFBS co-occurs in mixtures with PFHxS, 
PFNA, and/or HFPO-DA in PWSs with a frequency and at levels of public 
health concern; and that, in the sole judgment of the Administrator, 
regulation of PFBS in mixtures with PFHxS, PFNA, and/or HFPO-DA 
presents a meaningful opportunity for health risk reduction for persons 
served by PWSs. Therefore, PFBS will be regulated as part of a mixture 
with PFHxS, PFNA, and HFPO-DA.
    A few commenters provided feedback on occurrence thresholds the 
agency should consider when evaluating the second statutory criterion 
for regulatory determinations. Particularly, these commenters 
recommended that the EPA should define a threshold for frequency and 
level of public health concern that warrants a specific regulatory 
determination. A few commenters cited other previous regulatory 
determinations where the agency made a determination not to regulate 
contaminants with similar or lower levels of occurrence suggesting that 
this should be the same for some or all of these four PFAS. 
Furthermore, some of these commenters stated that it would be arbitrary 
and capricious and conflict with the SDWA if the EPA did not use the 
level of adverse health effect (i.e., the HRL) to represent the level 
at which a contaminant is considered a public health concern.
    The EPA disagrees with these commenters and as demonstrated in the 
proposal and noted earlier in section III of this preamble, for this 
regulatory determination, as well as past determinations, the agency 
did compare available occurrence data relative to the contaminant HRL 
as a factor in informing the occurrence level of public health concern. 
However, the level of public health concern for purposes of the second 
criterion is a contaminant-specific analysis that include consideration 
of the HRL, as well as other factors and not solely based on the direct 
comparison to the HRL. There is not just one simple threshold used for 
public health concern for all contaminants. In the case of PFAS, this 
is particularly relevant given the dose-additivity of mixtures.
    The EPA also disagrees with these commenters as SDWA does not 
define the occurrence level of public health

[[Page 32560]]

concern for contaminants, nor does it prescribe the level of adverse 
health effects that must be used for a regulatory determination. 
Ultimately, the overall decision to regulate a contaminant considers 
all three statutory criteria, including the comprehensive assessment of 
meaningful opportunity which is in the Administrator's sole discretion. 
In previous EPA regulatory determinations, the agency has considered 
the occurrence criteria unique to the contaminant it is evaluating and 
has made decisions not to regulate contaminants both where there was 
substantial likelihood of occurrence at frequency and/or at levels of 
public health concern and where there was limited or no substantial 
likelihood of occurrence at frequency and/or at levels of public health 
concern. Consistent with this past regulatory history and the 
Administrator's authority under the terms of the statute, the decision 
considers all three criteria and cannot be determined in the exact same 
manner for different contaminants. While the EPA may have made negative 
determinations for other contaminants demonstrating occurrence at 
different frequencies and levels of public health concern, the basis 
for those decisions was specific to those contaminants and does not 
apply to these PFAS or any other future contaminants for which the EPA 
would make regulatory determinations. Therefore, the statute does not 
require, and the EPA does not use a minimum or one-size-fits-all 
occurrence thresholds (for either frequency or precise level) for 
regulatory determinations.
    As described in section VI of this preamble, many commenters 
supported the EPA's proposal to regulate mixtures of PFAS. Specific to 
occurrence, some of these commenters particularly expressed support for 
the EPA's preliminary determination that mixtures of these four PFAS 
meet the second statutory occurrence criterion under SDWA, citing that 
the agency has used the best available information to determine that 
there is a substantial likelihood that combinations of these PFAS will 
co-occur in mixtures at a frequency and level of public health concern. 
One commenter stated that the additional occurrence data presented by 
the EPA in the proposal for the Hazard Index PFAS supports the EPA's 
proposed determination that these PFAS should be regulated under the 
SDWA. Conversely, several other commenters stated that there was not 
supporting evidence for the co-occurrence of the four Hazard Index 
PFAS. The EPA disagrees; the extent to which Hazard Index PFAS 
chemicals co-occur in the non-targeted state dataset is discussed 
extensively in the record for this rule and made evident through the 
system level analysis in section VI.C. of this preamble. As also 
discussed elsewhere in the record for this rule, in both system level 
and sample level analyses where PFOA and/or PFOS were reported present 
and all four Hazard Index PFAS were monitored, two or more Hazard Index 
PFAS were reported present more than half of the time. Further, the 
odds ratios tables in Exhibit 11 provide a statistical examination of 
pairwise co-occurrence. The odds ratio is a statistic that quantifies 
the strength of association between two events. In the context 
described here, an ``event'' is the reported presence of a specific 
PFAS contaminant. The odds ratio between PFOA and PFHxS, for example, 
reflects the strength of association between PFHxS being reported 
present and PFOA being reported present. If an odds ratio is greater 
than 1, the two events are associated. The higher the odds ratio, the 
stronger the association. For every pair of PFAS chemicals included in 
the proposed regulation, the odds ratio was found to be statistically 
significantly greater than 1. This means there was a statistically 
significant increase in the odds of a PFAS being present if the other 
PFAS compound was detected (e.g., if PFOA is detected, PFHxS is more 
likely to also be found). In most instances the odds appeared to 
increase in excess of a factor of ten. Thus, based on the large amount 
of available data, the chemicals are clearly demonstrated to co-occur 
rather than occur independently of one another, further supporting the 
agency's determination for combinations of mixtures of the four PFAS.
    After considering the public comments and additional occurrence 
data evaluated as requested by public commenters, the EPA finds that 
PFHxS, PFNA, and HFPO-DA individually and mixtures of these three PFAS 
and PFBS, meet the second statutory criterion for regulatory 
determinations under section 1412(b)(1)(A) of SDWA that the contaminant 
is known to occur or co-occur or there is a substantial likelihood that 
the contaminant will occur or co-occur in PWSs with a frequency and at 
levels of public health concern (USEPA, 2024b).

D. Statutory Criterion 3--Meaningful Opportunity

    The agency has determined that individual regulation of PFHxS, 
PFNA, and HFPO-DA and regulation of combinations of PFHxS, PFNA, HFPO-
DA, and PFBS in mixtures presents a meaningful opportunity for health 
risk reduction for persons served by PWSs. As discussed in section 
III.C. of this preamble, the EPA evaluated this third statutory 
criterion similarly to previous regulatory determinations using the 
Protocol developed under Regulatory Determination 3 (USEPA, 2014b) and 
also used in the Regulatory Determination 4. This evaluation includes a 
comprehensive assessment of meaningful opportunity for each unique 
contaminant including the nature of the health effects, sensitive 
populations affected, including infants, children and pregnant and 
nursing women, number of systems potentially affected, and populations 
exposed at levels of public health concern, geographic distribution of 
occurrence, technologies to treat and measure the contaminant, among 
other factors. The agency further reiterates that, per the statute, 
this determination of meaningful opportunity is in the Administrator's 
sole discretion.
    Accordingly, the EPA is making this determination of meaningful 
opportunity after evaluating health, occurrence, treatment, and other 
related information and factors including consideration of the 
following:
     PFHxS, PFNA, and HFPO-DA and combinations of these three 
PFAS and PFBS in mixtures may cause multiple adverse human health 
effects, often at very low concentrations, on several biological 
systems including the endocrine, cardiovascular, developmental, renal, 
hematological, reproductive, immune, and hepatic systems as well as are 
likely to produce dose-additive effects from co-exposures.
     The substantial likelihood that PFHxS, PFNA, and HFPO-DA 
individually occur or will occur and that mixtures of PFHxS, PFNA, 
HFPO-DA, and/or PFBS co-occur or will co-occur together at frequencies 
and levels of public health concern in PWSs as discussed in section III 
of this preamble above and in section VI of this preamble, and the 
corresponding significant populations served by these water systems 
which potentially include sensitive populations and lifestages, such as 
pregnant and lactating women, as well as children.
     PFHxS, PFNA, HFPO-DA and combinations of these three PFAS 
and PFBS in mixtures are expected to be persistent in the environment, 
with some (e.g., PFHxS, PFNA) also demonstrated to be very persistent 
in the human body.
     Validated EPA-approved measurement methods are available 
to measure PFHxS, PFNA, HFPO-DA, and

[[Page 32561]]

PFBS. See section VII of this preamble for further discussion.
     Treatment technologies are available to remove PFHxS, 
PFNA, and HFPO-DA and combinations of these three PFAS and PFBS from 
drinking water. See section X of this preamble for further discussion.
     Even though PFBS is very likely to be below its 
corresponding individual HRL when it occurs in a mixture, the record 
indicates that there is a substantial likelihood that it co-occurs with 
the regulated PFAS throughout public water systems nationwide. See 
sections III.C.5 and VI.C. of this preamble for further discussion. 
According to the 2023 Interagency PFAS Report to Congress (United 
States OSTP, 2023), PFBS has been shown to affect the following health 
endpoints: body weight, respiratory, cardiovascular, gastrointestinal, 
hematological, musculoskeletal, hepatic, renal, ocular, endocrine, 
immunological, neurological, reproductive, and developmental. Thus, 
including PFBS as a mixture component represents a meaningful 
opportunity to reduce PFBS' contributions to the overall hazard of the 
mixture and resulting dose additive health concerns. This is 
particularly relevant where the exposures of the other three PFAS in 
the mixture are also below their respective HRLs but when the hazard 
contributions of each mixture component are summed, the total exceeds 
the mixture HRL. In this scenario, the inclusion of PFBS allows for a 
more accurate picture of the overall hazard of the mixture so that PFBS 
can be reduced along with associated dose additive health concerns. In 
short, hazard would be underestimated if PFBS was not included in the 
regulated mixture. The EPA also considered the situation where PFHxS, 
PFNA, or HFPO-DA exceed one or more of their corresponding HRLs and co-
occur with PFBS below its corresponding HRL. Although the exceedance of 
the mixture HRL is driven by a PFAS other than PFBS, PFBS is 
contributing to the overall hazard of the mixture and resulting dose 
additive health concerns. Including PFBS in the regulated mixture 
offers a meaningful opportunity to reduce dose additive health concerns 
because, when PFBS and other Hazard Index PFAS are present, public 
water systems will be able to better design and optimize their 
treatment systems to remove PFBS and any other co-occurring Hazard 
Index PFAS. This optimization will be even more effective knowing both 
that PFBS is present in source waters and its measured concentrations.
     Regulating PFHxS, PFNA, and HFPO-DA and combinations of 
these three PFAS and PFBS in mixtures is anticipated to reduce the 
overall public health risk from other PFAS, including PFOA and PFOS, 
that co-occur and are co-removed. Their regulation is anticipated to 
provide public health protection at the majority of known PWSs with 
PFAS-impacted drinking water.
     There are achievable steps to manage drinking water that 
can be taken to reduce risk.
    As described in sections III.C, VI.C, VI.D, and USEPA (2024b), data 
from both the UCMR 3 and state monitoring efforts demonstrates the 
substantial likelihood of individual occurrence of PFHxS, PFNA, and 
HFPO-DA and co-occurrence of mixture combinations of PFHxS, PFNA, HFPO-
DA, and PFBS at frequencies and levels of public health concern. Under 
UCMR 3, 5.7 million and 526,000 people had reported detections (greater 
than or equal to their minimum reporting levels which were two to three 
times their HRLs of 10 ng/L), of PFHxS and PFNA, respectively. 
Additionally, based on the more recent available state monitoring data 
presented earlier in this section, a range of geographically diverse 
states monitored systems that reported individual detections of PFHxS, 
PFNA, and HFPO-DA and serve approximate populations of 26.5 million, 
2.5 million, and 8.4 million, respectively. Of these same systems, 
detections above the EPA's HRLs for PFHxS, PFNA, and HFPO-DA were seen 
in systems that serve approximate populations of 4.3 million, 227,000, 
and 177,000 people, respectively. As discussed previously, if these 
monitored systems were extrapolated to the nation, the EPA estimates 
that thousands of additional systems serving millions of people could 
have detectable levels of these three PFAS and hundreds of these 
systems may show values above the EPA's HRLs. Lastly, in evaluating the 
available state data, the EPA has found that mixtures of PFHxS, PFNA, 
HFPO-DA, and/or PFBS occur with a Hazard Index greater than 1 in 
systems serving approximately 4.7 million people. The agency further 
notes that while it has demonstrated through sufficient data that these 
four PFAS co-occur in mixtures at a frequency and level of public 
health concern in PWSs, throughout the nation it is extremely likely 
that additional systems and associated populations served would also 
demonstrate a Hazard Index greater than 1 if data for all PWSs were 
evaluated.
    Analytical methods are available to measure PFHxS, PFNA, HFPO-DA, 
and PFBS in drinking water. The EPA has published two multi-laboratory 
validated drinking water methods for individually measuring PFHxS, 
PFNA, HFPO-DA, and PFBS. Additional discussion on analytical methods 
can be found in section VII of this preamble.
    The EPA's analysis, summarized in section X of this preamble, found 
there are available treatment technologies capable of reducing PFHxS, 
PFNA, HFPO-DA, and PFBS. These technologies include granular activated 
carbon (GAC), anion exchange (AIX) resins, reverse osmosis (RO), and 
nanofiltration (NF). These treatment technologies remove PFHxS, PFNA, 
HFPO-DA, and PFBS and their mixtures. They also have been documented to 
co-remove other PFAS (S[ouml]reng[aring]rd et al., 2020; McCleaf et 
al., 2017; Mastropietro et al., 2021). Furthermore, as described in 
section VI of this preamble, PFHxS, PFNA, HFPO-DA, and PFBS also co-
occur with PFAS for which the agency is not currently making a 
regulatory determination. Many of these other emergent co-occurring 
PFAS are likely to also pose hazards to public health and the 
environment (Mahoney et al., 2022). Therefore, based on the EPA's 
findings that PFHxS, PFNA, HFPO-DA, and PFBS have a substantial 
likelihood to co-occur in drinking water with other PFAS and treating 
for PFHxS, PFNA, HFPO-DA, and PFBS is anticipated to result in removing 
these and other PFAS, individual regulation of PFHxS, PFNA, and HFPO-DA 
and regulation of mixtures of these three PFAS and PFBS also presents a 
meaningful opportunity to reduce the overall public health risk from 
all other PFAS that co-occur and are co-removed with PFHxS, PFNA, HFPO-
DA, and PFBS.
    With the ability to monitor for PFAS, identify contaminated 
drinking water sources and contaminated finished drinking water, and 
reduce PFAS exposure through management of drinking water, the EPA has 
identified meaningful and achievable actions that can be taken to 
reduce the human health risk of PFAS.
1. Proposal
    The EPA made a preliminary determination that regulation of PFHxS, 
PFNA, HFPO-DA, and PFBS, both individually and in a mixture, presents a 
meaningful opportunity for health risk reduction for persons served by 
PWSs. The EPA made this preliminary determination after evaluating 
health, occurrence, treatment, and other related information against 
the three SDWA statutory criteria including consideration of the 
factors previously

[[Page 32562]]

described in section III.D of this preamble above.
2. Summary of Major Public Comments and EPA Responses
    The EPA received many comments on the agency's evaluation of the 
third statutory criterion under section 1412(b)(1)(A) of SDWA. Most 
commenters supported the EPA's evaluation under the preliminary 
determination that regulation of PFHxS, PFNA, HFPO-DA, PFBS and 
mixtures of these four contaminants presents a meaningful opportunity 
for health risk reduction and that the EPA had sufficiently justified 
this statutory criterion as well as the health and occurrence 
criterion. This included comments highlighting the extensive amount of 
work done by several states developing regulatory and non-regulatory 
levels for several PFAS compounds, including the PFAS for which the EPA 
is making regulatory determinations either individually or as a 
mixture. These commenters also noted the need for a consistent national 
standard for use in states where a state-specific standard has not yet 
been developed. Several commenters have also noted that although some 
states have developed or are in the process of developing their own 
state-level PFAS drinking water standards, regulatory standards 
currently vary across states. These commenters expressed concern that 
absence of a national drinking water standard has resulted in risk 
communication challenges with the public and disparities with PFAS 
exposure. Some commenters noted there are populations particularly 
sensitive or vulnerable to the health effects of these PFAS, including 
newborns, infants, and children. The EPA agrees with commenters that 
there is a need for a national PFAS drinking water regulation and that 
moving forward with a national-level regulation for PFHxS, PFNA, HFPO-
DA, mixtures of these three PFAS and PFBS, as well as PFOA and PFOS, 
will provide improved national consistency in protecting public health 
and may reduce regulatory uncertainty for stakeholders across the 
country.
    A few commenters expressed support for the EPA's evaluation of 
meaningful opportunity based on the treatment technologies which can 
remove the six PFAS for which the EPA is finalizing regulation. 
Furthermore, these commenters noted the meaningful opportunity to not 
only provide protection from the six regulated PFAS, but also other 
PFAS that will not be regulated as a part of this action.
    Several commenters did not support the EPA's evaluation of the 
third statutory criterion, offering that in their opinion the EPA 
failed to justify that there is a meaningful opportunity for health 
risk reduction for the PFAS both individually and for their mixtures 
and stating that the EPA should consider other factors such as costs. A 
few of these commenters wrote that the EPA provided limited rationale 
and factors for its meaningful opportunity determination. The EPA 
disagrees with these commenters that the agency failed to justify that 
there is meaningful opportunity for health risk reduction or that the 
EPA provided limited rationale and factors in its meaningful 
opportunity evaluation for these contaminants individually and as 
mixtures. As described in the EPA's March 2023 proposal (USEPA, 2023f) 
and summarized previously, the EPA fully considered many factors both 
individually and within mixtures including individual contaminant and 
dose additive toxicity and health concerns, individual contaminant 
occurrence and co-occurrence of mixtures at frequencies and levels of 
public health concern, availability of similar treatment technologies 
to remove these four PFAS and analytical methods to measure them, and 
their individual and collective chemical and physical properties 
leading to their environmental persistence. Additionally, the EPA notes 
in this preamble, and as demonstrated through representative occurrence 
data, for the three contaminants individually and mixtures of the four, 
occurrence and co-occurrence is not only at a regional or local level, 
rather it covers multiple states throughout the country; therefore, a 
national level regulation is necessary to ensure all Americans served 
by PWSs are equally protected.
    Some comments indicate that the health and occurrence information 
do not support that establishing drinking water standards presents a 
meaningful opportunity for health risk reduction. The agency disagrees 
with the commenters' assertion that the health and occurrence 
information are insufficient to justify a drinking water standard as 
supported in sections III.B. and III.C. of this preamble, and the 
agency finds that there is a meaningful opportunity for health risk 
reduction potential based upon multiple considerations including the 
population exposed to PFHxS, PFNA, HFPO-DA, and mixtures of these three 
PFAS and PFBS including sensitive populations and lifestages, such as 
newborns, infants and children.
    Other comments assert that the EPA must evaluate the potential 
implementation challenges and cost considerations of regulation as part 
of the meaningful opportunity evaluation. The EPA disagrees with these 
commenters. The SDWA states that that the meaningful opportunity for 
overall health risk reduction for persons served by PWSs is in the sole 
judgement of the Administrator and does not require that the EPA 
consider costs for a regulatory determination. The SDWA does require 
that costs and benefits are presented and considered in the proposed 
rule's Health Risk Reduction Cost Analysis which the EPA did for the 
proposal and has updated as a part of the final rule within section 
XII.
    A few other commenters provided that due to all of the additional 
human health exposure pathways other than drinking water for these 
PFAS, that regulation of drinking water would not represent a 
meaningful opportunity for overall health risk reduction. While the EPA 
recognizes that drinking water is one of several exposure routes, the 
EPA disagrees with these commenters. Removing the PFAS that have been 
found to occur or are substantially likely to occur from drinking water 
systems will result in a significant improvement in public health 
protection. The EPA also notes that through its PFAS Strategic Roadmap 
and associated actions, the agency is working expeditiously to address 
PFAS contamination in the environment and reduce human health PFAS 
exposure through all pathways. While beyond the scope of this rule, the 
EPA is making progress implementing many of the commitments in the 
Roadmap, including those that may significantly reduce PFAS source 
water concentrations.

E. The EPA's Final Determination Summary

    The SDWA provides the EPA significant discretion when making a 
regulatory determination under section 1412(b)(1)(A). This decision to 
make a regulatory determination to individually regulate PFHxS, PFNA, 
and HFPO-DA and to regulate combinations of these three PFAS and PFBS 
in mixtures is based on consideration of the evidence supporting the 
factors individually and collectively.
    The EPA's determination that PFHxS, PFNA, and HFPO-DA individually 
and mixtures of these three PFAS and PFBS ``may have an adverse effect 
on the health of persons'' is strongly supported by numerous studies. 
These studies demonstrate several adverse health effects, such as 
immune, thyroid, liver,

[[Page 32563]]

kidney and developmental effects, and increased cholesterol levels, may 
occur following exposure to individual PFAS, and dose-additive health 
effects can occur following exposure to multiple PFAS at doses that 
likely would not individually result in these adverse health effects, 
but may pose health risks when combined in mixtures. Importantly, the 
best available peer reviewed science documents that these PFAS may have 
multiple adverse human health effects even at relatively low levels 
individually and when combined in mixtures (see section III.B.6.e f of 
this preamble or further information on studies supporting the 
conclusion of dose additivity).
    The EPA's determination there is a substantial likelihood that the 
contaminant will occur in PWS with a frequency and at levels of public 
health concern is supported by evidence documenting the measured 
occurrence of PFHxS, PFNA, and HFPO-DA, and co-occurrence of these 
three PFAS and PFBS above the HRL, the stability and persistence of the 
contaminant in humans and/or the environment, and the current or legacy 
production and use in commerce.
    Finally, the EPA's determination that individual regulation of 
PFHxS, PFNA, and HFPO-DA and regulation of these three PFAS and PFBS in 
mixtures presents a meaningful opportunity for health risks reductions 
is strongly supported by numerous factors, including the potential 
adverse human health effects at low levels and potential for exposure 
and co-exposure of these PFAS on sensitive populations and lifestages 
such as lactating and pregnant women and children, their persistence, 
and the availability of both analytical methods and treatment 
technologies to remove these contaminants in drinking water.
    After considering these factors individually and together, the EPA 
has determined that PFHxS, PFNA, and HFPO-DA individually and mixtures 
of these three PFAS and PFBS meet the statutory criteria for regulation 
under SDWA. The EPA has an extensive record of information to make this 
determination now and recognizes the public health burden of these PFAS 
as well as PFOA and PFOS. The EPA notes the public urgency to reduce 
PFAS concentrations in drinking water described in the public comments. 
A PFAS NPDWR provides a mechanism to reduce these PFAS expeditiously 
for these impacted communities. In addition to making this final 
regulatory determination, the EPA is exercising its discretion to 
concurrently finalize MCLGs and NPDWRs for these PFAS as individual 
contaminants and for the specified PFAS mixtures in part to allow 
utilities to consider these PFAS specifically as they design systems to 
remove PFAS and to ensure that they are reducing these PFAS in their 
drinking water to the extent feasible and as quickly as practicable.

IV. MCLG Derivation

    Section 1412(a)(3) of the Safe Drinking Water Act (SDWA) requires 
the Administrator of the Environmental Protection Agency (EPA) to 
publish a final MCLG simultaneously with the NPDWR. The MCLG is set, as 
defined in section 1412(b)(4)(A), at ``the level at which no known or 
anticipated adverse effects on the health of persons occur and which 
allows an adequate margin of safety.'' Consistent with SDWA section 
1412(b)(3)(C)(i)(V), in developing the MCLG, the EPA considers ``the 
effects of the contaminant on the general population and on groups 
within the general population such as infants, children, pregnant 
women, the elderly, individuals with a history of serious illness, or 
other subpopulations that are identified as likely to be at greater 
risk of adverse health effects due to exposure to contaminants in 
drinking water than the general population.'' Other factors considered 
in determining MCLGs can include health effects data on drinking water 
contaminants and potential sources of exposure other than drinking 
water. MCLGs are not regulatory levels and are not enforceable. The 
statute does not dictate that the MCLG take a particular form; however, 
it must represent a ``level'' that meets the MCLG statutory definition. 
Given that the MCL must be ``as close as feasible'' to the MCLG, and 
that the MCL is defined as the ``maximum permissible level of a 
contaminant in water which is delivered to any user of a public water 
system,'' the MCLG can take any form so long as it is a maximum level 
of a contaminant in water.
    Due to their widespread use and persistence, many PFAS are known to 
co-occur in drinking water and the environment--meaning that these 
contaminants are often together and in different combinations as 
mixtures (see sections III.C and VI of this preamble for additional 
discussion on occurrence). PFAS exposure can disrupt signaling of 
multiple biological pathways resulting in common adverse effects on 
several biological systems and functions, including thyroid hormone 
levels, lipid synthesis and metabolism, development, immune function, 
and liver function. Additionally, the EPA's examination of health 
effects information found that exposure through drinking water to a 
mixture of PFAS can act in a dose-additive manner (see sections III.B 
and IV.B of this preamble for additional discussion on mixture 
toxicity). Dose additivity means that exposure to multiple PFAS, at 
doses that individually would not be anticipated to result in adverse 
health effects, may pose health risks when combined in a mixture.

A. MCLG Derivation for PFOA and PFOS

    To establish an MCLG for individual contaminants, the EPA assesses 
the peer-reviewed science examining cancer and noncancer health effects 
associated with oral exposure to the contaminant. For known or likely 
linear carcinogenic contaminants, where there is a proportional 
relationship between dose and carcinogenicity at low concentrations or 
where there is insufficient information to determine that a carcinogen 
has a threshold dose below which no carcinogenic effects have been 
observed, the EPA has a long-standing practice of establishing the MCLG 
at zero (see USEPA, 1998a; USEPA, 2000c; USEPA, 2001; See S. Rep. No. 
169, 104th Cong., 1st Sess. (1995) at 3). For nonlinear carcinogenic 
contaminants, contaminants that are designated as Suggestive Human 
Carcinogens (USEPA, 2005a), and non-carcinogenic contaminants, the EPA 
typically establishes the MCLG based on a noncancer RfD. An RfD is an 
estimate of a daily oral exposure to the human population (including 
sensitive populations) that is likely to be without an appreciable risk 
of deleterious effects during a lifetime. A nonlinear carcinogen is a 
chemical agent for which the associated cancer response does not 
increase in direct proportion to the exposure level and for which there 
is scientific evidence demonstrating a threshold level of exposure 
below which there is no appreciable cancer risk.
1. Proposal
    To support the proposed rule, the EPA published PFOA and PFOS draft 
toxicity assessments and the proposed MCLGs for public comment (USEPA, 
2023g; USEPA, 2023h). Prior to conducting the systematic review for the 
PFOA and PFOS draft toxicity assessments, the EPA established the 
internal protocols for the systematic review steps of literature 
search, Population, Exposure, Comparator, and Outcomes (PECO) 
development, literature screen, and study quality evaluation. The EPA 
incorporated detailed, transparent, and complete protocols for all 
steps of the systematic

[[Page 32564]]

review process (USEPA, 2023g; USEPA, 2023h; USEPA, 2023i; USEPA, 
2023j). Additionally, the EPA updated and expanded the protocols and 
methods based on SAB recommendations to improve the transparency of the 
process the EPA used to derive the MCLGs for PFOA and PFOS and to 
improve consistency with the ORD Staff Handbook for Developing IRIS 
Assessments (USEPA, 2022f). The EPA followed this transparent 
systematic review process to evaluate the best available peer-reviewed 
science and to determine the weight of evidence for carcinogenicity and 
the cancer classifications for PFOA and PFOS according to agency 
guidance (USEPA, 2005a).
    Based on the EPA's analysis of the best available data and 
following agency guidance, the EPA determined that both PFOA and PFOS 
are Likely to be Carcinogenic to Humans based on sufficient evidence of 
carcinogenicity in humans and animals (USEPA, 2005a; USEPA, 2023g; 
USEPA, 2023h). The EPA also determined that a linear default 
extrapolation approach is appropriate for PFOA and PFOS as there is no 
evidence demonstrating a threshold level of exposure below which there 
is no appreciable cancer risk for either compound (USEPA, 2005a). 
Therefore, the EPA concluded that there is no known threshold for 
carcinogenicity. Based upon a consideration of the best available peer-
reviewed science and the statute's directive that the MCLG be ``set at 
the level at which no known or anticipated adverse effects on the 
health of persons occur and which allow an adequate margin of safety,'' 
the EPA proposed MCLGs of zero for both PFOA and PFOS in drinking 
water. Setting the MCLG at zero under these conditions is also 
supported by long standing practice at the EPA's Office of Water for 
Likely or Known Human Carcinogens (see USEPA, 1998a; USEPA, 2000c; 
USEPA, 2001; USEPA, 2016b; See S. Rep. No. 169, 104th Cong., 1st Sess. 
(1995) at 3).
2. Summary of Major Public Comments and EPA Responses
    The EPA requested comment on both the toxicity assessment 
conclusions and the proposed MCLG derivation for PFOA and PFOS. In this 
section the EPA focuses the summary of public comments and responses on 
comments related to the cancer classification determinations for PFOA 
and PFOS because that was the basis for the proposed MCLG derivations 
(USEPA, 2023g; USEPA, 2023h). The noncancer health effects that the EPA 
identified as hazards in the draft toxicity assessments (i.e., 
decreased immune response in children, increased alanine 
aminotransferase (ALT), decreased birth weight and increased 
cholesterol) were not the basis for the proposed MCLG derivation. 
Importantly, an MCLG of zero is also protective of noncancer endpoints 
which were evaluated in the EPA's HRRCA (Health Risk Reduction and Cost 
Analysis). Comments related to the benefits the EPA quantified that are 
associated with noncancer health effects are described in section XII.
    A few commenters agreed with the systematic review protocol the EPA 
used to evaluate the studies that supported the PFOA and PFOS cancer 
classification determinations in the draft toxicity assessments (USEPA, 
2023g; USEPA, 2023h; USEPA, 2023i; USEPA, 2023j), with one commenter 
stating that the approach was ``thorough and well-reasoned.'' 
Commenters stated that the systematic review protocol was clear because 
the EPA had addressed all concerns highlighted during the peer review 
process.
    One commenter stated that the EPA did not conduct a systematic 
review of the literature and did not follow the ORD Staff Handbook for 
Developing IRIS Assessments (USEPA, 2022f) to develop the toxicity 
assessments for PFOA and PFOS. This commenter stated the EPA lacked ``a 
predefined protocol'' and that the ``systematic review methods lack[ed] 
transparency and consistency.'' The commenter took particular issue 
with the EPA's protocols for study quality evaluations, stating that 
they were inconsistent and not aligned with the ORD Staff Handbook for 
Developing IRIS Assessments (USEPA, 2022f). The EPA disagrees with this 
commenter's claims. The EPA adopted the overall approach and steps in 
the ORD Staff Handbook for Developing IRIS Assessments (USEPA, 2022f) 
and the Systematic Review Protocol for the PFAS IRIS Assessments 
(USEPA, 2021h) to develop PFOA- and PFOS-specific protocols that then 
formed the basis for performing study quality evaluations, evidence 
integration, and critical study selection (see appendix A in USEPA, 
2023g; USEPA, 2023h; USEPA, 2023i; USEPA, 2023j). This predefined 
protocol was made available for public comment as appendix A of the 
toxicity assessments (USEPA, 2023i; USEPA, 2023j). Importantly, the 
EPA's Office of Water collaborated with the EPA's Office of Research 
and Development in conducting study quality evaluations, evidence 
integration, and selection of critical studies to ensure consistency 
with the ORD Staff Handbook for Developing IRIS Assessments (USEPA, 
2022f) and the Systematic Review Protocol for the PFAS IRIS Assessments 
(USEPA, 2021h).
    A few commenters claimed that the EPA did not use the best 
available science when developing the toxicity assessments for PFOA and 
PFOS, asserting that the EPA did not follow its own guidance or data 
quality standards and that the EPA's systematic review process was 
flawed (see discussion above). The EPA disagrees with these commenters' 
claims. The EPA has followed statutory requirements to use the best 
available peer-reviewed science in two respects: by (1) considering 
relevant peer-reviewed literature identified by performing systematic 
searches of the scientific literature or identified through public 
comment and (2) relying on peer-reviewed, published EPA human health 
risk assessment methodology as well as systematic review best practices 
(USEPA, 2021h; USEPA, 2022f). The risk assessment guidance and best 
practices serve as the basis for the PFOA and PFOS health effects 
systematic review methods used to identify, evaluate, and quantify the 
available data. Not only did the EPA incorporate literature identified 
in previous assessments, as recommended by the SAB (USEPA, 2022i), but 
the EPA also conducted several updated systematic literature searches, 
the most recent of which was completed in February 2023. This approach 
ensured that the literature under review encompassed studies included 
in the 2016 Health Effects Support Documents (HESDs) (USEPA, 2016c; 
USEPA, 2016d) and recently available studies. The results of the most 
recent literature search provide further support for the conclusions 
made in the draft toxicity assessments for PFOA and PFOS (USEPA, 2023g; 
USEPA, 2023h) and are described in appendix A of the final toxicity 
assessments (USEPA, 2024h; USEPA, 2024i).
    As described above, the PFOA and PFOS systematic review protocol is 
consistent with the ORD Staff Handbook for Developing IRIS Assessments 
(USEPA, 2022f) and also considers PFOA- and PFOS-specific protocol 
updates outlined in the Systematic Review Protocol for the PFBA, PFHxA, 
PFHxS, PFNA, and PFDA (anionic and acid forms) IRIS Assessments (USEPA, 
2021h). The EPA additionally followed human health risk assessment 
methods for developing toxicity values (e.g., USEPA, 2002a), conducting 
benchmark dose (BMD) modeling (USEPA, 2012), and other analyses. In the 
PFOA and PFOS toxicity assessments and the appendices, the EPA clearly 
describes

[[Page 32565]]

the methods used and how those methods and decisions are consistent 
with the EPA practices and recommendations (i.e., through quotes and 
citations) described in various guidance documents.
    One commenter stated that the EPA did not use the best available 
peer-reviewed science because the assessments did not follow 
methodological or statistical guidance. Specifically, this commenter 
stated the EPA did not follow A Review of the Reference Dose and 
Reference Concentration Processes (USEPA, 2002a) when selecting 
uncertainty factors and claimed the EPA did not follow guidance on data 
quality (USEPA, 2003; USEPA, 2006b; USEPA, 2014b). The commenter stated 
they believed the assessments contained flaws including exclusion of 
covariates in modeling, reliance on peer-reviewed studies published by 
non-EPA employees, and an inability to replicate results. The EPA 
disagrees with these comments. Regarding data quality control, data 
quality objectives are an integral part of the ORD Staff Handbook for 
Developing IRIS Assessments (USEPA, 2022f) and many of the concepts 
outlined in data quality guidance recommended by the commenter (USEPA, 
2003; USEPA, 2006b; USEPA, 2014b) are addressed through the EPA's use 
of the ORD Handbook (USEPA, 2022f). Furthermore, this work was 
conducted under a programmatic quality assurance project plan (QAPP) 
which ensures that all EPA data quality guidance is followed, including 
those cited by the commenter. Additionally, by developing and 
implementing a systematic review protocol consistent with the ORD 
Handbook (USEPA, 2022f), the EPA reduced potential confirmation bias, a 
concern raised by another commenter, by conducting multiple independent 
evaluations of studies, relying on a data-driven, weight of evidence 
approach, and by incorporating expertise from across the agency.
    In many cases the commenters have misinterpreted the methods and 
decisions the EPA used to analyze the data or misinterpreted the 
guidance itself. For example, one commenter mistakenly suggested that 
the EPA did not consider covariates in its analyses of epidemiological 
studies; the EPA described which covariates were considered in each 
analysis in several sections of the draft toxicity assessments and 
appendices (USEPA, 2023g; USEPA, 2023h; USEPA, 2023i; USEPA, 2023j), 
including in descriptions of the studies in section 3 and modeling of 
the studies in appendix E. The EPA also notes that the primary studies 
that provide the data describe covariate adjustments in their published 
analyses.
    A couple of commenters suggested that the toxicity assessments for 
PFOA and PFOS were not adequately peer-reviewed because changes were 
made post peer review (i.e., after publication of the final report by 
the SAB PFAS Review Panel (USEPA, 2022i)), the most significant of 
which was the updated cancer classification for PFOS, but also included 
the addition of figures and mechanistic syntheses. The EPA disagrees 
with this assertion. The toxicity assessments, including the 
conclusions that are material to the derivation of the MCLGs, were 
peer-reviewed by the SAB PFAS review panel (USEPA, 2022i). Notably, 
this panel ``agreed with many of the conclusions presented in the 
assessments, framework and analysis'' (USEPA, 2022i). The only 
assessment conclusion that changed and impacted MCLG derivation between 
SAB review and rule proposal was that the cancer classification for 
PFOS of Suggestive Evidence of Carcinogenicity was updated to Likely to 
be Carcinogenic to Humans according to the Guidelines for Carcinogen 
Risk Assessment (USEPA, 2005a). This conclusion for PFOS was based on a 
reevaluation of the available data in response to multiple comments 
from the SAB PFAS review panel stating that ``[s]everal new studies 
have been published that warrant further evaluation to determine 
whether the `likely' designation is appropriate'' for PFOS and that the 
EPA's ``interpretation of the hepatocellular carcinoma data from the 
Butenhoff et al. (2012) study in the 2016 HESD is overly conservative 
in dismissing the appearance of a dose-response relationship for this 
endpoint, particularly in females'' (USEPA, 2022i). In responding to 
the SAB's recommendation that the EPA provide an ``explicit description 
of why the available data for PFOS do not meet the EPA Guidelines for 
Carcinogen Risk Assessment (2005) criterion for the higher designation 
as `likely carcinogenic,' '' and taking into consideration recently 
published peer-reviewed epidemiological studies demonstrating 
concordance in humans identified through the final updated literature 
search recommended by the SAB, the EPA determined that PFOS meets the 
criterion for the higher designation of Likely to Be Carcinogenic to 
Humans (USEPA, 2005a). This decision was described in sections 3.5.5 
and 6.4 of the draft assessment (USEPA, 2023h). Additional discussion 
regarding the PFOS cancer descriptor decision is provided here.
    One commenter stated that the EPA addressed the SAB's concerns 
regarding the systematic review protocol in the documents supporting 
the proposed rulemaking. A few commenters reiterated the importance of 
the SAB's recommendations, including to more thoroughly describe 
systematic review methods used in the assessment (e.g., study inclusion 
and exclusion criteria), incorporate additional epidemiological 
studies, provide rationale for critical study selection, and derive 
candidate toxicity values from both human and animal data. In contrast, 
a few commenters claimed that the EPA did not adequately consider 
several recommendations made by the SAB PFAS Review Panel in their 
final report (USEPA, 2022i), including that the EPA did not incorporate 
studies from the 2016 HESDs (USEPA, 2016c; USEPA, 2016d) or develop 
multiple cancer slope factors (CSFs). One commenter requested 
clarification on whether the EPA had implemented the feedback from the 
SAB.
    The EPA disagrees with the comments that the agency did not 
``meaningfully implement'' SAB feedback. The EPA agrees with commenters 
that highlighted the importance of the SAB's suggestions, and notes 
that the EPA addressed the SAB's recommendations to more thoroughly 
explain the systematic review protocol and expand the systematic review 
protocol beyond study quality evaluation and data extraction in the 
draft toxicity assessments published at the time of rule proposal 
(USEPA, 2023g; USEPA, 2023h; USEPA, 2023i; USEPA, 2023j). As outlined 
in the EPA Response to Final Science Advisory Board Recommendations 
(August 2022) on Four Draft Support Documents for the EPA's Proposed 
PFAS National Primary Drinking Water Regulation (USEPA, 2023k), the EPA 
considered all of the comments and recommendations from the SAB and 
made substantial improvements to address the reported concerns prior to 
publishing the public comment draft assessments (USEPA, 2023g; USEPA, 
2023h). The EPA published a response to SAB comments document that 
detailed how the agency considered and responded to the SAB PFAS Review 
Panel's comments at the time of rule proposal (USEPA, 2023k). The 
resulting draft toxicity assessments and protocol released for public 
comment along with the proposed rule reflect improvements including 
thorough and detailed descriptions of the methods used during 
assessment development, inclusion of

[[Page 32566]]

epidemiological studies from the 2016 HESDs for PFOA and PFOS in the 
systematic review (USEPA, 2016c; USEPA, 2016d), updates to the 
literature, implementation of an evidence integration framework, 
expansion of rationale for critical study and model selections, 
development of toxicity values from both animal toxicological and 
epidemiological data, when warranted, and many other actions. The EPA 
appreciated the SAB's engagement, extensive review, and comments on the 
Proposed Approaches documents (USEPA, 2021i; USEPA, 2021j). 
Furthermore, the EPA provided its consideration of every recommendation 
the SAB provided when updating and finalizing the assessments for PFOA 
and PFOS at the time of rule proposal (USEPA, 2023k).
    Many commenters agreed that that available data indicate that 
exposure to either PFOA or PFOS is associated with cancer in humans and 
supported the EPA's determination that PFOA and PFOS are Likely to be 
Carcinogenic to Humans according to the Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005a). Multiple commenters agreed that studies 
published since the 2016 HESDs (USEPA, 2016c; USEPA, 2016d) have 
strengthened this conclusion. In particular, one commenter supported 
the EPA's conclusions regarding the human relevance of hepatic and 
pancreatic tumors observed in rats administered PFOS, citing their own 
independent health assessment conclusion that ``several lines of 
evidence do not support a conclusion that liver effects due to PFOS 
exposure are PPAR[alpha]-dependent'' and therefore, may be relevant to 
humans (NJDWQI, 2018).
    Several commenters disagreed with the EPA's determinations that 
PFOA and PFOS are each Likely to be Carcinogenic to Humans. Two 
commenters claimed that the tumor types observed in rats (e.g., hepatic 
tumors) after PFOA or PFOS administration are not relevant to humans. 
Some commenters also stated that the human data do not support an 
association between PFOS exposure and cancer. One commenter 
specifically claimed that Shearer et al. (2021) does not provide 
sufficient evidence for changing PFOS's cancer classification from 
Suggestive Evidence of Carcinogenicity to Likely to be Carcinogenic to 
Humans because it did not report associations between PFOS exposure and 
risk of renal cell carcinoma (RCC). Two commenters stated that the 
EPA's discussion using structural similarities between PFOA and PFOS to 
support evidence of the carcinogenicity of PFOS was inconsistent with 
the Guidelines for Carcinogen Risk Assessment (USEPA, 2005a). A few 
commenters additionally questioned or disagreed with the determination 
that PFOA is Likely to be Carcinogenic to Humans because of 
uncertainties in the epidemiological database and a lack of evidence 
indicating that PFOA is genotoxic.
    The EPA disagrees with these comments. With respect to the human 
relevance of the animal tumors observed in rats after chronic oral 
exposure to either PFOA or PFOS, the EPA considered all hypothesized 
modes of action (MOAs) and underlying carcinogenic mechanisms in its 
cancer assessments, including those that some commenters have argued 
are irrelevant to humans (e.g., peroxisome proliferator-activated 
receptor [alpha] (PPAR[alpha]) activation), the discussion for which is 
available in section 3.5.4.2 of the toxicity assessments for PFOA and 
PFOS (USEPA, 2024c; USEPA, 2024d). After review of the available 
mechanistic literature for PFOA and PFOS, the EPA concluded that there 
are multiple plausible mechanisms, including some that are independent 
of PPAR[alpha], that may contribute to the observed carcinogenicity of 
either PFOA or PFOS in rats. Further confirmatory support for the EPA's 
conclusions regarding multiple plausible mechanisms of carcinogenicity 
comes from literature reviews published by state and global health 
agencies which concluded that the liver tumors associated with PFOA 
and/or PFOS exposure may not entirely depend on PPAR[alpha] activation 
and therefore may be relevant to humans (CalEPA, 2021; IARC, 2016; 
NJDWQI, 2017; NJDWQI, 2018).
    Additionally, the EPA did not rely on results reported by Shearer 
et al. (2021) as a rationale for updating the cancer classification for 
PFOS to Likely to be Carcinogenic to Humans (USEPA, 2005a) and 
acknowledges uncertainties in the results from this study, including 
that the effect in the third PFOS exposure quartile was null, the 
effects were attenuated (i.e., reduced in magnitude) when adjusted for 
exposure to other PFAS, and there was no association when exposure to 
PFOS was considered as a continuous variable, rather than when PFOS 
exposure levels were stratified by quartiles (USEPA, 2023h). As 
described in sections 3.5.5 and 6.4 of the draft PFOS toxicity 
assessment, the available information exceeds the characteristics for 
the classification of Suggestive Evidence of Carcinogenic Potential 
(USEPA, 2005a) because there is statistically significant evidence of 
multi-sex and multi-site tumorigenesis from a high confidence animal 
toxicological study, as well as mixed but plausible evidence of 
carcinogenicity in humans and mechanistic data showing potential human 
relevance of the observed tumor data in animals (USEPA, 2023h). The EPA 
notes that the recently published studies reporting associations 
between PFOS exposure and hepatocellular carcinoma in humans (Goodrich 
et al., 2022; Cao et al., 2022) further strengthen the epidemiological 
database and support the cancer classification of Likely to be 
Carcinogenic to Humans for PFOS.
    Regarding commenters' claims that the EPA used the structural 
similarities between PFOA and PFOS as supporting evidence of the 
carcinogenic potential of PFOS, the EPA did not rely on structural 
similarities to draw conclusions about the cancer classification (see 
rationale listed above) but instead used this information as 
supplemental support for the Likely classification. The EPA originally 
included this supplemental line of evidence because the Guidelines for 
Carcinogen Risk Assessment (USEPA, 2005a) explicitly states that 
``[a]nalogue effects are instructive in investigating carcinogenic 
potential of an agent as well as in identifying potential target 
organs, exposures associated with effects, and potential functional 
class effects or modes of action.'' PFOA and PFOS differ in their 
chemical structure by a single functional group; nevertheless, since a 
full structure-activity relationship analysis was not conducted, the 
EPA removed discussion on this supplemental line of evidence from the 
final toxicity assessment for PFOS (USEPA, 2024d).
    Further, the EPA disagrees with comments stating that the 
epidemiological database for PFOA is too uncertain to support a 
classification of Likely to be Carcinogenic to Humans (USEPA, 2005a). 
As described in both the draft (USEPA, 2023g) and final toxicity 
assessments for PFOA (USEPA, 2024c), as well as the Maximum Contaminant 
Level Goals for Perfluorooctanoic Acid (PFOA) and Perfluorooctane 
Sulfonic Acid (PFOS) document (USEPA, 2024j) the available data support 
an increased risk of both kidney and testicular cancers associated with 
PFOA exposure. There is also evidence that PFOA exposure may be 
associated with an increased breast cancer risk, based on studies in 
populations with specific polymorphisms and for specific types of 
breast tumors. Taken together, these results provide consistent and 
plausible

[[Page 32567]]

evidence of PFOA carcinogenicity in humans. Additionally, the EPA notes 
that while genotoxicity is one potential MOA leading to 
carcinogenicity, there is no requirement that a chemical be genotoxic 
for the EPA to classify it as either Carcinogenic to Humans, Likely to 
be Carcinogenic to Humans, or Suggestive Evidence of Carcinogenic 
Potential according to the Guidelines for Carcinogen Risk Assessment 
(USEPA, 2005a). Importantly, the SAB PFAS Review Panel supported the 
Likely to be Carcinogenic to Humans designation for PFOA in its final 
report (USEPA, 2022i).
    Many commenters supported the EPA's proposed MCLGs of zero for both 
PFOA and PFOS, citing well-documented health effects, including cancer, 
resulting from exposure to either PFOA or PFOS as rationale for their 
support of the proposed rulemaking. Several commenters also agreed with 
the EPA's long-standing practice of establishing the MCLG at zero (see 
USEPA, 1998a; USEPA, 2000c; USEPA, 2001; See S. Rep. No. 169, 104th 
Cong., 1st Sess. (1995) at 3) for known or likely linear carcinogenic 
contaminants, with one commenter stating that it is ``appropriate based 
on the weight of evidence for carcinogenicity and other adverse health 
impacts of PFOA and PFOS at very low exposures.''
    Two commenters disagreed with MCLGs of zero for PFOA and PFOS, with 
one commenter claiming that the EPA's determinations were ``not 
consistent with the evidence the EPA presents nor with its own 
guidance'' (i.e., the EPA's cancer assessment was not consistent with 
assessment approaches recommended in the Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005a)). The EPA disagrees with these commenters' 
assertions because there is sufficient weight of evidence for 
carcinogenic risk of both PFOA and PFOS exposures supporting a 
classification of Likely to be Carcinogenic to Humans according to the 
Guidelines for Carcinogen Risk Assessment (USEPA, 2005a) from the 
available epidemiological and animal toxicological studies. Consistent 
with the guidelines, the EPA provided a narrative to ``explain the case 
for choosing one descriptor and discuss the arguments for considering 
but not choosing another'' (USEPA, 2005a) in the draft and final 
toxicity assessments (USEPA, 2024c; USEPA, 2024d; USEPA, 2023g; USEPA, 
2023h).
3. Final Rule
    Based on the best available peer-reviewed science and consistent 
with agency guidance (USEPA, 2005a), the EPA has determined that both 
PFOA and PFOS are Likely to be Carcinogenic to Humans. Therefore, 
following established agency practice regarding contaminants with this 
classification and consistent with the statutory directive to set an 
MCLG ``at the level at which no known or anticipated adverse effects on 
the health of persons occur and which allows for an adequate margin of 
safety,'' the EPA set individual MCLGs for both PFOA and PFOS at zero. 
As described above, the EPA used the best available peer-reviewed 
science, followed agency guidance and current human health risk 
assessment methodology, including the ORD Staff Handbook for Developing 
IRIS Assessments (USEPA, 2022f) and the Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005a), and adequately peer-reviewed (USEPA, 2022i) 
the science underlying the MCLG derivation for both PFOA and PFOS 
(USEPA, 2024c; USEPA, 2024d; USEPA, 2024j).
    Consistent with the Guidelines for Carcinogen Risk Assessment 
(USEPA, 2005a), the EPA reviewed the weight of evidence and determined 
that PFOA and PFOS are each designated as Likely to Be Carcinogenic to 
Humans, because ``the evidence is adequate to demonstrate carcinogenic 
potential to humans but does not reach the weight of evidence for the 
descriptor Carcinogenic to Humans.'' For PFOA, this determination was 
based on the evidence of kidney and testicular cancer in humans and 
Leydig cell tumors, pancreatic acinar cell tumors, and hepatocellular 
tumors in rats as described in USEPA (2024c). For PFOS, this 
determination was based on the evidence of hepatocellular tumors in 
male and female rats, which is further supported by recent evidence of 
hepatocellular carcinoma in humans (Goodrich et al., 2022; Cao et al., 
2022), pancreatic islet cell carcinomas in male rats, and mixed but 
plausible evidence of bladder, prostate, kidney, and breast cancers in 
humans (USEPA, 2024d). The EPA has updated and finalized the toxicity 
assessment for PFOS to reflect the new epidemiological evidence (USEPA, 
2024d; USEPA, 2024i).
    Consistent with the statutory definition of MCLG, the EPA 
establishes MCLGs of zero for carcinogens classified as either 
Carcinogenic to Humans or Likely to be Carcinogenic to Humans where 
there is a proportional relationship between dose and carcinogenicity 
at low concentrations or where there is insufficient information to 
determine that a carcinogen has a threshold dose below which no 
carcinogenic effects have been observed. In these situations, the EPA 
takes the health protective approach of assuming that carcinogenic 
effects should therefore be extrapolated linearly to zero. This is 
called the linear default extrapolation approach. This approach ensures 
that the MCLG is set at a level where there are no known or anticipated 
adverse health effects, allowing for an adequate margin of safety. 
Here, the EPA has determined that PFOA and PFOS are Likely to be 
Carcinogenic to Humans based on sufficient evidence of carcinogenicity 
in humans and animals (USEPA, 2024c; USEPA, 2024d). The EPA has also 
determined that a linear default extrapolation approach is appropriate 
as there is no evidence demonstrating a threshold level of exposure 
below which there is no appreciable cancer risk (USEPA, 2005a). Based 
on this lack of evidence, the EPA concluded that there is no known 
threshold for carcinogenicity. Based upon a consideration of the best 
available peer-reviewed science and statutory directive to set the MCLG 
``at the level at which no known or anticipated adverse effects on the 
health of persons occur and which allows an adequate margin of 
safety,'' the EPA has finalized MCLGs of zero for PFOA and PFOS in 
drinking water.
    While not a basis for the EPA's MCLG, the EPA notes that its 
toxicity assessments indicate either PFOA or PFOS exposure are also 
associated with multiple non-cancer adverse health effects. The PFOA 
and PFOS candidate non-cancer RfDs based on human epidemiology studies 
for various health outcomes (i.e., developmental, cardiovascular, 
immune, and hepatic) range from 2 x 10-7 to 3 x 
10-8 mg/kg/day (USEPA, 2024c; USEPA, 2024d; USEPA, 2024h; 
USEPA, 2024i).

B. MCLG Derivation for Additional PFAS

    Section 1412(b)(4)(A) requires the EPA to set the MCLG at a ``level 
at which no known or anticipated adverse effects on the health of 
persons occur and which allows an adequate margin of safety.'' In this 
action, the EPA is setting MCLGs (and MCLs) for five individual PFAS 
(section IV.C of this preamble) as well as for mixtures of three of 
these PFAS plus PFBS. In the context of this NPDWR, the Hazard Index is 
a method which determines when a mixture of two or more of four PFAS--
PFHxS, PFNA, HFPO-DA, and PFBS--exceeds the level of health concern 
with a margin of safety and thus the Hazard Index (equal to 1) is the 
MCLG for any mixture of those four PFAS. Based on the scientific 
record, each PFAS within the mixture has a HBWC, which is set at the 
level below which adverse effects

[[Page 32568]]

are not likely to occur and allows for an adequate a margin of safety. 
See USEPA, 2024f and section IV.B. of this preamble. The scientific 
record also shows that PFHxS, PFNA, HFPO-DA, and PFBS elicit the same 
or similar profiles of adverse health effects in several biological 
organs and systems, but with differing potencies for effect(s) (see 
USEPA, 2022i and 2024a; and section IV.B of this preamble). As a 
result, as discussed elsewhere in the preamble, PFAS that elicit 
similar observed adverse health effects following individual exposure 
should be assumed to act in a dose-additive manner when in a mixture 
unless data demonstrate otherwise (USEPA, 2024a). See USEPA, 2024a and 
section II and IV.B of this preamble. This means that where drinking 
water contains any combination of two or more of these PFAS, the hazard 
associated with each PFAS in the mixture must be added up to determine 
whether the mixture exceeds a level of public health concern.
    The Hazard Index is the method for calculating this level (i.e., 
the mixture MCLG) and reflects both the measured amount of each of the 
four PFAS in the mixture and the toxicity (represented by the HBWC) of 
each of the four PFAS. The PFAS mixture Hazard Index is an approach to 
determine whether any mixture of two or more of these four PFAS in 
drinking water exceeds a level of health concern by first calculating 
the ratio of the measured concentration of each of the four PFAS 
divided by its toxicity (the HBWC). This results in the ``hazard 
quotient'' (HQ) for each of the four PFAS. Because the health effects 
of these PFAS present dose additive concerns (USEPA, 2024a), the four 
HQs are added together, and if the result exceeds 1, then the hazard 
from the combined amounts of the four PFAS in drinking water exceeds a 
level of public health concern.
1. MCLG Derivation for a PFAS Mixture
a. Proposal
    The EPA proposed a Hazard Index MCLG to protect public health from 
exposure to mixtures of any combination of PFHxS, PFNA, HFPO-DA, and/or 
PFBS, four PFAS that elicit a shared set of adverse effects and co-
occur in drinking water. The Hazard Index is an approach based on dose 
additivity that has been validated and used by the EPA to assess 
chemical mixtures in several contexts (USEPA, 1986; USEPA, 2000a; 
USEPA, 2022i). The EPA's proposal was based on the agency's finding 
that the Hazard Index approach is the most practical approach for 
establishing an MCLG for PFAS mixtures that meets the statutory 
requirements outlined in section 1412(b)(1)(A) of SDWA. This is because 
the Hazard Index assesses the exposure level of each component PFAS 
relative to its HBWC, which is based on the most sensitive known 
adverse health effect (based on the weight of evidence) and considers 
sensitive population(s) and life stage(s) as well as potential exposure 
sources beyond drinking water. Furthermore, the Hazard Index accounts 
for dose additive health concerns by summing the hazard contribution 
from each mixture component to ensure that the mixture is not exceeding 
the level below which there are no known or anticipated adverse health 
effects and allows for an adequate margin of safety.
    The proposal defined a mixture as containing one or more of the 
four PFAS and therefore covered each contaminant individually if only 
one of the four PFAS occurred. Thus, the Hazard Index as proposed 
ensures that the level of exposure to an individual PFAS remains below 
that which could impact human health because the exposure for that 
measured PFAS is divided by its corresponding HBWC. For example, if the 
mixture only included PFNA, then under the Hazard Index approach as 
proposed any measured concentrations over 10.0 ng/L divided over the 
10.0 ng/L HBWC would be greater than the 1.0 Hazard Index MCLG. The 
proposed Hazard Index MCLG was 1.0 and the HBWCs of each mixture 
component were as follows: 9.0 ng/L \3\ for PFHxS; 10.0 ng/L for HFPO-
DA; 10.0 ng/L for PFNA; and 2000.0 ng/L for PFBS (USEPA, 2023e).
---------------------------------------------------------------------------

    \3\ Some commenters noted an error in the HBWC calculation for 
PFHxS which was reported as 9.0 ng/L in the proposal. The agency has 
corrected the value in this NPDWR and within the requirements under 
40 CFR part 141 subpart Z. The correct HRL/HBWC for PFHxS is 10 ng/
L.
---------------------------------------------------------------------------

b. Summary of Major Public Comments and EPA Responses
    Many commenters supported the EPA's proposal to regulate a mixture 
of PFAS and agreed with the EPA's scientific conclusions about PFAS 
dose additivity and the agency's use of the Hazard Index approach to 
develop an MCLG for a mixture of PFHxS, PFNA, HFPO-DA, and/or PFBS. 
Many commenters opposed the EPA's conclusion about dose additivity and 
the use of the Hazard Index approach to regulate co-occurring PFAS. A 
few commenters opposed the EPA's use of shared or similar health 
endpoints/outcomes rather than a shared MOA as a basis for assessing 
risks of PFAS mixtures. A few commenters agreed with the EPA's decision 
to regulate these PFAS as a mixture (that some commenters referred to 
as a ``group'') and supported the EPA's conclusion about dose 
additivity but questioned the EPA's use of the Hazard Index and 
suggested alternative approaches such as development of individual 
MCLGs or a target organ-specific Hazard Index (TOSHI). Some commenters 
claimed that the EPA did not appropriately seek review from the SAB, 
particularly on the application of the Hazard Index as an approach to 
regulate PFAS under SDWA. Comments on the number of significant digits 
applied in the HBWCs and the Hazard Index were varied. For a discussion 
of comments and the EPA responses on dose additivity and similarity of 
toxic effects, see section III.B of this preamble. Commenters referred 
to the HRLs and the HBWCs interchangeably; see section III of this 
preamble for comments on HBWCs and the EPA's responses. Responses to 
the other topics raised are discussed in the following paragraphs.
    The EPA disagrees with commenters that the agency did not seek 
adequate consultation from the EPA SAB in the development of the NPDWR. 
SDWA section 1412(e) requires that the EPA ``request comments'' from 
the SAB ``prior to proposal'' of the MCLG and NPDWR. Consistent with 
this statutory provision, the EPA consulted with the SAB from 2021-
2022. As discussed in the proposed rule, the SAB PFAS Review Panel met 
virtually via a video meeting platform on December 16, 2021, and then 
had three (3) subsequent meetings on January 4, 6 and 7, 2022 to 
deliberate on the agency's charge questions, which included a question 
specifically focused on the utility and scientific defensibility of the 
Hazard Index approach in the context of mixtures risk assessment in 
drinking water. Another virtual meeting was held on May 3, 2022, to 
discuss the SAB PFAS Review Panel's draft report. Oral and written 
public comments were considered throughout the advisory process. The 
SAB provided numerous recommendations to the EPA which can be found in 
the SAB's final report (USEPA, 2022i). The EPA addressed the SAB's 
recommendations and described the EPA's responses to SAB 
recommendations in its EPA Response to Final Science Advisory Board 
Recommendations (August 2022) on Four Draft Support Documents for the 
EPA's Proposed PFAS National Primary Drinking Water Regulation (USEPA, 
2023k) and also in the EPA's Response to Comments document in response 
to public comments on the proposed PFAS

[[Page 32569]]

NPDWR (USEPA, 2024k). Further discussion on the EPA consultations and 
stakeholder engagement activities can be found in section XIII of this 
preamble.
    The agency also disagrees with commenters who contend that the EPA 
must seek advice from the SAB on all aspects of the NPDWR. The statute 
does not dictate on which scientific issues the EPA must request 
comment from the SAB. In this case, the EPA sought comments on four 
documents: Proposed Approaches to the Derivation of a Draft Maximum 
Contaminant Level Goal for Perfluorooctanoic Acid (PFOA) in Drinking 
Water (USEPA, 2021i); Proposed Approaches to the Derivation of a Draft 
Maximum Contaminant Level Goal for Perfluorooctanesulfonic Acid (PFOS) 
in Drinking Water (USEPA, 2021j); Analysis of Cardiovascular Disease 
Risk Reduction as a Result of Reduced PFOA and PFOS Exposure in 
Drinking Water (USEPA, 2021k); and Draft Framework for Estimating 
Noncancer Health Risks Associated with Mixtures of PFAS (USEPA, 2021e).
    The approach of the EPA's Framework for Estimating Noncancer Health 
Risks Associated with Mixtures of PFAS (USEPA, 2024a) and this rule is 
to evaluate risks from exposure to mixtures of PFAS that elicit the 
same or similar adverse health effects (but with differing potencies 
for effect(s)) rather than similarity in MOA. This is consistent with 
the EPA's Supplementary Guidance for Conducting Health Risk Assessment 
of Chemical Mixtures (USEPA, 2000a) and expert opinion from the NAS 
National Research Council (NRC, 2008). MOA, which describes key changes 
in cellular or molecular events that may cause functional or structural 
changes that lead to adverse health effects, can be a useful metric by 
which risk can be assessed. It is considered a key determinant of 
chemical toxicity, and chemicals can often be classified by their type 
of toxicity pathway(s) or MOAs. However, because PFAS are an emerging 
chemical class, MOA data can be limited or entirely lacking for many 
PFAS. Therefore, the EPA's approach for assessing risks of PFAS 
mixtures is based on the conclusion that PFAS that share one or more 
adverse outcomes produce dose-additive effects from co-exposures. This 
evidence-based determination supports a health-protective approach that 
meets the statute's directive to set the MCLG at a level at which there 
are no known or anticipated adverse health effects and which allows for 
an adequate margin of safety (1412(b)(4)(A)). The EPA's evidence-based 
determination regarding dose additivity, based on similarity of adverse 
health effects rather than MOA, and use of the Hazard Index approach to 
assess risks of exposure to PFAS mixtures were supported by the SAB in 
its review of the Draft Framework for Estimating Noncancer Health Risks 
Associated with Mixtures of PFAS (USEPA, 2022i). For a detailed 
description of the evidence supporting dose additivity as the default 
approach for assessing mixtures of PFAS, see the final Framework for 
Estimating Noncancer Health Risks Associated with Mixtures of PFAS 
(USEPA, 2024a).
    A few commenters supported the EPA's approach to assessing risks of 
PFAS mixtures based on similarity of toxicity effect rather than 
similarity in MOA. A few commenters opposed the EPA's use of same or 
similar adverse health effects/outcomes rather than MOA as a basis for 
the approach to assessing risks of PFAS mixtures and suggested that the 
agency is not following its own chemical mixtures guidance (USEPA, 
2000a). The EPA disagrees with these commenters' assertions. The EPA's 
approach, to evaluate health risks of exposure to mixtures of these 
four PFAS based on shared or similar adverse health effects of the 
mixture components rather than a common MOA, is consistent with the 
EPA's Supplementary Guidance for Conducting Health Risk Assessment of 
Chemical Mixtures (USEPA, 2000a). Although a conclusion about dose 
additivity can be based on mixture components sharing a common MOA, 
dose additivity can also be based on ``toxicological similarity, but 
for specific conditions (endpoint, route, duration)'' (see the EPA's 
Supplementary Guidance for Conducting Health Risk Assessment of 
Chemical Mixtures, USEPA, 2000a). The EPA's Supplementary Guidance for 
Conducting Health Risk Assessment of Chemical Mixtures indicates that 
although basing a conclusion about dose additivity on a common MOA 
across mixture components is optimal, there is flexibility in the level 
of biological organization at which similarity among mixture components 
can be determined.
    The EPA directly asked the SAB for feedback on this issue during 
its 2021 review of the EPA's draft Framework for Estimating Noncancer 
Health Risks Associated with Mixtures of PFAS. Specifically, the EPA 
asked the SAB, ``If common toxicity endpoint/health effect is not 
considered an optimal similarity domain for those PFAS with limited or 
no available MOA-type data, please provide specific alternative 
methodologies for integrating such chemicals into a component-based 
mixture evaluation(s)'' (USEPA, 2022i). The SAB strongly supported the 
EPA's approach of using a similar toxicity endpoint/health effect 
instead of a common MOA as a default approach for evaluating mixtures 
of PFAS using dose additivity and did not offer an alternative 
methodology. For example, the SAB panel stated that:

    The Panel agreed with use of a similar toxicity endpoint/health 
effect instead of a common MOA as a default approach for evaluating 
mixtures of PFAS. This approach makes sense because multiple 
physiological systems and multiple MOAs can contribute to a common 
health outcome. Human function is based on an integrated system of 
systems and not on single molecular changes as the sole drivers of 
any health outcome. The Panel concluded that rather than the common 
MOA, as presented in the EPA draft mixtures document, common 
physiological outcomes should be the defining position (USEPA, 
2022i).

    The SAB panel also stated:

    Furthermore, many PFAS, including the four used in the examples 
in the draft EPA mixtures document and others, elicit effects on 
multiple biological pathways that have common adverse outcomes in 
several biological systems (e.g., hepatic, thyroid, lipid synthesis 
and metabolism, developmental and immune toxicities) (USEPA, 2022i).

    Some commenters expressed support for the EPA's proposed Hazard 
Index approach to regulating a mixture of one or more of the four PFAS 
in drinking water. The commenters also stated that occurrence and co-
occurrence of these four PFAS in PWSs, as well as individual and dose-
additive effects of these PFAS, justify the general Hazard Index 
approach. The EPA agrees that the general Hazard Index approach is the 
most scientifically sound and health-protective approach to deriving a 
PFAS mixtures MCLG which considers both their dose additive health 
concerns and co-occurrence in drinking water (see additional discussion 
in the following paragraphs).
    Some commenters opposed the EPA's use of a general Hazard Index as 
opposed to a target organ-specific Hazard Index (TOSHI) and suggested 
the use of a TOSHI instead. As discussed in this section, the EPA 
disagrees with these comments because the use of the general Hazard 
Index approach to develop an MCLG for a mixture of PFHxS, PFNA, HFPO-
DA, and/or PFBS is scientifically sound, supported by external peer 
review (SAB), and consistent with the EPA's Supplementary Guidance for 
Conducting Health Risk Assessment of Chemical Mixtures (USEPA, 2000a).
    The EPA considered the two main types of Hazard Index approaches: 
(1)

[[Page 32570]]

the general Hazard Index, which allows for component chemicals in the 
mixture to have different health effects or endpoints as the basis for 
their toxicity reference values (e.g., RfDs, minimal risk levels), and 
(2) the TOSHI, which relies on toxicity reference values based on the 
same specific target organ or system effects (e.g., effects on the 
liver or thyroid; effects on developmental or reproductive systems) 
(USEPA, 2000a). The general Hazard Index approach uses the most health-
protective RfD (or minimal risk levels) available for each mixture 
component, irrespective of whether the RfDs for all mixture components 
are based on effects in the same target organs or systems. These 
``overall'' RfDs (as they are sometimes called) are protective of all 
other adverse health effects because they are based on the most 
sensitive known endpoints as supported by the weight of the evidence. 
As a result, this approach is protective of all types of toxicity/
adverse effects, and thus ensures that the MCLG is the level at and 
below which there are no known or anticipated adverse human health 
effects with an adequate margin of safety with respect to certain PFAS 
mixtures in drinking water. The TOSHI produces a less health protective 
indicator of risk than the general Hazard Index because the basis for 
the component chemical toxicity reference values has been limited to a 
specific target organ or system effect, which may occur at higher 
exposure levels than other effects (i.e., be a less sensitive 
endpoint). Additionally, since a TOSHI relies on toxicity reference 
values aggregated for the same specific target organ or system 
endpoint/effect, an absence or lack of data on the specific target 
organ or system endpoint/effect for a mixture component may result in 
that component not being adequately accounted for in this approach 
(thus, underestimating health risk of the mixture). A TOSHI can only be 
derived for those PFAS for which the same target organ or system 
endpoint/effect-specific RfDs have been calculated. Many PFAS have data 
gaps in epidemiological or animal toxicological dose-response 
information for multiple types of health effects, thus limiting 
derivation of target organ-specific toxicity reference values; target 
organ-specific toxicity reference values are not currently available 
for PFHxS, PFNA, HFPO-DA, and PFBS. The EPA's Supplementary Guidance 
for Conducting Health Risk Assessment of Chemical Mixtures recognizes 
the potential for organ- or system-specific data gaps and supports use 
of overall RfDs in a general Hazard Index approach, stating, ``The 
target organ toxicity dose (TTD) is not a commonly evaluated measure 
and currently there is no official EPA activity deriving these values, 
as there is for the RfD and RfC'' . . . ``Because of their much wider 
availability than TTDs, standardized development process including peer 
review, and official stature, the RfD and RfC are recommended for use 
in the default procedure for the HI'' (USEPA, 2000a). The EPA 
determined that the general Hazard Index approach is the most 
scientifically defensible and health protective approach for 
considering PFAS mixtures in this rule because it is protective of all 
adverse health effects rather than just those associated with a 
specific organ or system, consistent with the statutory definition of 
MCLG.
    The EPA directly asked the SAB about the utility and scientific 
defensibility of the general Hazard Index approach (in addition to 
other methods, including TOSHI) during the 2021 review of the EPA's 
draft Framework for Estimating Noncancer Health Risks Associated with 
Mixtures of PFAS. Specifically, the EPA asked the SAB to ``Please 
provide specific feedback on whether the HI approach is a reasonable 
methodology for indicating potential risk associated with mixtures of 
PFAS. If not, please provide an alternative;'' and ``Please provide 
specific feedback on whether the proposed HI methodologies in the 
framework are scientifically supported for PFAS mixture risk 
assessment'' (USEPA, 2022i). In its report (USEPA, 2022i), the SAB 
stated its support for the general Hazard Index approach:

    In general, the screening level Hazard Index (HI) approach, in 
which Reference Values (RfVs) for the mixture components are used 
regardless of the effect on which the RfVs are based, is appropriate 
for initial screening of whether exposure to a mixture of PFAS poses 
a potential risk that should be further evaluated. Toxicological 
studies to inform human health risk assessment are lacking for most 
members of the large class of PFAS, and mixtures of PFAS that 
commonly occur in environmental media, overall. For these reasons, 
the HI methodology is a reasonable approach for estimating the 
potential aggregate health hazards associated with the occurrence of 
chemical mixtures in environmental media. The HI is an approach 
based on dose additivity (DA) that has been validated and used by 
the EPA. The HI does not provide quantitative risk estimates (i.e., 
probabilities) for mixtures, nor does it provide an estimate of the 
magnitude of a specific toxicity. This approach is mathematically 
straightforward and may readily identify mixtures of potential 
toxicological concern, as well as identify chemicals that drive the 
toxicity within a given mixture.

    A few commenters stated that it is inappropriate to use the general 
Hazard Index in the context of a drinking water rule because it is a 
screening tool. The EPA guidance (e.g., Risk Assessment Guidance for 
Superfund [RAGS], USEPA, 1991b) and the SAB does characterize the 
general Hazard Index as appropriate for screening, but the SAB did not 
say that the methodology's use was limited to screening, nor that the 
agency would or should be prohibited from considering its use in any 
regulatory or nonregulatory application. The general Hazard Index is a 
well-established methodology that has been used for several decades in 
at least one other regulatory context to account for dose additivity in 
mixtures. The EPA routinely uses the Hazard Index approach to consider 
the risks from multiple contaminants of concern in the Remedial 
Investigations and Feasibility Studies for cleanup sites on the 
Superfund National Priorities List under the Comprehensive 
Environmental Response, Compensation, and Liability Act (CERCLA). 
Noncarcinogenic effects are summed to provide a Hazard Index that is 
compared to an acceptable index, generally 1. This procedure assumes 
dose additivity in the absence of information on a specific mixture. 
These assessments of hazards from multiple chemical exposures are 
important factors to help inform the selection of remedies that are 
ultimately captured in the Superfund Records of Decision. Moreover, the 
EPA has determined that in the context of SDWA, the Hazard Index is 
also an appropriate methodology for determining the level at and below 
which there are no known or anticipated adverse human health effects 
with an adequate margin of safety with respect to certain PFAS mixtures 
in drinking water. The Hazard Index approach is the most practical 
approach for establishing an MCLG for PFAS mixtures that meets the 
statutory requirements outlined in section 1412(b)(1)(A) of SDWA. This 
is because the Hazard Index assesses the exposure level of each 
component PFAS relative to its HBWC, which is based on the most 
sensitive known adverse health effect (based on the weight of evidence) 
and considers sensitive population(s) and life stage(s) as well as 
potential exposure sources beyond drinking water. Furthermore, the 
Hazard Index accounts for dose additive health concerns by summing the 
hazard contribution from each mixture component to ensure that the 
mixture is not exceeding the level below which there are no known or 
anticipated adverse health effects and allows for an

[[Page 32571]]

adequate margin of safety. In addition, given the temporal and spatial 
variability of PFAS occurrence in drinking water across the nation 
(USEPA, 2024b), this methodology allows the EPA to regulate these 
chemicals in drinking water by taking into account site-specific data 
at each PWS. Component PFAS HQs (hazard quotients) are expected to 
differ across time and space depending on the actual measured 
concentrations of each of the four PFAS at each PWS. This approach thus 
allows for flexibility beyond a one-size-fits-all approach and is 
tailored to address risk at each PWS. The EPA has made a final 
regulatory determination for mixtures of two or more of these PFAS. The 
EPA's application of the Hazard Index approach to regulate such 
mixtures accounts for the dose additivity that was the basis for the 
EPA's final determination to regulate such mixtures.
    A Hazard Index greater than 1 is generally regarded as an indicator 
of adverse health risks associated with a specific level of exposure to 
the mixture; a Hazard Index less than or equal to 1 is generally 
regarded as not being associated with any appreciable risk (USEPA, 
1986; USEPA,1991b; USEPA, 2000a). Thus, in the case of this drinking 
water rule, a Hazard Index greater than 1 indicates that occurrence of 
two or more of these four component PFAS in a mixture in drinking water 
exceeds the health protective level(s) (i.e., HBWC(s)), indicating 
health risks.
    The EPA proposed a Hazard Index MCLG of 1.0, expressed with two 
significant digits. The EPA's proposal expressed the HBWCs to the 
tenths place, as follows: 9.0 ng/L for PFHxS, 10.0 ng/L for HFPO-DA; 
10.0 ng/L for PFNA; and 2000.0 ng/L for PFBS. The EPA's draft Hazard 
Index MCLG document expressed all of the HBWCs with one significant 
digit (9, 10, 10, 2000 ng/L, respectively) (USEPA, 2023e). A few 
commenters supported the use of two significant digits for the HBWCs, 
individual HQs, and the Hazard Index MCLG and stated that the use of 
two significant digits would not be expected to result in issues 
related to analytical methods precision. One commenter supported using 
all digits of precision in calculations but rounding to two significant 
digits for the final reported value of the Hazard Index, noting that 
the number of significant digits used only affects rounding during 
steps prior to the point at which a Hazard Index MCL is reached. 
Commenters noted the importance of clearly communicating the number of 
significant digits to be used in the documents, and that the choice of 
the number of significant digits could impact implementation of an MCL 
based on the Hazard Index. For example, a Hazard Index of 1 (i.e., 
using one significant digit) would not be exceeded unless the value is 
calculated to be at 1.5 or above. Alternatively, a Hazard Index of 1.0 
(reporting with more than one significant digit) would be exceeded when 
the Hazard Index is calculated to be 1.05 or above. For additional 
discussion on significant digit usage, please see sections V and VIII.
    A few commenters did not support more than a single significant 
digit for the HBWCs and Hazard Index MCLG, with some stating that using 
two or more significant digits for the Hazard Index contradicts the EPA 
chemical mixtures guidance (USEPA, 2000a) and the RAGS (USEPA, 1991b). 
The EPA agrees that one (1) significant digit is appropriate for the 
HBWCs and the Hazard Index MCLG (i.e., 1 rather than 1.0, as in the 
proposal) because although there is sufficient analytical precision for 
two significant digits at these concentrations, the RfVs (RfDs and 
minimal risk levels) used to derive the HBWCs have one significant 
digit. According to the EPA chemical mixtures guidance (USEPA, 2000a), 
``Because the RfDs (and by inference the TTDs) are described as having 
precision no better than an order of magnitude, the HI should be 
rounded to no more than one significant digit.'' This approach of using 
a Hazard Index of 1 is consistent with agency chemical mixtures 
guidance (USEPA, 1986; USEPA, 2000a) and RAGS (USEPA, 1991b; USEPA, 
2018c). The EPA's Risk Assessment Guidance for Superfund Volume 1 Human 
Health Evaluation Manual states, ``For noncarcinogenic effects, a 
concentration is calculated that corresponds to an HI of 1, which is 
the level of exposure to a chemical from all significant exposure 
pathways in a given medium below which it is unlikely for even 
sensitive populations to experience adverse health effects,'' and ``The 
total risk for noncarcinogenic effects is set at an HI of 1 for each 
chemical in a particular medium'' (USEPA, 1991b). Finally, ``Cancer 
risk values and hazard index (HI) values may express more than one 
significant figure, but for decision-making purposes one significant 
figure should be used'' (USEPA, 2018c).
c. Final Rule
    The EPA has made a final determination to regulate mixtures 
containing two or more of PFHxS, PFNA, HFPO-DA, and/or PFBS. For the 
final determination, the EPA's evaluation utilized an HRL as part of a 
general Hazard Index approach (for additional discussion on the EPA's 
Final Regulatory Determinations, please see section III of this 
preamble). The EPA's proposal included individual preliminary 
regulatory determinations for PFHxS, PFNA, HFPO-DA, and PFBS and a 
mixture regulatory determination for mixtures of those PFAS. The EPA's 
proposal addressed these regulatory determinations through the Hazard 
Index MCLG and MCL that would apply to a mixture containing one or more 
of PFHxS, PFNA, HFPO-DA, and PFBS. If two or more of these PFAS were 
present then the MCLG and MCL would account for dose additivity of all 
of the contaminants present, but if only one of the contaminants were 
present then the Hazard Index would operate as an individual MCLG and 
MCL. In this final rule, the EPA is promulgating individual MCLGs and 
MCLs to address the individual final regulatory determinations (PFHxS, 
PFNA, and HFPO-DA) and is promulgating a Hazard Index MCLG and MCL to 
address the final mixtures regulatory determination for two or more 
Hazard Index PFAS (PFHxS, PFNA, HFPO-DA, and PFBS) present.
    The EPA used the same general Hazard Index approach for the mixture 
MCLG. In the general Hazard Index approach, individual PFAS HQs are 
calculated by dividing the measured concentration of each component 
PFAS in water (e.g., expressed as ng/L) by the corresponding HBWC for 
each component PFAS (e.g., expressed as ng/L), as shown in the 
following equation (and described in USEPA, 2024f). For purposes of 
this NPDWR, the EPA is using the term ``health-based water 
concentration'' or ``HBWC'' given its role in calculating the Hazard 
Index (see the Executive Summary of this preamble). The EPA notes that 
the Hazard Index MCLG applies to the entire mixture but the EPA's 
technical justification for the HBWCs for the mixture components is the 
same as for the individual MCLGs provided in this rule. In this final 
rule, component PFAS HQs are summed across the PFAS mixture to yield 
the Hazard Index MCLG. The final PFAS mixture Hazard Index MCLG is set 
at 1 (one significant digit). A Hazard Index greater than 1 (rounded to 
one significant digit) indicates that exposure (i.e., PFAS occurrence 
in drinking water) exceeds the health protective level (i.e., HBWC) for 
two or more of the individual PFAS mixture components, and thus 
indicates health risks. The Hazard Index MCLG ensures that even when 
the individual

[[Page 32572]]

components are below a level of concern, the components when added 
together in the mixture do not result in a mixture that itself exceeds 
a level of concern. A Hazard Index less than or equal to 1 indicates 
that occurrence of these four PFAS in drinking water does not exceed 
the health protective level and is therefore generally regarded as 
unlikely to result in any appreciable risk (USEPA, 1986; USEPA, 1991b; 
USEPA, 2000a). For more details, please see USEPA (2024a; USEPA, 
2024f). The final Hazard Index MCLG for a mixture of PFHxS, PFNA, HFPO-
DA, and/or PFBS is derived as follows:
[GRAPHIC] [TIFF OMITTED] TR26AP24.004

Where

[PFASwater] = the measured component PFAS concentration 
in water and
[PFASHBWC] = the HBWC of a component PFAS.
2. MCLG Derivation for PFHxS, PFNA, and HFPO-DA
a. Proposal
    As described in section IV.B.1.a of this preamble, in March 2023, 
the EPA proposed a Hazard Index MCLG to protect public health from 
exposure to mixtures of PFHxS, PFNA, HFPO-DA, and PFBS, four PFAS that 
affect many similar health endpoints/outcomes and that occur and co-
occur in drinking water. At that time, the EPA also considered setting 
individual MCLGs for these PFAS either instead of or in addition to 
using a mixtures-based approach for PFHxS, PFNA, HFPO-DA, and PFBS. The 
EPA ultimately proposed the Hazard Index approach for establishing an 
MCLG for a mixture of these four PFAS.
b. Summary of Major Public Comments and EPA Responses
    Several commenters favored finalization of individual MCLGs (and 
MCLs) for some or all of the PFAS included in the proposed Hazard 
Index, with or without a Hazard Index approach to address mixtures of 
these PFAS. Specifically, commenters supported establishing individual 
MCLGs for PFHxS, PFNA, HFPO-DA, and PFBS because they questioned the 
EPA's scientific conclusions regarding PFAS dose additivity and raised 
concerns about potential risk communication issues and confusion about 
the EPA's use of the Hazard Index to establish drinking water standards 
(for additional discussion on MCLs, please see section V of this 
preamble). The EPA agrees with commenters who favored finalization of 
individual MCLGs for some of the PFAS included in the Hazard Index, and 
to do so in addition to the Hazard Index MCLG being finalized for the 
mixture of the four PFAS. The EPA believes this provides clarity for 
purposes of implementation of the rule. The EPA is finalizing 
individual MCLGs for PFHxS, PFNA, and HFPO-DA (for additional 
discussion on the final regulatory determinations, please see section 
III of this preamble). Regarding risk communication and potential 
confusion about the use of the Hazard Index, the EPA acknowledges that 
effective risk communication is important, and the agency will develop 
communication materials to facilitate understanding of all aspects of 
this NPDWR, including the Hazard Index MCL (for additional discussion 
on MCLs, please see section V of this preamble). The EPA has provided 
language for consumer notifications as part of CCR (see section IX of 
this preamble).
    One commenter stated that developing individual MCLGs (and MCLs) in 
addition to the Hazard Index mixture MCLG (and MCL) would have no 
practical impact, since an exceedance of an HBWC for an individual PFAS 
within a mixture would result in an exceedance of the Hazard Index even 
if none of the other PFAS included in the Hazard Index are detected. 
The EPA clarifies the final rule promulgates individual MCLs for PFHxS, 
PFNA and HFPO-DA as well as a mixture Hazard Index MCL for two or more 
of these PFAS and PFBS. There may be a practical impact of these 
individual MCLs (for PFHxS, PFNA and HFPO-DA) where one of these three 
PFAS occur in isolation (i.e., without one of the other four Hazard 
Index PFAS present) above their individual MCLs. The EPA notes that 
this regulatory structure is consistent with the intended effect of the 
proposed regulation, where as proposed, a single PFAS above its HBWC 
would have caused an exceedance of the MCL. Based on public comment, 
the EPA has restructured the rule such that two or more of these 
regulated PFAS would be necessary to cause an exceedance of the Hazard 
Index and instead will regulate individual exceedances of PFNA, PFHxS, 
and HFPO-DA as individual MCLs to improve risk communication. Risk 
communication is an important focus for water systems and the EPA 
believes that finalizing individual MCLs for PFHxS, PFNA, and HFPO-DA 
can support risk communication as utilities and the public may be more 
familiar with this regulatory framework. Additionally, the final 
individual MCLs for PFHxS, PFNA and HFPO-DA will address and 
communicate health concerns for these compounds where they occur in 
isolation. At the same time, since those individual MCLs do not address 
additional risks from co-occurring PFAS, the EPA is finalizing a Hazard 
Index MCL that provides a framework to address and communicate dose 
additive health concerns associated with mixtures of PFHxS, PFNA, HFPO-
DA, and PFBS that co-occur in drinking water. For the EPA's discussion 
on the practical impact of the establishment of stand-alone standards 
in lieu of or in addition to the Hazard Index MCL, please see sections 
V and IX.A of this preamble. The EPA's discussion on the practical 
impact of the establishment of stand-alone standards in lieu of or in 
addition to the Hazard Index MCL, please see sections V and IX.A of 
this preamble.
    A few commenters questioned why the EPA is developing an NPDWR for 
contaminants that do not have EPA Drinking Water Health Advisories 
(PFHxS, PFNA), and stated that the EPA should wait to propose an NPDWR 
for PFHxS and PFNA until after Health Advisories are finalized for 
these PFAS. The EPA disagrees with this comment. Health Advisories are 
not a pre-requisite for an NPDWR under SDWA and there is nothing in the 
statute or the EPA's historical regulatory practice that suggests that 
the agency must or should

[[Page 32573]]

delay regulation of a contaminant in order to develop a health advisory 
first.
c. Final Rule
    As described in section III of this preamble, the EPA has made a 
final determination to individually regulate PFHxS, PFNA, and HFPO-DA.
    The EPA is finalizing individual MCLGs for PFHxS, PFNA, and HFPO-DA 
as follows: PFHxS MCLG = 10 ng/L; HFPO-DA MCLG = 10 ng/L; and PFNA MCLG 
= 10 ng/L. The technical basis for why each of these levels satisfies 
the statutory definition for MCLG is described in section III of this 
preamble (and is the same technical basis the EPA used to explain the 
levels identified as the HBWCs). These MCLGs are expressed with one 
significant digit and are based on an analysis of each chemical's 
toxicity (i.e., RfD/minimal risk level) and appropriate exposure 
factors (i.e., DWI-BW, RSC) (USEPA, 2024f).
    The EPA is deferring its individual regulatory determination for 
PFBS and not finalizing an individual MCLG for PFBS at this time 
(please see section III of this preamble, Final Regulatory 
Determinations for Additional PFAS, for further information).

V. Maximum Contaminant Levels

    Under current law and as described in the proposed rule (USEPA, 
2023f), the Environmental Protection Agency (EPA) establishes drinking 
water standards through a multi-step process. See S. Rep. No. 169, 
104th Cong., 1st Sess. (1995) at 3. First, the agency establishes a 
non-enforceable Maximum Contaminant Level Goals (MCLG) for the 
contaminant in drinking water at a level which no known or anticipated 
adverse effects to the health of persons will occur and which allow for 
an adequate margin of safety. Second, the agency generally sets an 
enforceable Maximum Contaminant Level (MCL) as close to that public 
health goal as feasible, taking costs into consideration.
    In this second step, consistent with the definition of ``feasible'' 
in section 1412(b)(4)(D), the EPA evaluates the availability and 
performance of Best Available Technologies (BATs) for treating water to 
minimize the presence of the contaminant consistent with the MCLG (see 
section X for additional discussion on BATs) as well as the costs of 
applying those BATs to large metropolitan water systems when treating 
to that level (1412(b)(4)(E) and (5)).\4\ The definition of 
``feasible'' means feasible with the use of the best technology . . . 
``which includes consideration of the analytical limits of best 
available treatment and testing technology.'' see S. Rep. No. 169, 
104th Cong., 1st Sess. (1995) at 3; see also section 1401(1)(C)(i) 
stating that a NPDWR includes an MCL only ``if, in the judgment of the 
Administrator, it is economically and technologically feasible to 
ascertain the level of such contaminant in water in public water 
systems.'' In addition, the MCL represents ``the maximum permissible 
level of a contaminant in water which is delivered to any user of a 
public water system,'' section 1401(3). Thus, in setting the MCL level, 
the EPA also identifies the level at which it is technologically 
feasible to measure the contaminant in the public water system. To 
identify this level, the EPA considers (1) the availability of 
analytical methods to reliably quantify levels of the contaminants in 
drinking water and (2) the lowest levels at which contaminants can be 
reliably quantified within specific limits of precision and accuracy 
during routine laboratory operating conditions using the approved 
methods (known as the practical quantitation levels (PQLs)). The 
ability of laboratories to measure the level of the contaminant with 
sufficient precision and accuracy using approved methods is essential 
to ensure that any public water system nationwide can monitor, 
determine compliance, and deliver water that does not exceed the 
maximum permissible level of a contaminant in water to any of its 
consumers. (See section VII of this preamble for additional discussion 
on analytical methods and PQLs for the per- and polyfluoroalkyl 
substances (PFAS) regulated in this rule.)
---------------------------------------------------------------------------

    \4\ Based on legislative history, the EPA interprets ``taking 
cost into consideration'' in section 1412(b)(4)(D) to be limited to 
``what may be reasonably be afforded by large metropolitan or 
regional public water systems.'' H.R. Rep. No 93-1185 (1974), 
reprinted in 1974 U.S.C.C.A.N. 6454, 6470-71.
---------------------------------------------------------------------------

    In practice this means that where the MCLG is zero, the EPA 
typically sets MCLs at the PQLs when treatment is otherwise feasible, 
based on cost and treatment availability, because the PQL is the 
limiting factor. Conversely, for contaminants where the MCLG is higher 
than the PQL, the EPA generally sets the MCL at the MCLG when treatment 
is otherwise feasible, based on costs and treatment availability, 
because the PQL is not a limiting factor.
    The Safe Drinking Water Act (SDWA) defines an MCL as ``the maximum 
permissible level of a contaminant in water which is delivered to any 
user of a public water system.'' Like the MCLG, SDWA does not dictate 
that the MCL take a particular form; however, given this definition, an 
MCL establishes a ``maximum permissible level of a contaminant in 
water'' and as a practical matter the identified ``level'' must be 
capable of being validated so that it can be determined whether that 
public water systems are delivering water to any user meeting or 
exceeding that ``level.''

