[Federal Register Volume 91, Number 3 (Tuesday, January 6, 2026)]
[Proposed Rules]
[Pages 398-444]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2026-00021]
[[Page 397]]
Vol. 91
Tuesday,
No. 3
January 6, 2026
Part II
Environmental Protection Agency
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40 CFR Parts 141 and 142
National Primary Drinking Water Regulation for Perchlorate; Proposed
Rule
Federal Register / Vol. 91, No. 3 / Tuesday, January 6, 2026 /
Proposed Rules
[[Page 398]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 141 and 142
[EPA-HQ-OW-2024-0592; FRL 11689-01-OW]
RIN 2040-AG36
National Primary Drinking Water Regulation for Perchlorate
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule; request for public comment; notification of
public hearing.
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SUMMARY: The U.S. Environmental Protection Agency (``EPA'' or the
``Agency'') is proposing a National Primary Drinking Water Regulation
(NPDWR) for perchlorate and a health-based Maximum Contaminant Level
Goal (MCLG) under the Safe Drinking Water Act (SDWA). In this action,
the EPA is proposing to set the perchlorate MCLG at 0.02 mg/L (20
[micro]g/L). The EPA is also proposing and taking comment on setting an
enforceable Maximum Contaminant Level (MCL) for perchlorate at 0.02 mg/
L (20 [micro]g/L), 0.04 mg/L (40 [micro]g/L), or 0.08 mg/L (80
[micro]g/L). The EPA is also proposing requirements for water systems
to conduct monitoring for perchlorate in drinking water, take
mitigation actions if the level exceeds the MCL, provide information
about perchlorate to their consumers through public notification and
consumer confidence reports, and report to their respective primacy
agency. The Administrator has determined that the benefits of this
regulation would not justify the costs; however, the EPA is required to
issue an NPDWR and MCLG for perchlorate in response to the D.C.
Circuit's decision in NRDC v. Regan.
DATES: Comments must be received on or before March 9, 2026. Comments
on the information collection provisions of the proposed rule under the
Paperwork Reduction Act (PRA) must be received by the Office of
Management and Budget's Office of Information and Regulatory Affairs
(OMB-OIRA) on or before February 5, 2026. Please refer to the PRA
section under ``Statutory and Executive Order Reviews'' in this
preamble for specific instructions. Public hearing: The EPA will hold a
virtual public hearing on February 19, 2026, at https://www.epa.gov/sdwa/perchlorate-drinking-water. Please refer to the SUPPLEMENTARY
INFORMATION section for additional information on the public hearing.
ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OW-2024-0592, by any of the following methods:
Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting
comments.
Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Office of Water Docket, Mail Code 28221T, 1200 Pennsylvania
Avenue NW, Washington, DC 20460.
Hand Delivery or Courier: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operations are 8:30 a.m. to 4:30 p.m.,
Monday through Friday (except Federal Holidays).
Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov, including personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public Participation''
heading of the SUPPLEMENTARY INFORMATION section of this document.
FOR FURTHER INFORMATION CONTACT: Anne Lausier, Standards and Risk
Management Division, Office of Ground Water and Drinking Water (4607M),
Environmental Protection Agency, 1200 Pennsylvania Ave. NW; telephone
number: (202) 564-0518; email address: [email protected].
SUPPLEMENTARY INFORMATION:
I. Executive Summary
II. Public Participation
A. Written Comments
B. Participation in a Virtual Public Hearing
III. General Information
A. What is the EPA proposing?
B. Does this action apply to me?
C. What is the Agency's authority for taking this action?
D. What are the incremental costs and benefits of this action?
IV. Background
A. What is perchlorate?
B. Human Health Effects
C. Statutory Framework and Regulatory History
V. 2025 Health Effects Assessment for Perchlorate
A. Consistency of the EPA's Systematic Review Principles and
Process for Developing Human Health Assessments With Executive Order
14303 Restoring Gold Standard Science
B. Systematic Reviews of the Perchlorate Health Effects
Literature
C. Draft Oral Noncancer Reference Dose Derivation
VI. Maximum Contaminant Level Goal
VII. Maximum Contaminant Level
VIII. Occurrence
IX. Analytical Methods
X. Monitoring and Compliance Requirements
A. Proposed Monitoring Requirements
B. Can States grant monitoring waivers?
C. How are system MCL violations determined?
D. When must systems complete initial monitoring?
E. Can systems use previously collected data to satisfy the
initial monitoring requirements?