A. PFOA and PFOS

1. Proposal
    In the March 2023 proposal, the EPA proposed individually 
enforceable MCLs for PFOA and PFOS at the PQL which is 4.0 ng/L (USEPA, 
2023f). Section 1412(b)(4)(E) of SDWA requires that the agency ``list 
the technology, treatment techniques, and other means which the 
Administrator finds to be feasible for purposes of meeting [the MCL],'' 
which are referred to as Best Available Technologies (BATs). The EPA 
found multiple treatment technologies to be effective and available to 
treat PFOA and PFOS to at or below the proposed standards (please see 
and section X (10) of this preamble and USEPA, 2024l for additional 
discussion on feasible treatment technologies including BAT/SSCT 
identification and evaluation). In addition, the EPA found that there 
are analytical methods available to reliably quantify PFOA and PFOS at 
the PQL. The EPA requested comment on regulatory alternatives for both 
compounds at 5.0 ng/L and 10.0 ng/L. The EPA also requested comment on 
whether setting the MCL at the PQL for PFOA and PFOS is implementable 
and feasible.
2. Summary of Major Public Comments and EPA Responses
    The EPA received many comments that strongly support the proposed 
MCLs of 4.0 ng/L and the agency's determination that the standards are 
as close as feasible to the MCLG. These commenters request the agency 
to finalize the standards as expeditiously as possible. Consistent with 
these comments, through this action, the agency is establishing 
drinking water standards for PFOA and PFOS (and four other PFAS) to 
provide health protection against these contaminants found in drinking 
water.
    Many commenters assert that implementation of the PFOA and PFOS 
standards would be challenging because the MCLs are set at the PQLs for 
each compound, and some commenters recommended alternative standards 
(e.g., 5.0 ng/L or 10.0 ng/L). These commenters contend that by setting 
the

[[Page 32574]]

MCLs at the PQLs, utilities would not be able to reliably measure when 
the concentration of contaminants in their drinking water is 
approaching the MCLs. Some of these commenters suggest that having a 
buffer between the PQLs and the MCLs may allow utilities to manage 
treatment technology performance more efficiently because utilities 
generally aim to achieve lower than the MCLs to avoid a violation and 
that this buffer would provide some level of operational certainty for 
systems treating for PFAS. The EPA disagrees that the PFOA and PFOS 
standards are not implementable because the MCLs are set at their 
respective PQLs.
    As the agency noted in the proposed rule preamble, the EPA has 
promulgated, and both the EPA and water systems have successfully 
implemented, several NPDWRs with MCLs equal to the contaminant PQLs. As 
examples, in 1987, the EPA finalized the Phase I Volatile Organic 
Compounds (VOC) rule (USEPA, 1987), where the agency set the MCL at the 
PQL for benzene, carbon tetrachloride, trichloroethylene, vinyl 
chloride, and 1,2-dichloroethane (52 FR 25690). Other examples where 
MCLs were set at the PQL include benzo(a)pyrene, di(2-ethylhexyl) 
phthalate, dioxin, dichloromethane, hexachlorobenzene, and PCBs (see 
USEPA, 1991c and USEPA, 1992). Some commenters at the time stated they 
believed implementation would be challenging because the MCLs were set 
at the PQL in these examples; however, the EPA notes that those rules 
have been implemented successfully despite commenters initial concerns. 
The agency does not agree with commenters that operational flexibility 
(i.e., the inclusion of a `buffer' between the PQL and MCL) is relevant 
for purposes of setting an MCL. That is because the PQL is the lowest 
level that can be reliably achieved within specified limits of 
precision and accuracy and is therefore the metric by which the agency 
uses to evaluate the most feasible MCL pursuant to SDWA requirements. 
Considerations for operational flexibility may be relevant to other 
parts of the rule, such as determining monitoring and compliance with 
the rule. First, for purposes of determining compliance with the MCL, 
water systems must calculate the running annual average (RAA) of 
results, which could allow some results to exceed 4.0 ng/L for single 
measurements if the overall annual average is below the MCL. In other 
words, there is a buffer built into determining compliance with the 
MCL. Second, when calculating the RAA, zero will be used for results 
less than the PQL which provides an additional analytic buffer for 
utilities in their compliance calculations. This monitoring and 
compliance framework allows for temporal fluctuations in concentrations 
that may occur because of unexpected events such as premature PFOA and 
PFOS breakthrough or temporary elevated source water concentrations. 
Thus, periodic occurrences of PFOA or PFOS that are slightly above the 
PQLs do not necessarily result in a violation of the MCL if other 
quarterly samples are below the PQL. The agency notes that in general, 
PQLs are set above the limit of detection; for PFAS specifically, all 
the PQLs are well above their limits of detection. The PQL is also 
different than detection limits because the PQL is set considering a 
level of precision, accuracy, and quantitation. Systems may be able to 
use sample results below the PQL to understand whether PFOA and PFOS 
are present. While the EPA has determined that results below the PQL 
are insufficiently precise for determining compliance with the MCL, 
results below the PQL can be used to determine analyte presence or 
absence in managing a system's treatment operations and to determine 
monitoring frequency. See discussion in section VII of this preamble 
for further discussion of the PQL, results below the PQL, and how those 
results provide useful information.
    Some commenters contend that the PQLs for PFOA and PFOS are not set 
at an appropriate level (e.g., the PQLs are either too high or too low 
for laboratories to meet). Specifically, these commenters question 
whether enough laboratories have the ability to analyze samples at 4.0 
ng/L and, as a result, contend it is not a ``reasonable quantitation 
level.'' The EPA disagrees with commenters who suggest the PQLs for 
PFOA and PFOS are not set at an appropriate level or that they should 
be either higher or lower levels than that proposed. As discussed above 
and in the March 2023 proposal, the EPA derives PQLs that reflect the 
level of contaminants that laboratories can reliably quantify within 
specific limits of precision and accuracy during routine laboratory 
operating conditions. The ability to reliably measure is an important 
consideration for feasibility to ensure that water systems nationwide 
can monitor and dependably comply with the MCLs and deliver drinking 
water that does not exceed the maximum permissible level. In the rule 
proposal (USEPA, 2023f), the EPA explained that the minimum reporting 
levels under UCMR 5 reflect ``a minimum quantitation level that, with 
95 percent confidence, can be achieved by capable lab analysts at 75 
percent or more of the laboratories using a specified analytical 
method'' (USEPA, 2022k). The PQLs for the regulated PFAS are based on 
the UCMR 5 minimum reporting levels. The EPA calculated the UCMR 5 
minimum reporting levels using quantitation-limit data from multiple 
laboratories participating in multi-lab method validation studies 
conducted in the 2017-2019 timeframe, prior to the UCMR 5 Laboratory 
Approval Program (see appendix B of USEPA, 2020b). The calculations 
account for differences in the capability of laboratories across the 
country. Laboratories approved to analyze UCMR samples must demonstrate 
that they can consistently make precise measurements of PFOA and PFOS 
at or below the established minimum reporting levels. Therefore, the 
EPA finds that the UCMR 5 minimum reporting levels are appropriate for 
using as PQLs for this rule: the EPA estimates that laboratories across 
the nation can precisely and accurately measure PFOA and PFOS at this 
quantitation level. After reviewing data from laboratories that 
participated in the minimum reporting level setting study under UCMR 5 
and in consideration of public comment, the EPA finds that the minimum 
reporting levels set in UCMR 5 of 4.0 ng/L for PFOA and PFOS, that are 
also the PQLs, are as close as feasible to the MCLG. While lower 
quantitation levels may be achievable for some laboratories, it has not 
been demonstrated that these lower quantitation levels can be achieved 
for ``at 75 percent or more of the laboratories using a specified 
analytical method'' across laboratories nationwide. Moreover, though 
the EPA is confident of sufficient laboratory capacity to implement 
this PFAS National Primary Drinking Water Regulation (NPDWR) as 
finalized, a lower PQL could potentially limit the number of 
laboratories available to support analytical monitoring that would be 
otherwise available to support analytical monitoring with PFOA and PFOS 
PQLs of 4.0 ng/L.
    In the proposal, the EPA discussed how utilities may be able to use 
sample results below the PQL to determine analyte presence or absence 
in managing their treatment operations; however, a few commenters 
contend that this is not practical to determine compliance with the MCL 
as these values are less precise and violations may result in expensive 
capital

[[Page 32575]]

improvements. Commenters are conflating two different issues. While 
commenters are referring to quantitation of a sampling result for 
compliance with the rule, the EPA's discussion on results below the PQL 
refers to determining simple presence or absence of a contaminant for 
other purposes. Sampling results below the PQL may not have the same 
precision as a sampling result at or above the PQL but they are useful 
for operational purposes such as understanding that PFOA and PFOS may 
be present, which can inform treatment decisions and monitoring 
frequency. For example, a utility may use sampling results below 4.0 
ng/L as a warning that they are nearing the PFOA and PFOS MCLs of 4.0 
ng/L prior to an exceedance. Then, the utility can make informed 
treatment decisions about managing their system (e.g., replacing GAC). 
Additionally, the EPA evaluated data submitted as part of the UCMR 5 
Laboratory Approval Program (LAP) and found that 47 of 53 laboratories 
(89 percent) that applied for UCMR 5 approval generated a minimum 
reporting level confirmation at 2 ng/L (one-half the proposed MCL) or 
less for Method 533 (USEPA, 2022j). This suggests that the majority of 
laboratories with the necessary instrumentation to support PFAS 
monitoring have the capability to provide useful screening measurement 
results below the PQL. Further, as discussed in section VII of this 
preamble, all labs are required per the approved methods to demonstrate 
whether laboratory reagent blank (LRB) quality control (QC) samples 
have background concentrations of less than one-third the minimum 
reporting level (i.e., the minimum concentration that can be reported 
as a quantitated value for a method analyte in a sample following 
analysis). Therefore, for a laboratory to be compliant with the 
methods, they must be able to detect, not necessarily quantify, 
analytes at or above \1/3\ the minimum reporting level.
    The EPA agrees with commenters that it is inappropriate to make 
potentially costly compliance decisions based on measurements below the 
PQL because they do not have the same level of precision and accuracy 
as results at or above the PQL. As previously discussed, for MCL 
compliance purposes, results less than the PQL will be recorded as 
zero. For additional details on monitoring and compliance requirements, 
please see section VIII of this preamble.
    Some commenters argue that the EPA did not sufficiently consider 
cost in the agency's feasibility analysis of the proposed MCLs and 
therefore disagreed with the EPA that the standards are feasible. In 
particular, these commenters suggest that the agency did not adequately 
consider costs associated with implementation (e.g., costs for labor, 
materials, and construction of capital improvements) and compliance 
(e.g., costs to monitor) with the proposed MCLs. Based on these 
factors, many of these commenters suggest either raising the MCLs or 
re-proposing the standard in its entirety. The EPA did consider these 
costs and therefore disagrees with commenters' assertions that the 
agency did not consider these issues in establishing the proposed MCLs 
for PFOA and PFOS (USEPA, 2024g; USEPA, 2024l; USEPA, 2024m). The EPA 
considers whether these costs are reasonable based on large 
metropolitan drinking water systems. H.R. Rep. No 93-1185 (1978), 
reprinted in 1974 U.S.C.C.A.N. 6454, 6470-71. The EPA considered costs 
of treatment technologies that have been demonstrated under field 
conditions to be effective at removing PFOA and PFOS and determined 
that the costs of complying with an MCL at the PQL of 4.0 are 
reasonable for large metropolitan water systems at a system and 
national level (USEPA, 2024e; USEPA, 2024g). To designate technologies 
as BATs, the EPA evaluated each technology against six BAT criteria, 
including whether there is a reasonable cost basis for large and medium 
water systems. The EPA evaluated whether the technologies are currently 
being used by systems, whether there were treatment studies available 
with sufficient information on design assumptions to allow cost 
modeling, and whether additional research was needed (USEPA, 2024l). In 
considering the results of this information, the EPA determined that 
these costs are reasonable to large metropolitan water systems.
    Pursuant to SDWA section 1412(b)(4)(E)(ii), the agency also 
evaluated ``technolog[ies], treatment technique[s], or other means that 
is affordable'' for small public water systems. In this evaluation, the 
agency determined that the costs of small system compliance 
technologies (SSCTs) to reach 4.0 ng/L are affordable for households 
served by small drinking water systems. Additionally, the EPA notes 
that SDWA section 1412(b)(4)(D) states that ``granular activated carbon 
is feasible for the control of synthetic organic chemicals'' which the 
agency lists as a BAT for this rule (section X). All PFAS, including 
PFOA and PFOS, are SOCs, and therefore, GAC is BAT as defined by the 
statute. For additional discussion on BATs and SSCTs, please see 
section X of this preamble.
    Some commenters disagreed with the EPA's determination that the 
rule is feasible under SDWA asserting that there is insufficient 
laboratory capacity and other analytic challenges to measure samples at 
these thresholds. As described above in the agency's approach toward 
evaluating feasibility, the EPA assesses (1) the availability of 
analytical methods to reliably quantify levels of the contaminants in 
drinking water and (2) the lowest levels at which contaminants can be 
reliably quantified within specific limits of precision and accuracy 
during routine laboratory operating conditions using the approved 
methods (i.e., the PQLs). This framework inherently considers both the 
capacity and capability of labs available to meet the requirements of 
the NPDWR. Based on the EPA's analysis of these factors, the EPA 
disagrees with commenter assertions that there is insufficient 
laboratory capacity at this time to support implementation of the 
NPDWR. Currently, there are 53 laboratories for PFAS methods (Method 
533 or 537.1) in the EPA's Unregulated Contaminant Monitoring Rule 
(UCMR) 5 Laboratory Approval Program, more than double the 
participation in UCMR 3 (21 laboratories), with several laboratory 
requests to participate after the lab approval closing date. At a 
minimum, these 53 labs alone have already demonstrated sufficient 
capacity for current UCMR 5 monitoring, which requires monitoring for 
all systems serving above 3,300 or more persons and 800 systems serving 
less than 3,300 persons over a three-year period. The 21 laboratories 
participating in UCMR 3 provided more than sufficient capacity for that 
monitoring effort, which required monitoring for all systems serving 
greater than 10,000 persons and 800 systems serving less than 10,000. 
Further, a recent review of state certification and third-party 
accreditation of laboratories for PFAS methods found an additional 25 
laboratories outside the UCMR 5 LAP with a certification or 
accreditation for EPA Method 533 or 537.1. Additionally, as has 
happened with previous drinking water regulations, the EPA anticipates 
laboratory capacity to grow once the rule is finalized to include an 
even larger laboratory community, as the opportunity for increased 
revenue by laboratories would be realized by filling the analytical 
needs of the utilities (USEPA, 1987; USEPA, 1991c; USEPA, 1991d; USEPA, 
1992; USEPA, 2001). Finally, with the use of a reduced monitoring 
schedule to once every three years for eligible systems, and the

[[Page 32576]]

ability for systems that are reliably and consistently below the MCLs 
of 4.0 ng/L to only monitor once per year, the EPA anticipates that the 
vast majority of utilities may be able to take advantage of reduced or 
annual monitoring, and will not require a more frequent monitoring 
schedule, thus easing the burden of laboratory capacity as well.
    The EPA also disagrees with commenter assertions that there is 
insufficient laboratory capability at this time. As discussed above and 
in the proposed rule preamble, the EPA proposed a PQL of 4.0 ng/L for 
both PFOA and PFOS based on current analytical capability and from the 
minimum reporting levels generated for the UCMR 5 program. The EPA 
evaluated data submitted as part of the UCMR 5 LAP and found that 47 of 
53 laboratories (89 percent) that applied for UCMR 5 approval generated 
a minimum reporting level confirmation at 2 ng/L (one-half the proposed 
MCL) or less for Method 533. The MCLs for PFOA and PFOS were also set 
at 4.0 ng/L as a result of the analytical capability assessment under 
the minimum reporting level setting study for UCMR 5, as well as 
consideration of other factors (e.g., treatment, costs) as required 
under SDWA. For UCMR 5, all UCMR-approved laboratories were able to 
meet or exceed the PFOS and PFOA UCMR minimum reporting levels, set at 
4 ng/L, the proposed MCL for both. The UCMR 5 minimum reporting levels 
of 4 ng/L for PFOS and PFOA are based on a multi-laboratory minimum 
reporting level calculation using lowest concentration minimum 
reporting level (LCMRL) data. The LCMRL and minimum reporting level 
have a level of confidence associated with analytical results. More 
specifically, the LCMRL calculation is a statistical procedure for 
determining the lowest true concentration for which future analyte 
recovery is predicted with 99% confidence to fall between 50 and 150% 
recovery (Martin et al., 2007). The multi-laboratory minimum reporting 
level is a statistical calculation based on the incorporation of LCMRL 
data collected from multiple laboratories into a 95% one-sided 
confidence interval on the 75th percentile of the predicted 
distribution referred to as the 95-75 upper tolerance limit. This means 
that 75% of participating laboratories will be able to set a minimum 
reporting level with a 95% confidence interval. The quantitation level 
of 4 ng/L has been demonstrated to be achieved with precision and 
accuracy across laboratories nationwide, which is important to ensure 
that systems can dependably comply with the MCL and deliver drinking 
water that does not exceed the maximum permissible level. The agency 
anticipates that these quantitation levels for labs will continue to 
improve over time, as technology advances and as laboratories gain 
experience with the PFAS Methods. The EPA's expectation is supported by 
the record borne out by the significant improvements in analytical 
capabilities for measuring certain PFAS, including PFOA and PFOS, 
between UCMR 3 and UCMR 5. For example, the minimum reporting levels 
calculated for UCMR 3 (2012-2016) were 40 ng/L and 20 ng/L for PFOS and 
PFOA, respectively, the minimum reporting levels calculated for UCMR 5 
(2022-2025) were 4 ng/L each for PFOA and PFOS.
    Some commenters recommend a different regulatory framework than 
what the EPA proposed to alleviate perceived implementation concerns 
(e.g., reduce the potential of inundating laboratories or providing 
more time to plan and identify opportunities for source water 
reduction). For example, a few commenters suggest a phased-in MCL, 
where systems demonstrating higher concentrations are addressed first 
in the NPDWR, or MCL approaches where interim targets are set for 
compliance. Upon consideration of information submitted by commenters, 
particularly issues related to supply chain complications that are 
directly or indirectly related to the COVID-19 pandemic residual 
challenges, the EPA has determined that a significant number of systems 
subject to the rule will require an additional 2 years to complete the 
capital improvements necessary to comply with the MCLs for PFAS 
regulated under this action. Thus, the EPA also disagrees with 
recommendations to create a phased schedule for rule implementation 
based on the concentrations of PFAS detected because the EPA has 
granted a two-year extension for MCL compliance to all systems. For 
additional discussion on this extension and the EPA responses to public 
comment on this issue, please see section XI.D.
    Some commenters argue for a lower PFOA and PFOS MCL due to the 
underlying health effects of these contaminants. These commenters 
suggest the EPA establish MCLs lower than the agency's proposed 
standard of 4.0 ng/L due to the capability of some laboratories to 
quantitate lower concentrations. Some of these commenters also argue 
that since PFOA and PFOS are likely human carcinogens, the EPA should 
consider an MCL at zero. While the EPA agrees with the health concerns 
posed by PFAS that are the basis for the proposed health based MCLGs 
for these contaminants, the agency disagrees with commenters on these 
alternative MCL thresholds given the EPA's consideration of feasibility 
as required by SDWA. These commenters did not provide evidence 
demonstrating the feasibility of achieving lower MCL thresholds 
(including an MCL at zero) consistent with SDWA requirements in 
establishing an MCL. For example, commenters did not provide evidence 
to support a lower PQL that can be consistently achieved by 
laboratories across the country. They also did not provide arguments 
supporting why the EPA should accept less than 75% of participating 
laboratories will be able to set a minimum reporting level with a 95% 
confidence interval. Thus, the agency is finalizing the MCLs for PFOA 
and PFOS at 4.0 ng/L (at the PQL) as this is the closest level to the 
MCLG that is feasible due to the ability of labs using approved 
analytical methods to determine with sufficient precision and accuracy 
whether such a level is actually being achieved. The record supports 
the EPA's determination that the lowest feasible MCL for PFOA and PFOS 
at this time is 4.0 ng/L.
    A few commenters suggest the EPA did not appropriately consider 
disposal concerns for spent treatment media as part of the agency's 
feasibility determination. These commenters state that they believe 
disposal options are currently limited for liquid brine, reject waters 
resulting from RO, or solid waste from GAC treatment and that disposal 
capacity will be further limited should the EPA designate PFAS waste as 
hazardous. These commenters contend that these limitations increase 
operating expenses for utilities and should be factored in the 
establishment of the PFOA and PFOS MCLs. The EPA disagrees with these 
commenters that the agency did not adequately consider disposal of 
spent treatment media in the rule. First, disposal options for PFAS are 
currently available. These destruction and disposal options include 
landfills, thermal treatment, and underground injection. Systems are 
currently disposing of spent media, such as activated carbon, through 
thermal treatment, to include reactivation, and at landfills. While 
precautions should be taken to minimize PFAS release to the environment 
from spent media, guidance exists that explains the many disposal 
options with relevant precautions. See section X for further 
discussion. Furthermore, the EPA has provided guidance for pretreatment 
and wastewater disposal to manage PFAS

[[Page 32577]]

that enters the sanitary sewer system and must be managed by publicly 
owned treatment works (POTWs) (USEPA, 2022d; USEPA, 2022e). As 
discussed in the proposed rule (USEPA, 2023f), the EPA assessed the 
availability of studies of full-scale treatment of residuals that fully 
characterize residual waste streams and disposal options. Although the 
EPA anticipates that designating chemicals as hazardous substances 
under CERCLA generally should not result in limits on the disposal of 
PFAS drinking water treatment residuals, the EPA has estimated the 
treatment costs for systems both with the use of hazardous waste 
disposal and non-hazardous disposal options to assess the effects of 
potentially increased disposal costs. Specifically, the EPA assessed 
the potential impact on public water system (PWS) treatment costs 
associated with hazardous residual management requirements in a 
sensitivity analysis. The EPA's sensitivity analysis demonstrates that 
potential hazardous waste disposal requirements may increase PWS 
treatment costs marginally; however, the increase in PWS costs is not 
significant enough to change the agency's feasibility determination nor 
the determination made at proposal that benefits of the rulemaking 
justify the costs. These estimates are discussed in greater detail in 
the HRRCA section of this final rule and in appendix N of the Economic 
Analysis (EA) (USEPA, 2024e). For the discussion on management of 
treatment residuals and additional responses to stakeholder concerns on 
this topic, please see section X of this preamble. While beyond the 
scope of this rule, the EPA further notes that the agency is proposing 
to amend its regulations under the Resource Conservation and Recovery 
Act (RCRA) by adding nine specific per-and polyfluoroalkyl substances 
(PFAS), their salts, and their structural isomers, to the list of 
hazardous constituents at 40 CFR part 261, appendix VIII (89 FR 8606). 
The scope of the proposal is limited and does not contain any 
requirements that would impact disposal of spent drinking water 
treatment residuals. This is because listing these PFAS as RCRA 
hazardous constituents does not make them, or the wastes containing 
them, RCRA hazardous wastes. The principal impact of the proposed rule, 
if finalized, will be on the RCRA Corrective Action Program. 
Specifically, when corrective action requirements are imposed at a RCRA 
treatment, storage, and disposal facility (TSDF), these specific PFAS 
would be among the hazardous constituents expressly identified for 
consideration in RCRA facility assessments and, where necessary, 
further investigation and cleanup through the RCRA corrective action 
process.
    Some commenters suggest that the EPA failed to consider the costs 
and impacts of the proposed MCLs in non-drinking water contexts, such 
as its potential uses as CERCLA clean-up standards. As required by 
SDWA, this rule and analyses supporting the rulemaking only includes 
costs that ``are likely to occur solely as a result of compliance with 
the [MCL].'' (SDWA section 1412(b)(3)(C)(i)(III)) Thus, the EPA's cost 
analyses focused on the compliance costs of meeting the MCL to public 
water systems that are directly subject to this regulation. The same 
provision expressly directs the EPA to exclude ``costs resulting from 
compliance with other proposed or promulgated regulations.'' Thus, the 
EPA cannot consider the costs of use of the MCLs under other EPA 
statutes (such as CERCLA) as part of its EA because SDWA specifically 
excludes such consideration (42 U.S.C. 300g-1(b)(3)(C)(i)(III)). See 
also City of Waukesha v. EPA, 320 F.3d 228, 243-244 (D.C. Cir. 2003) 
(finding that SDWA excludes consideration of the costs of, for example, 
CERCLA compliance, as part of the required cost/benefit analysis). In 
addition, whether and how MCLs might be used in any particular clean-up 
is very site-specific and as a practical matter cannot be evaluated in 
this rule.
    Many commenters compared the proposed MCLs to existing state and 
international standards, regulations, and guidelines. In particular, 
these commenters acknowledge the fact that several states have 
conducted their own rulemakings to promulgate MCLs and suggest that the 
EPA's analysis in support of the proposed MCLs are inconsistent with 
these state approaches. Further, these commenters ask the EPA to 
explain why certain states' cost-benefit analyses supported their 
respective levels and why the EPA's analysis is different. Regarding 
state PFAS regulations, the EPA disagrees with commenters who suggested 
that the agency should develop regulations consistent with current 
state-led actions in setting a national standard in accordance with 
SDWA. While some states have promulgated drinking water standards for 
various PFAS prior to promulgation of this NPDWR, this rule provides a 
nationwide, health protective level for PFOA and PFOS (as well as four 
other PFAS) in drinking water and reflects regulatory development 
requirements under SDWA, including the EPA's analysis of the best 
available and most recent peer-reviewed science; available drinking 
water occurrence, treatment, and analytical feasibility information 
relevant to the PQL; and consideration of costs and benefits. After the 
NPDWR takes effect, SDWA requires primacy states to have a standard 
that is no less stringent than the NPDWR. Additionally, analyses 
conducted by the agency in support of an NPDWR undergo a significant 
public engagement and peer review process. The EPA notes that the EA 
for this rule accounts for existing state standards at the time of 
analysis. Specifically, to estimate the costs and benefits of the final 
rule, the EPA assumed that occurrence estimates exceeding state limits 
are equivalent to the state-enacted limit. For these states, the EPA 
assumed that the state MCL is the maximum baseline PFAS occurrence 
value for all EP in the state. Additionally, while states may establish 
drinking water regulations or guidance values absent Federal regulation 
as they deem appropriate, the presence of state regulations does not 
preclude the EPA from setting Federal regulations under the authority 
of SDWA that meets that statute's requirements. For additional 
information on the EPA's EA, please see section XII.
3. Final Rule
    After considering public comments, the EPA is finalizing 
enforceable MCLs for PFOA and PFOS at 4.0 ng/L as the closest feasible 
level to the MCLG. First, the agency is establishing non-enforceable 
MCLGs at zero for contaminants where no known or anticipated adverse 
effects to the health of persons will occur, allowing for an adequate 
margin of safety. The EPA then examined the treatment capability of 
BATs and the accuracy of analytical techniques as reflected in the PQL 
in establishing the closest feasible level. In evaluating feasibility, 
the agency has determined that multiple treatment technologies (e.g., 
GAC, AIX) ``examined for efficacy under field conditions and not solely 
under laboratory conditions'' are found to be both effective and 
available to treat PFOA and PFOS to the standards and below. The EPA 
also determined that there are available analytical methods to measure 
PFOA and PFOS in drinking water and that the PQLs for both compounds 
reflect a level that can be achieved with sufficient precision and 
accuracy across laboratories nationwide using such methods. Since 
limits of analytical measurement for PFOA and PFOS require the MCL to 
be set at some

[[Page 32578]]

level greater than the MCLG, the agency has determined that 4.0 ng/L 
(the PQL for each contaminant) represents the closest feasible level to 
the MCLG and the level at which laboratories using these methods can 
ensure, with sufficient accuracy and precision, that water systems 
nationwide can monitor and determine compliance so that they are 
ultimately delivering water that does not exceed the maximum 
permissible level of PFOA and PFOS to any user of their public water 
system. The EPA evaluates the availability and performance of BATs for 
treating water to minimize the presence of the contaminant consistent 
with the MCLG as well as the costs of applying those BATs to large 
metropolitan water systems when treating to that level. In 
consideration of these factors, the EPA is therefore establishing the 
MCL of 4.0 ng/L for both PFOA and PFOS. The EPA further notes that the 
agency has determined that the costs of SSCTs to reach 4.0 ng/L are 
affordable for households served by small drinking water systems. For 
additional discussion on the EPA's EA, please see section XII of this 
preamble. For additional discussion on the PQLs for the PFAS regulated 
as part of this NPDWR, please see section VII of this preamble. The EPA 
notes that upon consideration of information submitted by commenters 
regarding the implementation timeline for the rule, the agency is also 
exercising its authority under SDWA section 1412(b)(10) to allow two 
additional years for systems to comply with the MCL. For additional 
discussion on this extension, please see section XI.
    The EPA clarifies that the MCLs for PFOA and PFOS are set using two 
significant digits in this final rule. In the proposed rule, the EPA 
proposed MCLGs for PFOA and PFOS at zero (0) and an enforceable MCL for 
PFOA and PFOS in drinking water with two significant digits at 4.0 ng/
L. As previously discussed in section IV of this preamble, the MCLG for 
PFOA and PFOS is zero because these two PFAS are likely human 
carcinogens. Because the MCLGs are zero, the number of significant 
digits in the MCLGs are not the appropriate driver for considering the 
number of significant digits in the MCLs. This approach is consistent 
with other MCLs the EPA has set with carcinogenic contaminants, 
including for arsenic and bromate.
    By setting the MCLs at 4.0, the EPA is setting the MCLs as close as 
feasible to the MCLGs. The EPA guidance states that all MCLs should be 
expressed in the number of significant digits permitted by the 
precision and accuracy of the specified analytical procedure(s) and 
that data reported should contain the same number of significant digits 
as the MCL (USEPA, 2000h). The EPA determined that two significant 
digits were appropriate for PFOA and PFOS considering existing 
analytical feasibility and methods. The EPA drinking water methods 
typically use two or three significant digits to determine 
concentrations. The EPA methods 533 and 537.1, those authorized for use 
in determining compliance with the MCLs, state that ``[c]alculations 
must use all available digits of precision, but final reported 
concentrations should be rounded to an appropriate number of 
significant digits (one digit of uncertainty), typically two, and not 
more than three significant digits.'' The EPA has determined that both 
methods 533 and 537.1 provide sufficient analytical precision to allow 
for at least two significant digits.

B. PFAS Hazard Index: PFHxS, PFNA, HFPO-DA, and PFBS

1. Proposal
    The EPA proposed an MCL for mixtures of PFHxS, PFNA, HFPO-DA, and 
PFBS expressed as a Hazard Index to protect against additive health 
concerns when present in mixtures in drinking water. As discussed in 
the March 2023 proposal (USEPA, 2023f), a Hazard Index is the sum of 
hazard quotients (HQs) from multiple substances. An HQ is the ratio of 
exposure to a substance and the level at which adverse effects are not 
anticipated to occur. The EPA proposed the MCL for mixtures of PFHxS, 
PFNA, HFPO-DA, and PFBS as the same as the MCLG: as proposed, the 
Hazard Index must be equal to or less than 1.0. This approach would set 
a permissible level for the contaminant mixture (i.e., a resulting PFAS 
mixture Hazard Index greater than 1.0 is an exceedance of the health 
protective level and has potential human health risk for noncancer 
effects from the PFAS mixture in water). The proposal defined a mixture 
as containing one or more of the four PFAS and therefore covered each 
contaminant individually if only one of the four PFAS occurred. Thus, 
the Hazard Index as proposed ensures that the level of exposure to an 
individual PFAS remains below that which could impact human health 
because the exposure for that measured PFAS is divided by its 
corresponding HBWC. The EPA proposed HBWCs of 9.0 ng/L \5\ for PFHxS; 
10.0 ng/L for HFPO-DA; 10.0 ng/L for PFNA; and 2000.0 ng/L for PFBS 
(USEPA, 2023e).
---------------------------------------------------------------------------

    \5\ Some commenters noted an error in the HBWC calculation for 
PFHxS which was reported as 9.0 ng/L in the proposal. The agency has 
corrected the value in this NPDWR and within the requirements under 
40 CFR part 141 subpart Z. The correct HRL/HBWC for PFHxS is 10 ng/
L.
---------------------------------------------------------------------------

    The EPA requested comment on the feasibility of the proposed Hazard 
Index MCL, including analytical measurement and treatment capability, 
as well as reasonable costs, as defined by SDWA.
2. Summary of Major Public Comments and EPA Responses
    The EPA received many comments supporting the use of the Hazard 
Index approach and regulation of additional PFAS. Consistent with these 
comments, through this action, the agency is establishing drinking 
water standards for PFHxS, PFNA, HFPO-DA, and PFBS (as well as PFOA and 
PFOS) to provide health protection against these contaminants found in 
drinking water. The EPA considered PFAS health effects information, 
evidence supporting dose additive health concerns from co-occurring 
PFAS, as well as national and state data for the levels of multiple 
PFAS in finished drinking water.
    A few commenters disagreed with the EPA's feasibility evaluation in 
setting the MCL at the MCLG (i.e., Hazard Index value of 1.0). Some of 
these commenters assert that technologies to remove the Hazard Index 
PFAS are not the same as those that effectively remove PFOA and PFOS. A 
couple of commenters were concerned that meeting the Hazard Index MCL 
may require more frequent media change-outs (e.g., GAC), thereby 
increasing operating costs such that the Hazard Index MCL of 1.0 is not 
feasible. The agency disagrees with these commenters. As described 
above in part A of this section for PFOA and PFOS, the agency similarly 
considered feasibility as defined by SDWA for PFHxS, PFNA, HFPO-DA, and 
PFBS. First, the EPA established a Hazard Index MCLG as a Hazard Index 
of 1 for mixtures of PFHxS, PFNA, HFPO-DA, and PFBS. As part of setting 
the Hazard Index MCLG, the agency defined an HBWC for PFHxS, PFNA, 
HFPO-DA, and PFBS used in the calculation (see discussion in section IV 
of this preamble for further information).\6\
---------------------------------------------------------------------------

    \6\ The EPA notes that the HBWC are akin to an MCLG in that they 
reflect a level below which there are no known or anticipated 
adverse effects over a lifetime of exposure, including for sensitive 
populations and life stages, and allows for an adequate margin of 
safety.
---------------------------------------------------------------------------

    In considering the feasibility of setting the MCLs as close as 
feasible to the MCLG, the EPA first evaluated the (1) the availability 
of analytical methods to reliably quantify levels of the contaminants 
in drinking water and (2)

[[Page 32579]]

the lowest levels at which contaminants can be reliably quantified 
within specific limits of precision and accuracy during routine 
laboratory operating conditions using the approved methods (i.e., the 
PQLs). The EPA determined that there are available analytical methods 
approved (i.e., Methods 533 and 537.1, version 2.0) to quantify levels 
below these HBWC levels. In addition, the PQLs for PFHxS, PFNA, HFPO-
DA, and PFBS (between 3.0 to 5.0 ng/L) are all lower than the 
respective HBWCs used in setting the Hazard Index MCLG for each of 
these PFAS (10 ng/L for PFHxS, PFNA, and PFHxS, and 2000 ng/L for 
PFBS). Thus, the PQLs are not a limiting factor in determining the MCL. 
Second, the EPA evaluated the availability and performance of Best 
Available Technologies (BATs) for treating water to minimize the 
presence of these contaminants consistent with the MCLGs (see section X 
for additional discussion on BATs) as well as the costs of applying 
those BATs to large metropolitan water systems when treating to that 
level. The EPA has found the same technologies identified for PFOA and 
PFOS are also both available and have reliably demonstrated PFAS 
removal efficiencies that may exceed >99 percent and can achieve 
concentrations less than the proposed Hazard Index MCL for PFHxS, PFNA, 
HFPO-DA, and PFBS, and that the cost of applying those technologies is 
reasonable for large metropolitan water systems. As discussed above, 
for contaminants where the MCLG is higher than the PQL, the EPA sets 
the MCL at the MCLG if treatment is otherwise feasible because the PQL 
is not a limiting factor. In consideration of the availability of 
feasible treatment technologies, approved analytical methods to 
reliably quantify levels of the contaminants in drinking water, the 
EPA's cost analysis, and the fact that the PQLs are below the HBWCs 
used in setting the Hazard Index MCLG, the agency determines that 
setting the MCL at the same level as the MCLG for mixtures of PFHxS, 
PFNA, HFPO-DA and PFBS is feasible. Thus, the EPA is setting the Hazard 
Index MCL of 1 for mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS. For 
additional discussion and considerations surrounding BATs, please see 
section X.A of this preamble. For more information about the EPA's cost 
estimates, please see section XII of this preamble.
    Many commenters support excluding PFOA and PFOS from the Hazard 
Index MCL. The EPA agrees with these commenters as there are analytical 
limitations that would complicate including PFOA and PFOS in the Hazard 
Index. As discussed in section IV of this preamble of the Hazard Index 
approach, individual PFAS hazard quotients (HQs) are calculated by 
dividing the measured concentration of each component PFAS in water 
(e.g., expressed as ng/L) by the corresponding health-based water 
concentration (HBWC) for each component PFAS (e.g., expressed as ng/L). 
The HBWC is akin to an MCLG in that they reflect a level below which 
there are no known or anticipated adverse effects over a lifetime of 
exposure, including for sensitive populations and life stages, and 
allows for an adequate margin of safety. Since PFOA and PFOS are likely 
human carcinogens, the MCLG (and if included in the Hazard Index, the 
HBWC) for each contaminant is zero. The only feasible way to represent 
PFOA and PFOS in the Hazard Index approach would be to only consider 
values for PFOA and PFOS at or above the PQL of 4.0 ng/L, however the 
level at which no known or anticipated adverse effects on the health of 
persons would occur is well below the PQL. As a result, any measured 
concentration above 4.0 ng/L for PFOA and PFOS would result in an 
exceedance of the Hazard Index MCL. The Hazard Index is intended to 
capture the aggregate risks of the Hazard Index PFAS when the monitored 
concentration is above the PQL but below the HBWC. These risks are not 
relevant to PFOA and PFOS given their PQLs. Because of the PQL 
considerations discussed in the preceding section V.A of this preamble, 
the EPA is not including PFOA and PFOS in the final rule Hazard Index. 
Therefore, the EPA is finalizing individual MCLs for PFOA and PFOS but 
not including these contaminants in the Hazard Index.
    A few commenters provided feedback on the EPA's request for comment 
regarding the usage of significant figures to express the MCLs. See 
discussion on this issue in section IV of this preamble above. In 
summary, after considering public comment, the EPA agrees that one (1) 
significant digit is appropriate for the individual PFAS for PFHxS, 
PFNA and HFPO-DA (i.e., 10 ng/L rather than 10.0 ng/L), and Hazard 
Index MCL (i.e., 1 rather than 1.0).
    Some commenters asked about inclusion of other PFAS in the Hazard 
Index in future revisions. The agency believes the Hazard Index 
approach can be an adaptive and flexible framework for considering 
additional PFAS. The EPA is required to review NPDWRs every six years 
and determine which, if any, need to be revised (i.e., the Six-Year 
Review Process). The purpose of the review is to evaluate current 
information for regulated contaminants and to determine if there is any 
new information on health effects, treatment technologies, analytical 
methods, occurrence and exposure, implementation and/or other factors 
that provides a health or technical basis to support a regulatory 
revision that will improve or strengthen public health protection. This 
process allows the agency to consider these and other information as 
appropriate in deciding whether existing NPDWRs should be identified as 
candidates for revision as required by SDWA.
    Many commenters compared the proposed MCLs to existing state and 
international standards, regulations, and guidelines. In particular, 
these commenters acknowledge that several states have conducted their 
own rulemakings to promulgate MCLs and suggest that the EPA's analysis 
in support of the proposed MCLs is inconsistent with these state 
approaches. Further, these commenters ask the EPA to explain why 
certain states' cost-benefit analyses supported their respective levels 
and why the EPA's analysis is different. Regarding state PFAS 
regulations, the EPA disagrees with commenters who suggested that the 
agency should not develop regulations different from state-led actions. 
SDWA mandates Federal regulation where the EPA determines that a 
contaminant meets the criteria for regulation under the statute. 
Moreover, the EPA's rule sets a national standard in accordance with 
SDWA for certain PFAS in drinking water that provides important 
protections for all Americans served by PWSs. Please see discussion 
above in part A under this section for consideration for existing state 
and international standards.
    A few commenters suggest a need for effective data management 
systems to implement the Hazard Index. These commenters indicated that 
it will be challenging to implement the Hazard Index as proposed due to 
the tracking of multiple contaminants and automating these data into 
existing data management systems. For discussion on rule implementation 
issues, including primacy agency record keeping and reporting 
requirements, please see section XI of this preamble.
    Some commenters raised concerns that the EPA did not consider a 
sufficient range of regulatory alternatives. For example, a few 
commenters contend that the EPA violated 1412(b)(3)(C)(i) of SDWA and 
the Unfunded Mandates Reform Act (UMRA) because the agency did not 
identify and consider what they deem a

[[Page 32580]]

reasonable number of regulatory alternatives for PFHxS, PFNA, HFPO-DA 
and its ammonium salts, and PFBS. Specifically, these commenters cite 
that the EPA only considered a single HBWC and did not consider any 
alternatives to the Hazard Index MCL of 1 itself. The EPA disagrees 
with these commenters.
    SDWA does not require the agency to consider any certain number of 
alternative MCLs or a range of alternatives. SDWA 1412(b)(3)(C)(i)(IV) 
only requires that in developing the HRRCA, the agency must consider 
the ``incremental costs and benefits associated with each alternative 
maximum contaminant level considered.'' Thus, the agency must conduct a 
cost-benefit analysis with each alternative MCL that is considered, if 
any. The EPA maintains that the proposed rule and regulatory 
alternatives considered at proposal met all requirements to consider 
alternatives. In the proposed rule, the EPA did not separately present 
changes in quantified costs and benefits for these approaches because 
the agency described that including individual MCLs in addition to the 
Hazard Index approach will be not change costs and benefits relative to 
the proposal (i.e., the same number of systems will incur identical 
costs to the proposed option and the same benefits will be realized). 
For the final rule, the EPA has also estimated the marginal costs for 
the individual PFHxS, PFNA, and HFPO-DA MCLs in the absence of the 
Hazard Index (See chapter 5.1.3 and appendix N.4 of the EA for 
details). The EPA notes that the costs for the individual PFHxS, PFNA, 
and HFPO-DA MCLs have been considered in this final rule. For further 
discussion of how the EPA considered the costs of the five individual 
MCLs and the HI MCL, see section XII.A.4 of this preamble.
    The EPA identified and analyzed a reasonable number of regulatory 
alternatives to determine the MCL requirement in the proposed rule as 
required by UMRA. UMRA's requirement to identify and consider a 
reasonable number of regulatory alternatives builds on the assessment 
of feasible alternatives required in E.O. 12866.\7\ Specifically, as 
described in the proposed rule, the EPA considered an alternative 
approach to the one proposed that only used the Hazard Index MCL. The 
proposal took comment on establishing individual MCLs instead of and in 
addition to using a mixture-based approach for PFHxS, PFNA, HFPO-DA, 
and/or PFBS in mixtures. In that proposal, the EPA described how a 
traditional approach may be warranted should the EPA not finalize a 
regulatory determination for mixtures of these PFAS. Under this 
alternative, ``the proposed MCLG and MCL for PFHxS would be 9.0 ng/L; 
for HFPO-DA the MCLG and MCL would be 10.0 ng/L; for PFNA the MCLG and 
MCL would be 10.0 ng/L; and for PFBS the MCLG and MCL would be 2000.0 
ng/L.'' The agency requested comment on these alternatives for PFHxS, 
PFNA, HFPO-DA, and PFBS and whether these individual MCLs instead of or 
in addition to the Hazard Index approach would change public health 
protection, improve clarity of the rule, or change costs. Additionally, 
the EPA considered alternative mixture-based approaches such as a 
target organ-specific Hazard Index (TOSHI) or relative potency factor 
(RPF) approach. The agency requested comment on these approaches. Based 
on the EPA's technical expertise, the agency determined that the Hazard 
Index is the most cost-effective and least burdensome alternative for 
purposes of UMRA because this approach for mixtures that achieves the 
objectives of the rule because of the level of protection afforded for 
the evaluation of chemicals with diverse (but in many cases shared) 
health endpoints. The EPA followed agency chemical mixture guidance 
(USEPA, 1986; USEPA, 1991b; USEPA, 2000a, which explain that when the 
Hazard Index value is greater than one (1) then risk is indicated 
(because exposure exceeds toxicity). The agency did not propose 
alternative Hazard Index values (i.e., higher Hazard Index values) 
because the EPA determined that a Hazard Index MCL of 1 is feasible: 
multiple treatment technologies are available and are found effective 
to treat to or below the MCL; the costs of applying these technologies 
to large metropolitan water systems are reasonable; and there are 
analytical methods available to reliably quantify the four PFAS 
captured in the Hazard Index MCL. In addition, these alternative Hazard 
Index or mixture-based approaches would not provide sufficient 
protection against dose-additive health concerns from co-occurring 
PFAS. For example, a higher Hazard Index value (e.g., Hazard Index 
equal to 2) allows for exposure to be greater than the toxicity and 
will not result in a sufficient health-protective standard that is 
close as feasible to the MCLG, which is a level at which there are no 
known or anticipated adverse effects on human health and allows for an 
adequate margin of safety. The EPA notes that commenters have not 
provided support justifying an alternative MCL standard for the Hazard 
Index. For additional discussion on UMRA, please see chapter 9 of USEPA 
(2024g).
---------------------------------------------------------------------------

    \7\ See OMB Memorandum M-95-09, Guidance for Implementing Title 
II of S.1.
---------------------------------------------------------------------------

3. Final Rule
    Through this action, the EPA is promulgating the Hazard Index MCL 
for mixtures of two or more of PFHxS, PFNA, HFPO-DA and PFBS. The 
following equation provides the calculation of the PFHxS, PFNA, HFPO-
DA, and PFBS Hazard Index MCL as finalized:
[GRAPHIC] [TIFF OMITTED] TR26AP24.005

Where:

HFPO-DAwater = monitored concentration of HFPO-DA in ng/
L;
PFBSwater = monitored concentration of PFBS;
PFNAwater = monitored concentration of PFNA and
PFHxSwater = monitored concentration of PFHxS

    The presence of PFBS can only trigger an MCL violation if it is 
present as part of a mixture with at least one of the other three PFAS 
(PFHxS, PFNA and

[[Page 32581]]

HFPO-DA). As such, elevated PFBS concentrations that would normally 
cause a Hazard Index exceedance in isolation will not cause a violation 
if none of the other three PFAS are present in the mixture. The EPA is 
promulgating individual MCLs for PFHxS, PFNA, and HFPO-DA as well the 
Hazard Index MCL for mixtures of PFHxS, PFNA, HFPO-DA and PFBS 
concurrent with final regulatory determinations for these contaminants 
(please see section III of this preamble for additional discussion on 
the EPA's regulatory determinations).
    The EPA has determined that it is feasible to set the MCL at the 
same level as the MCLG for mixtures of PFHxS, PFNA, HFPO-DA and PFBS as 
current BATs can remove each contaminant to a level equal to or below 
their respective HBWC. In addition, there are analytical methods 
available for these contaminants and the PQL for each contaminant is 
below the level established by the MCLG. The EPA also considered costs 
and determined that establishing a Hazard Index MCL of 1 is reasonable 
based on consideration of the costs to large metropolitan water 
systems. These considerations support a determination that a Hazard 
Index MCL of 1 for mixtures of two or more of PFHxS, PFNA, HFPO-DA and 
PFBS is feasible and therefore the EPA is setting the MCL at the same 
level as the MCLG. The EPA's MCL of 1 establish a ``maximum permissible 
level of contaminant in water'' because it is a limit for a mixture 
with PFAS components that must be met before the water enters the 
distribution system. Public water systems use their monitoring results 
as inputs into the Hazard Index equation to determine whether they are 
delivering water to any user that meets the MCL. For additional 
discussion regarding the derivation of the individual HBWCs and MCLGs, 
please see discussion in section III and IV of this preamble above.

C. Individual MCLs: PFHxS, PFNA and HFPO-DA

1. Proposal
    As described in section V.B of this preamble above, the EPA 
proposed an MCL for mixtures of PFHxS, PFNA, HFPO-DA and PFBS based on 
a Hazard Index. The EPA proposed to address its preliminary regulatory 
determinations for PFHxS, PFNA, HFPO-DA, and/or PFBS and mixtures of 
these PFAS together through the Hazard Index approach. The proposal 
defined a mixture as containing one or more of the four PFAS and 
therefore covered each contaminant individually if only one of the four 
PFAS occurred. The EPA considered and took comment on establishing 
individual MCLGs and MCLs in lieu of or in addition to the Hazard Index 
approach for mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS.
2. Summary of Major Public Comments and EPA Responses
    Commenters were mixed on the EPA's request for public comment on 
the establishment of stand-alone MCLs in lieu of or in addition to the 
Hazard Index MCL. Many of the comments were related to risk 
communications and messaging to consumers. While several commenters 
favored stand-alone MCLs in lieu of the Hazard Index to improve 
communications to their customers, several other commenters recommended 
stand-alone MCLs in addition to the Hazard Index MCL to achieve this 
purpose. Several commenters opposed individual MCLs for some or all of 
the PFAS because they believe it may complicate risk communication. 
After consideration of public comments, the EPA is addressing the final 
individual regulatory determination for PFHxS, HFPO-DA, and PFNA by 
promulgating individual MCLGs and NPDWRs for PFHxS, HFPO-DA, and PFNA. 
The EPA is addressing the final mixture regulatory determination by 
promulgating a Hazard Index MCLG and NPDWR for mixtures containing two 
or more of PFHxS, PFNA, HFPO-DA, and PFBS. This approach avoids 
confusion caused by the EPA's proposal that covered all the preliminary 
regulatory determinations in one Hazard Index standard. The EPA agrees 
that proper risk communication is an important focus for water systems 
and believes that finalizing individual MCLs for PFHxS, PFNA and HFPO-
DA may help support risk communication as utilities and the public may 
be more familiar with this regulatory framework. At the same time, 
since those individual MCLs do not address additional risks from co-
occurring PFAS, the EPA is finalizing a Hazard Index MCL to address 
dose additive health concerns associated with mixtures of two or more 
of PFHxS, PFNA, HFPO-DA, and PFBS that co-occur in drinking water. For 
additional discussion on the Hazard Index approach and other mixture-
based approaches (e.g., TOSHI), please see section IV of this preamble 
above.
3. Final Rule
    The EPA is promulgating individual MCLs for PFHxS, PFNA and HFPO-DA 
at the same level as their respective MCLGs (which are equivalent to 
the HBWCs). The EPA is finalizing individual MCLs as follows: HFPO-DA 
MCL = 10 ng/L; PFHxS MCL = 10 ng/L; and PFNA MCL = 10 ng/L. The EPA is 
promulgating individual MCLs for PFHxS, PFNA, and HFPO-DA as well the 
Hazard Index MCL for mixtures of PFHxS, PFNA, HFPO-DA and PFBS 
concurrent with final determinations for these contaminants (please see 
section III of this preamble for additional discussion on the EPA's 
regulatory determinations).
    The agency considered feasibility as defined by SDWA and the EPA's 
feasibility justification for these individual PFHxS, PFNA and HFPO-DA 
MCLs are the same and based on the same information as the Hazard Index 
MCL discussed in V.B above. The EPA further notes that the Hazard Index 
MCLG applies to the entire mixture but the EPA's technical 
justification for the underlying values (i.e., HBWCs) are the same as 
the individual MCLGs in this rule. In summary, the EPA has determined 
that it is feasible to set the individual MCLs at the MCLGs for PFHxS, 
PFNA and HFPO-DA because current BATs can remove each contaminant to a 
level equal to or below their respective MCLGs. In addition, there are 
analytical methods available for these contaminants and the practical 
quantitation level (PQL) for each contaminant is below the level 
established by the MCLG. The EPA also considered costs and determined 
that establishing individual MCLs of 10 ng/L for PFHxS, PFNA, and HFPO-
DA is reasonable based on consideration of the costs to large 
metropolitan water systems. These considerations support a 
determination that individual MCLs of 10 ng/L for PFHxS, PFNA, and 
HFPO-DA are feasible and therefore the EPA is setting the MCL at the 
same level as the MCLG. For additional discussion regarding the 
derivation of the individual HBWCs and MCLGs, please see section III 
and IV of this preamble above.

VI. Occurrence

    The EPA relied on multiple data sources, including Unregulated 
Contaminant Monitoring Rule (UCMR) 3 and state finished water data, to 
evaluate the occurrence of PFOA, PFOS, PFHxS, PFNA, and HFPO-DA and 
probability of co-occurrence of these PFAS and PFBS. The EPA also 
incorporated both the UCMR 3 and some state data into a Bayesian 
hierarchical model which supported exposure estimates for select PFAS 
at lower levels than were measured under UCMR 3. The EPA has utilized 
similar statistical approaches in past regulatory actions to inform its 
decision making, particularly where a contaminant's occurrence is at 
low concentrations

[[Page 32582]]

(USEPA, 2006c). The specific modeling framework used to inform this 
regulatory action is based on the peer-reviewed model published in 
Cadwallader et al. (2022). Collectively, these data and the occurrence 
model informed estimates of the number of water systems (and associated 
population) expected to be exposed to levels of the final and proposed 
alternative MCLs for PFOA and PFOS, the final MCLs for PFHxS, PFNA, and 
HFPO-DA, and the final Hazard Index MCL for PFHxS, PFNA, HFPO-DA, and 
PFBS.
    The EPA notes that, as described in sections III and V of this 
preamble, the EPA is finalizing individual Maximum Contaminant Levels 
(MCLs) for three of the four Hazard Index PFAS (PFHxS, PFNA, and HFPO-
DA) at 10 ng/L each. An analysis of occurrence relative to HRLs for 
PFHxS, PFNA, and HFPO-DA (which are the same as the final individual 
MCLs for these compounds at 10 ng/L) using UCMR 3 data and updated 
state datasets is presented in section III.C of this preamble and 
further described in the Occurrence Technical Support Document (USEPA, 
2024b). The information in the following sections supports the agency's 
finding that PFHxS, PFNA, and HFPO-DA occur at a frequency and level of 
public health concern as discussed in section III.C of this preamble.

A. UCMR 3

1. Proposal
    UCMR 3 monitoring occurred between 2013 and 2015 and is currently 
the best nationally representative finished water dataset for any PFAS, 
including PFOA, PFOS, PFHxS, PFNA, and PFBS. Under UCMR 3, 36,972 
samples from 4,920 public water systems (PWSs) were analyzed for these 
five PFAS. PFOA was found above the UCMR 3 minimum reporting level (20 
ng/L) in 379 samples at 117 systems serving a population of 
approximately 7.6 million people located in 28 states, Tribes, or U.S. 
territories. PFOS was found in 292 samples at 95 systems above the UCMR 
3 minimum reporting level (40 ng/L). These systems serve a population 
of approximately 10.4 million people located in 28 states, Tribes, or 
U.S. territories. PFHxS was found above the UCMR 3 minimum reporting 
level (30 ng/L) in 207 samples at 55 systems that serve a population of 
approximately 5.7 million located in 25 states, Tribes, and U.S. 
territories. PFBS was found in 19 samples at 8 systems above the UCMR 3 
minimum reporting level (90 ng/L). These systems serve a population of 
approximately 350,000 people located in 5 states, Tribes, and U.S. 
territories. Lastly, PFNA was found above the UCMR 3 minimum reporting 
level (20 ng/L) in 19 samples at 14 systems serving a population of 
approximately 526,000 people located in 7 states, Tribes, and U.S. 
territories.
2. Summary of Major Public Comments and EPA Responses
    Some commenters supported the EPA's use of the best available 
public health information including data from UCMR 3 and state 
occurrence data. A few commenters criticized the use of UCMR 3 data, 
stating that the data suffer from limitations. These commenters 
expressed concern over the high minimum reporting levels, the exclusion 
of many small systems, and the lack of national monitoring of HFPO-DA. 
Some of these commenters assert that UCMR 3 does not represent best 
available occurrence data for this rule. The EPA disagrees with these 
commenters. While UCMR 3 does have higher reporting limits than those 
available through current analytical methods, the data still provides 
the best available nationwide occurrence data to inform the occurrence 
and co-occurrence profile for the regulated PFAS for which monitoring 
was conducted. These data are also a critical component of the EPA's 
model to estimate national level occurrence for certain PFAS and ensure 
it is nationally representative (see subsection E of this section). The 
EPA also disagrees that the UCMR 3 excludes small water systems as it 
included a statistically selected, nationally representative sample of 
800 small drinking water systems. Regarding commenter concerns for lack 
of UCMR monitoring data on HFPO-DA, the agency notes that the EPA 
examined recent data collected by states who have made their data 
publicly available. A discussion of these data and public comments on 
this information is presented in sections III.C and VI.B of this 
preamble.
3. Final Rule
    After considering public comment, the EPA maintains that UCMR 3 
data are the best available, complete nationally representative dataset 
and they play an important role in supporting the EPA's national 
occurrence analyses, demonstrating occurrence and co-occurrence of the 
monitored PFAS in drinking water systems across the country that serve 
millions of people.

B. State Drinking Water Data

1. Proposal
    The agency has supplemented the UCMR 3 data with more recent data 
collected by states who have made their data publicly available. In 
general, the large majority of these more recent state data were 
collected using newer EPA-approved analytical methods and state results 
reflect lower reporting limits than those in the UCMR 3. State results 
show continued occurrence of PFOA, PFOS, PFHxS, PFNA, and PFBS in 
multiple geographic locations. These data also show these PFAS occur at 
lower concentrations and significantly greater frequencies than were 
measured under the UCMR 3 (likely because the more recent monitoring 
was able to rely on more sensitive analytical methods). Furthermore, 
these state data include results for more PFAS than were included in 
the UCMR 3, including HFPO-DA.
    At the time of proposal, the EPA evaluated publicly available state 
monitoring data from 23 states, representing sampling conducted on or 
before May 2021. The EPA acknowledged that the available data were 
collected under varying circumstances; for example, targeted vs. non-
targeted monitoring (i.e., monitoring not conducted specifically in 
areas of known or potential contamination). Due to the variability in 
data quality, the EPA further refined this dataset based on 
representativeness and reporting limitations, resulting in detailed 
technical analyses using a subset of the available state data. A 
comprehensive discussion of all the available state PFAS drinking water 
occurrence data was included in the Occurrence Technical Support 
Document (USEPA, 2023l).
2. Summary of Major Public Comments and EPA Responses
    Commenters generally supported the use of state datasets. A few 
commenters discussed their own PFAS occurrence data, some of which were 
provided to the EPA, relative to the EPA's proposed regulatory levels 
and/or provided summaries of other monitoring efforts. Where possible, 
the EPA presents this information within its occurrence analysis--see 
the Other Data sections of USEPA (2024b). A few commenters recommended 
that the EPA expand the datasets used for the final rule to include 
additional and updated state sampling information. The EPA agrees with 
these suggestions to rely on additional and updated sampling 
information in order to evaluate PFAS occurrence in drinking water. 
Therefore,

[[Page 32583]]

the agency has included updated information in its occurrence analyses 
as described in section VI.B.3 of this preamble. The EPA notes that 
this information is consistent with the analyses contained in the 
proposal for this action.
    A few commenters criticized the use of state datasets in occurrence 
analyses. These commenters claimed that the state datasets were 
insufficient for national extrapolation and not dependable due to being 
collected under variable circumstances. These commenters expressed the 
need for enhanced quality control (QC) by the EPA to exclude data below 
reasonable reporting thresholds. The agency disagrees with commenters 
who contend that state datasets are insufficient for national 
extrapolation. For both the rule proposal and this final action, the 
EPA took QC measures to ensure the EPA used the best available data for 
national extrapolation. For example, the EPA acknowledged in the 
proposal that states used various reporting thresholds when presenting 
their data, and for some states there were no clearly defined reporting 
limits. The EPA identified state reporting thresholds where possible 
and, when appropriate, incorporated individual state-specific 
thresholds when conducting data analyses. For other states, the EPA 
presented the data as provided by the state. Due to the reporting 
limitations of some of the available state data (e.g., reporting 
combined analyte results rather than individual analyte results), the 
EPA did not utilize all of these data in the subsequent occurrence 
analyses/co-occurrence analyses. Specific data analysis criteria (e.g., 
separation of non-targeted and targeted monitoring results) were also 
applied. Additionally, the agency also verified that the vast majority 
of the data were collected using EPA-approved methods. Further, the EPA 
reviewed all available data thoroughly to ensure that only finished 
drinking water data were presented. A description of the scope and 
representativeness of the state data was provided in the proposal of 
this action in the PFAS Occurrence and Contaminant Background Support 
Document (USEPA, 2023l). These include describing the states the EPA 
found to have publicly available data, identifying the reporting 
thresholds where possible, and distinguishing whether monitoring was 
non-targeted or targeted (i.e., monitoring in areas of known or 
potential PFAS contamination). These QC measures ensured that the EPA 
utilized the best available data for national extrapolation.
3. Final Rule
    In the proposed rule preamble, the EPA discussed how states may 
have updated data available and that additional states have or intend 
to conduct monitoring of finished drinking water and that the agency 
would consider these additional data to inform this final regulatory 
action. After consideration of all the public comments on this issue, 
the EPA has updated its analysis of state monitoring data by including 
results that were available as of May 2023. This updated state dataset 
includes publicly available data from 32 states: Alabama, Arizona, 
California, Colorado, Delaware, Georgia, Idaho, Illinois, Indiana, 
Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, 
Missouri, New Hampshire, New Jersey, New Mexico, New York, North 
Carolina, North Dakota, Ohio, Oregon, Pennsylvania, South Carolina, 
Tennessee, Vermont, Virginia, West Virginia, and Wisconsin. The dataset 
includes data from 9 states that were not available at the time of 
proposal.
    Tables 4 and 5 in this section demonstrate the number and percent 
of samples with PFOA and PFOS based on state-reported detections, and 
the number and percent of systems with PFOA and PFOS based on state-
reported detections, respectively, for the non-targeted state finished 
water monitoring data. Section III.B. of this preamble describes the 
state reported finished water occurrence data for PFHxS, PFNA, HFPO-DA, 
and PFBS data.
BILLING CODE 6560-50-P

[[Page 32584]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.006


[[Page 32585]]


[GRAPHIC] [TIFF OMITTED] TR26AP24.007

    As illustrated in Tables 4 and 5, there is a wide range in PFOA and 
PFOS results between states. Nonetheless, more than one-third of states 
that conducted non-targeted monitoring observed PFOA and/or PFOS at 
more than 25 percent of systems. Among the detections, PFOA 
concentrations ranged from 0.21 to 650 ng/L with a range of median 
concentrations from 1.27 to 5.61 ng/L, and PFOS concentrations ranged 
from 0.24 to 650 ng/L with a range of median concentrations from 1.21 
to 12.1 ng/L.
    Monitoring data for PFOA and PFOS from states that conducted 
targeted monitoring efforts, including 15 states, demonstrate results 
consistent with the non-targeted state monitoring. For example, in 
Pennsylvania, 26.3 and 24.9 percent of monitored systems found PFOA and 
PFOS, respectively, with reported concentrations of PFOA ranging from 
1.7 to 59.6 ng/L and PFOS ranging from 1.8 to 94 ng/L. California 
reported 35.8 and 39.0 percent of monitored systems found PFOA and 
PFOS, respectively, including reported concentrations of PFOA ranging 
from 0.9 to 190 ng/L and reported concentrations of PFOS from 0.4 to 
250 ng/L. In Maryland, PFOA and PFOS were found in 57.6 and 39.4 
percent of systems monitored, respectively, with reported 
concentrations of PFOA ranging from 1.02 to 23.98 ng/L and reported 
concentrations of PFOS ranging from 2.05 to 235 ng/L. In Iowa,

[[Page 32586]]

PFOA and PFOS were found in 11.2 and 12.1 percent of systems monitored, 
respectively, with reported concentrations of PFOA ranging from 2 to 32 
ng/L and reported concentrations of PFOS ranging from 2 to 59 ng/L.
    As discussed above in section V of this preamble, the EPA is 
finalizing individual MCLs of 4.0 ng/L for PFOA and PFOS, individual 
MCLs for PFHxS, PFNA, and HFPO-DA, and a Hazard Index level of 1 for 
PFHxS, PFNA, HFPO-DA, and PFBS. The EPA also evaluated occurrence for 
the regulatory alternatives discussed in section V of this preamble, 
including alternative MCLs for PFOA and PFOS of 5.0 ng/L and 10.0 ng/L. 
Table 6, Table 7, and Table 8 demonstrate, based on available state 
data, the total reported number and percentages of monitored systems 
that exceed these proposed and alternative MCL values across the non-
targeted state finished water monitoring data.
[GRAPHIC] [TIFF OMITTED] TR26AP24.008


[[Page 32587]]


[GRAPHIC] [TIFF OMITTED] TR26AP24.009


[[Page 32588]]


[GRAPHIC] [TIFF OMITTED] TR26AP24.010

BILLING CODE 6560-50-C
    Based on the available state data presented in Table 6, Table 7, 
and Table 8, within 20 states that conducted non-targeted monitoring 
there are 1,260 systems with results above the PFOS MCL of 4.0 ng/L and 
1,577 systems with results above the PFOA MCL of 4.0 ng/L. These 
systems serve populations of 12.5 and 14.4 million people, 
respectively. As expected, the number of systems exceeding either of 
the proposed alternative MCLs decreases as the values are higher; 
however, even at the highest alternative PFOS and PFOA MCL values of 
10.0 ng/L, there are still 491 and 612 systems with exceedances, 
serving populations of approximately 5.3 and 6.0 million people, 
respectively.
    Monitoring data for PFOA and PFOS from states that conducted 
targeted sampling efforts shows additional systems that would exceed 
the final and alternative MCLs. For example, in California, Maine, 
Maryland, and Pennsylvania, 30.9 percent (38 PWSs), 27.8 percent (5 
PWSs), 25 percent (18 PWSs), and 19.3 percent (66 PWSs) of monitored 
systems reported results above the proposed PFOS MCL of 4.0 ng/L, 
respectively, and 29.3 percent (36 PWSs), 27.8 percent (5 PWSs), 25 
percent (18 PWSs), and 21.1 percent (72 PWSs) of monitored systems 
reported results above the proposed PFOA MCL of 4.0 ng/L, respectively. 
While these frequencies may be anticipated given the sampling 
locations, within only these four states that conducted limited, 
targeted monitoring, the monitored

[[Page 32589]]

systems with results above the proposed PFOS MCL and proposed PFOA MCL 
serve significant populations of approximately 5.7 million people and 
approximately 5.6 million people, respectively.

C. PFAS Co-Occurrence

    While the discussions in sections III.B, VI.A. and VI.B of this 
preamble describe how PFOA, PFOS, PFHxS, PFNA, and HFPO-DA occur 
individually, numerous studies and analyses have documented that PFAS 
co-occur in finished drinking water (Adamson et al., 2017; Cadwallader 
et al., 2022; Guelfo and Adamson, 2018). As discussed in section V of 
this preamble, the EPA is finalizing regulation of mixtures that 
include at least two of PFHxS, PFNA, HFPO-DA, and PFBS (collectively 
referred to as ``Hazard Index PFAS'') as part of a Hazard Index 
approach.
1. Proposal
    In the March 2023 proposal preamble, the EPA presented occurrence 
data that illustrated the extent to which PFOA, PFOS, PFHxS, PFNA, 
HFPO-DA, and PFBS co-occur in drinking water. Co-occurrence analyses 
primarily utilized available non-targeted state PFAS finished drinking 
water data, though UCMR 3 data analysis is presented in the PFAS 
Occurrence and Contaminant Background Support Document (USEPA, 2024b). 
The EPA also conducted two separate analyses using state datasets to 
determine the extent to which these six PFAS co-occur: a groupwise 
analysis and a pairwise analysis.
    When analyzing PFAS co-occurrence, groupwise analysis is important 
for determining whether the presence of PFOA and PFOS provides insight 
regarding the likelihood of Hazard Index PFAS being present as well, 
which has broad implications for public health. This is because 
occurrence information for the Hazard Index PFAS is less extensive than 
the occurrence information for PFOA and PFOS due to fewer states 
monitoring the Hazard Index PFAS; therefore, establishing co-occurrence 
with PFOA and PFOS helps with understanding the extent of general 
Hazard Index PFAS occurrence. For the groupwise analysis, the six PFAS 
were separated into two groups--one consisted of PFOS and PFOA and the 
other group included the four Hazard Index PFAS. The analysis broke 
down the systems and samples according to whether chemicals from the 
respective groups were detected. Results were also shown separated by 
state. Results generally indicated that when PFOA or PFOS were found, 
Hazard Index PFAS were considerably more likely to also be found. This 
implies that, for systems that only measured PFOA and/or PFOS, detected 
those PFAS, and did not measure the Hazard Index PFAS, the Hazard Index 
PFAS are more likely to also be present than if PFOA and/or PFOS were 
not detected. At a national level, since many systems monitored for 
PFOA and PFOS only and detected these PFAS, this means that estimates 
of Hazard Index PFAS occurrence based on state Hazard Index PFAS data 
alone are likely to be underestimated. Given that the state datasets 
varied in the specific PFAS that were monitored, the analysis also 
compared the number of Hazard Index PFAS analyzed with the number of 
Hazard Index PFAS reported present. As more Hazard Index PFAS were 
analyzed, more Hazard Index PFAS were found. Further, systems and 
samples where Hazard Index PFAS were found were more likely to find 
multiple Hazard Index PFAS than a single Hazard Index PFAS (when 
monitoring for 3 or 4 Hazard Index PFAS).
    Given that the groupwise co-occurrence analysis established that 
the Hazard Index PFAS, as a group, occur with a substantial level of 
frequency, particularly alongside PFOA or PFOS, the pairwise co-
occurrence is relevant for understanding how the individual PFAS 
included in the rule co-occur with each other. The pairwise co-
occurrence analysis explored the odds ratios for each unique pair of 
PFAS included in the regulation. Pairwise co-occurrence through odds 
ratios showed statistically significant relationships between nearly 
all unique pairs of PFAS included in the proposed rule. Odds ratios 
reflect the change in the odds of finding one chemical (e.g., Chemical 
A) given that the second chemical (e.g., Chemical B) is known to be 
present compared to the odds of finding it if the second chemical is 
not present. For example, an odds ratio of 2 would indicate that the 
presence of the second chemical would be expected to double the odds of 
the first chemical being reported present. An odds ratio of 1 indicates 
that there is no association between the two chemicals. At the system 
level, point odds ratios estimates ranged from 1.7-142.7, indicating 
that in some instances the odds of finding one PFAS increased by more 
than two orders of magnitude if the other PFAS was reported present (in 
other words, for some PFAS combinations, if one PFAS is present, there 
is more than 100 times the odds of certain other PFAS being present). 
HFPO-DA and PFHxS was the only pair of PFAS chemicals included in the 
proposed regulation that did not have a statistically significant 
relationship; 1 fell within the 95 percent confidence interval, 
indicating that the odds ratio was not determined to be statistically 
significantly different from 1.
    In the proposed rule, the agency determined that, both as a group 
and as individual chemicals, the Hazard Index PFAS had a higher 
likelihood of being reported if PFOS or PFOA were present, First, the 
groupwise analysis established that the Hazard Index PFAS, in addition 
to PFOA and PFOS, occur at a significant frequency in drinking water. 
Then, the pairwise analysis demonstrated that PFOA, PFOS, PFHxS, PFNA, 
HFPO-DA, and PFBS (the individual PFAS) generally co-occur with each 
other, as opposed to occurring independently. These data further 
support the EPA's finding that these PFAS are likely to occur, and that 
there is a substantial likelihood that combinations of PFHxS, PFNA, 
HFPO-DA, and PFBS co-occur in mixtures with a frequency of public 
health concern in drinking water systems.
2. Summary of Major Public Comments and EPA Responses
    Some commenters agreed with the agency's conclusion in the March 
2023 proposal that the PFAS included in the regulation appeared to 
meaningfully co-occur. However, some other commenters stated that they 
believed the data used to assess PFAS co-occurrence were too limited to 
make substantive conclusions. The EPA disagrees that the data were too 
limited or that the co-occurrence analysis was inconclusive. Based on 
the non-targeted state monitoring data used in the co-occurrence 
analysis (from 11 states), findings of the pairwise and groupwise 
analyses established a strong likelihood that these chemicals 
meaningfully co-occur in drinking water. This was observed through odds 
ratios statistically significantly greater than 1 in the pairwise 
analysis as well as frequency at which multiple chemicals were detected 
in the groupwise analysis. Based on public comment, the agency has 
updated its analysis to include more recent non-targeted state data 
that became publicly available after the proposal analyses were 
finalized. This ensures that findings are up to date; as discussed 
further in the following subsection, the more recent data confirms the 
proposal analysis.
3. Final Rule
    After considering public comment and updating analyses, the EPA 
concluded that the co-occurrence analyses continue to support the

[[Page 32590]]

premise in the proposed rule that PFAS are likely to co-occur and 
support the EPA's final rule approach. Following is a discussion and 
presentation of information related to the EPA's co-occurrence analysis 
for this final rule effort. These data include all data from the rule 
proposal, in addition to the updated data the EPA incorporated based on 
public comment. As discussed elsewhere in this preamble, the newer data 
confirm the EPA's conclusions from proposal.
a. Groupwise Chemical Co-Occurrence
    Table 9 shows the distribution of systems and samples according to 
whether states reported detections for any Hazard Index PFAS (PFHxS, 
PFNA, HFPO-DA, and PFBS) and whether they also reported detections of 
PFOS or PFOA. USEPA (2024b) provides additional information for this 
analysis.
[GRAPHIC] [TIFF OMITTED] TR26AP24.011

    Considering eligible samples and systems within the aggregated 
state dataset, states reported either PFOA, PFOS, or one or more Hazard 
Index PFAS in 42.2 percent (20,640 of 48,889) of samples and 29.4 
percent (3,569 of 12,145) of systems. When any PFAS (among PFOA, PFOS, 
and the Hazard Index PFAS) were reported, at least one Hazard Index 
PFAS was also reported in 64.3 percent (13,275 of 20,640) of samples 
and at 69.8 percent (2,490 of 3,569) of systems. Further, among samples 
and systems that reported PFOS or PFOA, at least one Hazard Index PFAS 
was reported in 61.9 percent (11,954 of 19,319) of samples and at 65.9 
percent (2,089 of 3,168) of systems. This demonstrated strong co-
occurrence of Hazard Index PFAS with PFOA and PFOS and a substantial 
likelihood (over 60 percent) of at least one Hazard Index PFAS being 
present at systems reporting the presence of PFOS or PFOA. Overall, one 
or more Hazard Index PFAS were reported at about 20.5 percent (2,490 of 
12,145) of systems included in the aggregated state dataset of non-
targeted monitoring. If this percentage were extrapolated to the 
nation, one or more Hazard Index PFAS would be found in over 13,000 
systems. Table 10 shows the distribution of systems in a similar manner 
but provides a breakdown by state and includes only systems that 
monitored for either three or four of the Hazard Index PFAS.
BILLING CODE 6560-50-P

[[Page 32591]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.012

    Tennessee only had data from one system which did not report the 
presence of any of the six PFAS. Otherwise, the percentage of systems 
included in Table 10 that reported any Hazard Index PFAS ranged from 
3.9 to 52.4 percent of systems when broken down by state, with eight 
states exceeding 20 percent of systems. The percentage of systems that 
reported any PFAS ranged from 5.5 to 73.0 percent. Many systems and/or 
samples that were included in the aggregated state dataset did not 
monitor for all four Hazard Index PFAS. It is possible that more 
systems would have reported the presence of Hazard Index PFAS if they 
had monitored for all four Hazard Index PFAS. Additionally, as 
demonstrated in Table 10, when PFOA and/or PFOS were reported, at least 
one of the Hazard Index PFAS chemicals were also frequently reported. 
For systems that did not measure Hazard Index PFAS but measured and 
detected PFOA and/or PFOS, the groupwise analysis demonstrates that the 
Hazard Index PFAS were more likely to have been present in those 
systems as well. Table 11 presents system counts for systems where PFOS 
or PFOA were reported according to a) how many Hazard Index PFAS were 
monitored and b) how many Hazard Index PFAS were reported present.

[[Page 32592]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.013

    Among systems that reported the presence of PFOS and/or PFOA, the 
fraction of systems that also reported any Hazard Index PFAS tended to 
increase as systems monitored for more of the Hazard Index PFAS. At 
systems monitoring for a single Hazard Index PFAS, 34.5 percent 
reported a positive result at some point during sampling. This 
increased to 73.5 percent of systems reporting the presence of at least 
one Hazard Index PFAS when monitoring for all four Hazard Index PFAS. 
Not only did the fraction of systems reporting the presence of any 
Hazard Index PFAS increase as the number of Hazard Index PFAS monitored 
increased, so did the number of Hazard Index PFAS that were reported as 
present. When four Hazard Index PFAS were monitored, nearly 50 percent 
of systems reported the presence of two to three of the Hazard Index 
PFAS. Thus, if PFOS or PFOA are reported, there is a reasonable 
likelihood that multiple Hazard Index PFAS would be present as well.
b. Pairwise Chemical Co-Occurrence
    In addition to considering the co-occurrence of six PFAS as two 
groups, the EPA conducted a pairwise analysis to further explore co-
occurrence relationships. Table 12 shows the calculated system-level 
odds ratios for every unique pair of PFAS chemicals evaluated. The 
equation for calculating odds ratios is symmetrical. Because of this, 
in a given row it does not matter which chemical is ``Chemical A'' and 
which is ``Chemical B.'' Additional information on odds ratios may be 
found in USEPA (2024b) and a brief explanation is described following 
Table 12 as well as in section III.C of this preamble.

[[Page 32593]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.014

BILLING CODE 6560-50-C
    Odds ratios reflect the change in the odds of finding one chemical 
(e.g., Chemical A) given that the second chemical (e.g., Chemical B) is 
known to be present compared to the odds of finding it if the second 
chemical is not present. For example, as shown in Table 12, the point 
estimate of 92.4 for the odds ratio between PFOA and PFOS indicates 
that the odds of finding PFOA after knowing that PFOS has been observed 
are 92.4 times what the odds would have been if PFOS was not observed, 
and vice versa. For every pair of chemicals, both the point estimate 
and 95 percent confidence interval (CI) were above 1, indicating 
significant increases in the likelihood of detecting one chemical if 
the other is present.
    Both as a group and as individual chemicals, the Hazard Index PFAS 
had a higher likelihood of being reported if PFOS or PFOA were present. 
PFHxS, PFNA, HFPO-DA, and PFBS (the individual Hazard Index PFAS) are 
demonstrated to generally co-occur with each other, as well. These data 
support that there is a substantial likelihood that PFHxS, PFNA, HFPO-
DA, and PFBS co-occur in mixtures with a frequency of public health 
concern in drinking water systems as discussed in section III.C of this 
preamble.

[[Page 32594]]

D. Occurrence Relative to the Hazard Index

1. Proposal
    In the proposed rule, the EPA analyzed the available state data in 
comparison to the proposed Hazard Index MCL of 1.0 to evaluate the co-
occurrence of PFHxS, PFNA, HFPO-DA, and PFBS. The EPA requested comment 
on the number of systems estimated to solely exceed the Hazard Index 
(but not the PFOA or PFOS MCLs) according to the approach outlined in 
USEPA (2024b).
2. Summary of Major Public Comments and EPA Responses
    The EPA received comments on the analyses presented in the proposal 
of occurrence relative to the Hazard Index. Many commenters agreed that 
the Hazard Index PFAS co-occurred in mixtures at levels of health 
concern. Two of these comments came from states that conducted 
monitoring of Hazard Index PFAS post-UCMR 3 and stated that those 
occurrence data supported the EPA's findings. Several state agencies 
provided a summarized analysis of the number of systems expected to 
exceed the proposed Hazard Index of 1.0 in their state. The EPA notes 
that these estimates were based on the proposed Hazard Index, which 
included two significant figures. Since the EPA has determined to 
finalize the Hazard Index with one significant figure, these 
estimations are likely high. Nonetheless, these state data and the 
analyses provided by commenters provide illustrative confirmatory 
insight of the EPA's Hazard Index analyses (please see section IV of 
this preamble for additional discussion on the usage of significant 
figures).
    One commenter suggested that a national dataset and model complete 
with all four Hazard Index PFAS are necessary to accurately estimate 
the number of systems that may exceed the Hazard Index. The EPA 
disagrees with the commenter; as described in section F, state data and 
model outputs were appropriately combined to estimate exceedance of the 
Hazard Index on a national level. Several commenters stated that there 
was a limited amount of available data to determine the prevalence of 
co-exposure of the Hazard Index compounds, and that further review 
would be needed prior to establishing the Hazard Index. The EPA 
disagrees with these commenters and believes that sufficient data were 
available to reasonably assess the occurrence of Hazard Index PFAS. An 
analysis of co-occurrence of Hazard Index compounds using a substantial 
amount of data encompassing tens of thousands of samples across over 
10,000 systems is provided in section VI.C. of this preamble above and 
demonstrates that the four Hazard Index PFAS co-occur with each other 
as well as with PFOA and PFOS. One commenter suggested that more 
systems may exceed the Hazard Index than the PFOA and PFOS MCLs, since 
current treatment technologies have been optimized for PFOA and PFOS 
and not for other PFAS. The EPA's analysis of state datasets clearly 
contradicts this claim; using the best available data and 
scientifically robust analytical approaches, the EPA estimates more 
systems will exceed the PFOA and PFOS MCLs than the Hazard Index MCL. 
The use of a single significant figure for the Hazard Index MCL in this 
final rule will further increase the likelihood of this being the case.
3. Final Rule
    The EPA used its updated state dataset to update analyses related 
to Hazard Index occurrence and found the analyses generally consistent 
with the proposal analyses. In the final rule, the EPA is reducing the 
number of significant figures used to determine Hazard Index exceedance 
following all calculations and rounding from two to one; this change 
had the effect of reducing system counts expected to exceed the Hazard 
Index. For purposes of the final analyses, only systems with an 
unrounded Hazard Index of 1.5 or greater were counted as an exceedance. 
Table 13 presents the total number and percentage of monitored systems 
with results above the proposed Hazard Index MCL based on state 
reported Hazard Index PFAS data for the states that conducted non-
targeted monitoring and that sampled all four Hazard Index PFAS as a 
part of their overall monitoring efforts. The EPA notes that for 
equivalent comparison purposes Table 13 only accounts for samples that 
included reported values (including non-detects) of all four Hazard 
Index PFAS. As shown within the table, the majority of states evaluated 
had monitored systems with results above the proposed Hazard Index MCL, 
ranging from 0.35 to 3.17 percent of total monitored systems. For 
additional discussion on the usage of significant figures in this rule, 
please see section IV of this preamble.

[[Page 32595]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.015

    Further evaluating the available state data related to the proposed 
Hazard Index MCL of 1, Table 14 presents the total number of systems 
that exceed the final Hazard Index of 1 based on state reported Hazard 
Index PFAS results for the same states shown in Table 13. However, in 
this case, the EPA also analyzed the same non-targeted state data, 
including additional samples even if those samples did not contain 
reported values (including non-detects) for all four Hazard Index PFAS 
(i.e., exceeding the Hazard Index based on two or three Hazard Index 
PFAS with reported values included within a sample). Moreover, while 
these states did monitor for all four Hazard Index PFAS as a part of 
their overall monitoring, in a subset of those states some samples did 
not include reported data on all four Hazard Index PFAS (i.e., values 
of one or more of the Hazard Index PFAS were not reported as non-
detect, rather no value was reported). This analysis, presented in 
Table 14, shows an increase in the number of monitored systems 
exceeding the proposed Hazard Index of 1 and demonstrates prevalence of 
these PFAS at levels of concern, even when all four PFAS may not be 
included within a sample.

[[Page 32596]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.016

    Combining the non-targeted monitoring results shown previously with 
targeted state monitoring conducted for all four Hazard Index PFAS 
showed at least 864 samples from 211 PWSs in 21 states had results 
above the final Hazard Index of 1. These systems serve approximately 
4.7 million people. More information on occurrence in state monitoring 
is available in section III.C of this preamble and in USEPA (2024b).
    In summary, the finished water data collected under both non-
targeted and targeted state monitoring efforts from 32 states showed 
there are at least 1,772 PWSs serving a total population of 
approximately 24.3 million people that have at least one result 
exceeding the final PFOA MCL of 4.0 ng/L. In those same 32 states, 
there are also at least 1,432 PWSs serving a total population of 
approximately 21.0 million people that have at least one result 
exceeding the final PFOS MCL of 4.0 ng/L. Finished water data showed 
that there are at least 187 systems in 23 states serving a total 
population of approximately 4.4 million people with at least one result 
exceeding the final PFHxS MCL of 10 ng/L. Finished water data from 12 
states showed there are at least 52 systems serving a total population 
of approximately 176,000 people that have at least one result exceeding 
the final PFNA MCL of 10 ng/L. Finished water data showed 13 systems 
from 5 states serving over 226,000 people have at least one result 
exceeding the final HFPO-DA MCL of 10 ng/L. Related to the Hazard 
Index, finished water data collected under both non-targeted and 
targeted state monitoring efforts in 21 states showed there are at 
least 211 systems serving a total population of approximately 4.7 
million people with results above the final Hazard Index value of 1 for 
PFHxS, PFNA, HFPO-DA, and PFBS. Samples that only had monitoring 
results for one Hazard Index PFAS were not included. USEPA (2024b) 
presents a detailed discussion on state PFAS monitoring information.

E. Occurrence Model

    A Bayesian hierarchical occurrence model was developed to 
characterize national occurrence of the four PFAS that were most 
frequently detected in the UCMR 3: PFOA, PFOS, PFHxS, and PFHpA.\8\ 
This model was used to generate the baseline national occurrence 
estimates for PFOA, PFOS, and PFHxS, which were used in the subsequent 
economic analysis in USEPA (2024g). Bayesian hierarchical models are a 
widely used statistical approach in which subsets of data may be 
recognized as more related than others (such as samples from the same 
PWS are more related than samples between different PWSs) to capture 
complex relationships between levels of data and can aid in 
understanding the factors that influence outcomes. The objective of 
this model was to use both UCMR 3 data and supplemental state data to 
develop national estimates of

[[Page 32597]]

PFAS occurrence that inform occurrence distributions both within and 
across PWSs. Supplemental state data were incorporated to improve the 
model's ability to estimate PFAS occurrence at levels below the UCMR 3 
minimum reporting levels (20 ng/L for PFOA, 40 ng/L for PFOS, and 30 
ng/L for PFHxS). The state data incorporated to supplement the model 
came from publicly available datasets. In order to maintain the 
statistically robust UCMR 3 sampling framework, thereby enabling the 
agency to make conclusions about national representativeness of the 
model results, incorporation of state data into the model was limited 
only to data from systems that took part in the UCMR 3. The model does 
not include PFNA and PFBS due to data limitations; PFNA and PFBS lacked 
sufficient reported values above the UCMR 3 minimum reporting levels to 
be incorporated into the model. The model has been peer reviewed and is 
described extensively in Cadwallader et al. (2022).
---------------------------------------------------------------------------

    \8\ PFHpA was included in the model because of its UCMR 3 
occurrence data availability.
---------------------------------------------------------------------------

    The model uses Markov chain Monte Carlo (MCMC) simulation and the 
assumption of lognormality in PFAS chemical occurrence. Markov chain 
Monte Carlo is a powerful statistical tool used to understand 
uncertainty and making informed decisions when analyzing data. The EPA 
has used similar hierarchical models to inform regulatory decision 
making in the past, such as for development of the NPDWR for Arsenic 
and Cryptosporidium parvum (USEPA, 2006c; USEPA, 2000e).
    After log-transformation of data informing the model, system-level 
means (where each system has a mean concentration for each chemical) 
were assumed to be distributed multivariate normally. Further, within-
system occurrence was assumed to be distributed normally for each 
chemical. Since system-level means were modeled multivariate normally, 
correlation between estimated system-level means across chemicals could 
also be assessed. The assumption of lognormality as well as the 
incorporation of state data with lower reporting limits allowed the 
model to generate reasonable estimates for PFAS occurrence at levels 
below the UCMR 3 minimum reporting levels.
    After the model was fit with available data from PWSs that were 
included in the UCMR 3, it was used to simulate occurrence at an 
inventory of active community water systems (CWS) and non-transient 
non-community water systems (NTNCWS) extracted from the Safe Drinking 
Water Information System (SDWIS). System-level means for non-UCMR 3 
systems were simulated by sampling from the multivariate normal 
distribution of system-level means that was produced during the model 
fitting process. For systems that were included in the UCMR 3, the 
fitted system-level mean was used directly. This approach allowed 
national occurrence distributions to be estimated alongside the 
associated populations when combined with population data from SDWIS.
1. Proposal
    In the March 2023 proposal preamble, model estimates of contaminant 
occurrence were presented. For the analysis presented in the proposal, 
UCMR 3 data were supplemented with 23,130 analytical results from 771 
systems across 17 states that were available from public state websites 
through August 2021. Key model results that were presented directly 
included correlation coefficients across pairs of chemicals included in 
the model, extrapolated estimates of the number of system level means 
anticipated to exceed various threshold, and the estimated population 
associated with systems that had mean concentrations exceeding the 
various thresholds. The results indicated that system-level mean 
concentrations were moderately to strongly correlated across the 
modeled PFAS and that thousands of systems were estimated to have mean 
PFAS concentrations in the range of single digit ng/L.
2. Summary of Major Public Comments and EPA Responses
    A few commenters stated that they believed the model was an overly 
complicated approach to characterizing chemical occurrence and found it 
difficult to understand. Further, a few commenters stated that they 
believed the model was not transparent. The EPA disagrees; the 
occurrence approach used by the agency in this rule is based on a 
widely utilized and accepted statistical approach which is used in a 
variety of fields from education to health care and from business to 
the environment. These models allow exploration of the relationships 
among groups of data and the EPA used this model to better inform the 
agency's understanding of probable PFAS occurrence. For more 
information about Bayesian statistics and the wide variety of potential 
applications, see, for example, Hoff (2009); van de Schoot et al. 
(2021); Aguilera et al. (2011); and Messner et al. (2001). While the 
model uses an advanced statistical method and requires some statistical 
background to fully understand, Bayesian hierarchical models have 
previously been employed to assess occurrence for drinking water 
contaminants, as was discussed in the March 2023 proposal preamble as 
well as Cadwallader et al. (2022). Cadwallader et al. (2022) describes 
the model structure while the annotated model code and inputs were 
provided directly as supporting information alongside the manuscript. 
This information was incorporated into the docket for this rule's 
proposal. Sufficient information to replicate the model run was 
provided. Thus, the agency disagrees with the assertion that the model 
was not transparent.
    Regarding the model complexity, the core structure of this specific 
model is comparatively simple among Bayesian hierarchical models. The 
model uses a multivariate normal distribution of system-level means (of 
log transformed data) for the four modeled PFAS. It also includes a 
parameter for small systems to assess whether they appear to have 
systematically different (higher or lower) concentrations than large 
systems. As stated in Cadwallader et al. (2022), the model extrapolates 
to the nation by sampling from the multivariate normal distribution and 
accounting for whether the system being simulated was small. The 
multivariate normal distribution and the parameter to distinguish small 
systems from large systems are two simple but important pieces of the 
model structure.
    Many commenters stated that the model relied on insufficient data 
and produced substantial underestimates of the number of systems that 
would fail to meet MCL requirements. The agency disagrees both that the 
approach taken would systematically underestimate PFAS occurrence and 
that the data were insufficient inform the model. The Bayesian approach 
used here makes a precedented assumption about drinking water 
contaminant occurrence distributions (lognormality) and uses the 
available data to generate iterative estimates of distribution 
parameters that capture uncertainty through MCMC simulation. Across 
these iterations, the density of the posterior distribution for model 
parameters is proportionate to the likelihood that a given value would 
have produced the observed data. The subsequent national extrapolations 
also reflect this uncertainty.
    For the results presented in the March 2023 proposal preamble, the 
model was fit using 171,017 analytical results across the 4,920 UCMR 3 
systems. This was a nationally representative set of systems. 147,887 
of the analytical results were collected as part of UCMR 3 while 23,130 
were aggregated from 17 subsequently collected state datasets. The 
model was designed to utilize both results reported as observed 
concentrations (8,209 results) and

[[Page 32598]]

results reported as less than a reporting limit (162,808 results). 
While the UCMR 3 used higher reporting limits than are currently 
available, both reported concentrations and values reported as below 
the minimum reporting level cumulatively make substantial contributions 
to informing the model's estimates of the PFAS occurrence distribution 
because of this statistically robust framework. Due to this efficient 
use of data, and the steps taken to maintain a nationally 
representative set of systems, the agency believes that the over 
170,000 analytical results were sufficient to generate reasonable 
estimates of occurrence for the modeled contaminants.
    Several commenters expressed concern with model bias resulting from 
the supplemental state data that was incorporated when fitting the 
model. The hierarchical structure of the model minimizes the bias 
impact of introducing additional state data for only some UCMR 3 
systems (those with additional data available) because the data are 
explicitly linked to their parent systems rather than being pooled with 
all other data informing the model. The primary impact that these data 
have is on the model's estimate of specific system means for those 
systems that had additional data and informing the within-system 
variability parameters in the model. Refinement of a single system's 
mean estimate has a much smaller impact on the high-level distribution 
of system-level means and such shifts are proportionate to the added 
evidence derived from the supplemental data.
    The addition of data from systems not included in the UCMR 3 would 
pose a much greater concern for bias, since not all states have 
publicly available data. States with additional data would become 
disproportionately represented in the fit of the high-level 
distribution, since each system acts as a data point in fitting the 
distribution. The resulting high-level distribution would shift to 
resemble the states more closely with higher system representation in 
the source dataset. This would also be reflected in the subsequent 
national extrapolation. This same bias concern applies to national 
extrapolation approaches where some fraction of systems in a subset are 
identified as exceeding a given threshold and the national inventory of 
systems is multiplied by that fraction to generate a national estimate 
of systems that would exceed the threshold. If certain states have a 
disproportionate number of systems included in the subset compared to 
in the nation as a whole, the national estimate will be biased towards 
the tendencies of those states. In addition to this bias, the simple 
example approach discussed above would not naturally reflect 
uncertainty. Thus, for the purpose of national extrapolation, a 
nationally representative set of systems is more appropriate, even if 
data from other systems are available.
    While the EPA believes the model design and data selected for the 
analysis presented in the March 2023 proposal remain appropriate given 
the data availability at the time, the EPA has also continued to 
collect newly available data from publicly available state datasets, as 
the agency committed to in the proposed rulemaking (USEPA, 2023f). The 
Bayesian hierarchical model has been refit using the updated dataset 
with the same methods and criteria for data selection that were used 
for the analysis presented in the March 2023 proposal.
3. Final Rule
    After considering public comment, the agency has used the Bayesian 
statistical model described in Cadwallader et al. (2022) to support the 
economic analysis for this final regulation by combining the available 
occurrence information from UCMR 3 and state data subsequently 
collected at UCMR 3 systems to maintain the nationally representative 
nature of the set of drinking water systems informing the model, 
utilizing those data to compute estimates of national occurrence for 
PFAS contaminants, and providing estimates on the number of systems 
impacted by this final rule. These estimates directly informed the 
economic analysis in USEPA (2024g). For the final rule, the model was 
updated with additional state data collected through May 2023. In 
total, based on public comment, the EPA supplemented the state dataset 
with 65,537 analytical results from 1,156 systems across 28 states. Of 
these supplemental data, 24,950 analytical results were observed 
concentrations while 40,587 results were reported as below some 
reporting limit. The previously presented results have been updated and 
are presented in Table 15. The EPA notes that results from the updated 
dataset and model were confirmatory of its proposal analyses and did 
not result in changes to the EPA's final decisions. Median estimates 
and 90 percent credible intervals are shown for counts of systems with 
system-level means at or above various PFAS concentrations in Table 15 
and the population served by those systems in Table 16.
[GRAPHIC] [TIFF OMITTED] TR26AP24.017


[[Page 32599]]


[GRAPHIC] [TIFF OMITTED] TR26AP24.018

    For PFOA, PFOS, and PFHxS, thousands of systems were estimated to 
have mean concentrations over the lowest thresholds (i.e., 4.0 and 5.0 
ng/L) presented in Tables 15 and 16 with the total population served 
estimated to be in the tens of millions. The populations shown here 
represent the entire populations served by systems estimated to have 
system-level means over the various thresholds. It is likely that 
different subpopulations would be exposed to different mean PFAS 
concentrations if multiple source waters are used.
    In addition to the estimates of individual chemical occurrence, the 
multivariate normal distribution of system-level means allowed the 
model to provide insight on estimated co-occurrence. The model results 
support the co-occurrence of PFOA, PFOS and Hazard Index PFAS. The 
model evaluated whether untransformed (i.e., expressed in the original 
units of measurement) estimates of system-level means were correlated 
across each unique pair of the four modeled chemicals included in the 
model. Estimates of the Pearson correlation coefficient are shown in 
Table 17. The Pearson correlation coefficient serves as an indicator of 
the strength of the linear relationship between two variables and may 
range from -1 to 1. Positive values indicate a positive relationship 
(i.e., as one variable increases, so does the other). shown in Table 
17. The Pearson correlation coefficient serves as an indicator of the 
strength of the linear relationship between two variables and may range 
from -1 to 1. Positive values indicate a positive relationship (i.e., 
as one variable increases, so does the other).
[GRAPHIC] [TIFF OMITTED] TR26AP24.019

    The EPA considered a moderate strength correlation as greater than 
0.5 and a strong correlation as greater than 0.7. Each point estimate 
of correlation coefficients between two chemicals was above the 
threshold for a moderate strength correlation. The carboxylic acids 
(PFOA-PFHpA) and sulfonic acids (PFOS-PFHxS) had the highest estimated 
correlation strengths, with both the point estimate and the 90 percent 
credible interval above the threshold for a strong correlation. PFOS-
PFOA and PFOS-PFHpA had similar point estimates and 90 percent credible 
interval ranges, spanning the moderate-to-strong correlation range. 
Both PFOA-PFHxS and PFHpA-PFHxS had the bulk of their posterior 
distributions fall in the range of a moderate strength correlation. 
Thus, the

[[Page 32600]]

model predicted significant positive relationships among system-level 
means of all four chemicals that were included. These results support 
the co-occurrence discussion presented in section VI.C of this preamble 
that indicated extensive co-occurrence of PFOA, PFOS, and the Hazard 
Index PFAS observed in state datasets from both groupwise and pairwise 
chemical perspectives.

F. Combining State Data With Model Output To Estimate National 
Exceedance of Either MCLs or Hazard Index

    In order to broadly estimate the number of systems that would be 
impacted by the regulation, including MCLs of 4.0 ng/L for PFOA and 
PFOS alongside a Hazard Index of 1 for PFHxS, PFNA, HFPO-DA, and PFBS, 
findings from non-targeted monitoring in state datasets were combined 
with model estimates. Specific details on the methodology can be found 
in USEPA (2024b). Briefly, information collected from non-targeted 
state datasets included the fractions of systems that reported a 
measurement at or above the UCMR 5 minimum reporting level for a given 
analyte and an empirical cumulative distribution function (eCDF) 
consisting of system-level maximum observed concentrations of that 
chemical at these systems. The UCMR 5 minimum reporting levels for 
PFNA, HFPO-DA, and PFBS are equivalent to 4 ng/L, 5 ng/L, and 3 ng/L, 
respectively (USEPA, 2022j). This applies the assumption that the 
fraction of systems that observed PFNA, HFPO-DA, and PFBS at or above 
UCMR 5 minimum reporting levels and the maximum concentrations observed 
at those systems are reasonably representative of the nation.
1. Proposal
    The model was used to simulate EP-level concentrations of the four 
modeled PFAS (PFOA, PFOS, PFHpA, and PFHxS) under the assumption that 
within-system concentrations are lognormally distributed (a common 
assumption for drinking water contaminants, see (Cadwallader et al. 
(2022)) and that variability in concentrations is entirely across EP 
(thus a given EP is assumed to have a constant concentration). For each 
system, the maximum estimated EP PFOA or PFOS concentration was 
selected to determine whether the system exceeded either of the 
proposed MCLs of 4.0 ng/L. The EP with the maximum concentration is the 
point that determines whether a system has an EP that is above an MCL. 
Estimates of the system-level maximum for PFHxS were also selected for 
the Hazard Index calculation. The maximum value of the sum of the four 
modeled PFAS at each system was selected and used as a basis for 
determining which systems would receive superimposed concentrations of 
the three remaining Hazard Index chemicals (PFNA, HFPO-DA, and PFBS). 
This approach was selected due to the extensive observed co-occurrence 
of PFAS in the UCMR 3, state data, and modeled estimates.
    Multiple methods of system selection were used that reflected 
different degrees of co-occurrence. The chemical concentration that was 
applied to selected systems were randomly sampled from the eCDF for 
each chemical. Based on the model output, this assumes that system-
level maximums for PFNA, HFPO-DA, and PFBS would occur at the same 
location within a system. Given the substantial co-occurrence among 
PFAS observed and estimated across various analyses, combination of 
system-level maximums independently pulled from chemical eCDFs is a 
reasonable simplifying assumption. This is particularly true since 
systems selected for each chemical are not necessarily the same and in 
most cases were probability weighted. Estimates of the range of systems 
impacted were developed by taking Q5 and Q95 estimates for each method. 
The low end of the range was taken as the lowest Q5 estimate across 
methods, rounded down, while the high end of the range was taken as the 
highest Q95 estimate across methods, rounded up. This was also done for 
the total population served by these systems.
    The analysis to support the March 2023 proposal estimated that 100-
500 systems that were not already exceeding an MCL for PFOA or PFOS 
would exceed the Hazard Index. This resulted in a total of 3,400-6,300 
systems estimated to be exceeding either the Hazard Index, the MCL for 
PFOA, or the MCL for PFOS.
2. Summary of Major Public Comments and EPA Responses
    One commenter stated that they believed it is difficult to 
determine whether the estimated number of systems exceeding the Hazard 
Index is a reasonable estimate until a complete national dataset is 
available. The EPA disagrees with this commenter. The agency believes 
that it has taken steps to produce reasonable estimates using a robust 
set of available data, and that the data and analyses are sufficient to 
inform the EPA's regulatory decisions. Namely, this includes the use of 
non-targeted state datasets and multiple scenarios reflecting varying 
degrees of co-occurrence as described in USEPA (2024b). Among other 
important uses for these data, the EPA considered them to inform the 
regulatory determination for the mixture of the Hazard Index PFAS and 
the EA. The EPA has used these data to clearly demonstrate that there 
is a substantial likelihood that combinations of the Hazard Index PFAS 
co-occur as mixtures in public water systems with a frequency and at 
levels of public health concern. See section III of this preamble for 
additional discussion. Additionally, these data support the EPA's EA, 
and considerations of costs and benefits consistent with SDWA's 
requirements. See section XII of this preamble for further discussion.
3. Final Rule
    The method to combine state data for non-modeled Hazard Index PFAS 
with model estimates has largely remained the same for this final rule 
as it was for the March 2023 proposal. One key change, based on public 
comments, was to use an updated set of non-targeted state data to 
inform Hazard Index contaminant prevalence above UCMR 5 minimum 
reporting levels and eCDFs. Another key alteration, also based on 
public comments, was accounting for significant figures when counting 
systems exceeding the MCL for PFOA, the MCL for PFOS or the Hazard 
Index. For a system to be exceeding the Hazard Index, it must be 
greater than or equal to 2 (i.e., greater than 1) after rounding (for 
additional discussion on significant figure usage in the final rule, 
please see section IV of this preamble). To exceed the MCLs for PFOA or 
PFOS, the concentration must be greater than or equal to 4.1 ng/L after 
rounding. Finally, model estimates of PFHxS were converted to zero for 
the purposes of calculating the Hazard Index if they fell below the PQL 
of 3 ng/L.
    The total number of systems estimated to be exceeding one or more 
MCLs in the rule was 4,100-6,700 (compared to 3,400-6,300 in the 
proposal) serving a total population of 83-105 million people. Among 
these systems, 100-300 are estimated to be exceeding the Hazard Index 
without exceeding the PFOA or PFOS MCLs. The EPA used these modeled 
estimates to inform the costs and benefits determination as described 
in section XII of this preamble. Additional details regarding the 
approach used here can be found in USEPA (2024b).

[[Page 32601]]

G. UCMR 5 Partial Dataset Analysis

1. Summary of Major Public Comments and EPA Responses
    UCMR 5 occurrence data were not available to inform the proposal, 
but the agency discussed that additional nationwide monitoring data 
would be available for systems participating in the monitoring program. 
Some commenters called for the EPA to delay issuance of the final PFAS 
rule until the complete UCMR 5 occurrence dataset can be analyzed, and 
some commenters stated that rule promulgation should be delayed until 
at least a portion of the UCMR 5 data is obtained. The EPA disagrees 
with these commenters. The EPA is not required under the statute to 
wait for another round of UCMR data to be collected before proposing or 
finalizing a regulation; in this case, the completion of UCMR 5 data 
reporting is expected at the end of 2025, with the final dataset not 
being available until 2026. Rather, SDWA section 1412(b)(1)(B)(ii)(II) 
expressly provides that the EPA must use the ``best available public 
health information'' in making a regulatory determination (emphasis 
added). The EPA has sufficiently robust occurrence information to make 
regulatory determinations and promulgate a regulation for the six PFAS 
in this regulation. In addition to serving as a significant way for 
helping many utilities reduce initial monitoring costs, the final full 
UCMR 5 dataset will also be valuable for informing future regulatory 
decisions for the 23 PFAS included in UCMR 5 that are not directly 
addressed by this rulemaking. The agency believes that the best 
currently available occurrence data demonstrate sufficient occurrence 
or substantial likelihood of occurrence for the contaminants included 
in the final rule.
2. Final Rule
    While the EPA is under no legal obligation to consider the 
preliminary, partial UCMR 5 dataset prior to rule promulgation, based 
on public comment and interest, the agency examined UCMR 5 data 
released as of February 2024 (USEPA, 2024n). While these data were not 
available for this rule's proposal, are not complete, and are not a 
basis for informing the agency's decisions for the final rule, the EPA 
notes that they generally confirm the extensive occurrence analyses the 
agency has conducted: namely, that all six regulated PFAS occur in 
finished drinking water and that the six regulated PFAS co-occur with 
one another. The EPA notes some important caveats when considering 
these data. First, as of February 2024, the partial UCMR 5 dataset is a 
subset of data that will be collected, representing approximately 24 
percent of the total data that might be collected under that effort. 
Additionally, under UCMR 5, systems must collect either 2 or 4 samples, 
depending on their source water characteristics. In this preliminary 
dataset, systems have varying degrees of completeness in their sample 
collection and results may shift at the system level as additional 
samples are collected. Analyses included examination of sample-level 
results as well as EP mean-level results.
    The UCMR 5 data publicly available as of February 2024 included a 
combined total of 100,629 analytical results for PFOA, PFOS, PFHxS, 
PFNA, HFPO-DA, and PFBS ranging from 16,766 to 16,778 analytical 
results for each chemical. 16,743 complete sample sets where an 
analytical result was reported for each chemical were available. 9,528 
EPs and 3,719 PWS had at least one analytical result for each of the 
six PFAS and one sample for which the Hazard Index could be calculated. 
As mentioned previously, this partial dataset is estimated to contain 
approximately 24 percent of the data that will be available once the 
dataset is completed and finalized.
    The preliminary dataset was assessed for sample-level threshold 
exceedances of PFOA (4.0 ng/L), PFOS (4.0 ng/L), PFHxS (10 ng/L), PFNA 
(10 ng/L), HFPO-DA (10 ng/L), and the Hazard Index (1). Note that for 
PFOA and PFOS, two significant figures were considered (i.e., 
analytical results had to meet or exceed 4.05 to be considered 
exceedances) while for PFHxS, PFNA, HFPO-DA, and the Hazard Index one 
significant figure was considered (i.e., an analytical result had to 
meet or exceed 15 to be considered an exceedance for PFHxS, PFNA, and 
HFPO-DA and 1.5 to be considered an exceedance for the Hazard Index). 
Sample-level analysis only included complete sample sets while EP and 
system-level analysis included only systems that provided sufficient 
data to determine maximum PFOA, PFOS, PFHxS, PFNA, and HFPO-DA, and 
Hazard Index (which required at least one sample set where the Hazard 
Index could be calculated). The EPA notes that this analysis does not 
represent an estimate for the number of systems that will be in 
compliance with the MCL; as discussed in section V of this preamble, 
MCL compliance is determined based on an RAA. Additionally, samples 
below the PQL would be treated as zero in the compliance calculation. 
In the preliminary UCMR 5 dataset, PFOA exceeded 4.0 ng/L in 6.1 
percent of samples (1,024 samples), at 7.5 percent of EPs (719 EPs), 
and at 11.2 percent of systems (415 systems). PFOS exceeded 4.0 ng/L in 
6.6 percent of samples (1,100 samples), at 8.0 percent of EPs (766 
EPs), and at 12.4 percent of systems (462 systems). PFHxS exceeded 10 
ng/L in 0.4 percent of samples (66 samples), at 0.6 percent of EPs (53 
EPs), and at 1.1 percent of systems (42 systems). PFNA exceeded 10 ng/L 
in <0.1 percent of samples (5 samples), at <0.1 percent of EPs (5 EPs), 
and at 0.1 percent of systems (5 systems). HFPO-DA exceeded 10 ng/L in 
<0.1 percent of samples (2 samples), at <0.1 percent of EPs (1 EP), and 
at <0.1 percent of systems (1 system). The Hazard Index exceeded 1 in 
0.5 percent of samples (76 samples), at 0.6 percent of EPs (60 EPs), 
and at 1.3 percent of systems (48 systems). When the thresholds were 
considered simultaneously, 9.0 percent of samples (1,504 samples), 10.9 
percent of EPs (1,043 EPs), and 15.8 percent of systems (589 systems) 
exceeded a threshold. Note that single sample exceedances of thresholds 
do not necessarily reflect the averages that might be observed in the 
completed dataset. Specifically, the EPA notes that it is likely that 
many of the 15.8 percent of systems with an exceedance would not exceed 
the MCLs because additional samples used to determine an RAA may 
produce lower results.
    To further illustrate this point, though there is insufficient data 
to fully evaluate RAAs,\9\ EP-level means and systems with EP-level 
means exceeding an MCL threshold were also assessed with the 
preliminary dataset. For this analysis, only complete sample sets and 
EPs with multiple complete sample sets were included. 5,269 EPs and 
2,498 systems had data that met these criteria. When calculating EP 
means, results reported as less than the minimum reporting limit were 
treated as zero. Note that for PFOA and PFOS, two significant figures 
were considered (i.e., calculated means had to meet or exceed 4.05 to 
be considered exceedances) while for PFHxS, PFNA, HFPO-DA, and the 
Hazard Index one significant figure was considered (i.e., calculated 
mean had to meet or exceed 15 to be considered an exceedance for PFHxS, 
PFNA, and HFPO-DA and 1.5 to be considered an exceedance for the Hazard 
Index). Mean PFOA concentration exceeded 4.0 ng/L at 4.8

[[Page 32602]]

percent of EPs (253 EPs) and at 6.0 percent of systems (149 systems). 
Mean PFOS concentration exceeded 4.0 ng/L at 5.3 percent of EPs (278 
EPs) and at 7.2 percent of systems (179 systems). Mean PFHxS 
concentration exceeded 10 ng/L at 0.3 percent of EPs (15 EPs) and at 
0.4 percent of systems (11 systems). Mean PFNA concentration exceeded 
10 ng/L at <0.1 percent of EPs (1 EP) and at <0.1 percent of systems (1 
system). Mean HFPO-DA concentration exceeded 10 ng/L at <0.1 percent of 
EPs (1 EP) and at <0.1 percent of systems (1 system). Mean Hazard Index 
exceeded 1 at 0.3% of EPs (18 EPs) and at 0.6% of systems (14 systems). 
Considered simultaneously, an MCL was exceeded at 7.2 percent of EPs 
(381 EPs) and 9.4 percent of systems (235 systems). While the EP means 
described above include multiple sample sets, observed mean 
concentrations are likely to change as systems complete UCMR 5 
sampling.
---------------------------------------------------------------------------

    \9\ An RAA is calculated using results for samples taken at a 
particular monitoring location during the previous four consecutive 
quarters (see section XIII.B for more information).
---------------------------------------------------------------------------

    Among 16,743 completed sample sets and 9,529 EPs and 3,719 systems 
which had at least one result for each analyte, 13.9 percent of samples 
(2,335 samples), 16.5 percent of EPs, and 22.6 percent of systems (842 
systems) had an observed concentration at or above the minimum 
reporting level for at least one of the 6 PFAS. Table 18 shows counts 
of samples, EPs, and systems according to how many of the 6 PFAS 
included in this final rule were present at or above the minimum 
reporting level. As shown in Table 18, about 7.5 percent of samples, 
9.4 percent of EPs, and 14.2 percent of systems observed multiple PFAS 
at or above the minimum reporting level.
[GRAPHIC] [TIFF OMITTED] TR26AP24.020

    Groupwise co-occurrence was also examined in the preliminary UCMR 5 
dataset. Table 19 provides the counts and percentages of systems, EPs, 
and samples where PFOA and/or PFOS were reported as well as whether any 
of the Hazard Index PFAS were reported. Sample-level results only 
included completed sample sets while system-level results only included 
systems which provided one analytical result for each of the 6 PFAS.

[[Page 32603]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.021

    In samples, at EPs, and at systems where PFOA and/or PFOS were 
reported present, one or more Hazard Index contaminant was reported at 
or above the minimum reporting level about 68, 70, and 76 percent of 
the time, respectively. As UCMR 5 monitoring continues, it is possible 
that additional systems from this subset will report the presence of 
PFOA, PFOS or a Hazard Index PFAS. The percentage of systems detecting 
neither PFOA, PFOS, nor a Hazard Index PFAS would then decrease. Table 
20 shows the number of Hazard Index PFAS that were observed in samples, 
at EPs, and at systems where PFOA and/or PFOS were reported.
[GRAPHIC] [TIFF OMITTED] TR26AP24.022


[[Page 32604]]


    At systems where Hazard Index PFAS were reported in addition to 
PFOA/PFOS, about 51.0 percent of systems reported multiple Hazard Index 
PFAS. As described above, it is possible that systems may detect 
additional PFAS as sample collection continues under UCMR 5. System-
level pairwise odds ratios based on the first release of UCMR 5 data 
are shown in Table 21.
[GRAPHIC] [TIFF OMITTED] TR26AP24.023


[[Page 32605]]


    Except for two chemical pairings with HFPO-DA, each pairwise odds 
ratio estimate between PFAS is statistically significantly greater than 
one. As previously described, this indicates an increased likelihood of 
reporting one chemical given that the other chemical is known to be 
present. HFPO-DA odds ratios with PFBS, PFOS, and PFOA were also 
statistically significantly above 1. Given that the UCMR 5 dataset is 
not complete, it is important to note that, for chemical pairs where 
very few systems have fallen into one or more of the categories of 
chemical pairings, subsequent sampling may result in substantial shifts 
in the odds ratio estimate and the associated CI. For example, if one 
more system reported both HFPO-DA and PFHxS, the odds ratio estimate 
would increase by 33 percent. On the other hand, if one more system 
detected both PFOA and PFOS, the odds ratio estimate would shift by 
less than 1 percent. As the count of systems in each category 
increases, the odds ratio estimate becomes more stable with subsequent 
sampling. This may be particularly relevant for relationships with 
HFPO-DA and other Hazard Index PFAS, given the relatively low number of 
systems (17 systems) that reported HFPO-DA at or above the minimum 
reporting level in the preliminary UCMR 5 dataset as of February 2024.
    After the release of approximately 24 percent of the data that will 
be available in the full UCMR 5 dataset, there appears to be 
considerable PFAS occurrence and co-occurrence demonstrated (USEPA, 
2024n). Over 15 percent of systems with appropriate data described 
above have observed a sample-level exceedance of any of the MCLs while 
over 9 percent of systems have had an EP with a mean concentration 
exceeding an MCL. Approximately 75 percent of systems that reported the 
presence of PFOA or PFOS also observed at least one Hazard Index 
contaminant. Over half of these systems reported the presence of 
multiple Hazard Index contaminants. The national PFAS occurrence model 
estimated between about 6.2 percent and 10.1 percent of all CWS and 
NTNCWS would have an exceedance of an MCL. The 9.4 percent of UCMR 5 
systems that had an EP mean concentration over an MCL is not a direct 
comparison to this because not all EPs have sampled a year worth of 
quarterly data and because large systems make up a larger fraction of 
UCMR systems than systems in the national inventory (the model 
estimated generally higher concentrations at larger systems). However, 
separating these UCMR 5 results by system size and weighting according 
to system counts in the national inventory of systems would result in 
an estimation of 7.8 percent of all systems having an EP with a mean 
concentration exceeding an MCL threshold. These estimates are likely to 
shift as UCMR 5 sampling continues and system sampling regimes are 
completed.

VII. Analytical Methods

A. Analytical Methods and Practical Quantitation Levels (PQLs) for 
Regulated PFAS

1. Proposal
    The agency proposed two EPA methods to support the monitoring 
requirements of this regulation. The EPA developed the two liquid 
chromatography/tandem mass spectrometry (LC/MS/MS) analytical methods 
to quantitatively monitor drinking water for targeted PFAS: EPA Method 
533 (USEPA, 2019b) and EPA Method 537.1, Version 2.0 (USEPA, 2020c). 
The agency found that all six PFAS proposed for regulation can be 
measured by both EPA Methods 533 and 537.1, ver. 2.0 and both methods 
are acceptable for meeting the monitoring requirements of this 
regulation.
    Additionally, the EPA proposed PQLs for the six PFAS proposed for 
regulation, as outlined in Table 22.
[GRAPHIC] [TIFF OMITTED] TR26AP24.024

    In the proposed rule preamble (USEPA, 2023f), the EPA discussed 
laboratory performance in the EPA's Unregulated Contaminant Monitoring 
Rule (UCMR) 5 Laboratory Approval Program (LAP) and found that the UCMR 
5 minimum reporting levels are appropriate as the basis for the 
practical quantitation level (PQL) in this rule. These quantitation 
levels account for the measurement precision and accuracy that the EPA 
estimates can be achieved across laboratories nationwide.
2. Summary of Major Public Comments and EPA Responses
    Several commenters note analytical differences between EPA Methods 
533 and 537.1 such as differences in the quality control (QC) 
acceptance levels between the methods, sample preservation and holding 
times, as well as variability in sample and spike duplicates. In some 
instances, these commenters request specific modification to the 
methods, revisions to the EPA laboratory certification manual, or for 
the agency to develop guidance that laboratories and state 
accreditation/certification bodies could use. These commenters note 
that while both methods are valid under the proposed rule, variability 
between the two may lead to differences in sampling results and may 
impact a water system's compliance status. The EPA agrees that Methods 
533 and 537.1 have some differences that allow for analysis of varying 
chain lengths and molecular structures of PFAS. Method 533 generally 
captures ``short chain'' PFAS (i.e., those with carbon chain lengths of 
4 to 12) and fluorotelomer sulfonic acids. Method 537.1 includes some 
overlap with Method 533's analyte list while including some longer-
chain PFAS. However, the agency notes that

[[Page 32606]]

all six PFAS proposed for regulation can be analyzed by either Method 
533 or 537.1 and neither method has inherent QC issues that lead to 
significant variation in sampling results when followed. While there 
are differences between the methods and how they measure their 
respective target analytes, both EPA Methods 533 and 537.1 perform 
comparably. The methods are clear and outline specific instructions 
regarding requirements that are needed for compliance monitoring 
measurements.
    Some public commenters suggested that the EPA allow alternate 
analytical procedures or modifications to the two published EPA methods 
for meeting the monitoring requirements in the final rule. The EPA 
continues to specify the use of Methods 533 and 537.1 because 
consistent, reliable compliance data are necessary for implementation 
of the regulation at the maximum contaminant level (MCL) However, the 
EPA recognizes that improvements in analytical technology and 
methodology occur. The EPA's Drinking Water Alternate Test Procedure 
(ATP) Program provides a mechanism for submission and review of 
alternative methods to measure a contaminant for nationwide use under 
40 CFR 141.27. A method developer may apply for the EPA review of a 
method modification or a new method through the ATP Program. In the 
meantime, the agency has concluded that Methods 533 and 537.1 are 
reliable for use in compliance monitoring with respect to accuracy and 
recovery (lack of bias) and precision (good reproducibility) at the MCL 
levels.
    Several commenters requested that all laboratories be required to 
identify their quantitation limits (i.e., the smallest detectable 
concentration of an analyte greater than the detection limit where the 
accuracy (precision and bias) achieves the objectives of the intended 
purpose) and/or method detection limits (i.e., the minimum result which 
can be reliably discriminated from a blank). Specifically, some 
commenters note if labs have to demonstrate they can get below the PQL, 
the EPA should establish reporting or detection limits demonstrating 
they can get to these levels. The EPA is finalizing rule trigger levels 
below the PQL to support the monitoring provisions discussed in section 
VIII of this preamble. The EPA disagrees with these commenters that 
such reporting is needed to support compliance monitoring for the rule 
and that such reporting would be a cost burden on laboratories. All 
labs are required per the approved methods to demonstrate whether 
laboratory reagent blank (LRB) QC samples have background 
concentrations of less than one-third the minimum reporting level 
(i.e., the minimum concentration that can be reported as a quantitated 
value for a method analyte in a sample following analysis). Therefore, 
for a laboratory to be compliant with the methods, they must be able to 
detect, not necessarily quantify, analytes at or above \1/3\ the 
minimum reporting level.
    Some commenters sought clarity on which methods are approved for 
use in compliance monitoring for the final PFAS National Primary 
Drinking Water Regulation (NPDWR). Some of these commenters requested 
that only Method 533 be approved for monitoring under the final NPDWR, 
noting that it may be more suitable should additional PFAS analytes 
within its scope be targeted for regulation at the future date. Others 
requested that they be permitted to use Method 537, version 1.1. The 
EPA disagrees and reaffirms that Methods 537.1, version 2.0 and Method 
533 are both applicable and suitable for use in compliance monitoring 
in the final rule. The EPA notes that HFPO-DA is one of the PFAS 
regulated under this action and only Method 537.1, version 1.0 and 
version 2.0, and Method 533 support the collection of data for HFPO-DA. 
The agency notes that the primary difference between Method 537.1, 
version 1.0 and Method 537.1, version 2.0 is the field reagent blank 
(FRB) preparation: version 2.0 exposes the FRB to the preservative 
(Trizma) at the time of field sample collection. Version 1.0 combines 
the lab reagent water and the preservative together in the FRB prior to 
field sampling. Version 2.0 was created to more-closely mimic the FRB 
process used in Method 533. Additionally, Version 2.0 explicitly states 
that the solid phase extraction (SPE) cartridge sorbents may not be 
modified with monomers other than styrene divinylbenzene (SDVB).
    A few commenters critiqued how the proposed PQLs were established 
for the rule. Some of these commenters provided feedback on the 
feasibility of the proposed PQL and suggested that it may be too low, 
resulting in recurring QC failures that will necessitate repeat sample 
analysis, increased cost, and reduced laboratory capacity. Other 
commenters suggest that lower PQLs can be attainable by larger labs 
with advanced analytical instruments. The agency disagrees that PQLs 
should be established at either a higher or lower level than that 
proposed. As discussed in the proposed rule preamble, the PQLs are 
based on a multi-laboratory assessment of analytical capacity. The EPA 
derives PQLs which reflect the level that can be reliably quantified 
within specific limits of precision and accuracy during routine 
laboratory operating conditions. Based on the multi-laboratory data 
acquired for the UCMR 5 rule, the EPA has defined the PQL for the PFAS 
regulated in this rule (Table 22). This quantitation level considers 
the precision and accuracy that the EPA estimates can be achieved 
across laboratories nationwide. The EPA anticipates that over time, as 
technology advances and as laboratories gain experience with the PFAS 
Methods, laboratories will generally improve their capability to 
measure at lower levels.
3. Final Rule
    The EPA is establishing the following approved methods for use in 
compliance monitoring in the final PFAS NPDWR: EPA Method 533 (USEPA, 
2019b) and EPA Method 537.1, Version 2.0 (USEPA, 2009b; USEPA, 2020c). 
The PFAS addressed by this regulation can be measured by both EPA 
Methods 533 and 537.1 and either method is acceptable for meeting the 
monitoring requirements of this regulation. Table 1 to paragraph 
(f)(1)(iv) of Sec.  141.903 of subpart Z lists the PQLs for the PFAS 
regulated under this action.

VIII. Monitoring and Compliance Requirements

A. What are the Monitoring Requirements?

1. Proposal
    The EPA proposed requirements for community water systems (CWS) and 
non-transient non-community water systems (NTNCWSs) to monitor for six 
PFAS. The agency proposed to amend 40 CFR part 141 by adding a new 
subpart to incorporate the regulated PFAS discussed in this preamble. 
Under this new subpart, public water systems (PWSs) would be required 
to sample EP using a monitoring regime based on the EPA's Standard 
Monitoring Framework (SMF) for Synthetic Organic Contaminants (SOCs).
    The EPA proposed the following requirements for initial monitoring, 
which systems would be required to complete by the date three years 
after the date of rule promulgation (see section VIII.F of this 
preamble for more information). The EPA proposed that, consistent with 
the SMF for SOCs, groundwater systems serving greater than 10,000 
persons and all surface water systems would be initially required to 
monitor quarterly within a 12-month period for regulated PFAS. To 
provide additional flexibilities for small groundwater systems, the EPA 
proposed to modify the SMF for SOCs such that

[[Page 32607]]

groundwater systems serving 10,000 or fewer persons would be initially 
required to monitor only twice for regulated PFAS within a 12-month 
period, each sample at least 90 days apart. In the proposal, all 
systems would be allowed to use previously acquired monitoring data to 
satisfy the initial monitoring requirements (see section VIII.C of this 
preamble for additional details about using previously acquired 
monitoring data to satisfy initial monitoring requirements). Based on 
the SMF, the EPA also proposed that primacy agencies be able to use 
initial monitoring results to reduce compliance monitoring frequency 
for a system to once or twice every three years (depending on system 
size) if the monitoring results are below the proposed rule trigger 
level (defined in the following paragraphs).
    The EPA proposed that, after initial monitoring, water systems 
would conduct compliance monitoring to demonstrate that finished 
drinking water does not exceed the maximum contaminant levels (MCLs) 
for regulated PFAS. The EPA proposed that systems with multiple EP may 
establish different compliance monitoring schedules for those EP 
depending on their monitoring results.
    The EPA proposed to base compliance monitoring requirements on 
initial monitoring results and on system size. Then subsequent 
monitoring requirements would be based on results from compliance 
monitoring and, for systems on triennial monitoring, also on system 
size. To determine compliance monitoring frequency only, the EPA 
proposed a rule trigger level of one-third the MCLs (1.3 ng/L for PFOA 
and PFOS and 0.33 for Hazard Index PFAS (PFHxS, PFNA, HFPO-DA, and 
PFBS)). If results for an EP are below the trigger level, systems would 
be eligible for reduced monitoring. To implement this provision, the 
EPA proposed to include the ``trigger level'' concept in the new 
subpart.
    As proposed, each water system would be eligible for reduced 
compliance monitoring at each EP for which all PFAS results are below 
the rule trigger level, according to the following schedule:
     A water system that serves 3,300 or fewer customers would 
be required to analyze one sample for all regulated PFAS per three-year 
compliance period at each EP where the water system does not have 
results for any regulated PFAS at or above the rule trigger level (1.3 
ng/L for PFOA and PFOS and 0.33 for the Hazard Index PFAS (PFHxS, PFNA, 
HFPO-DA, and PFBS)),
     A water system that serves more than 3,300 persons would 
be required to analyze two samples for all regulated PFAS at least 90 
days apart in one calendar year per three-year compliance period at 
each EP where the water system does not have results for any regulated 
PFAS at or above the rule trigger level (1.3 ng/L for PFOA and PFOS and 
0.33 for the Hazard Index PFAS (PFHxS, PFNA, HFPO-DA, and PFBS).
    In the proposal, if any result for an EP is at or above the rule 
trigger level for regulated PFAS, the water system would be required to 
monitor at that EP for all regulated PFAS quarterly. For compliance 
monitoring collection schedules, the EPA did not specify the required 
number of days between sampling events and only required collection 
during a quarter. Systems monitoring an EP less frequently than 
quarterly whose sample result is at or above the rule trigger level 
would also be required to begin quarterly sampling at the EP where 
regulated PFAS were observed at or above the trigger level. In either 
case, the primacy agency would be able to allow a system to move an 
individual EP to a reduced monitoring frequency when the primacy agency 
determines that the EP is below the rule trigger level and reliably and 
consistently below the MCL. However, primacy agencies would not be 
permitted to determine that the EP is below the rule trigger level and 
reliably and consistently below the MCL until at least four consecutive 
quarters of quarterly compliance monitoring have occurred with all 
sample results below the rule trigger level.
    Additionally, related to laboratory capacity considerations, the 
EPA described in the proposal that it anticipates that laboratories 
will be able to adjust to demand and that the demand will be 
distributed across the three-year implementation period.
2. Summary of Major Public Comments and EPA Responses
    The following discussion details numerous comments the EPA received 
on the proposed monitoring requirements, both for initial monitoring 
and long-term compliance monitoring.
    The majority of comments the EPA received on the initial monitoring 
requirements related to the number of initial samples systems would be 
required to collect and the intervals between required samples. Most 
commenters were generally supportive of the EPA's proposed initial 
monitoring requirements, including the flexibilities to use previously 
acquired monitoring data to satisfy some or all the initial monitoring 
requirements and, for those groundwater systems serving 10,000 or fewer 
that do not have this data, that they be required to only collect two 
samples at each EP to satisfy initial monitoring requirements. For a 
discussion of comments and final rule requirements specific to the use 
of previously acquired monitoring data to satisfy the initial 
monitoring requirements see section VIII.C of this preamble.
    While most commenters were supportive of the number of initial 
monitoring samples the EPA proposed, a few commenters indicated they 
thought the EPA should not allow the flexibility for groundwater 
systems serving 10,000 or fewer to collect only two samples and instead 
require quarterly samples be collected by all systems to meet initial 
monitoring requirements, which would be fully consistent with the SMF 
framework for other SOCs. A couple of these commenters suggested that 
there are no data demonstrating that smaller systems are less likely to 
have elevated levels of PFAS than large systems or that groundwater 
systems are less likely to have elevated levels of PFAS than surface 
water systems. Additionally, other commenters generally suggested that 
two samples may not generate enough data to accurately capture the 
level of PFAS in drinking water and any potential seasonal variability. 
Related to potential seasonal changes in measured PFAS concentrations, 
some commenters from state agencies indicated that they have not 
observed seasonal variations in concentrations of PFAS measured by 
groundwater systems, whereas other commenters suggested the opposite 
and that they have seen changes seasonally based on their state's 
monitoring data.
    The EPA disagrees with commenters that suggest two samples for 
small groundwater systems would not accurately capture the baseline 
level of regulated PFAS in drinking water. The EPA determined the 
initial monitoring requirements based on both source water type and 
system size considerations. First, from a national-level perspective, 
the EPA's model for estimating national PFAS drinking water occurrence 
(see section VI.E of this preamble) indicates that, regardless of 
source water type, small systems generally have lower mean PFAS 
concentrations and lower within-system variability than large systems. 
Further accounting for source water type, as compared to all 
groundwater systems, all surface water systems potentially have a 
larger number of sources of contamination and greater hydrology 
variability so more monitoring data is

[[Page 32608]]

necessary to ensure an appropriately protective monitoring schedule. 
Both the differences in the occurrence estimations for large and small 
sized systems as well as the general source water characteristics of 
groundwater systems were collectively considered as part of 
establishing the proposed initial monitoring requirements for small 
groundwater systems. Consequently, the agency expects that small 
groundwater systems would be less likely to experience variations 
throughout a year and, where there may be seasonal variations, 
requiring the samples to be collected in different parts of a year 
would provide sufficient information to determine the appropriate 
compliance monitoring schedule. Furthermore, given the different 
experiences cited by commenters, possible seasonal variation is likely 
based on the specific geographic location and other localized factors. 
If there are regional factors that suggest more frequent sampling is 
warranted, the rule provides that primacy agencies may increase the 
required monitoring frequency, where necessary, to detect variations 
within the system (e.g., fluctuations in concentrations due to seasonal 
use or changes in water source).
    In response to comments about the alignment of Unregulated 
Contaminant Monitoring Rule (UCMR) 5 sampling with initial monitoring 
requirements, a couple of commenters indicated that requiring larger 
groundwater systems to collect four samples would translate into these 
systems needing to collect two additional samples beyond those 
collected for the UCMR 5 monitoring effort. The EPA acknowledges that 
while the initial monitoring requirements generally align with the UCMR 
5 sampling requirements, groundwater systems serving greater than 
10,000 would need to collect two additional samples and notes that they 
have the three years following rule promulgation to complete this 
monitoring. As described previously, the model for estimating national 
PFAS drinking water occurrence indicates that larger systems have 
greater within-system variability than smaller systems, therefore it is 
appropriate that these larger groundwater systems collect four initial 
monitoring samples; this is consistent with initial monitoring 
requirements for groundwater systems under existing SOC National 
Primary Drinking Water Regulations (NPDWRs).
    In addition, a couple of commenters recommended that the number of 
required samples for initial monitoring be based on the results of the 
first two samples, with subsequent monitoring only required if 
regulated PFAS are detected in those earlier samples. The EPA 
recognizes there is some logic to this approach; however, there would 
be challenges implementing it. Specifically, it could be challenging 
for primacy agencies to track and implement the proposed approach, 
particularly for groundwater systems serving 10,000 or fewer which 
would require the additional samples to occur in quarters not 
represented by the first two samples. Furthermore, tracking this 
varying monitoring would result in additional administrative burden and 
oversight challenges for primacy agencies, rather than having a 
consistently defined schedule for monitoring requirements as is used 
for other SOCs.
    The EPA also received several comments from state agencies about 
the required intervals associated with initial quarterly and semiannual 
sample collection. In its proposal, the EPA specified that samples be 
collected at least 90 days apart, whether the samples were required of 
a system monitoring on a quarterly basis or a system monitoring semi-
annually. A couple of commenters noted that they believed that 
semiannual samples should be separated by more than 90 days to better 
capture seasonal variations (e.g., seasonal changes in the percent 
contributions of water blended from different sources, other 
fluctuations in concentrations). One commenter suggested semiannual 
samples should be collected at least 180 days apart, which would also 
be in better alignment with the required schedule for UCMR 5 semiannual 
sampling. The EPA agrees with these comments. In the final rule, the 
EPA is requiring that the samples be collected 5 to 7 months apart for 
semiannual initial monitoring (see table 2 to paragraph (a)(4)(i)(B) of 
the regulations governing the UCMR program in 40 CFR 141.40).
    With respect to the sample collection timing requirements for 
quarterly initial monitoring (for all surface water systems and 
groundwater systems serving greater than 10,000), a few commenters 
indicated that they were opposed to the proposed requirement for 
samples to be spaced at least 90 days apart. These commenters indicated 
that such a requirement was unnecessarily prescriptive and would make 
sample collection logistically challenging for public water systems. 
These commenters suggested the EPA change the required spacing in a way 
that still satisfies the EPA's intent to not have samples collected 
only a few days apart, but in different quarters, so that quarterly 
samples are more representative of fluctuations in concentrations over 
time. The EPA agrees with these comments and sees the value of systems 
being able to use four existing samples collected in separate quarters 
but also allow flexibility that they are not all spaced at least 90 
days apart. In the final rule, the EPA is modifying the required 
spacing of quarterly initial monitoring samples to be 2 to 4 months 
apart if samples are collected in a 12-month period. For systems that 
would need to supplement previously acquired data to satisfy all the 
initial monitoring requirements, the final rule requires that they must 
also be 2 to 4 months apart from the months of available pre-existing 
data. This will also better parallel the language outlining the 
required spacing of quarterly samples collected for the UCMR 5 
monitoring effort.
    Some commenters asked the EPA to clarify which systems would be 
subject to the initial monitoring requirements for surface water 
systems and which systems would be subject to the requirements for 
groundwater systems, in some cases presenting examples of specific 
scenarios. One example is when a system relies on surface water at some 
EP and groundwater at other EP. The EPA has modified the language of 
the final rule in Sec.  141.902(b)(1)(ii) to clarify that initial 
monitoring requirements are to be determined based on the type(s) of 
water serving as the source for a given EP; thus, one system may have 
different initial monitoring requirements that apply to different EP. 
In response to questions, the EPA is clarifying in Sec.  
141.902(b)(1)(iv) that, if an EP uses water blended from multiple 
sources (some groundwater and some surface water), or if it uses 
different types of sources throughout the year, the system must follow 
the monitoring frequency for a surface water system (since water from 
surface water sources is used at least in part, for at least a portion 
of the year). This approach is more protective of public health 
because, as described earlier, generally surface water systems have 
more variable hydrology and potentially more sources of contamination 
so more monitoring data is necessary to ensure an appropriately 
protective monitoring schedule.
    A couple of commenters asked for clarification about whether EP 
supplying groundwater under the direct influence of surface water 
(GWUDI) would qualify for semiannual initial monitoring. As noted in 
Sec.  141.902(b)(1)(iii), GWUDI systems follow the requirements for 
surface water systems. GWUDI systems may be as susceptible to 
contamination as surface water systems; thus, these systems must use 
the sampling

[[Page 32609]]

requirements for surface water during the initial sampling phase to 
establish baseline levels of regulated PFAS.
    Regarding the requirements for longer-term compliance monitoring, 
the comments the EPA received related primarily to the frequency with 
which sampling would occur under different circumstances, whether each 
EP would be allowed to be on a different compliance monitoring 
schedule, and the trigger levels that would support decisions about 
reduced triennial monitoring. Regarding the latter point, commenters 
also addressed laboratory capabilities to measure levels below 
practical quantitation levels (PQLs).
    The EPA's proposal would allow systems eligible for reduced 
monitoring, and serving 3,300 or fewer, to collect one sample 
triennially and would allow eligible larger systems to collect two 
samples during a three-year compliance period. The EPA specifically 
requested comment on whether all water systems, regardless of system 
size, should be allowed to collect and analyze one sample per three-
year compliance period if the system does not measure any regulated 
PFAS in their system at or above the rule trigger level. A few 
commenters stated that they did not agree with a different number of 
triennial samples eligible systems must collect based on the size of 
the population a system serves. These commenters indicated that they 
believe that one sample collected every three years is sufficient for 
systems of any size on reduced monitoring. The EPA agrees with these 
commenters that systems eligible for triennial monitoring should be 
allowed to collect one sample every three years, regardless of system 
size, especially considering other changes to the compliance monitoring 
framework, as described subsequently.
    Several commenters recommended that an annual sampling frequency 
tier be added to the required monitoring framework for various reasons 
including the mobility and persistence of PFAS in the environment, to 
ensure that systems that have demonstrated elevated levels of regulated 
PFAS are not allowed to move directly from quarterly to triennial 
monitoring, and based on their concerns that some laboratories may not 
be able to produce results at or below the rule trigger levels 
(resulting in some systems remaining on quarterly monitoring 
indefinitely even if they can consistently demonstrate they are below 
the MCLs). A few commenters supported offering three possible 
monitoring frequencies: quarterly, annually, and triennially, whereas 
many other commenters recommended against allowing triennial sampling 
at all and recommended that sampling be required no less than annually, 
to best protect public health. Those commenters supportive of allowing 
both annual and triennial monitoring, depending on prior sample 
results, suggested that annual monitoring should be an option for 
systems with regulated PFAS concentrations that are reliably and 
consistently below the MCLs. This modification would parallel the three 
tiers of monitoring allowed for other organic chemicals under the SMF.
    The EPA does not agree with the comments suggesting that no systems 
should be allowed to sample triennially and that the longest sampling 
interval at any location should be one year. Based on the EPA's 
national occurrence estimates, most water systems subject to the rule's 
requirements will not have results for regulated PFAS that exceed the 
MCLs, and many will not identify PFAS at or above the triggers for 
reduced monitoring. These systems, after demonstrating results below 
the trigger level and therefore no or very little presence of regulated 
PFAS during the initial monitoring period or through ongoing compliance 
monitoring, should be able to reduce their monitoring burden and 
conduct triennial sampling. These monitoring requirements will 
sufficiently maintain public health protection. If a system monitoring 
triennially did have a sample result with elevated levels of a 
regulated PFAS (at or above the trigger level), it would be required to 
immediately initiate quarterly monitoring. Additionally, the rule 
specifically provides that primacy agencies may increase the required 
monitoring frequency for compliance sampling for a variety of reasons, 
including to detect variations within specific systems (e.g., 
fluctuations in concentrations due to seasonal use patterns or changes 
in water sources).
    For any system that has regulated PFAS concentrations at or above 
the trigger level, but reliably and consistently below the applicable 
MCL, the EPA is introducing in the final rule an annual monitoring 
frequency within the compliance monitoring framework, consistent with 
the SMF for SOCs. A demonstration of reliably and consistently below 
the MCL would include consideration of at least four quarterly samples 
below the MCL. Annual samples would be collected during the quarter 
with the highest concentration measured during the prior round of 
quarterly sampling. The EPA expects this modification in the final rule 
to reduce the number of systems that are required to be on quarterly 
monitoring for extended periods of time, compared to the EPA's 
proposal.
    In adopting a three-tiered monitoring framework, the EPA is 
modifying the required sampling frequency from triennial to annual for 
systems determined by states to be reliably and consistently below the 
MCL and changing the threshold for this determination from the trigger 
level to the MCL. To further reduce monitoring, any system that 
transitions into annual sampling will be required to collect three 
years of annual samples each of which show concentrations of regulated 
PFAS below trigger levels (i.e., not an average of the three annual 
sample results) before then being eligible for triennial monitoring. 
Moreover, no system required to collect quarterly samples during 
compliance monitoring would be allowed to transition to triennial 
monitoring without first conducting three years of annual monitoring, 
with all results below the trigger level. If eligible for triennial 
monitoring, the sample collected triennially would need to be collected 
in the same quarter during which prior results were highest.
    This additional tier is intended to create a gradual step-down 
schedule for affected EP to confirm levels of regulated PFAS are 
remaining consistently low or decreasing. The modifications to the 
requirements for a reliable and consistent determination and the 
creation of the new annual sampling tier in the final rule make the 
requirements for regulated PFAS more consistent with the NPDWR 
requirements for SOCs. They also represent flexibilities that address 
concerns about laboratory capability concerns. The EPA believes this 
three-tier approach, including the eligibility criteria for each 
outlined above, provides the best approach to protect public health and 
moderate the total cost of sampling borne by a system.
    The EPA also received a few comments about the practice by systems 
that have installed treatment for PFAS to regularly sample finished 
water to ensure the efficacy of their treatment media (e.g., filters), 
above and beyond what they would do for compliance monitoring. A few 
commenters suggested systems that have installed treatment would 
conduct this additional sampling voluntarily, typically for process 
control purposes. A few state agency commenters suggested that any 
system that is treating its water for PFAS should be required to sample 
more frequently than triennially (e.g., annually) no matter the levels 
of previous PFAS detections, since the effectiveness of treatment media 
may decline over time, if not replaced. The EPA disagrees with the 
commenters

[[Page 32610]]

recommending a greater sampling frequency for systems that treat their 
water for PFAS and does not see a compelling reason to depart from the 
three-tier compliance monitoring program for a system that has 
installed treatment. In the final rule, the EPA is adding an annual 
tier of sampling for any system with concentrations reliably and 
consistently below the MCL but not consistently below the trigger 
level. The EPA believes this tier will likely apply to most systems 
treating their water for regulated PFAS, at least for the first three 
years of treatment, as the EPA estimates as part of its rule costs that 
systems needing to install treatment will assume a treatment target of 
80 percent of the MCLs. The majority of systems with elevated levels of 
regulated PFAS contamination are likely to sample quarterly, at least 
initially (unless they have treatment for PFAS in place prior to the 
collection of initial monitoring samples). In practice, the result is 
that most systems with PFAS contamination will likely not be eligible 
for triennial sampling unless their PFAS treatment is consistently 
optimized and maintained. However, the rule provides that primacy 
agencies may increase the required monitoring frequency, where 
necessary to detect variations within the system, and this approach 
could be applied to those systems that have installed treatment. In 
addition, the EPA notes that, when systems are treating for other 
regulated chemicals pursuant to NPDWRs, no distinctions are made 
between the monitoring frequency required of a system that is treating 
for a chemical and a system that has not installed treatment. Thus, not 
establishing a different monitoring frequency specifically for systems 
that are treating their water for PFAS is consistent with existing 
NPDWRs.
    The EPA requested comment on the proposed allowance of a water 
system to potentially have each EP on a different compliance monitoring 
schedule based on specific EP sampling results (i.e., some EP being 
sampled quarterly and other EP sampled only once or twice during each 
three-year compliance period), or if compliance monitoring frequency 
should be consistent across all of a system's sampling points. A few 
commenters recommended that all EP used by a system monitor at the same 
frequency, or that doing so be optional, to reduce the complexity of 
monitoring requirements or the potential for mistakes to be made with 
respect to sampling windows. However, the overwhelming majority of 
those who commented on this topic indicated they supported allowing 
different sampling frequencies for different EP. The EPA agrees that it 
would be beneficial to allow different sampling frequencies for 
different EP because it would allow utilities to realize cost savings 
if only the EP with elevated levels of PFAS are required to sample most 
frequently. In addition, the EPA notes it allows systems to use 
different sampling frequencies for different EP for compliance with 
other NPDWRs.
    The EPA requested comment on monitoring-related flexibilities that 
should be considered to further reduce burden while also maintaining 
public health protection, including setting a rule trigger level at 
different values than the proposed values of 1.3 ng/L for PFOA and PFOS 
and 0.33 for the Hazard Index PFAS (PFHxS, PFNA, HFPO-DA, and PFBS). 
Alternative values of 2.0 ng/L for PFOA and PFOS and 0.50 for the 
Hazard Index PFAS were identified as possibilities. The EPA received 
numerous comments on the proposed rule trigger levels. Comments 
addressed the proposed values, specifically for PFOA and PFOS, and 
their intended purpose for determination of compliance monitoring 
frequency. Several commenters suggested that the proposed values (i.e., 
1.3 ng/L for PFOA and PFOS and 0.33 for the Hazard Index) are too high 
and the EPA should instead set lower trigger level to ensure greater 
public health protection. Many other commenters suggested the opposite, 
stating that the proposed levels are too low, that laboratories will 
not be able to achieve these levels, and that it may exacerbate any 
laboratory capacity issues. Consequently, some of these commenters were 
concerned that water systems would be ineligible for reduced monitoring 
based on their laboratory's analytical limitations. Several commenters 
suggested that the proposed values are inconsistent with the SMF for 
SOCs.
    Many who commented on the subject were fully supportive of the 
EPA's proposed alternative trigger level values of 2.0 ng/L for PFOA 
and PFOS and 0.50 for the Hazard Index, while others expressed support 
for the inclusion of trigger levels only if these higher levels were 
incorporated. Some noted that these higher trigger levels would better 
align with current laboratory capabilities and allow greater use of 
previously collected drinking water data (to demonstrate systems are 
eligible for reduced triennial monitoring under the rule's initial 
monitoring requirements). A few commenters recommended alternative 
values of 70-80 percent of the MCLs be used as the trigger levels.
    The EPA agrees with commenters that the trigger levels should be 
finalized as one-half of the MCLs (i.e., PFOA and PFOS at 2.0 ng/L 
each, PFHxS, PFNA, and HFPO-DA at 5 ng/L each, and Hazard Index at 
0.5). Using data submitted as part of the UCMR 5 LAP as a reference 
point, the EPA notes that 47 of 53 laboratories (89 percent) that 
applied for UCMR 5 approval generated a minimum reporting level 
confirmation at 2 ng/L (one-half the proposed MCL) or less for Method 
533. This suggests that most laboratories with the necessary 
instrumentation to support PFAS monitoring have the capability to 
provide screening measurement results at the revised trigger level of 
one-half of the MCL. This corresponds with other comments described in 
section VIII.C of this preamble that provided their experience that 
laboratories are capable of reliably quantifying values below the PQLs, 
particularly to 2.0 ng/L for PFOA and PFOS.
    Additionally, based on the EPA's evaluation of state drinking water 
data, updating the final rule trigger levels (to one-half of the MCL) 
will result in a considerable number of additional water systems 
significantly reducing their ongoing monitoring frequency from 
quarterly or annual monitoring to triennial monitoring. Although this 
modification from one-third of the MCL to one-half of the MCLs may 
provide slightly less information on a water system's measured PFAS 
levels as a result of their less frequent monitoring, the trigger 
levels for the final rule (i.e., one-half of the MCLs) will ensure 
sufficient public health protection while reducing burden for water 
systems.
    Many other commenters stated that either trigger levels should be 
removed from the rule entirely or that trigger levels should not be set 
to any levels below PQLs since these represent the level that can be 
reliably measured with a high degree of precision and accuracy across 
all laboratories. Several of these commenters suggested that data below 
the PQL are unreliable, would result in higher costs, and should not be 
used as the basis for any regulatory decisions. Thus, they suggested 
that if trigger levels are incorporated, they should be the same as the 
PQLs. These commenters also cited laboratory challenges in achieving 
measurement below the PQLs and suggested that water systems would not 
be eligible for reduced triennial monitoring as a result of these 
limitations. Additionally, some of these commenters suggested that 
decision making based on any values below the PQLs may exacerbate 
laboratory capacity issues, claiming that such trigger levels would 
result in

[[Page 32611]]

errors, such as false positives, which would lead to increased 
monitoring where samples need to be re-tested.
    The EPA emphasizes that the use of trigger levels set at values 
below the MCLs is consistent with other SOCs under the SMF and not 
novel for drinking water regulations (as described in the subsequent 
paragraph). Their use allows water systems the opportunity to reduce 
their monitoring schedule and burden where it can be demonstrated 
through sampling results that they are at low risk of PFAS 
contamination. In the absence of trigger levels, or some other 
threshold, all water systems would be deprived of the opportunity for 
reduced monitoring. At a national level, were the EPA to eliminate 
reduced monitoring options, this would result in a significant increase 
in costs to utilities. Consequently, the EPA is choosing to incorporate 
these levels to allow flexibility and reduce burden for water systems 
while maintaining health protection.
    For commenters that suggest the trigger levels should be identical 
to the PQLs, particularly for PFOA and PFOS, the EPA disagrees as the 
agency must have greater assurance that the levels are below the 
regulatory standard, the systems are actually lower risk, and a reduced 
monitoring schedule is appropriate. Specifically, in the case of PFOA 
and PFOS, the EPA believes it would represent an unacceptable public 
health risk to set trigger levels at the PQLs because the EPA is 
setting the MCL at the PQL which means that it represents the ``maximum 
permissible level.'' Moreover, the approach of considering measured 
levels lower than PQLs for determining monitoring frequency is not 
novel but has been part of the drinking water standards for many years. 
Many drinking water standards even use a method detection limit, which 
by definition is lower than the PQL. Under the SMF for SOCs, for 
example, results both at or below detection limits and between 
detection limits and the MCL are utilized for monitoring frequency 
determination. Additionally, 40 CFR 141.24(h)(7) prescribes the 
monitoring frequency for organic contaminants based on sample results 
relative to detection limits (as defined in in paragraph (h)(18) of the 
same section). In each of these cases, detection limits are below their 
PQLs (often by a factor of 10). The approach in this rule--using levels 
lower than the PQL to determine monitoring frequency--is consistent 
with the EPA's approach for other NPDWRs (see section V of this 
preamble).
    As described earlier, some commenters raised concerns about 
potential laboratory analytical and capacity issues. Some suggested 
that laboratories cannot achieve levels below the PQLs, which would 
result in water systems not being eligible for reduced monitoring based 
on not demonstrating results below trigger levels. The EPA recognizes 
that some laboratories may not be able to produce results at these 
lower levels with the same degree of accuracy and precision as results 
at or above the PQLs, and notes that there is not a requirement that 
they do so for these purposes. The EPA uses the PQL to inform the MCL 
feasibility determination and the same level of precision and accuracy 
is not required to determine monitoring frequency. Along these lines, 
several commenters questioned if the sample results must be quantified 
to be used for the determination of monitoring frequency, given the 
proposed trigger level values were set below the PQLs, requesting 
further clarity from the EPA on how to interpret and utilize quantified 
and non-quantified data. Furthermore, some commenters suggested that if 
values below the PQLs are used, only quantified results should be used 
for determining monitoring frequency. Other commenters stated there 
should not be a numerical value associated with results below the PQL 
(e.g., results between the trigger levels and the PQLs) and instead 
such results should only be reported on an absence/presence basis.
    The EPA agrees that results below the PQL may not have the same 
precision and accuracy as higher-level measurements; however, results 
below the PQL can be sufficiently determined for these purposes. Data 
below the PQL will be critical to ensuring that systems are monitoring 
at the correct frequency and whether a contaminant is present within a 
certain range. Moreover, while results near the trigger level may be 
less definitive than results at or above the PQL, such results are 
appropriate for establishing monitoring frequency, as well as for 
reporting as part of the annual Consumer Confidence Report (CCR). CCR 
reporting is based on detected contaminants and for the purposes of the 
PFAS NPDWR, Sec.  141.151(d) defines ``detections'' as results at or 
above the rule trigger levels (see section IX of this preamble for more 
information on CCR requirements).
    Under this final rule, for monitoring frequency determination 
purposes, systems are required to use all compliance sample results, 
including those below the PQLs and not quantified with the same 
precision and accuracy as is associated with the MCL compliance 
calculation determination. Additionally, the determination of 
monitoring frequency is not based on a running annual average result, 
but each individual sampling result. As an illustration of the 
approach, if a water system has quarterly sampling results at an EP 
from initial monitoring for PFOA that are 2.0, 1.5, 5.0, and 1.5 ng/L, 
there are two results (i.e., 2.0 and 5.0 ng/L) at or above the EPA's 
final trigger level for PFOA (i.e., 2.0 ng/L). Thus, the water system 
would not be eligible for triennial monitoring at this EP for all 
regulated PFAS when compliance monitoring begins. Providing a different 
example, if a water system that is currently required to conduct 
quarterly compliance monitoring has quarterly sampling results at an EP 
for PFOA that are 2.0, 3.5, 2.5, and 1.5 ng/L, all results are below 
the MCL for PFOA (i.e., 4.0 ng/L), however three results are above the 
PFOA trigger level. In this case, because four quarters of data have 
been collected and assuming all other regulated PFAS sampling results 
are below their MCLs as well, the water system could be deemed 
reliability and consistently below the MCL by the primacy agency and be 
eligible to monitor annually at this EP. For all frequencies of ongoing 
compliance monitoring, including quarterly, annual and triennial, this 
determination would be done the same where all sample results are used, 
even those below the PQLs.
    Many commenters requested that the EPA provide clarification on how 
laboratories and PWSs should report levels below the PQLs for 
monitoring frequency purposes. All results at or above the trigger 
level are to be reported as numeric values and used for determining 
monitoring frequency. Under the EPA approved analytical methods 
discussed in section XII, numeric values as low as the rule trigger 
levels will be available because of the need to meet ongoing QC 
requirements of the methods for blanks, demonstrating no background 
contamination. Within each analytical batch of samples, the laboratory 
must document passing blank QC criteria by attaining qualitative 
measurements of the regulated PFAS that are no higher than one-third of 
the laboratories reporting limit, which must be at or below the PQL. 
The EPA intends to provide guidance materials with details and examples 
on this to support successful implementation of the final rule.
    Some commenters suggested the potential for confusion related to 
the differences in how results less than PQLs are used in monitoring 
frequency determination and the MCL compliance determination. Several 
commenters

[[Page 32612]]

suggested that there should be a consistent approach. Most commenters 
suggested that the approach should follow that of the MCL compliance 
determination, where zero is used in the calculation of annual averages 
when measured values are below PQLs. The EPA reiterates that the 
trigger levels are used for establishing appropriate monitoring 
frequency. For certain regulated PFAS, they are set at a defined 
threshold that shows if these PFAS are present or absent. The PQLs, 
which are used for the MCL compliance determination, are set at 
specific concentrations that laboratories nationwide can measure with 
high certainty. To alleviate possible confusion, the EPA intends to 
provide communication materials on these monitoring requirements to 
support successful implementation of the final rule. Nevertheless, the 
difference in approach (between data used for compliance monitoring 
determinations and data used to determine monitoring frequency) 
reflects the most appropriate application of the data for each of the 
intended purposes and assures that adequate monitoring is occurring in 
systems where the regulated PFAS have been shown to be present at the 
trigger level or higher. The EPA's rationale is described in detail in 
section VIII.B of this preamble.
    Several other issues related to monitoring flexibilities were 
raised in public comments. One commenter asked, if one EP has a result 
for a single regulated PFAS at a concentration above the trigger level, 
but other regulated PFAS are below trigger levels, must the system 
initiate quarterly sampling for all regulated PFAS at the EP or are 
they only required to initiate quarterly sampling for PFAS observed at 
or above the trigger level. As described in the rule proposal, if a 
regulated PFAS is detected at or above a trigger level, the system must 
monitor quarterly at that sampling point for all regulated PFAS. This 
is appropriate as the same analytical methods are used for the analysis 
of all regulated PFAS (no extra analyses need to be performed to 
measure the other PFAS) and the regulated PFAS have been shown to 
significantly co-occur.
    In addition, commenters questioned whether quarterly sampling would 
be triggered when a result is equal to but does not exceed the trigger 
level for systems monitoring triennially. One commenter pointed out 
that the language proposed for inclusion in Sec.  141.905(b)(2) stated 
that systems monitoring triennially whose sample result is at or 
exceeds the trigger level must begin quarterly sampling, whereas Sec.  
141.902(b)(2)(ii) stated the trigger level must be exceeded before 
quarterly monitoring is required. The EPA is clarifying this point in 
the final rule to reflect the EPA's intent that quarterly sampling 
would be triggered when a result is at or above the trigger level as 
prescribed in Sec.  141.905(b)(2). This same approach has been used in 
other NPDWRs (e.g., for SOC trigger levels).
3. Final Rule
    This final rule establishes initial monitoring requirements and 
reflects minor modifications to the proposed approach. Groundwater CWS 
and NTNCWS serving 10,000 or fewer must collect two (semiannual) 
samples in a consecutive 12-month period and must collect the samples 5 
to 7 months apart, to better capture seasonal variation. Groundwater 
CWS and NTNCWS serving greater than 10,000 and all surface water CWS 
and NTNCWS must collect four (quarterly) samples 2 to 4 months apart in 
a consecutive 12-month period. The EPA is maintaining the provision 
described in the proposed rule that allows PWSs to use previously 
collected data to satisfy initial monitoring requirements; see Sec.  
141.902(b)(1)(vi). Systems that need to collect additional quarterly 
samples to meet the initial monitoring requirements may sample outside 
of a 12-month period, if all quarters are represented with sample 
months 2 to 4 months apart. This 2-to-4-month interval also aligns with 
UCMR 5 sampling requirements for surface water systems subject to this 
rule and better captures possible seasonal variability establishing a 
well-informed baseline. In addition, the EPA is modifying the proposed 
initial monitoring requirements to now specify that if the water source 
for the EP is surface water, a blend of surface water and groundwater, 
or GWUDI, the initial monitoring requirements for surface water source 
(4 quarterly samples) apply. If the EP source is only groundwater, 
initial semiannual monitoring is required.
    The EPA is modifying the number of samples required for some 
systems with sampling locations eligible for triennial monitoring. 
Regardless of the population served, all systems with sampling 
locations eligible for triennial sampling will collect one sample every 
three years. The sample is to be collected during the quarter with the 
highest prior concentration identified in the most recent year when 
samples were collected.
    In the final rule the EPA is establishing a third tier for 
monitoring frequencies and updating the proposed requirements for each 
tier. The new monitoring frequency tier provides for annual monitoring 
at sampling locations that have collected at least four consecutive 
quarterly samples following initial monitoring if the primacy agency 
determines the results at that EP are reliably and consistently below 
the MCL. In establishing this tier, the EPA is removing the proposed 
rule requirement for a state to determine that the running annual 
average (RAA) concentration is below the trigger levels to reach this 
reliably and consistently below the MCL determination. Instead, in the 
final rule, reliably and consistently below the MCL means that each of 
the sample results for the regulated PFAS are below the applicable 
MCLs. In this new annual monitoring tier, if EP receive the reliably 
and consistently below the MCL determination and remain below the MCLs 
in subsequent sampling, even if above a trigger level, they may 
continue on an annual monitoring schedule.
    The criteria eligibility for triennial monitoring have been changed 
accordingly. EP with all results below the trigger levels during 
initial monitoring are eligible for triennial monitoring, as described 
in the proposed rule. But, under the final rule, if an EP is required 
to conduct quarterly sampling during the compliance monitoring period, 
then triennial monitoring is only available after the EP has three 
consecutive annual samples that each contain concentrations below the 
trigger level. For EP that consistently have results between the 
trigger levels and the MCLs, as described previously most would remain 
on annual monitoring, rather than quarterly monitoring, which provides 
a sufficient indication of contaminant level while reducing the total 
sampling costs.
    With respect to whether different EP for a particular water system 
may be sampled at different compliance monitoring frequencies, based on 
specific EP sampling results, the final NPDWR affirms this flexibility, 
as proposed. In addition, there is no change to the language in the 
final rule discussing the timing for taking quarterly samples during 
the long-term compliance monitoring period. The EPA does not specify a 
required interval between samples; the requirement is quarterly.
    The EPA is finalizing rule trigger levels for compliance monitoring 
frequency purposes only at one-half of the MCLs for regulated PFAS 
(i.e., 2.0 ng/L for PFOA and PFOS, 5 ng/L for PFHxS, PFNA, and HFPO-DA, 
and 0.5 for Hazard Index). If all PFAS results for an EP are below 
these levels, the EP

[[Page 32613]]

would be eligible for triennial monitoring, with the following 
exception. If sampling location is under an annual monitoring schedule, 
it would be eligible for triennial monitoring following three 
consecutive annual samples with all sample results below the trigger 
levels.
    The EPA's proposed rule included monitoring requirements specific 
to PFAS. To avoid possible confusion, the EPA is amending 40 CFR 
141.24(h) to clarify that the applicable monitoring requirements for 
PFAS are in 40 CFR 141.902 and that the monitoring requirements for 
non-PFAS SOCs in 40 CFR 141.24(h) do not apply to PFAS.

B. How are PWS compliance and violations determined?

1. Proposal
    Consistent with existing rules for determining compliance with 
NPDWRs, the EPA proposed that compliance would be determined based on 
the analytical results obtained at each sampling point. For systems 
monitoring quarterly, compliance with the proposed MCLs would be 
determined by calculating RAAs for each sampling point. As proposed, 
eligibility for reduced monitoring would be determined by the sample 
result(s) at the sampling point. If the sample result(s) are at or 
exceed the rule trigger level, the system would be required to revert 
to quarterly sampling, for all regulated PFAS, at each EP where a 
result is at or above the trigger level. In such case, the sample event 
that included a result(s) at or above the trigger level would be 
considered the first quarter of monitoring in calculating the RAA.
    An RAA is calculated using results for samples taken at a 
particular monitoring location during the previous four consecutive 
quarters. As proposed, if a system takes more than one compliance 
sample during each quarter at a particular monitoring location, the 
system must average all samples taken in the quarter at that location 
to determine the quarterly average, which would then be used in 
calculating the RAAs. Conversely, if a system does not collect required 
samples for a quarter, the RAA would be based on the total number of 
samples collected for the quarters in which sampling was conducted. As 
proposed, MCL compliance determinations would not be made until a 
system has completed one year of quarterly sampling, except in the case 
where a quarterly sampling result is high enough that it will clearly 
cause the RAA to exceed an MCL (i.e., the analytical result is greater 
than four times the MCL). In that case, the system would be in 
violation with the MCL immediately.
    In the proposal, when calculating the RAAs, if a sample result is 
less than the PQL for the monitored PFAS, the EPA proposed to use zero 
to calculate the average for compliance purposes.
2. Summary of Major Public Comments and EPA Responses
    The agency received a few different types of comments on how the 
compliance determination and violations were proposed to be assessed. 
Many commenters supported the EPA's approach to assess violations, 
including that violations are only assessed through an RAA for systems 
conducting quarterly monitoring. A couple of commenters suggested that 
in a scenario where a particular high quarterly sample (i.e., result 
greater than four times the MCL) would cause the RAA to exceed an MCL, 
the system should not be deemed out of compliance until the end of the 
quarter (to allow utilities to conduct additional monitoring during 
that quarter and average the results from the multiple samples). The 
EPA disagrees with commenters that suggest additional voluntary 
sampling be used in calculating the quarterly average. The final rule 
requires that a compliance sample be taken during each quarter for 
those systems conducting quarterly monitoring. Further, as prescribed 
under 141.902(b)(2)(v), the state may require a confirmation sample for 
any sampling results and, if this sample is required, the result must 
be averaged with the first sampling results and used for the compliance 
determination. Therefore, any samples other than a state-required 
confirmation sample should not be averaged within the quarterly 
compliance result which will be assessed at the end of the quarter.
    A couple of other commenters suggested changing the time periods 
for determining compliance (for both systems conducting quarterly 
monitoring and those conducting triennial monitoring). These 
recommendations included assessing compliance based on the results from 
eight consecutive quarterly samples (rather than four). For those 
systems conducting triennial monitoring, some commenters proposed that 
the compliance determination be based on one triennial sample result. 
For systems determining compliance through an RAA calculation, the EPA 
believes four consecutive quarterly samples is an adequate 
representation of the regulated PFAS levels while also assessing 
compliance in a timely manner. For systems conducting triennial 
monitoring, if a water system has a sample result at or above the EPA's 
trigger levels, the system will immediately be required to begin 
quarterly monitoring. This is consistent with other monitoring 
requirements for other SOCs and, given the change in measured 
concentration, will provide additional information over a consistent 
and longer period of time to better assess the average level of 
regulated PFAS within the water supply and ensure the water system is 
reliably and consistently below the MCL.
    In the proposed rule, the EPA requested comment on whether the 
agency should consider an alternative to the approach of using zero 
when calculating the RAAs if a sample result is less than the PQL. 
Specifically, in the case where a regulated PFAS is detected but the 
result is below its proposed PQL, the proposed rule invited comment on 
whether the trigger level (proposed as one third of the PQL) should be 
used as the value in calculating the RAA for compliance purposes.
    The EPA received numerous comments related to the proposed approach 
for calculating the RAA for compliance with the NPDWRs, particularly on 
the incorporation of sample results below the PQLs for the regulated 
PFAS (see sections V and VII for more information on PQLs.) Many 
commenters, including some states, supported the EPA's proposed 
approach to utilize zero for results below PQL to calculate the average 
for compliance purposes. These commenters cited the definition of the 
PQL as the lowest concentration of an analyte that can be reliably 
measured within specified limits of precision and accuracy during 
routine laboratory conditions and noted that this is a level that all 
laboratories should be able to achieve. Consequently, they suggested 
that values below these PQLs should not be used for the compliance 
calculation. Several of these commenters expressed concern that using 
estimated or other values with less precision in the compliance 
calculation could result in utilities needing to take actions to 
address levels of regulated PFAS that are not well-quantified and may 
not be representative of regulated PFAS levels. Many commenters 
suggested that since all laboratories cannot achieve values less than 
the PQLs, this would result in equity issues with respect to disparate 
laboratories capabilities. Some also suggested that the approach could 
exacerbate any potential laboratory capacity issues.
    The EPA agrees with these commenters that values below the PQLs

[[Page 32614]]

for the regulated PFAS should not be used in the compliance 
calculation. As cited previously by commenters and the EPA in sections 
V and VII, PQLs are the lowest concentration that can be reliably 
measured within specified limits of precision and accuracy during 
routine laboratory operations. As noted in the rule proposal, ``the 
agency must have a high degree of confidence in the quantified result 
as it may compel utilities to make potentially costly compliance 
decisions in order to comply with the MCL.'' Moreover, because 
compliance with the MCL is determined by analysis with approved 
analytical techniques, the ability to analyze consistently and 
accurately for a contaminant is important to enforce a regulatory 
standard. The EPA recognizes the potential for minor analytical 
variabilities within sampling procedures and laboratory analyses below 
the PQL and this approach offers operational certainty to utilities, 
provides assurances of precision and accuracy in the concentrations at 
or above the PQL that are achievable for all laboratories, ensures 
equitable access to all laboratories with comparable analytical 
capabilities for the purposes of compliance sample results, and reduces 
the potential for laboratory capacity issues.
    Many other commenters did not support the EPA's proposed approach 
and offered that all sample results between method detection limits and 
PQLs, even if estimated, should be used. Alternatively, some suggested 
that any results that laboratories are able to quantify should be used 
in calculating the RAA for compliance. A subset of these commenters 
suggested that using zero (instead of an estimated or semi-quantitative 
value) biases the RAA compliance calculation, is even less precise and 
accurate than using the values below the PQLs, is contrary to the RAA 
compliance calculation for other SOC NPDWRs and demonstrates a 
reduction in public health protection. Some commenters also suggested 
that this could result in public communication challenges if 
laboratories are able to estimate or quantify values below the PQLs and 
zero is instead used in the calculation. Further, several commenters 
submitted that, in their experiences, some laboratories are capable of 
reliably and accurately reporting below the PQLs.
    While the EPA recognizes that using zero for values below the PQL 
would result in a differing RAA compliance calculation result than if 
the values below the PQL were instead used, on a national scale, these 
values below the PQL do not consistently represent values with the 
precision, accuracy, and reliability the EPA believes are necessary for 
compliance determination purposes. Therefore, the EPA's national 
approach to achieve consistency (recognizing that laboratories have 
varying analytical capabilities) is to judge compliance based on 
results at or above the PQL. Using inconsistent values below the PQL 
may result in MCL compliance determination inequities across systems.
    The EPA agrees that some laboratories are capable of reliably 
measuring the regulated PFAS below the EPA's PQLs. This is supported by 
a subset of state PFAS monitoring data that represents some sampling 
with quantified values below the EPA's PQLs. Further, in the March 2023 
proposal, the EPA recognized that ``quantitation of the contaminants 
can be achieved between the method detection limit and the PQL'' though 
the EPA also noted in the proposal that this is ``not necessarily with 
the same precision and accuracy that is possible at and above the 
PQL.'' The EPA must set requirements evaluating the circumstances of 
all PWSs and laboratory capabilities throughout the country. The agency 
notes that states must establish requirements at least as stringent as 
the EPA to maintain primacy; however, under the Safe Drinking Water Act 
(SDWA), states with primacy may establish more stringent requirements. 
In instances where a laboratory can demonstrate it is capable of 
precisely and accurately quantifying values below the PQLs, some states 
may choose to establish their own requirements that are more stringent 
and use these values for the compliance calculation.
    The agency also received a few comments on the possible alternative 
approach of using the proposed trigger level as the value in 
calculating the RAA for compliance purposes when the result is 
estimated as between the trigger level and PQL. Most commenters did not 
agree with using the trigger levels as an estimate instead of zero when 
values are below the PQL and noted that these values could result in 
inequitable implementation of the rule based on laboratory analytical 
capabilities.
    After consideration of all these comments and for the reasons 
described previously, the EPA does not believe it is appropriate to use 
trigger level values or any other values above defined detection limits 
but below the PQL as part of the RAA compliance calculation based on 
the information available to the agency today. Trigger levels are 
appropriate to determine if the contaminant is present (i.e., detected) 
and for the determination of reduced monitoring frequency, however the 
EPA concludes that values below the PQL would not consistently and 
reliably demonstrate the accuracy and reliability necessary for 
compliance determination purposes that can result in make potentially 
costly expenditures for PWSs.
3. Final Rule
    For the final rule, the EPA is maintaining the proposed compliance 
calculation determination approach. For systems with sampling locations 
monitoring quarterly, compliance with the MCLs for regulated PFAS is 
determined by calculating RAAs using compliance results for particular 
sampling points. Based on final rule changes to the compliance 
monitoring requirements previously described in section VIII.A of this 
preamble above, systems with sampling locations monitoring less 
frequently than quarterly are required to revert to quarterly sampling 
for all regulated PFAS in the next quarter at each EP with the 
exceedance where either the sample result(s) are at or above the rule 
trigger level (for those on triennial monitoring) or the sample 
result(s) are at or exceed the MCL (for those on annual monitoring). In 
both cases, the triggered sample result is required to be used for the 
first quarter of monitoring in calculating the RAA. If a system takes 
more than one compliance sample during each quarter at a particular 
monitoring location, the system must average all samples taken in the 
quarter at that location to determine the quarterly average and this 
will be used in calculating the RAAs. Conversely, if a system does not 
collect the required compliance samples for a quarter, the RAA will be 
based on only those quarters where samples were collected during the 
past four quarters. A system will generally not be considered in 
violation of an MCL until it has completed one year of quarterly 
sampling (i.e., a system on an annual or triennial monitoring schedule 
with an exceedance of the MCL is not in violation until it completes 
one year of quarterly sampling with the sample exceeding the MCL used 
as the sample result for the first quarter of the RAA). However, 
regardless of the result of subsequent monitoring, if a quarterly 
sample result will cause the RAA to exceed an MCL at any sampling point 
(e.g., the first quarter sample result is greater than twice the MCL 
and the second quarter sample result is also greater than twice the 
MCL) or if an annual or triennial sample result causes the RAA to 
exceed an MCL at any sampling point (i.e., the analytical result

[[Page 32615]]

is greater than four times the MCL), then the system is out of 
compliance with the MCL immediately.
    The EPA is also retaining the proposed approach for the MCL 
compliance calculation where, if a sample result is less than the PQL 
for the monitored PFAS, zero will be used to calculate the RAA (if 
monitoring quarterly). To clarify how to implement approach, the EPA is 
providing a few different examples related to calculating the RAA for 
the PFOA/PFOS MCLs, the individual MCLs for PFHxS, PFNA, and HFPO-DA, 
and the Hazard Index MCL for the mixtures of PFHxS, PFNA, HFPO-DA, and 
PFBS.
    If a system conducting quarterly monitoring has sample results for 
PFOA that are 2.0, 1.5, 5.0, and 1.5 ng/L for their last four quarters 
at a sample location, the values used to calculate the RAA for that 
sample location would be 0, 0, 5.0, and 0 ng/L with a resulting PFOA 
RAA of 1.3 ng/L (i.e., (0 + 0 + 5.0 + 0)/4 = 1.3 ng/L). For PFOA and 
PFOS, as described in section V of this preamble, the MCLs of 4.0 ng/L 
are promulgated with two significant figures and must be expressed as 
such in the calculation with any rounding not occurring until the end 
of the calculation. Data reported to the primacy agency must contain 
the same number of significant digits as the MCL. In calculating data 
for compliance purposes, the number must be rounded to two significant 
digits. The last significant digit should be increased by one unit if 
the digit dropped is 5, 6, 7, 8, or 9, and if the digit is 0, 1, 2, 3, 
or 4, the preceding number does not change (e.g., 1.37 is reported as 
1.4).
    As described in section V of this preamble, the EPA is finalizing 
individual MCLs and Health Based Water Concentrations (HBWCs) for PFHxS 
(10 ng/L), HFPO-DA (10 ng/L), and PFNA (10 ng/L), the HBWC for PFBS 
(2000 ng/L), and the Hazard Index MCL (1 unitless) with one significant 
figure. Similar to PFOA and PFOS, if a sample result is less than the 
respective PQLs for these PFAS (i.e., 3.0 ng/L for PFHxS, 5.0 ng/L for 
HFPO-DA, and 4.0 ng/L for PFNA), zero will be used to calculate 
compliance both for the PFHxS, PFNA, and HFPO-DA MCLs and the Hazard 
Index MCL for mixtures of PFHxS, PFNA, HFPO-DA, and PFBS. As an 
example, for the HFPO-DA MCL compliance calculation (which would be the 
same for the PFHxS and PFNA MCLs using their respective PQLs), if a 
system conducting quarterly monitoring has HFPO-DA sample results that 
are 3.2, 6.1, 5.5, and 2.7 ng/L for the last four quarters at a sample 
location, the values used to calculate the RAA for that sample location 
would be 0, 6.1, 5.5, and 0 ng/L with a resulting HFPO-DA RAA of 3 ng/L 
after rounding to one significant figure at the end of the calculation 
(i.e., (0 + 6.1 + 5.5 + 0)/4 = 2.9 ng/L). Therefore, this system has 
not violated the MCL for HFPO-DA. The EPA notes that for all MCL RAA 
calculations, water systems are required to retain the unrounded RAA 
value (2.9 ng/L in this example) for use in the next RAA calculation as 
no rounding should occur until the end of the overall compliance 
calculation (i.e., 2.9 ng/L, not 3 ng/L, should be used).
    To provide an example calculation for determining compliance with 
the Hazard Index MCL for mixtures of PFHxS, PFNA, HFPO-DA, and PFBS, if 
the quarterly sample results at a sample location are 2.1 ng/L for 
PFHxS, 3.4 for HFPO-DA, 4.1 for PFNA, and 20.0 for PFBS, the water 
system would first determine the Hazard Index value for that quarter, 
which is 0.42 (i.e., ((0/10) + (0/10) + (4.1/10) + (20.0/2000) = 0.42). 
To then calculate the RAA Hazard Index MCL, if the preceding three 
quarters had unrounded Hazard Index values of 0.76, 1.10, and 0.53 at 
the same sample location, the resulting RAA Hazard Index MCL would be 
0.7 after rounding to one significant figure at the end of the 
calculation (i.e., (0.76 + 1.10 + 0.53 + 0.42)/4 = 0.70). Consequently, 
this system has not violated the Hazard Index MCL.

C. Can systems use previously collected data to satisfy the initial 
monitoring requirement?

1. Proposal
    The EPA proposed that systems be allowed to use previously 
collected monitoring data to satisfy the initial monitoring 
requirements. In general, a system with appropriate historical 
monitoring data for each EP, collected using EPA Methods 533 or 537.1 
as part of UCMR 5 or a state-level or other appropriate monitoring 
campaign, could use that monitoring data to satisfy initial monitoring 
requirements. The EPA notes that for systems monitoring under UCMR 5, 
all surface water systems are required to collect four quarterly 
samples and all groundwater systems are required to collect two 
quarterly samples over a period of 12 months.
    While the EPA expects most systems serving 3,300 or greater will 
have some UCMR 5 data, the EPA also proposed that systems with 
previously acquired monitoring data from outside UCMR 5, including 
state-led or other appropriate occurrence monitoring using EPA Methods 
533 or 537.1 would also be permitted to use these other monitoring data 
in lieu of separate initial monitoring for regulated PFAS. The proposed 
approach may have allowed systems serving fewer than 3,300 (many of 
whom do not participate in UCMR 5) to otherwise satisfy the initial 
monitoring requirements. The EPA proposed that data collected after 
January 1, 2023, be accepted for EP samples, and data collected between 
January 1, 2019, and December 31, 2022, also be accepted if it is below 
the proposed rule trigger level of 1.3 ng/L for PFOA and PFOS and a 
Hazard Index of 0.33 for PFHxS, PFNA, HFPO-DA, and PFBS. Additionally, 
the EPA proposed that if systems have multiple years of data, the most 
recent data were to be used.
    In the proposal, the EPA stated that if a system had conducted 
prior monitoring involving fewer than the number of samples required 
for initial monitoring under this PFAS NPDWR, then all surface water 
systems, GWUDI systems, and groundwater systems serving greater than 
10,000 would be required to collect at least one sample in each quarter 
of a calendar year that was not acquired and groundwater systems 
serving 10,000 or fewer would be required to collect one sample in a 
different quarter of the calendar year than the one in which the 
previous sample was acquired.
2. Summary of Major Public Comments and EPA Responses
    The EPA requested comment on the proposal to allow the use of 
previously acquired monitoring data to satisfy the initial monitoring 
requirements. This included a request for feedback on the data 
collection timeframe requirements and on whether particular QA 
requirements should be established for such data. Of commenters that 
provided input on the proposed allowance, nearly all supported the use 
of previously collected data to support the initial monitoring 
requirements. The EPA agrees with these commenters that appropriate, 
previously collected data should be allowed and notes that there will 
be significant data available from UCMR 5 monitoring and from the many 
states that have been proactively conducting PFAS drinking water 
monitoring. This will allow for a significant opportunity to reduce 
burden for numerous water systems, as well as decrease the potential 
for laboratory capacity issues. One commenter suggested that the use of 
this data may not be sufficiently representative of current PFAS 
concentrations in drinking water systems as the laboratory analyses 
previously used may not have been

[[Page 32616]]

sufficiently sensitive to detect the analytes, relative to the proposed 
PFAS regulatory standards. The EPA disagrees with this commenter as the 
analytical methods proposed for PFAS analysis were available for the 
majority of the time period (i.e., 2019 and after) in which data are 
allowed to be used to satisfy the initial monitoring requirements. 
Furthermore, the rule provides that a primacy agency may choose to not 
allow these data to satisfy initial monitoring requirements and may 
require more frequent monitoring on a system-specific basis. 
Additionally, the EPA clarifies that previous monitoring does not 
automatically qualify water systems for reduced compliance monitoring; 
rather it is the results from that monitoring that determine the 
eligibility for a reduced compliance monitoring schedule.
    Many commenters suggested that the use of these data should be at 
the state's discretion and requested that the EPA provide additional 
flexibility to the primacy agencies in the determination of which data 
are allowed, including the number of samples and the QA requirements. 
Moreover, several commenters asked that the EPA clarify how much 
additional data would be needed to satisfy the initial monitoring 
requirements if a previous monitoring campaign included less sampling 
than required under the rule initial monitoring requirements. 
Specifically, a few commenters noted that, under the requirements of 
UCMR 5 monitoring, groundwater systems serving greater than 10,000 
would have results from two sampling events, not the four needed to 
satisfy the initial monitoring requirements of this rule. Commenters 
requested that the EPA explain if these UCMR 5 systems would need to 
collect additional (supplemental) samples. A few commenters suggested 
UCMR 5 monitoring should sufficiently meet the requirements for all 
systems, even though the proposed rule requires quarterly sampling for 
all groundwater systems serving greater than 10,000.
    Having considered the public comments, the EPA is establishing in 
the final rule that water systems that have collected fewer samples 
(under UCMR or other programs) than required in this rule for initial 
monitoring must conduct supplemental monitoring that allows them to 
meet the minimum requirements. Additional details on this requirement 
are in section VIII.C.3 of this preamble. In the case of UCMR 5, for 
example, groundwater systems serving greater than 10,000 will be 
required to collect two additional samples beyond the two collected for 
UCMR 5. For more information on the initial monitoring requirements, 
please see section VIII.A of this preamble.
    Several commenters requested that the EPA clarify whether only 
samples collected under UCMR 5 would be allowed to fulfill initial 
monitoring requirements, or if data under other monitoring efforts, 
such as state monitoring, would also be acceptable. As provided in the 
proposal and final rule, a state may accept results from all 
appropriate monitoring efforts, as determined by the state, including, 
but not limited to, UCMR 5 and other state-led efforts.
    Several commenters provided various comments related to QA 
requirements for previously collected data, including data analysis 
methods, minimum reporting levels, and data collection timeframe. A few 
commenters expressed that the EPA should allow the use of results from 
modified EPA methods and/or other state-developed analytical methods. 
The EPA disagrees with these commenters. While there are other methods 
that have been used for data collection and analysis, the EPA is 
requiring that any data used for this rule be collected and analyzed 
using Methods 533 and 537.1 to ensure consistency across analytical 
results, as well as to align with the final rule analytical method 
requirements described in Sec.  141.901. A few commenters requested 
that the EPA provide additional information on reporting level 
requirements of the data, with one commenter suggesting that the EPA 
should not allow this data to be used for initial monitoring purposes 
if the reporting limits of the laboratory are higher than the EPA's 
proposed PQLs. The rule provides that the available data can be used 
regardless of reporting or detection limits to satisfy the initial 
monitoring requirements; however, given these factors, the results may 
not support determinations for reduced compliance monitoring. Regarding 
data collection timeframes, a few commenters questioned why data 
collected prior to 2023 would not be accepted where the results are 
higher than the proposed rule trigger levels. In response, the EPA has 
modified the rule to allow data from January 1, 2019, and later to 
satisfy initial monitoring requirements, even if it is not below the 
final rule trigger levels if it meets all other requirements (including 
being analyzed using Methods 533 and 537.1). Data collected prior to 
2019 may not be representative of water quality conditions and likely 
would not have been analyzed using these methods (given when they were 
published). The EPA notes if the results exceed the final rule trigger 
levels the system will not be eligible for a reduced monitoring 
schedule at that EP.
3. Final Rule
    The EPA is retaining the proposed allowance of using previously 
collected monitoring data to satisfy some or all of the initial 
monitoring requirements. The agency notes that while use of this data 
is allowed, water systems may choose to conduct additional monitoring 
to satisfy their initial monitoring requirement in lieu of using pre-
existing data. As described previously in section VIII.A of this 
preamble, the final rule initial monitoring requirements specify that 
all system sizes with surface water or GWUDI sources and groundwater 
systems serving greater than 10,000 are required to collect four 
quarterly samples, and groundwater systems serving 10,000 or fewer are 
required to collect two samples. The EPA is clarifying that the number 
of samples required is based at the EP; therefore, if a system serving 
10,000 or fewer has EP with different source water types, the required 
monitoring is based on the source water type of that EP (i.e., a system 
serving 10,000 or fewer that has surface water, groundwater, and/or 
GWUDI sources during the initial monitoring period must collect two 
samples at the EP sourced by groundwater and four samples at the EP 
sourced by surface water or GWUDI). For systems serving 10,000 or fewer 
that change the source water type at EP throughout the initial 
monitoring period (i.e., one part of the year is surface water, and the 
remaining part of the year is groundwater and/or GWUDI), the EP must 
follow the sampling requirements of surface water systems.
    In the final rule under Sec.  141.902(b)(1)(viii), the EPA is 
maintaining that if a system has some previously collected results, but 
fewer than the number required to satisfy the initial monitoring 
requirements, they must conduct additional monitoring such that it, 
coupled with the previous monitoring, meets the requirements of this 
rule. All surface water and GWUDI systems, and groundwater systems 
serving greater than 10,000, must collect the required additional 
samples 2-4 months apart from the months with available data, without 
regard to year, such that all quarters are represented (see section 
VIII.A of this preamble for more information).
    In Sec.  141.902(b)(1)(vi), the final rule maintains the 
requirement that the data must have been collected and analyzed using 
EPA Methods 533 or 537.1, and eliminates the requirement that data 
collected between January 1, 2019, and December 31, 2022, must reflect 
the

[[Page 32617]]

laboratory's ability to measure at or below the rule trigger level to 
satisfy initial monitoring requirements. Data collected before January 
1, 2019, cannot be used to satisfy these requirements. Additionally, 
any results above the final rule trigger levels of 2.0 ng/L each for 
PFOA and PFOS, 5 ng/L each for PFHxS, PFNA, and HFPO-DA, and a Hazard 
Index of 0.5 for PFHxS, PFNA, HFPO-DA, and PFBS would not allow the 
associated EP to be eligible for reduced monitoring.

D. Can systems composite samples?

1. Proposal
    Subpart C of 40 CFR 141.24 describes instances where primacy 
agencies may reduce the samples a system must analyze by allowing 
samples to be composited. Composite sampling can potentially reduce 
analytical costs because the number of required analyses is reduced by 
combining multiple samples into one and analyzing the composited 
sample. However, in the proposal, the EPA noted that based on input the 
agency received from consulting with state regulators and small 
business entities (operators of small PWSs), PFAS are ubiquitous in the 
environment at low concentrations, which necessitates robust laboratory 
analytical precision at these low concentrations. Based on these 
potential implementation issues, the EPA proposed that compositing of 
samples would not be allowed.
2. Summary of Major Public Comments and EPA Responses
    The EPA received comments related to composite sampling. The 
majority of these commenters agreed with the EPA's proposal to not 
allow samples to be composited due to analytical limitations and the 
increased potential for background contamination, along with the 
physical and chemical characteristics of PFAS. A few commenters 
suggested that they believed composite sampling could be implemented 
and would reduce the cost of analyses. Further, some of these 
commenters suggested that with proper guidelines and procedures for 
analyzing samples, possible contamination issues could be mitigated and 
asserted that issues with false negative and positive samples also 
impact discrete samples (i.e., that they are not unique to composite 
sampling).
    The EPA received other comments regarding the specifics of 
composite monitoring. One commenter noted grab samples as more 
appropriate and suggested that individual systems be permitted to 
request alternative sampling methodologies if needed. One other 
commenter suggested that compositing samples from varying EP should not 
be allowed. In addition, one commenter requested that the EPA provide 
information as to the increased risk of compositing samples, along with 
discussion of the proposed departure from the SMF for SOC ahead of rule 
finalization.
    For commenters who offered that composite sampling could be 
implemented, the EPA agrees it would potentially decrease sampling 
analysis costs and that sampling errors can occur when handling and 
analyzing discrete samples. However, the compositing of samples 
necessarily involves additional handling, opening, and transfer steps 
than are required for the collection and analysis of individual 
samples. Therefore, the combining of samples that must be done for 
composite sample analysis represents an increased risk of sampling 
error, which could result in decreased public health protection and 
additional sampling costs. The agency also does not agree that 
alternative sampling methodologies should be permitted and requires the 
use of EPA Methods 533 and 537.1 for monitoring per the requirements of 
the rule. Please see section VII of this preamble for more information 
on methods.
    As discussed previously, PFAS are pervasive in the environment and 
require robust laboratory analytical precision, particularly at low 
concentrations. Accordingly, the EPA agrees with commenters that do not 
support the allowance of composite sampling and maintains that discrete 
sampling is the most appropriate type of sampling for regulated PFAS.
3. Final Rule
    Based on consideration of public comments (many of which supported 
the EPA's concerns about the ubiquitous nature of PFAS at low 
concentrations in the environment, the necessary robust laboratory 
analytical precision required, and potential implications for 
implementation), the final rule does not allow composite samples.

E. Can primacy agencies grant monitoring waivers?

1. Proposal
    Subpart C of 40 CFR 141.24 describes instances where the primacy 
agency may grant waivers predicated on proximity of the system to 
contaminant sources (i.e., susceptibility to contamination) and 
previous uses of the contaminant within the watershed (including 
transport, storage, or disposal). The EPA did not include a provision 
to allow primacy agencies to grant monitoring waivers as a regulatory 
flexibility in the proposed rule. The EPA did, however, request public 
comment on whether to allow systems to apply to the primacy agency for 
a monitoring waiver of up to nine years (one full compliance cycle) if, 
after at least one year of quarterly sampling, the results are below 
the rule trigger level, or for systems that may be approved for reduced 
monitoring, if at least two consecutive results are below the rule 
trigger level. The EPA also requested comment on allowing similar 
monitoring waivers to be granted based on previously acquired 
monitoring data as described in section VIII.C of the preamble for the 
proposed rulemaking. The EPA additionally sought comment on possible 
alternatives to traditional vulnerability assessments that should be 
considered in order to identify systems as low risk and potentially 
eligible for monitoring waivers.
2. Summary of Major Public Comments and EPA Responses
    Several commenters suggested that monitoring waivers should not be 
allowed for this rule. Several additional commenters cited the 
persistence and mobility of PFAS in the environment and advised that 
reduced monitoring frequencies should be no less than every three years 
on the basis that drinking water consumers in unmonitored areas may 
unknowingly be exposed to these PFAS. Furthermore, many other 
commenters suggested that PFAS contamination can migrate significantly 
over a three-year period.
    Many other commenters were supportive of monitoring waivers for 
this rule under certain circumstances. Several commenters indicated 
that waivers would be appropriate if they were based on monitoring 
results. A few commenters recommended that if monitoring waivers were 
to be allowed, that they should not be based solely on a traditional 
vulnerability assessment. A couple of commenters stated that waivers 
based on vulnerability alone should not be allowed during the initial 
monitoring period. One commenter recommended waiting until UCMR 5 
monitoring is complete before allowing monitoring waivers to be granted 
through vulnerability assessments. A couple of commenters suggested 
that waivers be considered if they are based on a combination of 
vulnerability and monitoring results, while one other commenter 
suggested that assessing watershed characteristics to demonstrate 
eligibility for monitoring waivers would be protective of chronic 
health risks. One commenter noted that

[[Page 32618]]

merely allowing waivers to be granted would not necessarily reduce 
public health protection under the rule, as primacy agencies will 
retain the ability to deny waiver applications.
    After consideration of these comments, and due to the mobility and 
persistence characteristics of the regulated PFAS, the final rule does 
not allow monitoring waivers. These specific properties of the 
regulated PFAS and their observed ubiquity in both drinking water and 
within many other sources make waivers impractical and complicate the 
ability to maintain public health protection if such a provision were 
included as part of this rule. Moreover, the EPA is not confident that 
allowing monitoring any less frequently than every three years or 
conducting vulnerability assessments will accurately capture potential 
concentration variations over the long term or protect against risks 
from new contamination sources.
3. Final Rule
    Consistent with the proposal, the final rule does not include a 
provision that would allow primacy agencies to issue monitoring 
waivers. These waivers would increase the potential for public health 
risks and the EPA does not consider them necessary to reduce burdens on 
primacy agencies, water systems and communities given the other 
flexibilities provided in the rule.

F. When must systems complete initial monitoring?

1. Proposal
    Pursuant to section 1412(b)(10), the proposed rule required 
compliance with all aspects of the NPDWR three years after 
promulgation. This included satisfying initial monitoring requirements 
as described in sections VIII.A and VIII.C within the three years 
following rule promulgation.
2. Summary of Major Public Comments and EPA Responses
    In the proposal, the EPA requested public comment on the proposed 
initial monitoring timeframe, particularly for NTNCWS or all systems 
serving 3,300 or fewer. Many commenters expressed support for the EPA 
requiring initial monitoring as soon as possible with a few commenters 
explicitly supporting the EPA's proposed initial monitoring timeframe 
noting it allows sufficient time for water systems to comply with the 
initial monitoring requirements. However, other commenters suggested 
that water systems would not be able to utilize the full three years 
following rule promulgation to perform initial monitoring and take 
actions to ensure compliance with the MCL if monitoring results showed 
elevated levels of PFAS. While the agency agrees that it may be 
difficult to conduct initial monitoring and take necessary remedial 
actions (e.g., treatment installation) within three years, the EPA 
finds that it is practicable for all systems to complete their initial 
monitoring within three years. This is particularly the case since the 
large majority of systems serving greater than 3,300 will have 
sufficient monitoring data from UCMR 5 and many other systems will have 
at least some data to satisfy the rule's initial monitoring 
requirements. Moreover, as described in section XI.D. of this preamble, 
the EPA is exercising its authority under SDWA section 1412(b)(10) to 
implement a nationwide two-year capital improvement extension to comply 
with MCL. Consequently, water systems will have up to the full three 
years following rule promulgation to plan and conduct monitoring and 
still have two additional years to complete any actions needed to 
comply with the MCLs.
    Several commenters suggested that the EPA consider a staggered 
initial monitoring timeframe by system size, such as those used in 
other previous NPDWRs, where, for example, larger sized systems conduct 
monitoring first followed by smaller systems. In the examples provided 
by commenters, this staggered monitoring could also allow systems to 
achieve compliance on a staggered schedule. A few commenters suggested 
that this is necessary to address potential laboratory capacity issues 
and to allow smaller systems additional time to plan and obtain 
resources to conduct the monitoring. The EPA disagrees that staggering 
the monitoring requirements to allow different compliance dates is 
necessary. SDWA 1412(b)(10) specifies that all systems must demonstrate 
compliance three years following rule promulgation except where a state 
or the EPA may grant an extension of up to two additional years to 
comply with MCL(s) if the EPA or the state (for an individual system) 
needs additional time for capital improvements. Therefore, the intent 
of the statute is to allow extensions to complete the capital 
improvements necessary to comply with the MCL. The EPA considers the 
three years sufficient for completing the rule's initial monitoring 
requirement. The EPA's allowance of previously collected monitoring 
data will also significantly reduce the potential for laboratory 
capacity challenges. As previously noted in section VIII.A of this 
preamble, the EPA has revised the required intervals between samples 
collected for initial monitoring under this rule to closely parallel 
the intervals required for UCMR 5, to promote the useability of 
existing data.
    The EPA is not prescribing any staggering of monitoring (e.g., 
based on system size) but encourages primacy agencies to work with the 
systems they oversee to ensure their initial monitoring occurs and 
adjust schedules (within the three years following rule promulgation) 
as appropriate.
3. Final Rule
    The EPA is finalizing the requirement that initial monitoring, or 
demonstration of previously collected data to satisfy initial 
monitoring requirements, must be completed within the three years 
following rule promulgation (i.e., April 26, 2027) to ensure that water 
systems have the information needed to inform decisions to meet the MCL 
compliance date. As described previously and in section XI.D, the EPA 
is providing a two-year capital improvement extension under SDWA 
1412(b)(10), allowing additional time for those systems to comply with 
the MCL. Requiring water systems to conduct initial monitoring within 
the three years following rule promulgation will ensure public health 
protection as soon as practicable and allow these water systems to 
maximize utilization of the capital-improvement extension time. 
Additionally, the flexibility in the final rule for systems to use 
previously acquired monitoring data to satisfy some or all of their 
initial monitoring will reduce the potential for laboratory capacity 
challenges. The EPA encourages systems that may not have available data 
and/or choose to conduct additional monitoring to conduct their initial 
monitoring as soon as practicable following rule promulgation to allow 
for remedial actions that may needed, based on monitoring results, and 
to comply with the MCL by the compliance date.