F. Can systems composite samples?
XI. Safe Drinking Water Act (SDWA) Right To Know Requirements
A. What are the proposed consumer confidence report (CCR)
requirements?
B. What are the proposed public notification (PN) requirements?
XII. Treatment Technologies
A. Best Available Technologies
B. Small System Compliance Technologies
XIII. Rule Implementation and Enforcement
A. Compliance Date
B. Primacy Requirements
C. State Recordkeeping Requirements
D. State Reporting Requirements
E. Exemptions and Extensions
F. Funding and Technical Assistance Availability
XIV. Health Risk Reduction and Cost Analysis
A. Comparison of Benefits and Costs
B. Uncertainty Analysis
C. Benefit-Cost Determination
XV. Request for Comment on Proposed Rule
XVI. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review
B. Executive Order 14192: Unleashing Prosperity Through
Deregulation
C. Paperwork Reduction Act (PRA)
D. Regulatory Flexibility Act (RFA)
E. Unfunded Mandates Reform Act (UMRA)
F. Executive Order 13132: Federalism
G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
H. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
I. Executive Order 132311: Actions That Significantly Affect
Energy Supply, Distribution, or Use
J. National Technology Transfer and Advancement Act of 1995
K. Consultations With the Science Advisory Board, National
Drinking Water Advisory Council, and the Secretary of Health and
Human Services
XVII. References
I. Executive Summary
The EPA is proposing a NPDWR for perchlorate and a health-based
MCLG under SDWA section 1412, 42 U.S.C. 300g-1, in response to the D.C.
Circuit's decision in NRDC v. Regan, 67 F.4th 397 (D.C. Cir. 2023). In
that decision, the D.C. Circuit held that the EPA must proceed to
regulate a contaminant after finalizing a determination to regulate
even where the Agency later determines that the contaminant does not
satisfy the statutory standard for regulation. To comply with that
decision and a separate consent decree obligation
[[Page 399]]
specifying the date by which the EPA must take final action, the EPA is
proposing to set the perchlorate MCLG at 0.02 mg/L (20 [micro]g/L). The
EPA is also proposing and taking comment on setting an enforceable MCL
for perchlorate at 0.02 mg/L (20 [micro]g/L), 0.04 mg/L (40 [micro]g/
L), or 0.08 mg/L (80 [micro]g/L). The EPA is also proposing
requirements for water systems to conduct monitoring for perchlorate in
drinking water, mitigate perchlorate where it is found in drinking
water, provide information about perchlorate to customers through
public notification and consumer confidence reports, and report to
their respective primacy agency. The EPA's assessment of this proposed
regulation (including less stringent alternatives) is that regulating
perchlorate in this manner fails to satisfy the SDWA prerequisite that
a nationwide regulation must present a meaningful opportunity for
health risk reduction for persons served by public water systems.
Further, the Administrator has determined that the benefits of this
regulation would not justify the costs. However, the D.C. Circuit
decision in NRDC v. Regan requires the Agency to promulgate a NPDWR
based on a regulatory determination the EPA finalized in 2011, which
was based on information and analyses regarding the health effects of
perchlorate exposure and prevalence of perchlorate in drinking water
that has since been updated and now suggest the statutory criteria for
a determination to regulate are no longer met.