G. What are the laboratory certification requirements?

1. Proposal
    The EPA proposed that laboratories demonstrate their capability to 
meet the objectives of this regulation. The proposal would require 
laboratories to analyze performance evaluation (PE) samples every year 
for each method and contaminant in order to achieve and maintain 
certification from their primacy agency.
2. Summary of Major Public Comments and EPA Responses
    A few commenters requested that the EPA develop guidance and 
training for

[[Page 32619]]

drinking water laboratory certification programs to evaluate 
laboratories seeking certification. The EPA agrees that training for 
laboratory certification officers is appropriate. The EPA will develop 
training materials and guidance for drinking water certification 
programs to evaluate laboratories to ensure adherence to the 
requirements of EPA Methods 533 and 537.1 (USEPA, 2005b).
    One commenter requested that the EPA establish reciprocity between 
laboratory certification programs to utilize all potential laboratory 
capacity available. As described in the EPA's Manual for the 
Certification of Laboratories Analyzing Drinking Water, laboratory 
certification programs may recognize drinking water laboratory 
certifications (or comparable ``accreditation'') from other laboratory 
certification programs, by reciprocity (USEPA, 2005b). Most laboratory 
certification programs do utilize the practice of reciprocal 
certification. Reciprocal certification can only be granted to 
laboratories utilizing EPA Methods 533 and 537.1.
3. Final Rule
    Under the final rule, certified laboratories must demonstrate their 
capability to meet the objectives of this regulation. Laboratories are 
required to analyze PE samples every year for each method and 
contaminant in order to achieve and maintain certification from their 
primacy agency.

H. Laboratory Quality Assurance/Quality Control

    In the proposal, the EPA requested comment on other monitoring-
related considerations including quality assurance/quality control (QA/
QC) associated with drinking water sampling and analysis.
    Many commenters suggested the potential for false positives to 
misrepresent actual levels of the regulated PFAS within the drinking 
water sample due to the ubiquity of PFAS and the possible background 
interference. The EPA is aware of the potential for background 
contamination due to the ubiquitous nature of PFAS in the environment. 
The EPA agrees that PFAS sampling is highly sensitive and there is 
potential for sample contamination. However, with proper training tools 
and communications, that potential can be mitigated, though not 
sufficiently enough to allow for composite sampling as discussed in 
section VIII.D of this preamble. For example, the UCMR program has 
released several sampling guidance documents and a small-systems 
sampling video to assist small and medium utilities with the PFAS 
sampling. These products have also been distributed to the UCMR 
laboratory community, which has been encouraged to share them with 
their PWS clients.
    Also, Method 533 and Method 537.1 require the analysis of an LRB 
with each extraction batch. If method analytes are detected at or above 
\1/3\ the minimum reporting level, suggestive of background 
contamination, all positive field sample results associated with that 
extraction batch are invalid for the impacted analytes. Both methods 
also require the analysis of an FRB (a blank that is prepared at the 
sampling location) when any PFAS are detected above the minimum 
reporting level in field samples. The use of laboratory and field 
blanks were incorporated into the methods as QC to reduce the potential 
for false positives due to background contamination.

IX. Safe Drinking Water Act (SDWA) Right To Know Requirements

A. What are the Consumer Confidence Report requirements?

1. Proposal
    A community water system (CWS) must prepare and deliver to its 
customers an annual Consumer Confidence Report (CCR) in accordance with 
requirements in 40 CFR part 141, subpart O. A CCR provides customers 
with information about their local drinking water quality as well as 
information regarding the water system's compliance with drinking water 
regulations. The EPA proposed that CWSs be required to report detected 
PFAS in their CCRs, specifically, PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and 
PFBS, and the Hazard Index for mixtures of PFHxS, PFNA, HFPO-DA, and 
PFBS. The EPA also proposed adding paragraph (g) to 40 CFR 141.154 that 
would require health effects language be provided when any regulated 
PFAS is measured above the maximum contaminant level (MCL), in addition 
to those with an MCL violation.
2. Summary of Major Public Comments and EPA Responses
    A few commenters requested clarification of the health effects 
language included in the CCR. Specifically, a couple of commenters said 
the proposed standard health effects language included in the CCR for a 
Hazard Index MCL exceedance was not clear. Commenters found some of the 
language regarding the Hazard Index MCL to be confusing and offered 
suggestions for clarification. The EPA has considered this input and 
revised the health effects language associated with PFAS exposure, 
including the Hazard Index.
    A few of commentors raised concerns about requiring reporting of 
results below the practical quantitation level (PQL) in the CCR as 
these data may not be quantified with what they deem is appropriate 
precision. One commentor requested that any detected PFAS, not just the 
six regulated contaminants, be reported in the CCR. The EPA disagrees 
with commenters who voice concern over reporting measurements below the 
PQLs for PFOA and PFOS as ``detected'' contaminants in the CCR. 
Reporting these measurements in the CCR will allow customers to 
understand that the contaminant was detected in the water supply. While 
measurements below the PQL will not be used to calculate compliance 
with MCLs for the final rule, measurements lower than the PQL are 
achievable by individual laboratories, and therefore these measurements 
can be used for screening, to determine compliance monitoring 
frequency, and to educate consumers about the existence of PFAS (for 
further discussion of PQLs for regulated PFAS, please see section VII 
of this preamble). As such, the EPA believes that measurements below 
the PQL can reasonably be reported as ``detected'' for purposes of the 
CCR. This requirement is consistent with the CCR Rule in 40 CFR 
141.153(d) which requires CWSs to report information on detected 
contaminants for which monitoring was required by the EPA or the state. 
The CCR reporting requirement includes unregulated contaminants for 
which monitoring is required pursuant to the Unregulated Contaminant 
Monitoring Rule (UCMR) as well as regulated contaminants in accordance 
with SDWA (Safe Drinking Water Act) 1414(c)(4). If the system has 
performed additional monitoring, the EPA strongly encourages them to 
include the results in the CCR, consistent with 40 CFR 141.153(e)(3).
3. Final Rule
    As part of this action, the EPA has modified the trigger level 
value for quarterly monitoring from one-third of the MCL to one-half of 
the MCL in response to concerns that laboratories would not have the 
capacity to consistently measure as low as the threshold of one-third 
of the MCL (for further discussion of the EPA's trigger levels for the 
final rule, please see section VIII of this preamble). To reflect this 
change in the trigger level, the EPA has modified 40 CFR 141.151(d), 
which identifies what is considered detected

[[Page 32620]]

for purposes of reporting in CCRs consistent with SDWA 1414(c)(4). The 
EPA had also proposed adding a provision to require CWSs that detect 
any PFAS above the MCL to include health effects language for PFAS and 
stated in the preamble for the rule proposal that CWSs would be 
required to report detected PFAS as part of their CCRs. Because SDWA 
1414(c)(4)(B) specifies that the Administrator may only require health 
effects language be reported in the CCR for situations other than an 
MCL violation for not more than three regulated contaminants, the EPA 
has removed the amendment to paragraph (g) of 40 CFR 141.154 included 
in the proposed rule from the final rule and has instead updated 
appendix O to part 141 for the final rule to only require CWSs that 
have violations of the PFAS MCLs to include health effects language for 
PFAS. Since systems must complete initial monitoring within three years 
of rule promulgation, systems will be required to report results and 
other required information in CCRs beginning with 2027 reports. As the 
MCL compliance date is set at five years following rule promulgation, 
systems will be required to report MCL violations in the CCR, 
accompanied by the required health effects language and information 
about violations, starting in 2029.
    The EPA acknowledges the need to protect public health with clear 
and concise language that outlines the risks associated with exposures 
exceeding the MCLs and Hazard Index. The EPA's broad review of the most 
current research provides a comprehensive understanding of how exposure 
to PFAS may result in adverse impacts on the health of individuals. In 
response to commenter requests for plain language explanations of the 
Hazard Index, the EPA is adding the following definition of the Hazard 
Index in 40 CFR 141.153(c)(3)(v) of the CCR Rule to improve clarity and 
understandability for consumers (for more information on how the Hazard 
Index is calculated for this rule, please see table to paragraph (b) 
under 40 CFR 141.50):
    Hazard Index or HI: The Hazard Index is an approach that determines 
the health concerns associated with mixtures of certain PFAS in 
finished drinking water. Low levels of multiple PFAS that individually 
would not likely result in adverse health effects may pose health 
concerns when combined in a mixture. The Hazard Index MCL represents 
the maximum level for mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS 
allowed in water delivered by a public water system. A Hazard Index 
greater than one (1) requires a system to take action.
    Additionally, in response to commenters' request for clearer 
mandatory health effects language, the final rule includes revised 
mandatory health effects language required as part of CCRs, in cases 
when MCL violations have occurred.\10\ Identical mandatory health 
effects language is also required for public notification (PN) under 
the final rule (PN requirements are described further in section IX.B 
of this preamble). The mandatory health effects language in the final 
rule reads as follows:
---------------------------------------------------------------------------

    \10\ The EPA has developed the existing mandatory health effects 
language to communicate accurate, clear health information to a non-
technical audience. Although the EPA believes additional detail is 
not necessary to include in the mandatory health effects language 
which is required only where MCL violations have occurred, the EPA 
also recognizes that, in general, a single exposure at a critical 
time in development may produce an adverse developmental effect (see 
USEPA, 1991a).
---------------------------------------------------------------------------

    Health effects language for PFOA: Some people who drink water 
containing PFOA in excess of the MCL over many years may have increased 
health risks such as cardiovascular, immune, and liver effects, as well 
as increased incidence of certain types of cancers including kidney and 
testicular cancer. In addition, there may be increased risks of 
developmental and immune effects for people who drink water containing 
PFOA in excess of the MCL following repeated exposure during pregnancy 
and/or childhood.
    Health effects language for PFOS: Some people who drink water 
containing PFOS in excess of the MCL over many years may have increased 
health risks such as cardiovascular, immune, and liver effects, as well 
as increased incidence of certain types of cancers including liver 
cancer. In addition, there may be increased risks of developmental and 
immune effects for people who drink water containing PFOS in excess of 
the MCL following repeated exposure during pregnancy and/or childhood.
    Health effects language for PFHxS: Some people who drink water 
containing PFHxS in excess of the MCL over many years may have 
increased health risks such as immune, thyroid, and liver effects. In 
addition, there may be increased risks of developmental effects for 
people who drink water containing PFHxS in excess of the MCL following 
repeated exposure during pregnancy and/or childhood.
    Health effects language for PFNA: Some people who drink water 
containing PFNA in excess of the MCL over many years may have increased 
health risks such as elevated cholesterol levels, immune effects, and 
liver effects. In addition, there may be increased risks of 
developmental effects for people who drink water containing PFNA in 
excess of the MCL following repeated exposure during pregnancy and/or 
childhood.
    Health effects language for HFPO-DA: Some people who drink water 
containing HFPO-DA in excess of the MCL over many years may have 
increased health risks such as immune, liver, and kidney effects. There 
is also a potential concern for cancer associated with HFPO-DA 
exposure. In addition, there may be increased risks of developmental 
effects for people who drink water containing HFPO-DA in excess of the 
MCL following repeated exposure during pregnancy and/or childhood.
    Health effects language for Hazard Index PFAS: Per- and 
polyfluoroalkyl substances (PFAS) can persist in the human body and 
exposure may lead to increased risk of adverse health effects. Low 
levels of multiple PFAS that individually would not likely result in 
increased risk of adverse health effects may result in adverse health 
effects when combined in a mixture. Some people who consume drinking 
water containing mixtures of PFAS in excess of the Hazard Index (HI) 
MCL may have increased health risks such as liver, immune, and thyroid 
effects following exposure over many years and developmental and 
thyroid effects following repeated exposure during pregnancy and/or 
childhood.

B. What are the Public Notification (PN) requirements?

1. Proposal
    As part of SDWA, the PN Rule ensures that consumers will know if 
there is a problem with their drinking water. Notices alert consumers 
if there is risk to public health. They also notify customers: if the 
water does not meet drinking water standards; if the water system fails 
to test its water; if the system has been granted a variance; or if the 
system has been granted an exemption (that is, more time to comply with 
a new regulation).
    All public water systems (PWSs) must give the public notice for all 
violations of National Primary Drinking Water Regulations (NPDWRs) and 
for other situations. Under the EPA's PN Rule, the public notice 
requirements for each violation or situation are determined by the tier 
to which it is assigned. The EPA specifies three categories, or tiers, 
of PN requirements, to take into account the seriousness of the 
violation or situation and any potential adverse health effects that 
may occur (USEPA, 2000f). The

[[Page 32621]]

EPA proposed that violations of the three MCLs in the proposal be 
designated as Tier 2 and as such, PWSs would be required to comply with 
40 CFR 141.203. Per 40 CFR 141.203(b)(1), notification of an MCL 
violation should be provided as soon as practicable but no later than 
30 days after the system learns of the violation. The proposed rule 
also designated monitoring and testing procedure violations as Tier 3, 
which would require systems to provide notice no later than one year 
after the system learns of the violation. The system would then be 
required to repeat the notice annually for as long as the violation 
persists.
2. Summary of Major Public Comments and EPA Responses
    Many commenters support the Tier 2 PN requirement for MCL 
violations. Commenters assert that Tier 2 notification is appropriate 
and consistent with other MCLs for chemicals with chronic effects. 
Conversely, many commenters suggest that the PN tiering be raised from 
Tier 2 to Tier 1 or that the EPA consider other PN approaches given 
concerns about health impacts resulting from exposure on timescales 
shorter than chronic exposure. Commenters assert that raising PN for 
MCL violations from Tier 2 to Tier 1 would ensure that consumers are 
informed of potential harm associated with elevated PFAS levels in a 
timelier manner so they can make informed risk management decisions. 
Additionally, a few commenters request the EPA re-categorize repeat MCL 
violations to Tier 3 due to the expected length of time needed for a 
PWS to design and construct treatment. Commenters argue that quarterly 
PN would not offer added value and could possibly result in confusion 
for consumers.
    The EPA agrees with commenters that Tier 2 PN is appropriate for 
MCL violations based on analysis of a wide range of scientific studies 
that shows that long-term exposure may have adverse health effects. The 
EPA disagrees with commenters who recommend issuing Tier 1 notification 
for MCL violations. Tier 1 notices must ``be distributed as soon as 
practicable, but no later than 24 hours, after the public water system 
learns of the violation'' pursuant to section 1414(c)(2)(C)(i) of SDWA. 
The PN Rule preamble characterizes contaminants with violations 
routinely requiring a Tier 1 notice as those with ``a significant 
potential for serious adverse health effects from short-term 
exposure'', stating that other violations do not require Tier 1 notice 
because elevated levels of these contaminants are not ``strongly or 
consistently linked to the occurrence of the possible acute health 
effects'' (USEPA, 2000f). The EPA has not characterized health risks 
resulting from acute exposure (i.e., < or = 24 hours) to PFAS and the 
EPA believes that issuing Tier 2 PN for MCL violations constitutes a 
health protective approach given that the MCLG values are based on 
health effects that occur after chronic exposure to PFAS (i.e., 
cancer). Based on the available health effects information, the EPA has 
characterized developmental effects, including immune impacts, 
associated with developmental PFAS exposure in addition to health 
effects that occur after chronic exposure. The agency considers it 
reasonable to notify consumers within 30 days of a PWS learning of an 
MCL violation because it generally provides protection of the adverse 
health effects that may occur from exposure to PFAS during sensitive 
lifestages such as gestation. The EPA typically reserves Tier 1 
notifications for acutely toxic contaminants. For example, nitrate, 
nitrite, or total nitrate and nitrite require Tier 1 notice because 
exceedances can result in immediate life-threatening health impacts for 
infants (i.e., methemoglobinemia). Based on the currently available 
information, the developmental and chronic effects associated with 
exposure to these PFAS are not known to represent immediate acute 
health effects. For more information on the EPA's characterization of 
health effects resulting from PFAS exposure, please see (USEPA, 2024c; 
USEPA, 2024d). This approach is also consistent with the PN 
requirements for other synthetic organic contaminants regulated under 
SDWA. The EPA acknowledges that there may be instances in which it is 
appropriate to elevate the tiering of PN on a case-by-case basis. Under 
the existing PN Rule in 40 CFR 141.202(a), a violation that routinely 
requires a Tier 2 notice but poses elevated risk from short-term 
exposure may be elevated to Tier 1 at the discretion of the primacy 
agency (USEPA, 2000f). Additionally, the EPA will develop appropriate 
implementation guidance to assist in the understanding of PN 
requirements among other final rule requirements.
    The EPA disagrees with commenters that recommended reclassifying 
ongoing MCL violations to Tier 3 for repeat notices. The EPA believes 
there is sufficient flexibility in the existing PN Rule 40 CFR 
141.203(b)(2) that allows primacy agencies to allow a less frequent 
repeat notice on a case-by-case basis for unresolved violations, but no 
less than once per year, and the determination must be in writing. The 
EPA believes repeat notices are valuable to consumers that may not 
receive the initial notice and allow water systems to provide any 
updates to consumers, such as actions being taken to resolve the 
situation and estimated timelines.
    A few commenters recommended that the EPA update the proposed PN 
health effects language. Commenters stated that the proposed health 
effects language was confusing and needed to be clarified as it did not 
sufficiently explain the health effects resulting from PFAS exposure. 
Additionally, commenters stated that further clarifying the health 
effects language would mitigate confusion from customers when receiving 
PN from their water system.
    The EPA agrees with commenters that additional explanation of the 
health effects of PFAS exposure will more effectively communicate risk 
to consumers when they receive PN from their water system. The EPA has 
considered this input and has revised health effects language for the 
final rule to further clarify the health effects associated with PFAS 
exposure.
3. Final Rule
    The final rule requires the PN of violations of all MCLs 
promulgated under this final rule to be designated as Tier 2 and as 
such, PWSs would be required to comply with 40 CFR 141.203. The final 
rule also designates monitoring and testing procedure violations as 
Tier 3, requiring systems to provide notice no later than one year 
after the system learns of the violation. Systems are also required to 
repeat the notice annually for as long as the violation persists. As 
systems must comply with initial monitoring requirements within three 
years of rule promulgation, systems will be required to provide Tier 3 
notification for monitoring and testing procedure violations starting 
in 2027. As the MCL compliance date is set at five years following rule 
promulgation, systems will be required to provide Tier 2 notification 
for MCL violations starting in 2029. However, the EPA acknowledges that 
primacy agencies have the authority in the existing PN Rule (table 1 to 
Sec.  141.201) to require systems to provide notices to consumers prior 
to the MCL compliance date. The EPA encourages primacy agencies to use 
this flexibility to require systems to provide notices to consumers for 
PFAS detections that precede the date that MCL compliance will take 
effect, as they deem appropriate. By encouraging systems to provide 
timely notification, it

[[Page 32622]]

allows customers to take actions to protect their health, such as using 
a filter, while systems take necessary steps to apply treatment.
    With respect to violations and reporting associated with the 
individual MCLs and Hazard Index MCL, the EPA recognizes that a utility 
may have two or more of these PFAS present that, over the course of 
four quarterly samples, may result in violation of multiple MCLs. For 
example, if, following four quarterly samples, a utility has PFHxS and 
HFPO-DA present and the RAA is above their respective MCLs and HBWCs of 
10 ng/L, the system would be in violation of both the individual MCLs 
for PFHxS and HFPO-DA, as well as the Hazard Index MCL. Issuing 
multiple notifications (three in this example) for these violations may 
cause public confusion as the adverse health effects and exposure 
concern in this instance is not meaningfully different from either a 
Hazard Index or individual MCL perspective. To simplify implementation 
of PN in this scenario, the EPA is finalizing requirements in appendix 
A to subpart Q of part 141 such that utilities who violate the Hazard 
Index MCL and one or more individual MCLs because of the same compounds 
can issue one notification to satisfy the PN requirements for the 
multiple violations.
    The EPA has also made edits to clarify the mandatory health effects 
language required in the PN of an MCL violation, as well as the CCR. 
The mandatory health effects language required for both PN and CCRs is 
summarized in section IX.A.3 of this preamble above.

X. Treatment Technologies

    Section 1412(b)(4)(E) of the Safe Drinking Water Act (SDWA) 
requires that the agency ``list the technology, treatment techniques, 
and other means which the Administrator finds to be feasible for 
purposes of meeting [the MCL],'' which are referred to as best 
available technologies (BATs). The EPA generally uses the following 
criteria for identifying ``feasible'' BATs: (1) The capability of a 
high removal efficiency; (2) a history of full-scale operation; (3) 
general geographic applicability; (4) reasonable cost based on large 
metropolitan water systems; (5) reasonable service life; (6) 
compatibility with other water treatment processes; and (7) the ability 
to bring all the water in a system into compliance. Section 
1412(b)(4)(E)(ii) of SDWA requires that the agency identify small 
system compliance technologies (SSCTs), which are affordable treatment 
technologies, or other means that can achieve compliance with the 
maximum contaminant level (MCL).
    In the proposed rule, the EPA requested comments on: technologies 
designated as BATs, costs associated with nontreatment options; whether 
employing these treatment technologies are sound strategies to address 
PFAS as well as whether the BATs could feasibly treat to below the 
proposed MCLs; the type of assistance that would help public water 
systems (PWSs); potential benefits from co-removal; treatment residual 
disposal estimates; the capacity to address the increased demand for 
BATs as well as residuals disposal or reuse; impacts that PFAS 
residuals disposal may have in communities adjacent to the disposal 
facilities; the most appropriate disposal means for PFAS contaminated 
residuals and waste the systems may be generating; and SSCT selection 
as well as national affordability analysis, specifically on the 
methodologies.

A. What are the best available technologies?

1. Proposal
    The agency proposed GAC, AIX, NF, and RO as BATs for the six PFAS 
under consideration in the proposed rule. The EPA also acknowledged 
that there are nontreatment options which may be used for compliance 
such as replacing a PFAS-contaminated drinking water source with a new 
uncontaminated source. The EPA also stated that conventional and most 
advanced water treatment methods are ineffective at removing PFAS.
2. Summary of Major Public Comments and EPA Responses
    The vast majority of comments germane to the BAT designations 
support the EPA's designation of granular activated carbon (GAC), anion 
exchange resins (AIX), and high-pressure membranes (nanofiltration (NF) 
and reverse osmosis (RO)) as BATs that are technologically feasible for 
treating drinking water to the proposed standards or below. Many 
commenters shared practical experience with installed treatment 
including successes, costs, implementation considerations, challenges, 
and other areas. The EPA agrees that GAC, AIX, RO, and NF are BATs and 
consistent with the criteria outlined in the BAT/SSCT document for 
identifying ``feasible'' treatment for PFAS in this rule, and the 
comments providing information on practical full-scale experience with 
these technologies further support for this finding.
    A few commenters suggested either that the designated BATs could 
not treat to or below the MCL or that not enough data was available to 
support the conclusion that the BATs could treat to at or below the 
proposed MCL. The EPA disagrees with these commenters based on the 
history of full-scale use as documented in the Best Available 
Technologies and Small System Compliance for Per- and Polyfluoroalkyl 
Substances (PFAS) in Drinking Water document (USEPA, 2024l), the 
information in the rule preamble, and in the comments that provided 
full-scale data as well as case studies. For example, commenters 
highlighted more than 45 military installations that have treated PFAS, 
including those in this rule, successfully for more than 15 years, a 
major water treatment company provided information on over 150 
successful installations they had performed, and comments supported 
that there are significant numbers of industrial users successfully 
treating PFAS, including those in this rule. One commenter noted the 
example of the Chemours Fayetteville facility which used GAC to 
eliminate PFAS, including those in this rule, as high as 345,000 ng/L 
and has reduced PFAS in effluent to non-detect levels for several PFAS. 
Finally, the Water Quality Association reviewed proprietary performance 
data from its accredited laboratory demonstrating that this standard is 
feasible for the BATs selected to effectively remove the PFAS regulated 
in this rule from drinking water.
    Many commenters pointed out site-specific issues with particular 
BATs. The EPA acknowledges that not every BAT represents the best 
treatment option for an individual system and site-specific 
considerations can limit BAT selection. For instance, residuals 
management considerations can limit the choice of RO/NF; particularly 
in states with limited water resources. While many commenters agreed 
that high pressure membranes such as RO and NF can remove the six PFAS 
included in the proposal, many commenters also suggested that high 
pressure membranes may not be the most feasible treatment option for 
some systems because of residual management considerations, which are 
discussed in the residuals management section. There are, however, 
documented RO/NF facilities for treating PFAS in California, Illinois, 
North Carolina, and Alabama (USEPA, 2024l). In response to public 
comment and residual management concerns surrounding high pressure 
membrane technologies, the EPA has adjusted RO/NF's technology 
projection compliance forecast to 0% in the EA. While the EPA

[[Page 32623]]

does not estimate any water systems will elect to install RO/NF to 
comply with the PFAS rule, it remains a BAT for water systems to 
consider. For additional details on the EPA's EA, please see section 
XII.
    The EPA also acknowledges that due to technical site-specific 
considerations, some BATs may not be the best choice for particular 
water types. PFAS treatment option selection should consider conditions 
for a given utility including water quality, available space, disposal 
options, and currently installed unit operations. AIX may be the 
preferred technology for some utilities based on expected treatment 
needs, while others may select GAC or other technologies. However, as 
many commenters indicated, the BAT designations are appropriate for 
water systems across the country.
    Several commenters pointed out that GAC may release arsenic at 
levels exceeding arsenic's MCL temporarily when installed and upon 
changing media, deleteriously impacting finished water quality. While 
the EPA has documented challenges surrounding GAC and arsenic (USEPA, 
2024l), the EPA disagrees that the arsenic release poses an exposure 
concern so long as appropriate procedures are followed. Those 
procedures include discarding the initial bed volumes (BVs) after 
installation or replacement of media. A bed volume is the volume of 
liquid contained within a GAC contactor, it is the container volume 
minus the solids volume and void space. The quantity of treated water 
discarded can be significant (e.g., as high as 350 BVs as one commenter 
noted). However, this amount of discarded water is low in comparison to 
the normal service life between GAC replacement, which is approximately 
84,000 BVs or approximately about 0.5% of the total treated volume. The 
total water volume discarded is also low in comparison to water loss 
through leaks across the United States, which account for about 15% of 
treated water or what would be approximately 12,600 BV equivalents for 
this system. While conserving water is a significant issue, the water 
discarded due to GAC applications is relatively low. Systems can reduce 
water discard associated with BAT implementation by using acid washed 
and/or prerinsed GAC or using buffered/pre-flushed resins for AIX. Any 
treatment technology can create problems if improperly maintained and 
operated. Finally, GAC has been statutorily designated as ``feasible 
for the control of synthetic organic chemicals,'' such as PFAS, in SDWA 
section 1412(b)(5).
    The EPA received many suggestions for additional BATs including 
powdered activated carbon (PAC), alternative sorbents, and new 
destructive technologies. However, these alternative BATs proposed, 
except for PAC, currently lack demonstrated full-scale removal of the 
six PFAS under consideration. The EPA notes that there are some reports 
of PAC use on a temporary basis and that it can reduce PFAS 
concentrations in drinking water. PAC may be an appropriate choice of 
technology in certain circumstances, however, its efficacy for trace 
removal tends to be variable due to factors such as carbon particle 
size, background organics, and plant efficiency. Therefore, PAC is not 
as effective as GAC overall, and the agency has not designated it as a 
BAT. The EPA periodically reevaluates treatment technologies and may 
add additional technologies based on updated information. It is 
important to note that water systems may use any technology or practice 
to meet the PFAS MCLs and are not limited to the BATs in this rule. 
Other technologies may be chosen in lieu of BAT because they may be 
more cost effective or better suited to the specific operating 
conditions of the particular site to meet the MCL. Electing not to use 
a BAT, however, means that a system will not be eligible for a variance 
under SDWA section 1415(a)(1)(A). For example, if a facility does not 
install GAC where it is the designated BAT, but uses PAC instead, and 
fails to meet the MCL, the facility would not be eligible for a 
variance under SDWA section 1415(a)(1)(A). On the other hand, the same 
facility may be eligible for an exemption under SDWA section 1416 if, 
for example, GAC could not be installed due to an inability to obtain 
financing and PAC was used instead, and the facility failed to meet the 
MCL.
    Many commenters pointed out the need for increased research, 
technological innovation, and guidance in treating drinking water for 
PFAS. The available information is sufficient to finalize the BATs as 
proposed but the EPA agrees that more research may be beneficial 
(USEPA, 2022c). With respect to the EPA's request for public comment on 
additional guidance materials that would be helpful to support 
successful technical implementation of the rule, the EPA received many 
comments related to the need for technical materials to support rule 
implementation. The agency plans to collaborate with states, technical 
assistance providers, industry associations and interested 
stakeholders, including small systems, following the rule promulgation 
to provide technical materials that can assist water systems in 
complying with the regulations. The EPA is currently funding many 
technical assistance efforts associated with PFAS, including supporting 
treatment infrastructure projects through the Drinking Water State 
Revolving Fund (DWSRF) and the Emerging Contaminant grant program as 
designated and funded through the Bipartisan Infrastructure Law (BIL).
    Many commenters supplied information related to capital as well as 
operations and maintenance costs. Many commenters expressed concerns 
over potential costs and capacity while some commenters expressed the 
opposite opinion. These issues are further addressed in the EPA cost 
analysis in section XII and within the EPA's Response to Public 
Comments on the Proposed PFAS NPDWR (USEPA, 2024k). For additional 
discussion regarding the feasibility of the final MCLs, please see 
section V of this preamble above.
    Many comments pointed to potential supply chain issues in both 
material and technical capacity such as qualified personnel, including 
certified operators. While there may be some supply chain issues in the 
short-term, comments from BAT suppliers indicate excess capacity as 
well as investment in production. Furthermore, while there may be 
temporary difficulties in supply chain and technical capacity, the 
structural demand increase is expected to lead to supply increases as 
well as innovation such as proposed technologies which were not 
designated as BATs. This has been historically demonstrated multiple 
times in prior drinking water rules. For example, activated alumina was 
listed as one of the BATs and a SSCT for arsenic removal in the Arsenic 
Rule (USEPA, 2001), and acknowledgement was given to granular ferric 
hydroxide media as a developing technology. While the granular ferric 
hydroxide media was not selected as a BAT/SSCT at the time due to lack 
of full-scale demonstration, these media became the predominant 
approach to addressing arsenic: Rubel (2003) stated that new iron-based 
materials could be ``employed economically on a spent media basis 
without the incorporation of pH adjustment chemicals and equipment.'' 
McCullough et al. (2005) cited over a dozen demonstration sites across 
the US implementing granular iron media treatment technologies, 
providing further supporting evidence that new technologies evolved in 
the wake of the Arsenic rule to provide more efficient and economical 
treatment

[[Page 32624]]

systems. Additionally, the present statutory standard for ``best 
available technology'' under 1412(b)(4)(D) represents a change from the 
provision prior to 1986, which required the EPA to judge feasibility on 
the basis of ``best technologies generally available'' (BTGA). The 1986 
Amendments to the SDWA changed BTGA to BAT and added the requirement 
that BAT must be tested for efficacy under field conditions, not just 
under laboratory conditions. The legislative history explains that 
Congress removed the term ``generally'' to assure that MCLs ``reflect 
the full extent of current technology capability'' [S. Rep. No. 56, 
99th Cong., 1st Sess. at 6 (1985)]. Read together with the legislative 
history, the EPA has concluded that the statutory term ``best available 
technology'' is a broader standard than ``best technology generally 
available,'' and that this standard allows the EPA to select a 
technology that is not necessarily in widespread use, as long as its 
performance has been validated in a reliable manner. Indeed, the 1991 
Lead and Copper Rule stated, ``as long as it has been tested beyond the 
laboratory under full-scale conditions for other contaminants, and the 
performance of the technology for lead and copper may reasonably be 
projected based upon other available treatment data (i.e., laboratory 
or pilot scale), the EPA believes the technology can be established as 
BAT.''
    With respect to the challenges raised by commenters surrounding 
capital improvement, the EPA has provided compliance flexibility by 
providing a two-year capital improvements extension of the MCL 
compliance deadline allowed by section 1412(b)(10) of SDWA. 
Additionally, the EPA will continue its research as well as outreach 
efforts to help develop technical and operator capacities. For comments 
and additional information regarding the implementation timeframe for 
this rule, please see section XI.D.
    Many commenters stated that permitting needs to be streamlined and 
that more assistance should be proffered to primacy agencies, 
utilities, and other interested stakeholders. While SDWA does not 
require permits, state and local authorities often require permits for 
the installation of treatment facilities at water systems. The EPA has 
developed supporting rule documents such as the Best Available 
Technologies and Small System Compliance for Per- and Polyfluoroalkyl 
Substances (PFAS) in Drinking Water document (USEPA, 2024l) that can be 
used to help permitting authorities develop more familiarity with these 
technologies over time. After finalization of the PFAS National Primary 
Drinking Water Rule (NPDWR), the EPA also intends to work with 
stakeholders to provide support to utilities, primacy agencies, and 
other interested parties to ensure successful rule implementation.
3. Final Rule
    In the final rule, the EPA is codifying GAC, AIX, NF, and RO as 
BATs. The record does not support including additional BATs at this 
time. A BAT designation is informational, and while installation of the 
BAT is a condition of a variance under section 1415(a)(1)(A), systems 
without a variance are not required to use a BAT for MCL compliance. 
The owner/operator of a PWS will need to consider site specific 
circumstances as well as technical, economic, and local regulatory 
considerations when choosing a compliance technology for this rule. To 
address the challenges raised by commenters surrounding capital 
improvement, the EPA has provided a two-year compliance extension for 
capital improvements which is discussed in greater detail in section XI 
(Rule Implementation and Enforcement) and will continue its research 
efforts. The two-year capital improvement extension should also provide 
time for development of technical capacities and qualified personnel 
including certified operators. In response to public comment and in 
acknowledgement of residuals management concerns surrounding high 
pressure membrane separation technologies, the EPA is lowering RO/NF's 
technology projection compliance forecast in the EA. For comments and 
additional information related to the EPA's cost analysis, please see 
section XII. For comments and additional information regarding the 
implementation timeframe for this rule, please see section XI.D.

B. PFAS Co-Removal

1. Proposal
    The EPA stated that AIX and GAC are effective at removing PFAS and 
there is generally a linear relationship between PFAS chain length and 
removal efficiency shifted by functional group. The EPA also notes that 
perfluoroalkyl sulfonates (PFSA), such as PFOS, are removed with 
greater efficiency than the corresponding perfluoroalkyl carboxylic 
acid (PFCA), such as PFOA, of the same carbon backbone length. 
Additionally, the compounds with longer carbon chains display a smaller 
percentage decrease in average removal efficiency over time (McCleaf et 
al., 2017). These same technologies also remove other long-chain and 
higher carbon/higher molecular weight PFAS as well as total organic 
carbon (TOC, DBP precursors). RO and NF may also remove other 
contaminants including arsenic, TOC, and chromium-VI. In short, the EPA 
noted that this regulation, if finalized, would result in a reduction 
of the six PFAS proposed for regulation, other co-occurring PFAS, and 
other co-occurring contaminants.
2. Summary of Major Public Comments and EPA Responses
    A significant majority of commenters supported the EPA's position 
that treatment technologies which remove PFAS provide ancillary 
benefits by removing other known or potential contaminants. One 
commenter disputed the ability of these technologies to provide 
ancillary benefits, and others suggested that the EPA's proposed 
regulation would provide only limited protection against the many PFAS 
not under consideration in the rule. The EPA disagrees with the 
commenters who state that the proposed regulation would not result in a 
reduction in co-occurring PFAS and other contaminants. Burkhardt et al. 
(2023) used a theoretical approach \11\ to estimate that all but one of 
the PFAS that are quantified by EPA Methods 533 and 537.1 could be 
economically removed by GAC in typical water qualities and that of 428 
PFAS evaluated, 76-87 percent could be cost-effectively treatable. The 
co-removal benefits are well documented in the scientific literature 
and in the evidence submitted by public comment. The Best Available 
Technologies and Technologies and Cost support documents summarize 
literature demonstrating the co-removal capabilities of treatment 
technologies.
---------------------------------------------------------------------------

    \11\ While PFAS are often discussed as a group, the individual 
PFAS species can have a range of different removal efficacies using 
GAC. A theoretical approach for PFAS fills information gaps where 
analytical methods do not exist for all PFAS and testing is 
expensive and time consuming
---------------------------------------------------------------------------

    Some commenters stated that treatment for one PFAS does not 
inherently imply removal of other PFAS. The EPA agrees, as discussed in 
the proposed rule preamble. In general, there is an inverse 
relationship between treatability and toxicity which is tied to the 
carbon backbone (Bellia et al., 2023). Generally, the longer the carbon 
backbone length, the more easily the PFAS is removed by a given 
treatment technology. For example, if PFOA (C8) is targeted for removal 
by the water system, perfluorodecanoic acid (PFDA, C10) would most 
likely be removed as well. However, the converse would not

[[Page 32625]]

be true (i.e., a system targeting PFNA (C9) removal would reduce PFHxA 
(C6) to a lesser extent).
    Some commenters suggested that co-removal would decrease the 
removal efficiency of GAC or AIX and that removal efficiency of non-
target contaminants is lower than it could otherwise be. The EPA agrees 
that the removal of non-targeted contaminants by GAC or AIX can lower 
the PFAS removal efficiency; the agency has accounted for this 
uncertainty in appendix N of the EA (USEPA, 2024e). The EPA also agrees 
that targeting contaminants for removal will be more effective than 
relying on other non-targeted removal. For example, a GAC facility 
designed to remove PFAS will not be as effective at removing DBP 
precursors as a facility designed for that; however, there will still 
be co-removal of DBP precursors which may lead to a reduction in DBPs. 
Ultimately, treatment facilities operate best when tailored to specific 
contaminants or mixture of contaminants unique to that location. For 
additional information on the EPA's co-benefit analysis, please see 
section XII.
    Some commenters expressed concern about co-removal taking 
beneficial ions from water, specifically fluoride ions, and suggested 
that would be an added cost to the rule. The EPA notes that fluoride 
has a legally enforceable MCL of 4.0 mg/L, and a non-enforceable 
secondary standard of 2.0 mg/L to prevent mild or moderate dental 
fluorosis. The EPA also notes that while some PFAS do contain organic 
fluorine bound to carbon, fluorine and fluoride are not the same. The 
BATs identified for the removal of PFAS for drinking water are not 
optimized for the removal of fluoride and do not necessarily provide 
effective removal of naturally occurring fluoride. For example, GAC is 
ineffective for fluoride removal at environmentally relevant pHs 
(USEPA, 2024o).
    Some commenters suggested that co-removal may make it more 
difficult to dispose of materials left over from the drinking water 
treatment processes, known as treatment residuals. For example, GAC may 
remove and concentrate radon or other contaminants to such an extent 
that the spent media is considered hazardous. The EPA believes that 
removing hazardous constituents from drinking water is generally 
beneficial even though it could complicate residual management. More 
details on treatment residuals, are discussed in part C of this 
section.
    Some commenters also suggest more research may be beneficial to 
understanding co-removal. The EPA agrees (USEPA, 2022c).
3. Final Rule
    GAC, AIX, NF, and RO are codified in the final rule as BATs. As 
discussed elsewhere in the record for this final rule, because of PFAS 
co-occurrence and the ability for treatment technologies to co-remove 
co-occurring PFAS and other contaminants, the EPA anticipates the final 
rule will result in significant co-removal public health benefits in 
addition to those benefits from removing the six PFAS being directly 
regulated by this action.

C. Management of Treatment Residuals

1. Proposal
    As part of the BAT evaluation, the EPA reviews full-scale studies 
that fully characterize residual waste streams and disposal options. 
The EPA found that the most likely management options for spent 
material containing PFAS is reactivation for GAC, incineration for 
spent IX resin, and for disposal of RO/NF retentate, treatment and 
discharge via a NPDES compliant facility to surface water or, sanitary 
sewer, or in limited circumstances, underground injection. Large 
volumes of spent GAC and AIX containing PFAS are periodically generated 
and must be removed which does not lend itself to on-site storage over 
time. The EPA stated that the disposal options identified in the 2020 
Interim PFAS Destruction and Disposal Guidance (USEPA, 2020d) are 
landfill disposal, thermal treatment, and in limited circumstances, 
underground injection.
    The EPA recognizes that future actions through statutory 
authorities other than SDWA may have direct or indirect implications 
for the residuals from drinking water treatment. Future hazardous waste 
listings for certain PFAS may limit disposal options for spent drinking 
water treatment residuals containing PFAS and/or potentially increase 
costs. A CERCLA designation as a hazardous substance does not restrict, 
change, or recommend any specific activity or type of waste (USEPA, 
2022l). The EPA evaluated the potential impact on PWS treatment costs 
to PWSs associated with hazardous residual management should PFAS be 
listed as a hazardous waste in the future. For comments and additional 
information related to the EPA's cost analysis, please see section XII.
2. Summary of Major Public Comments and EPA Responses
    While some commenters stated that more research can be beneficial 
to further our understanding of managing PFAS treatment residuals, 
others urged the EPA to proceed with this rulemaking as expeditiously 
as possible in the interest of public health. Others argued that the 
EPA should delay this action until the PFAS Destruction and Disposal 
Guidance is updated. The National Defense Authorization Act for Fiscal 
Year 2020, Public Law 116-92, section 7361, directs the EPA to revise 
the PFAS Destruction and Disposal Guidance triennially; the new 
destruction and disposal guidance is anticipated to be released 
approximately concurrently with this rule and further revisions may be 
expected before the effective dates for this rule. The EPA disagrees 
that the projected significant and direct public health protections for 
drinking water consumers in this rule should be delayed for the 
revision of guidance on management of PFAS waste streams.
    Many commenters expressed concern that not enough was being done to 
manage spent drinking water treatment residuals containing PFAS at the 
end of their useful working life and that residual management amounted 
to media shifting (i.e., taking PFAS from water via sorption media then 
landfilling that media does nothing to reduce the overall amount of 
PFAS). Many commenters stated that landfills and thermal treatment 
facilities can potentially be PFAS sources as the BATs in this rule are 
separative as opposed to destructive technologies.
    The EPA notes that from a mass balance perspective, PFAS removal 
from drinking water is generally anticipated to result in lower 
concentrations of PFAS in the environment. With appropriate controls, 
landfills, and thermal treatment of PFAS contaminated media can 
minimize PFAS releases to the environment (USEPA, 2020d). Sorptive 
media can be incinerated or reactivated. There is also ongoing research 
into destructive and sequestration technologies that may help quantify 
the extent to which PFAS may be destroyed some of which is funded by 
the EPA (USEPA, 2022c).
    Furthermore, it is also important to distinguish between a 
potential environmental release and a direct exposure. A PFAS release 
does not inherently imply human exposure and a release is not 
inherently risky to specific populations. From a risk management 
perspective, while the EPA acknowledges that while each destruction and 
disposal technology has limitations, a potential environmental release 
under point source management is anticipated to be a more health

[[Page 32626]]

protective alternative than human exposure through drinking water.
    Some commenters recommended the EPA consider additional destruction 
and disposal technologies. The EPA notes that disposal and destruction 
technologies are currently available to manage drinking water 
residuals. The EPA appreciates the example destructive technologies, 
and while beyond the scope of finalizing this NPDWR, the agency intends 
to consider additional destruction and disposal technologies in future 
destruction and disposal guidance.
    Many commenters, including destruction and disposal trade 
associations, stated there would be difficulties managing spent 
residuals containing PFAS generated from drinking water treatment. In 
contrast, other commenters stated that there was existing national 
capacity and at least one company stated they were actively evaluating 
investment for additional capacity to handle residuals. The record 
demonstrates that there is existing national capacity to handle spent 
drinking water residuals containing PFAS in a manner that minimizes 
risk to human health. Destruction and disposal of PFAS-containing 
materials is currently not subject to certain hazardous waste 
regulation and therefore the materials may be managed in non-hazardous 
and hazardous waste treatment and disposal systems (USEPA, 2020d). 
Hazardous waste is regulated pursuant to RCRA authority 42 U.S.C. 6921-
6939 (also known as RCRA ``Subtitle C''). The regulatory definition of 
hazardous waste is found in 40 CFR 261.3. PFAS are currently not a 
listed hazardous waste or characterized as a hazardous waste, but a 
PFAS-containing waste may meet the regulatory definition of hazardous 
waste if PFAS is mixed with a listed hazardous waste or if a PFAS-
containing mixture exhibits a hazardous characteristic (e.g., 
corrosivity or another characteristic stemming from the material that 
is mixed with PFAS). PFAS which are commingled with hazardous 
substances and/or hazardous wastes will be subject to the appropriate 
rules and regulations and may be included as Applicable or Relevant and 
Appropriate Requirements on a site-specific basis. Not all disposal 
sites may be appropriate for spent drinking water treatment residuals 
containing PFAS and the EPA strongly encourages owners and operators of 
treatment facilities to refer to appropriate and up-to-date guidance on 
treatment residual management such as the 2020 Interim Guidance on the 
Destruction and Disposal of Perfluoroalkyl and Polyfluoroalkyl 
Substances and Materials Containing Perfluoroalkyl and Polyfluoroalkyl 
Substances (USEPA, 2020d) and subsequent updates.
    The EPA anticipates approximately 226,500 short tons of spent 
drinking water media such as activated carbon and AIX resin to be 
generated annually as a result of this rule; in calendar year 2018 
alone, the U.S. generated about 290 million short tons of waste (USEPA, 
2022m). The increase in total waste caused by this action is 
approximately 0.08% of the total U.S. waste produced. This is a minor 
change in aggregate waste produced; the same amount as a pound 
contributes to a ton. Even if PFAS were to be designated in the future 
as regulatory hazardous waste, there is existing capacity to handle 
these waste streams through existing hazardous waste facilities in 
every state. Some water systems may have to ship hazardous wastes 
significant distances; however, the main cost driver is disposal fees 
not transportation. The EPA rejects the assertion that it has not 
evaluated if sufficient capacity exists for disposal and storage of 
PFOA and PFOS contaminated materials. The EPA also acknowledges that 
CERCLA section 104(c)(9) does not allow the agency to initiate a 
remedial action, unless the state first enters into a state Superfund 
State Contract or Cooperative Agreement (CA) that assures the 
availability of adequate capacity to manage hazardous wastes generated 
in the state for 20 years following the date of the response agreement. 
The EPA's rulemaking designating PFOA and PFOS as CERCLA hazardous 
substances, if finalized, does not impose any capacity concerns that 
require further action under section 104(c)(9). In that action, the EPA 
is designating PFOA and PFOS as CERCLA hazardous substances. No PFAS 
are currently listed, or being proposed to be listed, as hazardous 
wastes under RCRA. The 2021 Biennial Report Summary Results indicate 
about 18 million tons of hazardous wastes are normally generated 
annually. Drinking water treatment materials then would constitute 
about a 1.26% increase in hazardous wastes generated annually. Since 
there is over twenty years' capacity, the relatively small magnitude of 
the increase indicates that waste management capacity is sufficient in 
the short term should PFAS be designated as regulatory hazardous 
wastes.
    Many commenters conveyed concern over the cost of drinking water 
residuals management resulting from finalizing this rule. The EPA 
conducted an EA to help address these concerns. For comments and 
additional information related to the EPA's cost analysis, please see 
section XII.
    While no PFAS are currently listed as regulatory hazardous wastes 
under RCRA, in response to stakeholder feedback, the EPA included a 
sensitivity analysis to determine the impact on water systems should 
they be required to handle and dispose of PFAS treatment materials as 
hazardous waste in the future. The results of this analysis can be 
found in the EA for this rule (USEPA, 2024g). Some commenters suggested 
that accounting for future potential regulations is uncommon, and 
trying to account for all potential future contingencies would make 
economic analyses impossible. The EPA strongly agrees and has not 
attempted to do so here; this analysis was limited to looking at a 
hypothetical future hazardous waste listing situation because that has 
been of particular concern in this rule. Some commenters stated that 
the EPA should account for the public health benefits of treating PFAS 
as hazardous wastes, not just additional costs incurred. The EPA agrees 
and has modified the analysis to include a qualitative statement about 
the public health benefits which could potentially arise from treating 
PFAS as hazardous wastes. Many commenters stated that the EPA hazardous 
waste cost would drive the total cost higher than the 3-5% estimated by 
the EPA. After considering public comment, the EPA has revised the 
final cost estimates in this rule. The EPA estimated increased cost 
would be approximately $99M at the 2% discount rate. The increased cost 
was driven by updating the dollar year of cost curves from 2021 to 2022 
which increased waste management unit costs by approximately 12%; 
implementing a cap on media life even if not indicated; changing the 
technology compliance forecast by eliminating RO/NF while increasing 
GAC and AIX (thereby increasing spent media volume); and increasing 
occurrence estimates for the final rule compared to the proposed rule, 
triggering more systems into treatment. The increased costs were not 
driven by changes to unit cost estimates for hazardous waste 
management. The EPA believes its assessment is accurate; the total cost 
encompasses capital costs, maintenance, design, and operations, 
including waste management. Waste management costs are thus a subset of 
operational cost which in turn is a subset of total costs; generally, 
changes in the cost of one subcomponent would not significantly 
influence total costs, and the record does not reflect that a change in 
waste disposal costs would

[[Page 32627]]

have a significant impact on total costs under this rule. These 
estimates are discussed in greater detail in the HRRCA section of this 
rule and in appendix N of the EA (USEPA, 2024e).
    Many commenters suggested that regulations under other statutes, 
particularly a potential CERCLA hazardous substance designation, will 
increase disposal costs. The EPA disagrees that, if finalized, the 
CERCLA hazardous substance designation for PFOA and PFOS will increase 
disposal costs for water treatment facilities. The designation of PFOA 
and PFOS as CERCLA hazardous substances would not require waste (e.g., 
biosolids, treatment residuals, etc.) to be treated in any particular 
fashion, nor disposed of at any specific particular type of landfill. 
The designation also does not restrict, change, or recommend any 
specific activity or type of waste at landfills. Along with other 
release notification requirements, CERCLA designation would require 
that any person in charge of a vessel or facility report a release of 
PFOA and/or PFOS of one pound or more within a 24-hour period. The EPA 
does not expect spent drinking water treatment residuals containing 
PFAS to be released into the environment at or above the reportable 
quantity as a part of standard residuals management practices used by 
water systems. This is because the PFAS loading onto sorptive media is 
very small. The weight percent of PFAS onto GAC under normal treating 
scenarios will vary widely; however, a reasonable order of magnitude 
estimate is 1 x 10-5 grams PFAS per gram of sorbent in full-
scale applications. High pressure membranes split water into a treated 
stream and concentrated waste stream. The concentrated waste stream 
will contain about 5-12 times more PFAS than the influent which is 
likely to still be in the ng/L scale. A drinking water facility which 
takes reasonable precautions is unlikely to release enough low 
concentration residuals to release one pound of PFOA and/or PFOS within 
a 24-hour period. At the concentrations discussed above, to exceed a 
one-pound threshold, a facility using sorptive techniques would have to 
release approximately 50 tons of sorbent, within a 24-hour period. A 
one-pound uncontrolled release from RO or NF facilities, assuming 500 
ng/L of PFAS in the reject water, would require approximately 240 
million gallons of high-pressure membrane concentrate to be released 
within 24 hours. Additionally, neither a release nor a report of a 
release automatically requires any response action under CERCLA. The 
EPA makes CERCLA response decisions based on site-specific information, 
which includes evaluating the nature, extent, and risk to human health 
and/or the environment from the release. Hazardous substance 
designations do not automatically result in CERCLA liability for any 
specific release. Whether an entity may be subject to litigation or 
held liable under CERCLA are site-specific and fact-dependent 
inquiries. Likewise, CERCLA affords the Federal Government broad 
discretion as to whether or how to respond to a release. For those 
reasons, the EPA cannot assess with reasonable certainty what 
litigation or liability outcomes may indirectly result from this 
designation since those outcomes are often linked to the EPA's 
discretionary decisions with respect to CERCLA response actions as well 
as site-specific and fact-dependent court rulings.
    Many commenters suggested that high pressure membranes, which 
separate PFAS from one stream and concentrate it in another stream, may 
not be feasible as a BAT because utilities treating and discharging 
reject water from high pressure membranes typically require a NPDES 
permit. The EPA disagrees because there are currently full-scale 
facilities which use this technology to treat PFAS and high-pressure 
membranes may be the best viable option in a multi-contaminant setting. 
The brine may undergo further pre-treatment as part of a process train 
to enable discharge, such as GAC or AIX treatment. Some RO/NF 
applications discharge directly to surface water or through an 
interconnection to a wastewater treatment plant. The EPA, however, does 
agree that brine treatment or disposal may be challenging and in 2022, 
the EPA issued memorandum that recommended NPDES and POTW pretreatment 
program permitting conditions for PFAS discharges (USEPA, 2022d; USEPA, 
2022e). In conclusion, in limited applications, high pressure membranes 
may still serve as a viable treatment strategy, such as for facilities 
with access to brine treatment or disposal.
    Some commenters suggested that reactivation was not permissible 
under the 2020 Interim PFAS Destruction and Disposal Guidance or that 
interim storage was required. Commenters are incorrect in their 
interpretation of the plain language in that guidance. The guidance 
does not state that reactivation or thermal treatment are prohibited. 
The guidance does acknowledge a need for further refinement and 
research and that interim storage may be an option if the immediate 
dispensation of PFAS-containing materials is not imperative. However, 
nowhere does that guidance mandate interim storage or prohibit other 
forms of PFAS destruction and disposal.
3. Final Rule
    The final rule does not specifically require any specific 
destruction or disposal practices for spent media containing PFAS. The 
EPA has considered residual waste streams and disposal options and 
found that management options exist for treatment residuals containing 
PFAS.

D. What are Small System Compliance Technologies (SSCTs)?

1. Proposal
    Section 1412(b)(4)(E)(ii) requires that the agency identify SSCTs, 
which are affordable treatment technologies, or other means that can 
achieve compliance with the MCL. The EPA identified SSCTs using the 
affordability criteria methodology developed for drinking water rules 
(USEPA, 1998b) and proposed the following table which shows which of 
the BATs listed above are also affordable for each small system size 
category listed in section 1412(b)(4)(E)(ii) of SDWA.

[[Page 32628]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.025

    Point-of-use (POU) and point-of-entry (POE) were not listed as 
compliance options because the regulatory options under consideration 
require treatment to concentrations below the current NSF 
International/American National Standards Institute (NSF/ANSI) 
certification standard for POU device removal of PFAS. As the EPA has 
determined that affordable SSCTs are available, the agency is not 
proposing any variance technologies.
2. Summary of Major Public Comments and EPA Responses
    Many commenters stated that the POU/POE water treatment industry 
may already have multiple products that can reduce PFAS chemicals to 
below the proposed MCL. Additionally, some commenters stated that the 
influent used (i.e., the challenge water) to test these POU/POE 
products often contains much higher concentrations of PFAS than would 
normally be found in most source waters. Commenters also pointed out 
that under NSF/ANSI, 53 and 58 certifications exist for total PFAS 
(PFOA, PFOS, PFHxS, PFHxA, and PFDA), as well as PFHpA, PFHxS, and PFNA 
individually. However, SDWA section 1412(b)(4)(E)(ii) requires that 
SSCTs achieve compliance with the MCL or treatment technique. While 
devices certified to the NSF/ANSI standards must be demonstrated to 
significantly reduce PFAS concentrations and, in many cases, can 
reasonably be expected to treat below this rule's MCLs, the current 
standards and certification procedures do not assure compliance with 
this rule. In particular, PFBS and HFPO-DA, have no certification 
standards at this time and the certification standards for PFOA, PFOS, 
and PFHxS are above this rule's MCL. The certification standards for 
PFOA, PFOS, and PFHxS are 20 ng/L, compared to the MCLs of 4.0 ng/L for 
PFOA and PFOS, as well as 10 ng/L for PFHxS; the total PFAS 
certification standard is 20 ng/L effluent comprised of PFOA, PFOS, 
PFHxS, PFHxA, and PFDA compared to a Hazard Index of 1 for mixtures of 
PFHxS, PFNA, HFPO-DA and PFBS. Since the NPDWR has standards that NSF/
ANSI are currently unable to verify, POE/POU technologies could 
potentially not achieve compliance contrary to SDWA section 
1412(b)(4)(E)(ii) which requires that SSCTs achieve compliance with the 
MCL. While POU/POE technologies may provide significant levels of 
protection, and the EPA anticipates they will eventually comply with 
the NPDWR, there is not yet a systematic verification process in place 
for the level of protection provided by these devices. As mentioned in 
the proposal, the EPA is aware that the NSF/ANSI Drinking Water 
Treatment Unit Joint Committee Task Group is in the process of updating 
their standards; should these future standards meet the NPDWR, the EPA 
could revise the SSCT list to include POE/POU.
    Many commenters also correctly pointed out numerous challenges 
surrounding POU/POE as a compliance option for some PWSs such as 
resident cooperation, operation and maintenance, monitoring, and 
implementation of distributed treatment approaches. The EPA agrees 
implementation of POU/POE as a compliance option for any NPDWR can be 
challenging for some PWSs but also agrees with commenters who noted 
that POU/POE can provide flexibility and compliance options to very 
small water systems or certain NTNCWS such as schools, factories, 
office buildings, and hospitals that provide their own water.
    The EPA received many comments that other POU devices other than 
RO/NF should be acceptable ways to meet the MCLs for small systems. For 
instance, commenters noted that a combination GAC/AIX device with 
filters could reduce PFAS concentrations to below the MCL values. The 
EPA agrees and has changed wording in the final rule preamble and 
related supporting documents that implied that only RO/NF POU devices 
would be able to meet a future certification standard. The EPA notes 
that for small systems, as long as the proposed POU/POE devices are 
certified by an appropriate third-party certifier (e.g., ANSI/NSF) to 
meet the regulatory MCL, they would meet the requirements of this 
regulation. The EPA also received many requests to change the way data 
was displayed in tables 20 and 22 of the proposed rule which summarized 
proposed SSCTs for PFAS removal and total annual cost per household for 
candidate technologies. In the proposal, the EPA wrote that this data 
was ``Not Applicable'' because of the economies of scale for 
centralized treatment. While the EPA still believes that a POU program 
that large is likely to be impractical, the EPA has changed the way 
this is displayed by replacing the term ``Not Applicable'' with ``Data 
Unavailable.'' The EPA notes that neither of these changes imposes nor 
relieves any rule requirements and only serve to recharacterize the way 
the EPA reports available technologies.
    The EPA asked for comment on the national level analysis of 
affordability of SSCTs and specifically on the potential methodologies 
presented in the EA for the proposed rule section 9.12. A couple of 
commenters recommended the EPA not use median household income (MHI) in 
the affordability analysis. The EPA decided to retain the MHI measure 
of income in its primary national level SSCT affordability methodology, 
and specifically use 2.5% of the MHI as the affordability threshold, 
given the value is easily understandable and available, providing a 
central tendency for income which is representative of a whole 
community's ability to pay and is not unduly influenced by outlier 
values. However, in this rule, the EPA

[[Page 32629]]

recognizes the value in examining alternative measures of a community's 
ability to afford an SSCT, so the agency chose to include supplemental 
analyses that use alternative metrics, specifically 1% of MHI, 2.5% of 
lowest quintile income (LQI), and an analysis accounting for financial 
assistance. See chapter 9.13.2 of the EA for more details. These 
supplemental analyses help to characterize affordability when 
considering the marginal impact, disadvantaged community groups, and 
subsidization.
    Some commenters stated that the data the EPA used to inform current 
water rates from the 2006 Community Water System Survey (CWSS) is 
outdated. While dated, the data from the 2006 CWSS remains the best 
available dataset for this national level analysis and affordability 
determination for the following reasons: (1) the CWSS survey used a 
stratified random sample design to ensure the sample was representative 
and (2) these responses can be extrapolated to national estimates since 
the survey has a known sampling framework; and the data can be 
organized by system size, source, and ownership (USEPA, 2020e).
    Some commenters recommended the EPA extend the affordability 
analysis to medium and large systems. The EPA disagrees with this 
recommendation, as the purpose of this analysis is to determine if 
available SSCTs are affordable, per SDWA section 1412(b)(4)C(ii). 
Therefore, the EPA chose to continue to analyze small system 
technologies rather than include medium and large systems.
    Some commenters specifically disagreed with one of the EPA's 
supplemental affordability analyses that examined the impact of the 
rule when accounting for the financial assistance through BIL and other 
sources that are generally available to small systems. These commenters 
stated that the EPA should not assume that this funding will be 
available or enough to cover the small system capital costs associated 
with the rule. The EPA conducted this supplemental analysis in response 
to the recommendations of the SAB, which stated, ``[i]f this funding is 
readily available to many or most systems facing affordability 
problems, it seems appropriate to take the availability of this funding 
into account in determining national level affordability.'' (USEPA, 
2002b) The EPA disagrees with these commenters as this significant 
funding will be generally available, and the EPA continues its efforts 
to help PWSs access it. It is therefore reasonable to consider the 
burden reduction in the supplemental affordability analysis.
    Some commenters disagreed with the EPA's affordability 
determination because they stated it was based on inaccurate treatment 
cost information. A couple of commenters presented their own estimates 
for small system household costs and compared these estimates to the 
EPA's affordability threshold and concluded the rule is unaffordable. 
The EPA disagrees with many of the underlying assumptions in the 
commenters' cost estimates which, on whole, result in overestimated 
household costs, see section XII.A. These commenters cited cost 
information that is not representative of the range of treatment costs 
nationally, and the EPA disagrees with the commenter's cost model that 
systematically overestimates capital operation and treatment costs. The 
EPA updated the affordability analysis for the national affordability 
determination using the updated treatment cost curves (discussed in 
section XII.D) and found for systems serving between 25 and 500 people, 
that the upper bound estimated annual household treatment costs for GAC 
exceed the expenditure margin. Lower bound estimated annual household 
treatment costs for GAC do not exceed the expenditure margin; for more 
information see section XII. These exceedances are primarily driven by 
capital costs and attributable to the use of high-cost materials (e.g., 
stainless steel) in the upper bound estimates. Systems using low-cost 
materials, but with source water characteristics otherwise set to the 
upper bound (e.g., influent PFAS at approximately 7,000 ng/L, influent 
TOC at 2 mg/L), would fall below the expenditure margin. Although costs 
increase in some scenarios, the increases are not significant enough to 
change the conclusions about affordability. The small system compliance 
technologies available to meet the requirements of the final rule are 
affordable for all small systems when the technologies do not use the 
high-end materials. Technologies that do not use high end materials may 
be less durable but nonetheless are available for small systems and can 
meet the requirements of the final rule. For more information on the 
EPA's response to comments on treatment costs see section XII. The EPA 
also disagrees that there are no affordable compliance technologies for 
small systems as the EPA has demonstrated that SCCTs are available 
below the affordability threshold using the best available peer 
reviewed information to support the agency's cost estimates.
3. Final Rule
    The final rule includes sorptive devices as well as combination 
devices, should they meet third party verification standards and the 
MCL. In USEPA, 2024l, the EPA also changed the way data are presented 
by replacing the term ``Not Applicable'' with ``Data Unavailable'' in 
response to public comment. Finally, the final affordability analysis 
reflects updates made to the unit cost curves after considering public 
comments. The EPA has determined that affordable SSCTs are available 
that meet the requirements of the final rule (see table 6 to paragraph 
(e) of 40 CFR 141.61).
    The EPA's affordability determination for the final rule, using 
long standing EPA methodology and supplemental affordability analyses 
can be found in the EA chapter 9.12.
    The EPA notes that POU RO devices are not currently listed as a 
SSCT because the NPDWR requires treatment to concentrations below the 
current NSF International/American National Standards Institute (NSF/
ANSI) certification standard for POU device removal of PFAS. However, 
POU treatments are reasonably anticipated to become a compliance option 
for small systems in the future if NSF/ANSI develop a new certification 
standard that mirrors or is more stringent than the final regulatory 
standards. Other third-party entities including NSF can independently 
certify drinking water treatment units (DWTUs) that meet these 
standards. NSF/ANSI is considering lowering its current standard to 
levels closer to final standards in this NPDWR. Based on efficacy of 
reverse osmosis technology, RO POU devices can reasonably be 
anticipated to remove the majority of PFAS when they are properly 
designed and maintained. Other POU devices (e.g., activated carbon) may 
also meet future EPA PFAS regulatory limits. These devices would also 
need third-party testing and certified against the regulatory 
standards. Further, the EPA notes that water systems may use any 
technology or practice to meet the MCLs promulgated in this NPDWR and 
are not limited to the BATs nor SSCTs discussed in this section. Other 
technologies or nontreatment options may be chosen in lieu of a BAT or 
SSCT because they may be more cost effective or better suited to the 
specific operating conditions of the particular site to meet any MCL.

[[Page 32630]]

XI. Rule Implementation and Enforcement

A. What are the requirements for primacy?

1. Proposal
    SDWA section 1413 establishes requirements that primacy agencies 
(states, Tribes and territories) must meet to have primary enforcement 
responsibility (primacy) for its PWSs. These include: (1) adopting 
drinking water regulations that are no less stringent than Federal 
NPDWRs in effect under sections 1412(a) and 1412(b) of SDWA; (2) 
adopting and implementing adequate procedures for enforcement; (3) 
keeping records and making reports available on activities that the EPA 
requires by regulation; (4) issuing variances and exemptions (if 
allowed by the state) under conditions no less stringent than allowed 
by SDWA sections 1415 and 1416; and (5) adopting and being capable of 
implementing an adequate plan for the provision of safe drinking water 
under emergency situations. The regulations in 40 CFR part 142 set out 
the specific program implementation requirements for states to obtain 
primacy for the Public Water System Supervision (PWSS) Program, as 
authorized under section 1413 of the Act.
    Under 40 CFR 142.12(b), all primacy agencies are required to submit 
a revised program to the EPA for approval within two years of 
promulgation of any final PFAS NPDWR or request an extension of up to 
two years in certain circumstances. To be approved for a program 
revision, primacy agencies are required to adopt revisions at least as 
stringent as the revised PFAS-related provisions. To obtain primacy for 
this rule, primacy applications must address the general requirements 
specified in subpart B of part 142. The EPA proposed special primacy 
requirements for the PFAS NPDWR (Sec.  142.16(r)), to outline 
additional requirements for a primacy agency related to identifying its 
plan for implementing the initial monitoring requirements.
2. Summary of Major Public Comments and EPA Responses
    The EPA received one comment that most of the initial monitoring 
may occur before primacy applications will be submitted, which are not 
due until two years after final rule promulgation. A couple of 
commenters assert that it is unclear why states are required to include 
an initial monitoring plan in their primacy application and that states 
will not be able to implement and demonstrate that this monitoring plan 
is enforceable under state law until state regulations have been 
promulgated. The EPA recognizes that some initial monitoring by water 
systems may occur prior to a state, territory, or Tribe receiving the 
EPA approval for primacy and agrees with the commentor that for states 
to develop a monitoring plan that addresses when systems will be 
scheduled to conduct initial monitoring is not a necessary requirement 
for a primacy application. However, where states are approved for 
primacy before the compliance date for the water systems, primacy 
agencies should have procedures for evaluating whether data that a CWS 
or NTNCWS submits to satisfy the initial monitoring requirements are 
acceptable. It is therefore appropriate to require primacy agencies to 
include in their primacy application a description of their procedures 
for reviewing water system's use of pre-existing data to meet initial 
monitoring requirements, including the criteria that will be used to 
determine if the data are acceptable and the primacy agency's 
procedures for ensuring water system compliance within the required 
timeframes. The compliance deadline for this initial monitoring by 
systems is three-years from promulgation, by which time primacy 
agencies should have primacy or interim primacy. To address the 
possibility that a state, Tribe, or territory may get an extension to 
apply for primacy, the final rule provides that these special primacy 
requirements are not applicable after the initial monitoring deadline 
(i.e., three years after publication of the rule in the Federal 
Register). When a primacy agency does not yet have primacy for a new 
drinking water rule, an NPDWR is nonetheless applicable to water 
systems and may be enforced by the EPA following the compliance dates 
specified in Sec.  141.900(b).
3. Final Rule
    The EPA is revising the requirements for primacy as proposed in 40 
CFR 142.16(r) by removing the requirements to develop an initial 
monitoring plan, although the EPA is finalizing the proposed 
requirement for primacy agency procedures for ensuring all systems 
complete the initial monitoring period requirements, including for 
determining whether pre-existing data are acceptable, but clarifying 
that these requirements would not apply after the deadline for initial 
monitoring has passed (i.e., three years after publication of the rule 
in the Federal Register). The EPA also corrected two grammatical 
errors. In the final rule, the EPA requires that a PWS complete the 
initial monitoring by three years following date of promulgation (for 
additional discussion on monitoring and compliance requirements, please 
see section VIII of this preamble). It is the EPA's expectation that 
primacy agencies will have completed the requirements for primacy 
within the two years (i.e., without an extension) and in that case, 
they will have the authority in place to ensure that systems comply 
with the initial monitoring requirements. If a primacy agency is 
applying for primacy after the deadline for initial monitoring has 
passed, then the requirement is no longer applicable. In that case, an 
NPDWR is nonetheless applicable to water systems and implementation 
would be overseen and enforced by the EPA consistent with any 
agreements with the state pursuant to the primacy application extension 
approval.

B. What are the record keeping requirements?

1. Proposal
    The current regulations in 40 CFR 142.14 require primacy agencies 
to keep records of analytical results to determine compliance, system 
inventories, sanitary surveys, state approvals, vulnerability and 
waiver determinations, monitoring requirements, monitoring frequency 
decisions, enforcement actions, and the issuance of variances and 
exemptions. The primacy agency record keeping requirements remain 
unchanged and would apply to PFAS as with any other regulated 
contaminant.
2. Summary of Major Public Comments and EPA Responses
    The EPA received a few comments about the record keeping that 
primacy agencies must maintain for compliance determinations and 
reporting, storing PWS facility data, tracking monitoring schedules, 
and keeping the public informed of the quality of their drinking water. 
As noted in the comments, most primacy agencies rely on SDWIS, 
developed by the EPA, to support this record keeping requirement. It 
was recommended that the EPA develop a data system, either SDWIS or a 
replacement, that is capable of fully managing the data associated with 
the proposed rule. Further, it was recommended that the EPA develop 
data management solutions such as a mechanism for migrating UCMR data 
into SDWIS State to reduce or eliminate the burden of ensuring 
compliance with the initial monitoring. The EPA agrees that appropriate 
data management solutions are needed to effectively comply with SDWA 
requirements; however, the agency does not believe

[[Page 32631]]

these systems must be available at the time of rule promulgation. 
Additionally, while beyond the scope of this rulemaking itself, the EPA 
is actively working on PFAS data management solutions, including DW-
SFTIES support and potentially updating the SDWIS suite of applications 
to manage data reported from this rule.
3. Final Rule
    The primacy agency record keeping requirements in 40 CFR 142.14 
remain unchanged and would apply to PFAS as with any other regulated 
contaminants. Water system recordkeeping requirements are referenced 
within subpart Z in Sec.  141.904. In the final rule, the EPA updated 
this regulatory text to cross-reference the record retention provisions 
in Sec.  141.33. The EPA is developing the Drinking Water State-
Federal-Tribal Information Exchange System (DW-SFTIES) that will 
support all SDWA drinking water rules. The EPA plans to continue to 
provide support for necessary updates to SDWIS State, including for 
reporting requirements for new rules, until the DW-SFTIES is in 
production and in use by primacy agencies. SDWIS State support and 
updates will continue until the DW-SFTIES Board recommends a sunset 
date after DW-SFTIES is in production and in use by primacy agencies. 
The EPA will evaluate the migration of UCMR data into the suite of 
SDWIS applications.

C. What are the reporting requirements?

1. Proposal
    Under 40 CFR 142.15, primacy agencies must report to the EPA 
information regarding violations, variances and exemptions, enforcement 
actions, and general operations of state PWS programs. The primacy 
agency reporting requirements remain unchanged and would apply to PFAS 
as with any other regulated contaminant. The water system reporting 
requirements are mentioned in Sec.  141.904 and cross-reference the 
reporting timeframes and provisions in Sec.  141.31.
2. Summary of Major Public Comments and EPA Responses
    A few commenters recommended that the EPA provide Data Entry 
Instructions within six months of the promulgation of the rule to allow 
primacy agencies, particularly those that do not use SDWIS State, to 
implement their data systems for reporting to the EPA, prepare their 
PWS, and train staff. The EPA acknowledges this comment and will work 
to develop Data Entry Instructions as soon as possible. One commentor 
recommended that the EPA provide separate tracking of reporting and 
monitoring violations. The EPA acknowledges this comment and will 
consider this as data reporting tools are developed. A couple of 
commentors recommended that the reporting and recordkeeping 
requirements for compliance within the rule should provide an option 
for not requiring the RAA to be reported by the laboratories if the 
primacy agency performs the RAA calculations for the water system. In 
addition, one commenter requested that the primacy agency calculate the 
RAA, and another commentor inquired whether the EPA intended to allow 
the water systems not to perform the RAA calculations if the primacy 
agency performs the RAA calculations. The EPA disagrees with these 
comments. To ensure that the water system has immediate knowledge of 
their compliance status, the final rule requires that water systems 
calculate the RAA and report this to the primacy agency. Primacy 
agencies or laboratories may also calculate the RAA, to confirm the 
results of the water system, but it is not a required reporting element 
under this regulation. Lastly another commentor suggested that 
utilities be required to report the occurrence and concentration of 
other PFAS listed in the method (preferably 533) to facilitate data 
collection and to better inform water treatment objectives. The EPA 
notes that many water systems are currently collecting samples and 
reporting monitoring data for 29 PFAS that can be measured with EPA 
Methods 533 and 537.1 under UCMR 5 where EPA has the regulatory 
authority.
3. Final Rule
    The reporting requirements for primacy agencies under 40 CFR 142.15 
remain unchanged and apply to PFAS as with any other regulated 
contaminant. The EPA intends to develop and provide access to Data 
Entry Instructions within one year after rule publication. The EPA will 
follow the usual protocol of engaging with a State-EPA workgroup for 
drafting the Data Entry Instructions. In this process, the EPA will 
consider the use of separate monitoring and reporting violation codes, 
like is used for the Revised Total Coliform Rule (RTCR). In this final 
regulation, the cross-reference to the water system reporting 
timeframes and provisions in Sec.  141.31 at the start of Sec.  141.904 
is retained, and, at 40 CFR 141.904(b), table 2, the EPA requires water 
systems to report PFAS RAAs to their primacy agency. As a general 
process, the laboratory will conduct the analysis of the sample and the 
system will use the result to calculate their RAA; the RAA calculation 
may subsequently be completed by the primacy agency as a compliance 
check. The EPA does recognize that state laboratories often directly 
report results to the state as allowed in 40 CFR 141.31(c) and that 
electronic reporting tools, such as the Compliance Monitoring Data 
Portal (CMDP), may be used by systems to comply with this reporting 
requirement.

D. Exemptions and Extensions

1. Proposal
    Pursuant to SDWA section 1412(b)(10), the EPA proposed that all 
systems must comply with the NPDWR three years after rule promulgation. 
The EPA's proposal acknowledged that a primacy agency or the EPA may 
grant an extension of up to two additional years to comply with an 
NPDWR's MCL(s) if the primacy agency or the EPA determines an 
individual system needs additional time for capital improvements. The 
EPA stated that ``[a]t this time, the EPA does not intend to provide a 
two-year extension nationwide.'' 88 FR 18689. The proposal also 
discussed how a state which has primary enforcement responsibility may 
exempt any individual system facing compelling factors, such as 
economic factors, additional time to comply with any requirement 
respecting an MCL of any applicable NPDWR under SDWA section 1416 
(USEPA, 2023f).
2. Summary of Major Public Comments and EPA Responses
    SDWA section 1412(b)(10) requires that a ``NPDWR shall take effect 
``3 years after the date on which the regulation is promulgated unless 
the administrator determines that an earlier date is practicable.'' 
Section 1412(b)(2) also authorizes ``the Administrator, or a State (in 
the case of an individual system), may allow up 2 additional years to 
comply with a maximum contaminant level . . . if the Administrator or 
the State . . . determines that additional time is necessary for 
capital improvements'' (emphasis added). Congress intended the 
extension under this provision to allow for a total of five years to 
comply with the MCL. Thus, if the EPA provides a two-year extension of 
the MCL compliance deadline for all systems based on the need for 
capital improvements, a state cannot provide an additional two-year 
extension under section 1412(b)(10) for capital improvements but may 
grant exemptions under section 1416

[[Page 32632]]

consistent with applicable requirements.
    Many commenters, including utilities and state primacy agencies, 
expressed difficulty in meeting the three-year compliance deadline. 
Commenters expressed that it will be very challenging to both conduct 
initial monitoring and take actions (e.g., installing treatment) to 
comply with the MCL within three years. Many of these commenters shared 
their on-the-ground experience in managing facilities that required 
capital improvements and provided evidence that additional time is 
needed to procure, design, pilot, permit, and ultimately construct 
treatment systems. Additionally, several commenters provided evidence 
of on-going labor and workforce challenges as well as recent experience 
with supply chain difficulties to obtain materials necessary to design 
and construct treatment facilities, which many attributed as a direct 
or indirect result of the COVID-pandemic residual impacts (AWWA, 2023).
    The agency has evaluated the data and information shared by 
commenters regarding their experience with the time it takes to 
implement capital improvement projects. The EPA estimates that 
approximately 4,100-6,700 systems will be impacted by the MCLs in this 
final rule. Based on the EPA's initial compliance forecast, the agency 
anticipates that many of these systems will be installing advanced 
treatment technologies to meet the final PFAS standards (for additional 
discussion on the compliance forecast, please see section XII). The 
treatment technologies listed as BAT for the final rule include GAC, 
ion exchange resins, and centralized RO/NF (please see section X for 
more information). To ensure cost effective compliance with the PFAS 
MCLs, systems often need to evaluate their treatment technology options 
as a first step. Several commenters have noted that this planning step 
may include pilot studies with potential treatment systems, or it may 
be limited to an evaluation of the raw water characteristics. Further, 
some commenters have submitted data and project management plans for 
systems choosing to conduct pilot testing, indicating that it may take 
a year or more to contract with vendors and to perform pilot testing. 
Once the planning step is completed, systems must design and construct 
the treatment systems. Several commenters submitted information to the 
EPA indicating that the design and permitting of the treatment systems 
can take an additional year or longer, and construction of the 
treatment system can take another year or longer. Because systems will 
also need time to obtain funding, obtain local government approval of 
the project, or acquire the land necessary to construct these 
technologies, many commenters contend that systems will need additional 
time beyond the three-year effective date to comply with the MCLs.
    While the EPA stated in the proposed rule that the agency did not 
intend to provide a two-year extension nationwide necessary for capital 
improvements, the EPA finds that the evidence submitted by commenters 
strongly supports that a significant number of systems covered by this 
rule will need two additional years to make capital improvements to 
meet the MCL. Specifically, the EPA reviewed data from applicants 
seeking DWSRF funding for capital improvement projects (e.g., 
installation of advanced treatment technologies such as GAC or IX) and 
confirmed that these projects, on average, take about three or more 
years to complete (which excludes the time and activities that may 
occur to ensure these capital improvement projects are implemented 
successfully, such as the time it may take to secure funding or to 
conduct pilot testing). This evidence along with the breadth of 
practicable experience shared by utilities and primacy agencies 
demonstrate that additional time is necessary for a significant number 
of system sizes and types located throughout the country to make 
capital improvements. Additionally, the EPA notes that the number of 
systems estimated to be impacted by the MCLs are greater than what the 
agency anticipated in the proposal (i.e., an increase from 3,400-6,300 
systems to 4,100-6,700 systems nationally). This increase provides 
further evidence that a capital improvement extension is warranted as 
the agency expects that many of these systems will be installing 
advanced treatment technologies to meet the final PFAS standards. The 
agency also agrees with commenters that on-going labor and workforce 
challenges exist and can limit the ability to design, construct and 
operate treatment facilities. These workforce challenges facing water 
utilities and other sector organizations support the need for a capital 
improvement extension as a sufficient availability of qualified 
personnel is necessary to implement and sustain capital improvement 
projects. These issues may be attributed as a direct or indirect result 
of the recent COVID-19 pandemic and are clearly documented in data 
submitted to the agency as part of the public comment process (AWWA, 
2023). Based upon these considerations, the EPA determined, in 
accordance with section 1412(b)(10) of SDWA, that the compliance date 
for the PFAS MCLs, regardless of system size, will be 5 years from the 
date of promulgation of the standard.
    Some commenters recommend the EPA to follow a staggered 
implementation timeframe similar to what was done in some previous 
NPDWRs where compliance deadlines were staggered based on system size 
(USEPA, 2001; USEPA, 2006a). In these prior examples, larger systems 
typically conducted their monitoring and implemented the MCL first, 
followed by smaller systems. Upon consideration of information 
submitted by commenters, particularly issues related to supply chain 
complications that are directly or indirectly related to the COVID-19 
pandemic residual challenges, the EPA has determined that a significant 
number of systems subject to the rule, including large systems, will 
require two additional years to complete the capital improvements 
necessary to comply with the MCLs for PFAS regulated under this action. 
For this reason, the EPA disagrees with commenters that staggered 
implementation based on system size is warranted for this rule. While 
large systems may have greater resources to implement capital 
improvements (e.g., engineering and construction management staff to 
manage the projects), they still require time to design, pilot, permit, 
and construct treatment facilities.
    Some commenters note that it will be challenging for systems to 
conduct their initial monitoring and install treatment within three 
years, particularly for those systems not conducting UCMR 5 monitoring 
that is ongoing until 2026. The EPA notes that the agency is finalizing 
a flexibility for systems to use previously acquired monitoring data 
from UCMR 5 or an equivalent state-led monitoring program for their 
initial monitoring which is intended to alleviate the burden placed on 
water systems in collecting additional data (see section VIII of this 
preamble for additional information on monitoring). While the agency 
agrees that systems need an additional two years to make capital 
improvements, the EPA finds that it is practicable for most systems to 
complete their initial monitoring within three years because all 
systems serving greater than 3,300 people will have appropriate 
monitoring data from UCMR 5. Many systems smaller than 3,300 people 
will also have appropriate monitoring data from state-led

[[Page 32633]]

monitoring programs that may be eligible to meet the rule's initial 
monitoring requirements, and some will have UCMR 5 or other data. If 
systems find elevated levels of PFAS, these systems have an additional 
two years to comply with the MCL. If a system does not have eligible 
previously collected monitoring data and are concerned about 
insufficient time to install capital improvements, the EPA encourages 
these facilities to collect monitoring data as soon as possible after 
rule promulgation, allowing them the bulk of the five-year period to 
plan for and install any capital improvements if necessary.
    Some commenters point to concerns regarding laboratory capability 
and capacity in supporting the proposed three-year compliance timeline. 
Additionally, a couple of commenters noted that if additional time were 
allowed, water systems that are close to the MCL may have time to 
identify and address sources of PFAS in their watersheds rather than 
investing resources on treatment initially. Finally, a couple of 
commenters recommend the EPA consider implementation flexibilities for 
small and rural water systems and suggest that these types of utilities 
may not have staff capacity nor expertise to compete for funding to 
implement the rule. The EPA notes that these issues are not directly 
related to capital improvements and thus were not the basis for the 
EPA's decision to extend the compliance date for the PFAS MCLs. 
Although the EPA disagrees with assertions about insufficient 
laboratory capacity and capability at this time to support 
implementation of the NPDWR, to the extent there are initial 
implementation issues just after promulgation, extending the compliance 
date will also provide ancillary benefits toward addressing any such 
laboratory capability and capacity issues and may provide opportunities 
for systems who are close to exceeding the MCLs to investigate sources 
of contamination. Additionally, the extended compliance deadline may 
give smaller and rural water utilities more time to apply for funding 
under BIL (please see section II of this preamble above for a 
discussion on BIL). Further, other assistance programs such as the 
Environmental Justice Thriving Communities Technical Assistance Centers 
may provide additional fundamental training and capacity building 
activities for underserved and overburdened communities toward 
navigating Federal grant applications and managing funding 
opportunities.
    The EPA requested comment as to whether there are specific 
conditions, in addition to the statutory conditions, that should be 
mandated for systems to be eligible for exemptions from the PFAS NPDWR 
under SDWA section 1416. Several commenters requested the EPA provide 
additional guidance to primacy Agencies on when exemptions are 
appropriate under SDWA section 1416 similar to what was done for the 
final Arsenic NPDWR (USEPA, 2002c). The EPA is not issuing additional 
guidance around implementation of SDWA section 1416 at this time but 
may consider it in the future. The EPA notes primacy agencies who have 
adopted the 1998 Variance and Exemptions Regulation (USEPA, 1998c) may 
choose to grant exemptions consistent with the requirements under this 
regulation to encourage systems facing compelling circumstances to come 
into compliance with the MCLs in an appropriate period of time.
3. Final Rule
    Pursuant to SDWA section 1412(b)(10), the final PFAS NPDWR is 
effective June 25, 2024. The compliance date for the PFAS NPDWR, other 
than the MCLs, is April 26, 2027. As discussed above and upon 
consideration of information submitted by commenters, the EPA is 
exercising its authority under SDWA section 1412(b)(10) to implement a 
nationwide capital improvement extension to comply with the MCLs. All 
systems must comply with the MCLs by April 26, 2029. All systems must 
comply with other requirements of the NPDWR, including initial 
monitoring, by April 26, 2027.
    Systems must comply with initial monitoring requirements within 
three years of rule promulgation and will be required to summarize PFAS 
monitoring results and applicable information beginning with CCRs 
delivered in 2027. As the MCL compliance date is set at five years from 
rule promulgation, systems must report MCL violations in the CCR, 
accompanied by the required health effects language and information 
about violations, starting in 2029. Monitoring and testing procedure 
violations require Tier 3 notification: systems must provide notice no 
later than one year after the system learns of the violation. Systems 
must repeat the notice annually for as long as the violation persists. 
Systems must comply with initial monitoring requirements within three 
years of rule promulgation and systems must provide Tier 3 notification 
for monitoring and testing procedure violations starting in 2027. As 
the MCL compliance date is set at five years from rule promulgation, 
systems must provide Tier 2 notification for MCL violations, starting 
in 2029. For more information on SDWA Right-to-Know requirements, 
please see section IX of this preamble above.
    The agency notes that SDWA section 1416(a) and (b)(2)(C) describe 
how the EPA or states may also grant an exemption for systems meeting 
specified criteria that provides an additional period for compliance. 
PWSs that meet the minimum criteria outlined in the SDWA may be 
eligible for an exemption from the MCLs for up to three years. For 
smaller water systems (<=3,300 population), exemptions can provide up 
to six additional years to achieve compliance with the MCLs. States 
exercising primacy enforcement responsibility must have adopted the 
1998 Variance and Exemption Regulation (USEPA, 1998c) for water systems 
in those jurisdictions to be eligible for an exemption.

XII. Health Risk Reduction and Cost Analysis

    This section summarizes the final rule Health Risk Reduction and 
Cost Analysis (HRRCA) supporting document (USEPA, 2024g) for the per- 
and polyfluoroalkyl substances (PFAS) National Primary Drinking Water 
Regulation (NPDWR), which is prepared in compliance with section 
1412(b)(3)(C) of the Safe Drinking Water Act (SDWA) and under Executive 
Order (E.O.) 12866. Section 1412(b)(3)(C)(i) lists the analytical 
elements required in a HRRCA applicable to an NPDWR that includes a 
Maximum Contaminant Level (MCL). The prescribed HRRCA elements include:
    (1) Quantifiable and nonquantifiable health risk reduction 
benefits;
    (2) quantifiable and nonquantifiable health risk reduction benefits 
from reductions in co-occurring contaminants;
    (3) quantifiable and nonquantifiable costs that are likely to occur 
solely as a result of compliance;
    (4) incremental costs and benefits of each alternative MCL 
considered;
    (5) effects of the contaminant on the general population and 
sensitive subpopulations including infants, children, pregnant women, 
the elderly, and individuals with a history of serious illness;
    (6) any increased health risks that may occur as a result of 
compliance, including risks associated with co-occurring contaminants; 
and
    (7) other relevant factors such as uncertainties in the analysis 
and factors with respect to the degree and nature of the risk.
    Based on this analysis, the Administrator confirms the finding

[[Page 32634]]

made at proposal under section 1412(b)(4)(C) of SDWA that the 
quantified and nonquantifiable benefits of the MCLs justify the costs. 
The complete HRRCA for the final NPDWR is commonly referred to as the 
``Economic Analysis'' (or EA) in this final rule and can be found in 
the docket at USEPA (2024g).
    Because this NPDWR is promulgated in 2024 and provides a 2-year 
nationwide extension of the date for MCL compliance, the EA assumes 
that capital improvements (i.e., installation of treatment 
technologies) for systems taking action under the rule will be 
completed by five years from the date promulgated, or in 2029. All 
other requirements, including initial monitoring, are assumed to be 
completed within three years of rule promulgation, or by 2027. Based on 
an assumed mean human lifespan of 80 years, the Environmental 
Protection Agency (EPA) evaluates costs and benefits under the final 
rule through the year 2105.
    The EPA selected this period of analysis to capture health effects 
from chronic illnesses that are typically experienced later in life 
(i.e., cardiovascular disease [CVD] and cancer). Capital costs for 
installation of treatment technologies are spread over the useful life 
of the technologies. The EPA does not capture effects of compliance 
with the final rule after the end of the period of analysis. Costs and 
benefits discussed in this section are presented as annualized present 
values in 2022 dollars. The EPA determined the present value of these 
costs and benefits using a discount rate of 2 percent, which is the 
discount rate prescribed by the Office of Management and Budget (OMB; 
OMB, 2023). All future cost and benefit values are discounted back to 
the initial year of the analysis, 2024, providing the present value of 
the cost or benefit.
    Estimates of PFAS occurrence used for cost-benefit modeling rely on 
a Bayesian hierarchical estimation model of national PFAS occurrence in 
drinking water (Cadwallader et al., 2022) discussed in section VI.E. of 
this preamble. The model was fitted using sample data from systems 
participating in PFAS sampling under the third Unregulated Contaminant 
Monitoring Rule (UCMR 3) and included all systems serving over 10,000 
customers and a subset of 800 smaller systems. A best-fit model was 
selected using sample data to define occurrence and co-occurrence of 
perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), 
and perfluorohexane sulfonic acid (PFHxS \12\) in water systems 
stratified by system size and incorporating variations within and among 
systems. Sample data were derived from state-level datasets as well as 
from UCMR 3. For more information on the EPA's occurrence model, please 
see section VI.E. of this preamble.
---------------------------------------------------------------------------

    \12\ The EPA notes that perfluoroheptanoic acid (PFHpA) is not 
included in the proposed or final PFAS NPDWR; however, it was 
included in the occurrence model because of its UCMR 3 occurrence 
data availability; please see Cadwallader et al., 2022 for 
additional details.
---------------------------------------------------------------------------

    In the EA, the EPA analyzes the costs and benefits of the final 
rule, which includes MCLs for PFOA and PFOS at 4.0 ng/L each and MCLs 
for PFHxS, perfluorononanoic acid (PFNA), and hexafluoropropylene oxide 
dimer acid (HFPO-DA) at 10 ng/L each and a unitless Hazard Index (HI) 
of 1 for any mixtures of PFHxS, PFNA, HFPO-DA, and PFBS. The EPA also 
analyzed the costs and benefits for several regulatory alternatives. 
The EPA analyzed the costs and benefits of setting individual MCLs for 
PFOA and PFOS at 4.0 ng/L, 5.0 ng/L, and 10.0 ng/L, referred to as 
regulatory alternative MCLs under option 1a, option 1b, and option 1c, 
respectively. The EPA assessed these regulatory alternative MCLs in the 
EA to understand the impact of less stringent PFOA and PFOS MCLs. 
Additionally, the EPA has separately estimated national level marginal 
costs associated with the individual MCL for PFHxS if this MCL were to 
be promulgated in the absence of the Hazard Index; see chapter 5.1.3 of 
the EA for details. The EPA has also estimated the marginal costs for 
the individual PFNA and HFPO-DA MCLs if there were no Hazard Index in 
the sensitivity analysis found in appendix N.4. The EPA notes that the 
costs for the individual PFHxS, PFNA, and HFPO-DA MCLs have been 
considered in this final rule.
    Section A summarizes public comments received on the EA for the 
proposed rule and the EPA's responses to comments. Section B summarizes 
the entities which would be affected by the final rule and provides a 
list of key data sources used to develop the EPA's baseline water 
system characterization. Section C provides an overview of the cost-
benefit model used to estimate the national costs and benefits of the 
final rule. Section D summarizes the methods the EPA used to estimate 
costs associated with the final rule. Section E summarizes the 
nonquantifiable costs of the final rule.\13\ Section F summarizes the 
methods the EPA used to estimate quantified benefits associated with 
the final rule. Section G provides a summary of the nonquantifiable 
benefits associated with reductions in exposure to both PFOA and PFOS 
expected to result from the final rule. Section H provides a 
qualitative summary of benefits expected to result from the removal of 
PFAS included in the Hazard Index component of the final rule and 
additional co-removed PFAS contaminants. Section I of this preamble 
summarizes benefits expected to result from the co-removal of 
disinfection byproducts (DBPs). Section J provides a comparison of cost 
and benefit estimates. Section K summarizes and discusses key 
uncertainties in the cost and benefit analyses. Quantified costs and 
benefits for the final rule and regulatory alternative MCLs under 
options 1a-1c are summarized in section XII.J, specifically Tables 68-
71. Tables 72-73 summarize the non-quantified costs and benefits and 
assess the potential impact of nonquantifiable costs and benefits on 
the overall cost and benefit estimates for the final rule.
---------------------------------------------------------------------------

    \13\ This section includes costs with generally greater 
uncertainty that the EPA assesses in quantified sensitivity 
analyses.
---------------------------------------------------------------------------

A. Public Comment on the Economic Analysis for the Proposed Rule and 
EPA Response

1. Methods for Estimating Benefits
a. Methods for Estimating Benefits in the Proposed Rule
    In the EA for the proposed rule, the EPA presented quantified and 
nonquantifiable health benefits expected from reductions in PFAS 
exposures. Quantified benefits are assessed as avoided cases of illness 
and deaths (or morbidity and mortality, respectively) associated with 
exposure to some of the regulated PFAS contaminants. The EPA provided a 
quantitative estimate of CVD, birth weight, and renal cell carcinoma 
(RCC) avoided morbidity and mortality associated with reductions in 
PFOA and PFOS consistent with the proposed rule. The EPA also developed 
a quantitative analysis for reductions in bladder cancer morbidity and 
mortality that stem from removal of DBP precursors as a function of 
PFAS treatment. Adverse human health outcomes associated with PFAS 
exposure that cannot be quantified and valued are assessed as 
nonquantifiable benefits.
    The EPA qualitatively summarized potential health benefits 
associated with reduced exposure to PFAS other than PFOA and PFOS in 
drinking water. In the proposal, the EPA discussed non quantified 
benefits associated with health endpoints including developmental 
effects, cardiovascular effects, hepatic effects, immune effects,

[[Page 32635]]

endocrine effects, metabolic effects, renal effects, reproductive 
effects, musculoskeletal effects, hematological effects, other non-
cancer effects, and COVID-19.
b. Summary of Major Public Comments on Method for Estimating Benefits 
and EPA Responses
Overestimation of Quantified Benefits
    The EPA received comments from industry groups and organizations 
representing water utilities about the EPA's methodology for estimating 
quantitative benefits associated with the NPDWR. While some commenters 
supported the EPA's analysis, a few commenters stated that the agency 
overestimated quantified benefits. These commenters asserted that the 
EPA overstated the benefits of the rule and that the HRRCA is flawed 
because the existing health evidence does not support the quantified 
benefits. The EPA disagrees with commenters that the existing evidence 
does not support the EPA's estimate of quantified benefits from avoided 
adverse health effects likely to occur as a result of treatment and 
that these benefits are overstated. Among other things, the EPA has 
used the best available science in three key respects: by (1) 
considering relevant peer-reviewed literature identified by performing 
systematic searches of the scientific literature or identified through 
public comment, (2) relying on peer-reviewed, published EPA human 
health risk assessment methodology (USEPA, 2022f), and (3) utilizing 
peer-reviewed methodologies to valuing and quantifying avoided adverse 
health outcomes. Specifically, the EPA identified the full range of 
expected human health outcomes, including quantified benefits 
associated with co-removal of co-occurring contaminants (i.e., DBPs). 
This process was built upon multidisciplinary research, including 
hazard identification and dose-response analysis, exposure assessment, 
and economic valuation methods recommended by the EPA's Guidelines for 
Preparing Economic Analyses (USEPA, 2016e) and updated Circular A-4 
Guidance (OMB, 2023) to enumerate all beneficial outcomes, identify 
beneficiaries, and determine human health endpoints that can be valued. 
The EPA notes that the benefits analysis contains uncertainties 
associated with the modeling inputs in each of the steps listed above. 
In accordance with OMB Circular A-4 guidance (OMB, 2023), the EPA 
characterizes sources of uncertainty in its quantitative benefits 
analysis and reports uncertainty bounds for benefits estimated for each 
health endpoint category modeled in the final rule. See Table 75 and 
also section 6.1 of the EA for the final rule (USEPA, 2024g) for the 
list of quantified sources of uncertainty in benefits estimates. The 
reported uncertainty bounds reflect the best available data on health 
effect-serum slope factors, baseline PFAS occurrence, population size 
and demographic composition, and the magnitude of PFAS concentration 
reductions. In addition, some model inputs did not have sufficient 
distributional data to be included in the quantitative uncertainty 
analysis, and there are also uncertainties that could not be assessed 
quantitatively. These sources of uncertainty are described in Table 62 
and also in section 6.8 of the EA for the final rule (USEPA, 2024g). 
Although some imprecision in the estimated benefits may be expected due 
to the lack of perfect information, the EPA has demonstrated, using the 
best science and data available, that there is sufficient health 
evidence to support the estimation of quantified benefit values and 
that these values are not systematic overestimates of the welfare 
improvements derived from implementation of the NPDWR.
    Another commenter claimed that ``for the large majority of health 
endpoints discussed, the EPA has not provided a factual basis by which 
to conclude that such benefits are likely to occur when the EPA 
decreases the levels of PFAS in drinking water.'' The EPA disagrees 
with the commenter's assertion that the agency has not provided a 
factual basis for the benefits that are likely to occur as a result of 
the rule, which is amply supported in the HRRCA by the best available 
peer-reviewed science, consistent with SDWA section 1412(b)(3). 
Moreover, the commenter did not provide any additional or contrary 
factual information for the EPA to consider.
    One commenter stated that the EPA did not provide data to support 
the analysis of benefits predicted from the implementation of the 
Hazard Index MCL. The EPA disagrees with commenter that the EPA did not 
provide evidence to support Hazard Index MCL benefits. In section XII 
of the preamble and in section 6.2 of the EA (USEPA, 2024g), the EPA 
qualitatively summarized and considered the potential health benefits 
resulting from reduced exposure to PFAS other than PFOA and PFOS in 
drinking water. These qualitative potential health benefits are based 
on summaries of a significant body of peer reviewed science. As 
summarized in the EA, the qualitatively discussed health effects of the 
Hazard Index PFAS are considerable; reducing human exposure to the 
Hazard Index PFAS is expected to reduce the incidence of multiple 
adverse health impacts. The qualitative benefits discussion of the 
impacts of the four PFAS which are regulated through the Hazard Index, 
as well as their co-occurrence in source waters containing PFOA and/or 
PFOS and additive health concerns, supports the EPA's decision to 
regulate them through the Hazard Index in this rulemaking.
    Additionally, the EPA evaluated the impacts of PFNA (one of the 
Hazard Index PFAS) on birthweight in quantitative sensitivity analyses 
(USEPA, 2024e). The EPA notes that new evidence since the release of 
the current, best available peer reviewed scientific assessment for 
PFNA (ATSDR, 2021) provides further justification for the EPA's 
analysis of potential economic benefits of PFNA exposure reduction and 
avoided birthweight effects. Specifically, this new evidence confirms 
that in instances where PFNA is present, the national quantified 
benefits may be underestimated; however, birth weight benefits are 
considered quantitatively as part of this EA in the sensitivity 
analysis and support the EPA's decision to regulate PFNA.
    The EPA received a number of comments on the quantitative analysis 
for CVD risk reduction. These commenters disagree with the EPA's 
assessment that cardiovascular benefits are likely to occur as a result 
of PFOA and PFOS exposure reduction. One commenter stated that the 
associations with total cholesterol (TC) are not biologically 
significant and criticized the EPA's use of linear models in the CVD 
meta-analysis, stating that this approach biases the analysis by 
excluding higher-quality studies. The EPA disagrees with the 
commenter's statement that associations between PFOA/PFOS and TC are 
not biologically significant. Such serum lipid changes may or may not 
result in a concentration considered clinically elevated in a 
particular individual; however, given the distribution of individual 
concentrations within the population, small changes in average serum 
lipid concentrations can result in substantial adverse health effects 
at the population level (Gilbert and Weiss, 2006). The EPA disagrees 
with the commenter's suggestions that linear assumptions are 
inappropriate for use in this context. The EPA presents the exposure-
response estimates evaluated considering all studies, studies with 
linear models only, and a variety of sensitivity analyses in appendix F 
of the

[[Page 32636]]

EA (Tables F-2 and F-3, USEPA, 2024e). Meta-analyses of studies 
reporting linear associations had statistically significant 
relationships. These relationships are supported by the EPA's review of 
epidemiological studies showing positive associations between PFOA/PFOS 
and TC. The EPA used data from peer-reviewed studies, and the 
assumption of linear exposure-response function to explain associations 
between PFAS and serum lipids such as TC which are supported by data 
from numerous studies, including those used in the meta-analysis. Other 
studies have explored log-linear or linear-log relationships between 
PFAS and serum lipids, while acknowledging only ``slight improvements'' 
in model fit, especially for serum lipids with least skewed 
distributions (Steenland et al., 2009).
    A couple of commenters stated that the downward trend in decreasing 
total and low-density lipid cholesterol since the 1970s coupled with 
the decreasing PFOA and PFOS serum levels suggests that there is a 
substantial likelihood that the proposed MCLs for PFOA and PFOS are 
unlikely to result in benefits as great as those reported in the 
proposal. The EPA disagrees with these comments asserting that 
decreasing trends in cholesterol levels over time indicate that PFAS 
exposure is unlikely to contribute to a measurable increase in CVD 
risk. The EPA relied on recent National Health and Nutrition 
Examination Study (NHANES) data (2011-2016) to inform baseline 
cholesterol and blood pressure conditions in the population evaluated 
under the proposed rule. These data reflect the current population and 
do not reflect cholesterol conditions in the population between 1970 
and 2010. Therefore, the CVD benefits analysis examines how the 
probability of the current population might benefit from reduced 
incidence of hard CVD events.\14\
---------------------------------------------------------------------------

    \14\ Hard CVD events include fatal and non-fatal myocardial 
infarction (i.e., heart attack), fatal and non-fatal stroke, and 
other coronary heart disease mortality.
---------------------------------------------------------------------------

    The EPA received a comment stating that the benefits associated 
with high-density lipoprotein cholesterol (HDLC, often referred to as 
the `good cholesterol') changes are not likely to accrue because the 
evidence of the relationship between PFAS and the health outcome is not 
conclusive, and that this endpoint should not have been quantified. The 
EPA disagrees; although the evidence of a relationship between PFAS 
exposure and HDLC is not conclusive, the SAB recommended that the EPA 
evaluate how the inclusion of HDLC effects would influence results. 
Thus, the EPA evaluated how benefits results are affected by the 
inclusion of HDLC effects in a sensitivity analysis presented in 
appendix K of the EA for the proposed (USEPA, 2023f) and final rule 
(USEPA, 2024e). Additionally, the same commenter and one other 
commenter challenged the EPA's quantification of PFOS and blood 
pressure, stating that the EPA's finding that PFOS might have ``the 
potential'' to affect blood pressure does not meet the SDWA standard 
for inclusion in a benefits analysis and that the ``rationale for 
including changes in BP in relation to PFOS is not clear.'' Another 
comment identified a study that utilized NHANES data and ``did not 
observe an association'' between PFOA and blood pressure. Finally, 
another commenter mentioned that ``neither the ATSDR nor the National 
Academy of Sciences (NAS) have found an association between PFOA/PFAS 
and increased blood pressure.'' While the EPA is aware of this previous 
work, in the EPA's own, more recent assessment, the strength of the 
evidence is determined both by the number but also the quality of 
studies investigating the relationship. One high confidence study 
conducted using U.S. general population data from NHANES showed a 
relationship between PFOS exposure and systolic blood pressure in 
humans (Liao et al., 2020). In addition, several medium and low 
confidence studies provided evidence for an association between PFOS 
and blood pressure and/or hypertension (Mitro et al., 2020; Bao et al., 
2017; Mi et al., 2020; Liu et al., 2018). Because blood pressure is an 
important component of the Atherosclerotic Cardiovascular Disease 
(ASCVD) model used to estimate hard CVD event risk, and because 
epidemiology reports show consistent evidence of an association between 
PFOS and blood pressure in general adult populations (i.e., the 
populations evaluated using the ASCVD model), the EPA included the 
relationship between PFOS exposure and blood pressure in the analysis. 
The EPA further notes that the Science Advisory Board recommended 
modeling the impacts of changes in all ASCVD model predictors 
(including blood pressure and HDLC) for which there is evidence of a 
likely causal relationship (USEPA, 2022i).
    A few commenters questioned the evidence or stated that the 
evidence supporting an association between exposure to PFOA and PFOS 
and CVD is insufficient. The EPA disagrees with these comments. The 
agency's approach to estimating reductions in CVD risk was reviewed and 
supported by SAB panelists (USEPA, 2022i). Numerous studies have shown 
consistent associations between PFOA/PFOS exposure and changes in TC 
and blood pressure which are biomarkers for CVD risk. TC and blood 
pressure are well-established CVD risk biomarkers, are clearly 
associated with CVD events, and are important inputs to the ASCVD model 
that the EPA used to estimate CVD outcomes.
    The EPA received public comments on the benefits analysis for 
developmental effects. A few commenters claimed that the studies used 
for developmental modeling did not provide sufficient evidence of an 
association between PFOA and PFOS exposure and stated that the studies 
which the EPA used to model the developmental effects relationship did 
not consider confounders including pregnancy hemodynamics and other 
chemical and non-chemical stressors, including other PFAS. One 
commenter stated that the EPA's findings are inconsistent with other 
regulatory agency findings that small decreases in birth weight are 
associated with maternal exposure to PFOA and PFOS but not increased 
risk of low birth weight. Other commenters stated that the EPA did not 
address these concerns and inappropriately used these studies to 
support quantitative analysis, and one commenter stated that because of 
the shortcomings of the studies used and the modeling uncertainties, 
peer review of the developmental effects modeling should be completed. 
Although there are some uncertainties in the developmental 
epidemiological effects data (e.g., differences seen across biomarker 
sample timing), the EPA disagrees with these comments: the 
developmental benefits analysis is supported by a wide body of peer 
reviewed science (Verner et al., 2015; Negri et al., 2017; ATSDR, 2021; 
Waterfield et al., 2020; USEPA, 2016c; USEPA, 2016d; USEPA, 2024c; 
USEPA, 2024d). Specifically, birth weight was determined to be a 
critical effect based on findings in the EPA's health assessments (see 
USEPA, 2024c; USEPA, 2024d), and low birth weight is linked to a number 
of health effects that may be a source of economic burden to society in 
the form of medical costs, infant mortality, parental and caregiver 
costs, labor market productivity loss, and education costs.
    Discussion regarding the selection of decreased birth weight as a 
critical effect, including the selection of specific studies for 
candidate RfD derivation and the evidence supporting associations 
between PFOA or PFOS and

[[Page 32637]]

developmental effects, is available in sections 3.4.4 and 4.1 of the 
final toxicity assessments for PFOA and PFOS (USEPA, 2024c; USEPA, 
2024d). In estimating benefits of reducing PFOA and PFOS in drinking 
water, the agency selected results from Steenland et al. (2018) as the 
birth weight exposure-response function for PFOA and results from 
Dzierlenga et al. (2020) as the birth weight exposure-response function 
for PFOS. The agency chose the results from these studies because they 
include the most recent meta-analyses on PFOA- and PFOS-birth weight 
relationships, and they included a large number of studies, including 
multiple studies with first trimester samples (seven studies in 
Steenland et al., 2018 and eight studies in Dzierlenga et al., 2020). 
To provide insights into the potential effects of sample timing and 
pregnancy hemodynamics, the EPA also performed a sensitivity analysis 
considering only first trimester estimates from Steenland et al (2018) 
for PFOA and Dzierlenga et al. (2020) for PFOS in section K.4 of the EA 
appendices (USEPA, 2024e). While reports prior to 2019 found 
``plausible'' or ``suggestive'' (USEPA, 2016d; ATSDR, 2018) evidence of 
relationships between PFOA and PFOS and developmental outcomes, the 
EPA's assessment found clear evidence of an association for PFOA and 
PFOS in both toxicological and epidemiological studies (USEPA, 2024h; 
USEPA, 2024i). The agency further disagrees with the commenter's 
statement that further peer review is needed, as the EPA relies 
extensively on peer-reviewed studies in its developmental benefits 
model. Furthermore, the EPA characterizes the uncertainty in the PFOA 
and PFOS exposure-response functions as described in appendix L of the 
EA (USEPA, 2024e). In short, the benefits analysis for developmental 
effects relies on a wide body of the best available, peer-reviewed 
science, and the epidemiological evidence provides a reliable basis for 
quantifying the risks of low birth weight.
    A different commenter claimed that the EPA relied on equivocal 
epidemiological evidence to estimate developmental benefits, stating 
that the RfDs calculated from animal studies in the EPA's health 
assessment documents for PFOA and PFOS are significantly higher than 
those based on human studies used for benefits analysis and that the 
animal studies represent a more appropriate estimate of the risk of 
PFOA and PFOS exposure. The EPA disagrees with the commenter that the 
analysis relies on equivocal epidemiological evidence to estimate 
benefits. The systematic literature review and assessment conducted by 
the EPA, the most comprehensive evaluation of the current literature to 
date, concluded that there is moderate evidence for developmental 
effects based on consistent adverse effects for fetal growth 
restriction including birthweight measures which are the most accurate 
endpoint (USEPA, 2024c; USEPA, 2024d). One commenter raised concerns 
about the EPA's reliance on the study (Steenland et al., 2018) that the 
EPA uses to model PFOA dose response for benefits analysis, stating 
that the EPA's benefits analysis for PFOA and developmental effects is 
not supported by the underlying publication. The same commenter 
questioned the EPA's reliance on the study that is used to model PFOS 
dose response for benefits analysis (Dzierlenga et al., 2020), stating 
that the study found that there was no evidence of a relationship at 
the beginning of pregnancy. The commenter contended that the meta-
analysis was not peer reviewed and thus the validity of the EPA's 
methods should be questioned. The EPA disagrees with the commenter's 
criticism of the studies used to assess dose response in developmental 
benefits analysis. The selected meta-analyses on the relationship 
between PFOA/PFOS exposure and birth weight produced statistically 
significant results, are based on recent data, and include a large 
number of studies in each meta-analysis.
    One commenter stated that given the discussion about changes over 
time in infant mortality, a dataset containing only two years of data 
is insufficient to build infant mortality regression models. The EPA 
disagrees that two years of data is insufficient to build regression 
models relating infant birth weight to infant mortality. The EPA's 
regression analysis improves upon earlier analyses relating birth 
weight to infant mortality (Almond et al., 2005; Ma and Finch, 2010) by 
evaluating two years of recent data. Sample sizes among the Centers for 
Disease Control and Prevention (CDC) National Center for Health 
Statistics (NCHS) linked birth/infant death data per year are large (n 
= approximately 3.8 million infants) and contribute to the overall 
statistical significance of regression results. As described in 
appendix E of the EA (section E.2, USEPA, 2024e), there has been a 
notable decline in U.S. infant mortality rates since the analyses 
reported in Ma and Finch (2010) and Almond et al. (2005). Using recent 
data from two CDC NCHS linked birth/infant death data cohorts results 
is a more accurate and conservative characterization of recent infant 
mortality trends than if the EPA had included older CDC NCHS data.
    The EPA received comments on the benefits analysis for RCC. Two 
commenters expressed concerns with the EPA's use of Shearer et al. 
(2021) to estimate RCC risk in benefits analysis and claimed flaws in 
the study related to outliers in the RCC group and inconsistent 
evidence of an association across epidemiological studies. One 
commenter stated that given what they perceive as SAB concerns and 
uncertainties in the modeling, further peer review is warranted. The 
EPA disagrees with the comments critical of the agency's use of 
information from the Shearer et al (2021) study for purposes of PFOA 
health assessment and benefits analysis. As noted in section 3.5.1 of 
the Final Toxicity Assessment for PFOA (USEPA, 2024c), the EPA 
determined that Shearer et al. (2021) is a medium confidence study 
after conducting study quality evaluation consistent with the ORD Staff 
Handbook for Developing IRIS Assessments (USEPA, 2022f). The 
biomonitoring measures of PFOA levels in Shearer et al. (2021) were 
reliable measures of PFOA exposure due to the chemical's well-
established long half-life. The commenters failed to acknowledge 
multiple studies further supporting a positive association between PFOA 
exposure and RCC risk (Bartell and Vieira, 2021; Vieira et al., 2013; 
Steenland et al., 2022). Critically, the SAB PFAS Review Panel 
supported the Likely to be Carcinogenic to Humans designation for PFOA 
in its final report (USEPA, 2022i). Shearer et al (2021) has been 
sufficiently peer reviewed and it represents the best available science 
for purposes of health and benefits assessment in the PFAS NPDWR.
    The EPA received comments on uncertainties associated with bladder 
cancer reductions. One commenter incorrectly stated that the ``EPA does 
not recognize the uncertainty that there is not always direct 
correlation between THM4 levels and TOC in all public water systems''. 
In response, the EPA notes that the THM concentrations in this co-
removal analysis were not calculated based on TOC reduction. TOC was 
used to bin systems in the universe of PWSs using the fourth Six-Year 
Review (SYR4) database and PFAS occurrence model with the THM4 
reduction calculated from the formation potential experiments before 
and after GAC treatment in the DBP Information Collection Rule 
Treatment Study Database. This dataset reflects the current best 
available data to determine THM4 reduction based on TOC removal

[[Page 32638]]

using GAC treatment. Another commenter stated that the causal link of 
DBPs and bladder cancer has not been established. The EPA notes that an 
extensive body of epidemiological studies have shown that increased 
exposure to chlorinated DBPs is associated with higher risk of bladder 
cancer and other adverse health outcomes (Cantor et al., 1998; Freeman 
et al., 2017). Weisman et al. (2022) found that approximately 8,000 of 
the 79,000 annual bladder cancer cases in the U.S. were potentially 
attributable to chlorinated DBPs in drinking water systems. While 
research has not established a causal link between THM4 and bladder 
cancer, there is strong evidence that there is a correlation between 
THM4 and bladder cancer.
    One commenter stated that the DBP co-removal benefit analysis did 
not meet the standards required by SDWA for estimating benefits since 
it was not reviewed by the SAB. The commenter is incorrect. SDWA 
1412(e) directs the EPA to request comments from the SAB prior to 
proposing an MCLG and NPDWR. The EPA sought and received comment from 
the SAB prior to proposing this NPDWR (see USEPA, 2022i). The statute 
does not dictate the precise level of scientific questions for which 
the EPA must seek comments from the SAB. The EPA sought SAB comment on 
the four most significant areas that informed derivation of the MCLGs 
for all six PFAS regulated by this action and for other parts of the 
benefits analysis that informed the overall development of the NPDWR. 
The EPA did seek additional peer review of its DBP co-removal benefit 
analysis prior to its inclusion in the EA for which it received 
overwhelmingly favorable comments from reviewers (see USEPA, 2023m). 
Furthermore, this rule is based on the EPA's consideration of a wide 
body of existing peer-reviewed science on this subject (e.g., Regli et 
al., 2015; Weisman et al., 2022). In short, the EPA has used peer 
reviewed science and sought further peer review to support its DBP co-
removal analysis, and as part of the supporting material for the rule 
proposal, the EPA included the comments from the expert peer reviewers 
as well as how each comment was addressed or the rationale for why it 
was not changed. Please see Response to Letter of Peer Review for DBP 
Co-benefits (USEPA, 2023m) for discussion of that peer review and the 
EPA's responses to peer reviewed comments.
    Another commenter claimed that the EPA improperly quantified 
benefits of co-removed substances rather than co-occurring substances. 
The EPA disagrees with these assertions since the analysis of DBP co-
removal is focused on co-occurring contaminants. As demonstrated 
elsewhere in the record for this action, PFAS commonly co-occur with 
each other. Additionally, in waters where disinfection is required, TOC 
(i.e., a DBP precursor) and PFAS may co-occur. The DBP co-removal 
benefits analysis relied on DBP formation potential experiments that 
highlighted the changes to TOC with and without GAC treatment. 
Furthermore, as discussed above, the methodology to estimate THM4 
reductions was externally peer reviewed by three experts in GAC 
treatment for PFAS removal and DBP formation potential.
    A few commenters stated that the EPA already had initiatives to 
reduce THMs in drinking water and suggested that reduction of bladder 
cancer cases is better addressed through existing DBP rules. While the 
EPA agrees that there are existing DBP regulations to reduce DBP 
exposure and risks, this rule will provide additional health risk 
reduction benefits associated with enhanced DBP reduction. The EPA has 
considered those co-removal benefits as part of the EA. The EPA notes 
that it is required under the SDWA 1412(b)(3)(C)(i)(II) to assess 
quantifiable and nonquantifiable health risk reduction benefits for 
which there is a factual basis in the rulemaking record to conclude 
that such benefits are likely to occur from reductions in co-occurring 
contaminants that may be attributed solely to compliance with the MCL, 
excluding benefits resulting from compliance with other proposed or 
promulgated regulations. DBP reductions presented in the EPA's HRRCA 
are those that are anticipated to result solely from compliance with 
the PFAS MCLs. As required under the SDWA, any quantifiable and 
nonquantifiable benefits from future actions concerning DBPs in 
drinking water will be addressed at the time of those actions and are 
independent from benefits stemming as a result of the PFAS rulemaking. 
A couple of commenters supported the EPA's analysis of DBP benefits but 
recommended that the EPA also consider other co-removed contaminants. 
The EPA agrees with the commenters that multiple co-occurring 
contaminants will be removed as a result of this rule. Furthermore, the 
EPA acknowledges in the EA that additional co-removal benefits would be 
realized due to treatment for PFAS. With the exception of DBPs co-
removed, the EPA has not quantified other co-removal benefits at this 
time because of data limitations, the agency included discussion of 
nonquantifiable benefits for multiple other PFAS and for other 
contaminants.
Nonquantifiable Benefits of PFAS Exposure Reduction
    One commenter expressed that the EPA's characterization of benefits 
is inadequate and not supported by science. The commenter specifically 
discussed hepatic effects, endocrine effects, and musculoskeletal 
effects and asserted that the EPA's characterization is based on mixed 
findings and inconsistent evidence regarding PFAS exposures and 
specific health outcomes. The EPA disagrees with this comment, as the 
EPA has evaluated the best available peer reviewed science, as required 
under SDWA. The EPA did not quantify or monetize benefits where there 
are inadequate data. For hepatic effects, the EPA's toxicity 
assessments determined that there is moderate evidence supporting the 
association between exposure to PFOA/PFOS and hepatic toxicity in 
humans. However, the EPA did not quantify benefits for hepatic effects 
because although there will be benefits delivered by reducing PFOA and 
PFOS in drinking water, there is a lack of adequate data available to 
accurately quantify those benefits. Further information on health 
effects related to PFAS exposures is provided in the health assessments 
within the MCLG documents (USEPA, 2024c; USEPA, 2024d).
    Conversely, some commenters expressed support for the 
quantification that the EPA has already performed, stated that the 
benefits of the rule are underestimated, and urged the EPA to quantify 
and monetize additional health endpoints, particularly mammary gland 
and lactational effects, immunotoxicity, and liver disease. These 
commenters also provided additional resources and information with the 
intention of the EPA using that information to update analyses 
regarding lactational effects, expand analyses to include immune 
effects, and adjust analyses to characterize hepatotoxicity as a 
quantifiable benefit, as opposed to a non-quantifiable one. Commenters 
also urged the EPA to quantify some of the benefit categories, even if 
monetization is not possible, and to highlight the magnitude of some of 
the qualitatively discussed benefits. The EPA agrees with these 
commenters that the quantified benefits of the rule are underestimated. 
Where appropriate, the EPA used medical cost information provided by 
the commenters to supplement qualitative discussion of adverse effects. 
Additionally, and based on these comments, the EPA considered

[[Page 32639]]

information in the record and added additional quantified benefits 
analysis in the sensitivity analysis evaluating the reductions in liver 
cancer cases expected by reducing concentrations of PFAS. This 
additional analysis was confirmatory of the EPA's previous analysis and 
did not result in changes to the NPDWR's requirements.
    Some commenters also provided recommendations regarding the 
inclusion of additional costs and benefits beyond health endpoints. 
These included the opportunity cost of time, environmental benefits, 
and psychosocial benefits that are expected to result from the rule. 
The opportunity cost of time was suggested to be incorporated into 
morbidity estimates, while the other benefits were suggested to be 
encapsulated in a qualitative summary.
    In the EA document, the EPA describes that the cost of illness 
(COI)-based approach does not account for the pain and suffering 
associated with non-fatal CVD events. Based on the above comments, for 
quantified cancer endpoints (i.e., RCC and bladder cancers), the EPA 
has included a new sensitivity analysis using willingness to pay values 
for risk reductions which can inform the direction of benefits when 
opportunity cost is included. This additional analysis was confirmatory 
of the EPA's previous analysis and did not result in changes to the 
NPDWR's requirements.
c. Final Rule Analysis
    For the final rule, the EPA retained the quantitative benefits 
analyses from the proposal for developmental, CVD, and cancer endpoints 
as well as the bladder cancer benefits from DBP exposure reduction as a 
result of the rule. In response to comments described above, the agency 
identified new information on willingness to pay values for non-fatal 
cancer risk reductions and added additional sensitivity analyses for 
RCC and bladder cancer in appendix K to the final rule EA (USEPA, 
2024e). In light of new epidemiological studies on PFOS exposure and 
liver cancer that strengthened the weight of evidence and supported the 
toxicological information that was identified in the proposed rule, and 
comments received requesting that the EPA monetize additional health 
endpoints, the EPA developed a sensitivity analysis assessing the liver 
cancer impacts in appendix O of the final rule EA (USEPA, 2024e). The 
EPA estimates that PFOS liver cancer benefits would add $4.79 million 
annually to the national benefits estimates. The EPA retained 
discussion of nonquantifiable benefits associated with PFAS exposure 
reduction from the proposed rule for the final rule EA.
2. Treatment Costs
a. Treatment Cost Estimates in the Proposal
    The EPA estimated costs associated with engineering, installing, 
operating, and maintaining PFAS removal treatment technologies, 
including treatment media replacement, and spent media destruction or 
disposal, as well as nontreatment actions that some PWSs may take in 
lieu of treatment, such as constructing new wells in an uncontaminated 
aquifer or interconnecting with and purchasing water from a neighboring 
PWS. To evaluate the treatment costs to comply with the proposed PFAS 
NPDWR, the EPA used the agency's Work Breakdown Structure (WBS) models, 
a spreadsheet-based engineering models for individual treatment 
technologies, linked to a central database of component unit costs. The 
WBS models are extensively peer-reviewed engineering models for 
individual treatment technologies and discussed in section XII.D of 
this preamble. The EPA used PFAS occurrence outputs from a Bayesian 
hierarchical estimation model of national PFAS occurrence in drinking 
water (Cadwallader et al., 2022), to estimate the number of water 
systems exceeding the proposed MCLs, and therefore triggered into 
action to comply with the proposed MCLs.
b. Summary of Major Public Comments on Treatment Costs and EPA 
Responses
    Many commenters state that the EPA has underestimated the treatment 
costs required to comply with the proposed MCLs. One commenter 
suggested that the EPA has not complied ``with its statutory 
requirements by conducting an analysis that fully captures these 
costs.'' The EPA disagrees with the few commenters that suggested the 
EPA has not met its requirements under SDWA, and the EPA emphasizes the 
agency has used the best available peer reviewed science to inform it 
cost estimates, including treatment costs, of the MCLs. Specific 
aspects of comments related to treatment costs and the EPA's response 
are discussed further in this section.
    Many commenters cited rising costs in the drinking water sector and 
discussed the effects of inflation and the COVID-19 pandemic on the 
costs of labor, construction, and capital, among other materials 
related to compliance with the MCLs. These commenters emphasized the 
significant impacts felt from supply chain and workforce issues. The 
EPA recognizes these impacts, and as recommended by commenters, 
adjusted the cost estimates by escalating unit costs using indices 
including the Bureau of Labor Statistics producer price indices (USBLS, 
2010). The EPA updated each unit cost using the change in the relevant 
price index from year 2020 to 2022. For example, the EPA applied the 
percent increase of the price of metal tanks and vessels (50 percent 
increase from 2020 to 2022) to the price of metal tanks and vessels in 
the WBS cost models. The EPA also collected new vendor price quotes for 
cost driver equipment components (e.g., pressure vessels, treatment 
media) and made several other adjustments to WBS model assumptions, 
described further in this section. Taken together, these adjustments 
increased the system level capital cost estimates in the EPA's cost 
assessment by a percentage that varied depending on the system size and 
treatment technology. For small systems using GAC and IX, the increase 
ranged from approximately 40 percent to 110 percent. For medium 
systems, the increase was approximately 20 to 60 percent; for large 
systems, 10 to 40 percent. Additionally, while revising the SafeWater 
model to incorporate new information from public comments, the EPA 
identified and corrected a coding error related to the discounting of 
future operation and maintenance costs resulting in increased estimated 
annualized treatment costs. The result of these changes are increased 
cost estimates for the final rule.
    Some commenters state that while BIL funding is available, it is 
not enough to cover the compliance costs of the rule. For example, one 
commenter noted that, ``[t]his amount of funding support, while 
crucial, will come nowhere near the cost to ratepayers that must be 
borne to implement necessary compliance actions for these MCLs.'' The 
EPA disagrees with the commenter that BIL funding will be nowhere near 
the cost'' necessary to implement compliance actions. The EPA estimates 
that the initial capital costs of the rule in undiscounted dollars is 
approximately $14.4 billion (see appendix P of the EA for more 
information). Given the BIL appropriations of $11.7 billion in DWSRF 
and an additional $5 billion for emerging contaminants, the EPA 
reasonably anticipates BIL funding is likely to be able support a 
substantial portion of the initial capital costs of the final rule. BIL 
funding appropriations began in the Federal Fiscal Year (FFY) 2022 and 
appropriations are anticipated to continue through FFY 2026.
    Many commenters shared some information about the costs that they

[[Page 32640]]

have incurred or estimated they would incur at a system level to 
install, operate, and maintain treatment to remove PFAS. Some system 
level cost information provided by commenters fell within the ranges of 
costs presented in the EPA's supporting documentation for the proposal 
and other information provided by commenters exceeded the EPA's system 
level cost ranges. The EPA does not dispute the commenters stated 
experience of costs to install, operate and maintain treatment to 
remove PFAS; however, many of these comments lacked supporting details. 
Many of the comments cited preliminary or conceptual estimates and did 
not specify the methods and assumptions used to develop the estimate. 
Furthermore, most comments did not include information to confirm that 
all of the reported or estimated costs were or would be directly 
associated with PFAS treatment, as opposed to other infrastructure 
improvements (e.g., capacity expansion, administrative facilities, 
distribution system improvements) that happened to be completed as part 
of the same project. Most commenters also did not include information 
to confirm that key design and operating parameters (e.g., empty bed 
contact time, media replacement frequency) would be similar to the 
typical values assumed in the EPA's estimates. To fully evaluate the 
commenters' reported or estimated costs in comparison to WBS model 
results, the EPA would need itemized line-item cost details and 
engineering design parameters. To inform the cost estimates of the 
proposed and final PFAS NPDWR, the EPA conducted an extensive review of 
the literature. The EPA has further validated the unit costs in the 
PFAS rule with equipment cost information from 2023 from a major 
supplier of treatment media. While the EPA recognizes there are likely 
site-specific instances where costs exceed the EPA's cost ranges, there 
are also likely site-specific instances where costs are less than the 
EPA's cost ranges, and this level of accuracy is appropriate for a 
national level analysis.
    Other commenters compared state-level costs to the EPA's national 
level cost estimates, noting that the EPA's estimates appeared too low. 
Utilizing this permit data and project cost data submitted by water 
systems in applications to the DWSRF, one state estimated that total 
capital costs for installation of PFAS treatment to meet the EPA's 
proposed standards across the state could be as high as $1.065 billion. 
The EPA's EA analysis, however, presents national level cost estimates 
that are annualized over the period of analysis and are therefore not 
directly comparable to a single year estimate of capital costs.
    A few commenters stated that the EPA incorrectly omitted the costs 
associated with performance monitoring, which commenters believe will 
be necessary because a water system needs to know how often it needs to 
replace its media. The EPA disagrees that large amounts of additional 
samples in performance monitoring will be required, and the commenter 
provided no data to support their assertion that this would be 
necessary. The EPA anticipates that many water systems will conduct a 
pilot test before implementing a full-scale treatment installation and 
that the operational results from the pilot test will be a sufficient 
indicator of performance; therefore, water systems should not have to 
collect large amounts of performance samples indefinitely during the 
full-scale operation of treatment technologies. The EPA includes the 
costs of pilot testing, and sampling during that time, in the treatment 
capital cost estimates. In response to public comments, the EPA 
increased the estimated length of the pilot study and the frequency of 
sampling during the pilot study. Additionally, the EPA added a full 
year of confirmation sampling after full-scale installation to the 
estimated pilot study costs. Taken together, these changes doubled to 
more than tripled the pilot study costs included in the EPA's 
estimates.
    In response to public comments about residual management concerns 
for high pressure membrane technologies, the EPA has adjusted RO/NF's 
technology projection compliance forecast to zero percent in the EA for 
the final rule. Therefore, the EPA assumes that RO/NF will not 
generally be used solely for the purpose of complying with the final 
rule. For more information on public comments on residuals management 
and the EPA's response please see section X.
    A few commenters stated that the EPA underestimated or 
insufficiently incorporated contingency in its cost estimates. For 
example, one commenter stated that the EPA's contingency assumptions in 
the proposal were ``. . . inconsistent with recommended best practices 
for cost estimators and [are] expected to be a major contributor to the 
EPA WBS' failure to accurately capture costs for PFAS treatment 
facility implementation.'' In response to these comments, the EPA 
changed its approach and incorporated contingency for all systems, not 
just high-cost systems. The EPA also increased the complexity factor 
applied to estimate contingency for systems using GAC. Taken together, 
these changes result in a contingency factor of 5 to 10 percent 
depending on total project cost at all cost levels for systems 
installing treatment. Additionally, the EPA includes a miscellaneous 
allowance of 10 percent. This allowance can be viewed as either as a 
form of contingency or a method to increase the level of project 
definition (thus reducing the amount of contingency required).
    One commenter stated that the EPA underestimated the costs 
associated with interconnection.\15\ This commenter stated that it was 
``unrealistic to assume that booster pumps are unlikely to be 
necessary. Pressure loss associated with friction could be significant, 
especially for an interconnection that may span 10,000 feet or more,'' 
and recommended that the EPA include booster pumps in the cost 
estimate. Commenters also pointed out that ``. . . systems considering 
interconnections will need to thoroughly investigate this option and 
determine if it is both cost effective and appropriate given the water 
quality impacts.'' In response to these comments, the EPA made several 
changes to the assumptions used to estimate costs for interconnection 
in the WBS model for nontreatment options. The EPA agrees that booster 
pumps may be needed and added the costs of booster pumps designed to 
account for friction loss in interconnecting piping. The EPA also 
agreed that there are many considerations for water systems pursuing 
interconnections including elevated water age, nitrification, and DBPs, 
as pointed out by commenters, and therefore the EPA increased the 
complexity factor applied to estimate contingency for systems using 
nontreatment options. Taken together with the escalation to 2022 
dollars, these changes increased the system level capital costs for 
interconnection by approximately 60 to 100 percent.
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    \15\ Interconnection is when a system replaces their 
contaminated water source by purchasing water from another nearby 
system that is in compliance. Booster pumps can be needed when the 
pressure from the supplying system is lower than required at the 
purchasing system and also to overcome pressure losses due to 
friction in interconnecting piping.
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    Many commenters cited and expressed agreement with the conclusions 
of a study conducted by Black & Veatch on behalf of the American Water 
Works Association (AWWA) (hereafter referred to as AWWA's B&V report) 
(AWWA, 2023). The EPA disagrees with many of the assumptions in AWWA's 
B&V report and the report's overall conclusions

[[Page 32641]]

about the estimated national costs of the PFAS NPDWR. Tables 24-26 
detail some of the key assumptions related to (1) PWSs that exceed the 
MCL, (2) capital costs and (3) operation and maintenance costs that 
overestimate national treatment costs in AWWA's B&V report and the 
EPA's response to those assumptions and resulting estimates. In 
combination, all these factors result in an overestimate of treatment 
costs. For example, AWWA's B&V report Table 6-1 reports an average 
capital cost per EP for the smallest size category of $900,000. Using 
AWWA's B&V report's (overestimated) design flow calculations, the 
treatment system design flow at each EP would be approximately 0.062 
million gallons per day (mgd). For comparison, Forrester (2019) reports 
capital equipment costs of approximately $300,000 for a 1 mgd GAC PFAS 
treatment system. Even after adding indirect capital and building 
costs, the $900,000 estimate appears substantially overestimated, given 
that it is for a treatment system designed for approximately 1/16th of 
the flow of the system in the Calgon Carbon estimate (Forrester, 2019). 
When AWWA's B&V report's EP level results are aggregated nationally to 
an overestimated number of systems treating for PFAS, the overestimates 
are compounded at the national level.
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c. Treatment Costs in the Final Rule Analysis
    The cost estimates in the EA for the final PFAS NPDWR reflects the 
adjustments made to the WBS curves and decision tree based on public 
comments discussed above as well as the additional occurrence 
information available since the publication of the proposed PFAS NPDWR. 
For detailed information on the EPA's occurrence analysis, see section 
VI of this preamble. For detailed information on the EPA's cost 
analysis and the EPA's estimates of the national annualized costs of 
the final MCLs, see section XII.D.
3. Primacy Agency Costs
a. Primacy Agency Cost Estimates in the Proposal
    In the EA for the proposed rule, the EPA estimated the costs 
incurred by primacy agencies associated with the rule, including up 
front implementation costs as well as costs associated with system 
actions related to sampling and treatment.
b. Summary of Major Public Comments on Primacy Agency Costs and EPA 
Responses
    Many commenters state that the EPA has underestimated the costs to 
primacy agencies required to comply with the rule. One commenter 
stated, ``EPA's analysis of primacy agency costs does not accurately 
capture all the activities that primacy agencies will undergo for PFAS 
implementation and underestimates the number of hours for the primacy 
tasks.'' Commenters recommend that the EPA use findings from ASDWA's 
PFAS Cost of State Transactions Study (PCoSTS) to reevaluate the 
primacy agency costs estimated in the EA. The EPA's response to 
specific recommendations is discussed here.
    The EPA agrees with commenters on the burdens associated with 
regulatory start up; primacy package adoption; technical, managerial, 
and financial (TMF) assistance to water systems; and reviewing and 
approving treatment. Commenters pointed out activities not explicitly 
accounted for in the regulatory start up estimate in the EA for 
proposal including accreditation of laboratories for PFAS testing; 
SDWIS updates; monitoring schedule updates; time spent responding to 
questions from members of the public; inquiries from public officials; 
and media requests immediately following the final publication of the 
NPDWR. Commenters also pointed out that adopting primacy packages is a 
significant undertaking with ``specific and very detailed 
administrative procedures that must be adhered to in order to adopt 
water quality regulations'' and that ``some primacy agencies have 
requirements for robust public comment periods as a component of new 
rule adoption.'' As recommended by commenters, the EPA created a new 
cost item for primacy package adoption. Commenters stated the EPA's 
assumption in the proposal that the amount of time a primacy agency 
will need to review treatment plans directly correlates with the size 
of the water system was inaccurate. Commenters noted that ``. . . small 
systems often take the most time as they need significant assistance to 
navigate the process for the design and construction of new treatment 
and get into compliance.'' After considering these comments, the EPA 
agrees that reviewing and approving treatment for small systems is 
likely to take more time given the assistance needed for these systems. 
Because small systems often lack the technical, managerial, and 
financial capacity, it is likely that primacy agencies will spend more 
time assisting these systems in navigating compliance with the PFAS 
NPDWR. As such, the EPA adjusted burden estimates in the final rule to 
reflect the largest primacy agency burden per EP at the smallest 
systems and decreased burden hours with increasing system size, as 
commenters suggested.
    Several commenters disagreed with the EPA's exclusion of additional 
costs to primacy agencies associated with reporting regarding 
violations, variances and exemptions, enforcement actions, and other 
compliance related primacy agency activities in the national cost 
analysis. One commenter estimated the PFAS NPDWR will likely result in 
hundreds of violations once in effect. The EPA recognizes that these 
activities do have an associated burden for primacy agencies but 
disagrees that these costs should be included in the EA. The EPA 
assumed 100 percent compliance for its national level analysis in the 
EA for the final rule because the EPA has determined that the final 
rule is feasible given known occurrence concentrations and efficacy of 
the technologies available. Further, this is consistent with the 
approach taken in EAs for other NPDWRs (USEPA, 2005c; USEPA, 2019c; 
USEPA, 2020f). Commenters recommended that the EPA include hours for 
additional annual reporting. The EPA disagrees and expects that adding 
PFAS results to already-required reports will have no discernable 
incremental burden for quarterly or annual reports to SDWIS Fed.
    Commenters recommended that the EPA include the costs associated 
with various compliance activities. Given the EPA's assumption of 100 
percent compliance for its national level analysis in the EA discussed 
above, the EPA disagrees and did not take commenters' recommendations 
to include the costs associated with assisting out of compliance 
systems and assisting systems to remain in compliance, pursuing 
enforcement actions, staff time checking in with system violations and 
reviewing system variances and exemptions. The EPA did include the 
costs associated with compliance activities for systems in compliance, 
including updating inspection SOPs and additional sanitary survey 
burden at water systems that have installed treatment to comply with 
the PFAS NPDWR.
c. Primacy Agency Costs in the Final Rule Analysis
    After considering public comments on the burden hours associated 
with primacy agency activities, the EPA made the following changes. The 
EPA increased the estimate from 416 hours to ``read and understand the 
rule as well as adopt reg requirements'' to 4,000 hours per primacy 
agency to conduct a suite of regulatory start up activities. Per 
commenters' recommendation, the EPA included a new line item for 
primacy package adoption and estimated 300 hours per primacy agency. 
The EPA lowered the water system operator TMF training from 2,080 hours 
to 1,500 hours per primacy agency based on commenter recommendations. 
The EPA added a one-time burden estimate of 20 hours to inspection SOPs 
and an additional 2-5 burden hours for the primacy agency, by water 
system size, per sanitary survey per system installing treatment to 
comply with the rule. For more information see section XII.D.
4. Costs of the Hazard Index
a. Hazard Index Cost Estimates in the Proposal
    In the EA for the proposed rule, the EPA estimated national costs 
associated with PFOA, PFOS, and PFHxS. Given available occurrence data 
for the other compounds in the proposed rule (PFNA, HFPO-DA, and PFBS) 
and the regulatory thresholds under consideration, the EPA did not use 
SafeWater to model national costs associated with potential Hazard 
Index (HI) exceedances as a direct result of these contaminants. To 
assess the potential impact of these compounds in the proposed rule, 
the EPA conducted an analysis of the additional, or

[[Page 32649]]

incremental, system level impact that occurrence of these contaminants 
would have on treatment costs. The EPA estimated that the Hazard Index 
would increase costs by 0-77 percent at the system level, with costs 
varying due to PFAS occurrence scenario and treatment technology used.
b. Summary of Major Public Comments on Hazard Index Costs and EPA 
Responses
    A few commenters recommended that the EPA further consider the 
costs associated with compliance with the Hazard Index (HI) MCL. 
Specifically, commenters stated that the EPA's analysis of system level 
costs associated with the Hazard Index does not adequately characterize 
the overall costs that will be incurred due to the Hazard Index 
standard. One commenter stated that ``EPA should not move forward with 
the Hazard Index until it has satisfied its statutory and policy 
obligation to conduct a cost-benefit analysis.'' Some commenters voiced 
concern regarding the EPA's assumption that costs associated with 
compliance with the Hazard Index MCL are insignificant and asserted 
that these costs must be reexamined, stating that this assessment 
``requires more knowledge on the nationwide occurrence of these 
compounds'' and that the EPA ``cannot assume that addressing the costs 
of PFOA and PFOS is sufficient when the additional four PFAS will be 
driving treatment decisions at some PWSs.'' Conversely, one commenter 
asserted that available occurrence data demonstrate that few systems 
will be required to install treatment to comply with the Hazard Index 
MCL that would not already be treating to comply with the PFOA and PFOS 
MCLs.
    The EPA disagrees with commenters who state that the agency did not 
meet its requirements under SDWA, which requires the agency to analyze 
``quantifiable and nonquantifiable costs . . . that are likely to occur 
solely as a result of compliance with the maximum contaminant level.'' 
In the proposal, the EPA analyzed the quantifiable costs of the Hazard 
Index at the system level, using the best available information at the 
time of publication, and analyzed the nonquantifiable costs of the 
Hazard Index by including a qualitative discussion of the national 
level impacts and therefore met the statutory requirements under SDWA 
1412(b)(3)(C). After considering recommendations from the public 
comments to further analyze the costs of the Hazard Index and the data 
available to support a quantitative analysis of the costs of the Hazard 
Index, the EPA decided to conduct a sensitivity analysis of the costs 
of the Hazard Index at the national level. The results of the 
sensitivity analysis supported the EPA's assumption in the proposal 
that quantified national costs are marginally underestimated as a 
result of this lack of sufficient nationally representative occurrence 
data. The EPA's consideration of Hazard Index costs in the final rule 
analysis are discussed in the following subsection.
c. Hazard Index and PFHxS, PFNA, and HFPO-DA MCL Costs in the Final 
Rule Analysis
    To estimate quantified costs of the final rule presented in the 
national-level summary tables, the EPA first estimated baseline PFAS 
occurrence using a Bayesian hierarchical model fitted with sampling 
data collected from systems participating in UCMR 3. The model included 
three of the six PFAS compounds regulated through this NPDWR: PFOA, 
PFOS, and PFHxS (see section VI of this preamble). This permitted the 
agency to quantify costs at a national level with a higher degree of 
confidence and precision for these three PFAS than if simple 
extrapolations had been used. Since there are some limitations with 
nationally representative occurrence information for the other 
compounds that were either not included in UCMR 3 (HFPO-DA) or did not 
have a sufficient number of observed values above the UCMR 3 reporting 
limits (PFNA, PFBS), the EPA has a lesser degree of confidence and 
precision for its quantified estimates of these three PFAS, which are 
informed by a significant amount of available state-level data. 
Therefore, the EPA presented the cost estimates for PFNA, HFPO-DA, and 
PFBS in a sensitivity analysis in the EA (i.e., national-level 
sensitivity analysis, see appendix N.3) instead of including these 
costs in the summary tables of quantified national level costs.\16\
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    \16\ When available, nationally representative occurrence 
information is preferable for an economic analysis of national level 
costs and benefits. In the case of PFOA, PFOS, and PFHxS, the EPA 
has a sufficiently robust nationally representative dataset from 
UCMR 3. The EPA used additional state data that were available at 
systems that were part of this UCMR 3 set of systems to fit the 
national occurrence model that informed cost estimates for PFOA, 
PFOS, and PFHxS (see Cadwallader et al., 2022). In the case of PFNA, 
HFPO-DA, and PFBS, the EPA lacks the same level of precision as 
described above for PFOA, PFOS, and PFHxS. State-led data collection 
efforts provided valuable information about occurrence for PFNA, 
HFPO-DA, and PFBS, however they did not provide the nationally 
representative foundation provided by UCMR3 for PFOA, PFOS, and 
PFHxS to be incorporated into the MCMC national occurrence model.
---------------------------------------------------------------------------

    In the EA for the proposed PFAS NPDWR, the EPA used a model system 
approach \17\ to illustrate the potential incremental costs for 
removing PFAS not included in the national economic model (i.e., PFNA, 
HFPO-DA, and PFBS). After considering public comments on the 
incremental cost analysis, many of which encouraged the EPA to further 
evaluate and consider quantified costs of the Hazard Index MCL where 
feasible, the EPA updated and combined existing analyses contained in 
the rule proposal to evaluate the incremental costs associated with the 
Hazard Index MCL and individual MCLs for PFNA and HFPO-DA with a 
quantified national level sensitivity analysis in the final rule. The 
updated analysis for the final rule builds on the proposal analysis by 
combining information that was presented separately at proposal. The 
analysis in appendix N of the final EA utilizes the system level 
treatment cost information presented at proposal (See appendix N of 
USEPA, 2023n, 2023o) with updates to the cost models for the final rule 
detailed in section XII.A.2. These treatment costs were applied to the 
number of systems expected to exceed the standards based on PFNA, PFBS, 
and HFPFO-DA occurrence using the approaches for estimating occurrence 
of these compounds presented at proposal (see section 10.3 of USEPA, 
2023l). This modified analysis was primarily conducted to ensure that 
the EPA has not, as some commenters claim, substantially underestimated 
the potential magnitude of these costs. The EPA notes the approach 
presented in appendix N for the final rule and summarized here, by 
connecting analyses for proposed rule, allows the agency to consider 
and compare the relative degree of the potential overall costs of these 
otherwise nonquantifiable costs of the Hazard Index and PFNA and HFPO-
DA MCLs relative to overall national rule costs. This analysis confirms 
the EPA's findings at proposal that the Hazard Index costs (and those 
costs for regulating PFNA and HFPO-DA individually) make up a small 
portion of

[[Page 32650]]

the overall rule costs. Likewise, the EPA notes that while these costs 
are presented in appendix N because of the lesser degree of confidence 
and precision in the estimates, the EPA has considered these costs as 
part of this final regulation. It has done so by evaluating 
nonquantifiable costs and accounting for uncertainty, characterizing 
these otherwise nonquantifiable costs in appendix N to generate cost 
estimates that, while useful, are not as statistically robust as the 
national cost estimates presented in chapter 5 of the EA. Using this 
analysis, the agency has confirmed the Hazard Index and PFNA and HFPO-
DA MCLs drive a relatively low percentage of the overall rule costs. 
The EPA has also considered these costs in the context that the Hazard 
Index and PFHxS, PFNA, and HFPO-DA MCLs are expected to deliver 
important nonquantifiable health benefits, including PFNA birth weight 
benefits \18\ and other nonquantifiable benefits associated with the 
reduction of the Hazard Index PFAS (PFNA, PFHxS, HFPO-DA, and PFBS) 
\19\ described in chapter 6.2 of the EA.
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    \17\ At proposal, the EPA used a model system approach for 
estimating potential incremental treatment costs associated with co-
occuring PFAS at systems already required to treat in the national 
model framework and the potential per system costs for the set of 
systems triggered into treatment as a result of Hazard Index MCL 
exceedances not already captured in the national analysis. For 
further detail on the assumptions and findings of the EPA's analysis 
of incremental costs of other PFAS at rule proposal, please see 
appendix N.3 in the Economic Analysis for the Proposed Per- and 
Polyfluoroalkyl Substances National Primary Drinking Water 
Regulation (USEPA, 2023n, 2023o).
    \18\ As discussed in appendix K.4, a 1 ppt reduction in both 
PFOA and PFOS for a system serving a population of 100,000 would 
result in $0.101 million in annualized birth weight benefits. If 
including a 1 ppt PFNA reduction, in addition to a 1 ppt reduction 
in both PFOA and PFOS, for a system serving a population of 100,000, 
the resulting annualized birth weight benefits would increase by 
$0.464 to $0.689 million, depending on the slope factor used for 
PFNA. The EPA estimates that 208 water systems may exceed the PFNA 
MCL.
    \19\ The EPA also anticipates additional substantial benefits to 
PWS customers associated with reduced exposure to Hazard Index 
compounds (PFHxS, HFPO-DA, PFNA, and PFBS) not included in the 
primary analysis. The nonquantifiable benefits impact categories 
include developmental, cardiovascular, immune, hepatic, endocrine, 
metabolic, reproductive, musculoskeletal, and carcinogenic effects. 
See chapter 6.2 of the EA for more information.
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    The proposed rule included a Hazard Index MCLG and MCL for any 
mixture of one or more of PFHxS, HFPO-DA, PFNA, and PFBS. The final 
rule includes a Hazard Index MCLG and MCL for any mixture of two or 
more of PFHxS, HFPO-DA, PFNA, and PFBS. The final rule also includes 
individual MCLGs and MCLs for PFHxS, PFNA, and HFPO-DA. The EPA's cost 
analysis at proposal considered the costs associated with the 
individual MCLs for PFHxS, PFNA, and HFPO-DA because the proposed 
Hazard Index MCL would function as individual MCLs when these 
contaminants occur in isolation. While the rule structure has changed 
in the final NPDWR, the costing framework used at proposal is still 
applicable in the final rule: what was considered a Hazard Index MCL 
exceedance at proposal would be an individual MCL exceedance under the 
final rule should those contaminants occur in isolation. Further, a 
Hazard Index exceedance in the final rule (defined as two or more of 
PFHxS, PFNA, HFPO-DA, and PFBS) is unchanged from a costing perspective 
to what the EPA proposed. Whether a system exceeds a Hazard Index MCL 
or individual MCL in the final rule, these costs are captured in the 
cost estimates the EPA considered and presented in appendix N.3 of the 
EA and summarized in this section. Specifically, if a system exceeds 
only one of the individual MCLs for PFHxS, PFNA, or HFPO-DA that 
exceedance is costed by estimating the removal needed to achieve 
compliance with a given individual MCL. If a system exceeds the Hazard 
Index MCL, that exceedance is costed by estimating the removal of the 
combination of contaminants needed to achieve compliance with the 
Hazard Index MCL. Therefore, the national level cost estimate for PFHxS 
is reflective of both the total national cost of the PFHxS individual 
MCL and instances of Hazard Index MCL exceedances where PFHxS is 
present above its HBWC while other Hazard Index PFAS are present.
    To understand the totality of national-level cost impacts for the 
Hazard Index MCL, the EPA considered both the contribution of PFHxS 
(estimated as part of the national level cost analysis), as well as the 
costs for PFNA, HFPO-DA, and PFBS (estimated in the appendix N 
sensitivity analysis). Together, these provide information on the costs 
for the Hazard Index MCL and the individual MCLs for PFHxS, PFNA, and 
HFPO-DA, as a whole. Due to available data informing the Bayesian 
hierarchical occurrence model, the EPA was only able to quantify the 
portion of total costs for the Hazard Index MCL attributable to PFHxS 
\20\ in the national level analysis. The EPA notes that this estimate 
also represents the national level quantified costs for the individual 
PFHxS MCL. The EPA acknowledges that this $11.6 million estimate is 
only a portion of the costs imposed by the Hazard Index MCL and also 
does not account for the costs imposed by the individual PFNA and HFPO-
DA MCLs. The EPA accounted for those potential additional costs through 
the sensitivity analysis described in appendix N, in which the EPA 
found that costs of treating for PFNA, HFPO-DA, and PFBS to meet the 
Hazard Index MCL and individual MCLs for PFNA and HFPO-DA increased 
national costs by approximately 5 percent, from $1,549 million to 
$1,631 million. These costs represent the total costs of the final 
rule; in other words, this includes the costs associated with 
individual MCLs for PFOA, PFOS, PFHxS, HFPO-DA, and PFNA, as well as 
the Hazard Index MCL. Due to data limitations, the EPA has not 
separately estimated the costs of the Hazard Index in the absence of 
the individual MCLs. The sensitivity analysis demonstrates that the 
quantified national analysis cost estimate that includes only PFOA, 
PFOS, and PFHxS (where PFHxS represents only a portion of the Hazard 
Index costs) marginally underestimates total rule costs when also 
considering the potential cost impacts attributable to HFPO-DA, PFNA, 
and PFBS. The cost estimates stemming from both the quantified national 
estimate for PFOA, PFOS, and PFHxS, and from the sensitivity analysis 
conducted for PFNA, HFPO-DA, and PFBS together inform the impact of the 
Hazard Index MCL as required by the HRRCA under SDWA.
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    \20\ The EPA notes that there are anticipated to be 
circumstances where PFHxS exceeds its individual MCL and HBWC where 
PFNA, PFBS, and HFPO-DA do not co-occur. While resulting in an 
exceedance of the PFHxS MCL, if PFHxS exceeds its HBWC without other 
Hazard Index PFAS present, this would not result in an exceedance of 
the Hazard Index MCL. At rule proposal, a single exceedance of any 
of the four Hazard Index PFAS would have resulted in an exceedance 
of the Hazard Index MCL. However, to improve rule implementation and 
to support effective risk communication, the EPA has structured the 
final rule such that a Hazard Index exceedance only occurs when 
there are two or more of the Hazard Index PFAS present. Therefore, 
while for purposes of informing its quantified cost analysis the EPA 
is assuming that every PFHxS exceedance of the MCL also causes an 
exceedance of the Hazard Index MCL, this approach results in the EPA 
overestimating PFHxS-attributable Hazard Index costs in its national 
cost analysis.
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    To fully weigh the costs and benefits of the action, the agency 
considered the totality of the monetized values, the potential impacts 
of the nonquantifiable uncertainties, the nonquantifiable costs and 
benefits, and public comments received by the agency related to the 
quantified and qualitative assessment of the costs and benefits. For 
the final rule, the EPA is reaffirming the Administrator's 
determination made at proposal that the quantified and nonquantifiable 
benefits of the rule justify its quantified and nonquantifiable costs.
    In light of the individual MCLs, the EPA has separately presented 
national level marginal costs associated with the individual MCLs for 
PFHxS, PFNA and HFPO-DA in the absence of the Hazard Index MCL; see 
chapter 5.1.3 and appendix N.4 of the EA for details. Therefore, the 
costs for the individual PFHxS, PFNA, and HFPO-DA MCLs have been 
considered both in the

[[Page 32651]]

proposed and final rule. For more information on the agency's 
methodology, findings, and limitations of the EPA's updated analysis of 
costs associated with compliance with the Hazard Index, please see 
appendix N.3 of the EA (USEPA, 2024e).
5. Benefit-Cost Determination
a. Benefit-Cost Determination in the Proposal
    When proposing an NPDWR, the Administrator shall publish a 
determination as to whether the benefits of the MCL justify, or do not 
justify, the costs based on the analysis conducted under section 
1412(b)(3)(C). For the proposed rule, the Administrator determined that 
the quantified and nonquantifiable benefits of the proposed PFAS NPDWR 
justified the costs.
b. Summary of Major Public Comments on Benefit-Cost Determination and 
EPA Responses
    Many commenters agreed with the Administrator's determination that 
the benefits of the rule justify its costs. Specifically, commenters 
asserted that the EPA's estimation of the net benefits of enacting the 
MCLs is reasonable, stating that ``even if the costs are very 
substantial, the benefits associated with the anticipated drinking 
water improvements justify such expenditures.'' Commenters also stated 
that it is likely that ``the analysis understates the benefits'' of the 
rule, particularly given the ``significant unquantified risk reduction 
benefits and co-benefits'' that are anticipated to result from the 
rule.
    In response to these comments, the EPA agrees that its quantified 
benefits likely significantly understate the benefits of the rule due 
to the large share of nonquantifiable benefits that are expected to be 
realized as avoided adverse health effects, in addition to the benefits 
that the EPA has quantified. The EPA anticipates additional benefits 
associated with developmental, cardiovascular, liver, immune, 
endocrine, metabolic, reproductive, musculoskeletal, and carcinogenic 
effects beyond those benefits associated with decreased PFOA and PFOS 
that the EPA has quantified. In response to commenters urging the EPA 
to quantify additional health endpoints associated with PFAS exposure, 
the EPA has developed a quantitative sensitivity analysis of PFOS 
effects and liver cancer, further strengthening the justification for 
this determination. Due to occurrence, health effects, and/or economic 
data limitations, the EPA is unable to quantitatively assess additional 
benefits of the rule.
    Conversely, several commenters stated that the EPA has failed to 
demonstrate that the benefits of the rule justify its costs. 
Specifically, commenters disagreed with this determination because the 
EPA's analysis ``significantly underestimates the costs of the proposed 
MCLs. . .and overestimates its benefits.'' Commenters asserted that the 
EPA needs to update its EA to more accurately reflect the true costs of 
compliance of the rule to make the determination that the rule's costs 
are justified by its benefits. A few commenters urged the EPA to 
consider whether the benefits of finalizing the rule at regulatory 
alternative MCLs (e.g., 5.0 or 10.0 ng/L) would better justify the 
costs of the rule.
    After considering public comments, the EPA has made a number of 
adjustments to the cost model and collectively these changes have 
increased the agency's estimated annualized costs. The EPA has used the 
best available peer reviewed science to inform the cost estimates, 
including treatment costs, of the final PFAS NPDWR. For more 
information on the EPA's responses to comments on the rule costs, see 
sections XII.A.2-XII.A.4 of this preamble. The EPA disagrees with 
commenters that the EPA has overstated the benefits. As discussed in 
section XII.A.1, the EPA has used the best available peer reviewed 
science to quantify the benefits of the rule. The EPA also disagrees 
with commenters that suggested the benefits ``better justify'' the 
costs of PFOA and PFOS standards at 5.0 or 10.0 ng/L. These commenters 
pointed to the quantified net benefits of the regulatory alternatives 
and noted that net benefits are positive at 3 and 7 percent discount 
rates for a standard of 10.0 ng/L for PFOA and PFOS. The commenters' 
sole reliance on the quantified costs and benefits of the rule to 
support their argument is incorrect, as SDWA requires the agency to 
consider both the quantifiable and nonquantifiable impacts of the rule 
in the determination. Under SDWA 1412(b)(4)(B), the EPA is required to 
set an MCL as close as feasible to the MCLG, taking costs into 
consideration. In other words, SDWA does not mandate that the EPA 
establish MCLs at levels where the quantified benefits exceed the 
quantified costs. This was many commenters' justification for the 
recommendation to promulgate a standard of 10.0 ppt each for PFOA and 
PFOS in lieu of the proposed rule, and the EPA therefore disagrees that 
quantified costs and benefits can or should be the sole determinant of 
an MCL value. The Administrator's assessment that the benefits of the 
proposed rule justified its costs was based on the totality of the 
evidence, specifically the quantified and nonquantifiable benefits, 
which are anticipated to be substantial, as well as the quantified and 
nonquantifiable costs. Other commenters incorrectly stated that SDWA 
requires the EPA to set an MCL at a level `` . . . that maximizes 
health risk reduction benefits at a cost that is justified by the 
benefits.'' This test is found in section 1412(b)(6)(A) of SDWA and 
applies only when the Administrator determines based on the HRRCA that 
the benefits of a proposed MCL developed in accordance with paragraph 
(4) would not justify the costs of complying with the level. In the 
case of the proposed PFAS NPDWR, the Administrator determined that the 
benefits justify the costs for MCLs set as close as feasible to the 
MCLGs. For more information on the EPA's response to comments on the 
regulatory alternative MCLs considered in this rule, see section V of 
this preamble.
c. Benefit-Cost Determination in the Final Rule Analysis
    For the final rule, considering both quantifiable and 
nonquantifiable costs and benefits of the rule as discussed in the EA 
and EA Appendices, the EPA is reaffirming the Administrator's 
determination made at proposal that the quantified and nonquantifiable 
benefits of the MCLs justify their costs.

B. Affected Entities and Major Data Sources Used To Develop the 
Baseline Water System Characterization

    The entities potentially affected by the final rule are primacy 
agencies and PWSs. PWSs subject to final rule requirements are either 
CWSs or NTNCWSs. These water systems can be publicly or privately 
owned. PWSs subject to the rule would be required to meet the MCL and 
comply with monitoring and reporting requirements. Primacy agencies 
would be required to adopt and enforce the drinking water standard as 
well as the monitoring and reporting requirements.
    Both PWSs and primacy agencies are expected to incur costs, 
including administrative costs, monitoring, and reporting costs, and in 
some cases, anticipated costs to reduce PFAS levels in drinking water 
to meet the final rule using treatment or nontreatment options. Section 
D of this preamble summarizes the method the EPA used to estimate these 
costs.
    The systems that reduce PFAS concentrations will reduce associated

[[Page 32652]]

health risks. The EPA developed methods to estimate the potential 
benefits of reduced PFAS exposure among the service populations of 
systems with PFAS levels exceeding the final drinking water standard. 
Section E summarizes the method used to estimate these benefits.
    In its Guidelines for Preparing Economic Analyses, the EPA 
characterizes the ``baseline'' as a reference point that reflects the 
world without the final regulation (USEPA, 2016e). It is the starting 
point for estimating the potential benefits and costs of the final 
NPDWR. The EPA used a variety of data sources to develop the baseline 
drinking water system characterization for the regulatory analysis. 
Table 27 lists the major data sources and the baseline data derived 
from them. Additional detailed descriptions of these data sources and 
how they were used in the characterization of baseline conditions can 
be found in chapter 4 of USEPA (2024g).
[GRAPHIC] [TIFF OMITTED] TR26AP24.032

C. Overview of the Cost-Benefit Model

    The EPA's existing SafeWater Cost Benefit Model (CBX) was designed 
to calculate the costs and benefits associated with setting a new or 
revised MCL. Since the final rule simultaneously regulates multiple 
PFAS contaminants, the EPA developed a new model version called the 
SafeWater Multi-Contaminant Benefit Cost Model (MCBC) to efficiently 
handle more than one contaminant. SafeWater MCBC allows for inputs that 
include differing mixtures of contaminants based on available 
occurrence data as well as multiple regulatory thresholds. The model 
structure allows for assignment of compliance technology or 
technologies that achieve all regulatory requirements and estimates 
costs and benefits associated with multiple PFAS contaminant 
reductions. SafeWater MCBC is designed to model co-occurrence, 
sampling, treatment, and administrative costs, and simultaneous 
contaminant reductions and resultant benefits. The modifications to the 
SafeWater model are consistent with the methodology that was developed 
in the single MCL SafeWater CBX Beta version that was peer reviewed. 
More detail on the modifications to the SafeWater model can be found in 
section 5.2 of the EPA's EA.
    The costs incurred by a PWS depend on water system characteristics; 
SDWIS

[[Page 32653]]

Fed provides information on PWS characteristics that typically define 
PWS categories, or strata, for which the EPA developed cost estimates 
in rulemakings, including system type (CWS, NTNCWS), number of people 
served by the PWS, the PWS's primary raw water source (ground water or 
surface water), the PWS's ownership type (public or private), and the 
state in which the PWS is located.
    Because the EPA does not have complete PWS-specific data across the 
approximately 49,000 CWSs and 17,000 NTNCWSs in SDWIS Fed for many of 
the baseline and compliance characteristics necessary to estimate costs 
and benefits, such as design and average daily flow rates, water 
quality characteristics, treatment in-place, and labor rates, the EPA 
adopted a ``model PWS'' approach. SafeWater MCBC creates model PWSs by 
combining the PWS-specific data available in SDWIS Fed with data on 
baseline and compliance characteristics available at the PWS category 
level. In some cases, the categorical data are simple point estimates. 
In this case, every model PWS in a category is assigned the same value. 
In other cases, where more robust data representing system variability 
are available, the category-level data include a distribution of 
potential values. In the case of distributional information, SafeWater 
MCBC assigns each model PWS a value sampled from the distribution. 
These distributions are assumed to be independent.
    For a list of PWS characteristics that impact model PWS compliance 
costs, please see chapter 5 of USEPA (2024g). These data include 
inventory data specific to each system and categorical data for which 
randomly assigned values are based on distributions that vary by 
category (e.g., ground water and surface water TOC distributions or 
compliance forecast distributions that vary by system size category).
    Once model PWSs are created and assigned baseline and compliance 
characteristics, SafeWater MCBC estimates the quantified costs and 
benefits of compliance for each model PWS under the final rule. Because 
of this model PWS approach, SafeWater MCBC does not output any results 
at the PWS level. Instead, the outputs are cost and benefit estimates 
for 36 PWS categories, or strata. Each PWS category is defined by 
system type (CWS and NTNCWS), primary water source (ground or surface), 
and size category. Note the EPA does not report state-specific strata 
although state location is utilized in the SafeWater MCBC model (e.g., 
current state-level regulatory limits on PFAS in drinking water). The 
detailed output across these strata can be found in the chapter 5 of 
USEPA (2024g).
    For each PWS category, the model then calculates summary statistics 
that describe the costs and benefits associated with final rule 
compliance. These summary statistics include total quantified costs of 
the final rule, total quantified benefits of the final rule, the 
variability in PWS-level costs (e.g., 5th and 95th percentile system 
costs), and the variability in household-level costs.

D. Method for Estimating Costs

    This section summarizes the cost elements and estimates total cost 
of compliance for the PFAS NPDWR discounted at 2 percent. The EPA 
estimated the costs associated with monitoring, administrative 
requirements, and both treatment and nontreatment compliance actions 
associated with the final rule (USEPA, 2024g).
1. Public Water System (PWS) Costs
a. PWS Treatment and Nontreatment Compliance Costs
    The EPA estimated costs associated with engineering, installing, 
operating, and maintaining PFAS removal treatment technologies, 
including treatment media replacement and spent media destruction or 
disposal, as well as nontreatment actions that some PWSs may take in 
lieu of treatment, such as constructing new wells in an uncontaminated 
aquifer or interconnecting with and purchasing water from a neighboring 
PWS. The EPA used SafeWater MCBC to apply costs for one of the 
treatment technologies or nontreatment alternatives at each EP in a PWS 
estimated to be out of compliance with the final rule. For each 
affected EP, SafeWater MCBC selected from among the compliance 
alternatives using a decision tree procedure, described in more detail 
in USEPA (2024j). Next, the model estimated the cost of the chosen 
compliance alternative using outputs from the EPA's WBS cost estimating 
models. The WBS models are spreadsheet-based engineering models for 
individual treatment technologies, linked to a central database of 
component unit costs.
    Specifically, the EPA used cost equations generated from the 
following models (USEPA, 2024m):
     the GAC WBS model (USEPA, 2024p);
     the PFAS-selective IX WBS model (USEPA, 2024q); and
     the nontreatment WBS model (USEPA, 2024r).
    The Technologies and Costs (T&C) document (USEPA, 2024m) provides a 
comprehensive discussion of each of the treatment technologies, their 
effectiveness, and the WBS cost models as well as the equations used to 
calculate treatment costs. In total, there are more than 2,600 
individual cost equations across the categories of capital and 
operation and maintenance (O&M) cost, water source, component level, 
flow, bed life (for GAC and IX), residuals management scenarios (for 
GAC and IX), and design type (for GAC). These models are available on 
the EPA's website at https://www.epa.gov/sdwa/drinking-water-treatment-technology-unit-cost-models as well as in the docket for this rule.
b. Decision Tree for Technology Selection
    For EP at which baseline PFAS concentrations exceed regulatory 
thresholds, SafeWater MCBC selects a treatment technology or 
nontreatment alternative using a two-step process that both:
     Determines whether to include or exclude each alternative 
from consideration given the EP's characteristics and the regulatory 
option selected, and
     Selects from among the alternatives that remain viable 
based on percentage distributions derived, in part, from data on recent 
PWS actions in response to PFAS contamination.
    Inputs to SafeWater MCBC used in Step 1 include the following:
     Influent concentrations of individual PFAS contaminants in 
ng/L (ppt)
     EP design flow in MGD
     TOC influent to the new treatment process in mg/L.
    The EPA relied on information from the national PFAS occurrence 
model to inform influent PFAS concentrations. The EPA relied on 
Geometries and Characteristics of Public Water Supplies (USEPA, 2000g) 
and SDWIS inventory information to derive EP design flow. SafeWater 
MCBC selects influent TOC using the distribution shown in Table 28.

[[Page 32654]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.033

    In Step 1, SafeWater MCBC uses these inputs to determine whether to 
include or exclude each treatment alternative from consideration in the 
compliance forecast. For the treatment technologies (GAC and IX), this 
determination is based on estimates of each technology's performance 
given available data about influent water quality and the regulatory 
option under consideration.
    The EPA assumes a small number of PWSs may be able to take 
nontreatment actions in lieu of treatment. The viability of 
nontreatment actions is likely to depend on the quantity of water being 
replaced because the ability to purchase from another water system is 
limited by the seller water system's capacity and the ability to drill 
another well is limited by the ability to find an accessible, 
sufficiently large source. Therefore, SafeWater MCBC considers 
nontreatment only for EP with design flows less than or equal to 3.536 
MGD. The EPA estimates approximately 2 percent of systems of this size 
will develop new wells and approximately 6-7 percent of systems will 
elect to interconnect with another system to achieve compliance.
    In Step 2, SafeWater MCBC selects a compliance alternative for each 
EP from among the alternatives that remain in consideration after Step 
1. Table 29 shows the initial compliance forecast that is the starting 
point for this step. The percentages in Table 29 consider data 
presented in the T&C document (USEPA, 2024m) on actions PWSs have taken 
in response to PFAS contamination.
    To date, the majority of PWSs for which data are available have 
installed GAC (USEPA, 2024m). USEPA (2024m) includes data for 52 
systems, 34 of which (65%) have installed GAC. The data in USEPA 
(2024m) also suggest that an increasing share of PWSs have selected IX 
in response to PFAS since the first full-scale system treated with 
PFAS-selective IX in 2017. Specifically, for systems installed prior to 
2017, 78% used GAC. The EPA expects this trend to continue, so the 
initial percentages include adjustments to account for this 
expectation. In addition, the performance of GAC is affected by the 
presence of TOC, as further described in the cost chapter of the EA 
(USEPA, 2024g). Accordingly, the table includes adjusted distributions 
for systems with higher influent TOC. Finally, while central RO/NF 
remains a BAT for the final rule, the EPA does not anticipate water 
systems will select this technology to comply with the rule, largely 
due to the challenges presented by managing the treatment residuals 
from this process.
    The list of compliance alternatives in Table 29 does not include 
POU devices for small systems. At this time, the EPA is not including 
POU devices in the national cost estimates because the final rule 
require treatment to concentrations below the current NSF/ANSI 
certification standard for POU devices. However, POU treatment is 
reasonably anticipated to become a compliance option for small systems 
in the future if independent third-party certification organizations, 
such as NSF or ANSI develop a new certification standard that mirrors 
the EPA's final regulatory standard. Therefore, the decision tree 
excludes POU devices from consideration.

[[Page 32655]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.034

    If all the compliance alternatives remain in consideration after 
Step 1, the decision tree uses the forecast shown in Table 29 above. If 
Step 1 eliminated one or more of the alternatives, SafeWater MCBC 
proportionally redistributes the percentages among the remaining 
alternatives and uses the redistributed percentages.
    The EPA's approach to estimating GAC and IX performance for the 
final rule and all alternatives considered is discussed in detail 
within the cost chapter of the EA (USEPA, 2024g).
c. Work Breakdown Structure Models
    The WBS models are spreadsheet-based engineering models for 
individual treatment technologies, linked to a central database of 
component unit costs. The EPA developed the WBS model approach as part 
of an effort to address recommendations made by the Technology Design 
Panel (TDP), which convened by the EPA in 1997 to review the agency's 
methods for estimating drinking water compliance costs (USEPA, 1997). 
The TDP consisted of nationally recognized drinking water experts from 
the EPA, water treatment consulting companies, public as well as 
private water utilities along with suppliers, equipment vendors, and 
Federal along with state regulators in addition to cost estimating 
professionals.
    In general, the WBS approach involves breaking a process down into 
discrete components for the purpose of estimating unit costs. The WBS 
models represent improvements over past cost estimating methods by 
increasing comprehensiveness, flexibility, and transparency. By 
adopting a WBS-based approach to identify the components that should be 
included in a cost analysis, the models produce a more comprehensive, 
flexible, and transparent assessment of the capital and operating 
requirements for a treatment system.
    Each WBS model contains the work breakdown for a particular 
treatment process and preprogrammed engineering criteria and equations 
that estimate equipment requirements for user-specified design 
requirements (e.g., system size and influent water quality). Each model 
also provides unit and total cost information by component (e.g., 
individual items of capital equipment) and totals the individual 
component costs to obtain a direct capital cost. Additionally, the 
models estimate add-on costs (e.g., permits and land acquisition), 
indirect capital costs, and annual O&M costs, thereby producing the 
EPA's best estimates of complete compliance costs.
    Primary inputs common to all the WBS models include design flow and 
average daily flow in MGD. Each WBS model has default designs (input 
sets) that correspond to specified categories of flow, but the models 
can generate designs for many other combinations of flows. To estimate 
costs for PFAS compliance, the EPA fit cost curves to the WBS estimates 
across a range of flow rates, which is described in chapter 5 of the EA 
(USEPA, 2024g).
    Another input common to all the WBS models is ``component level'' 
or ``cost level.'' This input drives the selection of materials for 
items of equipment that can be constructed of different materials. For 
example, a low-cost system might include fiberglass pressure vessels 
and polyvinyl chloride (PVC) piping. A high-cost system might include 
stainless steel pressure vessels and stainless-steel piping. The 
component level input also drives other model assumptions that can 
affect the total cost of the system, such as building quality and 
heating and cooling. The component level input has three possible 
values: low cost, mid cost, and high cost. The components used in each 
of the estimated component/cost levels provide the treatment efficacy 
needed to meet the regulatory requirements. Note that the level of 
component (e.g., plastic versus resin or stainless-steel piping and 
vessels) may impact the capital replacement rate but does not interfere 
with treatment efficacy. The EPA estimates the three levels of cost 
because it has found that the choice of materials associated with the 
installation of new treatment equipment often varies across drinking 
water systems. These systems may, for example, choose to balance 
capital cost with staff familiarity with certain materials and existing 
treatment infrastructure. Given this experience, the EPA models the 
potential variability in treatment cost based on the three component/
cost levels. To estimate costs for PFAS treatment, the EPA generated 
separate cost equations for each of the three component levels, thus 
creating a range of cost estimates for use in national compliance cost 
estimates.
    The third input common to all the WBS models is system automation, 
which allows the design of treatment systems that are operated manually 
or with varying degrees of automation (i.e., with control systems that 
reduce the need for operator intervention). Cost

[[Page 32656]]

equations for system automation are described in chapter 5 of the EA 
(USEPA, 2024g).
    The WBS models generate cost estimates that include a consistent 
set of capital, add-on, indirect, and O&M costs. Table 30 identified 
these cost elements, which are common to all the WBS models and 
included in the cost estimates. As described and summarized in Tables 
31-34 the WBS models also include technology-specific cost elements. 
The documentation for the WBS models provides more information on the 
methods and assumptions in the WBS models to estimate the costs for 
both the technology-specific and common cost elements (USEPA, 2024p; 
USEPA, 2024q; USEPA, 2024r). WBS model accuracy as well as limitations 
and uncertainty are described in chapter 5 of the EA (USEPA, 2024g).
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR26AP24.035


[[Page 32657]]


    The GAC model can generate costs for two types of design:
     Pressure designs where the GAC bed is contained in 
stainless steel, carbon steel, or fiberglass pressure vessel.
     Gravity designs where the GAC bed is contained in open 
concrete basins.
    Table 31 shows the technology-specific capital equipment and O&M 
requirements included in the GAC model. These items are in addition to 
the common WBS cost elements listed in the Table 30 above.
[GRAPHIC] [TIFF OMITTED] TR26AP24.036

BILLING CODE 6560-50-C
    For small systems (less than 1 MGD) using pressure designs, the GAC 
model assumes the use of package treatment systems that are pre-
assembled in a factory, mounted on a skid, and transported to the site. 
These assumptions are based on common vendor practice for these 
technologies, for example, see Khera et al. (2013) which says ``. . . 
small systems are often built as packaged, pre-engineered, or skid-
mounted systems.'' The model estimates costs for package systems by 
costing all individual equipment line items (e.g., vessels, 
interconnecting piping and valves, instrumentation, and system 
controls) in the same manner as custom-engineered systems. This 
approach is based on vendor practices of partially engineering these 
types of package plants for specific systems (e.g., selecting vessel 
size to meet flow and treatment criteria). The model applies a variant 
set of design inputs and assumptions that are intended to simulate the 
use of a package plant and that reduce the size and cost of the 
treatment system. USEPA (2024p) provides complete details on the 
variant design assumptions used for package plants.
    To generate the GAC cost equations, the EPA used the following key 
inputs in the GAC model:
     For pressure designs, two vessels in series with a minimum 
total empty bed contact time (EBCT) of 20 minutes;
     For gravity designs, contactors in parallel with a minimum 
total EBCT of 20 minutes; and
     Bed life varying over a range from 5,000 to 75,000 BV.
    The EPA generated separate cost equations for two spent GAC 
management scenarios:
     Off-site reactivation under current RCRA non-hazardous 
waste regulations;
     Off-site disposal as a hazardous waste in a RCRA Subtitle 
C landfill and replacement with virgin GAC (i.e., single use 
operation).
    The T&C document (USEPA, 2024m) provides a comprehensive discussion 
of

[[Page 32658]]

these and other key inputs and assumptions.
    Table 32 shows the technology-specific capital equipment and O&M 
requirements included in the PFAS selective IX model. These items are 
in addition to the common WBS cost elements listed in the Table 30 
above.
[GRAPHIC] [TIFF OMITTED] TR26AP24.037

    For small systems (less than 1 MGD), the PFAS-selective IX model 
assumes the use of package treatment systems that are pre-assembled in 
a factory, mounted on a skid, and transported to the site. The IX model 
estimates costs for package systems using an approach similar to that 
described for the GAC model, applying a variant set of inputs and 
assumptions that reduce the size and cost of the treatment system. 
USEPA (2024q) provides complete details on the variant design 
assumptions used for IX package plants.
    To generate the IX cost equations, the EPA used the following key 
inputs in the PFAS-selective IX model:

 Two vessels in series with a minimum total EBCT of 6 minutes
 Bed life varying over a range from 20,000 to 260,000 BV

    The EPA generated separate cost equations for two spent resin 
management scenarios:
     Spent resin managed as non-hazardous and sent off-site for 
incineration.
     Spent resin managed as hazardous and sent off-site for 
incineration.
    The T&C document (USEPA, 2024m) provides a comprehensive discussion 
of these and other key inputs and assumptions.
    USEPA (2024r) provides a complete description of the engineering 
design process used by the WBS model for nontreatment actions. The 
model can estimate costs for two nontreatment alternatives: 
interconnection with another system and drilling new wells to replace a 
contaminated source. Table 33 shows the technology-specific capital 
equipment and O&M requirements included in the model for each 
alternative.

[[Page 32659]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.038

    To generate the cost equations, the EPA used the following key 
inputs in the nontreatment model for interconnection:

 An interconnection distance of 10,000 feet
 Includes booster pumps designed to account for friction loss 
in interconnecting piping
 An average cost of purchased water of $3.35 per thousand 
gallons in 2022 dollars.

    For new wells, the EPA used the following key inputs:

 A maximum well capacity of 500 gallons per minute (GPM), such 
that one new well is installed per 500 GPM of water production capacity 
required
 A well depth of 250 feet
 500 feet of distance between the new wells and the 
distribution system.

    The T&C document (USEPA, 2024m) provides a comprehensive discussion 
of these and other key inputs and assumptions.
d. Incremental Treatment Costs
    The EPA has estimated the national level costs of the final rule 
associated with PFOA, PFOS, and PFHxS. As discussed in chapter 4 of the 
EA and detailed in the Technical Support Document for PFAS Occurrence 
and Contaminant Background chapter 10.1 and 10.3, there are limitations 
with nationally representative occurrence information for the other 
contaminants in the final rule (PFNA, HFPO-DA and PFBS). Specifically, 
HFPO-DA does not currently have a completed nationally representative 
dataset while PFNA and PFBS were not included in the national 
occurrence model because of limited results reported above the minimum 
reporting levels in UCMR 3. As described in the Technical Support 
Document for PFAS Occurrence and Contaminant Background chapter 10.3.2, 
non-targeted state monitoring datasets were used for extrapolation of 
PFNA, HFPO-DA, and PFBS in lieu of a nationally representative dataset. 
The EPA used conservative assumptions in this extrapolation to generate 
conservative cost estimates. As demonstrated in this analysis, the 
Hazard Index, PFNA, and HFPO-DA MCLs meaningfully increase public 
health protection at modest additional costs. Because of the increased 
uncertainty associated with PFNA, HFPO-DA and PFBS, the additional 
treatment cost from co-occurrence of PFNA, HFPO-DA, PFBS at systems 
already required to treat because of PFOA, PFOS, or PFHxS MCL and 
Hazard Index exceedances are not quantitatively assessed in the 
national cost estimates. These three PFAS' treatment costs are 
summarized here in this section and detailed in appendix N.3 of the EA 
(USEPA, 2024e). Likewise, treatment costs for systems that exceed the 
Hazard Index based on the combined occurrence of PFNA, HFPO-DA, PFBS, 
and PFHxS (where PFHxS itself does not exceed its HBWC of 10 ng/L) are 
not included in the national monetized cost estimates and are also 
summarized in this section and detailed in appendix N.3 of the EA 
(USEPA, 2024e).
    In the EA for the proposed PFAS NPDWR, the EPA used a model system 
approach to illustrate the potential incremental costs for removing 
PFAS not included in the national economic model. After considering 
public comments on the incremental cost analysis, the EPA decided to 
further explore the incremental costs associated with the Hazard Index 
and MCLs with a national level sensitivity analysis for the final rule.
    When the modeled occurrence data for PFNA, HFPO-DA, PFBS is 
incorporated into the SafeWater MCBC model, the estimated number of EP

[[Page 32660]]

exceeding one or more MCLs, and therefore required to treat or use a 
different water source, increases to 9,471 from 9,043. This results in 
an increase in the expected national costs. Under the primary analyses, 
the expected total national cost is $1,549 million over the EPA's 
period of analysis (2024-2105) for the PFOA, PFOS, and PFHxS MCLs. When 
considering the additional incremental national cost impacts of the 
Hazard Index MCL for, PFNA, HFPO-DA, and PFBS (and individual MCLs for 
PFNA and HFPO-DA) the expected national costs of the final rule 
increase to $1,631 million at, or approximately a 5 percent national 
cost increase.
    For further detail on the assumptions and findings of the EPA's 
analysis of incremental costs of other PFAS, see appendix N.3 and 
section XII.A of this preamble.
e. PWS Implementation Administration Costs
    The EPA estimated PWS costs associated with one-time actions to 
begin implementation of the rule including reading and understanding 
the rule and attending training provided by primacy agencies. The 
average unit costs for PWSs are based on the following burden 
assumptions: (1) The EPA anticipates that the majority of water systems 
will likely not read the entirety of the rule preamble (as they are not 
required to do so) but focus their time and attention on understanding 
the regulatory requirements through the CFR regulatory text, relevant 
portions of the preamble, the EPA provided fact sheets and small system 
guidance documents, and state provided summaries documents; (2) 
Additionally, the EPA anticipates that system staff will attend primacy 
agency PFAS rule trainings to reenforce the systems' understanding of 
the final rule. The EPA assumes that systems will conduct these 
activities during years one through three of the analysis period. Table 
34 lists the data elements and corresponding values associated with 
calculating the costs of these one-time implementation administration 
actions.
[GRAPHIC] [TIFF OMITTED] TR26AP24.039

    Estimated national annualized PWS implementation and administration 
startup costs for the final rule are $1.33 million. National annualized 
PWS cost estimates are further summarized in Table 39.
f. PWS Monitoring Costs
    The final rule requires initial and long-term monitoring. As Table 
35 shows, surface and ground water systems serving greater than 10,000 
people will collect one sample each quarter, at each EP, during the 
initial 12-month monitoring period. Surface water systems serving 
10,000 or fewer people are also required to collect a quarterly sample 
at each EP during the initial 12-month period. Ground water systems 
that serve 10,000 or fewer people will be required to sample once at 
each EP on a semi-annual basis for the first 12-month monitoring 
period.
    Long-term monitoring schedules are based on specific EP sampling 
results (i.e., water systems can have different EP within the system on 
different monitoring schedules). Long-term monitoring requirements 
differ based on whether a system can demonstrate during the initial 
monitoring period or once conducting long-term monitoring that an EP is 
below the trigger levels for regulated PFAS. The trigger levels are set 
as one-half the MCLs: 2.0 ng/L for PFOA and PFOS, 5 ng/L each for 
PFHxS, PFNA, and HFPO-DA, and 0.5 for the Hazard Index. EP below the 
trigger level values during the initial 12-month monitoring period and 
in future long-term monitoring periods may conduct triennial monitoring 
and collect one triennial sample at that EP. For EP with concentration 
values at or above a trigger level, a quarterly sample must be taken at 
that EP following initial monitoring. EP that demonstrate they are 
``reliably and consistently'' \21\ below the MCLs following four 
consecutive quarterly samples are eligible to conduct annual 
monitoring. After three annual samples at that EP showing no results at 
or above a trigger level, the location can further reduce to triennial 
monitoring.
---------------------------------------------------------------------------

    \21\ The definition of reliably and consistently below the MCL 
means that each of the samples contains regulated PFAS 
concentrations below the applicable MCLs. For the PFAS NPDWR, this 
demonstration of reliably and consistently below the MCL would 
include consideration of at least four quarterly samples at an EP 
below the MCL, but states will make their own determination as to 
whether the detected concentrations are reliably and consistently 
below the MCL.
---------------------------------------------------------------------------

    For any samples that are above detection, the system will analyze 
the FRB samples collected at the same time as the monitoring sample. 
Systems that have an MCL exceedance will collect one additional sample 
from the relevant EP to confirm the results.

[[Page 32661]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.040

    For the national cost analysis, the EPA assumes that systems with 
either UCMR 5 data or monitoring data in the State PFAS Database (see 
section 3.1.4 in USEPA, 2024g) will not conduct the initial year of 
monitoring as allowed by the final rule. As a simplifying assumption 
for the cost analysis, the EPA assumes all systems serving a population 
of greater than 3,300 have UCMR 5 data and those with 3,300 or less do 
not. For the State PFAS Database, the EPA relied on the PWSIDs stored 
in the database and exempted those systems from the first year of 
monitoring in the cost analysis. Note these simplifying assumptions may 
result in a small underestimate of initial monitoring costs. Under UCMR 
5, individual water systems would be able to request the full release 
of data from the labs for use in determining their compliance 
monitoring frequency. PWSs may be able to use these lab analyses to 
demonstrate a ``below trigger level'' concentration using the UCMR 5 
analyses by following up with the lab for a more detailed results 
report.
    The EPA used system-level distributions of PFOA, PFOS, and PFHxS, 
as described in Cadwallader et al. (2022), to simulate EP 
concentrations and estimate PFAS occurrence relative to the final rule 
MCLs and trigger levels. Based on these occurrence distributions, the 
EPA estimates that the large majority of water systems subject to the 
rule (approx. 52,000-57,000) will have EP with concentrations below the 
trigger levels and would conduct reduced monitoring on a triennial 
basis. The EPA estimates that the remainder of water systems subject to 
the rule (approx. 9,000-15,000) will have at least one or more EP 
exceed the trigger level and therefore would be required to conduct 
quarterly monitoring.
    The EPA assumes that systems with an MCL exceedance will implement 
actions to comply with the MCL by the compliance date. The EPA assumes 
a treatment target,\22\ for systems required to treat for PFAS, that 
includes a margin of safety so finished water PFAS levels at these 
systems are 80 percent of the MCLs. In the final rule, in order to 
reduce burden associated with monitoring, the EPA is adding an annual 
tier of sampling for any system with concentrations ``reliably and 
consistently'' \23\ below the MCL but not consistently below the 
trigger level. The EPA believes this tier would likely

[[Page 32662]]

apply to most systems treating their water for regulated PFAS, at least 
for the first three years of treatment. Therefore, in the model, the 
EPA assumes EP that have installed treatment will take one year of 
quarterly samples, then continue to sample on an annual basis after 
that. The final rule allows EP showing no results at or above a trigger 
level after three annual samples to further reduce to triennial 
monitoring. In the national cost analysis, the EPA does not model this 
possibility nor does the EPA model instances where water systems are 
triggered back into quarterly monitoring after installing treatment.
---------------------------------------------------------------------------

    \22\ A treatment target is a contaminant concentration that a 
PWS has designed and operated their water system to meet. The EPA 
assumes all PWS will target 80% of the MCLs.
    \23\ The definition of reliably and consistently below the MCL 
means that each of the samples contains regulated PFAS 
concentrations below the applicable MCLs. For the PFAS NPDWR, this 
demonstration of reliably and consistently below the MCL would 
include consideration of at least four quarterly samples at an EP 
below the MCL, but states will make their own determination as to 
whether the detected concentrations are reliably and consistently 
below the MCL.
---------------------------------------------------------------------------

    For all systems, the activities associated with the sample 
collection in the initial 12-month monitoring period are the labor 
burden and cost for the sample collection and analysis, as well as a 
review of the sample results. Table 36 presents the data elements and 
corresponding values associated with calculating sampling costs during 
the implementation monitoring period.
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[[Page 32663]]

    Estimated national annualized PWS sampling costs for the final rule 
have an expected value of $36.23 million. National annualized PWS cost 
estimates are further summarized in Table 39.
g. Treatment Administration Costs
    Any system with an MCL exceedance adopts either a treatment or 
nontreatment alternative to comply with the rule. The majority of 
systems are anticipated to install treatment technologies while a 
subset of systems will choose alternative methods. The EPA assumes that 
systems will bear administrative costs associated with these treatment 
or nontreatment compliance actions (i.e., permitting costs). The EPA 
assumes that systems will install treatment in the fifth year of the 
period of analysis. In addition, after installation of treatment, the 
EPA assumes that systems will spend an additional 2 hours per treating 
EP compiling data for and reviewing treatment efficacy with their 
primacy agency during their triennial sanitary survey. Table 37 
presents the data elements and corresponding values associated with 
calculating treatment administration costs.
[GRAPHIC] [TIFF OMITTED] TR26AP24.042

h. Public Notification (PN) Costs
    The EPA's cost analysis assumes full compliance with the rule 
throughout the period of analysis and, as a result, the EPA does not 
estimate costs for the PN requirements in the final rule for systems 
with certain violations. The final rule designates MCL violations for 
PFAS as Tier 2, which requires systems to provide PN as soon as 
practical, but no later than 30 days after the system learns of the 
violation. The system must repeat notice every three months if the 
violation or situation persists unless the primacy agency determines 
otherwise. At a minimum, systems must give repeat notice at least once 
per year. The final rule also designates monitoring and testing 
procedure violations as Tier 3, which requires systems to provide 
public notice no later than one year after the system learns of the 
violation. The system must repeat the notice annually for as long as 
the violation persists. CWSs may deliver Tier 3 PNs in their CCR if the 
timing, content, and delivery requirements are met according to 40 CFR 
141.204(d). Using the CCR to deliver Tier 3 PNs can minimize the burden 
on systems by reducing delivery costs. For approximate estimates of the 
potential burden associated with Tier 2 and 3 PNs, please see USEPA 
(2024g).
i. Primacy Agency Costs
    The EPA assumes that primacy agencies will have upfront 
implementation costs as well as costs associated with system actions 
related to sampling and treatment. The activities that primacy agencies 
are expected to carry out under the final rule include:
     Reading and understanding the rule, providing internal 
primacy agency officials training for the rule implementation, updating 
sanitary survey standard operating procedures,
     Primacy package application, including making regulatory 
changes to the Federal rule where applicable,
     Providing systems with training and technical assistance 
during the rule implementation,
     Reporting to the EPA on an ongoing basis any PFAS-specific 
information under 40 CFR 142.15 regarding violations as well as 
enforcement actions and general operations of PWS programs,
     Performing inspection of PFAS related treatment during 
sanitary surveys every three years

[[Page 32664]]

     Reviewing the sample results during the implementation 
monitoring period and the SMF period, and
     Reviewing and consulting with systems on the installation 
of treatment technology or alternative methods, including source water 
change.
    For the last three activities listed above, the primary agency 
burdens are incurred in response to action taken by PWSs; for instance, 
the cost to primacy agencies of reviewing sample results depends on the 
number of samples taken at each EP by each system under an agency's 
jurisdiction. Table 38 presents the data elements and corresponding 
values associated with calculating primacy agency costs.
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[GRAPHIC] [TIFF OMITTED] TR26AP24.043

    Estimated national annualized primacy agency costs for the final 
rule have an expected value of $4.65 million. National annualized cost 
estimates are further summarized in Table 39.