Perchlorate is an inorganic chemical compound that occurs naturally
and can also be manufactured. It is commonly used in solid rocket
propellants, munitions, fireworks, airbag initiators for vehicles,
matches, signal flares, and may also be found in fertilizers and as a
byproduct of improper handling of hypochlorite solutions used for
drinking water treatment. Perchlorate exposure to humans occurs
primarily through the ingestion of contaminated food and drinking
water. Other routes of exposure may include tobacco products, household
products such as bleach, dietary supplements, use of signal flares and
fireworks, and occupational exposure to contaminated dust at
perchlorate production facilities. Exposure to perchlorate can
interfere with the function of a person's thyroid gland by inhibiting
iodide uptake, thereby affecting thyroid hormone production. Thyroid
hormones help regulate metabolism and are critical for development,
including brain development. Changes in thyroid hormone levels in
pregnant women are associated with adverse neurodevelopmental effects
in their offspring. Additionally, changes in thyroid hormone levels at
other life stages can lead to hypothyroidism, adverse reproductive and
developmental outcomes, and impacts to the cardiovascular system.
Over the last two decades, the EPA has consistently found that
perchlorate is present in a small percentage of U.S. public drinking
water systems. As envisioned by the SDWA statutory framework, the EPA's
understanding of the adverse human health effects from perchlorate
exposure, and ability to accurately estimate the level at which those
health effects would occur in the population at greater risk, has
evolved over time. Consideration of these two factors--occurrence of
perchlorate in drinking water and the health effects information from
exposure to perchlorate--are critical in informing the Agency's
determination regarding whether to regulate perchlorate under SDWA.
Specifically, SDWA section 1412(b)(1)(A), 42 U.S.C. 300g-1(b)(1)(A),
provides that the EPA shall proceed to regulate a contaminant if the
Administrator finalizes a determination that a contaminant may have
adverse effects on the health of persons, is known or substantially
likely to occur in public water systems (PWSs) with a frequency and at
levels of public health concern, and, in the sole judgement of the
Administrator, regulation of the contaminant presents a meaningful
opportunity for health risk reduction for persons served by PWSs.\1\
SDWA section 1412(b)(4), 42 U.S.C. 300g-1(b)(4), requires that each
MCLG shall be set at the level that avoids adverse effects to human
health, with an adequate margin of safety. Additionally, SDWA section
1412(b)(3)(C)(i)(V), 42 U.S.C. 300g-1(b)(3)(C)(i)(V), requires the EPA
to consider effects on grounds ``at greater risk of adverse health
effects'' from exposure than the general population. Accordingly, the
EPA reviewed the available information to identify the population at
greater risk to adverse health effects following perchlorate exposure,
i.e., the most sensitive population(s), to derive the MCLG. Deriving
the MCLG based on the most sensitive population(s) ensures that the
statutory definition for the MCLG is met and that the level of
perchlorate in drinking water protects both the population at greatest
risk of adverse health effects due to perchlorate exposure and the
general population as well.
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\1\ SDWA section 1401(4), 42 U.S.C. 300f(4), defines ``public
water system'' as ``a system for the provision to the public of
water for human consumption through pipes or other constructed
conveyances, if such system has at least fifteen service connections
or regularly serves at least twenty-five individuals.''
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In 2008, the EPA issued a preliminary determination not to regulate
perchlorate based on its finding that perchlorate was present in very
few PWSs at levels that the available science indicated would adversely
affect human health (73 FR 60262, USEPA, 2008a). At the time, the EPA
estimated health effects from perchlorate exposure using a National
Research Council (NRC) recommended reference dose for perchlorate
exposure for pregnant women and their fetuses, which the NRC identified
as the most sensitive population. In 2009, the EPA issued a
supplemental request for public comment on the EPA's preliminary
determination, noting the complexity of the scientific issues with
determining the level of perchlorate exposure that caused adverse
effects, and the lack of human data for relevant life stages (74 FR
41883, USEPA, 2009a). Given this lack of data and uncertainty, the EPA
proposed using several alternative health reference levels for
perchlorate exposure at sensitive life stages (i.e., developing infants
and children, in addition to pregnant women) which resulted in a much
lower estimate of the level of perchlorate exposure that would
correspond to health impacts. In February 2011, the EPA used these
lower health reference levels, which were not based on a peer-reviewed
model, to finalize a determination to regulate perchlorate (76 FR 7762,
USEPA, 2011).\2\
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\2\ When evaluating adverse health effects in support of the
regulatory determination process, the EPA has historically derived
health reference levels (HRLs) against which the EPA evaluates
occurrence data to determine if contaminants occur at levels of
potential health concern in drinking water. HRLs are not final
values for establishing a protective level of a contaminant in
drinking water; they are derived as part of the regulatory
determination process prior to the development of more-detailed
health analyses that are required under SDWA to support a proposed
NPDWR.