[[Page 32665]]

    In addition to the costs described above, a primacy agency may also 
have to review the certification of any Tier 2 or 3 PNs sent out by 
systems. The EPA assumes full compliance with the final rule and 
therefore does not include this cost in national estimated cost totals 
but provides a brief discussion of the possible primacy agency burden 
associated with this component in USEPA (2024g).
    In Table 39, the EPA summarizes the total annualized quantified 
cost of the final rule at a 2 percent discount rate expressed in 
millions of 2022 dollars. The first three rows show the annualized PWS 
sampling costs, the annualized PWS implementation and administrative 
costs, and the annualized PWS treatment costs. The fourth row shows the 
sum of the annualized PWS costs. The expected annualized PWS costs are 
$1,544 million. The uncertainty range for annualized PWS costs are 
$1,431 million to $1,667 million. Finally, annualized primacy agency 
implementation and administrative costs are added to the annualized PWS 
costs to calculate the total annualized cost of the final rule. The 
expected total annualized cost of the final rule is $1,549 million. The 
uncertainty range for the total annualized costs of the final rule is 
$1,436 million to $1,672 million. The EPA notes that treatment costs 
associated with the rule are the most significant contribution to 
overall rule costs for the final rule and the regulatory alternatives.

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[GRAPHIC] [TIFF OMITTED] TR26AP24.044

    In Tables 40, 41, and 42, the EPA summarizes the total annualized 
quantified cost of options 1a, 1b, and 1c, respectively.

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j. Data Limitations and Uncertainties in the Cost Analysis
    Table 43 lists data limitations and characterizes the impact on the 
quantitative cost analysis. The EPA notes that in most cases it is not 
possible to judge the extent to which a particular limitation or 
uncertainty could affect the cost analysis. The EPA provides the 
potential direction of the impact on the cost estimates when possible 
but does not prioritize the entries with respect to the impact 
magnitude.

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E. Nonquantifiable costs of the final rule

    As described in section j. (Data Limitations and Uncertainties in 
the Cost Analysis) above, given the available occurrence data for the 
other compounds in the rule (PFNA, HFPO-DA, and PFBS) and the 
regulatory thresholds under consideration, the EPA considered national 
costs associated with potential Hazard Index exceedances as a direct 
result of these compounds in a sensitivity analysis; therefore, the 
additional treatment cost,

[[Page 32672]]

from co-occurrence of PFNA, HFPO-DA, PFBS, at systems already required 
to treat because of PFOA, PFOS, or PFHxS MCL and Hazard Index 
exceedances are not presented in the national cost estimates above. Nor 
are treatment costs for systems that exceed the Hazard Index based on 
the combined occurrence of PFHxS (where PFHxS itself does not exceed 10 
ng/L), PFNA, HFPO-DA, and PFBS presented in the national monetized cost 
estimates above. Treatment costs for the individual PFNA and HFPO-DA 
MCLs are also not considered above. For further discussion of how the 
EPA considered the costs of the five individual MCLs and the HI MCL, 
see section XII.A.4 of this preamble. These potential additional costs 
are described in greater detail in section 5.3.1.4 of USEPA (2024g) and 
appendix N.3 of USEPA (2024e). When considering the national cost 
impacts of the Hazard Index MCL for PFNA, HFPO-DA, and PFBS (and 
individual MCLs for PFNA and HFPO-DA) the expected national costs 
increase from $1,549 million to $1,631 million, or approximately a 5 
percent national cost increase.
    PFAS-contaminated wastes are not considered RCRA regulatory or 
characteristic hazardous wastes at this time and therefore total costs 
reported in this table do not include costs associated with hazardous 
waste disposal of spent filtration materials. To address stakeholder 
concerns, including those raised during the Small Business Regulatory 
Enforcement Fairness Act (SBREFA) process, the EPA conducted a 
sensitivity analysis with an assumption of hazardous waste disposal for 
illustrative purposes only. As part of this analysis, the EPA generated 
a second full set of unit cost curves that are identical to the curves 
used for the national cost analysis with the exception that spent GAC 
and spent IX resin are considered hazardous. If in the future PFAS-
contaminated wastes require handling as hazardous wastes, the residuals 
management costs are expected to be higher. See appendix N.2 of the EA 
for a sensitivity analysis describing the potential increase in costs 
associated with hazardous waste disposal (USEPA, 2024e).

F. Method for Estimating Benefits

    The EPA's quantification of health benefits resulting from reduced 
PFAS exposure in drinking water was driven by PFAS occurrence 
estimates, PK model availability, information on exposure-response 
relationships, and economic data to monetize the impacts. In the EA, 
the EPA either quantitatively assesses or qualitatively discusses 
health endpoints associated with exposure to PFAS. The EPA assesses 
potential benefits quantitatively if there is evidence of an 
association between PFAS exposure and health effects, if it is possible 
to link the outcome to risk of a health effect, and if there is no 
overlap in effect with another quantified endpoint in the same outcome 
group. Particularly, the most consistent epidemiological associations 
with PFOA and PFOS include decreased immune system response, decreased 
birthweight, increased serum lipids, and increased serum liver enzymes 
(particularly alanine transaminase, ALT). The available evidence 
indicates effects across immune, developmental, cardiovascular, and 
hepatic organ systems at the same or approximately the same level of 
exposure.
    Table 44 presents an overview of the categories of health benefits 
expected to result from the implementation of treatment that reduces 
PFAS levels in drinking water. Of the PFAS compounds included in the 
final rule, the EPA quantifies some of the adverse health effects 
associated with PFOA and PFOS. These compounds have likely evidence 
linking exposure to a particular health endpoint and have reliable PK 
models connecting the compound to PFAS blood serum. PK models are tools 
for quantifying the relationship between external measures of exposure 
and internal measures of dose. Benefits from avoided adverse health 
effects of PFHxS, PFNA, HFPO-DA, and PFBS are discussed qualitatively 
in this section.
    As Table 44 demonstrates, only a subset of the potential health 
effects of reduced PFAS in drinking water can be quantified and 
monetized. The monetized benefits evaluated in the EA for the final 
rule include changes in human health risks associated with CVD and 
infant birth weight from reduced exposure to PFOA and PFOS in drinking 
water and RCC from reduced exposure to PFOA. The EPA also quantified 
benefits from reducing bladder cancer risk due to the co-removal of 
non-PFAS pollutants via the installation of drinking water treatment, 
discussed in greater detail in USEPA (2024g). The EPA quantified 
benefits associated with PFOS effects on liver cancer and PFNA effects 
on birth weight in sensitivity analyses.
    The EPA was not able to quantify or monetize other benefits, 
including those related to other reported health effects including 
immune, liver, endocrine, metabolic, reproductive, musculoskeletal, or 
other cancers. The EPA discusses these benefits qualitatively in more 
detail in this section, as well as in section 6.2 of USEPA (2024g).
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    The EPA developed PK models to evaluate blood serum PFAS levels in 
adults resulting from exposure to PFAS via drinking water. To date, the 
EPA has developed PK models for PFOA and PFOS. The EPA used baseline 
and regulatory alternative PFOA/PFOS drinking water concentrations as 
inputs to its PK model to estimate blood serum PFOA/PFOS concentrations 
for adult males and females. For further detail on the PK model and its 
application in the EPA's benefits analysis, please see the EPA's Final 
Human Health Toxicity Assessments for PFOA and PFOS (USEPA, 2024c; 
USEPA, 2024d) and section 6.3 of USEPA (2024g).
1. Quantified Developmental Effects
    Exposure to PFOA and PFOS is linked to developmental effects, 
including decreased infant birth weight (Steenland et al., 2018; 
Dzierlenga et al., 2020; Verner et al., 2015; USEPA, 2016c; USEPA, 
2016d; USEPA, 2024c; USEPA, 2024d; Negri et al., 2017; ATSDR, 2021; 
Waterfield et al., 2020). The route through which infants are exposed 
prenatally to PFOA and PFOS is through maternal blood via the placenta. 
Most studies of the association between maternal serum PFOA/PFOS and 
birth weight report inverse relationships (Verner et al., 2015; Negri 
et al., 2017; Steenland et al., 2018; Dzierlenga et al., 2020). The 
EPA's PK model assumes that mothers were exposed to PFOA/PFOS from 
birth to the year in which pregnancy occurred.
    The EPA quantified and valued changes in birth weight-related risks 
associated with reductions in exposure to PFOA and PFOS in drinking 
water. EP-specific time series of the differences between serum PFOA/
PFOS concentrations under baseline and regulatory alternatives are 
inputs into this analysis. For each EP, evaluation of the changes in 
birth weight impacts involves the following key steps:
    1. Estimating the changes in birth weight based on modeled changes 
in serum PFOA/PFOS levels and exposure-response functions for the 
effect of serum PFOA/PFOS on birth weight;
    2. Estimating the difference in infant mortality probability 
between the baseline and regulatory alternatives based on changes in 
birth weight under the regulatory alternatives and the association 
between birth weight and mortality;
    3. Identifying the infant population affected by reduced exposure 
to PFOA/PFOS in drinking water under the regulatory alternatives;
    4. Estimating the changes in the expected number of infant deaths 
under the regulatory alternatives based on the difference in infant 
mortality rates and

[[Page 32675]]

the population of surviving infants affected by increases in birth 
weight due to reduced PFOA/PFOS exposure; and
    5. Estimating the economic value of reducing infant mortality based 
on the Value of a Statistical Life and infant morbidity based on 
reductions in medical costs associated with changes in birth weight for 
the surviving infants based on the cost of illness.
    The EPA also considered the potential benefits from reduced 
exposure to PFNA that may be realized as a direct result of the final 
rule. The agency explored the birth weight impacts of PFNA in a 
sensitivity analysis based on epidemiological studies published before 
2018 cited in the current, best available final human health analysis 
of PFNA (ATSDR, 2021), as well as a recently published meta-analysis of 
mean birth weight that indicates the birth weight results for PFNA are 
robust and consistent, even if associations in some studies may be 
small in magnitude (Wright et al., 2023). The EPA used a unit PFNA 
reduction scenario (i.e., 1.0 ng/L change) and the PFAS serum 
calculator developed by Lu and Bartell (2020) to estimate PFNA blood 
serum levels resulting from PFNA exposures in drinking water. To 
estimate blood serum PFNA based on its drinking water concentration, 
the EPA used a first-order single-compartment model whose behavior was 
previously demonstrated to be consistent with PFOA pharmacokinetics in 
humans (Bartell et al., 2010). In addition to the PFOA-birth weight and 
PFOS-birth weight effects analyzed in the EA, the EPA examined the 
effect of inclusion of PFNA-birth weight effects using estimates from 
two studies (Lenters et al., 2016; Valvi et al., 2017). The EPA found 
that inclusion of a 1.0 ng/L PFNA reduction increased annualized birth 
weight benefits by between a factor of 5.6 to 7.8, relative to the 
scenario that quantifies a 1.0 ng/L reduction in PFOA and a 1.0 ng/L 
reduction in PFOS only. The range of estimated PFNA-related increases 
in benefits is driven by the exposure-response, with smaller estimates 
produced using the slope factors from Lenters et al. (2016), followed 
by Valvi et al. (2017). The EPA notes that the PFNA slope factor 
estimates are orders of magnitude larger than the slope factor 
estimates used to evaluate the impacts of PFOA/PFOS reductions. The EPA 
also notes that the PFNA slope factor estimates in this analysis are 
not precise, with 95 percent CIs covering wide ranges that include zero 
(i.e., serum PFNA slope factor estimates are not statistically 
significant at 5 percent level). Caution should be exercised in making 
judgements about the potential magnitude of change in the national 
benefits estimates based on the results of these sensitivity analyses, 
although conclusions about the directionality of these effects can be 
inferred. The EPA did not include PFNA effects in the national benefits 
estimates for the final rule because there was insufficient data above 
the UCMR 3 MRL to reasonably fit model parameters for PFNA. For the 
EPA's PFNA sensitivity analysis, see appendix K of USEPA (2024g).
    To estimate changes in birth weight resulting from reduced exposure 
to PFOA and PFOS under the regulatory alternatives, the EPA relied on 
the estimated time series of changes in serum PFOA/PFOS concentrations 
specific to women of childbearing age and serum-birth weight exposure-
response functions provided in recently published meta-analyses. For 
more detail on the evaluation of the studies used in these meta-
analyses, please see the EPA's Final Human Health Toxicity Assessments 
for PFOA and PFOS (USEPA, 2024c; USEPA, 2024d) and section 6.4 of USEPA 
(2024g).
    Changes in serum PFOA and PFOS concentrations are calculated for 
each PWS EP during each year in the analysis period. The EPA assumes 
that, given the long half-lives of PFOS and PFOA (with median half-
lives of 2.7 and 3.5 years, respectively (Li et al., 2018)), any one-
time measurement during or near pregnancy is reflective of a critical 
exposure window and not subject to considerable error. In other words, 
blood serum concentrations in a single year are expected to correlate 
with past exposures and are reflective of maternal exposures regardless 
of the timing of pregnancy. The mean change in birth weight per 
increment in long-term PFOA and PFOS exposure is calculated by 
multiplying each annual change in PFOA and PFOS serum concentration 
(ng/mL serum) by the PFOA and PFOS serum-birth weight exposure-response 
slope factors (g birth weight per ng/mL serum) provided in Table 45, 
respectively. The mean annual change in birth weight attributable to 
changes in both PFOA and PFOS exposure is the sum of the annual PFOA 
and PFOS-birth weight change estimates. Additional detail on the 
derivation of the exposure-response functions can be found in appendix 
D in USEPA (2024e). appendix K in USEPA (2024e) presents an analysis of 
birth weight risk reduction considering slope factors specific to the 
first trimester.
[GRAPHIC] [TIFF OMITTED] TR26AP24.052

    The EPA places a cap on estimated birth weight changes in excess of 
200 g, assuming that such changes in birth weight are unreasonable 
based on existing studies that found that changes to environmental 
exposures result in relatively modest birth weight changes (Windham and 
Fenster, 2008; Klein and Lynch, 2018; Kamai et al., 2019). Modest 
changes in birth weight even as a result of large changes in PFOA/PFOS 
serum concentrations may be due to potential bias from studies only 
including live births (Liew et al., 2015). Additionally, the magnitude 
of birth

[[Page 32676]]

weight changes may be correlated with other developmental outcomes such 
as preterm birth, gestational duration, fetal loss, birth defects, and 
developmental delays.
    Low birth weight is linked to a number of health effects that may 
be a source of economic burden to society in the form of medical costs, 
infant mortality, parental and caregiver costs, labor market 
productivity loss, and education costs (Chaikind and Corman, 1991; 
Behrman and Butler, 2007; Behrman and Rosenzweig, 2004; Joyce et al., 
2012; Kowlessar et al., 2013; Colaizy et al., 2016; Nicoletti et al., 
2018; Klein and Lynch, 2018). Recent literature also linked low birth 
weight to educational attainment and required remediation to improve 
student outcomes, childhood disability, and future earnings (Jelenkovic 
et al., 2018; Temple et al., 2010; Elder et al., 2020; Hines et al., 
2020; Chatterji et al., 2014; Dobson et al., 2018).
    The EPA's analysis focuses on two categories of birth weight 
impacts that are amenable to monetization associated with incremental 
changes in birth weight: (1) medical costs associated with changes in 
infant birth weight and (2) the value of avoiding infant mortality at 
various birth weights. The birth weight literature related to other 
sources of economic burden to society (e.g., parental and caregiver 
costs and productivity losses) is limited in geographic coverage, 
population size, and range of birth weights evaluated and therefore 
cannot be used in the EA of birth weight effects from exposure to PFOA/
PFOS in drinking water (ICF, 2021).
    Two studies showed statistically significant relationships between 
incremental changes in birth weight and infant mortality: Almond et al. 
(2005) and Ma and Finch (2010). Ma and Finch (2010) used 2001 NCHS 
linked birth/infant death data for singleton and multiple birth infants 
among subpopulations defined by sex and race/ethnicity to estimate a 
regression model assessing the associations between 14 key birth 
outcome measures, including birth weight and infant mortality. They 
found notable variation in the relationship between birth weight and 
mortality across race/ethnicity subpopulations, with odds ratios for 
best-fit birth weight-mortality models ranging from 0.8-1 (per 100 g 
birth weight change). Almond et al. (2005) used 1989-1991 NCHS linked 
birth/infant death data for multiple birth infants to analyze 
relationships between birth weight and infant mortality within birth 
weight increment ranges. For their preferred model, they reported 
coefficients in deaths per 1,000 births per 1 g increase in birth 
weight that range from -0.420 to -0.002. However, the data used in 
these studies (Almond et al., 2005 and Ma and Finch, 2010) are outdated 
(1989-1991 and 2001, respectively). Given the significant decline in 
infant mortality over the last 30 years (ICF, 2020) and other maternal 
and birth characteristics that are likely to influence infant mortality 
(e.g., average maternal age and rates of maternal smoking), the birth 
weight-mortality relationship estimates from Almond et al. (2005) and 
Ma and Finch (2010) are likely to overestimate the benefits of birth 
weight changes.
    Considering the discernible changes in infant mortality over the 
last 30 years, the EPA developed a regression analysis to estimate the 
relationship between birth weight and infant mortality using the 
Period/Cohort Linked Birth-Infant Death Data Files published by NCHS 
from the 2017 period/2016 cohort and the 2018 period/2017 cohort (CDC, 
2017; CDC, 2018). These data provide information on infants who are 
delivered alive and receive a birth certificate. The EPA selected 
variables of interest for the regression analysis, including maternal 
demographic and socioeconomic characteristics, maternal risk, and risk 
mitigation factors (e.g., number of prenatal care visits, smoker 
status), and infant birth characteristics. The EPA included several 
variables used in Ma and Finch (2010) (maternal age, maternal 
education, marital status, and others) as well as additional variables 
to augment the set of covariates included in the analyses. In addition, 
the EPA developed separate models for different race/ethnicity 
categories (non-Hispanic Black, non-Hispanic White, and Hispanic) and 
interacted birth weight with categories of gestational age, similar to 
Ma and Finch (2010). Appendix E of USEPA (2024e) provides details on 
model development and regression results.
    Table 46 presents the resulting odds ratios and marginal effects 
(in terms of deaths per 1,000 births for every 1 g increase in birth 
weight) estimated for changes in birth weight among different 
gestational age categories in the mortality regression models for non-
Hispanic Black, non-Hispanic White, and Hispanic race/ethnicity 
subpopulations. Marginal effects for birth weight among gestational age 
categories vary across different race/ethnicity subpopulations. The 
marginal effects for birth weight among different gestational age 
categories are higher in the non-Hispanic Black model than in the non-
Hispanic White and Hispanic models, particularly for extremely and very 
preterm infants, indicating that low birth weight increases the 
probability of mortality within the first year more so among non-
Hispanic Black infants than among non-Hispanic White and Hispanic 
infants.
    The EPA relies on odds ratios estimated using the birth weight-
mortality regression model to assess mortality outcomes of reduced 
exposures to PFOA/PFOS in drinking water under the regulatory 
alternatives. To obtain odds ratios specific to each race/ethnicity and 
100 g birth weight increment considered in the birth weight benefits 
model,\24\ the EPA averaged the estimated odds ratios for 1 g increase 
in birth weight over the gestational age categories using the number of 
infants (both singleton and multiple birth) that fall into each 
gestational age category as weights. Separate gestational age category 
weights were computed for each 100 g birth weight increment and race/
ethnicity subpopulation within the 2017 period/2016 cohort and 2018 
period/2017 cohort Linked Birth-Infant Death Data Files. The weighted 
birth weight odds ratios are then used in conjunction with the 
estimated change in birth weight and baseline infant mortality rates to 
determine the probability of infant death under the regulatory 
alternatives, as described further in section 6.4 of USEPA (2024g).
---------------------------------------------------------------------------

    \24\ The birth weight risk reduction model evaluates changes in 
birth weight in response to PFOA/PFOS drinking water level 
reductions for infants who fall into 100 g birth weight increments 
(e.g., birth weight 0-99 g, 100-199 g, 200-299 g. . . 8,000-8,099 g, 
8,100-8,165 g).
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[GRAPHIC] [TIFF OMITTED] TR26AP24.139

    The EPA weighted the race/ethnicity-specific odds ratios in Table 
46 by the proportions of the infant populations who fell into each 
gestational age within a 100 g birth weight increment, based on the 
2016/17 and 2017/18 period cohort data, to obtain a weighted odds ratio 
estimate for each modeled race/ethnicity subpopulation and 100 g birth 
weight increment.
    Based on reduced serum PFOA/PFOS exposures under the regulatory 
alternatives and the estimated relationship between birth weight and 
infant mortality, the EPA estimates the subsequent change in birth 
weight for those infants affected by decreases in PFOA/PFOS and changes 
in the number of infant deaths. The EPA evaluated these changes at each 
PWS EP affected by the regulatory alternatives and the calculations are 
performed for each race/ethnicity group, 100 g birth weight category, 
and year of the analysis. Additional detail on the calculations the EPA 
used to estimate changes in birth

[[Page 32678]]

weight, the affected population size, and infant deaths avoided, and 
the number of surviving infants is provided in chapter 6 of USEPA 
(2024g).
    The EPA used the Value of a Statistical Life to estimate the 
benefits of reducing infant mortality and the cost of illness to 
estimate the economic value of increasing birth weight in the 
population of surviving infants born to mothers exposed to PFOA and 
PFOS in drinking water. The EPA's approach to monetizing benefits 
associated with incremental increases in birth weight resulting from 
reductions in drinking water PFOA/PFOS levels relies on avoided medical 
costs associated with various ranges of birth weight. Although the 
economic burden of treating infants at various birth weights also 
includes non-medical costs, very few studies to date have quantified 
such costs (Klein and Lynch, 2018; ICF, 2021). The EPA selected the 
medical cost function from Klein and Lynch (2018) to monetize benefits 
associated with the estimated changes in infant birth weight resulting 
from reduced maternal exposure to PFOA/PFOS.\25\
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    \25\ The Klein and Lynch (2018) report was externally peer 
reviewed by three experts with qualifications in economics and 
public health sciences. The EPA's charge questions to the peer 
reviewers sought input on the methodology for developing medical 
cost estimates associated with changes in birth weight. The agency's 
charge questions, and peer reviewer responses are available in the 
docket.
---------------------------------------------------------------------------

    Using the incremental cost changes from Klein and Lynch (2018), the 
EPA calculates the change in medical costs resulting from changes in 
birth weight among infants in the affected population who survived the 
first year following birth, provided in Table 47.

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    Tables 48 to 51 provide the health effects avoided and valuation 
associated with birth weight impacts. The EPA estimated that, over the 
evaluation period, the final rule will result in annualized benefits 
from avoided reductions in birth weight of $209 million.

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2. Quantified Cardiovascular Effects
    CVD is one of the leading causes of premature mortality in the 
United States (D'Agostino et al., 2008; Goff et al., 2014; Lloyd-Jones 
et al., 2017). As discussed in the EPA's Final Human Health Toxicity 
Assessments for PFOA and PFOS, exposure to PFOA and PFOS through 
drinking water contributes to increased serum PFOA and PFOS 
concentrations and elevated levels of TC, as well as suggestive 
evidence of changes in levels of HDLC and elevated levels of systolic 
blood pressure (USEPA, 2024c; USEPA, 2024d). Changes in TC and blood 
pressure are associated with changes in incidence of CVD events such as 
myocardial infarction (i.e., heart attack), ischemic stroke, and 
cardiovascular mortality occurring in populations without prior CVD 
event experience (D'Agostino et al., 2008; Goff et al., 2014; Lloyd-
Jones et al., 2017).
    The EPA recognizes that the epidemiologic literature that provides 
strong support for an effect of PFOA and PFOS on cholesterol and blood 
pressure does not provide direct support for an effect of PFOA and PFOS 
on the risk of CVD. Therefore, the EPA uses the approach outlined here 
to link changes in CVD risk biomarkers (i.e., cholesterol and blood 
pressure) to changes in CVD risk.
    For each EP, evaluation of the changes in CVD risk involves the 
following key steps:
    1. Estimation of annual changes in TC and blood pressure levels 
using exposure-response functions for the potential effects of serum 
PFOA/PFOS on these biomarkers;
    2. Estimation of the annual incidence of fatal and non-fatal first 
hard CVD events, defined as fatal and non-fatal myocardial infarction, 
fatal and non-fatal ischemic stroke or other coronary heart disease 
death occurring in populations without prior CVD event experience 
(D'Agostino et al., 2008; Goff et al., 2014; Lloyd-Jones et al., 2017), 
and post-acute CVD mortality corresponding to baseline and regulatory 
alternative TC and blood pressure levels in all populations alive 
during or born after the start of the evaluation period; and
    3. Estimation of the economic value of reducing CVD mortality and 
morbidity from baseline to regulatory alternative levels, using the 
Value of a Statistical Life and cost of illness measures, respectively.
    Given the breadth of evidence linking PFOA and PFOS exposure to 
effects on TC and blood pressure in general adult populations, the EPA 
quantified public health impacts of changes in these well-established 
CVD risk biomarkers (D'Agostino et al., 2008; Goff et al., 2014; Lloyd-
Jones et al., 2017) by estimating changes in incidence of several CVD 
events. Specifically, the EPA assumed that PFOA/PFOS-related changes in 
TC and blood pressure had the same effect on the CVD risk as the 
changes unrelated to chemical exposure and used the Pooled Cohort ASCVD 
model (Goff et al., 2014) to evaluate their impacts on the incidence of 
myocardial infarction, ischemic stroke, and cardiovascular mortality 
occurring in populations without prior CVD event experience.
    The ASCVD model includes TC as a predictor of first hard CVD 
events. The EPA did not identify any readily available relationships 
for PFOA or PFOS and TC that were specifically relevant to the age 
group of interest (40-89 years, the years for which the ASCVD model 
estimates the probability of a first hard CVD event). Therefore, the 
agency developed a meta-analysis of studies reporting associations 
between serum PFOA or PFOS and TC in general populations (e.g., 
populations that are not a subset of workers or pregnant women). 
Statistical analyses that combine the results of multiple studies, such 
as meta-analyses, are widely applied to investigate the associations 
between contaminant levels and associated health effects. Such analyses 
are suitable for economic assessments because they can improve 
precision and statistical power (Engels et al., 2000; Deeks, 2002; 
R[uuml]cker et al., 2009).
    The EPA identified 14 studies from which to derive slope estimates 
for PFOA and PFOS associations with serum TC levels. Appendix F of 
USEPA (2024e) provides further detail on the studies selection 
criteria, meta-data development, meta-analysis results, and discussion 
of the uncertainty and limitations inherent in the EPA's exposure-
response analysis.
    The EPA developed exposure-response relationships between serum 
PFOA/PFOS and TC for use in the CVD analysis using the meta-analyses 
restricted to studies of adults in the general population reporting 
similar models. When using studies reporting linear associations 
between TC and serum PFOA or PFOS, the EPA estimated a positive 
increase in TC of 1.57 (95 percent CI: 0.02, 3.13) mg/dL per ng/mL 
serum PFOA (p-value=0.048), and of 0.08 (95 percent CI: -0.01, 0.16) 
mg/dL per ng/mL serum PFOS (p-value=0.064). Based on the systematic 
review conducted by the EPA to develop the EPA's Final Human Health 
Toxicity Assessments for PFOA and PFOS, the available evidence supports 
a positive association between PFOS and TC in the general population. 
For more information on the systematic review and results, see USEPA 
(2024c) and USEPA (2024d).
    PFOS exposure has been linked to other cardiovascular outcomes, 
such as systolic blood pressure and hypertension (Liao et al., 2020; 
USEPA, 2024d). Because systolic blood pressure is another predictor 
used by the ASCVD model, the EPA included the estimated changes in 
blood pressure from reduced exposure to PFOS in the CVD analysis. The 
EPA selected the slope from the Liao et al. (2020) study--a high 
confidence study conducted based on U.S. general population data from 
NHANES cycles 2003-2012. The evidence on the associations between PFOA 
and blood pressure is not as consistent as for PFOS. Therefore, the EPA 
is not including effect estimates for the serum PFOA-blood pressure 
associations in the CVD analysis.
    The EPA relies on the life table-based approach to estimate CVD 
risk reductions because (1) changes in serum PFOA/PFOS in response to 
changes in drinking water PFOA/PFOS occur over multiple years, (2) CVD 
risk, relying on the ASCVD model, can be modeled only for those older 
than 40 years without prior CVD history, and (3) individuals who have 
experienced non-fatal CVD events have elevated mortality implications 
immediately and within at least five years of the first occurrence. 
Recurrent life table calculations are used to estimate a PWS EP-
specific annual time series of CVD event incidence for a population 
cohort characterized by sex, race/ethnicity, birth year, age at the 
start of the PFOA/PFOS evaluation period (i.e., 2024), and age- and 
sex-specific time series of changes in TC and blood pressure levels 
obtained by combining serum PFOA/PFOS concentration time series with 
exposure-response information. Baseline and regulatory alternatives are 
evaluated separately, with regulatory alternative TC and blood pressure 
levels estimated using baseline information on these biomarkers from 
external statistical data sources and modeled changes in TC and blood 
pressure due to conditions under the regulatory alternatives.
    The EPA estimated the incidence of first hard CVD events based on 
TC serum and blood pressure levels using the ASCVD model (Goff et al., 
2014), which predicts the 10-year probability of a hard CVD event to be 
experienced by a person without a prior CVD history. The EPA adjusted 
the modeled

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population cohort to exclude individuals with pre-existing conditions, 
as the ASCVD risk model does not apply to these individuals. For blood 
pressure effects estimation, the EPA further restricts the modeled 
population to those not using antihypertensive medications for 
consistency with the exposure-response relationship. Modeled first hard 
CVD events include fatal and non-fatal myocardial infarction, fatal and 
non-fatal ischemic stroke, and other coronary heart disease mortality. 
The EPA has also estimated the incidence of post-acute CVD mortality 
among survivors of the first myocardial infarction or ischemic stroke 
within 6 years of the initial event.
    The estimated CVD risk reduction resulting from reducing serum PFOA 
and serum PFOS concentrations is the difference in annual incidence of 
CVD events (i.e., mortality and morbidity associated with first-time 
CVD events and post-acute CVD mortality) under the baseline and 
regulatory alternatives. Appendix G of USEPA (2024e) provides detailed 
information on all CVD model components, computations, and sources of 
data used in modeling.
    The EPA uses the Value of a Statistical Life to estimate the 
benefits of reducing mortality associated with hard CVD events in the 
population exposed to PFOA and PFOS in drinking water. The EPA relies 
on cost of illness-based valuation that represents the medical costs of 
treating or mitigating non-fatal first hard CVD events (myocardial 
infarction, ischemic stroke) during the three years following an event 
among those without prior CVD history, adjusted for post-acute 
mortality.
    The annual medical expenditure estimates for myocardial infarction 
and ischemic stroke are based on O'Sullivan et al. (2011). The 
estimated expenditures do not include long-term institutional and home 
health care. For non-fatal myocardial infarction, O'Sullivan et al. 
(2011) estimated medical expenditures are $53,246 ($2022) for the 
initial event and then $33,162, $14,635, $13,078 annually within 1, 2, 
and 3 years after the initial event, respectively. For non-fatal 
ischemic stroke, O'Sullivan et al. (2011) estimated medical 
expenditures are $16,503 ($2022) for the initial event and then 
$11,988, $788, $1,868 annually within 1, 2, and 3 years after the 
initial event, respectively. Annual estimates within 1, 2, and 3 years 
after the initial event include the incidence of secondary CVD events 
among survivors of first myocardial infarction and ischemic stroke 
events.
    To estimate the present discounted value of medical expenditures 
within 3 years of the initial non-fatal myocardial infarction, the EPA 
combined O'Sullivan et al. (2011) myocardial infarction-specific 
estimates with post-acute survival probabilities based on Thom et al. 
(2001) (for myocardial infarction survivors aged 40-64) and Li et al. 
(2019) (for myocardial infarction survivors aged 65+). To estimate the 
present discounted value of medical expenditures within 3 years of the 
initial non-fatal ischemic stroke, the EPA combined O'Sullivan et al. 
(2011) ischemic stroke-specific estimates with post-acute survival 
probabilities based on Thom et al. (2001) (for ischemic stroke 
survivors aged 40-64, assuming post-acute myocardial infarction 
survival probabilities reasonably approximate post-acute ischemic 
stroke survival probabilities) and Li et al. (2019) (for ischemic 
stroke survivors aged 65+). The EPA did not identify post-acute 
ischemic stroke mortality information in this age group, but instead 
applied post-acute myocardial infarction mortality estimates for 
ischemic stroke valuation. Table 52 presents the resulting myocardial 
infarction and ischemic stroke unit values.
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    Tables 53 to 56 provide the health effects avoided and valuation 
associated with CVD. The EPA estimated that, over the evaluation 
period, the final rule will result in annualized benefits from avoided 
CVD cases and deaths of $606 million.

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BILLING CODE 6560-50-C
3. Quantified Kidney Cancer Effects
    Data on the association between PFOA exposure and kidney cancer 
(i.e., RCC), particularly from epidemiological studies, indicate a 
positive association between exposure and increased risk of RCC. 
Epidemiology studies indicated that exposure to PFOA was associated 
with an increased risk of RCC (CalEPA, 2021; ATSDR, 2021; USEPA, 2016c; 
USEPA, 2024c, USEPA, 2024j). In the PFOA HESD (USEPA, 2016c), the EPA 
determined that PFOA is likely to be carcinogenic to humans (USEPA, 
2005a) based in part on evidence of associations between PFOA exposure 
and kidney cancer in humans. A recent study of the relationship between 
PFOA and RCC in U.S. general populations found strong evidence of a 
positive association between exposure to PFOA and RCC in humans 
(Shearer et al., 2021). A meta-analysis of epidemiological literature 
also concluded that there was an increased risk of kidney cancer 
associated with increased PFOA serum concentrations (Bartell and 
Vieira, 2021). As such, the EPA selected RCC as a key outcome when 
assessing the health impacts of reduced PFOA exposures.
    The EPA quantified and valued the changes in RCC risk associated 
with reductions in serum PFOA levels that are in turn associated with 
reductions in drinking water PFOA concentrations under the regulatory 
alternatives. PWS EP-specific time series of the differences between 
serum PFOA concentrations under baseline and regulatory alternatives 
are inputs into this analysis. For each PWS EP, evaluation of the 
changes in RCC impacts involves the following key steps:
    1. Estimating the changes in RCC risk based on modeled changes in 
serum PFOA levels and the exposure-response function for the effect of 
serum PFOA on RCC;
    2. Estimating the annual incidence of RCC cases and excess 
mortality among those with RCC in all populations corresponding to 
baseline and regulatory alternative RCC risk levels, as well as 
estimating the regulatory alternative-specific reduction in cases 
relative to the baseline, and
    3. Estimating the economic value of reducing RCC mortality from 
baseline to regulatory alternative levels, using the Value of a 
Statistical Life and cost of illness measures, respectively.
    To identify an exposure-response function, the EPA reviewed studies 
highlighted in the HESD for PFOA (USEPA, 2016c) and a recent study 
discussed in both the California Environmental Protection Agency's 
Office of Environmental Health Hazard Assessment (OEHHA) PFOA Public 
Health Goals report (CalEPA, 2021) and the EPA's Final Human Health 
Toxicity Assessment for PFOA (USEPA, 2024c; USEPA, 2024j). Steenland et 
al. (2015) observed an increase in kidney cancer deaths among workers 
with high exposures to PFOA. Vieira et al. (2013) found that kidney 
cancer was positively associated with ``high'' and ``very high'' PFOA 
exposures. Barry et al. (2013) found a slight trend in cumulative PFOA 
serum exposures and kidney cancer among the C8 Health Project 
population. In a large case-control general population study of the 
relationship between PFOA and kidney cancer in 10 locations across the 
U.S., Shearer et al. (2021) found evidence that exposure to PFOA is 
associated with RCC, the most common form of kidney cancer, in humans.
    To evaluate changes between baseline and regulatory alternative RCC 
risk resulting from reduced exposure to PFOA, the EPA relied on the 
estimated time series of changes in serum PFOA concentrations (section 
6.3) and the

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serum-RCC exposure-response function provided by Shearer et al. (2021): 
0.00178 (ng/mL)-1. The analysis reported in Shearer et al. 
(2021) was designed as a case-control study with population controls 
based on 10 sites within the U.S. population. Shearer et al. (2021) 
accounted for age, sex, race, ethnicity, study center, year of blood 
draw, smoking, and hypertension in modeling the association between 
PFOA and RCC. Results showed a strong and statistically significant 
association between PFOA and RCC. The EPA selected the exposure-
response relationship from Shearer et al. (2021) because it included 
exposure levels typical in the general population and the study was 
found to have a low risk of bias when assessed in the EPA's Final Human 
Health Toxicity Assessment for PFOA (USEPA, 2024c; USEPA, 2024j).
    The linear slope factor developed by the agency (see section 4.2 of 
USEPA, 2024c) based on Shearer et al. (2021) enables estimation of the 
changes in the lifetime RCC risk associated with reduced lifetime serum 
PFOA levels. Because baseline RCC incidence statistics are not readily 
available from the National Cancer Institute (NCI) public use data, the 
EPA used kidney cancer statistics in conjunction with an assumption 
that RCC comprises 90 percent of all kidney cancer cases to estimate 
baseline lifetime probability of RCC (USEPA, 2024c; American Cancer 
Society, 2020). The EPA estimated the baseline lifetime RCC incidence 
for males at 1.89 percent and the baseline lifetime RCC incidence for 
females at 1.05 percent. Details of these calculations are provided in 
appendix H of USEPA (2024e).
    Similar to the EPA's approach for estimating CVD risk reductions, 
the EPA relies on the life table approach to estimate RCC risk 
reductions. The outputs of the life table calculations are the PWS EP-
specific estimates of the annual change in the number of RCC cases and 
the annual change in excess RCC population mortality. For more detail 
on the EPA's application of the life table to cancer benefits analyses, 
please see appendix H of USEPA (2024e).
    Although the change in PFOA exposure likely affects the risk of 
developing RCC beyond the end of the analysis period (the majority of 
RCC cases manifest during the latter half of the average individual 
lifespan; see appendix H of USEPA (2024e), the EPA does not capture 
effects after the end of the period of analysis, 2105. Individuals 
alive after the end of the period of analysis likely benefit from lower 
lifetime exposure to PFOA. Lifetime health risk model data sources 
include the EPA SDWIS, age-, sex-, and race/ethnicity-specific 
population estimates from the U.S. Census Bureau (2020), the 
Surveillance, Epidemiology, and End Results (SEER) program database 
(Surveillance Research Program--National Cancer Institute, 2020a; 
National Cancer Institute, 2020b), and the CDC NCHS. Appendix H of 
USEPA (2024e) provides additional detail on the data sources and 
information used in this analysis as well as baseline kidney cancer 
statistics. Appendix B of USEPA (2024e) describes estimation of the 
affected population.
    The EPA uses the Value of a Statistical Life to estimate the 
benefits of reducing mortality associated with RCC in the population 
exposed to PFOA in drinking water. The EPA uses the cost of illness-
based valuation to estimate the benefits of reducing morbidity 
associated with RCC.
    The EPA used the medical cost information from a recent RCC cost-
effectiveness study by Ambavane et al. (2020) to develop cost of 
illness estimates for RCC morbidity. Ambavane et al. (2020) used a 
discrete event simulation model to estimate the lifetime treatment 
costs of several RCC treatment sequences, which included first and 
second line treatment medication costs, medication administration 
costs, adverse effect management costs, and disease management costs 
on- and off-treatment. To this end, the authors combined RCC cohort 
data from CheckMate 214 clinical trial and recent US-based healthcare 
cost information assembled from multiple sources (see supplementary 
information from Ambavane et al. (2020)).
    The EPA received public comments on the EA for the proposed rule 
related to the EPA's use of cost of illness information for morbidity 
valuation. Specifically, some commenters recommended that the EPA use 
willingness to pay information (instead of cost of illness information) 
when valuing the costs associated with non-fatal illnesses, stating 
that willingness to pay information better accounts for lost 
opportunity costs (e.g., lost productivity and pain and suffering) 
associated with non-fatal illnesses (USEPA, 2024k). To better account 
for these opportunity costs, the EPA used recently available 
willingness to pay values in a sensitivity analysis for morbidity 
associated with RCC. The sensitivity analysis results show that when 
willingness to pay values are used in RCC benefits analysis, morbidity 
benefits are increased by approximately 2 percent. See appendix O of 
the EA for full details and results on the willingness to pay 
sensitivity analyses.
    Table 57 summarizes RCC morbidity cost of illness estimates derived 
by the EPA using Ambavane et al. (2020)-reported disease management 
costs on- and off-treatment along with medication, administration, and 
adverse effect management costs for the first line treatment that 
initiated the most cost-effective treatment sequences as identified by 
Ambavane et al. (2020), i.e., the nivolumab and ipilimumab drug 
combination. This is a forward-looking valuation approach in that it 
assumes that the clinical practice would follow the treatment 
recommendations in Ambavane et al. (2020) and other recent studies 
cited therein. The EPA notes that the second line treatment costs are 
not reflected in the EPA's cost of illness estimates, because Ambavane 
et al. (2020) did not report information on the expected durations of 
the treatment-free interval (between the first line treatment 
discontinuation and the second line treatment initiation) and the 
second line treatment phase, conditional on survival beyond 
discontinuation of the second line treatment. As such, the EPA valued 
RCC morbidity at $261,175 ($2022) during year 1 of the diagnosis, 
$198,705 ($2022) during year 2 of the diagnosis, and $1,661 ($2022) 
starting from year 3 of the diagnosis. Additionally, the EPA assumed 
that for individuals with RCC who die during the specific year, the 
entire year-specific cancer treatment regimen is applied prior to the 
death event. This may overestimate benefits if a person does not 
survive the entire year.
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    Tables 58 to 61 provide the health effects avoided and valuation 
associated with RCC. The EPA estimated that, over the evaluation 
period, the final rule will result in annualized benefits from avoided 
RCC cases and deaths of $354 million.

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4. Key Limitations and Uncertainties in the Benefits Analysis
    The following section discusses the uncertainty information 
incorporated in the quantitative benefits analysis. There are 
additional sources of uncertainty and limitations that could not be 
modeled quantitatively as part of the national benefits analysis. These 
sources of uncertainty are characterized in detail in section 6.8 of 
USEPA (2024g). This summary includes uncertainties that are specific to 
application of PK models for blood serum PFAS concentration estimation, 
developmental effects (i.e., infant birth weight) modeling, CVD impacts 
modeling, RCC impacts modeling, and modeling of bladder cancer impacts 
from GAC treatment-related reductions in the sum of four 
trihalomethanes (THM4). Table 62 presents the key limitations and 
uncertainties that apply to the benefits analysis for the final rule. 
The EPA notes that in most cases it is not possible to judge the extent 
to which a particular limitation or uncertainty could affect the 
magnitude of the estimated benefits. Therefore, in each of the 
following tables, the EPA notes the potential direction of the impact 
on the quantified benefits (e.g., a source of uncertainty that tends to 
underestimate quantified benefits indicates expectation for larger 
quantified benefits) but does not prioritize the entries with respect 
to the impact magnitude.

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BILLING CODE 6560-50-C

G. Nonquantifiable Benefits of PFOA and PFOS Exposure Reduction

    In this section, the EPA qualitatively discusses the potential 
health benefits resulting from reduced exposure to PFOA and PFOS in 
drinking water. These nonquantifiable benefits are expected to be 
realized as avoided adverse health effects as a result of the final 
NPDWR, in addition to the benefits that the EPA has quantified, because 
of their known toxicity and additive health concerns as well as 
occurrence and likely co-occurrence in drinking water. The EPA 
anticipates additional benefits associated with developmental, 
cardiovascular, liver, immune, endocrine, metabolic, reproductive, 
musculoskeletal, and carcinogenic effects beyond those benefits that 
the EPA has quantified. The evidence for these adverse health effects 
is briefly summarized here.
    The EPA identified a wide range of potential health effects 
associated with exposure to PFOA and PFOS using five comprehensive 
Federal Government health effects assessments that summarize the recent 
literature on PFAS (mainly PFOA and PFOS, although many of the same 
health effects have been observed for the other PFAS in this rule) 
exposure and its health impacts: the EPA's HESDs for PFOA and PFOS, 
hereafter referred to as the EPA HESDs (USEPA, 2016c; USEPA, 2016d); 
the EPA's Final Human Health Toxicity Assessments for PFOA and

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PFOS (USEPA, 2024c; USEPA, 2024d); and the U.S. Department of Health 
and Human Services (HHS) ATSDR Toxicological Profile for 
Perfluoroalkyls (ATSDR, 2021). Each source presents comprehensive 
literature reviews on adverse health effects associated with PFOA and 
PFOS. The EPA notes that NASEM also published a report which includes a 
review of the adverse health effects for numerous PFAS (NASEM, 2022). 
That document is included in the docket for this final rule.
    The most recent literature reviews on PFAS exposures and health 
impacts, which are included in the EPA's Final Human Health Toxicity 
Assessments for PFOA and PFOS (USEPA, 2024c; USEPA, 2024d), describe 
the weight of evidence supporting PFOA and PFOS associations with 
health outcomes as either demonstrative, indicative (likely), 
suggestive, inadequate, or strong evidence supportive of no effect 
according to the evidence integration judgments outlined in the ORD 
Staff Handbook for Developing IRIS Assessments (USEPA, 2022f; USEPA, 
2024c; USEPA, 2024d). For the purposes of the reviews conducted to 
develop the Final Human Health Toxicity Assessments for PFOA and PFOS, 
an association is deemed demonstrative when there is a strong evidence 
base demonstrating that the chemical exposure causes a health effect in 
humans. The association is deemed indicative (likely) when the evidence 
base indicates that the chemical exposure likely causes a health effect 
in humans, although there might be outstanding questions or limitations 
that remain, and the evidence is insufficient for the higher conclusion 
level. The association is suggestive if the evidence base suggests that 
the chemical exposure might cause a health effect in humans, but there 
are very few studies that contributed to the evaluation, the evidence 
is very weak or conflicting, or the methodological conduct of the 
studies is poor. The association is inadequate if there is a lack of 
information or an inability to interpret the available evidence (e.g., 
findings across studies). The association supports no effect when 
extensive evidence across a range of populations and exposure levels 
has identified no effects/associations. Note that the EPA considered 
information available as of September 2023 for the analyses presented 
herein.
    Developmental effects: Exposure to PFOA and PFOS is linked to 
developmental effects including but not limited to the infant birth 
weight effects that the EPA quantified. Other developmental effects 
include small for gestational age (SGA), birth length, head 
circumference at birth, and other effects (Verner et al., 2015; Negri 
et al., 2017; ATSDR, 2021; Waterfield et al., 2020; USEPA, 2016c; 
USEPA, 2016d; USEPA, 2024c; USEPA, 2024d). SGA is a developmental 
health outcome of interest when studying potential effects of PFOA/PFOS 
exposure because SGA infants have increased health risks during 
pregnancy and delivery as well as post-delivery (Osuchukwu and Reed, 
2022). The majority of epidemiology studies indicated increased risk of 
SGA with PFOA/PFOS exposure, although some studies reported null 
results (USEPA, 2024c; USEPA, 2024d). For instance, some studies 
suggested a potentially positive association between PFOA exposure and 
SGA (Govarts et al., 2018; Lauritzen et al., 2017; Wang et al., 2016; 
Souza et al., 2020; Wikstr[ouml]m et al., 2020; Chang et al., 2022; 
USEPA, 2024c). In addition to decreases in offspring weight, toxicology 
studies on PFOA and PFOS exposures in rodents demonstrated 
relationships with multiple other developmental toxicity endpoints, 
including increased offspring mortality, decreased maternal body weight 
and body weight change, skeletal and soft tissue effects, and delayed 
eye-opening (USEPA, 2024c; USEPA, 2024d). For additional details on 
developmental studies and their individual outcomes, see chapter 3.4.4 
(Developmental) in USEPA (2024c) and USEPA (2024d).
    Cardiovascular effects: In addition to the CVD effects that the EPA 
quantified associated with changes in TC and blood pressure from 
exposure to PFOA and PFOS (see section 6.2 of USEPA (2024g)), available 
evidence suggests an association between exposure to PFOA and PFOS and 
increased low-density lipoprotein cholesterol (LDLC) (ATSDR, 2021; 
USEPA, 2024c; USEPA, 2024d). High levels of LDLC are known as the `bad' 
cholesterol because it can lead to the buildup of cholesterol in the 
arteries, which can raise the risk of heart disease and stroke. 
Epidemiology studies showed a positive association between PFOA or PFOS 
exposure and LDLC levels in adults and children (USEPA, 2024c; USEPA, 
2024d). In particular, the evidence suggested positive associations 
between serum PFOA and PFOS levels and LDLC levels in adolescents ages 
12-18, while positive associations between serum levels and LDLC levels 
in younger children were observed only for PFOA (ATSDR, 2021). 
Additionally, available evidence supports a relatively consistent 
positive association between PFOA or PFOS and low-density lipoprotein 
(LDL) in adults, especially those who are obese or prediabetic. 
Associations with other lipoprotein cholesterol known to increase 
cardiovascular risks were also positive, which increased confidence in 
the findings for LDLC. Available evidence regarding the impact of PFOA 
and PFOS exposure on pregnant women was too limited for the EPA to 
determine an association (ATSDR, 2021; USEPA, 2024c; USEPA, 2024d). 
Toxicology studies generally reported alterations in serum lipid levels 
in mice and rats following oral exposure to PFOA (USEPA, 2024d) or PFOS 
(USEPA, 2024c), indicating a disruption in lipid metabolism, which is 
coherent with effects observed in humans. For additional details on 
LDLC studies and their individual outcomes, see chapter 3.4.3 
(Cardiovascular) in USEPA (2024c) and USEPA (2024d).
    Liver effects: Several biomarkers can be used clinically to 
diagnose liver diseases, including alanine aminotransferase (ALT). 
Serum ALT measures are considered a reliable indicator of impaired 
liver function because increased serum ALT is indicative of leakage of 
ALT from damaged hepatocytes (Boone et al., 2005; Z. Liu et al., 2014; 
USEPA, 2002d). Additionally, evidence from both human epidemiological 
and animal toxicological studies indicates that increased serum ALT is 
associated with liver disease (Ioannou et al., 2006a; Ioannou et al., 
2006b; Kwo et al., 2017; Roth et al., 2021). Human epidemiological 
studies have demonstrated that even low magnitude increases in serum 
ALT can be clinically significant (Mathiesen et al., 1999; Park et al., 
2019). Additionally, numerous studies have demonstrated an association 
between elevated ALT and liver-related mortality (reviewed by Kwo et 
al., 2017). Furthermore, the American Association for the Study of 
Liver Diseases (AASLD) recognizes serum ALT as an indicator of overall 
human health and mortality (Kim et al., 2008). Epidemiology data 
provides consistent evidence of a positive association between PFOS/
PFOA exposure and ALT levels in adults (ATSDR, 2021; USEPA, 2024c; 
USEPA, 2024d). Studies of adults showed consistent evidence of a 
positive association between PFOA exposure and elevated ALT levels at 
both high exposure levels and exposure levels typical of the general 
population (USEPA, 2024c). There is also consistent epidemiology 
evidence of associations between PFOS and elevated ALT levels. A 
limited number of studies reported

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inconsistent evidence on whether PFOA/PFOS exposure is associated with 
increased risk of liver disease (USEPA, 2024d). It is also important to 
note that while evaluation of direct liver damage is possible in animal 
studies, it is difficult to obtain biopsy-confirmed histological data 
in humans. Therefore, liver injury is typically assessed using serum 
biomarkers of hepatotoxicity (Costello et al., 2022). Associations 
between PFOA/PFOS exposure and ALT levels in children were less 
consistent than in adults (USEPA, 2024c; USEPA, 2024d).
    PFOA toxicology studies showed increases in ALT and other serum 
liver enzymes across multiple species, sexes, and exposure paradigms 
(USEPA, 2024c). Toxicology studies on the impact of PFOS exposure on 
ALT also reported increases in ALT and other serum liver enzyme levels 
in rodents, though these increases were modest (USEPA, 2024d). Several 
studies in animals also reported increases in the incidence of liver 
lesions or cellular alterations, such as hepatocellular cell death 
(USEPA, 2024c; USEPA, 2024d). For additional details on the ALT studies 
and their individual outcomes, see section 3.4.1 (Hepatic) in USEPA 
(2024c) and USEPA (2024d).
    Immune effects: Proper antibody response helps maintain the immune 
system by recognizing and responding to antigens. The available 
evidence indicates a relationship between PFOA exposure and 
immunosuppression; epidemiology studies showed suppression of at least 
one measure of the antibody response for tetanus and diphtheria among 
people with higher prenatal and childhood serum concentrations of PFOA 
(ATSDR, 2021; USEPA, 2024c). Data reporting on associations between 
PFOA exposure and antibody response to vaccinations other than tetanus 
and diphtheria (i.e., rubella and hand, foot, and mouth disease) are 
limited but supportive of associations between PFOA and decreased 
immune response in children (USEPA, 2024c). Available studies supported 
an association between PFOS exposure and immunosuppression in children, 
where increased PFOS serum levels were associated with decreased 
antibody production in response to tetanus, diphtheria, and rubella 
vaccinations (USEPA, 2024d). Studies reporting associations between 
PFOA or PFOS exposure and immunosuppression in adults are less 
consistent, though this may be due to a lack of high confidence data 
(USEPA, 2024c; USEPA, 2024d). Toxicology evidence suggested that PFOA 
and PFOS exposure results in effects similarly indicating immune 
suppression, such as reduced response of immune cells to challenges 
(e.g., reduced natural killer cell activity and immunoglobulin 
production) (USEPA, 2024c; USEPA, 2024d). For additional details on 
immune studies and their individual outcomes, see section 3.4.2 
(Immune) in USEPA (2024c) and USEPA (2024d).
    Endocrine effects: Elevated circulating thyroid hormone levels can 
accelerate metabolism and cause irregular heartbeat; low levels of 
thyroid hormones can cause neurodevelopmental effects, tiredness, 
weight gain, and increased susceptibility to the common cold. There is 
suggestive evidence of a positive association between PFOA/PFOS 
exposure and thyroid hormone disruption (ATSDR, 2021; USEPA, 2024c; 
USEPA, 2024d). Epidemiology studies reported inconsistent evidence 
regarding associations between PFOA and PFOS exposure and general 
endocrine outcomes, such as thyroid disease, hypothyroidism, and 
hypothyroxinemia (USEPA, 2024c; USEPA, 2024d). However, for PFOA, 
epidemiological studies reported suggestive evidence of positive 
associations for serum levels of thyroid stimulating hormone (TSH) and 
the thyroid hormone triiodothyronine (T3) in adults, and the thyroid 
hormone thyroxine (T4) in children (USEPA, 2024c; USEPA, 2024d). For 
PFOS, epidemiological studies reported suggestive evidence of positive 
associations for TSH in adults, positive associations for T3 in 
children, and inverse associations for T4 in children (USEPA, 2024d). 
Toxicology studies indicated that PFOA and PFOS exposure leads to 
decreases in serum thyroid hormone levels \26\ and adverse effects to 
the endocrine system (ATSDR, 2021; USEPA, 2024c; USEPA, 2024d; USEPA, 
2024h). Overall, changes in serum thyroid hormone levels in animals 
indicate PFOS and PFOA toxicity potentially relevant to humans (USEPA, 
2024c; USEPA, 2024d). For additional details on endocrine effects 
studies and their individual outcomes, see appendix C.2 (Endocrine) in 
USEPA (2024h) and USEPA (2024i).
---------------------------------------------------------------------------

    \26\ Decreased thyroid hormone levels are associated with 
effects such as changes in thyroid and adrenal gland weight, hormone 
fluctuations, and organ histopathology, as well as adverse 
neurodevelopmental outcomes (ATSDR, 2021; USEPA, 2024c).
---------------------------------------------------------------------------

    Metabolic effects: Leptin is a hormone that, along with 
adiponectin, can be a marker of adipose tissue dysfunction. Chronic 
high levels of leptin lead to leptin resistance that mirrors many of 
the characteristics associated with diet-induced obesity, including 
reduced leptin receptors and diminished signaling. Therefore, high 
leptin levels are associated with higher body fat mass, a larger size 
of individual fat cells, overeating, and inflammation (e.g., of adipose 
tissue, the hypothalamus, blood vessels, and other areas). Evidence 
suggests an association between PFOA exposure and leptin levels in the 
general adult population (ATSDR, 2021; USEPA, 2024c). Based on a review 
of human epidemiology studies, evidence of associations between PFOS 
and metabolic outcomes appears inconsistent, but in some studies, 
positive associations were observed between PFOS exposure and leptin 
levels (USEPA, 2024d). Studies examining newborn leptin levels did not 
find associations with maternal PFOA levels (ATSDR, 2021). Maternal 
PFOS levels were also not associated with alterations in leptin levels 
(ATSDR, 2021). For additional details on metabolic effect studies and 
their individual outcomes, see appendix C.3 (Metabolic/Systemic) in 
USEPA (2024h) and USEPA (2024i).
    Reproductive effects: Studies of the reproductive effects from 
PFOA/PFOS exposure have focused on associations between exposure to 
these contaminants and increased risk of gestational hypertension and 
preeclampsia in pregnant women (ATSDR, 2021; USEPA, 2024c; USEPA, 
2024d). Gestational hypertension (high blood pressure during pregnancy) 
can lead to fetal problems such as poor growth and stillbirth. 
Preeclampsia--instances of gestational hypertension where the mother 
also has increased levels of protein in her urine--can similarly pose 
significant risks to both the fetus and mother. Risks to the fetus 
include impaired fetal growth due to the lack of oxygen and nutrients, 
stillbirth, preterm birth, and infant death (NIH, 2017). Even if born 
full term, the infant may be at risk for later problems such as 
diabetes, high blood pressure, and congestive heart failure. Effects of 
preeclampsia on the mother may include kidney and liver damage, blood 
clotting problems, brain injury, fluid on the lungs, seizures, and 
mortality (NIH, 2018). The epidemiology evidence yields mixed (positive 
and null) associations, with some suggestive evidence supporting 
positive associations between PFOA/PFOS exposure and both preeclampsia 
and gestational hypertension (ATSDR, 2021; USEPA, 2024c; USEPA, 2024d). 
For additional details on reproductive effects studies and their 
individual

[[Page 32699]]

outcomes, see appendix C.1 (Reproductive) in USEPA (2024h) and USEPA 
(2024i).
    Musculoskeletal effects: Adverse musculoskeletal effects such as 
osteoarthritis and decreased bone mineral density impact bone integrity 
and cause bones to become brittle and more prone to fracture. The 
available epidemiology evidence suggests that PFOA exposure may be 
linked to decreased bone mineral density, bone mineral density relative 
to bone area, height in adolescence, osteoporosis, and osteoarthritis 
(ATSDR, 2021; USEPA, 2024c). Some studies found that PFOA/PFOS exposure 
was linked to osteoarthritis, in particular among women under 50 years 
of age (ATSDR, 2021). There is limited evidence from studies pointing 
to effects of PFOS on skeletal size (height), lean body mass, and 
osteoarthritis (USEPA, 2024d). Evidence from some studies suggests that 
PFOS exposure has a harmful effect on bone health, particularly 
measures of bone mineral density, with greater statistically 
significance of effects occurring among females (USEPA, 2024d). 
However, other reviews reported mixed findings on the effects of PFOS 
exposure including decreased risk of osteoarthritis, increased risk for 
some demographic subgroups, or no association (ATSDR, 2021). For 
additional details on musculoskeletal effects studies and their 
individual outcomes, see appendix C.8 (Musculoskeletal) in USEPA 
(2024h) and USEPA (2024i).
    Cancer Effects: In the EPA's Final Human Health Toxicity Assessment 
for PFOA, the agency evaluates the evidence for carcinogenicity of PFOA 
that has been documented in both epidemiological and animal toxicity 
studies (USEPA, 2024c; USEPA, 2024j). The evidence in epidemiological 
studies is primarily based on the incidence of kidney and testicular 
cancer, as well as potential incidence of breast cancer in genetically 
susceptible subpopulations or for particular breast cancer types. Other 
cancer types have been observed in humans, although the evidence for 
these is generally limited to low confidence studies. The evidence of 
carcinogenicity in animal models is provided in three chronic oral 
animal bioassays in Sprague-Dawley rats which identified neoplastic 
lesions of the liver, pancreas, and testes (USEPA, 2024c; USEPA, 
2024j). The EPA determined that PFOA is Likely to Be Carcinogenic to 
Humans, as ``the evidence is adequate to demonstrate carcinogenic 
potential to humans but does not reach the weight of evidence for the 
descriptor Carcinogenic to Humans.'' This determination is based on the 
evidence of kidney and testicular cancer in humans and LCTs, PACTs, and 
hepatocellular adenomas in rats (USEPA, 2024c; USEPA, 2024j). The EPA's 
benefits analysis for avoided RCC cases from reduced PFOA exposure is 
discussed in section XII.E of this preamble and in section 6.6 of USEPA 
(2024g).
    In the EPA's Final Human Health Toxicity Assessment for PFOS, the 
agency evaluates the evidence for carcinogenicity of PFOS and found 
that several epidemiological studies and a chronic cancer bioassay 
comprise the evidence database for the carcinogenicity of PFOS (USEPA, 
2024d; USEPA 2024j). The available epidemiology studies report elevated 
risk of liver cancer, consistent with increased incidence of liver 
tumors reported in male and female rats. There is also mixed but 
plausible evidence of bladder, prostate, kidney, and breast cancers in 
humans. The animal chronic cancer bioassay study also provides evidence 
of increased incidence of pancreatic islet cell tumors in male rats. 
The EPA reviewed the weight of the evidence and determined that PFOS is 
Likely to Be Carcinogenic to Humans, as ``the evidence is adequate to 
demonstrate carcinogenic potential to humans but does not reach the 
weight of evidence for the descriptor Carcinogenic to Humans.'' The 
EPA's national-level benefits sensitivity analysis for avoided liver 
cancer cases from reduced PFOS exposure is detailed in appendix O of 
the EA.
    The EPA anticipates there are additional nonquantifiable benefits 
related to potential testicular, bladder, prostate, and breast cancer 
effects summarized above. Benefits associated with avoiding cancer 
cases not quantified in the EPA's analysis could be substantial. For 
example, a study by Obsekov et al. (2023) reports the number of breast 
cancer cases attributable to PFAS exposure ranges from 421 to 3,095 
annually, with an estimated direct cost of 6-month treatment ranging 
from $27.1 to $198.4 million per year ($2022). This study also finds 
that approximately 5 (0.076 percent) annual testicular cases are 
attributable to PFOA exposure with an estimated direct cost of 
treatment of $173,450 per year ($2022). Although the methods used by 
Obsekov et al. (2023) differ from those used to support the national 
quantified benefits of the rule, the information provided in the study 
is helpful in portraying the costs of cancers that are associated with 
PFAS exposures. For additional details on cancer studies and their 
individual outcomes, see chapter 3.5 (Cancer) in USEPA (2024c) and 
USEPA (2024d).
    After assessing available health and economic information, the EPA 
was unable to quantify the benefits of avoided health effects discussed 
above. The agency prioritized health endpoints with the strongest 
weight of evidence conclusions and readily available data for 
monetization, namely cardiovascular effects, developmental effects, and 
carcinogenic effects. Several other health endpoints that had 
indicative or suggestive evidence of associations with exposure to PFOA 
and PFOS have not been selected for the EA:
     While immune effects had indicative evidence of 
associations with exposure to PFOA and PFOS, the EPA did not identify 
the necessary information to connect the measured biomarker responses 
(i.e., decrease in antibodies) to a disease that could be valued in the 
EA;
     Evidence indicates associations between PFOA and PFOS 
exposure and hepatic effects, such as increases in ALT. While increased 
ALT is considered an adverse effect, ALT can be one of several 
contributors to a variety of diseases, including liver disease, and it 
is difficult to therefore quantify the relationship between this 
biomarker and a disease that can be monetized. Similar challenges with 
the biomarkers representing metabolic effects (i.e., leptin) and 
musculoskeletal effects (i.e., bone density) prevented economic 
analysis of these endpoints;
     There is evidence of association between exposure to PFOA 
and testicular cancer in human and animal studies; however, the 
available slope factor in rats implied small changes in the risk of 
this endpoint. Because testicular cancer is rarely fatal and the Value 
of Statistical Life is the driver of economic benefits evaluated in the 
EA, the benefit of decreased testicular cancer expected with this rule 
was smaller in comparison and not quantified;
     There is evidence of association between exposure to PFOS 
and hepatic carcinogenicity in human and animal studies. The EPA 
quantified benefits associated with reduced liver cancer cases and 
deaths as part of a sensitivity analysis for the final rule in response 
to public comments received on the proposed rule requesting that the 
EPA quantify additional health benefits (see appendix O of the EA 
(USEPA, 2024e));
     Finally, other health endpoints, such as SGA and LDLC 
effects, were not modeled in the EA because they overlap with effects 
that the EPA did model. More specifically, SGA infants are often born 
with decreased birth weight or

[[Page 32700]]

receive similar care to infants born with decreased birth weight. LDLC 
is a component of TC and could not be modeled separately as the EPA 
used TC as an input to the ASCVD model to estimate CVD outcomes.

H. Nonquantifiable Benefits of Removal of PFAS Included in the Final 
Regulation and Co-Removed PFAS

    The EPA also qualitatively summarized the potential health benefits 
resulting from reduced exposure to PFAS other than PFOA and PFOS in 
drinking water. The final rule and all regulatory alternatives are 
expected to result in additional benefits that have not been 
quantified. The final rule will reduce exposure to PFHxS, HFPO-DA, and 
PFNA to below their individual MCLs. It will also reduce exposure to 
PFBS to below the Hazard Index MCLG and MCL of 1 when the mixture 
contains two or more of PFHxS, PFNA, HFPO-DA, and PFBS. Benefits from 
avoided cases of the adverse health effects discussed in this section 
are expected from the final rule due to co-occurrence of these 
contaminants in source waters containing PFOA and/or PFOS, as described 
in the Per- and Polyfluoroalkyl Substances (PFAS) Occurrence & 
Contaminant Background Support Document (USEPA, 2024b) and part VI of 
this preamble. In addition, PFAS, including PFHxS, PFNA, HFPO-DA, and 
PFBS and their mixtures affect common target organs, tissues, or 
systems to produce dose-additive effects from their co-exposures with 
each other, as well as PFOA and PFOS (USEPA, 2024a). The EPA expects 
that compliance actions taken under the final rule will remove 
additional unregulated co-occurring PFAS contaminants where present 
because the best available technologies have been demonstrated to co-
remove additional PFAS. Treatment responses implemented to reduce PFOA 
and PFOS exposure under the final rule and Options 1a-c are likely to 
remove some amount of additional PFAS contaminants where they co-occur.
    Ion exchange (IX) and granulated activated carbon (GAC) are 
effective at removing PFAS; there is generally a linear relationship 
between PFAS chain length and removal efficiency, shifted by functional 
group (McCleaf et al., 2017; S[ouml]reng[aring]rd, 2020). 
Perfluoroalkyl sulfonates (PFSAs), such as PFOS, are removed with 
greater efficiency than corresponding perfluoroalkyl carboxylates 
(PFCAs), such as PFOA, of the same carbon backbone length (Appleman et 
al., 2014; Du et al., 2014; Eschauzier et al., 2012; Ochoa-Herrera and 
Sierra-Alvarez, 2008; Zaggia et al., 2016). Generally, for a given 
water type and concentration, PFSAs are removed approximately as 
effectively as PFCAs, which have two additional fully perfluorinated 
carbons in the carbon backbone. For example, PFHxS (i.e., sulfonic acid 
with a six-carbon backbone) is removed approximately as well as PFOA 
(i.e., carboxylic acid with an eight-carbon backbone) and PFHxA (i.e., 
carboxylic acid with a six-carbon backbone) is removed approximately as 
well as PFBS (i.e., sulfonic acid with a four-carbon backbone). 
Further, PFAS compounds with longer carbon chains display lower 
percentage decreases in average removal efficiency over time (McCleaf 
et al., 2017).
    In cases where the six PFAS included in the final rule occur at 
concentrations above their respective regulatory standards, there is 
also an increased probability of co-occurrence of additional 
unregulated PFAS. Further, as the same technologies also remove other 
long-chain and higher carbon/higher molecular weight PFAS, the EPA 
expects that treatment will provide additional public health protection 
and benefits due to co-removal of unregulated PFAS that may have 
adverse health effects. While the EPA has not quantified these 
additional benefits, the agency expects that these important co-removal 
benefits will further enhance public health protection.
    The EPA identified a wide range of potential health effects 
associated with exposure to PFAS other than PFOA and PFOS using 
documents that summarize the recent literature on exposure and 
associated health impacts: the ATSDR's Toxicological Profile for 
Perfluoroalkyls (ATSDR, 2021); the EPA's toxicity assessment of HFPO-DA 
(USEPA, 2021b); publicly available IRIS assessments for PFBA and PFHxA 
(USEPA, 2022g; USEPA, 2023p); the EPA's toxicity assessment of PFBS 
(USEPA, 2021a); and the recent National Academies of Sciences, 
Engineering, and Medicine Guidance on PFAS Exposure, Testing, and 
Clinical Follow-up (NASEM, 2022). Note that the determinations of 
associations between PFAS and associated health effects are based on 
information available as of September 2023.
    Developmental effects: Toxicology and/or epidemiology studies 
observed evidence of associations between birth weight and/or other 
developmental effects and exposure to PFBA, PFDA, PFHxS, PFHxA, PFNA, 
HFPO-DA, PFUnA, and PFBS. Specifically, data from toxicology studies 
support this association for PFBS, PFBA, PFHxA, and HFPO-DA, while both 
toxicology and epidemiology studies support this association for PFHxS, 
PFDA, PFUnA, and PFNA (ATSDR, 2021; USEPA, 2021b; USEPA, 2022g; USEPA, 
2023e; Wright et al., 2023). In general, epidemiological studies did 
not find associations between exposure and adverse pregnancy outcomes 
(miscarriage, preterm birth, or gestational age) for PFNA, PFUnA and 
PFHxS (ATSDR, 2021; NASEM, 2022). Epidemiological studies support an 
association between PFNA, PFHxS or PFDA exposure and developmental 
effects such as decreases in infant birth weight and birth length, 
small for gestational age and increased risk of low birth weight (Valvi 
et al., 2017; Bach et al., 2016; Louis et al., 2018; Wright et al., 
2023; Manzano-Salgado et al., 2017; Starling et al., 2017). Few 
epidemiologic studies also indicate that PFDA exposure is associated 
with developmental effects (Wikstr[ouml]m et al., 2020; Valvi et al., 
2017; Luo et al., 2021; Yao et al., 2021). The EPA has determined that 
evidence indicates that exposure to PFBA or PFHxA likely causes 
developmental effects, based on moderate evidence from animal studies 
and indeterminate evidence from human studies (USEPA, 2022g; USEPA, 
2023p).
    Cardiovascular effects: Epidemiology and/or toxicology studies 
observed evidence of associations between PFNA, PFDA, and PFHxS 
exposures and effects on total cholesterol, LDLC, and HDLC. 
Epidemiological studies report consistent associations between PFHxS 
and total cholesterol in adults (Cakmak et al., 2022; Dunder et al., 
2022; Canova et al., 2020; Lin et al., 2019; Liu et al., 2020; Fisher 
et al., 2013).
    In an analysis based on studies published before 2018, evidence for 
associations between PFNA exposure and serum lipid levels in 
epidemiology studies was mixed; associations have been observed between 
serum PFNA levels and total cholesterol in general populations of 
adults but not in pregnant women, and evidence in children is 
inconsistent (ATSDR, 2021). Most epidemiology studies did not observe 
associations between PFNA and LDLC or HDLC. Epidemiological studies 
report consistent associations between PFDA and effects on total 
cholesterol in adults (Cakmak et al., 2022; Dunder et al, 2022; Liu et 
al., 2020; Dong et al., 2019). Positive associations between PFDA and 
other serum lipids, adiposity, cardiovascular disease, and 
atherosclerosis were observed in some epidemiology studies, but 
findings were inconsistent (Huang et al., 2018; Mattsson et al., 2015; 
Christensen et al., 2016). A single animal study observed

[[Page 32701]]

decreases in cholesterol and triglyceride levels in rats at PFDA doses 
above 1.25 mg/kg/d for 28 days (NTP, 2018b). There was no association 
between PFBA and serum lipids in a single epidemiology study and no 
animal studies on PFBA evaluated cardiovascular endpoints (USEPA, 
2022g).
    Other PFAS for which lipid outcomes were examined in toxicology or 
epidemiology studies showed limited to no evidence of associations. 
Studies have examined possible associations between various PFAS and 
blood pressure in humans or heart histopathology in animals. 
Epidemiological studies report positive associations between PFHxS and 
hypertension in adolescents and young adults (Averina et al., 2021; Li 
et al., 2021; Pitter et al., 2020), but not in other adults (Lin et 
al., 2020; Chen et al., 2019; Christensen et al., 2018; Liu et al., 
2018; Bao et al., 2017; Christensen et al., 2016) or children 
(Papadopoulou et al., 2021; Khalil et al., 2018; Manzano-Salgado et 
al., 2017). No evidence was observed of associations between PFHxS and 
cardiovascular diseases (Huang et al., 2018; Mattsson et al., 2015). 
Overall, studies did not find likely evidence of cardiovascular effects 
for other PFAS except for PFOA and PFOS (USEPA, 2024c; USEPA, 2024d).
    Hepatic effects: Toxicology and/or epidemiology studies have 
reported associations between exposure to PFAS (PFBA, PFDA, PFUnA, 
PFDoDA, PFHxA, PFHxS, HFPO-DA, and PFBS) and hepatotoxicity. The 
results of the animal toxicology studies provide strong evidence that 
the liver is a sensitive target of PFHxS, PFNA, PFDA, PFUnA, PFBS, 
PFBA, PFDoDA, HFPO-DA and PFHxA toxicity. Observed effects in rodents 
include increases in liver weight, hepatocellular hypertrophy, 
hyperplasia, and necrosis (ATSDR, 2021; USEPA, 2021b; USEPA, 2022g; 
USEPA, 2023p). Increases in serum enzymes (such as ALT) and decreases 
in serum bilirubin were observed in several epidemiological studies of 
PFNA and PFDA (Nian et al., 2019; Jain and Ducatman, 2019; Liu et al., 
2022; Cakmak et al., 2022). Associations between exposure to PFHxS and 
effects on serum hepatic enzymes are less consistent (Cakmak et al., 
2022; Liu et al., 2022; Jain and Ducatman, 2019; Salihovic et al., 
2018; Gleason et al., 2015). Mixed effects were observed for serum 
liver enzymes in epidemiological studies for PFNA (ATSDR, 2021).
    Immune effects: Epidemiology studies have reported evidence of 
associations between PFDA or PFHxS exposure and antibody response to 
tetanus or diphtheria (Grandjean et al., 2012; Grandjean et al., 2017a; 
Grandjean et al., 2017b; Budtz-J[oslash]rgensen and Grandjean, 2018). 
There is also some limited evidence for decreased antibody response for 
PFNA, PFUnA, and PFDoDA, although there were notable inconsistencies 
across studies examining associations for these compounds (ATSDR, 
2021). There is limited evidence for associations between PFHxS, PFNA, 
PFDA, PFBS, and PFDoDA and increased risk of asthma due to the small 
number of studies evaluating the outcome and/or inconsistent study 
results (ATSDR, 2021). The small number of studies investigating 
immunotoxicity in humans following exposure to PFHpA and PFHxA did not 
find associations (ATSDR, 2021; USEPA, 2023p; NASEM, 2022). Toxicology 
studies have reported evidence of associations between HFPO-DA exposure 
and effects on various immune-related endpoints in animals (ATSDR, 
2021; USEPA, 2021b). No laboratory animal studies were identified for 
PFUnA, PFHpA, PFDoDA, or FOSA. A small number of toxicology studies 
evaluated the immunotoxicity of other perfluoroalkyls and most did not 
evaluate immune function. No alterations in spleen or thymus organ 
weights or morphology were observed in studies on PFHxS and PFBA. A 
study on PFNA found decreases in spleen and thymus weights and 
alterations in splenic lymphocyte phenotypes (ATSDR, 2021). Changes in 
spleen and thymus weights were reported in female mice and male/female 
rats in two 28-day gavage studies of PFDA, although the direction and 
dose-dependency of these changes in rats was inconsistent across 
studies (Frawley et al., 2018; NTP, 2018b).
    COVID-19: A cross-sectional study in Denmark (Grandjean et al., 
2020) showed that PFBA exposure was associated with increasing severity 
of COVID-19, with an OR of 1.77 (95% CI: 1.09, 2.87) after adjustment 
for age, sex, sampling site, and interval between blood sampling and 
diagnosis. A case-control study showed increased risk of COVID-19 
infection with high urinary PFAS (including PFOA, PFOS, PFHxA, PFHpA, 
PFHxS, PFNA, PFBS, PFDA, PFUnA, PFDoA, PFTrDA, PFTeDA) levels (Ji et 
al., 2021). Adjusted odds ratios were 1.94 (95% CI: 1.39, 2.96) for 
PFOS, 2.73 (95% CI: 1.71, 4.55) for PFOA, and 2.82 (95% CI: 1.97-3.51) 
for total PFAS (sum of 12 PFAS), while other PFAS were not 
significantly associated with COVID-19 susceptibility after adjusting 
for confounders. In a spatial ecological analysis, Catelan et al. 
(2021) showed higher mortality risk for COVID-19 in a population 
heavily exposed to PFAS (including PFOA, PFOS, PFHxS, PFBS, PFBA, 
PFPeA, PFHxA, and PFHpA) via drinking water. Overall, results suggested 
a general immunosuppressive effect of PFAS and/or increased COVID-19 
respiratory toxicity due to a concentration of PFBA in the lungs. 
Although these studies provide a suggestion of possible associations, 
the body of evidence does not permit conclusions about the relationship 
between COVID-19 infection, severity, or mortality, and exposures to 
PFAS.
    In addition to the adverse health effects listed above, there was 
little or no evidence that exposure to the various PFAS is associated 
with the additional health effects summarized in this section.
    Endocrine effects: Epidemiology studies have observed associations 
between serum PFHxS, PFNA, PFDA, and PFUnA and effects on thyroid 
stimulating hormone (TSH), triiodothyronine (T3), or thyroxine (T4) 
levels in serum or thyroid disease; however, there are notable 
inconsistencies across the studies identified in the available reports 
(ATSDR, 2021; NASEM, 2022). Toxicology studies have reported consistent 
associations between exposure to PFHxS, PFBA, PFHxA, and PFBS and 
effects on thyroid hormones, thyroid organ weight, and thyroid 
histopathology in animals; the endocrine system was a notable target of 
PFBS and PFHxS toxicity (ATSDR, 2021; USEPA, 2021a; USEPA, 2022g; 
USEPA, 2023p; NTP, 2018b; Ramh[oslash]j et al., 2018; Ramh[oslash]j et 
al., 2020; Butenhoff et al., 2009).
    Metabolic effects: Epidemiology and toxicology studies have 
examined possible associations between various PFAS and metabolic 
effects, including leptin, body weight, or body fat in humans or 
animals (ATSDR, 2021). Exposure to PFDA has been associated with an 
increase in adiposity in adults (Blake et al., 2018; Christensen et 
al., 2018; Liu et al., 2018). However, evidence of associations was not 
suggestive or likely for any PFAS in this summary except for PFOA and 
PFOS (USEPA, 2024c; USEPA, 2024d). Evidence for changes such as 
maternal body weight gain, pup body weight, or other developmentally 
focused weight outcomes is strong but is considered under the 
Developmental effects category (ATSDR, 2021; NASEM, 2022).
    Renal effects: A small number of epidemiology studies with 
inconsistent results evaluated possible associations

[[Page 32702]]

between PFHxS, PFNA, PFDA, PFBS, PFDoDA, or PFHxA and renal functions 
(including estimated glomerular filtration rate and increases in uric 
acid levels) (ATSDR, 2021; NASEM 2022; USEPA, 2023p). Toxicology 
studies have not observed impaired renal function or morphological 
damage following exposure to PFHxS, PFDA, PFUnA, PFBS, PFBA, PFDoDA, or 
PFHxA (ATSDR, 2021). Associations with kidney weight in animals were 
observed for PFBS and HFPO-DA and was a notable target for PFBS 
toxicity (ATSDR, 2021; USEPA, 2021a; USEPA, 2021b; USEPA, 2023p).
    Reproductive effects: A small number of epidemiology studies with 
inconsistent results evaluated possible associations between 
reproductive hormone levels and PFHxS, PFNA, PFDA, PFUnA, PFDoDA, or 
PFHxA. Some associations between PFAS (PFHxS, PFHxA, PFNA, PFDA) 
exposures and sperm parameters have been observed, but often only one 
sperm parameter was altered. While there is suggestive evidence of an 
association between PFHxS or PFNA exposure and an increased risk of 
early menopause, this may be due to reverse causation since an earlier 
onset of menopause would result in a decrease in the removal of PFAS in 
menstrual blood. Epidemiological studies provide mixed evidence of 
impaired fertility (increased risks of longer time to pregnancy and 
infertility), with some evidence for PFHxS, PFNA, PFHpA, and PFBS but 
the results are inconsistent across studies or were only based on one 
study (ATSDR, 2021; Bach et al., 2018; V[eacute]lez et al., 2015). 
Toxicology studies have evaluated the potential histological 
alterations in reproductive tissues, alterations in reproductive 
hormones, and impaired reproductive functions. No effect on fertility 
was observed for PFBS and PFDoDA, and no histological alterations were 
observed for PFBS and PFBA. One study found alterations in sperm 
parameters and decreases in fertility in mice exposed to PFNA, and one 
study for PFDoDA observed ultrastructural alterations in the testes 
(ATSDR, 2021). Decreased uterine weights, changes in hormone levels, 
and increased time spent in diestrus were observed in studies of PFDA 
or PFHxS exposures (NTP, 2018b; Yin et al., 2021).
    Musculoskeletal effects: Epidemiology studies observed evidence of 
associations between PFNA and PFHxS and musculoskeletal effects 
including osteoarthritis and bone mineral density, but data are limited 
to two studies (ATSDR, 2021; Khalil et al., 2016; Khalil et al., 2018). 
Toxicology studies reported no morphological alterations in bone or 
skeletal muscle in animals exposed to PFBA, PFDA, PFHxA, PFHxS, or 
PFBS, but evidence is based on a very small number of studies (NTP, 
2018b; ATSDR, 2021; USEPA, 2022g; USEPA, 2023p).
    Hematological effects: A single uninformative epidemiological study 
reported on blood counts in pregnant women exposed to PFHxA (USEPA, 
2023p). Epidemiological data were not identified for the other PFAS 
(ATSDR, 2021). A limited number of toxicology studies observed 
alterations in hematological indices following exposure to relatively 
high doses of PFHxS, PFDA, PFUnA, PFBS, PFBA, or PFDoDA (ATSDR, 2021; 
USEPA, 2022g; NTP, 2018b; 3M Company, 2000; Frawley et al., 2018). 
Toxicology studies observed robust evidence of association between 
PFHxA or HFPO-DA exposure and hematological effects, including 
decreases in red blood cell (RBC) number, hemoglobin, and percentage of 
RBCs in the blood (USEPA, 2021b; USEPA, 2023p). A small number of 
toxicology studies observed slight evidence of associations between 
exposure to PFHxS, PFDA, or PFBA and decreases in multiple red blood 
cell parameters and in prothrombin time; however, effects were not 
consistent (USEPA, 2022g; Butenhoff et al., 2009).
    Other non-cancer effects: A limited number of epidemiology and 
toxicology studies have examined possible associations between various 
PFAS and dermal, ocular, and other non-cancer effects. However, the 
evidence does not support associations for any PFAS in this summary 
except for PFOA and PFOS (ATSDR, 2021; USEPA, 2021a; USEPA, 2023p).
    Cancer effects: A small number of epidemiology studies reported 
limited associations between multiple PFAS (i.e., PFHxS, PFDA, PFUnA, 
and FOSA) and cancer effects. No consistent associations were observed 
for breast cancer risk for PFHxS, PFHxA, PFNA, PFHpA, or PFDoDA; 
increased breast cancer risks were observed for PFDA and FOSA, but this 
was based on a single study (Bonefeld-J[oslash]rgensen et al., 2014), 
and one study observed non-significant increased risk for breast cancer 
risk and PFDA (Tsai et al., 2020). Exposure to PFHxS was associated 
with increased breast cancer risk in one study and with decreased 
breast cancer risk in two related studies (Bonefeld-J[oslash]rgensen et 
al., 2014; Ghisari et al., 2017; Tsai et al., 2020). No associations 
between exposure to PFHxS, PFNA, PFDA, or PFUnA and prostate cancer 
risk were observed. However, among men with a first-degree relative 
with prostate cancer, associations were observed for PFHxS, PFDA 
(Hardell et al., 2014), and PFUnA, but not for PFNA (ATSDR, 2021; 
USEPA, 2022g; USEPA, 2023p). A decreased risk of thyroid cancer was 
associated with exposure to PFHxS and PFDA in a single study (Liu et 
al., 2021). Epidemiological studies examining potential cancer effects 
were not identified for PFBS or PFBA (ATSDR, 2021; USEPA 2022g). No 
animal studies examined carcinogenicity of PFHxS or PFBA. Aside from a 
study that suggested an increased incidence of liver tumors in rats 
exposed to high doses of HFPO-DA, the limited number of available 
toxicology studies reported no evidence of associations between 
exposure to other PFAS (i.e., PFDA and PFHxA) and risk of cancer 
(ATSDR, 2021; USEPA, 2021b; USEPA, 2023p). At this time, there is 
inadequate information to assess carcinogenic potential for PFAS other 
than PFOA, PFOS, and HFPO-DA.

I. Benefits Resulting From Disinfection By-Product Co-Removal

    As part of its HRRCA, the EPA is directed by SDWA to evaluate 
quantifiable and nonquantifiable health risk reduction benefits for 
which there is a factual basis in the rulemaking record to conclude 
that such benefits are likely to occur from reductions in co-occurring 
contaminants that may be attributed solely to compliance with the MCL 
(SDWA 1412(b)(3)(C)(II)). These co-occurring contaminants are expected 
to include additional PFAS contaminants not directly regulated by the 
final PFAS NPDWR, co-occurring chemical contaminants such as SOCs, 
VOCs, and DBP precursors. In this section, the EPA presents a 
quantified estimate of the reductions in DBP formation potential that 
are likely to occur as a result of compliance with the final PFAS 
NPDWR. The methodology detailed here and in section 6.7.1 of USEPA 
(2024g) to estimate DBP reductions was externally peer reviewed by 
three experts in GAC treatment for PFAS removal and DBP formation 
potential (USEPA, 2023m). The external peer reviewers supported the 
EPA's approach and edits based on their recommendations for clarity and 
completeness are reflected in the following analysis and discussion.
    DBPs are formed when disinfectants react with naturally occurring 
materials in water. There is a substantial body of literature on DBP 
precursor occurrence and THM4 formation mechanisms in drinking water 
treatment. Under the Stage 2 Disinfectants and Disinfection Byproducts 
Rule (Stage 2 DBP Rule, USEPA, 2006a), the EPA regulates 11

[[Page 32703]]

individual DBPs from three subgroups: THM4, HAA5, and two inorganic 
compounds (bromate and chlorite). The formation of THM4 in a particular 
drinking water treatment plant is a function of several factors 
including disinfectant type, disinfectant dose, bromide concentration, 
organic material type and concentration, temperature, pH, and system 
residence times. Epidemiology studies have shown that THM4 exposure, a 
surrogate for chlorinated drinking water, is associated with an 
increased risk of bladder cancer, among other diseases (Cantor et al., 
1998; Cantor et al., 2010; Costet et al., 2011; Beane Freeman et al., 
2017; King and Marrett, 1996; Regli et al., 2015; USEPA, 2019d; 
Villanueva et al., 2004; Villanueva et al., 2006; Villanueva et al., 
2007). These studies considered THM4 as surrogate measures for DBPs 
formed from the use of chlorination that may co-occur. The 
relationships between exposure to DBPs, specifically THM4 and other 
halogenated compounds resulting from water chlorination, and bladder 
cancer are further discussed in section 6.7 of USEPA (2024g). 
Reductions in exposure to THM4 is expected to yield public health 
benefits, including a decrease in bladder cancer incidence (Regli et 
al., 2015). Among other things, Weisman et al. (2022) found that there 
is even a stronger weight of evidence linking DBPs and bladder cancer 
since the promulgation of the 2006 Stage 2 DBP regulations (USEPA, 
2006a) and publication of Regli et al. (2015). While not the regulated 
contaminant for this rulemaking, the expected reduction of DBP 
precursors and subsequent DBPs that result from this rulemaking are 
anticipated to reduce cancer risk in the U.S. population.
    GAC adsorption has been used to remove SOCs, taste and odor 
compounds, and natural organic matter (NOM) during drinking water 
treatment (Chowdhury et al., 2013). Recently, many water utilities have 
installed or are considering installing GAC and/or other advanced 
technologies as a protective or mitigation measure to remove various 
contaminants of emerging concern, such as PFAS (Dickenson and Higgins, 
2016). Because NOM often exists in a much higher concentration (in mg/
L) than trace organics (in [mu]g/L or ng/L) in water, NOM, often 
measured as TOC, can interfere with the adsorption of trace organics by 
outcompeting the contaminants for adsorption sites and by general 
fouling (blockage of adsorption pores) of the GAC.
    NOM and inorganic matter are precursors for the formation of THMs 
and other DBPs when water is disinfected using chlorine and other 
disinfectants to control microbial contaminants in finished drinking 
water. Removal of DBP precursors through adsorption onto GAC has been 
included as a treatment technology for compliance with the existing DBP 
Rules and is a BAT for the Stage 2 DBP Rule. Dissolved organic matter 
(DOM) can be removed by GAC through adsorption and biodegradation 
(Crittenden et al., 1993; Kim et al., 1997; Yapsakli et al., 2010). GAC 
is well-established for removal of THM and HAA precursors (Cheng et 
al., 2005; Dastgheib et al., 2004; Iriarte-Velasco et al., 2008; 
Summers et al., 2013; Cuthbertson et al., 2019; Wang et al., 2019). In 
addition to removal of organic DBPs, GAC also exhibits some capacity 
for removal of inorganic DBPs such as bromate and chlorite (Kirisits et 
al., 2000; Sorlini et al., 2005) and removal of preformed organic DBPs 
via adsorption and biodegradation (Jiang et al., 2017; Terry and 
Summers, 2018). Further, GAC may offer limited removal of dissolved 
organic nitrogen (Chili et al., 2012).
    Based on an extensive review of published literature in sampling 
studies where both contaminant groups (PFAS and DBPs) were sampled, 
there is limited information about PFAS removal and co-occurring 
reductions in DBPs, specifically THMs. To help inform its EA, the EPA 
relied on the DBP Information Collection Rule Treatment Study Database 
and DBP formation studies to estimate reductions in THM4 ([Delta]THM4) 
that may occur when GAC is used to remove PFAS. Subsequently, these 
results were compared to THM4 data from PWSs that have detected PFAS 
and have indicated use of GAC.
    The objective of the EPA's co-removal benefits analysis is to 
determine the reduction in bladder cancer cases associated with the 
decrease of regulated THM4 in treatment plants due to the installation 
of GAC for PFAS removal. Evaluation of the expected reductions in 
bladder cancer risk resulting from treatment of PFAS in drinking water 
involves five steps:
    1. Estimating the number of systems expected to install GAC 
treatment in compliance with the final PFAS NPDWR and affected 
population size;
    2. Estimating changes in THM4 levels that may occur when GAC is 
installed for PFAS removal based on influent TOC levels;
    3. Estimating changes in the cumulative risk of bladder cancer 
using an exposure-response function linking lifetime risk of bladder 
cancer to THM4 concentrations in residential water supply (Regli et 
al., 2015);
    4. Estimating annual changes in the number of bladder cancer cases 
and excess mortality in the bladder cancer population corresponding to 
changes in THM4 levels under the regulatory alternative in all 
populations alive during or born after the start of the evaluation 
period; and
    5. Estimating the economic value of reducing bladder cancer 
morbidity and mortality from baseline to regulatory alternative levels, 
using COI measures and the Value of a Statistical Life, respectively.
    The EPA expects PWSs that exceed the PFAS MCLs to consider both 
treatment and nontreatment options to achieve compliance with the 
drinking water standard. The EPA assumes that the populations served by 
systems with EP expected to install GAC based on the compliance 
forecast detailed in section 5.3 of USEPA (2024g) will receive the DBP 
exposure reduction benefits. The EPA notes that other compliance 
actions included in the compliance forecast could result in DBP 
exposure reductions, including installation of RO. However, these 
compliance actions are not included in the DBP benefits analysis 
because this DBP exposure reduction function is specific to GAC. 
Switching water sources may or may not result in DBP exposure 
reductions, therefore the EPA assumed no additional DBP benefits for an 
estimated percentage of systems that elect this compliance option. 
Lastly, the EPA assumed no change in DBP exposure at water systems that 
install IX, as that treatment technology is not expected to remove a 
substantial amount of DBP precursors. The EPA also assumed that the 
PWSs included in this analysis use chlorine only for disinfection and 
have conventional treatment in place prior to GAC installation.
    The EPA used the relationship between median raw water TOC levels 
and changes in THM4 levels estimated in the 1998 DBP Information 
Collection Rule to estimate changes in THM4 concentrations in the 
finished water of PWSs fitted with GAC treatment. For more detail on 
the approach the EPA used to apply changes in THM4 levels to PWSs 
treating for PFAS under the final rule, please see section 6.7 of USEPA 
(2024g).
    The EPA models a scenario where reduced exposures to THM4 begin in 
2029. Therefore, the EPA assumed that the population affected by 
reduced THM4 levels resulting from implementation of GAC treatment is 
exposed to baseline THM4 levels prior to actions to comply with the 
rule (i.e.,

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prior to 2029) and to reduced THM4 levels from 2029 through 2105. 
Rather than modeling individual locations (e.g., PWS), the EPA 
evaluates changes in bladder cancer cases among the aggregate 
population per treatment scenario and source water type that is 
expected to install GAC treatment to reduce PFAS levels. Because of 
this aggregate modeling approach, the EPA used national-level 
population estimates to distribute the SDWIS populations based on 
single-year age and sex and to extrapolate the age- and sex-specific 
populations to future years. Appendix B of USEPA (2024g) provides 
additional details on estimation of the affected population.
    Regli et al. (2015) analyzed the potential lifetime bladder cancer 
risks associated with increased bromide levels in surface source water 
resulting in increased THM4 levels in finished water. To account for 
variable levels of uncertainty across the range of THM4 exposures from 
the pooled analysis of Villanueva et al. (2004), they derived a 
weighted mean slope factor from the odds ratios reported in Villanueva 
et al. (2004). They showed that, while the original analysis deviated 
from linearity, particularly at low concentrations, the overall pooled 
exposure-response relationship for THM4 could be well-approximated by a 
linear slope factor that predicted an incremental lifetime cancer risk 
of 1 in 10,000 exposed individuals (10-\4\) per 1 [micro]g/L 
increase in THM4. The linear slope factor developed by Regli et al. 
(2015) enables estimation of the changes in the lifetime bladder cancer 
risk associated with lifetime exposures to reduced THM4 levels. Weisman 
et al. (2022) applied the dose-response information from Regli et al. 
(2015) and developed a robust, national-level risk assessment of DBP 
impacts, where the authors estimated that approximately 8,000 of 79,000 
annual U.S. bladder cancer cases are attributable to chlorination DBPs, 
specifically associated with THM4 concentrations.
    The EPA estimated changes in annual bladder cancer cases and annual 
excess mortality in the bladder cancer population due to estimated 
reductions in lifetime THM4 exposure using a life table-based approach. 
This approach was used because (1) annual risk of new bladder cancer 
should be quantified only among those not already experiencing this 
chronic condition, and (2) bladder cancer has elevated mortality 
implications.
    The EPA used recurrent life table calculations to estimate a water 
source type-specific time series of bladder cancer incidence for a 
population cohort characterized by sex, birth year, and age at the 
beginning of the PFOA/PFOS evaluation period under the baseline 
scenario and the GAC regulatory alternative. The estimated risk 
reduction from lower exposure to DBPs in drinking water was calculated 
based on changes in THM4 levels used as inputs to the Regli et al. 
(2015)-based health impact function, described in more detail in 
section 6.7 of USEPA (2024g). The life table analysis accounts for the 
gradual changes in lifetime exposures to THM4 following implementation 
of GAC treatment under the regulatory alternative compared to the 
baseline. The outputs of the life table calculations are the water 
source type-specific estimates of the annual change in the number of 
bladder cancer cases and the annual change in excess bladder cancer 
population mortality.
    The EPA used the Value of a Statistical Life to estimate the 
benefits of reducing mortality associated with bladder cancer in the 
affected population. The EPA used the cost of illness-based valuation 
to estimate the benefits of reducing morbidity associated with bladder 
cancer. Specifically, the EPA used bladder cancer treatment-related 
medical care and opportunity cost estimates from Greco et al. (2019). 
Table 63 shows the original cost of illness estimates from Greco et al. 
(2019), along with the values updated to $2022 used in this analysis.
    The EPA received public comments on the EA for the proposed rule 
related to the EPA's use of cost of illness information for morbidity 
valuation. Specifically, a couple of commenters recommended that the 
EPA use willingness to pay information (instead of cost of illness 
information) when valuing the costs associated with non-fatal 
illnesses, stating that willingness to pay information better accounts 
for lost opportunity costs (e.g., lost productivity and pain and 
suffering) associated with non-fatal illnesses (USEPA, 2024k). To 
better account for these opportunity costs, the EPA used recently 
available willingness to pay values in a sensitivity analysis for 
morbidity associated with bladder cancer. The sensitivity analysis 
results show that when willingness to pay values are used in bladder 
cancer benefits analysis, morbidity benefits are increased by 
approximately 19.9 percent. See appendix O of the EA for full details 
and results on the willingness to pay sensitivity analyses.
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    Tables 64 to 67 presents the estimated changes in non-fatal bladder 
cancer cases and bladder cancer-related deaths from exposure to THM4 
due to implementation of GAC treatment by option. The EPA estimated 
that, over the evaluation period, the final rule will result in 
annualized benefits from avoided bladder cancer cases and deaths of 
$380 million.