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Following this determination, as required by SDWA section 1412(e),
42 U.S.C. 300g-1(e), the EPA sought recommendations from the Agency's
Science Advisory Board (SAB) in 2012. Specifically, the EPA sought
guidance from the SAB on the modeling approach and health effects
information that was available (and relied upon in the 2011 final
regulatory determination) to derive a MCLG for perchlorate. In
response, the SAB recommended fundamental changes to the approach that
the EPA had used to identify the levels of public health concern in its
2011 determination. The EPA had followed
[[Page 400]]
the NRC recommendation to use a precursor non-adverse effect, iodide
uptake inhibition, as a ``health protective and conservative point of
departure'' for developing a reference dose for perchlorate. When the
EPA brought this approach to the SAB, the SAB recommended that the
Agency appreciably expand the modeling approach beyond the precursor
effect to also account for potential adverse effects in offspring of
women exposed to perchlorate during pregnancy. The SAB noted this
approach ``offers the opportunity for much greater scientific rigor in
establishing quantitative relationships between perchlorate exposure
and adverse effects at sensitive life stages.'' The SAB noted the
previous approach, based on iodide uptake inhibition, ``describes a
precursor event and does not explicitly predict subsequent events or
adverse outcomes'' (USEPA, 2013). Responding to that recommendation,
the EPA undertook a time-intensive effort to develop a biologically
based dose-response model that estimates changes in thyroid hormone
levels as a result of iodine intake and perchlorate exposure in women
prior to pregnancy and early gestation. The new modeling approach
allowed the EPA to estimate adverse neurodevelopmental outcomes from
different levels of perchlorate exposure. To evaluate the scientific
and technical merit of the modeling approach, the EPA submitted this
new model to two independent and sequential peer reviews and revised it
in response to the peer review panels' feedback.
In 2016, while the EPA was finalizing its model, the NRDC sued the
Agency in Federal district court for failing to meet the statutory
deadlines to propose and promulgate an NPDWR for perchlorate. The
parties resolved the deadline suit by entering into a consent decree
with deadlines to issue an NPDWR and MCLG for perchlorate. The consent
decree initially required the Agency to propose an NPDWR and MCLG for
perchlorate in 2018 and finalize an NPDWR and MCLG for perchlorate no
later than December 19, 2019. Those deadlines were later extended to
2019 for proposal, with a final NPDWR and MCLG due by June 19, 2020.
In 2019, the EPA proposed an NPDWR and MCLG for perchlorate (84 FR
at 30524, USEPA, 2019a). In the preamble to the proposed rule, the EPA
sought comment on withdrawing the 2011 determination to regulate based
on the updated health effects information developed as a result of the
SAB recommendations and the EPA's updated analysis of the occurrence of
perchlorate in PWSs. Despite proposing an MCLG and MCL, the EPA's
analysis conducted in support of the 2019 proposal suggested that
perchlorate did not occur in PWSs with a frequency and at levels of
public health concern and that an NPDWR for perchlorate did not present
a meaningful opportunity for health risk reduction in persons served by
PWSs as required to regulate under SDWA section 1412(b)(1)(A), 42
U.S.C. 300g-1(b)(1)(A) (84 FR at 30557, USEPA, 2019a). This request for
comment to withdraw the determination to regulate relied upon the best
available science-based assessments of perchlorate in drinking water at
that time as required by SDWA section 1412(b)(3), 42 U.S.C. 300g-
1(b)(3), including the updated, peer-reviewed health effects assessment
developed with the new SAB-recommended modeling approach and additional
information showing that perchlorate was detected in relatively few
PWSs and at relatively low concentrations.