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J. Comparison of Costs and Benefits

    This section provides a comparison of the incremental costs and 
benefits of the final rule, as described in chapter 7 of the EA. 
Included here are estimates of total quantified annualized costs and 
benefits for the final rule and regulatory alternative MCLs under 
options 1a-1c, as well as considerations for the nonquantifiable costs 
and benefits. The EPA's determinations as to whether the costs are 
justified by the benefits must be based on an analysis of both the 
quantified costs and benefits as well as the nonquantifiable benefits 
and nonquantifiable costs, per SDWA 1412(b)(3)(C)(I)-(III).
    The incremental cost is the difference between quantified costs 
that will be incurred if the final rule is enacted over current 
baseline conditions. Incremental benefits reflect the avoided future 
adverse health outcomes attributable to PFAS reductions and co-removal 
of additional contaminants due to actions undertaken to comply with the 
final rule.
    Table 68 provides the incremental quantified costs and benefits of 
the final rule at a 2 percent discount rate in 2022 dollars. The top 
row shows total monetized annualized costs including total PWS costs 
and primacy agency costs. The second row shows total monetized 
annualized benefits including all endpoints that could be quantified 
and valued. For both, the estimates are the expected (mean) values and 
the 5th percentile and 95th percentile quantified estimates from the 
uncertainty distribution. These percentile estimates come from the 
distributions of annualized costs and annualized benefits generated by 
the 4,000 iterations of SafeWater MCBC. Therefore, these distributions 
reflect the joint effect of the multiple sources of variability and 
uncertainty for quantified costs, quantified benefits, and the baseline 
uncertainties such as PFAS occurrence, as detailed in sections 5.1.2, 
6.1.2, and chapter 4 of the EA, respectively (USEPA, 2024g). For 
further discussion of the quantified uncertainties in the EA, see 
section XII.K of this preamble.
    The third row shows net quantified benefits (benefits minus costs). 
The net annual quantified incremental benefits are $760,000. Because of 
the variation associated with the use of statistical models such as 
SafeWater MCBC, the modeled quantified net benefits are nearly at 
parity. The uncertainty range for net benefits is a negative $622 
million to $725 million. Additional uncertainties are presented in 
Table 72.
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    Tables 69 to 71 summarize the total annual costs and benefits for 
options 1a, 1b, and 1c, respectively.

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    The benefit-cost analysis reported dollar figures presented above 
reflect benefits and costs that could be quantified for each regulatory 
alternative MCL given the best available scientific data. The EPA notes 
that these quantified benefits are estimated using a cost-of-illness 
approach. In the sensitivity analysis, the EPA also calculated 
quantified benefits using a willingness-to-pay approach instead of cost 
of illness information, for non-fatal RCC and bladder cancer illnesses. 
In this case, the estimated expected quantified annualized costs are 
approximately $1,549 million and the estimated expected quantified 
annualized benefits increase to approximately $1,632 million, resulting 
in approximately $84 million in expected annualized net benefits. See 
appendix O of the EA for further discussion.
    The quantified benefit-cost results above are not representative of 
all benefits and costs anticipated under the final NPDWR. Due to 
occurrence, health, and economic data limitations, there are several 
adverse health effects associated with PFAS exposure and costs 
associated with treatment that the EPA could not estimate 
quantitatively.
    PFAS exposure is associated with a wide range of adverse health 
effects, including reproductive effects such as decreased fertility; 
increased high blood pressure in pregnant women; developmental effects 
or delays in children, including low birth weight, accelerated puberty, 
bone variations, or behavioral changes; increased risk of some cancers, 
including prostate, kidney, and testicular cancers; reduced ability of 
the body's immune system to fight infections, including reduced vaccine 
response; interference with the body's natural hormones; and increased 
cholesterol levels and/or risk of obesity. Based on the available data 
at rule proposal and submitted by public commenters, the EPA is only 
able to quantify three PFOA- and PFOS-related health endpoints (i.e., 
changes in birth weight, CVD, and RCC) in the national analysis.
    The EPA also evaluated the impacts of PFNA on birth weight and PFOS 
on liver cancer in quantitative sensitivity analyses (See appendices K 
and O of USEPA, 2024e, respectively). Those analyses demonstrate that 
there are potentially significant other quantified benefits not 
included in the national quantified benefits above: for example, the 
EPA's quantitative sensitivity analysis for PFNA (found in appendix K 
of USEPA, 2024e) found that the inclusion of a 1 ng/L PFNA reduction 
could increase annualized birth weight benefits by a factor of 5.6-7.8 
in a model system serving 100,000 people, relative to a scenario that 
quantified a 1 ng/L reduction in PFOA and a 1 ng/L reduction in PFOS 
only. In the case of PFOS impacts on liver cancer, the EPA has 
estimated an expected value of $4.79 million in benefits via the 
reduction in liver cancer cases anticipated to be realized by the final 
rule. All regulatory alternatives are

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expected to produce substantial additional benefits from all the other 
adverse health effects avoided, but that cannot be quantified at this 
time. Treatment responses implemented to remove PFOA and PFOS under 
regulatory alternative MCLs under options 1a-1c are likely to remove 
some amount of additional PFAS contaminants where they co-occur. Co-
occurrence among PFAS compounds has been observed frequently as 
discussed in the PFAS Occurrence & Contaminant Background Support 
Document (USEPA, 2024b). The final rule is expected to produce the 
greatest reduction in exposure to PFAS compounds as compared to the 
three regulatory alternative MCLs because it includes PFHxS, PFNA, 
HFPO-DA, and PFBS in the regulation. Inclusion of the Hazard Index will 
trigger more systems to treat (as shown in section 4.4.4 of the EA) and 
provides enhanced public health protection by ensuring reductions of 
these additional compounds when present above the Hazard Index of 1. 
Specifically, as Hazard Index PFAS are reduced, the EPA anticipates 
additional public health benefits from avoided cardiovascular, 
developmental, and immune effects. For further discussion of the 
quantitative and qualitative benefits associated with the final rule, 
see section 6.2 of the EA.
    The EPA also expects that the final rule will result in additional 
nonquantifiable costs. As noted above, the Hazard Index and individual 
MCLs are expected to trigger more systems into more frequent monitoring 
and treatment. In the national cost analysis, the EPA quantified the 
national treatment and monitoring costs associated with the PFHxS 
individual MCL and the Hazard Index associated costs based on PFHxS 
occurrence only. Due to occurrence data limitations, cost estimates for 
PFNA, PFBS, and HFPO-DA are less precise relative to those for PFOA, 
PFOS, and PFHxS compounds, and as such, the EPA performed a 
quantitative sensitivity analysis of the national cost impacts 
associated with Hazard Index exceedances resulting from PFNA, PFBS, and 
HFPO-DA and the PNFA and HFPO-DA individual MCLs to understand and 
consider the potential magnitude of costs associated with treating 
these three PFAS. The EPA found that in addition to the costs 
associated with PFHxS exceedances, which are included in the national 
cost estimate, the Hazard Index and individual MCLs for PFNA and HFPO-
DA could cost an additional $82.4 million per year. In cases where 
these compounds co-occur at locations where PFAS treatment is 
implemented because of nationally modeled PFOA, PFOS, and PFHxS 
occurrence, treatment costs are likely to be marginally higher as 
treatment media estimated bed-life is shortened. In instances where 
concentrations of PFNA, HFPO-DA, and PFBS are high enough to cause or 
contribute to a Hazard Index exceedance when the concentrations of 
PFOA, PFOS, and PFHxS would not have already otherwise triggered 
treatment, the national modeled costs may be underestimated. If these 
PFAS occur in isolation at levels that affect treatment decisions, or 
if these PFAS occur in combination with PFHxS when PFHxS concentrations 
were otherwise below its respective HBWC in isolation (i.e., less than 
10 ng/L) then the quantified costs underestimate the impacts of the 
final rule. See appendix N.3 of the EA for a sensitivity analysis of 
additional treatment costs at systems with Hazard Index exceedances 
(USEPA, 2024e). See appendix N.4 for a sensitivity analysis of the 
marginal costs of HFPO-DA and PFNA MCLs. For further discussion of how 
the EPA considered the costs of the five individual MCLs and the HI 
MCL, see section XII.A.4 of this preamble.
    Commenters suggested that another potential source of non-
quantified cost comes from the fact that the EPA has proposed 
designating PFOA and PFOS as CERCLA hazardous substances (USEPA, 
2022l). Stakeholders have expressed concern to the EPA that a hazardous 
substance designation for certain PFAS may limit their disposal options 
for drinking water treatment residuals (e.g., spent media, concentrated 
waste streams) and/or potentially increase costs. The designation of 
PFOA and PFOS as CERCLA hazardous substances would not require waste 
(e.g., biosolids, treatment residuals, etc.) to be treated in any 
particular fashion, nor disposed of at any specific particular type of 
landfill. The designation also would not restrict, change, or recommend 
any specific activity or type of waste at landfills. In its estimated 
national costs, the EPA has maintained the assumption that disposal 
does not have to occur in accordance with hazardous waste standards 
thus national costs may be underestimated. The EPA has conducted a 
sensitivity analysis that assumes hazardous waste disposal at all 
systems treating for PFAS to assess the potential increase in costs 
(see appendix N of USEPA, 2024e).
    Table 72 provides a summary of the likely impact of nonquantifiable 
benefit-cost categories. In each case, the EPA notes the potential 
direction of the impact on costs and/or benefits. For example, benefits 
are underestimated if the PFOA and PFOS reductions result in avoided 
adverse health outcomes that cannot be quantified and valued. Sections 
5.7 and 6.8 of the EA identify the key methodological limitations and 
the potential effect on the cost or benefit estimates, respectively. 
Additionally, Table 73 summarizes benefits and costs that are 
quantified and nonquantifiable under the final rule.
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    Sections XII.B to XII.K of this preamble summarize the results of 
this final rule analysis. The EPA discounted the estimated monetized 
cost and benefit values using a 2 percent discount rate, consistent 
with OMB Circular A-4 (OMB, 2003; OMB, 2023) guidance. The U.S. White 
House and Office of Management and Budget recently finalized and re-
issued the A-4 and A-94 benefit-cost analysis guidance (see OMB 
Circular A-4, 2023), and the update includes new guidance to use a 
social discount rate of 2 percent. The updated OMB Circular A-4 states 
that the discount rate should equal the real (inflation-adjusted) rate 
of return on long-term U.S. government debt, which provides an 
approximation of the social rate of time preference. This rate for the 
past 30 years has averaged around 2.0 percent per year in real terms on 
a pre-tax basis. OMB arrived at the 2 percent discount rate figure by 
considering the 30-year average of the yield on 10-year Treasury 
marketable securities, and the approach taken by OMB produces a real 
rate of 1.7 percent per year, to which OMB added a 0.3 percent per-year 
rate to reflect inflation as measured by the personal consumption 
expenditure (PCE) inflation index. The OMB guidance states that 
Agencies must begin using the 2 percent discount rate for draft final 
rules that are formally submitted to OIRA after December 31, 2024. The 
updated OMB Circular A-4 guidance further states that ``to the extent 
feasible and appropriate, as determined in consultation with OMB, 
agencies should follow this Circular's guidance earlier than these 
effective dates.'' Given the updated default social discount rate 
prescribed in the OMB Circular A-4 and also public input received on 
the discount rates considered by the EPA in the proposed NPDWR, for 
this final rule, the EPA estimated national benefits and costs at the 2 
percent discount rate for the final rule and incorporated those results 
into the final economic analysis. Since the EPA proposed this NPDWR 
with the 3 and 7 percent discount rates based on guidance in the 
previous version of OMB Circular A-4, the EPA has kept the presentation 
of results using these discount rates in appendix P. The Administrator 
reaffirms his determination that the benefits of the rule justify the 
costs. The EPA's determination is based on its analysis under in SDWA 
section 1412(b)(3)(C) of the quantifiable benefits and costs at the 2 
percent discount rate, in addition to at the 3 and 7 percent discount 
rate, as well as the nonquantifiable benefits and costs. The EPA found 
that significant nonquantifiable benefits are likely to occur from the 
final PFAS NPDWR.
    The quantified analysis is limited in its characterization of 
uncertainty. In section XII.I, Table 68 of this preamble, the EPA 
provides 5th and 95th percentile values associated with the 2 percent 
discounted expected values for net benefits. These values represent the 
quantified, or modeled, potential range in the expected net benefit 
values associated with the uncertainty resulting from the following 
variables; the baseline PFAS occurrence; the affected population size; 
the compliance technology unit cost curves, which are selected as a 
function of baseline PFAS concentrations and population size, the 
distribution of feasible treatment technologies, and the three 
alternative levels of treatment capital costs; the concentration of TOC 
in a system's source water (which impacts GAC O&M costs); the 
demographic composition of the system's population; the magnitude of 
PFAS concentration reductions; the health effect-serum PFOA and PFOS 
slope factors that quantify the relationship between changes in PFAS 
serum level and health outcomes for birth weight, CVD, and RCC; and the 
cap placed on the cumulative RCC risk reductions due to reductions in 
serum PFOA. These modeled sources of uncertainty are discussed in more 
detail in section XII.K of this preamble. While the agency reports only 
the 5th and 95th percentile values, the EPA notes that additional 
information can be obtained from looking at the whole uncertainty 
distribution of annualized net benefits (i.e., the distribution of 
annualized differences between total monetize benefits and total 
monetized costs).
    The quantified 5th and 95th percentile values do not include a 
number of factors that impact both costs and benefits but for which the 
agency did not have sufficient data to include in the quantification of 
uncertainty. The factors influencing the final rule cost estimates that 
are not quantified in the uncertainty analysis are detailed in Table 43 
of this preamble. These uncertainty sources include: the specific 
design and operating assumptions used in developing treatment unit 
cost; the use of national average costs that may differ from the 
geographic distribution of affected systems; the possible future 
deviation from the compliance technology forecast; and the degree to 
which actual TOC source water values differ from the EPA's estimated 
distribution. The EPA has no information to indicate a directional 
influence of the estimated costs with regard to these uncertainty 
sources. To the degree that uncertainty exists across the remaining 
factors it would most likely influence the estimated 5th and 95th 
percentile range and not significantly impact the expected value 
estimate of costs.
    Table 62 of this preamble discusses the sources of uncertainty 
affecting the estimated benefits not captured in the estimated 5th and 
95th reported values. The modeled values do not capture the uncertainty 
in: the exposure that results from daily population changes at NTNCWSs 
or routine population shifting between PWSs, for example spending 
working hours at a NTNCWS or CWS and home hours at a different CWS; the 
exposure-response functions used in the benefits analyses assume that 
the effects of serum PFOA/PFOS on the health outcomes considered are 
independent, additive, and that there are no threshold serum 
concentrations below which effects (cardiovascular, developmental, and 
renal cell carcinoma) do not occur; the distribution of population by 
size and demographics across EP within modeled systems and future 
population size and demographic changes; and the Value of Statistical 
Life reference value or income elasticity used to update the Value of 
Statistical Life. Given information available to the agency, four of 
the listed uncertainty sources would not affect the benefits expected 
value but the dispersion around that estimate. They are the unmodeled 
movements of populations between PWSs with potentially differing PFAS 
concentrations; the independence and additivity assumptions with regard 
to the effects of serum PFOA/PFOS on the health outcomes; the 
uncertainty in the population and demographic distributions among EP 
within individual systems; and the Value of Statistical Life value and 
the income elasticity measures. Two of the areas of uncertainty not 
captured in the analysis would tend to indicate that the quantified 
benefits numbers are overestimates. First, the data available to the 
EPA with regard to population size at NTNCWSs, while likely capturing 
peaks in populations utilizing the systems, does not account for the 
variation in use and population and would tend to overestimate the 
exposed population. The second source of uncertainty, which 
definitionally would indicate overestimates in the quantified benefits 
values, is the assumption that there are no threshold serum 
concentrations below which health effects (cardiovascular, 
developmental, and renal cell carcinoma) do not occur. One source of 
possible underestimation of benefits not accounted for in the

[[Page 32717]]

quantified analysis is the impact of general population growth over the 
extended period of analysis.
    In addition to the quantified cost and benefit expected values, the 
modeled uncertainty associated within the 5th and 95th percentile 
values, and the un-modeled uncertainty associated with a number of 
factors listed above, there are also significant nonquantifiable costs 
and benefits which are important to the overall weighing of costs and 
benefits. Table 72 provides a summary of these nonquantifiable cost and 
benefit categories along with an indication of the directional impact 
each category would have on total costs and benefits. Tables 43 and 62 
also provide additional information on a number of these 
nonquantifiable categories.
    For the nonquantifiable costs, the EPA had insufficient nationally 
representative data to precisely characterize occurrence of HFPO-DA, 
PFNA, and PFBS at the national level and therefore could not include 
complete treatment costs associated with: the co-occurrence of these 
PFAS at systems already required to treat as a result of estimated 
PFOA, PFOS, or PFHxS levels, which would shorten the filtration media 
life and therefore increase operation costs; and the occurrence of 
HFPO-DA, PFNA, and/or PFBS at levels high enough to cause systems to 
exceed the individual MCLs for PFNA and HFPO-DA or the Hazard Index and 
have to install PFAS treatment. The EPA expects that the quantified 
national costs, which do not include HFPO-DA, PFNA, and PFBS treatment 
costs are marginally underestimated (on the order of 5%) as a result of 
this lack of sufficient nationally representative occurrence data. In 
an effort to better understand and consider the costs associated with 
treatment of the PFNA and HFPO-DA MCLs and potentially co-occurring 
HFPO-DA, PFNA, and PFBS at systems both with and without PFOA, PFOS and 
PFHxS occurrence in exceedance of the MCLs the EPA performed a 
quantitative sensitivity analysis of the national cost impacts 
associated with Hazard Index MCL exceedances resulting from HFPO-DA, 
PFNA, and PFBS and/or individual MCL exceedances of PFNA and HFPO-DA. 
The analysis is discussed in section 5.3.1.4 and appendix N.3 of the EA 
(USEPA, 2024l; USEPA, 2024e). Two additional nonquantifiable cost 
impacts stemming from insufficient co-occurrence data could also 
potentially shorten filtration media life and increase operation costs. 
The co-occurrence of other PFAS and other non-PFAS contaminants not 
regulated in the final rule could both increase costs to the extent 
that they reduce media life. The EPA did not include POU treatment in 
the compliance technology forecast because current POU units are not 
certified to remove PFAS to the standards required in the final rule. 
Once certified, this technology may be a low-cost treatment alternative 
for some subset of small systems. Not including POU treatment in this 
analysis has resulted in a likely overestimate of costs. Additionally, 
appendix N.2 of the EA (USEPA, 2024e) contains a sensitivity analysis 
that estimates possible additional national annualized costs of $99 
million, which would accrue to systems if the waste filtration media 
from GAC and IX were handled as RCRA regulatory or characteristic 
hazardous waste. This sensitivity analysis includes only disposal costs 
and does not consider other potential environmental benefits and costs 
associated with the disposal of the waste filtration media.
    There are significant nonquantifiable sources of benefits that were 
not captured in the quantified benefits estimated for the proposed 
rule. While the EPA was able to monetize some of the PFOA and PFOS 
benefits related to CVD, infant birth weight, and RCC effects, the 
agency was unable to quantify additional reductions in negative health 
impacts in the national quantitative analysis. In addition to the 
national analysis for the final rule, the agency developed a 
sensitivity analysis assessing liver cancer impacts, which is detailed 
in appendix O of the EA (USEPA, 2024e). The EPA did not quantify PFOA 
and PFOS benefits related to health endpoints including developmental, 
cardiovascular, hepatic, immune, endocrine, metabolic, reproductive, 
musculoskeletal, and other types of carcinogenic effects. See section 
XII.F of this preamble for additional information on the 
nonquantifiable impacts of PFOA and PFOS. Further, the agency did not 
quantify any health benefits associated with the potential reductions 
in Hazard Index PFAS, which include PFHxS, HFPO-DA, PFNA, and PFBS, or 
other co-occurring non-regulated PFAS which would be removed due to the 
installation of required filtration technology at those systems that 
exceed the final MCLs. The nonquantifiable benefits categories 
associated with exposure to PFHxS, HFPO-DA, PFNA, and PFBS include 
developmental, cardiovascular, immune, hepatic, endocrine, metabolic, 
reproductive, musculoskeletal, and carcinogenic effects. In addition, 
the EPA did not quantify the potential developmental, cardiovascular, 
immune, hepatic, endocrine, metabolic, reproductive, musculoskeletal, 
or carcinogenic impacts related to the removal of other co-occurring 
non-regulated PFAS. See section XII.G of this preamble for additional 
information on the nonquantifiable impacts of PFHxS, HFPO-DA, PFNA, and 
PFBS and other non-regulated co-occurring PFAS.
    The treatment technologies installed to remove PFAS can also remove 
numerous other non-PFAS drinking water contaminants which have negative 
health impacts including additional regulated and unregulated DBPs (the 
quantified benefits assessment does estimate benefits associated with 
THM4), heavy metals, organic contaminants, and pesticides, among 
others. The removal of these co-occurring non-PFAS contaminants could 
have additional positive health benefits. In total these 
nonquantifiable benefits are anticipated to be significant and are 
discussed qualitatively in section 6.2 of the EA (USEPA, 2024g).
    To fully weigh the costs and benefits of the action, the agency 
considered the totality of the monetized values, the potential impacts 
of the nonquantifiable uncertainties described above, the 
nonquantifiable costs and benefits, and public comments received by the 
agency related to the quantified and qualitative assessment of the 
costs and benefits. For the final rule, the EPA is reaffirming the 
Administrator's determination made at proposal that the quantified and 
nonquantifiable benefits of the rule justify its quantified and 
nonquantifiable costs (88 FR 18638; USEPA, 2023f).

K. Quantified Uncertainties in the Economic Analysis

    The EPA characterized sources of uncertainty in its estimates of 
costs expected to result from the final rule. The EPA conducted Monte-
Carlo based uncertainty analysis as part of SafeWater MCBC. With 
respect to the cost analysis, the EPA modeled the sources of 
uncertainty in Table 74.

[[Page 32718]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.082

    For each iteration, SafeWater MCBC assigned new values to the three 
sources of modeled uncertainty as described in Table 74, and then 
calculated costs for each of the model PWSs. This was repeated 4,000 
times to reach an effective sample size for each parameter. At the end 
of the 4,000 iterations, SafeWater MCBC outputs the expected value as 
well as the 90 percent CI for each cost metric (i.e., bounded by the 
5th and 95th percentile estimates for each cost component). Detailed 
information on the data used to model uncertainty is provided in 
appendices A and L of USEPA (2024e).
    Additionally, the EPA characterized sources of uncertainty in its 
analysis of potential benefits resulting from changes in PFAS levels in 
drinking water. The analysis reports uncertainty bounds for benefits 
estimated in each health endpoint category modeled for the final rule. 
Each lower (upper) bound value is the 5th (95th) percentile of the 
category-specific benefits estimate distribution represented by 4,000 
Monte Carlo draws.
    Table 75 provides an overview of the specific sources of 
uncertainty that the EPA quantified in the benefits analysis. In 
addition to these sources of uncertainty, reported uncertainty bounds 
also reflect the following upstream sources of uncertainty: baseline 
PFAS occurrence, affected population size and demographic composition, 
and the magnitude of PFAS concentration reductions. These analysis-
specific sources of uncertainty are further described in appendix L of 
USEPA (2024e).

[[Page 32719]]

[GRAPHIC] [TIFF OMITTED] TR26AP24.138

XIII. Statutory and Executive Order Reviews

    Additional information about these statutes and Executive orders 
can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 14094 Modernizing Regulatory Review

1. Significant Regulatory Action
    This action is a ``significant regulatory action,'' as defined 
under section 3(f)(1) of Executive Order (E.O.) 12866, as amended by 
E.O. 14094. Accordingly, the EPA submitted this action to the Office of 
Management and Budget (OMB) for E.O. 12866 review. Documentation of any 
changes made in response to E.O. 12866 review is available in the 
docket. The EPA prepared an analysis of the potential costs and 
benefits associated with this action. This analysis, the Economic 
Analysis (EA; USEPA, 2024g), is also available in the docket and is 
summarized in section XII of this preamble.
2. Additional Analysis Under E.O. 12866
    The EPA evaluated commenters recommendations summarized in this 
section to quantify the greenhouse gas (GHG) impacts associated with 
the rule in light of E.O. 12866, Regulatory Planning and Review, and 
E.O. 13990, Protecting Public Health and the Environment and Restoring 
Science to Tackle the Climate Crisis. For the final rule, the EPA has 
conducted an additional analysis of the disbenefits associated with 
operation of treatment technologies to comply with the standard. This 
analysis is summarized here and detailed in the EA for the Final per- 
and polyfluoroalkyl substances (PFAS) National Primary Drinking Water 
Regulation (NPDWR; USEPA, 2024g).
a. Proposed Rule
    In the proposed rule, the EPA did not quantify and monetize 
potential GHG emissions impacts that would occur as a result of 
operating treatment technologies to comply with the proposed rule 
because quantification of such impacts is not required for the Health 
Risk Reduction and Cost Analysis (HRRCA) under the Safe Drinking Water 
Act (SDWA). The EPA evaluated commenters recommendations and summarized 
that the EPA should quantify and monetize the GHG emissions impacts 
associated with the rule in light of E.O. 13990, Protecting Public 
Health and the Environment and Restoring Science to Tackle the Climate 
Crisis.
b. Summary of Major Public Comments and EPA Responses
    Several commenters recommend ``. . . that the agency consider the 
social costs of carbon as part of any PFAS rule's cost analysis to be 
comprehensive as well as to understand how this rule may have 
unintended consequences like increased social costs relating to carbon 
dioxide emissions.'' Commenters asserted that ``[n]ot including the 
social costs of carbon and other social costs hinders the Administrator 
from having all necessary information to set the perfluorooctanoic acid 
(PFOA) and perfluorooctane sulfonic acid (PFOS) drinking water standard 
at a level that maximizes health risk reduction benefits at a cost that 
is justified, given those benefits.'' Commenters pointed to the GHG 
emissions associated with production, reactivation, and delivery of 
treatment media, focusing on granular activated carbon (GAC) in 
particular; construction associated with the installation of the 
treatment technology at the entry point (EP); electricity used to 
operate treatment technologies; and transportation and disposal of 
drinking water treatment residuals to comply with the PFAS NPDWR. Two 
commenters provided their own quantified estimates for some aspects of 
CO2 emissions. One commenter estimated that the climate 
disbenefits from CO2 emissions associated with increased 
electricity use for additional pumping, lighting, and ventilation in

[[Page 32720]]

treatment plants would be ``$2.5M to $6.8M at 2.5 and 1.5 percent 
discount rates, respectively, in 2026; and $3.6M to $8.6M at 2.5 and 
1.5 percent discount rates, respectively, in 2046.'' Another commenter 
used a life cycle analysis paper that provides one estimate for the 
carbon footprint of producing and using GAC and estimates that the 
climate damages from the CO2 emissions associated with 
increased GAC media use ``. . . could have a social cost of more than 
$160 million annually.'' One commenter stated that the EPA has 
performed this analysis in other rulemakings, specifically a 2023 
proposed air rulemaking (88 FR 25080), and notes that in that 
regulatory impact analysis (RIA; USEPA, 2023u), ``EPA included the 
social cost of carbon for the electricity required to operate the air 
pollution controls.''
    The EPA disagrees with commenters that SDWA requires the EPA to 
quantify and consider the climate disbenefits associated with GHG 
emission increases from this final rule in the HRRCA. The HRRCA 
requirements of SDWA 1412 (b)(3)(C) require the agency to analyze 
``quantifiable and nonquantifiable costs . . . that are likely to occur 
solely as a result of compliance with the maximum contaminant level'' 
(emphasis added). Therefore, the EPA considered as part of its HRRCA 
analysis the compliance costs to facilities, including the costs to 
purchase electricity required to operate the treatment technologies. 
Since the climate disbenefits from GHG emissions associated with 
producing electricity necessary to operate the treatment technologies 
account for climate impacts associated with the CO2 
emissions and associated costs to society, they do not qualify as 
compliance costs to public water systems (PWSs) that are part of the 
required HRRCA analysis under SDWA. For this reason, the EPA included 
compliance costs to PWSs but not climate disbenefits from GHG emissions 
associated with the production, reactivation, and delivery of treatment 
media; construction associated with the installation of the treatment 
technology at EP; electricity used to operate treatment technologies; 
and transportation and disposal of drinking water treatment residuals 
in the cost consideration for the final PFAS NPDWR.
    The EPA is committed to understanding and addressing climate change 
impacts in carrying out the agency's mission of protecting human health 
and the environment. While the EPA is not required by SDWA 
1412(b)(3)(C) to consider climate disbenefits under the HRRCA the 
agency has estimated the potential climate disbenefits caused by 
increased on-site electricity demand associated with removing PFAS from 
drinking water. As explained in section V of this preamble, the EPA's 
final rule is based on the EPA's record-based analysis of the statutory 
factors in SDWA 1412(b), and this disbenefits analysis is presented 
solely for the purpose of complying with E.O. 12866. Circular A-4 
states ``[l]ike other benefits and costs, an effort should be made to 
quantify and monetize additional effects when feasible and 
appropriate'' (OMB, 2023). The scope of the monetized climate 
disbenefits analysis is limited to the climate impacts associated with 
the CO2 emissions from increased electricity to operate the 
treatment technologies that will be installed to comply with the PFAS 
NPDWR.
    The EPA did not quantify the potential CO2 emissions 
changes associated with the production and delivery of treatment media, 
construction required for the installation of treatment technology, and 
transportation and disposal of treatment residuals. The EPA recognizes 
that many activities directly and indirectly associated with drinking 
water treatment produce GHG emissions; however, the agency determined 
that it could not accurately quantify all the potential factors that 
could increase and decrease greenhouse gas emissions that are not 
solely attributable to the direct onsite operations of the plant beyond 
increased electricity use at the plant. The EPA has information, to 
varying degrees, that the agency could use to potentially estimate 
emissions from some of these activities. To accurately understand the 
total potential climate disbenefits of this rule, the EPA should 
consider GHG emissions in the baseline scenario where the agency also 
takes no action. However, the EPA lacks the data needed to consider the 
potentially significant climate disbenefits and other costs to society 
of the EPA taking no action (i.e., not finalizing the PFAS NPDWR). If 
the EPA were to not finalize the rule, this could likely trigger other 
activities that would increase GHG emissions. For example, significant 
climate disbenefits may be realized from the public increasing 
purchases of bottled water in an effort to avoid PFAS exposure from 
drinking water provided by PWSs. More members of the public switch to 
drinking bottled water if they do not trust the safety of their utility 
supplied drinking water (Grupper et al. 2021, Lev[ecirc]que and Burns, 
2017). Bottled water has a substantially larger carbon footprint than 
the most highly treated tap water, including the significant energy 
necessary to produce plastic bottles and transport water from where it 
is bottled to the point of consumption (Gleick and Cooley, 2009). This 
carbon footprint can be hundreds of times greater than tap water on a 
per volume basis (e.g., see Botto, 2009). In addition, this is the 
first drinking water regulation in which the EPA has estimated 
disbenefits associated with increases or reductions in GHG emissions. 
The EPA expects that the approach for quantifying such benefits or 
disbenefits will continue to evolve as our understanding of the 
potential relationships between quality of drinking water treatment, 
impacts on consumer behavior, and other factors influencing GHG 
emissions improves. Considering the limitations described above and 
consistent with past EPA rulemakings,\27\ the EPA is limiting the scope 
of the analysis to the major sources of emissions from the direct 
operation of treatment technologies. The EPA did not quantify the 
CO2 emissions associated with production of treatment 
technologies, construction, transportation, and disposal, as these 
activities are not solely attributable to the direct onsite operations 
of the plant and are beyond the scope of this analysis.
---------------------------------------------------------------------------

    \27\ Recent examples include New Source Performance Standards 
(NSPS) for the SOC Manufacturing Industry and National Emission 
Standards for Hazardous Air Pollutants (NESHAP) for the SOC 
Manufacturing Industry and Group I and Group II polymers and Resins 
Industry, NESHAP Gasoline Distribution NRPM, Supplemental Effluent 
Limitations Guidelines (ELGs) and Standards for the Steam Electric 
Power Generating Point Source Category.
---------------------------------------------------------------------------

    Furthermore, while some data exists to inform an estimate of the 
CO2 emissions associated with production and reactivation of 
GAC, the EPA did not do so in this analysis due to significant 
uncertainties associated with the future CO2 emissions 
associated with these technologies. The carbon footprint of GAC is 
likely to reduce over time, as research continues on novel applications 
for PFAS removal (e.g., advanced reduction/oxidation processes, novel 
sorbents, foam fractionation, sonolysis, among others), alternative 
sources of materials to produce GAC (e.g., biomass and other waste 
materials), and use of carbon capture technology expands in the future. 
Given these compounding uncertainties, the EPA did not quantify the 
climate disbenefits of GAC production and reactivation.
    In this rule, the EPA determined that increased electricity use is 
the major source of emissions from the direct operation of treatment 
technologies to

[[Page 32721]]

remove PFAS. In this analysis conducted pursuant to E.O. 12866, the EPA 
first quantified the CO2 emissions from the additional 
electricity that is expected to be used for pumping, building lighting, 
heating, ventilation, and operation of other technology-specific 
equipment to remove PFAS. The EPA then monetized the climate 
disbenefits resulting from these CO2 emissions by applying 
the social cost of carbon dioxide (SC-CO2) estimates 
recommended by the commenter, as described in the following paragraphs.
    After considering public comments that recommended the EPA consider 
the climate disbenefits of the rule, the EPA conducted an analysis 
similar to the one recommended by one commenter. As suggested by the 
commenter, the EPA used the estimates of consumption of purchased 
electricity available from the EPA's peer reviewed work breakdown 
structure (WBS) cost models to estimate the national electricity use 
associated with operation of PFAS removal treatment technologies. The 
EPA deviated from the commenter's suggested approach when estimating 
associated CO2 emissions over time from producing 
electricity. The commenter estimates carbon emissions in a single year 
and presents that value as a constant reoccurring annual cost. Instead, 
the EPA estimated how CO2 emissions would change through 
2070, the calendar year to which the EPA has estimated CO2 
emissions from electricity production. The EPA applied readily 
available information from the latest reference case of the EPA's 
Integrated Planning Model (IPM) to represent CO2 emissions 
associated with electricity production over time.\28\ Given that 
emissions from producing electricity are expected to significantly 
decrease over time, this is a logical application consistent with other 
agency rulemakings estimating future emissions from the power sector 
including the EPA's final Good Neighbor Plan (USEPA, 2023q) and the 
EPA's New Source Performance Standards for GHG Emissions from New, 
Modified, and Reconstructed Electric Utility Generating Units (USEPA, 
2023r). Finally, the EPA monetized the climate disbenefits resulting 
from the estimated CO2 emissions by applying the SC-
CO2 estimates presented in the regulatory impact analysis of 
the EPA's December 2023 Final Rule, ``Standards of Performance for New, 
Reconstructed, and Modified Sources and Emissions Guidelines for 
Existing Sources: Oil and Natural Gas Sector Climate Review'' (USEPA 
2023s). These are the same SC-CO2 estimates the EPA 
presented in a sensitivity analysis in the RIA for the agency's 
December 2022 supplemental proposed Oil and Gas rulemaking that the 
commenter recommended for use in this action. The SC-CO2 
estimates incorporate recent research addressing recommendations of the 
National Academies of Science, Engineering, and Medicine (NASEM 2017), 
responses to public comments on the December 2022 supplemental proposed 
Oil and Gas rulemaking, and comments from a 2023 external peer review 
of the accompanying technical report. The methodology underlying the 
SC-CO2 estimates is described in the agency's technical 
report Report on the Social Cost of Greenhouse Gases: Estimates 
Incorporating Recent Scientific Advances (USEPA, 2023t), and is 
included in the docket for this final rule. For additional details on 
the climate disbenefits analysis see chapter 9.1 of the EPA's EA for 
the final PFAS NPDWR.
---------------------------------------------------------------------------

    \28\ See https://www.epa.gov/power-sector-modeling.
---------------------------------------------------------------------------

c. Final Analysis
    The EPA did not include an estimate of the monetized climate 
disbenefits from increased GHG emissions associated with the rule in 
the HRRCA as recommended by commenters because under the SDWA, the EPA 
only analyzes compliance costs to PWSs solely as a result of the 
Maximum Contaminant Level (MCL). The EPA analyzed the climate 
disbenefits of CO2 emissions associated with the increased 
electricity use at PWSs as a result of compliance with the PFAS NPDWR, 
the EPA estimates annualized climate disbenefits associated with this 
rule of $5.5 million per year \29\ (under a 2 percent near term 
discount rate \30\), which constitutes less than 0.4 percent of the 
monetized benefits of the rule at a 2 percent discount rate. As noted 
earlier, the EPA's action is justified based on the statutory factors 
in SDWA section 1412(b) and this disbenefits analysis is presented 
solely for the purposes of complying with E.O. 12866.
---------------------------------------------------------------------------

    \29\ Disbenefits are annualized over the years 2024-2080.
    \30\ See the EPA's EA for the Final PFAS NPDWR for results at 
all discount rates.
---------------------------------------------------------------------------

B. Paperwork Reduction Act (PRA)

    The information collection activities in this final rule have been 
submitted for approval to the Office of Management and Budget under the 
PRA. The Information Collection Request (ICR) document that the EPA 
prepared has been assigned the EPA ICR number 2732.02 and OMB control 
number 2040-0307. You can find a copy of the ICR in the docket for this 
rule at https://www.regulations.gov/docket/EPA-HQ-OW-2022-0114, and it 
is briefly summarized here. The information collection requirements are 
not enforceable until OMB approves them.
    The monitoring information collected as a result of the final rule 
should allow primacy agencies and the EPA to determine appropriate 
requirements for specific systems and evaluate compliance with the 
NPDWR. For the first three-year period following rule promulgation, the 
major information requirements concern primacy agency activities to 
implement the rule including adopting the NPDWR into state regulations, 
providing training to state and PWS employees, updating their 
monitoring data systems, and reviewing system monitoring data and other 
requests. Certain compliance actions for drinking water systems, 
specifically initial monitoring, would be completed during the three 
years following rule promulgation. Other compliance actions for 
drinking water systems (including ongoing compliance monitoring, 
administration, and treatment costs) would not begin until after three 
years due to the MCL compliance date of this rule. More information on 
these actions is described in section XII of this preamble and in 
chapter 9 from the EA of the Final PFAS NPDWR (USEPA, 2024g).
    Respondents/affected entities: The respondents/affected entities 
are PWSs and primacy agencies.
    Respondent's obligation to respond: The collection requirements are 
mandatory under SDWA (42 U.S.C. 300g-7).
    Estimated number of respondents: For the first three years after 
publication of the rule in the Federal Register, information 
requirements apply to an average of 33,594 respondents annually, 
including 33,538 PWSs and 56 primacy agencies.
    Frequency of response: During the initial three-year period, PWSs 
will conduct one-time startup activities. The one-time burden 
associated with reading and understanding the rule and adopting the 
rule is estimated to be an average of 4 hours per system. The one-time 
burden associated with attending one-time training provided by primacy 
agencies is an average of 16 hours for systems serving <=3,300 people 
and 32 hours for systems serving >3,300 people. The burden associated 
with initial sampling requirements is an estimated 207,000 hours. The 
total burden for these activities, for the three-year period, for all 
systems is estimated to be 1,519,000 hours. During the initial

[[Page 32722]]

three-year period, primacy agencies will incur burdens associated with 
one-time startup activities. The burden associated with reading and 
understanding the rule, adopting the regulatory requirements, and 
training internal staff is estimated to be an average of 4,320 hours 
per primacy agency. The burden associated with primacy agency review of 
initial monitoring data is 207,000 hours. The total burden for these 
activities, for the three-year period, for all 56 primacy agencies is 
estimated to be 533,000 hours.
    Total estimated burden: For the first three years after the final 
rule is published, water systems and primacy agencies will implement 
several requirements related to one-time startup activities and 
monitoring. The total burden hours for public water systems are 
1,519,000 hours. The total burden for primacy agencies is 533,000 
hours. The total combined burden is 2,052,000 hours.
    Total estimated cost: The total costs over the three-year period is 
$176.8 million, for an average of $58.9million per year (simple average 
over three years).
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collected for information unless it displays a 
currently valid OMB control number. The OMB control numbers for the 
EPA's regulations in 40 CFR are listed in 40 CFR part 9. When OMB 
approves this ICR, the agency will announce that approval in the 
Federal Register and publish a technical amendment to 40 CFR part 9 to 
display the OMB control number for the approved information collection 
activities contained in this final rule.

C. Regulatory Flexibility Act (RFA)

    Pursuant to sections 603 and 609(b) of the RFA, the EPA prepared an 
initial regulatory flexibility analysis (IRFA) for the proposed rule 
and convened a Small Business Advocacy Review (SBAR) Panel to obtain 
advice and recommendations from small entity representatives (SERs) 
that potentially would be subject to the rule's requirements. Summaries 
of the IRFA and Panel recommendations are presented in the proposed 
rule (USEPA, 2023f).
    As required by section 604 of the RFA, the EPA prepared a final 
regulatory flexibility analysis (FRFA) for this action. The FRFA 
addresses the issues raised by public comments on the IRFA for the 
proposed rule. The complete FRFA is available for review in section 9.4 
of the EA in the docket and is summarized here.
    For purposes of assessing the impacts of the final rule on small 
entities, the EPA considered small entities to be water systems serving 
10,000 people or fewer. This is the threshold specified by Congress in 
the 1996 Amendments to SDWA for small water system flexibility 
provisions. As required by the RFA, the EPA proposed using this 
alternative definition in the Federal Register (USEPA, 1998d), sought 
public comment, consulted with the Small Business Administration (SBA), 
and finalized the small water system threshold in the agency's Consumer 
Confidence Report (CCR) Regulation (USEPA, 1998e). As stated in the 
document, the alternative definition would apply to all future drinking 
water regulations.
    The SDWA is the core statute addressing drinking water at the 
Federal level. Under the SDWA, the EPA sets public health goals and 
enforceable standards for drinking water quality. As previously 
described, the final PFAS NPDWR requires water systems to reduce 
certain PFAS in drinking water below regulatory levels. The EPA is 
regulating these PFAS in drinking water to improve public health 
protection by reducing drinking water exposure to these and other PFAS 
in drinking water.
    The final rule contains provisions affecting approximately 62,000 
small PWSs. A small PWS serves between 25 and 10,000 people. These 
water systems include approximately 45,000 community water systems 
(CWSs) that serve the year-round residents and approximately 17,000 
non-transient non-community water systems (NTNCWSs) that serve the same 
persons over six months per year (e.g., a PWS that is an office or 
school). The final PFAS NPDWR includes legally enforceable regulatory 
standards with requirements for monitoring, public notification, and 
treatment or nontreatment options for water systems exceeding the 
regulatory standards. This final rule also includes reporting, 
recordkeeping, and other administrative requirements. States are 
required to implement operator certification (and recertification) 
programs under SDWA section 1419 to ensure operators of CWSs and 
NTNCWSs, including small water system operators, have the appropriate 
level of certification.
    Under the final rule requirements, small CWSs and NTNCWs serving 
10,000 or fewer people are required to conduct initial monitoring or 
demonstrate recent, previously collected monitoring data to determine 
the level of certain PFAS in their water system. Based on these initial 
monitoring results, systems are required to conduct ongoing monitoring 
at least every three years or as often as four times per year. Systems 
that exceed a drinking water standard will be required to choose 
between treatment and nontreatment as the compliance option. Under the 
final rule, the EPA estimates that approximately 16,542 small CWSs (37 
percent of small CWSs) could incur annual total PFAS NPDWR related 
costs of more than one percent of revenues, and that approximately 
8,199 small CWSs (18 percent of small CWSs) could incur annual total 
costs of three percent or greater of revenue. See section 9.3 of the 
final PFAS NPDWR EA for more information on the characterization of the 
impacts under the final rule.
    The EPA took a number of steps to solicit small entity stakeholder 
input during the development of the final PFAS NPDWR. Sections XIII.E 
and XIII.F of this preamble contain detailed information on stakeholder 
outreach during the rulemaking process, including material on the 
Federalism and Tribal consultation processes. The EPA also specifically 
sought input from small entity stakeholders through the SBAR Panel 
process. On May 24, 2022, the EPA's Small Business Advocacy Chairperson 
convened the Panel, which consisted of the Chairperson, the Director of 
the Standards and Risk Management Division within the EPA's Office of 
Ground Water and Drinking Water, the Administrator of the Office of 
Information and Regulatory Affairs within OMB, and the Chief Counsel 
for Advocacy of the SBA. Detailed information on the overall panel 
process can be found in the panel report available in the PFAS NPDWR 
docket (EPA-HQ-OW-2022-0114).
    In response to the proposal, the EPA received one comment 
specifically on the analytical approach used in the IRFA. The commenter 
states that ``[d]etailed analysis on the impacts to NTNCWSs should be 
conducted to inform the cost/benefit analysis. For example, treating 
PFAS with GAC at the low levels proposed is much more costly than 
current treatment for currently regulated contaminants, and a 2008 
study is not a reliable indicator of future costs. Lack of both actual 
data on occurrence in these systems and reliable information on cost of 
compliance makes finalizing the MCL as to NTNCWSs too uncertain.'' The 
EPA disagrees that the agency has not analyzed the impacts of the PFAS 
NPDWR on NTNCWS. The EPA has used both actual data on occurrence at 
NTNCWSs from the third Unregulated Contaminant Monitoring Rule (UCMR 3) 
and state data, as well as reliable information on costs to NTNCWSs 
using

[[Page 32723]]

the WBS treatment cost models to assess the impact of the rule on 
NTNCWSs. As the EPA stated in the proposal, the EPA lacks information 
on the revenues of NTNCWS, therefore the agency does not take the same 
approach used for CWSs in the Significant Economic Impact on a 
Substantial Number of Small Entities (SISNOSE) screening analysis where 
costs are compared to 1 and 3 percent of revenues. Instead, the EPA 
used the best available data, the EPA's Assessment of the Vulnerability 
of Noncommunity Water Systems to SDWA Cost Increases (USEPA, 1998f), to 
find that NTNCWSs are less vulnerable to SDWA related increases than a 
typical CWS. The EPA proceeded with the SBAR Panel process, as 
previously detailed in this section.
    The EPA received many comments on the rule proposal, including from 
the Chief Counsel for Advocacy of the SBA, on small system and IRFA 
related topics including lack of funding availability for small water 
systems, the EPA's alleged underestimation of the impacts of the rule 
on small systems, the EPA's alleged overestimation of reliance on 
Federal funding to defray compliance costs for small water systems, and 
``other factors that will further deter timely compliance'' such as 
personnel shortages, supply chain disruptions, limited lab and disposal 
capacity, and availability of treatment technologies. The EPA has 
addressed these comments and provided for maximum flexibility for small 
systems while ensuring sufficient public health protection for 
populations served by these systems. For the EPA's response to SBA and 
other comments on funding availability, please see section II of this 
preamble. For the EPA's response to SBA and other comments on the 
estimated costs to small water systems, please see section XII of this 
preamble. For the EPA's response to SBA and other comments on lab 
capacity, see sections V and VIII. For the EPA's response to SBA and 
other comments on technology and disposal capacity, see section X. For 
responses to SBA's and other commenters' recommendations to the EPA to 
provide burden-reducing flexibilities for small water systems, 
including finalizing one of the regulatory alternatives and phasing in 
the MCL, as well as providing additional time for compliance, see 
section V of this preamble. For response to SBA and other commenters 
concerned about the EPA's concurrent proposal of a preliminary 
determination and a proposed regulation for four PFAS, see section III 
of the preamble. The FRFA, available for review in section 9.4 of the 
EA in the docket, also provides detailed information on the 
recommendations of the SBAR Panel and the EPA's actions taken to 
minimize the significant economic impact of the final rule on small 
systems.
    As a mechanism to reduce the burden of the final rule requirements 
on small entities the EPA has promulgated compliance flexibilities for 
small CWSs serving 10,000 or fewer persons. These flexibilities include 
the use of previously collected PFAS monitoring data to satisfy initial 
monitoring requirements, allowing reduced initial monitoring for small 
groundwater systems serving 10,000 or fewer, the addition of annual 
monitoring to the ongoing compliance monitoring framework, and modified 
rule trigger levels for reduced monitoring eligibility. For more 
information on these flexibilities, see section VIII of this preamble. 
The EPA is also exercising its authority under SDWA section 1412(b)(10) 
to implement a nationwide two-year capital improvement extension to 
comply with MCL. The agency notes that SDWA section 1416(a) and 
(b)(2)(C) describe how the primacy agencies may also grant an exemption 
for systems meeting specified criteria that provides an additional 
period for compliance. PWSs that meet the minimum criteria outlined in 
the SDWA section 1416 may be eligible for an exemption of up to three 
years. Exemptions for smaller water systems (<=3,300 population), 
meeting certain specified criteria may be renewed for one or more two-
year periods, but not to exceed six years. States exercising primacy 
enforcement responsibility must have adopted the 1998 Variance and 
Exemption Regulation for a water system to be eligible for an exemption 
in that state. Finally, the EPA notes that if point-of-use (POU) 
devices are certified to meet the NPDWR standard in the future, this 
could reduce the economic impact of the final regulation on small PWSs, 
particularly on water systems in the smallest size category (e.g., 
those serving between 25 and 500 people).
    The EPA also assessed the degree to which the final PFAS NPDWR 
small system flexibilities would mitigate compliance costs. The EPA 
estimates that the use of previously collected PFAS monitoring data 
will reduce the economic burden on small systems nationally by $7 
million dollars per year for three years. The EPA expects that reduced 
monitoring for small groundwater systems will reduce the economic 
burden on small systems nationally by $21 million per year for three 
years. The EPA estimates that under the final rule approximately 4,300 
to 7,000 small PWSs may have regulated PFAS occurrence between the 
trigger levels and the MCLs, and therefore may be eligible for annual 
monitoring following four consecutive quarterly samples demonstrating 
they are ``reliably and consistently'' below the MCLs. The EPA 
anticipates further compliance cost mitigations stemming from the 
decision to set the reduced monitoring trigger levels at one-half of 
the MCLs, rather than one-third of the MCLs as proposed. While the MCL 
compliance period extension does not change the treatment or non- 
treatment actions that small systems will be compelled to undertake, it 
will reduce the compliance burden faced by small water systems by 
allowing for more time for them to obtain and install capital 
improvements. Finally, the EPA recognizes the possibility of small 
system compliance cost reduction particularly for very small water 
systems should POU certifications be updated in the future and POUs 
meet the small system compliance technology (SSCT) criteria for the 
final NPDWR. See chapter 9, section 9.3.4 of the final PFAS NPDWR EA 
(USEPA, 2024g) for more information on the characterization of the 
impacts under the final rule.
    In addition, the EPA is preparing a Small Entity Compliance Guide 
to help small entities comply with this rule. The EPA expects the Small 
System Compliance Guide will be developed in the first three years 
after rule promulgation and will be made available on the EPA's PFAS 
NPDWR website.

D. Unfunded Mandates Reform Act (UMRA)

    This action contains a Federal mandate under UMRA, 2 U.S.C. 1531-
1538, that may result in expenditures of $100 million or more for 
state, local, and Tribal governments, in the aggregate, or the private 
sector in any one year. Accordingly, the EPA has prepared a written 
statement required under section 202 of UMRA that is included in the 
docket for this action (see chapter 9 of the EA for the Final PFAS 
NPDWR) and briefly summarized here.
    Consistent with UMRA section 205, the EPA identified and analyzed a 
reasonable number of regulatory alternatives to determine the MCL 
requirement in the final rule. The agency notes, however, that the 
provisions of section 205 do not apply when they are inconsistent with 
applicable law; in the case of NPDWRs, the UMRA section 205 requirement 
to adopt the least costly, most cost-

[[Page 32724]]

effective, or least burdensome option is inconsistent with SDWA 
regulatory development requirements. See section XII of this preamble 
and chapter 9 of the EA for the Final PFAS NPDWR (USEPA, 2024g) for 
alternative options that were considered. Consistent with the 
intergovernmental consultation provisions of UMRA section 204, the EPA 
consulted with governmental entities affected by this rule. The EPA 
describes the government-to-government dialogue and comments from 
state, local, and Tribal governments in sections XIII.E. (E.O. 13132: 
Federalism) and XIII.F. (E.O. 13175: Consultation and Coordination with 
Indian Tribal Governments) of this document.
    This action may significantly or uniquely affect small governments. 
The EPA consulted with small governments concerning the regulatory 
requirements that might significantly or uniquely affect them. The EPA 
describes this consultation in the RFA, section XIII.C. of this 
preamble.

E. Executive Order 13132: Federalism

    The EPA has concluded that this action has federalism implications 
because it imposes substantial direct compliance costs on state or 
local governments, and the Federal Government will not provide the 
funds necessary to pay those costs. However, the EPA notes that the 
Federal Government will provide a potential source of funds necessary 
to offset some of those direct compliance costs through the Bipartisan 
Infrastructure Law (BIL). The EPA estimates that the net change in 
primacy agency related cost for state, local, and Tribal governments in 
the aggregate to be $4.7 million.
    The EPA provides the following federalism summary impact statement. 
The EPA consulted with state and local governments early in the process 
of developing the proposed action to allow them to provide meaningful 
and timely input into its development. The EPA held a federalism 
consultation on February 24, 2022. The EPA invited the following 
national organizations representing state and local elected officials 
to a virtual meeting on February 24, 2022: The National Governors' 
Association, the National Conference of State Legislatures, the Council 
of State Governments, the National League of Cities, the U.S. 
Conference of Mayors, the National Association of Counties, the 
International City/County Management Association, the National 
Association of Towns and Townships, the County Executives of America, 
and the Environmental Council of States. Additionally, the EPA invited 
the Association of State Drinking Water Administrators (ASDWA), the 
Association of Metropolitan Water Agencies (AMWA), the National Rural 
Water Association (NRWA), the American Water Works Association (AWWA), 
the American Public Works Association, the Western Governors' 
Association, the Association of State and Territorial Health Officials, 
the National Association of Country and City Health Officials, and 
other organizations to participate in the meeting. In addition to input 
received during the meeting, the EPA provided an opportunity to receive 
written input within 60 days after the initial meeting. A summary 
report of the views expressed during federalism consultations is 
available in the rule docket (EPA-HQ-OW-2022-0114). The EPA also 
received public comments from some of these organizations during the 
public comment period following the rule proposal. These individual 
organization comments are available in the docket.
    Comments provided by the organizations during both the consultation 
and public comment periods covered a range of topics. The overarching 
comments from multiple organizations related to the NPDWR compliance 
timeframe and implementation flexibilities, the proposed MCLs for PFOA 
and PFOS and the Hazard Index PFAS, the EPA's estimated costs of the 
NPDWR and funding considerations, PFAS treatment disposal, and other 
EPA actions to address PFAS in the environment. Specifically, several 
of these organizations expressed that the EPA should allow an extended 
compliance timeframe to comply with the MCLs due to supply chain 
disruptions and availability of treatment materials, as well as 
maximize the implementation flexibilities for water systems and primacy 
agencies, including those related to monitoring. Regarding rule costs, 
some organizations contended that the EPA's costs were underestimated, 
and that the EPA should consider the disposal of PFAS treatment 
residuals and associated costs particularly if determined to be 
hazardous wastes in the future under other EPA statutes such as the 
Resource Conservation and Recovery Act (RCRA). A couple of 
organizations requested that the EPA should provide more direct funding 
for local governments to comply with the NPDWR noting the available BIL 
funding would not be sufficient to cover the rule costs and these funds 
cannot be used for certain rule compliance costs. A few organizations 
suggested that the agency should raise the proposed PFOA and PFOS MCLs, 
with some of these commenters offering that the EPA should not move 
forward with the Hazard Index MCL for perfluorohexane sulfonic acid 
(PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer 
acid (HFPO-DA), and perfluorobutane sulfonic acid (PFBS). Finally, 
several organizations provided that the agency should focus on 
addressing PFAS holistically and expedite its efforts on source water 
protection and other actions to address PFAS in the environment beyond 
drinking water. The EPA considered these organizations' concerns and 
has taken this input to address many of these in the final PFAS NPDWR 
while ensuring sufficient public health protection those served by 
PWSs.
    Related to compliance timeline and other rule implementation 
flexibilities, the EPA is exercising its authority under SDWA section 
1412(b)(10) to implement a nationwide two-year capital improvement 
extension to comply with MCL. The agency notes that SDWA section 
1416(a) and (b)(2)(C) describe how the EPA or states may also grant an 
exemption for systems meeting specified criteria that provides an 
additional period for compliance. See section XI.D for more information 
on extensions and exemptions. The EPA has promulgated compliance 
flexibilities for monitoring implementation including the use of 
previously collected PFAS monitoring data to satisfy initial monitoring 
requirements and allowing reduced initial monitoring for small 
groundwater systems serving 10,000 or fewer. Other monitoring 
implementation flexibilities include the addition of annual monitoring 
to the ongoing compliance monitoring framework and higher rule trigger 
levels for reduced monitoring eligibility. For more information on 
these flexibilities, see section VIII of this preamble.
    For the final rule, the EPA has evaluated the concerns related to 
the rule costs and maintains that the estimated benefits of the rule 
justify the costs. Regarding financial costs to water systems if 
regulated PFAS were to be required to be disposed of as hazardous waste 
in the future, the EPA reaffirms that no PFAS are currently listed, or 
proposed to be listed, as hazardous wastes under RCRA. However, the EPA 
has included a sensitivity analysis to determine the impact on this 
action should be PFAS-containing treatment materials be considered RCRA

[[Page 32725]]

regulatory or characteristic hazardous waste in the future (see section 
X.C. for more detail). For funding concerns and information, the EPA 
has provided information, detailed further in section II.G. of this 
preamble related to potential funding opportunities, particularly those 
available through BIL funds including the EPA's Emerging Contaminants 
in Small or Disadvantaged Communities (EC-SDC) grants program.
    For organizations recommending that the EPA raise the proposed PFOS 
and PFOS MCLs, with some of these organizations suggesting that the 
Hazard Index MCL is not justified and should not be finalized, as 
described in section V of this preamble, the EPA has demonstrated these 
levels are justified under the requirements of SDWA. Therefore, the 
agency is maintaining these MCLs for the final rule but has offered 
compliance flexibilities as described previously.
    Lastly, several organizations provided that the agency should focus 
on addressing PFAS through source water protection efforts beyond 
drinking water, under the agency's PFAS Strategic Roadmap and 
associated actions, the EPA is swiftly working to address PFAS 
contamination in the environment and reduce human health PFAS exposure 
through all pathways. While beyond the scope of this rulemaking, the 
EPA is making progress implementing many of the commitments in the 
Roadmap, including those that may significantly reduce PFAS source 
water concentrations.
    In addition to the federalism consultation, regarding state 
engagement more specifically, the EPA notes there were multiple 
meetings held by ASDWA where the EPA gathered input from state 
officials and utilized this input to inform this rule. The EPA also 
considered all comments provided by individual states and state 
organizations provided during the public comment period and used these 
comments to inform the final rule.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This action has Tribal implications, it imposes direct compliance 
costs on Tribal governments, and the Federal Government will not 
provide funds necessary to pay those direct compliance costs. However, 
the EPA notes that the Federal Government will provide a potential 
source of funds necessary to offset some of those direct compliance 
costs through the BIL.
    The EPA has identified 998 PWSs serving Tribal communities, 84 of 
which are federally owned. The EPA estimates that Tribal governments 
will incur PWS compliance costs of $9.0 million per year attributable 
to monitoring, treatment or nontreatment actions to reduce PFAS in 
drinking water, and administrative costs, and that these estimated 
impacts will not fall evenly across all Tribal systems. The final PFAS 
NPDWR does offer regulatory relief by providing flexibilities for all 
water systems to potentially utilize pre-existing monitoring data in 
lieu of initial monitoring requirements and for groundwater CWSs and 
NTNCWSs serving 10,000 or fewer to reduce initial monitoring from 
quarterly monitoring during a consecutive 12-month period to only 
monitoring twice during a consecutive 12-month period. These 
flexibilities may result in implementation cost savings for many Tribal 
systems since 98 percent of Tribal CWSs and 94 percent of NTNCWs serve 
10,000 or fewer people.
    Accordingly, the EPA provides the following Tribal summary impact 
statement as required by section 5(b) of E.O. 13175. The EPA consulted 
with federally recognized Tribal governments early in the process of 
developing this action to permit them to have meaningful and timely 
input into its development. The EPA conducted consultation with Indian 
Tribes beginning on February 7, 2022, and ending on April 16, 2022. The 
consultation included two national webinars with interested Tribes on 
February 23, 2022, and March 8, 2022, where the EPA provided proposed 
rulemaking information and requested input. A total of approximately 35 
Tribal representatives participated in the two webinars. Updates on the 
consultation process were provided to the National Tribal Water Council 
and the EPA Region 6's Regional Tribal Operations Committee upon 
request at regularly scheduled monthly meetings during the consultation 
process. As part of the consultation, the EPA received written comments 
from the following Tribes: Little Traverse Bay Bands of Odawa Indians 
and Sault Ste. Marie Tribe of Chippewa Indians. In addition to the 
comments from these Tribal governments, the EPA received comments the 
National Tribal Water Council. A summary report of the consultation, 
webinars, and views expressed during the consultation is available in 
the Docket (EPA-HQ-OW-2022-0114).
    The EPA received a variety of comments from Tribal officials and 
representatives during both the consultation and public comment 
periods. These comments can be found in more detail within the Docket 
through the individual public comments and within the consultation 
summary report. Specifically, comments included those related to 
initial monitoring requirements, use of monitoring waivers, concerns 
related to treatment options and disposal of treatment materials, 
particularly if determined to be hazardous in the future, as well as 
funding concerns. The EPA has addressed these officials' comments 
through finalizing monitoring requirements which allow for small 
systems flexibilities including the use of previously collected 
monitoring data to be used to satisfy initial monitoring requirements 
and not allowing the use of monitoring waivers (see section VIII) of 
this preamble. Related to treatment considerations, the EPA has 
identified best available technologies (BATs) as described in section X 
which have been shown to reduce regulated PFAS levels, but also allows 
for other treatment technologies not identified as BATs to be used to 
address MCL exceedances if they can remove PFAS to the regulatory 
standards. Additionally, the EPA has developed a sensitivity cost 
analysis to describe the additional financial costs to water systems if 
the regulated PFAS were to be required to be disposed of as hazardous 
waste in the future (see appendix N, section 2 of the EA for additional 
detail). For funding concerns, the EPA has provided information, 
detailed further in section II of this preamble, related to potential 
funding opportunities, particularly those available through the EPA's 
EC-SDC grants program.
    The EPA reviewed these comments received from Tribal groups, the 
estimated cost data, and the quantified and nonquantifiable benefits 
associated with the PFAS NPDWR and determined that the regulatory 
burden placed on Tribes is outweighed by the positive benefits. Given 
that the majority of Tribal systems serve fewer than 10,000 persons, as 
noted previously, the EPA has provided regulatory relief in the form of 
small system compliance flexibilities related to monitoring 
requirements. For additional information on these compliance 
flexibilities and their estimated impacts see sections VIII of this 
preamble and chapter 9.4, of the final PFAS NPDWR EA (USEPA, 2024g).
    As required by section 7(a) of E.O. 13175, the EPA's Tribal 
Official has certified that the requirements of the E.O. have been met 
in a meaningful and timely manner. A copy of the

[[Page 32726]]

certification is included in the docket for this action.

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    Executive Order 13045 directs Federal agencies to include an 
evaluation of the health and safety effects of the planned regulation 
on children in Federal health and safety standards and explain why the 
regulation is preferable to potentially effective and reasonably 
feasible alternatives. This action is subject to E.O. 13045 because it 
is a significant regulatory action under section 3(f)(1) of E.O. 12866, 
and the EPA believes that the environmental health or safety risk 
addressed by this action has a disproportionate effect on children. 
Accordingly, the EPA has evaluated the environmental health or safety 
effects of the regulated PFAS found in drinking water on children and 
estimated the risk reduction and health endpoint impacts to children 
associated with adoption of treatment or nontreatment options to reduce 
these PFAS in drinking water. The results of these evaluations are 
contained in the EA of the Final PFAS NPDWR (USEPA, 2024g) and 
described in section XII of this preamble. Copies of the EA of the 
Final PFAS NPDWR and supporting information are available in the Docket 
(EPA-HQ-OW-2022-0114).
    Furthermore, the EPA's Policy on Children's Health also applies to 
this action. Information on how the Policy was applied is available in 
section II.B. of this preamble.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution, or use of energy. The public and private water systems 
affected by this action do not, as a rule, generate power. This action 
does not regulate any aspect of energy distribution as the water 
systems that are proposed to be regulated by this rule already have 
electrical service. Finally, the EPA has determined that the 
incremental energy used to implement the identified treatment 
technologies at drinking water systems in response to the regulatory 
requirements is minimal. The EPA estimates that the final rule will 
result in an increased electricity use of approximately 229 GWh per 
year, for more information see section XIII.A; total U.S. electricity 
consumption in 2022 was approximately 4.05 million GWh (USEIA, 2023). 
Therefore, the electricity consumed as a result of the final rule 
represents approximately 0.005 percent of total U.S. electricity 
consumption. Based on these findings, the EPA does not anticipate that 
this rule will have a significant adverse effect on the supply, 
distribution, or use of energy.

I. National Technology Transfer and Advancement Act of 1995

    This action involves technical standards. The rule could involve 
voluntary consensus standards in that it requires monitoring for 
regulated PFAS, and analysis of the samples obtained from monitoring 
based on required methods. As part of complying with this final rule, 
two analytical methods are required to be used for the identification 
and quantification of PFAS in drinking water. The EPA Methods 533 and 
537.1 incorporate quality control criteria which allow accurate 
quantitation of PFAS. Additional information about the analytical 
methods is available in section VII of this preamble. The EPA has made, 
and will continue to make, these documents generally available through 
www.regulations.gov and at the U.S. Environmental Protection Agency 
Drinking Water Docket, William Jefferson Clinton West Building, 1301 
Constitution Ave. NW, Room 3334, Washington, DC 20460, call (202) 566-
2426.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations and 
Executive Order 14096: Revitalizing Our Nation's Commitment to 
Environmental Justice for All

1. Proposal
    The EPA believes that the human health or environmental conditions 
that exist prior to this action result in or have the potential to 
result in disproportionate and adverse human health or environmental 
effects on communities with environmental justice (EJ) concerns. 
Consistent with the agency's Technical Guidance for Assessing 
Environmental Justice in Regulatory Analysis (USEPA, 2016f), for the 
proposed rule, the EPA conducted an EJ analysis to assess the 
demographic distribution of baseline PFAS drinking water exposure and 
impacts anticipated to result from the proposed PFAS NPDWR. The EPA 
conducted two separate analyses: an EJ exposure analysis using the 
agency's EJSCREENbatch R package, which utilizes data from EJScreen, 
the agency's Environmental Justice Screening and Mapping Tool (USEPA, 
2019e), and from the U.S. Census Bureau's American Community Survey 
(ACS) 2015-2019 five-year sample (United States Census Bureau, 2022), 
and an analysis of the EPA's proposed regulatory option and 
alternatives using SafeWater Multi-Contaminant Benefit Cost Model 
(MCBC; detailed in section XII of this preamble). The EPA's analyses 
examined EJ impacts on a subset of PWSs across the country, based on 
availability of PFAS occurrence data and information on PWS service 
area boundaries. In the EPA's analysis, results for income, race, and 
ethnicity groups were generally summarized separately due to how 
underlying ACS statistics are aggregated at the census block group 
level; for more information, please see: https://www.census.gov/data/developers/data-sets/acs-5year.html (United States Census Bureau, 
2022). Additional information on both analyses can be found in chapter 
8 of USEPA (2024g) and appendix M of USEPA (2024e).
    The EPA's EJ exposure analysis using the EJSCREENbatch R package 
utilized hypothetical regulatory scenarios, which differed from the 
EPA's proposed option and regulatory alternatives presented in the 
proposed rule. The EPA's analysis demonstrated that across hypothetical 
regulatory scenarios evaluated, elevated baseline PFAS drinking water 
exposures, and thus greater anticipated reductions in exposure, were 
estimated to occur in communities of color and/or low-income 
populations. For this analysis, the EPA examined individuals served by 
PWSs with modeled PFAS exposure above baseline concentration thresholds 
or a specific alternative policy threshold. The EPA also summarized 
population-weighted average concentrations in the baseline as well as 
reductions that would accrue to each demographic group from 
hypothetical regulatory scenarios.
    The EPA's analysis in SafeWater MCBC evaluated the demographic 
distribution of health benefits and incremental household costs 
anticipated to result from the PFAS NPDWR. The EPA's proposed option 
and all regulatory alternatives were anticipated to provide benefits 
across all health endpoint categories for all race/ethnicity groups. 
Across all health endpoints, communities of color were anticipated to 
experience the greatest reductions in adverse health effects associated 
with PFAS exposure, resulting in the greatest quantified benefits 
associated with the EPA's proposed rule, likely due to disproportionate 
baseline exposure. When examining costs anticipated to result from the 
rule, the EPA found that cost differences across demographic

[[Page 32727]]

groups were typically small, with no clear unidirectional trend in cost 
differences based on demographic group. In some cases, the EPA found 
that communities of color were anticipated to bear minimally increased 
costs but in other cases, costs to communities of color were 
anticipated to be lower than those across all demographic groups. In 
general, incremental household costs to all race/ethnicity groups were 
found to decrease with increasing system size, an expected result due 
to economies of scale.
    Additionally, on March 2, 2022, and April 5, 2022, the EPA held 
public meetings related to EJ and the development of the proposed 
NPDWR. The meetings provided an opportunity for the EPA to share 
information and for communities to offer input on EJ considerations 
related to the development of the proposed rule. During the meetings 
and in subsequent written comments, the EPA received public comment on 
topics including establishing an MCL for PFAS, affordability of PFAS 
abatement options, limiting industrial discharge of PFAS, and the EPA's 
relationship with community groups. For more information on the public 
meetings, please refer to the Environmental Justice Considerations for 
the Development of the Proposed PFAS Drinking Water Regulation Public 
Meeting Summary for each of the meeting dates in the public docket at 
https://www.regulations.gov/docket/EPA-HQ-OW-2022-0114. Additionally, 
the written public comments are included within the public docket.
2. Summary of Major Public Comments and EPA Responses
    Many commenters expressed support for the rule and the EPA's EJ 
analysis, underscoring the rule's alignment with the administration's 
commitment to advancing EJ. Commenters point to evidence which suggests 
that PFAS exposure disproportionately affects communities with EJ 
concerns. Further, commenters state that these communities are 
particularly vulnerable to PFAS exposure and the associated health 
outcomes. Several commenters also assert that the rule is anticipated 
to benefit these communities with EJ concerns who are at a higher risk 
of PFAS exposure. Through this rule, the EPA reaffirms the importance 
of EJ considerations in agency activities, including rulemaking.
    Many commenters expressed concern about potential EJ implications 
of the final rule and urged the EPA to further consider these 
implications prior to final rule promulgation. Specifically, commenters 
presented concerns that the rule will disproportionately impact 
communities that already are overburdened with sociodemographic and 
environmental stressors. Additionally, several commenters voiced EJ 
concerns associated with implementation of the rule. Many commenters 
asserted that communities with EJ concerns may not have sufficient 
financial capacity to implement the rule (e.g., install treatment) and 
that this may further exacerbate existing disparities associated with 
PFAS exposure. Additionally, commenters stated that additional 
resources would likely be needed for communities with EJ concerns to 
successfully implement the rule, including targeted monitoring and 
sampling in these areas.
    The EPA acknowledges commenters' concerns regarding potential EJ 
implications of the rule. Under E.O. 14096, the EPA is directed to 
identify, analyze, and address disproportionate and adverse human 
health or environmental effects of agency actions on communities with 
environmental justice concerns (USEPA, 2023v). The EPA believes that 
its EJ analysis accompanying the final rule has achieved this 
directive, as the EPA has assessed the demographic distribution of 
baseline PFAS exposure in drinking water as well as the anticipated 
distribution of benefits and costs that will result from the rule. For 
more information on the EPA's EJ analysis, please see chapter 8 of 
USEPA (2024g) and appendix M of USEPA (2024e). The EPA acknowledges the 
potential for implementation challenges for communities with EJ 
concerns; however, there may be opportunities for many communities to 
utilize external funding streams to address such challenges. The BIL, 
the Low-Income Water Household Assistance Program through the American 
Rescue Plan, and other funding sources may be able to provide financial 
assistance for addressing emerging contaminants. In particular, the BIL 
funding has specific allocations for disadvantaged and/or small 
communities to address emerging contaminants, including PFAS. For 
example, the Emerging Contaminants in Small or Disadvantaged 
Communities (EC-SDC) grants program, which does not have a cost-sharing 
requirement, will provide states and territories with $5 billion to 
provide grants to public water systems in small or disadvantaged 
communities to address emerging contaminants, including PFAS. Grants 
will be awarded non-competitively to states and territories.
    Many commenters stated that the costs of the rule will 
disproportionately fall on communities with EJ concerns. Additionally, 
some commenters asserted that the EPA's EJ analysis does not 
appropriately consider the distributional impacts of rule costs, with 
one commenter incorrectly stating that the analysis ``fails to consider 
how these increased compliance costs will impact EJ communities, as 
required by Executive Order 12898''. Commenters recommended that the 
EPA revise its analysis to reflect the impact that compliance costs of 
the rule will have on communities with potential EJ concerns.
    The EPA disagrees with commenters that the EPA has failed to 
appropriately consider the impact that costs required to implement the 
rule may have on communities with potential EJ concerns. The agency has 
fulfilled its commitments in this rulemaking by conducting an analysis 
consistent with E.O. 14096 and has shared information on the 
demographic distribution of impacts evaluated in its EJ analysis to 
facilitate the public's understanding on potential environmental 
justice impacts of the rule. In section 8.4.2.2 of its EJ Analysis 
(found in chapter 8 of the HRRCA (USEPA, 2024l)), the EPA estimated the 
distribution of annualized incremental household costs across different 
race/ethnicity groups. As described in section XIII.J.1 above, the EPA 
found that cost differences across demographic groups are typically 
small, with no clear unidirectional trend in cost differences based on 
demographic group. In some cases, the EPA found that communities of 
color are anticipated to bear minimally increased costs but in other 
cases, costs to communities of color are lower than those across all 
demographic groups. In response to commenters, the EPA has updated its 
analysis to also examine the distribution of benefits and costs across 
income groups. With respect to the distribution of costs, the EPA found 
that, similar to its findings based on race/ethnicity group, 
differences in annual incremental household costs across income groups 
were small with no unidirectional trend in cost differences based on 
income level.
    Additionally, one commenter recommended that the EPA disaggregate 
Asian and Pacific Islander data in its EJ analysis, asserting that the 
``EPA must comply with OMB Statistical Directive 15''. The EPA 
disagrees that its EJ analysis must disaggregate Asian and Pacific 
Islander data in order to comply with OMB Statistical Directive 15 (SPD 
15). SPD 15 establishes standards for maintaining, collecting, and 
presenting

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Federal data on race and ethnicity and applies to ``all Federal 
reporting purposes'' (OMB, 1977). This term is not defined and does not 
clearly apply to analyses developed to support rulemaking efforts. SPD 
15 is targeted primarily toward data collection efforts, the 
development of data for public consumption, and the enforcement of 
civil rights laws. As SPD 15 is not applicable in the context of 
rulemakings, the EPA is not required to revise its EJ analysis in 
accordance with the standards for data disaggregation set forth in the 
OMB directive. However, the EPA acknowledges that reporting results 
separately for these groups can help to reveal potential disparities 
that may exist across Asian and Pacific Islander subpopulations. In 
response to this comment, the EPA has added a qualitative summary of 
the literature provided by the commenter and has updated its analysis 
to include separate Asian and Pacific Islander demographic groups. 
These updates are reflected in chapter 8 of USEPA (2024g) and appendix 
M of USEPA (2024e) for the public's information and understanding.
3. Final Rule
    The EPA's EJ exposure analysis for the final rule demonstrates that 
some communities of color are anticipated to experience elevated 
baseline PFAS drinking water exposures compared to the entire sample 
population. The percentage of non-Hispanic Black and Hispanic 
populations with PFAS in drinking water detected above baseline 
thresholds is greater than the percentage of the total population 
served with PFAS exposure above these thresholds for all PFAS analytes 
examined in the EPA's analysis. Similarly, when results are separately 
analyzed by system size, non-Hispanic Black and Hispanic populations 
are more likely to be served by large systems with PFAS detected above 
baseline thresholds compared to the percentage of the total population 
served across all demographic groups. For small systems, non-Hispanic 
Asian and non-Hispanic Black populations are more likely to be served 
by systems with PFAS concentrations above baseline thresholds for some 
PFAS analytes compared to the total population served across all 
demographic groups.
    The EPA believes that this action is likely to reduce existing 
disproportionate and adverse effects on communities with EJ concerns. 
Across all hypothetical regulatory thresholds, elevated exposure--and 
thus reductions in exposure under the hypothetical regulatory 
scenarios--is anticipated to occur in communities of color and/or low-
income populations. The EPA estimates that the most notable reductions 
in exposure would be experienced by Hispanic populations, specifically 
when using UCMR 5 minimum reporting level values as hypothetical 
regulatory thresholds. Hispanic populations are estimated to experience 
exposure rates that are at least two percentage points higher than 
exposure for the total population served across all demographic groups 
and for all PFAS analytes included in this analysis. Hispanic 
populations are therefore also expected to have greater reductions in 
exposure compared to the entire sample population. In addition, under 
hypothetical regulatory thresholds set at the UCMR 5 minimum reporting 
levels, the EPA anticipates some of the largest reductions in exposure 
to PFOA and PFHxS occur for non-Hispanic Native American or Alaska 
Native and non-Hispanic Pacific Islander populations due to relatively 
high concentration levels when these PFAS are detected at PWSs serving 
these groups. For more information on the results of this EJ exposure 
analysis, see chapter 8 of USEPA (2024g) and appendix M of USEPA 
(2024e).
    For the final rule, the EPA has updated its EJ exposure analysis to 
include separate Asian and Pacific Islander demographic groups, which 
were previously combined for the proposed rule. Additionally, the EPA 
has updated the demographic categories utilized in the EJ exposure 
analysis to ensure that consistent information is used or applied 
throughout the PFAS NPDWR EA to the extent possible and to reduce 
double counting across demographic categories. For the proposed rule, 
the EPA's EJ exposure analysis used different demographic categories 
than its distributional analysis conducted in SafeWater, with the 
former partly including racial groups that were inclusive of Hispanic 
individuals and the latter including racial groups that were exclusive 
of Hispanic individuals. Because the EPA's EJ exposure analysis for the 
proposed rule employed some demographic categories that were inclusive 
of Hispanic individuals (e.g., American Indian or Alaska Native) and 
others that were not (e.g., non-Hispanic White), this introduced double 
counting across groups in the analysis, which complicated making 
comparisons of exposure across populations of concern. This issue was 
described in the EJ analysis at proposal, and the EPA solicited comment 
on alternative methods for defining affected population groups.
    Additionally, after considering public comments, the EPA has also 
updated its EJ analysis conducted in SafeWater MCBC to include an 
assessment of the distribution of benefits and costs anticipated to 
result from the final rule across income groups. Findings from the 
EPA's EJ analysis conducted in SafeWater MCBC for the final rule 
reaffirm the conclusions of the assessment of the distribution of 
benefits and costs conducted for the proposed rule across demographic 
groups. Across all health endpoints evaluated by the EPA, communities 
of color (i.e., Hispanic, non-Hispanic Black, and/or Other race/
ethnicity groups) are anticipated to experience the greatest reductions 
in adverse health effects associated with PFAS exposure, resulting in 
the greatest quantified benefits associated with the final rule. For 
instance, non-Hispanic Black populations are expected to experience 
7.48 avoided non-fatal ischemic stroke (IS) cases and 3.90 avoided 
cardiovascular disease (CVD) deaths per 100,000 people per year, as 
compared to 3.78 avoided non-fatal IS cases and 1.26 avoided CVD deaths 
per 100,000 people per year for non-Hispanic White populations. 
Additionally, under the final rule, while in most cases the difference 
in cases of illnesses and deaths avoided across income groups is small, 
quantified health benefits are higher for low-income communities (i.e., 
populations with income below twice the poverty level) across all 
health endpoints evaluated, compared to populations with income above 
twice the poverty level.
    As found in its analysis for the rule proposal, when examining 
costs anticipated to result from the final rule, the EPA found that 
cost differences across both race/ethnicity and income groups are 
typically small, with no clear unidirectional trend in cost differences 
based on demographic group. In some cases, the EPA found that 
communities of color and low-income communities are anticipated to bear 
minimally increased costs but in other cases, costs to communities of 
color and low-income communities are anticipated to be lower than those 
across all race/ethnicity groups or populations with income above twice 
the poverty level, respectively. Additionally, incremental household 
costs to all race/ethnicity and income groups generally decrease as 
system size increases, which is expected due to economies of scale. 
This is especially true if systems serving these communities are 
required to install treatment to comply with the final rule. For 
example, systems serving 3,300 to 10,000 people that will be required 
to install treatment to comply with the

[[Page 32729]]

final rule have substantially higher costs than systems in all larger 
size categories, irrespective of demographic group. To alleviate 
potential cost disparities identified by the EPA's analysis, there may 
be an opportunity for many communities to utilize BIL (Pub. L. 117-58) 
funding to provide financial assistance for addressing emerging 
contaminants. BIL funding has specific allocations for both 
disadvantaged and/or small communities and emerging contaminants, 
including PFAS.
    The information supporting this E.O. 12898 review is contained in 
chapter 8 of USEPA (2024g) and appendix M of USEPA (2024e) and is 
available in the public docket for this action. This documentation 
includes additional detail on the methodology, results, and conclusions 
of the EPA's EJ analysis.

K. Consultations With the Science Advisory Board, National Drinking 
Water Advisory Council, and the Secretary of Health and Human Services

    In accordance with sections 1412(d) and 1412(e) of the SDWA, the 
agency consulted with the National Drinking Water Advisory Council 
(NDWAC, or the Council); the Secretary of U.S. Department of Health and 
Human Services (HHS); and with the EPA Science Advisory Board (SAB).
1. Science Advisory Board
    The SAB PFAS Review Panel met virtually via a video meeting 
platform on December 16, 2021, and then at three (3) subsequent 
meetings on January 4, 6, and 7, 2022, to deliberate on the agency's 
charge questions. Another virtual meeting was held on May 3, 2022, to 
discuss their draft report. Oral and written public comments were 
considered throughout the advisory process. The EPA sought guidance 
from the SAB on how best to consider and interpret life stage 
information, epidemiological and biomonitoring data, the agency's 
physiologically based pharmacokinetic (PBPK) analyses, and the totality 
of PFAS health information to derive an MCLG for PFOA and PFOS, 
combined toxicity framework, and CVD. The documents sent to SAB were 
the EPA's Proposed Approaches to the Derivation of a Draft Maximum 
Contaminant Level Goal for Perfluorooctanoic Acid (PFOA) (CASRN 335-67-
1) in Drinking Water (USEPA, 2021i); the EPA's Proposed Approaches to 
the Derivation of a Draft Maximum Contaminant Level Goal for 
Perfluorooctane Sulfonic Acid (PFOS) (CASRN 1763-23-1) in Drinking 
Water (USEPA, 2021j); the EPA's Draft Framework for Estimating 
Noncancer Health Risks Associated with Mixtures of Per- and 
Polyfluoroalkyl Substances (PFAS) (USEPA, 2021e); and the EPA's 
Analysis of Cardiovascular Disease Risk Reduction as a Result of 
Reduced PFOA and PFOS Exposure in Drinking Water. On May 3 and July 20, 
2022, the EPA received input from SAB, summarized in the report Review 
of EPA's Analyses to Support EPA's National Primary Drinking Water 
Rulemaking for PFAS (USEPA, 2022i).
    In response to the EPA's request that the SAB review the EPA's four 
draft documents listed above, the SAB identified subject matter experts 
to augment the SAB Chemical Assessment Advisory Committee (CAAC) and 
assembled the SAB PFAS Review Panel to conduct the review.
    In general, the SAB recognized the time constraints for completing 
the rulemaking process and was supportive of the EPA's efforts to the 
utilize the latest scientific finding to inform their decisions. The 
SAB applauded the agency's efforts to develop new approaches for 
assessing the risk of PFAS mixtures and the benefits arising from 
reducing exposure to these chemicals as adopted by the EPA in the 
Hazard Index approach in this rule. In general, the SAB agreed with 
many of the conclusions presented in the assessments, framework, and 
analysis. The SAB also identified many areas that would benefit from 
further clarification to enhance their transparency and increase their 
utility. The SAB provided numerous recommendations which can be found 
in the SAB's final report (USEPA, 2022i) and some highlights are 
outlined in the following section.
a. Approaches to the Derivation of Draft MCLGs for PFOA and PFOS
    The primary purpose of the Proposed Approaches to the Derivation of 
Draft MCLGs for PFOA and PFOS (USEPA, 2021i; USEPA, 2021j) was to 
develop Maximum Contaminant Level Goals (MCLGs) based on the best 
available health effects information for PFOA and PFOS. Each MCLG draft 
document includes derivation of an updated chronic oral reference dose 
(RfD), cancer slope factor (CSF) when relevant data were available, and 
a relative source contribution (RSC) for SAB review. The health effects 
information used to derive these toxicity values and RSC values built 
upon the information in the 2016 EPA PFOA and PFOS Health Effects 
Support Documents (HESDs; USEPA, 2016c; USEPA, 2016d). The EPA has 
considered all SAB consensus advice in the development of the final 
values derived in this health effects assessment and subsequently 
derived MCLGs for the NPDWRs for PFOA and PFOS based on the best 
available science and the EPA guidance and precedent. Please see 
section IV of this preamble for discussions on the process for 
derivation of the MCLGs and the resulting proposed MCLG values for this 
final action.
    The SAB charge questions for the MCLG draft documents addressed the 
systematic review study identification and inclusion, non-cancer hazard 
identification, cancer hazard identification and slope factor, 
toxicokinetic (TK) modeling, RfD derivation, and RSC. The complete list 
of charge questions was included in the EPA's documents prepared for 
the SAB (USEPA, 2022i). The SAB provided numerous specific 
recommendations to consider alternative approaches, expand the 
systematic review steps for the health effects assessment, and to 
develop additional analyses in order to improve the rigor and 
transparency of the EPA's documents. The complete list of SAB consensus 
advice is described in their final report (USEPA, 2022i).
    Regarding the approaches to deriving MCLG draft documents, the SAB 
stated that the systematic review methods could be more transparent and 
complete. Specifically, study identification and criteria for inclusion 
could be improved. The EPA made revisions to the systematic review 
description and process by updating and expanding the scope of the 
literature search; providing greater transparency regarding the study 
inclusion criteria; and adding additional systematic review steps and 
transparently describing each of these steps in the PFOA and PFOS 
systematic review protocols.
    In the charge questions, the EPA sought advice on the noncancer 
health assessment, and the SAB recommended that the EPA separate hazard 
and dose-response assessment systematic review steps. In response, the 
EPA made revisions to the noncancer hazard identification by expanding 
systematic review steps beyond study quality evaluation to include 
evidence integration to address the need to separate hazard 
identification and dose-response assessment and to ensure consistent 
hazard decisions; and strengthening rationales for selection of points 
of departure for the noncancer health outcomes. Additionally, the SAB 
advised the EPA to focus on the health endpoints with the strongest 
evidence (i.e., liver, immune, serum lipids, development, and cancer).
    The EPA consulted with the SAB on the cancer risk assessment. On 
the cancer Hazard Index and CSF, the SAB agreed that PFOA was a 
``likely''

[[Page 32730]]

designation but recommended undertaking and describing a more 
structured and transparent discussion of the ``weight of evidence'' for 
both PFOA and PFOS. The EPA revised this assessment by following the 
structured approach in the EPA cancer guidelines (USEPA, 2005a) to 
develop a weight of evidence narrative for cancer, to consider the data 
for selecting the cancer classification, evaluating and integrating 
mechanistic information, and strengthening the rationales for 
decisions.
    With respect to the TK model for which the EPA sought advice, SAB 
requested more details on the TK modeling including model code and 
parameters and recommended that the EPA consider expressing the RfD in 
water concentration equivalents to better account for possible life-
stage specific differences in exposure rates and TKs. The EPA 
considered the alternate approach suggested by SAB and made revisions 
by evaluating alternative TK models and further validating the selected 
model.
    The EPA also sought advice on the draft RfD derivation. The SAB 
advised that the EPA consider multiple human and animal studies for a 
variety of endpoints and populations. The SAB also stated a need for 
stronger and more transparent justification of BMR selections and asked 
the EPA to consider adopting a probabilistic framework to calculate 
risk-specific doses. SAB also recommended that the EPA clearly state 
that RfDs apply to both short-term and chronic exposure. The EPA made 
revisions based on these recommendations by providing additional 
descriptions and rationale for the selected modeling approaches and 
conducting new dose-response analyses of additional studies and 
endpoints.
    On the RSC charge question, SAB supported the selection of a 20 
percent RSC, but asked that the EPA provide clarity and rationale to 
support the value. To address this recommendation, the EPA added 
clarifying language related to the RSC determination from the EPA 
guidance (USEPA, 2000d), including the relevance of drinking water 
exposures and the relationship between the RfD and the RSC.
b. Combined Toxicity Framework
    The EPA sought advice from the SAB on the Draft Framework for 
Estimating Noncancer Health Risks Associated with Mixtures of PFAS 
document (USEPA, 2021e). The main purpose of this document was to 
provide a data-driven framework for estimating human health risks 
associated with oral exposures to mixtures of PFAS. The charge 
questions for the SAB pertaining to the framework draft documents 
included whether the EPA provided clear support for the assumption of 
dose additivity, and application of the Hazard Index, relative potency 
factor (RPF), and mixtures benchmark dose (BMD) approaches for the 
evaluation of mixtures of PFAS. The full list of charge questions was 
included in the EPA's documents prepared for the SAB (USEPA, 2022i). 
The SAB agreed in general with dose additivity at the level of common 
health effect, and application of the Hazard Index, RPF and mixture BMD 
approaches for the evaluation of mixtures of PFAS. The SAB identified 
instances in which the communication of the analyses and approaches in 
the EPA's framework document could be improved to be clearer.
    On the EPA's charge question for dose additivity, the SAB agreed 
with the use of the dose additivity assumption when evaluating PFAS 
mixtures that have similar effects and concluded that this approach was 
health protective. The SAB recommended a more thoroughly and clearly 
presented list of the uncertainties associated with dose additivity 
along with information supporting this approach. The EPA made revisions 
that added clarity to the text by expanding upon the uncertainties and 
including additional support for using dose additivity.
    The SAB panel agreed with the use of the Hazard Index as a 
screening method and decision-making tool. The SAB advised that the EPA 
should consider using a menu-based framework to support selection of 
fit-for-purpose approaches, rather than a tiered approach as described 
in the draft mixtures document. Based on this feedback, the EPA has 
since reorganized the approach to provide a data-driven ``menu of 
options'' to remove the tiered logic flow and is adding text to clarify 
the flexibility in implementation.
    The EPA sought the SAB's opinion on the RPF approach for estimating 
health risks associated with PFAS mixtures and the SAB panel considered 
the RPF approach to be a reasonable methodology for assessing mixtures. 
On the mixture BMD, the SAB agreed that the mixture BMD approach was a 
reasonable methodology for estimating a mixture-based point of 
departure (POD). For both the RPF and mixture BMD approach, the SAB 
recommended that the EPA's approach be strengthened by the use of PODs 
from animal studies that are based on HEDs rather than administered 
doses. The SAB also requested clarification as to the similarities and 
differences among the RPF and mixture BMD approaches. The SAB also 
asked the EPA to provide additional information on how the proposed 
mixtures BMD approach would be applied in practice. To address these 
recommendations, the EPA made revisions to provide better context and 
delineation about the applicability of the data across these 
approaches.
c. Cardiovascular Disease Analysis
    The EPA consulted with the SAB on the agency's methodology to 
determine the avoided cases of CVD events (e.g., heart attack, stroke, 
death from coronary heart disease) associated with reductions in 
exposure to PFOA and PFOS in drinking water to support a benefits 
analysis. Specifically, the EPA sought SAB comment on the extent to 
which the approach to estimating reductions in CVD risk is 
scientifically supported and clearly described. The EPA posed specific 
charge questions on the exposure-response information used in the 
analysis, the risk model and approach used to estimate the avoided 
cases of CVD events, and the EPA's discussion of limitations and 
uncertainties of the analysis. Overall, the SAB supported the EPA's 
approach to estimating reductions in CVD risk associated with 
reductions in exposure to PFOA and PFOS in drinking water. The SAB 
provided feedback on several areas of the analysis; main points of 
their feedback and the EPA's responses are discussed in this section.
    The SAB noted a discrepancy between the draft CVD document's focus 
on CVD risk, and the draft MCLG documents' conclusions that the 
evidence of CVD was not sufficient to form the basis of a RfD. Based on 
SAB feedback on the draft MCLG document's assessment of CVD related 
risks, the EPA has developed an RfD for total cholesterol (TC). (For 
more information see USEPA, 2024c; USEPA, 2024d.) The derivation of an 
RfD for this endpoint addresses the SAB's concerns about inconsistency 
between the two documents. The SAB also recommended that the EPA ensure 
that recommendations for the draft MCLG documents relating to evidence 
identification and synthesis are applied to the CVD endpoint. All 
studies in the EPA's CVD benefits analysis were evaluated for risk of 
bias, selective reporting, and sensitivity as applied in the EPA's 
Public Comment Draft--Toxicity Assessment and Proposed MCLGs for PFOA 
and PFOS in Drinking Water (USEPA, 2023g; USEPA, 2023h).
    The SAB recommended that the EPA provide more discussion as to the 
rationale for selecting CVD for risk reduction analysis and that the

[[Page 32731]]

approach follows the pathway that links cholesterol to cardiovascular 
events rather than looking at the reported effects of PFAS directly on 
CVD. The SAB also recommended that the EPA consider risk reduction 
analyses for other endpoints. In section 6.5 of the EA, the EPA 
discusses the rationale for quantifying CVD and analytical assumptions. 
Sections 6.4 and 6.6 discusses the agency's quantified risk reduction 
analyses for other adverse health effects, including infant birthweight 
effects and renal cell carcinoma (RCC), respectively. In section 6.2.2, 
the EPA assesses the qualitative benefits of other adverse health 
effects of PFAS.
    Although the SAB generally agreed with the meta-analysis, life 
table and risk estimation methods, the SAB recommended that the EPA 
provide additional clarity as to the application of these approaches 
and conduct additional sensitivity analyses. In response to these 
comments, the EPA expanded documentation and conducted additional 
sensitivity analyses to evaluate the impact of inclusion or exclusion 
of certain studies in the meta-analyses of exposure-response estimates. 
Further, the EPA expanded documentation and conducted additional 
sensitivity analyses to assess the effects of using a key single study 
approach versus the meta-analysis approach to inform the exposure-
response estimates. The EPA identified two suitable key studies for use 
in the single study approach. The EPA found that the single study 
approach resulted in increased benefits, and this trend was driven by 
the larger estimates of PFAS-TC slope factors and inverse associations 
in the high-density lipoprotein cholesterol (HDLC) effect for one or 
both contaminants in the key single studies. The EPA elected to retain 
the meta-analysis approach in the benefits analysis because the agency 
identified several studies on adults in the general population with 
large numbers of participants and low risk of bias, and in this case 
the meta-analytical approach offers an increased statistical power over 
the single study approach. While the single study approach is common 
for RfD derivations, the meta-analysis pooled estimate provides a slope 
factor that represents the average response across a larger number of 
studies, which is useful in evaluating benefits resulting from changes 
in CVD risk on a national scale.
    The SAB also recommended that the EPA evaluate how inclusion of 
HDLC effects would influence the results and provide further 
justification for the inclusion or exclusion of HDLC and blood pressure 
effects. The EPA found that, as expected, inclusion of HDLC effects 
decreases annualized CVD benefits and inclusion of blood pressure 
effects slightly increases annualized CVD benefits. Because HDLC was 
shown to have a stronger effect than blood pressure on annualized CVD 
benefits, inclusion of blood pressure and HDLC effects together 
decreases annualized CVD benefits. For more information see sensitivity 
analyses evaluating these effects in appendix K of the EA. Inclusion of 
HDLC effects into the national analysis would reduce national benefits 
estimates but would not change the EPA's bottom-line conclusion that 
the quantifiable and nonquantifiable benefits of the rule justify the 
quantifiable and nonquantifiable costs. After further examination of 
the evidence for HDLC and blood pressure effects, the EPA elected to 
include blood pressure effects because the findings from a single high 
confidence study and several medium confidence studies conducted among 
the general population provided consistent evidence of an association 
between PFOS exposure and blood pressure. The EPA did not include HDLC 
effects in the national benefits analysis because available evidence of 
associations between PFOS exposures and HDLC levels is inconsistent and 
there is no evidence of an association between PFOA exposures and HDLC 
levels.
    Finally, the SAB noted that while the Atherosclerotic 
Cardiovascular Disease (ASCVD) model is a reasonable choice for 
estimating the probability of first time CVD events, it is not without 
limitations. The panel recommended that the EPA include more discussion 
of the accuracy of its predictions, particularly for sub-populations. 
The EPA expanded its evaluation of the ASCVD model's limitations, 
including a comparison of the ASCVD model predictions with race/
ethnicity and sex-specific CVD incidence from Centers for Disease 
Control and Prevention's (CDC's) public health surveys (See section 
6.5.3.2 and appendix G of the EA for details). Results show that the 
ASCVD model coefficients for the non-Hispanic Black model are more 
consistent with data on CVD prevalence and mortality for Hispanic and 
non-Hispanic other race subpopulations than the ASCVD model 
coefficients for the non-Hispanic White model.
    Comments on the SAB consultation and review were raised by public 
commenters. As a result, the comments have been addressed by the EPA in 
the final rule, supporting documents in the record, and throughout this 
preamble, specifically in sections III.B, IV, and XII.A.
2. National Drinking Water Advisory Council (NDWAC)
    The agency consulted with the NDWAC prior to the rule proposal 
during the Council's April 19, 2022, virtual meeting. During the 
meeting, the EPA provided information related to the development of the 
proposed rule. A summary of the NDWAC input from that meeting is 
available in the NDWAC, Fall 2022 Meeting Summary Report (NDWAC, 2022) 
and the docket.
    On August 8, 2023, the EPA consulted with the NDWAC prior to the 
final rule during a virtual meeting where the EPA presented on the 
proposed PFAS NPDWR, including the proposed MCLs, monitoring and PN 
requirements, and treatment and economic considerations. The EPA 
reiterated that the PFAS NPDWR was developed with extensive 
consultation from state, local and Tribal partners to identify avenues 
that would reduce PFAS in drinking water and reaffirmed its commitment 
to working with these partners on rule implementation. The EPA 
carefully considered the information provided by the NDWAC during the 
development of a final PFAS NPDWR. A summary of the NDWAC input from 
that meeting is available in the NDWAC Summary Report (NDWAC, 2023) and 
the docket.
3. Department of Health and Human Service
    On September 28, 2022, the EPA consulted with the Department of HHS 
on the proposed PFAS NPDWR. On November 2, 2023, the EPA consulted with 
the HHS on the final rule. The EPA received and considered comments 
from the HHS for both the proposed and final rules through the 
interagency review process described in section XIII.A.

L. Congressional Review Act (CRA)

    This action is subject to the CRA, and the EPA will submit a rule 
report to each House of the Congress and to the Comptroller General of 
the United States. This action meets the criteria set forth in 5 
U.S.C.804(2).

XIV. Severability

    The purpose of this section is to clarify the EPA's intent with 
respect to the severability of provisions of this rule. Each Maximum 
Contaminant Level (MCL) is independent of the others and can be 
implemented on its own. For that reason, if any individual or Hazard 
Index MCL is determined by judicial review or operation of law to be 
invalid, the EPA intends that the partial invalidation will not render 
any other

[[Page 32732]]

MCL invalid. In addition, each per- and polyfluoroalkyl substance 
(PFAS) included in the Hazard Index is independent from any other PFAS 
included in the Hazard Index. As a result, if any PFAS regulation is 
determined by judicial review or operation of law to be invalid, that 
partial invalidation should not render any other PFAS regulation 
included in the Hazard Index or the Hazard Index PFAS MCL invalid. 
Moreover, the Hazard Index approach and Hazard Index PFAS MCL can 
remain operable and applicable so long as there are at least two 
contaminants subject to the Hazard Index as a mixture because the EPA's 
definition of mixture in this final rule is of two or more of the 
Hazard Index PFAS. In addition, each individual Maximum Contaminant 
Level Goal (MCLG) is independent of each of the other MCLGs and, 
because they perform different functions under the Act, of each of the 
MCLs. As a result, if an MCL is determined to be invalid, that partial 
invalidation should not render the associated MCLG invalid. The 
monitoring requirements are independent and capable of operating 
without any MCLs. Likewise, if any provision of this rule other than 
the MCLGs, or MCLs, is determined to be invalid (such as monitoring 
waivers or the capital improvements extension), the remainder of the 
rule can still be sensibly implemented; as a result, the EPA intends 
that the rest of the rule (such as monitoring requirements) remain 
operable and applicable.

XV. Incorporation by Reference

    In this action, the EPA requires that systems must only use the 
analytical methods specified to demonstrate compliance with the rule. 
EPA Method 533: Determination of Per- and Polyfluoroalkyl Substances in 
Drinking Water by Isotope Dilution Anion Exchange Solid Phase 
Extraction and Liquid Chromatography/Tandem Mass Spectrometry, November 
2019, 815-B-19-020, and EPA Method 537.1,Version 2.0: Determination of 
Selected Per- and Polyfluorinated Alkyl Substances in Drinking Water by 
Solid Phase Extraction and Liquid Chromatography/Tandem Mass 
Spectrometry (LC/MS/MS), March 2020, EPA/600/R-20/006, are incorporated 
by reference in this final rule and are publicly available in the EPA's 
Docket ID No. EPA-HQ-OW-2022-0114. The EPA Method 533 and EPA Method 
537.1, Version 2.0 are solid phase extraction liquid chromatography-
tandem mass spectrometry methods for the detection and determination of 
select per-and polyfluoroalkyl substances in drinking water. In 
addition to being available in the aforementioned rule docket, both 
methods can be accessed online at https://www.epa.gov/pfas/epa-pfas-drinking-water-laboratory-methods.

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USEPA. 2012. Benchmark Dose Technical Guidance. EPA/100/R-12/001. 
June 2012. Available on the internet at: https://www.epa.gov/sites/default/files/2015-01/documents/benchmark_dose_guidance.pdf.
USEPA. 2014a. Protocol for the Regulatory Determinations 3. 
Including Appendices A-F. April 2014. EPA 815-R-14-005. Available on 
the internet at: https://www.regulations.gov/document/EPA-HQ-OW-2012-0217-0086.
USEPA. 2014b. Framework for Human Health Risk Assessment to Inform 
Decision Making. EPA 100-R-14-001. April 2014. Washington, DC: U.S. 
Environmental Protection Agency, Office of the Science Advisor, Risk 
Assessment Forum.
USEPA. 2016a. Drinking Water Contaminant Candidate List 4-Final. 
Federal Register. 81 FR 81099. November 17, 2016.
USEPA. 2016b. Six-Year Review 3--Health Effects Assessment for 
Existing Chemical and Radionuclide National Primary Drinking Water 
Regulations--Summary Report. EPA 822-R-16-008. Available on the 
internet at: https://www.epa.gov/sites/default/files/2016-12/documents/822r16008.pdf.
USEPA. 2016c. Health Effects Support Document for Perfluorooctanoic 
Acid (PFOA). EPA 822-R-16-003. Available on the internet at: https://www.epa.gov/sites/default/files/2016-05/documents/pfoa_hesd_final-plain.pdf.
USEPA. 2016d. Health Effects Support Document for Perfluorooctane 
Sulfonate (PFOS). EPA 822-R-16-002. Available on the internet at: 
https://www.epa.gov/sites/default/files/2016-05/documents/pfos_hesd_final_508.pdf.
USEPA. 2016e. Guidelines for Preparing Economic Analyses. Available 
on the internet at: https://www.epa.gov/sites/default/files/2017-08/documents/ee-0568-50.pdf.
USEPA. 2016f. Technical Guidance for Assessing Environmental Justice 
in Regulatory Analysis. Available on the internet at: https://www.epa.gov/sites/production/files/2016-06/documents/ejtg_5_6_16_v5.1.pdf.
USEPA. 2017. Third Unregulated Contaminant Monitoring Rule: 
Occurrence Data. Available on the internet at: https://www.epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule#3.
USEPA. 2018a. Basic Information on PFAS. Available on the internet 
at: https://19january2021snapshot.epa.gov/pfas/basic-information-pfas_.html.
USEPA. 2018b. Response to Peer Review Comments on the Draft Human 
Health Toxicity Values for Hexafluoropropylene Oxide (HFPO) Dimer 
Acid and Its Ammonium Salt (CASRN 13252-13-6 and CASRN 62037-80-3) 
Also Known as ``GenX Chemicals.'' EPA 823-R-18-003. November 2018. 
Available on the internet at: https://www.epa.gov/sites/default/files/2018-11/documents/genx_epa_response_to_peer_review_comments_nov2018-508.pdf.
USEPA 2018c. Region 4 Human Health Risk Assessment Supplemental 
Guidance. Scientific Support Section, Superfund Division, EPA Region 
4. March 2018 Update. Available on the internet at: https://www.epa.gov/sites/default/files/2018-03/documents/hhra_regional_supplemental_guidance_report-march-2018_update.pdf.
USEPA. 2018c. Region 4 Human Health Risk Assessment Supplemental 
Guidance. March 2018 Update. Available on the internet at: https://www.epa.gov/sites/default/files/2018-03/documents/hhra_regional_supplemental_guidance_report-march-2018_update.pdf.
USEPA. 2019a. Update for Chapter 3 of the Exposure Factors Handbook: 
Ingestion of Water and Other Select Liquids. EPA 600-R-18-259F. 
Available on the internet at: https://www.epa.gov/sites/default/files/2019-02/documents/efh_-_chapter_3_update.pdf.

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USEPA. 2019b. Method 533: Determination of Per- and Polyfluoroalkyl 
Substances in Drinking Water by Isotope Dilution Anion Exchange 
Solid Phase Extraction and Liquid Chromatography/Tandem Mass 
Spectrometry. EPA 815-B-19-020. Available on the internet at: 
https://www.epa.gov/sites/default/files/2019-12/documents/method-533-815b19020.pdf.
USEPA. 2019c. Health Risk Reduction and Cost Analysis of the 
Proposed Perchlorate National Primary Drinking Water Regulation. EPA 
816-R-19-004.
USEPA. 2019d. Supplemental Environmental Assessment for Proposed 
Revisions to Effluent Limitations Guidelines and Standards for the 
Steam Electric Power Generating Point Source Category (EA).
USEPA. 2019e. EJSCREEN Technical Documentation. Available on the 
internet at: https://www.epa.gov/sites/default/files/2021-04/documents/ejscreen_technical_document.pdf.
USEPA. 2020a. Announcement of Preliminary Regulatory Determinations 
for Contaminants on the Fourth Drinking Water Contaminant Candidate 
List. Federal Register. 85 FR 14098, March 10, 2020.
USEPA. 2020b. UCMR 5 Laboratory Approval Manual Version 2.0. 
December 2021. EPA 815-B-21-010. Available on the internet at: 
https://www.regulations.gov/document/EPA-HQ-OW-2020-0530-0129.
USEPA. 2020c. Determination of Selected Per- and Polyfluorinated 
Alkyl Substances in Drinking Water by Solid Phase Extraction and 
Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS). EPA 600-
R-20-006, Version 2.0, March 2020. Available on the internet at: 
https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=NERL&dirEntryId=348508.
USEPA. 2020d. Interim Guidance on the Destruction and Disposal of 
Perfluoroalkyl and Polyfluoroalkyl Substances and Materials 
Containing Perfluoroalkyl and Polyfluoroalkyl Substances. EPA-HQ-
OLEM-2020-0527-0002. Available on the internet at: https://www.epa.gov/system/files/documents/2021-11/epa-hq-olem-2020-0527-0002_content.pdf.
USEPA. 2020e. Labor Costs for National Drinking Water Rules. Report 
prepared for EPA under Contract # EP-B16C-0001.
USEPA. 2020f. Economic Analysis for the Final Lead and Copper Rule 
Revisions. EPA 816-R-20-008.
USEPA. 2021a. Human Health Toxicity Values for Perfluorobutane 
Sulfonic Acid (CASRN 375-73-5) and Related Compound Potassium 
Perfluorobutane Sulfonate (CASRN 29420-49-3). EPA/600/R-20/345F. 
Available on the internet at: https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=350888.
USEPA. 2021b. Human Health Toxicity Values for Hexafluoropropylene 
Oxide (HFPO) Dimer Acid and Its Ammonium Salt (CASRN 13252-13-6 and 
CASRN 62037-80-3). Also Known as ``GenX Chemicals.'' EPA/822/R-21/
010. Available on the internet at: https://www.epa.gov/system/files/documents/2021-10/genx-chemicals-toxicity-assessment_tech-edited_oct-21-508.pdf.
USEPA. 2021c. Assessing and Managing Chemicals under TSCA: Fact 
Sheet PFOA Stewardship Program. Available on the internet at: 
https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/fact-sheet-20102015-pfoa-stewardship-program.
USEPA. 2021d. Announcement of Final Regulatory Determinations for 
Contaminants on the Fourth Drinking Water Contaminant Candidate 
List. Federal Register. 86 FR 12272, March 3, 2021.
USEPA. 2021e. Draft Framework for Estimating Noncancer Health Risks 
Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS). EPA-822-D-21-003. Available on the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:10311539418988:::18:P18_ID:2601.
USEPA. 2021f. Response To Additional Focused External Peer Review of 
Draft Human Health Toxicity Values for Hexafluoropropylene Oxide 
(HFPO) Dimer Acid and Its Ammonium Salt (GenX Chemicals). Available 
on the internet at: https://www.epa.gov/system/files/documents/2021-10/epa_2nd-response-to-peer-review_genx_508.pdf.
USEPA. 2021g. EPA Response to Public Comments on Draft Human Health 
Toxicity Values for Hexafluoropropylene Oxide (HFPO) Dimer Acid and 
Its Ammonium Salt (CASRN 13252-13-6 and CASRN 62037-80-3) Also Known 
as ``GenX Chemicals''. EPA 822R-21-008. October 2021. Available on 
the internet at: https://www.epa.gov/system/files/documents/2021-10/final-genx-assessment-resp-to-public-comments_508.pdf.
USEPA. 2021h. Systematic Review Protocol for the PFAS IRIS 
Assessments. EPA/635/R-19/050, 2019. Available on the internet at: 
https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=345065#tab-3.
USEPA. 2021i. Proposed Approaches to the Derivation of a Draft 
Maximum Contaminant Level Goal for Perfluorooctanoic Acid (PFOA) 
(CASRN 335-67-1) in Drinking Water. EPA 822-D-21-001. Available on 
the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:16490947993:::RP,18:P18_ID:2601.
USEPA. 2021j. Proposed Approaches to the Derivation of a Draft 
Maximum Contaminant Level Goal for Perfluorooctane Sulfonic Acid 
(PFOS) (CASRN 1763-23-1) in Drinking Water. EPA 822-D-21-002. 
Available on the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:16490947993:::RP,18:P18_ID:2601.
USEPA. 2021k. Analysis of Cardiovascular Disease Risk Reduction as a 
Result of Reduced PFOA and PFOS Exposure in Drinking Water. EPA 815-
D-21-001. Available on the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:16490947993:::RP,18:P18_ID:2601.
USEPA. 2022a. Changes to Reporting Requirements for Per- and 
Polyfluoroalkyl Substances and to Supplier Notifications for 
Chemicals of Special Concern; Community Right-to-Know Toxic Chemical 
Release Reporting. Federal Register. 87 FR 74379, December 5, 2022.
USEPA. 2022b. Drinking Water Contaminant Candidate List 5--Final. 
Federal Register. 87 FR 68060, November 14, 2022.
USEPA. 2022c. PFAS Strategic Roadmap: EPA's Commitments to Action 
2021-2024. Available on the internet at: https://www.epa.gov/pfas/pfas-strategic-roadmap-epas-commitments-action-2021-2024.
USEPA. 2022d. Addressing PFAS discharges in EPA-issued NPDES permits 
and expectations where EPA is the pretreatment control authority 
(April 28, 2022). https://www.epa.gov/system/files/documents/2022-04/npdes_pfas-memo.pdf.
USEPA. 2022e. Addressing PFAS discharges in NPDES permits and 
through the pretreatment program and monitoring programs (December 
5, 2022). https://www.epa.gov/system/files/documents/2022-12/NPDES_PFAS_State%20Memo_December_2022.pdf.
USEPA. 2022f. ORD Staff Handbook for Developing IRIS Assessments. 
EPA 600/R-22/268. Available on the internet at: https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=356370.
USEPA. 2022g. IRIS Toxicological Review of Perfluorobutanoic Acid 
(PFBA) and Related Salts (Final Report, 2022). EPA/635/R-22/277F. 
Retrieved from https://www.epa.gov/chemical-research/iris-toxicological-review-perfluorobutanoic-acid-pfba-and-related-salts-final.
USEPA. 2022h. Letter is in response to the Request for Correction 
(RFC) received by the USEPA from Arnold & Porter Kaye Scholer LLP 
(A&P) on March 18, 2022. Available on the internet at: https://www.epa.gov/system/files/documents/2022-06/RFC_22001_Response_June2022.pdf.
USEPA. 2022i. Transmittal of the Science Advisory Board Report 
titled, ``Review of EPA's Analyses to Support EPA's National Primary 
Drinking Water Rulemaking for PFAS.'' EPA-22-008. Available on the 
internet at: https://sab.epa.gov/ords/sab/f?p=114:12:15255596377846.
USEPA. 20222j. Fifth Unregulated Contaminant Monitoring Rule. 
Available on the internet at: https://www.epa.gov/dwucmr/fifth-unregulated-contaminant-monitoring-rule.
USEPA. 2022k. MRL Data of UCMR 5 Approved Labs.
USEPA. 2022l. Comprehensive Environmental Response, Compensation, 
and Liability Act Hazardous Substances: Designation of 
Perfluorooctanoic Acid and Perfluorooctanesulfonic Acid. EPA-HQ-
OLEM-2019-0341-0001. Washington, DC. Retrieved from https://

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www.regulations.gov/document/EPA-HQ-OLEM-2019-0341-0001.
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Wastes and Recycling (updated: December 3, 2022). https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/national-overview-facts-and-figures-materials.
USEPA. 2023a. Emerging Contaminants (EC) in Small or Disadvantaged 
Communities Grant (SDC). Available on the internet at: https://www.epa.gov/dwcapacity/emerging-contaminants-ec-small-or-disadvantaged-communities-grant-sdc.
USEPA. 2023b. Water Technical Assistance (WaterTA). Available on the 
internet at: https://www.epa.gov/water-infrastructure/water-technical-assistance-waterta.
USEPA. 2023c. Advances in Dose Addition for Chemical Mixtures: A 
White Paper. U.S. Environmental Protection Agency, Washington, DC. 
EPA/100/R23/001.
USEPA. 2023d. IRIS Toxicological Review of Perfluorohexanesulfonic 
Acid (PFHxS) and Related Salts (Public Comment and External Review 
Draft). EPA/635/R-23/056. Washington, DC.
USEPA. 2023e. Public Comment Draft--Maximum Contaminant Level Goal 
(MCLG) Summary Document for a Mixture of Four Per- and 
Polyfluoroalkyl Substances (PFAS): GenX Chemicals, PFBS, PFNA and 
PFHxS. EPA-822-P-23-004.
USEPA. 2023f. PFAS National Primary Drinking Water Regulation 
Rulemaking. Federal Register. 88 FR 18638. March 29, 2023.
USEPA. 2023g. Public Comment Draft--Toxicity Assessment and Proposed 
Maximum Contaminant Level Goal (MCLG) for Perfluorooctanoic Acid 
(PFOA) (CASRN 335-67-1) in Drinking Water. EPA-822-P-23-005.
USEPA. 2023h. Public Comment Draft--Toxicity Assessment and Proposed 
Maximum Contaminant Level Goal (MCLG) for Perfluorooctane Sulfonic 
Acid (PFOS) (CASRN 1763-23-1) in Drinking Water. EPA-822-P-23-007.
USEPA. 2023i. Public Comment Draft--Appendix: Proposed Maximum 
Contaminant Level Goal for Perfluorooctanoic Acid (PFOA) (CASRN 335-
67-1) in Drinking Water.
USEPA. 2023j. Public Comment Draft--Appendix: Proposed Maximum 
Contaminant Level Goal for Perfluorooctane Sulfonic Acid (PFOS) 
(CASRN 1763-23-1) in Drinking Water.
USEPA. 2023k. EPA Response to Final Science Advisory Board 
Recommendations (August 2022) on Four Draft Support Documents for 
the EPA's Proposed PFAS National Primary Drinking Water Regulation. 
EPA-822-D-23-001.
USEPA. 2023l. PFAS Occurrence and Contaminant Background Support 
Document. EPA-822-P-23-010.
USEPA. 2023m. EPA Response to Letter of Peer Review for Disinfectant 
Byproduct Reduction as a Result of Granular Activated Carbon 
Treatment for PFOA and PFOS in Drinking Water: Benefits Analysis 
Related to Bladder Cancer. EPA-815-B23-001.
USEPA. 2023n. Economic Analysis of the Proposed National Primary 
Drinking Water Regulation for Per- and Polyfluoroalkyl Substances. 
EPA-822-P-23-001.
USEPA. 2023o. Appendix: Economic Analysis of the Proposed National 
Primary Drinking Water Regulation for Per- and Polyfluoroalkyl 
Substances. EPA-822-P-23-002.
USEPA. 2023p. IRIS Toxicological Review of Perfluorohexanoic Acid 
[PFHxA, CASRN 307-24-4] and Related Salts (EPA/635/R-23/027Fa). 
Retrieved from https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0704tr.pdf.
USEPA. 2023q. Federal ``Good Neighbor Plan'' for the 2015 Ozone 
National Ambient Air Quality Standards. Federal Register. 88 FR 
36654. June 5, 2023.
USEPA. 2023r. New Source Performance Standards for Greenhouse Gas 
Emissions From New, Modified, and Reconstructed Fossil Fuel-Fired 
Electric Generating Units; Emission Guidelines for Greenhouse Gas 
Emissions From Existing Fossil Fuel-Fired Electric Generating Units; 
and Repeal of the Affordable Clean Energy Rule. Federal Register. 88 
FR 33240. May 23, 2023.
USEPA. 2023s. Regulatory Impact Analysis of the Standards of 
Performance for New, Reconstructed, and Modified Sources and 
Emissions Guidelines for Existing Sources: Oil and Natural Gas 
Sector Climate Review. EPA-452/R-23-013.
USEPA. 2023t. Supplementary Material for the Regulatory Impact 
Analysis for the Final Rulemaking, ``Standards of Performance for 
New, Reconstructed, and Modified Sources and Emissions Guidelines 
for Existing Sources: Oil and Natural Gas Sector Climate Review''; 
EPA Report on the Social Cost of Greenhouse Gases: Estimates 
Incorporating Recent Scientific Advances.
USEPA. 2023u. New Source Performance Standards for the Synthetic 
Organic Chemical Manufacturing Industry and National Emission 
Standards for Hazardous Air Pollutants for the Synthetic Organic 
Chemical Manufacturing Industry and Group I & II Polymers and Resins 
Industry. Federal Register. 88 FR 25080. April 25, 2023.
USEPA. 2023v. Executive Order 14096--Revitalizing Our Nation's 
Commitment to Environmental Justice for All. Federal Register. 88 FR 
25251, April 26, 2023.
USEPA. 2023w. Framework for Estimating Noncancer Health Risks 
Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS). EPA-822-P-23-003.
USEPA. 2024a. Framework for Estimating Noncancer Health Risks 
Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS). 815-R-24-003.
USEPA. 2024b. PFAS Occurrence and Contaminant Background Support 
Document for the Final PFAS NPDWR. 815-R-24-013.
USEPA. 2024c. Office of Water Final Human Health Toxicity Assessment 
for Perfluorooctanoic Acid (PFOA). 815-R-24-006.
USEPA 2024d. Office of Water Final Human Health Toxicity Assessment 
for Perfluorooctane Sulfonic Acid (PFOS). 815-R-24-007.
USEPA. 2024e. Economic Analysis for the Final Per- and 
Polyfluoroalkyl Substances National Primary Drinking Water 
Regulation Appendices. 815-R-24-002.
USEPA 2024f. Maximum Contaminant Level Goals (MCLGs) for Three 
Individual Per- and Polyfluoroalkyl Substances (PFAS) and a Mixture 
of Four PFAS. 815-R-24-004.
USEPA. 2024g. Economic Analysis for the Final Per- and 
Polyfluoroalkyl Substances National Primary Drinking Water 
Regulation. 815-R-24-001.
USEPA. 2024h. Appendix--Office of Water Final Human Health Toxicity 
Assessment for Perfluorooctanoic Acid (PFOA). 815-R-24-008.
USEPA. 2024i. Appendix--Office of Water Final Human Health Toxicity 
Assessment for Perfluorooctane Sulfonic Acid (PFOS). 815-R-24-009.
USEPA. 2024j. OW Final Maximum Contaminant Level Goals (MCLGs) for 
Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid 
(PFOS) in Drinking Water. 815-R-24-010.
USEPA. 2024k. EPA's Responses to Public Comments on the Proposed 
PFAS National Primary Drinking Water Regulation. 815-R-24-005.
USEPA. 2024l. Best Available Technologies and Small System 
Compliance Technologies Per- and Polyfluoroalkyl Substances (PFAS) 
in Drinking Water. 815-R-24-011.
USEPA. 2024m. Technologies and Costs for Removing Per- and 
Polyfluoroalkyl Substances from Drinking Water. 815-R-24-012.
USEPA. 2024n. Fifth Unregulated Contaminant Monitoring Rule: 
Occurrence Data. Available on the internet at: https://www.epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule#5.
USEPA. 2024o. Fluoride Informational Links. Available on the 
internet at: https://tdb.epa.gov/tdb/contaminant?id=10700.
USEPA. 2024p. Work Breakdown Structure-Based Cost Model for Granular 
Activated Carbon Drinking Water Treatment.
USEPA. 2024q. Work Breakdown Structure-Based Cost Model for Ion 
Exchange Treatment of Per- and Polyfluoroalkyl Substances (PFAS) in 
Drinking Water.
USEPA. 2024r. Work Breakdown Structure-Based Cost Model for 
Nontreatment Options for Drinking Water Compliance.
United States Office of Science and Technology Policy (OSTP). 2023. 
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Joint Subcommittee on Environment, Innovation, and Public Health. 
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Zaggia, A., Conte, L., Falletti, L., Fant, M., and Chiorboli, A. 
2016. Use of strong anion exchange resins for the removal of 
perfluoroalkylated substances from contaminated drinking water in 
batch and continuous pilot plants. Water Research, 91:137-146. 
https://doi.org/10.1016/j.watres.2015.12.039.

List of Subjects

40 CFR Part 141

    Environmental protection, Incorporation by reference, Indians--
lands, Intergovernmental relations, Monitoring and analytical 
requirements, Per- and polyfluoroalkyl substances, Reporting and 
recordkeeping requirements, Water supply.

40 CFR Part 142

    Environmental protection, Administrative practice and procedure, 
Indians--lands, Intergovernmental relations, Monitoring and analytical 
requirements, Per- and polyfluoroalkyl substances, Reporting and 
recordkeeping requirements, Water supply.

Michael S. Regan,
Administrator.

    For the reasons stated in the preamble, the Environmental 
Protection Agency amends 40 CFR parts 141 and 142 as follows:

PART 141--NATIONAL PRIMARY DRINKING WATER REGULATIONS

0
1. The authority citation for part 141 continues to read as follows:

    Authority:  42 U.S.C. 300f, 300g-1, 300g-2, 300g-3, 300g-4, 
300g-5, 300g-6, 300j-4, 300j-9, and 300j-11.

0
2. Amend Sec.  141.2 by adding in alphabetical order the definitions 
for ``Hazard Index (HI)'', ``Hazard quotient (HQ)'', ``Health-based 
water concentration (HBWC)'', ``HFPO-DA or GenX chemicals'', ``PFBS'', 
``PFHxS'', ``PFNA'', ``PFOA'', and ``PFOS'' to read as follows:


Sec.  141.2  Definitions.

* * * * *
    Hazard Index (HI) is the sum of component hazard quotients (HQs), 
which are calculated by dividing the measured regulated PFAS component 
contaminant concentration in water (e.g., expressed as parts per 
trillion (ppt) or nanograms per liter (ng/l)) by the associated health-
based water concentration (HBWC) expressed in the same units as the 
measured concentration (e.g., ppt or ng/l). For PFAS, a mixture Hazard 
Index greater than 1 (unitless) is an exceedance of the MCL.
    Hazard quotient (HQ) means the ratio of the measured concentration 
in drinking water to the health-based water concentration (HBWC).
    Health-based water concentration (HBWC) means level below which 
there are no known or anticipated adverse health effects over a 
lifetime of

[[Page 32744]]

exposure, including sensitive populations and life stages, and allows 
for an adequate margin of safety.
    HFPO-DA or GenX chemicals means Chemical Abstract Service 
registration number 122499-17-6, chemical formula C6F11O3-, 
International Union of Pure and Applied Chemistry preferred name 
2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoate, along with its 
conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
* * * * *
    PFBS means Chemical Abstract Service registration number 45187-15-
3, chemical formula C4F9SO3-, perfluorobutane sulfonate, along with its 
conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
    PFHxS means Chemical Abstract Service registration number 108427-
53-8, chemical formula C6F13SO3-, perfluorohexane sulfonate, along with 
its conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
    PFNA means Chemical Abstract Service registration number 72007-68-
2, chemical formula C9F17O2-, perfluorononanoate, along with its 
conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
    PFOA means Chemical Abstract Service registration number 45285-51-
6, chemical formula C8F15O2-, perfluorooctanoate, along with its 
conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
    PFOS means Chemical Abstract Service registration number 45298-90-
6, chemical formula C8F17SO3-, perfluorooctanesulfonate, along with its 
conjugate acid and any salts, derivatives, isomers, or combinations 
thereof.
* * * * *

0
3. Amend Sec.  141.6 by revising paragraph (a) and adding paragraph (l) 
to read as follows:


Sec.  141.6  Effective dates.

    (a) Except as provided in paragraphs (b) through (l) of this 
section the regulations set forth in this part take effect on June 24, 
1977.
* * * * *
    (l) The regulations pertaining to the per- and polyfluoroalkyl 
substances (PFAS) chemicals set forth in subpart Z of this part are 
effective June 25, 2024. See Sec.  141.900 for the compliance dates for 
provisions under subpart Z. Compliance with reporting requirements 
under subpart Z, in accordance with subparts O (the consumer confidence 
rule) and Q (the public notification rule) of this part are required on 
April 26, 2027, except for notification requirements in Sec.  141.203 
related to violations of the MCLs. The compliance date for the PFAS 
MCLs in Sec.  141.61, as specified in Sec.  141.60, and for Sec.  
141.203 notifications of violations of the PFAS MCLs is April 26, 2029.

0
4. Amend Sec.  141.24 by revising paragraph (h) introductory text to 
read as follows:


Sec.  141.24  Organic chemicals, sampling and analytical requirements.

* * * * *
    (h) Analysis of the contaminants listed in Sec.  141.61(c) for the 
purposes of determining compliance with the maximum contaminant level 
shall be conducted as follows, with the exceptions that this paragraph 
(h) does not apply to regulated PFAS (see Sec.  141.902) and no 
monitoring is required for aldicarb, aldicarb sulfoxide, or aldicarb 
sulfone:
* * * * *

0
5. Amend Sec.  141.28 by revising paragraph (a) to read as follows:


Sec.  141.28  Certified laboratories.

    (a) For the purpose of determining compliance with Sec. Sec.  
141.21 through 141.27, 141.40, 141.74, 141.89, 141.402, 141.901, and 
141.902, samples may be considered only if they have been analyzed by a 
laboratory certified by EPA or the State except that measurements of 
alkalinity, disinfectant residual, orthophosphate, pH, silica, 
temperature, and turbidity may be performed by any person acceptable to 
the State.
* * * * *

0
6. Amend Sec.  141.50 by:
0
a. Adding periods at the ends of paragraphs (a)(1) through (23);
0
b. Adding paragraphs (a)(24) and (25); and
0
c. In the table to paragraph (b), revising the heading for the second 
column and adding in numerical order the entries ``(34),'' ``(35),'' 
``(36),'' and ``(37)'' and footnote 1.
    The additions and revision read as follows:


Sec.  141.50  Maximum contaminant level goals for organic contaminants.

    (a) * * *
    (24) PFOA.
    (25) PFOS.
    (b) * * *

 
                                          MCLG in mg/l (unless otherwise
              Contaminant                             noted)
 
 
                              * * * * * * *
(34) Hazard Index PFAS (HFPO-DA, PFBS,   1 (unitless).\1\
 PFHxS, and PFNA).
(35) HFPO-DA...........................  0.00001.
(36) PFHxS.............................  0.00001.
(37) PFNA..............................  0.00001.
 
\1\ The PFAS Mixture Hazard Index (HI) is the sum of component hazard
  quotients (HQs), which are calculated by dividing the measured
  component PFAS concentration in water by the corresponding
  contaminant's health-based water concentration (HBWC) when expressed
  in the same units (shown in ng/l). The HBWC for PFHxS is 10 ng/l; the
  HBWC for HFPO-DA is 10 ng/l; the HBWC for PFNA is 10 ng/l; and the
  HBWC for PFBS is 2000 ng/l. A PFAS Mixture Hazard Index greater than 1
  (unitless) indicates an exceedance of the health protective level and
  indicates potential human health risk from the PFAS mixture in
  drinking water.

Hazard Index = ([HFPO-DAwater ng/l]/[10 ng/l]) + 
([PFBSwater ng/l]/[2000 ng/l]) + ([PFNAwater ng/
l]/[10 ng/l]]) + ([PFHxSwater ng/l]/[10 ng/l])

HBWC = health-based water concentration
HQ = hazard quotient
ng/l = nanograms per liter
PFASwater = the concentration of a specific PFAS in water


0
7. Amend Sec.  141.60 by adding paragraph (a)(4) to read as follows:


Sec.  141.60  Effective dates.

    (a) * * *
    (4) The effective date for paragraphs (c)(34) through (40) of Sec.  
141.61 (listed in table 4 to paragraph (c)) is April 26, 2029.
* * * * *

0
8. Amend Sec.  141.61 by:

[[Page 32745]]

0
a. In paragraph (a), revising the introductory text and adding a table 
heading;
0
b. In paragraph (b), revising the introductory text and the table 
heading;
0
c. Revising and republishing paragraph (c); and
0
d. Adding paragraphs (d) and (e).
    The revisions and additions read as follows:


Sec.  141.61  Maximum contaminant levels for organic contaminants.

    (a) The following maximum contaminant levels for volatile organic 
contaminants apply to community and non-transient, non-community water 
systems.

    Table 1 to Paragraph (a)--Maximum Contaminant Levels for Volatile
                          Organic Contaminants
 
 

* * * * *
    (b) The Administrator, pursuant to section 1412 of the Act, hereby 
identifies as indicated in table 2 to this paragraph (b) granular 
activated carbon (GAC), packed tower aeration (PTA), or oxidation (OX) 
as the best technology, treatment technique, or other means available 
for achieving compliance with the maximum contaminant level for organic 
contaminants identified in paragraphs (a) and (c) of this section, 
except for per- and polyfluoroalkyl substances (PFAS).

Table 2 to Paragraph (b)--BAT for Organic Contaminants in Paragraphs (a)
                and (c) of This Section, Except for PFAS
 
------------------------------------------------------------------------

* * * * *
    (c) The following maximum contaminant levels (MCLs) in tables 3 and 
4 to this paragraph (c) for synthetic organic contaminants apply to 
community water systems and non-transient, non-community water systems; 
table 4 also contains health-based water concentrations (HBWCs) for 
selected per- and poly-fluoroalkyl substances (PFAS) used in 
calculating the Hazard Index.

   Table 3 to Paragraph (c)--MCLs for Synthetic Organic Contaminants,
                             Except for PFAS
------------------------------------------------------------------------
              CAS No.                    Contaminant        MCL (mg/l)
------------------------------------------------------------------------
(1) 15972-60-8....................  Alachlor............           0.002
(2) 116-06-3......................  Aldicarb............           0.003
(3) 1646-87-3.....................  Aldicarb sulfoxide..           0.004
(4) 1646-87-4.....................  Aldicarb sulfone....           0.002
(5) 1912-24-9.....................  Atrazine............           0.003
(6) 1563-66-2.....................  Carbofuran..........            0.04
(7) 57-74-9.......................  Chlordane...........           0.002
(8) 96-12-8.......................  Dibromochloropropane          0.0002
(9) 94-75-7.......................  2,4-D...............            0.07
(10) 106-93-4.....................  Ethylene dibromide..         0.00005
(11) 76-44-8......................  Heptachlor..........          0.0004
(12) 1024-57-3....................  Heptachlor epoxide..          0.0002
(13) 58-89-9......................  Lindane.............          0.0002
(14) 72-43-5......................  Methoxychlor........            0.04
(15) 1336-36-3....................  Polychlorinated               0.0005
                                     biphenyls.
(16) 87-86-5......................  Pentachlorophenol...           0.001
(17) 8001-35-2....................  Toxaphene...........           0.003
(18) 93-72-1......................  2,4,5-TP............            0.05
(19) 50-32-8......................  Benzo[a]pyrene......          0.0002
(20) 75-99-0......................  Dalapon.............             0.2
(21) 103-23-1.....................  Di(2-ethylhexyl)                 0.4
                                     adipate.
(22) 117-81-7.....................  Di(2-ethylhexyl)               0.006
                                     phthalate.
(23) 88-85-7......................  Dinoseb.............           0.007
(24) 85-00-7......................  Diquat..............            0.02
(25) 145-73-3.....................  Endothall...........             0.1
(26) 72-20-8......................  Endrin..............           0.002
(27) 1071-53-6....................  Glyphosate..........             0.7
(28) 118-74-1.....................  Hexacholorbenzene...           0.001
(29) 77-47-4......................  Hexachlorocyclopenta            0.05
                                     diene.
(30) 23135-22-0...................  Oxamyl (Vydate).....             0.2
(31) 1918-02-1....................  Picloram............             0.5
(32) 122-34-9.....................  Simazine............           0.004
(33) 1746-01-6....................  2,3,7,8-TCDD                3 x 10-8
                                     (Dioxin).
------------------------------------------------------------------------


                                Table 4 to Paragraph (c)--MCLs and HBWCs for PFAS
----------------------------------------------------------------------------------------------------------------
                                                                                                HBWC (mg/l) for
               CAS. No.                         Contaminant             MCL (mg/l)  (unless       hazard index
                                                                          otherwise noted)        calculation
----------------------------------------------------------------------------------------------------------------
(34) Not applicable..................  Hazard Index PFAS (HFPO-DA,    1 (unitless) \1\.......     Not applicable
                                        PFBS, PFHxS, and PFNA).
(35) 122499-17-6.....................  HFPO-DA......................  0.00001................            0.00001
(36) 45187-15-3......................  PFBS.........................  No individual MCL......              0.002
(37) 108427-53-8.....................  PFHxS........................  0.00001................            0.00001
(38) 72007-68-2......................  PFNA.........................  0.00001................            0.00001
(39) 45285-51-6......................  PFOA.........................  0.0000040..............     Not applicable

[[Page 32746]]

 
(40) 45298-90-6......................  PFOS.........................  0.0000040..............     Not applicable
----------------------------------------------------------------------------------------------------------------
\1\ The PFAS Mixture Hazard Index (HI) is the sum of component hazard quotients (HQs), which are calculated by
  dividing the measured component PFAS concentration in water by the relevant health-based water concentration
  when expressed in the same units (shown in ng/l for simplification). The HBWC for PFHxS is 10 ng/l; the HBWC
  for HFPO-DA is 10 ng/l; the HBWC for PFNA is 10 ng/l; and the HBWC for PFBS is 2000 ng/l.

Hazard Index = ([HFPO-DAwater ng/l]/[10 ng/l]) + 
([PFBSwater ng/l]/[2000 ng/l]) + ([PFNAwater ng/
l]/[10 ng/l]) + ([PFHxSwater ng/l]/[10 ng/l])

HBWC = health-based water concentration
HQ = hazard quotient
ng/l = nanograms per liter
PFASwater = the concentration of a specific PFAS in water

    (d) The Administrator, pursuant to section 1412 of the Act, hereby 
identifies in table 5 to this paragraph (d) the best technology, 
treatment technique, or other means available for achieving compliance 
with the maximum contaminant levels for all regulated PFAS identified 
in paragraph (c) of this section:

Table 5 to Paragraph (d)--Best Available Technologies for PFAS Listed in
                      Paragraph (c) of This Section
------------------------------------------------------------------------
              Contaminant                              BAT
------------------------------------------------------------------------
Hazard Index PFAS (HFPO-DA, PFBS,        Anion exchange, GAC, reverse
 PFHxS, and PFNA).                        osmosis, nanofiltration.
HFPO-DA................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFHxS..................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFNA...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFOA...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFOS...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
------------------------------------------------------------------------

    (e) The Administrator, pursuant to section 1412 of the Act, hereby 
identifies in table 6 to this paragraph (e) the affordable technology, 
treatment technique, or other means available to systems serving 10,000 
persons or fewer for achieving compliance with the maximum contaminant 
levels for all regulated PFAS identified in paragraph (c) of this 
section:

 Table 6 to Paragraph (e)--Small System Compliance Technologies (SSCTs)
                                for PFAS
------------------------------------------------------------------------
                                             Affordable for listed small
 Small system  compliance  technology \1\      system  categories \2\
------------------------------------------------------------------------
Granular Activated Carbon.................  All size categories.
Anion Exchange............................  All size categories.
Reverse Osmosis, Nanofiltration \3\.......  3,301-10,000.
------------------------------------------------------------------------
\1\ Section 1412(b)(4)(E)(ii) of SDWA specifies that SSCTs must be
  affordable and technically feasible for small systems.
\2\ The Act (ibid.) specifies three categories of small systems: (i)
  those serving 25 or more, but fewer than 501, (ii) those serving more
  than 500, but fewer than 3,301, and (iii) those serving more than
  3,300, but fewer than 10,001.
\3\ Technologies reject a large volume of water and may not be
  appropriate for areas where water quantity may be an issue.


0
9. Amend Sec.  141.151 by revising paragraph (d) to read as follows:


Sec.  141.151  Purpose and applicability of this subpart.

* * * * *
    (d) For the purpose of this subpart, detected means: at or above 
the levels prescribed by Sec.  141.23(a)(4) for inorganic contaminants, 
at or above the levels prescribed by Sec.  141.24(f)(7) for the 
contaminants listed in Sec.  141.61(a), at or above the levels 
prescribed by Sec.  141.24(h)(18) for the contaminants listed in Sec.  
141.61(c) (except PFAS), at or above the levels prescribed by Sec.  
141.131(b)(2)(iv) for the contaminants or contaminant groups listed in 
Sec.  141.64, at or above the levels prescribed by Sec.  141.25(c) for 
radioactive contaminants, and at or above the levels prescribed in 
Sec.  141.902(a)(5) for PFAS listed in Sec.  141.61(c).
* * * * *

0
10. Amend Sec.  141.153 by adding paragraph (c)(3)(v) to read as 
follows:


Sec.  141.153  Content of the reports.

* * * * *
    (c) * * *
    (3) * * *
    (v) Hazard Index or HI. The Hazard Index is an approach that 
determines the health concerns associated with mixtures of certain PFAS 
in finished drinking water. Low levels of multiple PFAS that 
individually would not likely result in adverse health effects may pose 
health concerns when combined in a mixture. The Hazard Index MCL 
represents the maximum level for mixtures of PFHxS, PFNA, HFPO-DA, and/
or PFBS allowed in water delivered by a public water system. A Hazard 
Index greater than 1 requires a system to take action.
* * * * *

0
11. Amend appendix A to subpart O, under the Contaminant heading 
``Synthetic organic contaminants including pesticides and 
herbicides:'', by adding in alphabetical order entries for ``Hazard 
Index PFAS (HFPO-DA, PFBS, PFHxS, and PFNA) (unitless)'', ``HFPO-DA 
(ng/l)'', ``PFHxS (ng/l)'', ``PFNA (ng/l)'', ``PFOA (ng/l)'', and 
``PFOS (ng/l)'' to read as follows:

[[Page 32747]]

Appendix A to Subpart O of Part 141--Regulated Contaminants

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                    To convert for
        Contaminant (units)           Traditional    CCR, multiply    MCL in CCR         MCLG       Major sources in drinking   Health effects language
                                      MCL in mg/L         by             units                                water
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
Synthetic organic contaminants                                                           * * * * * *
 including pesticides and
 herbicides:
 
                                                                      * * * * * * *
Hazard Index PFAS (HFPO-DA, PFBS,     1 (unitless)  ..............               1               1  Discharge from             Per- and polyfluoroalkyl
 PFHxS, and PFNA) (unitless).                                                                        manufacturing and          substances (PFAS) can
                                                                                                     industrial chemical        persist in the human
                                                                                                     facilities, use of         body and exposure may
                                                                                                     certain consumer           lead to increased risk
                                                                                                     products, occupational     of adverse health
                                                                                                     exposures, and certain     effects. Low levels of
                                                                                                     firefighting activities.   multiple PFAS that
                                                                                                                                individually would not
                                                                                                                                likely result in
                                                                                                                                increased risk of
                                                                                                                                adverse health effects
                                                                                                                                may result in adverse
                                                                                                                                health effects when
                                                                                                                                combined in a mixture.
                                                                                                                                Some people who consume
                                                                                                                                drinking water
                                                                                                                                containing mixtures of
                                                                                                                                PFAS in excess of the
                                                                                                                                Hazard Index (HI) MCL
                                                                                                                                may have increased
                                                                                                                                health risks such as
                                                                                                                                liver, immune, and
                                                                                                                                thyroid effects
                                                                                                                                following exposure over
                                                                                                                                many years and
                                                                                                                                developmental and
                                                                                                                                thyroid effects
                                                                                                                                following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.
 
                                                                      * * * * * * *
HFPO-DA (ng/l)....................         0.00001       1,000,000              10              10  Discharge from             Some people who drink
                                                                                                     manufacturing and          water containing HFPO-DA
                                                                                                     industrial chemical        in excess of the MCL
                                                                                                     facilities, use of         over many years may have
                                                                                                     certain consumer           increased health risks
                                                                                                     products, occupational     such as immune, liver,
                                                                                                     exposures, and certain     and kidney effects.
                                                                                                     firefighting activities.   There is also a
                                                                                                                                potential concern for
                                                                                                                                cancer associated with
                                                                                                                                HFPO-DA exposure. In
                                                                                                                                addition, there may be
                                                                                                                                increased risks of
                                                                                                                                developmental effects
                                                                                                                                for people who drink
                                                                                                                                water containing HFPO-DA
                                                                                                                                in excess of the MCL
                                                                                                                                following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.
 

[[Page 32748]]

 
                                                                      * * * * * * *
PFHxS (ng/l)......................         0.00001       1,000,000              10              10  Discharge from             Some people who drink
                                                                                                     manufacturing and          water containing PFHxS
                                                                                                     industrial chemical        in excess of the MCL
                                                                                                     facilities, use of         over many years may have
                                                                                                     certain consumer           increased health risks
                                                                                                     products, occupational     such as immune, thyroid,
                                                                                                     exposures, and certain     and liver effects. In
                                                                                                     firefighting activities.   addition, there may be
                                                                                                                                increased risks of
                                                                                                                                developmental effects
                                                                                                                                for people who drink
                                                                                                                                water containing PFHxS
                                                                                                                                in excess of the MCL
                                                                                                                                following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.
PFNA (ng/l).......................         0.00001       1,000,000              10              10  Discharge from             Some people who drink
                                                                                                     manufacturing and          water containing PFNA in
                                                                                                     industrial chemical        excess of the MCL over
                                                                                                     facilities, use of         many years may have
                                                                                                     certain consumer           increased health risks
                                                                                                     products, occupational     such as elevated
                                                                                                     exposures, and certain     cholesterol levels,
                                                                                                     firefighting activities.   immune effects, and
                                                                                                                                liver effects. In
                                                                                                                                addition, there may be
                                                                                                                                increased risks of
                                                                                                                                developmental effects
                                                                                                                                for people who drink
                                                                                                                                water containing PFNA in
                                                                                                                                excess of the MCL
                                                                                                                                following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.
PFOA (ng/l).......................       0.0000040       1,000,000             4.0               0  Discharge from             Some people who drink
                                                                                                     manufacturing and          water containing PFOA in
                                                                                                     industrial chemical        excess of the MCL over
                                                                                                     facilities, use of         many years may have
                                                                                                     certain consumer           increased health risks
                                                                                                     products, occupational     such as cardiovascular,
                                                                                                     exposures, and certain     immune, and liver
                                                                                                     firefighting activities.   effects, as well as
                                                                                                                                increased incidence of
                                                                                                                                certain types of cancers
                                                                                                                                including kidney and
                                                                                                                                testicular cancer. In
                                                                                                                                addition, there may be
                                                                                                                                increased risks of
                                                                                                                                developmental and immune
                                                                                                                                effects for people who
                                                                                                                                drink water containing
                                                                                                                                PFOA in excess of the
                                                                                                                                MCL following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.

[[Page 32749]]

 
PFOS (ng/l).......................       0.0000040       1,000,000             4.0               0  Discharge from             Some people who drink
                                                                                                     manufacturing and          water containing PFOS in
                                                                                                     industrial chemical        excess of the MCL over
                                                                                                     facilities, use of         many years may have
                                                                                                     certain consumer           increased health risks
                                                                                                     products, occupational     such as cardiovascular,
                                                                                                     exposures, and certain     immune, and liver
                                                                                                     firefighting activities.   effects, as well as
                                                                                                                                increased incidence of
                                                                                                                                certain types of cancers
                                                                                                                                including liver cancer.
                                                                                                                                In addition, there may
                                                                                                                                be increased risks of
                                                                                                                                developmental and immune
                                                                                                                                effects for people who
                                                                                                                                drink water containing
                                                                                                                                PFOS in excess of the
                                                                                                                                MCL following repeated
                                                                                                                                exposure during
                                                                                                                                pregnancy and/or
                                                                                                                                childhood.
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------

* * * * *

0
12. Amend appendix A to subpart Q by:
0
a. Adding under the Contaminant heading ``D. Synthetic Organic 
Chemicals (SOCs)'' entries for ``31'', ``32'', ``33'', ``34'', ``35'', 
and ``36'' in numerical order;
0
b. Adding, immediately before footnote 1, footnote *; and
0
c. Adding footnote 23 at the end of the table.
    The additions read as follows:

Appendix A to Subpart Q of Part 141--NPDWR Violations and Other 
Situations Requiring Public Notice \1\

----------------------------------------------------------------------------------------------------------------
                                                    MCL/MRDL/TT violations \2\    Monitoring & testing procedure
                                                 --------------------------------           violations
                                                                                 -------------------------------
                   Contaminant                    Tier of public                  Tier of public
                                                      notice         Citation         notice         Citation
                                                     required                        required
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
                                      D. Synthetic Organic Chemicals (SOCs)
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
31. Hazard Index PFAS...........................        \23\ * 2       141.61(c)               3      141.905(c)
32. HFPO-DA.....................................             * 2       141.61(c)               3      141.905(c)
33. PFHxS.......................................             * 2       141.61(c)               3      141.905(c)
34. PFNA........................................             * 2       141.61(c)               3      141.905(c)
35. PFOA........................................             * 2       141.61(c)               3      141.905(c)
36. PFOS........................................             * 2       141.61(c)               3      141.905(c)
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
Appendix A--Endnotes
 * * * * * * *
* Beginning April 26, 2029.
\1\ Violations and other situations not listed in this table (e.g., failure to prepare Consumer Confidence
  Reports), do not require notice, unless otherwise determined by the primacy agency. Primacy agencies may, at
  their option, also require a more stringent public notice tier (e.g., Tier 1 instead of Tier 2 or Tier 2
  instead of Tier 3) for specific violations and situations listed in this Appendix, as authorized under Sec.
  141.202(a) and Sec.   141.203(a).
\2\ MCL--Maximum contaminant level, MRDL--Maximum residual disinfectant level, TT--Treatment technique.
 * * * * * * *
\23\ Systems that violate the Hazard Index MCL and one or more individual MCLs based on the same contaminants
  may issue one notification to satisfy the public notification requirements for multiple violations pursuant to
  Sec.   141.203.


0
13. Amend appendix B to subpart Q by redesignating entries ``55'' 
through ``89'' as entries ``61'' through ``95'' and adding new entries 
``55'' through ``60'' under the heading ``E. Synthetic Organic 
Chemicals (SOCs)'' to read as follows:

Appendix B to Subpart Q of Part 141--Standard Health Effects Language 
for Public Notification

[[Page 32750]]



----------------------------------------------------------------------------------------------------------------
                                                                            Standard health effects language for
            Contaminant                MCLG \1\ mg/L       MCL \2\ mg/L             public notification
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                      E. Synthetic Organic Chemicals (SOCs)
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
55. Hazard Index PFAS (HFPO-DA,           1 (unitless)       1 (unitless)  Per- and polyfluoroalkyl substances
 PFBS, PFHxS, and PFNA).                                                    (PFAS) can persist in the human body
                                                                            and exposure may lead to increased
                                                                            risk of adverse health effects. Low
                                                                            levels of multiple PFAS that
                                                                            individually would not likely result
                                                                            in increased risk of adverse health
                                                                            effects may result in adverse health
                                                                            effects when combined in a mixture.
                                                                            Some people who consume drinking
                                                                            water containing mixtures of PFAS in
                                                                            excess of the Hazard Index (HI) MCL
                                                                            may have increased health risks such
                                                                            as liver, immune, and thyroid
                                                                            effects following exposure over many
                                                                            years and developmental and thyroid
                                                                            effects following repeated exposure
                                                                            during pregnancy and/or childhood.
56. HFPO-DA........................            0.00001            0.00001  Some people who drink water
                                                                            containing HFPO-DA in excess of the
                                                                            MCL over many years may have
                                                                            increased health risks such as
                                                                            immune, liver, and kidney effects.
                                                                            There is also a potential concern
                                                                            for cancer associated with HFPO-DA
                                                                            exposure. In addition, there may be
                                                                            increased risks of developmental
                                                                            effects for people who drink water
                                                                            containing HFPO-DA in excess of the
                                                                            MCL following repeated exposure
                                                                            during pregnancy and/or childhood.
57. PFHxS..........................            0.00001            0.00001  Some people who drink water
                                                                            containing PFHxS in excess of the
                                                                            MCL over many years may have
                                                                            increased health risks such as
                                                                            immune, thyroid, and liver effects.
                                                                            In addition, there may be increased
                                                                            risks of developmental effects for
                                                                            people who drink water containing
                                                                            PFHxS in excess of the MCL following
                                                                            repeated exposure during pregnancy
                                                                            and/or childhood.
58. PFNA...........................            0.00001            0.00001  Some people who drink water
                                                                            containing PFNA in excess of the MCL
                                                                            over many years may have increased
                                                                            health risks such as elevated
                                                                            cholesterol levels, immune effects,
                                                                            and liver effects. In addition,
                                                                            there may be increased risks of
                                                                            developmental effects for people who
                                                                            drink water containing PFNA in
                                                                            excess of the MCL following repeated
                                                                            exposure during pregnancy and/or
                                                                            childhood.
59. PFOA...........................               Zero          0.0000040  Some people who drink water
                                                                            containing PFOA in excess of the MCL
                                                                            over many years may have increased
                                                                            health risks such as cardiovascular,
                                                                            immune, and liver effects, as well
                                                                            as increased incidence of certain
                                                                            types of cancers including kidney
                                                                            and testicular cancer. In addition,
                                                                            there may be increased risks of
                                                                            developmental and immune effects for
                                                                            people who drink water containing
                                                                            PFOA in excess of the MCL following
                                                                            repeated exposure during pregnancy
                                                                            and/or childhood.
60. PFOS...........................               Zero          0.0000040  Some people who drink water
                                                                            containing PFOS in excess of the MCL
                                                                            over many years may have increased
                                                                            health risks such as cardiovascular,
                                                                            immune, and liver effects, as well
                                                                            as increased incidence of certain
                                                                            types of cancers including liver
                                                                            cancer. In addition, there may be
                                                                            increased risks of developmental and
                                                                            immune effects for people who drink
                                                                            water containing PFOS in excess of
                                                                            the MCL following repeated exposure
                                                                            during pregnancy and/or childhood.
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
 * * * * * * *
\1\ MCLG--Maximum contaminant level goal.
\2\ MCL--Maximum contaminant level.

* * * * *

0
14. Amend appendix C to subpart Q by adding entries for the acronyms 
``HI'' and ``PFAS'' in alphabetical order to read as follows:

Appendix C to Subpart Q of Part 141--List of Acronyms Used in Public 
Notification Regulation

* * * * *
HI Hazard Index
* * * * *
PFAS Per- and Polyfluoroalkyl Substances
* * * * *

0
15. Add subpart Z to read as follows:
Subpart Z--Control of Per- and Polyfluoroalkyl Substances (PFAS)
Sec.
141.900 General requirements.
141.901 Analytical requirements.
141.902 Monitoring requirements.
141.903 Compliance requirements.
141.904 Reporting and recordkeeping requirements.
141.905 Violations.

Subpart Z--Control of Per- and Polyfluoroalkyl Substances (PFAS)


Sec.  141.900  General requirements.

    (a) The requirements of this subpart constitute the national 
primary drinking water regulations for PFAS. Each community water 
system (CWS) and non-transient, non-community water system (NTNCWS) 
must meet the requirements of this subpart including the maximum 
contaminant levels for the PFAS identified in Sec.  141.61(c).

[[Page 32751]]

    (b) The deadlines for complying with the provisions of this subpart 
are as follows:
    (1) Each system must meet the analytical requirements in Sec.  
141.901 by June 25, 2024.
    (2) Each system must report the results of initial monitoring, as 
described in Sec.  141.902(b)(1), to the State by April 26, 2027.
    (3) Each system must meet the compliance monitoring requirements in 
Sec.  141.902(b)(2) by April 26, 2027.
    (4) Each system must meet the MCL compliance requirements in Sec.  
141.903 by April 26, 2029.
    (5) Each system must meet the reporting and recordkeeping 
requirements in Sec.  141.904 by April 26, 2027.
    (6) Violations described in Sec.  141.905 include monitoring and 
reporting violations and violations of MCLs. Monitoring and reporting 
violations may be assessed beginning on April 26, 2027. MCL violations 
may be assessed beginning on April 26, 2029.


Sec.  141.901  Analytical requirements.

    (a) General. (1) Systems must use only the analytical methods 
specified in this section to demonstrate compliance with the 
requirements of this subpart.
    (2) The following documents are incorporated by reference with the 
approval of the Director of the Federal Register in accordance with 5 
U.S.C. 552(a) and 1 CFR part 51. This material is available for 
inspection at the EPA and at the National Archives and Records 
Administration (NARA). Contact the EPA's Drinking Water Docket at: 1301 
Constitution Avenue NW., EPA West, Room 3334, Washington, DC 20460; 
phone: 202-566-2426. For information on the availability of this 
material at NARA, email: [email protected], or go to: 
www.archives.gov/federal-register/cfr/ibr-locations. The material may 
be obtained from the EPA at 1301 Constitution Avenue NW, the EPA West, 
Room 3334, Washington, DC 20460; phone: 202-566-2426; website: https://www.epa.gov/pfas/epa-pfas-drinking-water-laboratory-methods.
    (i) EPA Method 533: Determination of Per- and Polyfluoroalkyl 
Substances in Drinking Water by Isotope Dilution Anion Exchange Solid 
Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry, 
815-B-19-020, November 2019.
    (ii) Method 537.1, Version 2.0: Determination of Selected Per- and 
Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase 
Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/
MS), EPA/600/R-20/006, March 2020.
    (b) PFAS-(1) Analytical methods. Systems must measure regulated 
PFAS by the methods listed in the following table:

  Table 1 to Paragraph (b)(1)--Analytical Methods for PFAS Contaminants
------------------------------------------------------------------------
                                                          EPA method
                                                       (incorporated by
           Contaminant                Methodology       reference, see
                                                       paragraph (a) of
                                                         this section)
------------------------------------------------------------------------
Perfluorobutane Sulfonate (PFBS)  SPE LC-MS/MS......  533, 537.1,
                                                       version 2.0.
Perfluorohexane Sulfonate         SPE LC-MS/MS......  533, 537.1,
 (PFHxS).                                              version 2.0.
Perfluorononanoate (PFNA).......  SPE LC-MS/MS......  533, 537.1,
                                                       version 2.0.
Perfluorooctanesulfonic Acid      SPE LC-MS/MS......  533, 537.1,
 (PFOS).                                               version 2.0.
Perfluorooctanoic Acid (PFOA)...  SPE LC-MS/MS......  533, 537.1,
                                                       version 2.0.
2,3,3,3-Tetrafluoro-2-            SPE LC-MS/MS......  533, 537.1,
 (heptafluoropropoxy)propanoate                        version 2.0.
 (HFPO-DA or GenX Chemicals).
------------------------------------------------------------------------

    (2) Laboratory certification. Analyses under this section for 
regulated PFAS must only be conducted by laboratories that have been 
certified by EPA or the State. To receive certification to conduct 
analyses for the regulated PFAS, the laboratory must:
    (i) Analyze Performance Evaluation (PE) samples that are acceptable 
to the State at least once during each consecutive 12-month period by 
each method for which the laboratory desires certification.
    (ii) Beginning June 25, 2024, achieve quantitative results on the 
PE sample analyses that are within the following acceptance limits:

 Table 2 to Paragraph (b)(2)(ii)--Acceptance Limits for PFAS Performance
                           Evaluation Samples
------------------------------------------------------------------------
                                                            Acceptance
                                                              limits
                       Contaminant                          (percent of
                                                            true value)
------------------------------------------------------------------------
Perfluorobutane Sulfonate (PFBS)........................          70-130
Perfluorohexane Sulfonate (PFHxS).......................          70-130
Perfluorononanoate (PFNA)...............................          70-130
Perfluorooctanesulfonic Acid (PFOS).....................          70-130
Perfluorooctanoic Acid (PFOA)...........................          70-130
2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)propanoate              70-130
 (HFPO-DA or GenX Chemicals)............................
------------------------------------------------------------------------

    (iii) For all samples analyzed for regulated PFAS in compliance 
with Sec.  141.902, beginning June 25, 2024, report data for 
concentrations as low as the trigger levels as defined in Sec.  
141.902(a)(5).


Sec.  141.902  Monitoring requirements.

    (a) General requirements. (1) Systems must take all samples during 
normal operating conditions at all entry points to the distribution 
system.
    (2) If the system draws water from more than one source and the 
sources are combined before distribution, the system must sample at an 
entry point to the distribution system during periods of representative 
operating conditions.
    (3) Systems must use only data collected under the provisions of 
this subpart to qualify for reduced monitoring.
    (4) All new systems that begin operation after, or systems that use 
a new source of water after April 26, 2027, must demonstrate compliance 
with the MCLs within a period of time specified by the State. A system 
must also comply with initial sampling frequencies required by the 
State to ensure that the system can demonstrate compliance with the 
MCLs. Compliance monitoring frequencies must be conducted in accordance 
with the requirements in this section.

[[Page 32752]]

    (5) For purposes of this section, the trigger levels are defined as 
shown in the following table.

    Table 1 to Paragraph (a)(5)--Trigger Levels for PFAS Contaminants
------------------------------------------------------------------------
                Contaminant                         Trigger level
------------------------------------------------------------------------
Hazard Index PFAS (HFPO-DA, PFBS, PFHxS,    0.5 (unitless).
 PFNA).
HFPO-DA...................................  5 nanograms per liter (ng/
                                             l).
PFHxS.....................................  5 ng/l.
PFNA......................................  5 ng/l.
PFOA......................................  2.0 ng/l.
PFOS......................................  2.0 ng/l.
------------------------------------------------------------------------

    (6) Based on initial monitoring results, for each sampling point at 
which a regulated PFAS listed in Sec.  141.61(c) is detected at a level 
greater than or equal to the trigger level, the system must monitor 
quarterly for all regulated PFAS beginning April 26, 2027, in 
accordance with paragraph (b)(2) of this section.
    (7) For purposes of this section, each water system must ensure 
that all results provided by a laboratory are reported to the State and 
used for determining the required sampling frequencies. This includes 
values below the practical quantitation levels defined in Sec.  
141.903(f)(1)(iv); zero must not be used in place of reported values.
    (b) Monitoring requirements for PFAS--(1) Initial monitoring. (i) 
Groundwater CWS and NTNCWS serving greater than 10,000 persons and all 
surface water CWS and NTNCWS must take four consecutive samples 2 to 4 
months apart within a 12-month period (quarterly samples) for each 
regulated PFAS listed in Sec.  141.61(c).
    (ii) All groundwater CWS and NTNCWS serving 10,000 or fewer persons 
must take two samples for each regulated PFAS listed in Sec.  141.61(c) 
five to seven months apart within a 12-month period.
    (iii) All groundwater under the direct influence of surface water 
(GWUDI) CWS and NTNCWS must follow the surface water CWS and NTNCWS 
monitoring schedule in paragraph (b)(1)(i) of this section.
    (iv) All systems that use both surface water and groundwater must 
apply the requirements in paragraphs (b)(1)(i) through (iii) of this 
section depending on the source(s) of water provided at a given entry 
point to the distribution system (EPTDS). If the EPTDS provides surface 
water, the requirements for a surface water CWS/NTNCWS apply. If the 
EPTDS provides groundwater, the requirements for a groundwater CWS/
NTNCWS apply, based on system size. If an EPTDS provides a blend of 
surface water and groundwater, the requirements for a surface water 
system apply. For systems that change the source water type at an EPTDS 
during the initial monitoring period (i.e., one part of the year it is 
surface water and the remaining part of the year it is groundwater), 
the sampling requirements for a surface water system apply.
    (v) Systems must monitor at a frequency indicated in the following 
table, though a State may require more frequent monitoring on a system-
specific basis:

     Table 2 to Paragraph (b)(1)(v)--Initial Monitoring Requirements
------------------------------------------------------------------------
                                  Minimum monitoring
        Type of system                 frequency         Sample location
------------------------------------------------------------------------
Groundwater CWS and NTNCWS      Four consecutive        Sampling point
 serving greater than 10,000     quarters of samples     for EPTDS.
 persons, all surface water      per entry point to
 CWS and NTNCWS, and all GWUDI   the distribution
 systems.                        system (EPTDS) within
                                 a 12-month period,
                                 unless the exception
                                 in paragraph
                                 (b)(1)(viii) of this
                                 section applies.
                                 Samples must be taken
                                 two to four months
                                 apart..
Groundwater CWS and NTNCWS      Two consecutive         Sampling point
 serving 10,000 or fewer         samples per EPTDS       for EPTDS.
 persons.                        within a 12-month
                                 period, unless the
                                 exception in
                                 paragraph
                                 (b)(1)(viii) of this
                                 section applies.
                                 Samples must be taken
                                 five to seven months
                                 apart..
------------------------------------------------------------------------

    (vi) A State may accept data that has been previously acquired by a 
water system to count toward the initial monitoring requirements if the 
data meet the requirements of Sec.  141.901(b)(1), samples were 
collected starting on or after January 1, 2019, and otherwise meet the 
timing requirements specified in table 2 to paragraph (b)(1)(v) of this 
section. For the purposes of satisfying initial monitoring 
requirements, acceptable data may be reported to a concentration no 
greater than the MCLs. However, a system is only eligible for triennial 
monitoring at the start of the compliance monitoring period if the 
system demonstrates that concentrations in all samples it uses to 
satisfy the initial monitoring requirements are below the trigger 
levels as defined in paragraph (a)(5) of this section.
    (vii) If systems have multiple years of data, the most recent data 
must be used.
    (viii) For systems using previously acquired data that have fewer 
than the number of samples required in a continuous 12-month period for 
initial monitoring as listed in table 2 to paragraph (b)(1)(v) of this 
section: All surface water systems, GWUDI systems, and groundwater 
systems serving greater than 10,000 persons must collect in a calendar 
year one sample in each quarter that was not represented, two to four 
months apart from the months with available data; All groundwater 
systems serving 10,000 or fewer persons must collect one sample in the 
month that is five to seven months apart from the month in which the 
previous sample was taken.
    (ix) In determining the most recent data to report, a system must 
include all results provided by a laboratory whether above or below the 
practical quantitation levels. These results must be used for the 
purposes of determining the frequency with which a system must monitor 
at that sampling point at the start of the compliance monitoring 
period.
    (x) States may delete results of obvious sampling errors. If the 
State deletes a result because of an obvious sampling error and the 
system fails to collect another sample this is a monitoring violation 
as described in Sec.  141.905(c).
    (xi) Initial monitoring requirements, including reporting results 
to the State, must be completed by April 26, 2027.
    (2) Compliance monitoring. (i) Based on initial monitoring results, 
at the start of the monitoring period that begins on April 26, 2027, 
systems may reduce monitoring at each sampling point at which all 
reported sample concentrations were below all trigger levels defined in 
paragraph (a)(5) of this section, unless otherwise provided for by the 
State. At eligible sampling points,

[[Page 32753]]

each water system must analyze one sample for all regulated PFAS during 
each three-year monitoring period, at a time specified by the State, in 
the quarter in which the highest analytical result was detected during 
the most recent round of quarterly or semi-annual monitoring. If a 
sampling point is not eligible for triennial monitoring, then the water 
system must monitor quarterly at the start of the compliance monitoring 
period.
    (ii) If, during the compliance monitoring period, a system is 
monitoring triennially and a PFAS listed in Sec.  141.61(c) is detected 
at a level equal to or exceeding the trigger levels defined in 
paragraph (a)(5) of this section in any sample, then the system must 
monitor quarterly for all regulated PFAS beginning in the next quarter 
at the sampling point. The triggering sample must be used as the first 
quarter of monitoring for the running annual average calculation.
    (iii) For all source water types, a State may determine that all 
regulated PFAS at a sampling point are reliably and consistently below 
the MCL after considering, at a minimum, four consecutive quarterly 
samples collected during the compliance monitoring period. A sampling 
point that a State has determined to be reliably and consistently below 
the MCL is required to collect annual samples for at least the first 
three years after that determination is made. Annual samples must be 
collected in the quarter in which detected concentrations were highest 
during the most recent year of quarterly monitoring. If, after three 
consecutive years, annual samples all contain results that are below 
the trigger levels defined in paragraph (a)(5) of this section, the 
State may allow a system to begin triennial monitoring at the sampling 
point. The water system must collect triennial samples in the quarter 
with the highest concentrations during the most recent round of 
quarterly sampling. If an annual sample meets or exceeds an MCL or the 
State determines that the result is not reliably and consistently below 
the MCL for all regulated PFAS, then the system must monitor quarterly 
for all regulated PFAS beginning in the next quarter at the sampling 
point.
    (iv) The three different compliance monitoring sampling schedules 
that may be assigned and the criteria for each are summarized in the 
following table:
    Table 3 to paragraph (b)(2)(iv)--Compliance Monitoring Schedules 
and Requirements

----------------------------------------------------------------------------------------------------------------
          Sampling frequency                  Eligibility requirements \1\          Sample timing requirements
----------------------------------------------------------------------------------------------------------------
Triennial.............................  At an individual sampling point, either:  Sample must be collected at a
                                        (1) All initial monitoring results         time within the three-year
                                         demonstrate concentrations of all         period designated by the
                                         regulated PFAS below trigger levels;.     State, in the quarter that
                                        (2) The most recent three consecutive      yielded the highest
                                         annual monitoring results all             analytical result during the
                                         demonstrated concentrations of all        most recent round of
                                         regulated PFAS below trigger levels; or.  quarterly sampling (or the
                                        (3) The previous triennial sample          most recent semi-annual
                                         demonstrated all regulated PFAS           sampling, if no quarterly
                                         concentrations below trigger levels..     sampling has occurred).
                                        Note: After beginning compliance
                                         monitoring, a system may not transition
                                         directly from quarterly monitoring to
                                         triennial monitoring..
Annual................................  A State makes a determination that all    Sample must be collected at a
                                         regulated PFAS concentrations at the      time designated by the State,
                                         sampling point are reliably and           within the quarter that
                                         consistently below PFAS MCLs, after       yielded the highest
                                         considering, at a minimum, 4              analytical result during the
                                         consecutive quarterly samples collected   most recent round of
                                         during the compliance monitoring          quarterly sampling.
                                         period..
Quarterly.............................  At an individual sampling point, either:  Samples must be collected in
                                        (1) Any regulated PFAS concentration       four consecutive quarters, on
                                         meets or exceeds a trigger level during   dates designated by the
                                         initial monitoring;.                      State.
                                        (2) Sampling is occurring quarterly
                                         during compliance monitoring and a
                                         State has not made a determination that
                                         all levels of regulated PFAS at the
                                         sampling point are reliably and
                                         consistently below the regulated PFAS
                                         MCLs; or.
                                        (3) A sample collected by a system
                                         required to conduct triennial
                                         monitoring contains regulated PFAS
                                         concentrations that meet or exceed
                                         trigger levels. The first of these
                                         samples meeting or exceeding the
                                         trigger level is considered the first
                                         quarterly sample..
                                        (4) A sample collected by a system
                                         required to conduct annual monitoring
                                         contains regulated PFAS concentrations
                                         that meet or exceed an MCL. The first
                                         of these samples meeting or exceeding
                                         the MCL is considered the first
                                         quarterly sample..
----------------------------------------------------------------------------------------------------------------
\1\ The monitoring frequency at a sampling point must be the same for all regulated PFAS and is determined based
  on the most frequent sampling required for any regulated PFAS detected at a level at or exceeding the trigger
  level.

    (v) The State may require a confirmation sample for any sampling 
result. If a confirmation sample is required by the State, the system 
must average the result with the first sampling result and the average 
must be used for the determination of compliance with MCLs as specified 
by Sec.  141.903. A State may delete results of obvious sampling errors 
from the MCL compliance calculations described in Sec.  141.903. If the 
State deletes a result because of an obvious sampling error and the 
system fails to collect another sample this is a monitoring violation 
as described in Sec.  141.905(c).
    (vi) The State may increase the required monitoring frequency, 
where necessary, to detect variations within the system (e.g., 
fluctuations in concentration due to seasonal use, changes in water 
source).
    (vii) Each public water system must monitor at the time designated 
by the State within each monitoring period.
    (viii) When a system reduces its sampling frequency to annual or 
triennial sampling, the next compliance sample must be collected in the 
monitoring period that begins the calendar year following State 
approval of a reduction in monitoring frequency.


Sec.  141.903  Compliance requirements.

    (a) Compliance with MCLs for regulated PFAS in Sec.  141.61(c) must 
be determined based on the analytical results obtained at each sampling 
point.

[[Page 32754]]

    (b) For systems monitoring quarterly, compliance with the MCL is 
determined by the running annual average at each sampling point.
    (c) If a system fails to collect the required number of samples 
specified in Sec.  141.902, this is a monitoring violation as described 
in Sec.  141.905(c), and compliance calculations must be based on the 
total number of samples collected.
    (d) Systems monitoring triennially whose sample result equals or 
exceeds the trigger level of 2.0 ng/l for either PFOS or PFOA, 5 ng/l 
for HFPO-DA, PFHxS, or PFNA, or a Hazard Index of 0.5 for the Hazard 
Index PFAS, must begin quarterly sampling for all regulated PFAS in the 
next quarter at the sampling point. Systems monitoring annually whose 
sample result equals or exceeds the MCL of 4.0 ng/l for either PFOS or 
PFOA, 10 ng/l for HFPO-DA, PFHxS, or PFNA, or a Hazard Index of 1 for 
the Hazard Index PFAS, must begin quarterly sampling for all regulated 
PFAS in the next quarter at the sampling point.
    (e) Except as provided in this paragraph (e), if a sample result 
exceeds an MCL, the system will not be considered in violation of the 
MCL until it has completed one year of quarterly sampling at the 
sampling point with the triggering sample used as the first quarter of 
monitoring for the running annual average calculation. However, 
whenever a sample result in any quarter (or quarterly average, if more 
than one compliance sample is available in a quarter because a 
confirmation sample was required by the State) causes the running 
annual average to exceed the MCL at a sampling point regardless of the 
subsequent quarterly monitoring results required to complete a full 
year of monitoring (e.g., the results from a single sample are more 
than 4 times the MCL), the system is out of compliance with the MCL 
immediately.
    (f) Systems must calculate compliance using the following method to 
determine MCL compliance at each sampling point:
    (1) For each PFAS regulated by an individual MCL:
    (i) For systems monitoring quarterly, divide the sum of the 
measured quarterly concentrations for each analyte by the number of 
quarters samples were collected for that analyte during the consecutive 
quarters included in the calculation. If more than one compliance 
sample for that analyte is available in a quarter because a 
confirmation sample was required by the State, systems must average all 
the results in a quarter then average the quarterly averages. Rounding 
does not occur until the end of the calculation. If the running annual 
average exceeds the MCL, the system is not in compliance with the MCL 
requirements.
    (ii) For systems monitoring annually, if the concentration measured 
is equal to or exceeds an MCL for regulated PFAS, the system is 
required to initiate quarterly monitoring for all regulated PFAS 
beginning in the next quarter at the sampling point, with the 
triggering sample result used as the first quarter of monitoring for 
the running annual average calculation.
    (iii) For systems monitoring triennially, if the concentration 
measured is equal to or exceeds the trigger level, the system is 
required to initiate quarterly monitoring for all regulated PFAS 
beginning in the next quarter at the sampling point, with the 
triggering sample result used as the first quarter of monitoring for 
the running annual average calculation.
    (iv) For the purpose of calculating MCL compliance, if a sample 
result is less than the practical quantitation level (PQL) for a 
regulated PFAS, in accordance with the following table, zero is used 
for that analyte solely to calculate the running annual average.

  Table 1 to Paragraph (f)(1)(iv)--Practical Quantitation Levels (PQLs)
                          for PFAS Contaminants
------------------------------------------------------------------------
                                                           PQL (in parts
                       Contaminant                         per trillion)
------------------------------------------------------------------------
HFPO-DA.................................................             5.0
PFBS....................................................             3.0
PFHxS...................................................             3.0
PFNA....................................................             4.0
PFOA....................................................             4.0
PFOS....................................................             4.0
------------------------------------------------------------------------

    (2) For each PFAS regulated under the Hazard Index MCL:
    (i) For systems monitoring quarterly, divide the observed sample 
analytical result for each analyte included in the Hazard Index by the 
corresponding HBWC listed in Sec.  141.61(c) to obtain a hazard 
quotient for each analyte for each sampling event at each sampling 
point. Sum the resulting hazard quotients together to determine the 
Hazard Index for the quarter. If the State requires a confirmation 
sample for an analyte in the quarter, systems must average these 
results for each analyte in that quarter and then determine the hazard 
quotient(s) from those average values, then sum the hazard quotients. 
Once the Hazard Indices for the individual quarters are calculated, 
they are averaged to determine a running annual average. If the running 
annual average Hazard Index exceeds the MCL and two or more Hazard 
Index analytes had an observed sample analytical result at or above the 
PQL in any of the quarterly samples collected to determine the running 
annual average, the system is in violation of the Hazard Index MCL. No 
rounding occurs until after the running annual average Hazard Index is 
calculated.
    (ii) If the Hazard Index calculated using the results of an annual 
sample equals or exceeds the Hazard Index MCL, the system must initiate 
quarterly sampling for all regulated PFAS beginning in the next quarter 
at the sampling point, with the triggering sample result used as the 
first quarter of monitoring.
    (iii) If the Hazard Index calculated using the results of a 
triennial sample equals or exceeds the Hazard Index trigger level, the 
system must initiate quarterly sampling for all regulated PFAS 
beginning in the next quarter at the sampling point, with the 
triggering sample result used as the first quarter of monitoring.
    (iv) If a sample result is less than the practical quantitation 
level for a regulated PFAS, in accordance with the table 1 to paragraph 
(f)(1)(iv) of this section, zero is used for that analyte solely to 
calculate the running annual average.


Sec.  141.904  Reporting and recordkeeping requirements.

    Systems required to sample must report to the State according to 
the timeframes and provisions of Sec.  141.31 and retain records 
according to the provisions in Sec.  141.33.
    (a) Systems must report the information from initial monitoring 
specified in the following table:

[[Page 32755]]



    Table 1 to Paragraph (a)--Data To Report From Initial Monitoring
------------------------------------------------------------------------
           If you are a . . .                 You must report . . .
------------------------------------------------------------------------
System monitoring for regulated PFAS     1. All sample results,
 under the requirements of Sec.           including the locations,
 141.902(b)(1) on a quarterly basis.      number of samples taken at
                                          each location, dates, and
                                          concentrations reported.
                                         2. Whether a trigger level,
                                          defined in Sec.
                                          141.902(a)(5), was met or
                                          exceeded in any samples.
System monitoring for regulated PFAS     1. All sample results,
 under the requirements of Sec.           including the locations,
 141.902(b)(1) less frequently than       number of samples taken at
 quarterly.                               each location, dates, and
                                          concentrations reported.
                                         2. Whether a trigger level,
                                          defined in Sec.
                                          141.902(a)(5), was met or
                                          exceeded in any samples.
------------------------------------------------------------------------

    (b) Systems must report the information collected during the 
compliance monitoring period specified in the following table:

   Table 2 to Paragraph (b)--Data To Report From Compliance Monitoring
------------------------------------------------------------------------
           If you are a . . .                 You must report . . .
------------------------------------------------------------------------
System monitoring for regulated PFAS     1. All sample results,
 under the requirements of Sec.           including the locations,
 141.902(b)(2) on a quarterly basis.      number of samples taken at
                                          each location, dates, and
                                          concentrations during the
                                          previous quarter.
                                         2. The running annual average
                                          at each sampling point of all
                                          compliance samples.
                                         3. Whether a trigger level,
                                          defined in Sec.
                                          141.902(a)(5), was met or
                                          exceeded in any samples.
                                         4. Whether an MCL for a
                                          regulated PFAS in Sec.
                                          141.61(c) was met or exceeded
                                          in any samples.
                                         5. Whether, based on Sec.
                                          141.903, an MCL was violated.
System monitoring for regulated PFAS     1. All sample results,
 under the requirements of Sec.           including the locations,
 141.902(b)(2) less frequently than       number of samples taken at
 quarterly.                               each location, dates, and
                                          concentrations during the
                                          previous monitoring period.
                                         2. Whether a trigger level,
                                          defined in Sec.
                                          141.902(a)(5), was met or
                                          exceeded in any samples.
                                         3. Whether an MCL for a
                                          regulated PFAS in Sec.
                                          141.61(c) was met or exceeded
                                          in any samples.
                                         4. Whether, based on Sec.
                                          141.903, an MCL was violated
                                          (e.g., the results from a
                                          single sample are more than 4
                                          times the MCL).
------------------------------------------------------------------------

Sec.  141.905  Violations.

    (a) PFAS MCL violations, both for the individual PFOA, PFOS, HFPO-
DA, PFHxS, and PFNA MCLs, as well as the Hazard Index MCL, as listed in 
Sec.  141.61(c), are based on a running annual average, as outlined 
under Sec.  141.903.
    (b) Compliance with Sec.  141.61(c) must be determined based on the 
analytical results obtained at each sampling point. If one sampling 
point is in violation of an MCL, the system is in violation of the MCL.
    (c) Each failure to monitor in accordance with the requirements 
under Sec.  141.902 is a monitoring violation.
    (d) Failure to notify the State following a MCL violation and 
failure to submit monitoring data in accordance with the requirements 
of Sec. Sec.  141.904 and 141.31 are reporting violations.
    (e) Results for PFAS with individual MCLs as listed in Sec.  
141.61(c) are compared to their respective MCLs, and results for 
mixtures of two or more of the Hazard Index PFAS (HFPO-DA, PFBS, PFHxS, 
and PFNA) are compared to the Hazard Index MCL as listed in Sec.  
141.61(c). For determining compliance with the Hazard Index MCL, if 
only PFBS is reported at any concentration and no other regulated PFAS 
are in the mixture, it is not violation of the Hazard Index MCL. If 
only one of the other PFAS within the Hazard Index (HFPO-DA, PFHxS, and 
PFNA) is detected and the level of this PFAS exceeds its MCL as 
determined by Sec.  141.903(f)(1)(i), only an individual MCL violation 
is assessed for the individual PFAS detected, and it is not a violation 
of the Hazard Index MCL. Exceedances of the Hazard Index caused by two 
or more of the Hazard Index PFAS (HFPO-DA, PFBS, PFHxS, and PFNA) and 
exceedances of one or more individual MCLs can result in multiple MCL 
exceedances. However, in this instance, for purposes of public 
notification under appendix A to subpart Q of this part, a PWS must 
only report the Hazard Index MCL exceedance.

PART 142--NATIONAL PRIMARY DRINKING WATER REGULATIONS 
IMPLEMENTATION

0
16. The authority citation for part 142 continues to read as follows:

    Authority:  42 U.S.C. 300f, 300g-1, 300g-2, 300g-3, 300g-4, 
300g-5, 300g-6, 300j-4, 300j-9, and 300j-11.


0
17. Amend Sec.  142.16 by adding paragraph (r) to read as follows:


Sec.  142.16  Special primacy requirements.

* * * * *
    (r) Requirements for States to adopt 40 CFR part 141, subpart Z, 
PFAS. In addition to the general primacy requirements elsewhere in this 
part, including the requirements that State regulations be at least as 
stringent as Federal requirements, an application for approval of a 
State program revision that adopts 40 CFR part 141, subpart Z, must 
contain the following, in lieu of meeting the requirements of paragraph 
(e) of this section:
    (1) The State's procedures for reviewing the water system's use of 
pre-existing data to meet the initial

[[Page 32756]]

monitoring requirements specified in Sec.  141.902, including the 
criteria that will be used to determine if the data are acceptable. 
This paragraph (r)(1) is no longer applicable after the initial 
monitoring period ends on April 26, 2027.
    (2) The State's procedures for ensuring all systems complete the 
initial monitoring period requirements that will result in a high 
degree of monitoring compliance by the regulatory deadlines. This 
paragraph (r)(2) is no longer applicable after the initial monitoring 
period ends on April 26, 2027.
    (3) After the initial monitoring period, States establish the 
initial monitoring requirements for new public water systems and 
existing public water systems that plan to use a new source. States 
must explain their initial monitoring schedules and how these 
monitoring schedules ensure that new public water systems and existing 
public water systems that plan to use new sources comply with MCLs and 
monitoring requirements. States must also specify the time frame in 
which a new system or existing system that plans to use a new source 
must demonstrate compliance with the MCLs.

0
18. Amend Sec.  142.62 by revising and republishing paragraph (a) to 
read as follows:


Sec.  142.62  Variances and exemptions from the maximum contaminant 
levels for organic and inorganic chemicals.

    (a) The Administrator, pursuant to section 1415(a)(1)(A) of the 
Act, hereby identifies the technologies listed in tables 1 and 2 to 
this paragraph (a) as the best available technology, treatment 
techniques, or other means available for achieving compliance with the 
maximum contaminant levels for the organic chemicals, including per- 
and polyfluoroalkyl substances (PFAS), listed in Sec.  141.61(a) and 
(c) of this chapter, for the purposes of issuing variances and 
exemptions. A list of small system compliance technologies for the 
regulated PFAS for the purposes of providing variances and exemptions 
is provided in table 3 to this paragraph (a); for the purpose of this 
paragraph (a), small system is defined as a system serving 10,000 
persons or fewer.

   Table 1 to Paragraph (a)--BATs for PFAS Listed in Sec.   141.61(c)
------------------------------------------------------------------------
              Contaminant                              BAT
------------------------------------------------------------------------
Hazard Index PFAS (HFPO-DA, PFBS,        Anion exchange, GAC, reverse
 PFHxS, and PFNA).                        osmosis, nanofiltration.
HFPO-DA................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFHxS..................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFNA...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFOA...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
PFOS...................................  Anion exchange, GAC, reverse
                                          osmosis, nanofiltration.
------------------------------------------------------------------------


 Table 2 to Paragraph (a)--BATs for Other Synthetic Organic Contaminants Listed in Sec.   141.61(c) and Volatile
                                  Organic Chemicals Listed in Sec.   141.61(a)
----------------------------------------------------------------------------------------------------------------
                                                                            Best available technologies
                           Contaminant                           -----------------------------------------------
                                                                      PTA \1\         GAC \2\         OX \3\
----------------------------------------------------------------------------------------------------------------
(1) Benzene.....................................................               X               X
(2) Carbon tetrachloride........................................               X               X
(3) 1,2-Dichloroethane..........................................               X               X
(4) Trichloroethylene...........................................               X               X
(5) para-Dichlorobenzene........................................               X               X
(6) 1,1-Dichloroethylene........................................               X               X
(7) 1,1,1-Trichloroethane.......................................               X               X
(8) Vinyl chloride..............................................               X
(9) cis-1,2-Dichloroethylene....................................               X               X
(10) 1,2-Dichloropropane........................................               X               X
(11) Ethylbenzene...............................................               X               X
(12) Monochlorobenzene..........................................               X               X
(13) o-Dichlorobenzene..........................................               X               X
(14) Styrene....................................................               X               X
(15) Tetrachloroethylene........................................               X               X
(16) Toluene....................................................               X               X
(17) trans-1,2-Dichloroethylene.................................               X               X
(18) Xylense (total)............................................               X               X
(19) Alachlor...................................................  ..............               X
(20) Aldicarb...................................................  ..............               X
(21) Aldicarb sulfoxide.........................................  ..............               X
(22) Aldicarb sulfone...........................................  ..............               X
(23) Atrazine...................................................  ..............               X
(24) Carbofuran.................................................  ..............               X
(25) Chlordane..................................................  ..............               X
(26) Dibromochloropropane.......................................               X               X
(27) 2,4-D......................................................  ..............               X
(28) Ethylene dibromide.........................................               X               X
(29) Heptachlor.................................................  ..............               X
(30) Heptachlor epoxide.........................................  ..............               X
(31) Lindane....................................................  ..............               X
(32) Methoxychlor...............................................  ..............               X
(33) PCBs.......................................................  ..............               X
(34) Pentachlorophenol..........................................  ..............               X

[[Page 32757]]

 
(35) Toxaphene..................................................  ..............               X
(36) 2,4,5-TP...................................................  ..............               X
(37) Benzo[a]pyrene.............................................  ..............               X
(38) Dalapon....................................................  ..............               X
(39) Dichloromethane............................................               X
(40) Di(2-ethylhexyl)adipate....................................               X               X
(41) Di(2-ethylhexyl)phthalate..................................  ..............               X
(42) Dinoseb....................................................  ..............               X
(43) Diquat.....................................................  ..............               X
(44) Endothall..................................................  ..............               X
(45) Endrin.....................................................  ..............               X
(46) Glyphosate.................................................  ..............  ..............               X
(47) Hexachlorobenzene..........................................  ..............               X
(48) Hexachlorocyclopentadiene..................................               X               X
(49) Oxamyl (Vydate)............................................  ..............               X
(50) Picloram...................................................  ..............               X
(51) Simazine...................................................  ..............               X
(52) 1,2,4-Trichlorobenzene.....................................               X               X
(53) 1,1,2-Trichloroethane......................................               X               X
(54) 2,3,7,8-TCDD (Dioxin)......................................  ..............               X
----------------------------------------------------------------------------------------------------------------
\1\ Packed Tower Aeration.
\2\ Granular Activated Carbon.
\3\ Oxidation (Chlorination or Ozonation).


 Table 3 to Paragraph (a)--List of Small System Compliance Technologies
             (SSCTs) \1\ for PFAS Listed in Sec.   141.61(c)
------------------------------------------------------------------------
                                             Affordable for listed small
   Small system  compliance technologies        system categories \2\
------------------------------------------------------------------------
Anion Exchange............................  All size categories.
GAC.......................................  All size categories.
Reverse Osmosis,\3\ Nanofiltration \3\....  3,301-10,000.
------------------------------------------------------------------------
\1\ Section 1412(b)(4)(E)(ii) of SDWA specifies that SSCTs must be
  affordable and technically feasible for small systems.
\2\ The Act (ibid.) specifies three categories of small systems: (i)
  those serving 25 or more, but fewer than 501, (ii) those serving more
  than 500, but fewer than 3,301, and (iii) those serving more than
  3,300, but fewer than 10,001.
\3\ Technologies reject a large volume of water and may not be
  appropriate for areas where water quantity may be an issue.

* * * * *
[FR Doc. 2024-07773 Filed 4-25-24; 8:45 am]
 BILLING CODE 6560-50-P