The EPA reviewed all public comments on its 2019 proposal,
including comments related to the health effects of perchlorate
exposure and the occurrence of perchlorate in drinking water. In 2020,
based on the best available, peer-reviewed science, as required by SDWA
section 1412(b)(3), 42 U.S.C. 300g-1(b)(3), the EPA determined that
finalizing an NPDWR for perchlorate would not present a meaningful
opportunity for health risk reduction for persons served by PWSs, and
therefore revised its determination that a national regulation of
perchlorate was justified under the SDWA. The EPA took final action to
withdraw the 2011 determination to regulate perchlorate and did not
promulgate a final NPDWR (85 FR at 43990, USEPA, 2020a).
In the final action notice, the EPA recognized that a small number
of systems may need to address perchlorate in drinking water. The EPA
included a discussion on the ways in which the Agency would support
States and PWSs in managing perchlorate risk, where applicable.
Specifically, the EPA expressed its commitment to working with States
and communities in addressing perchlorate contamination in drinking
water, including through direct outreach, information, and technical
assistance. After issuing the proposed rule in 2019, the EPA contacted
the PWSs that the Agency had identified as having perchlorate levels
above 18 [micro]g/L and found that many systems had already taken
actions to reduce perchlorate levels in their drinking water. The EPA
released a report, Reductions of Perchlorate in Drinking Water,
detailing how perchlorate levels in drinking water supplies have
decreased since the EPA made a determination to regulate perchlorate in
2011 (USEPA, 2020b).
Additionally, the EPA released a fact sheet, Steps Water Systems
Can Take to Address Perchlorate in Drinking Water (USEPA, 2020c), with
recommendations and best practices for PWSs that may be concerned about
levels of perchlorate in drinking water. This includes recommendations
for voluntary sampling, treatment options, storage and handling of
hypochlorite solutions which can contribute to perchlorate
contamination, non-treatment options, and recommendations for
communicating with customers about any voluntary sampling and actions
taken.
Finally, the EPA stated in its 2020 final action notice that the
Agency may consider updating the 2008 interim perchlorate health
advisory in the future in the absence of an NPDWR. SDWA section
1412(b)(1)(F), 42 U.S.C. 300g-1(b)(1)(F), provides that the EPA may
publish health advisories or take other appropriate actions for
contaminants not subject to NPDWRs. The 2008 interim health advisory
for perchlorate (15 [micro]g/L) is non-regulatory and non-enforceable
but provides technical information to State agencies on health effects,
analytical methodologies, and treatment technologies associated with
drinking water contamination.
In NRDC v. Regan, the D.C. Circuit subsequently vacated the EPA's
withdrawal of its 2011 determination to regulate perchlorate. The panel
majority held that the EPA lacked authority under the SDWA to withdraw
a determination to regulate a contaminant and must proceed to regulate,
despite new and additional data and analyses that changed the
scientific underpinnings of the original regulatory determination.
Specifically, the panel majority held that when the EPA issues a final
determination to regulate a contaminant under the SDWA, the EPA must
propose and finalize a NPDWR and MCLG regardless of new scientific
information indicating that national regulation is not justified. 67
F.4th at 402. The D.C. Circuit's vacatur ultimately had the effect of
reviving the EPA's separate consent decree obligation to propose and
finalize an NPDWR and MCLG for perchlorate, and the district court
entered revised deadlines for the EPA to do so. Currently, the EPA is
required to sign a proposed NPDWR and MCLG for publication by January
2, 2026, and to sign a final rule and MCLG by May 21, 2027.
Since 2023, the EPA has conducted further review of the best
available
[[Page 401]]
science on perchlorate health effects and occurrence data to include
new information that was not factored into its 2019 proposal or 2020
decision to withdraw the determination to regulate perchlorate. The
additional information evaluated by the EPA reaffirms the science-based
conclusions that perchlorate does not occur in public drinking water
systems at levels of public health concern as required under SDWA
section 1412(b)(1)(A), 42 U.S.C. 300g-1(b)(1)(A). Furthermore, the EPA
has evaluated the best available information on benefits and costs of
this proposed rule as required by SDWA section 1412(b)(3)(C), 42 U.S.C.
300g-1(b)(3)(C), including the benefits and costs of alternative
regulatory options developed and considered. The EPA again finds, as in
2020, that the benefits do not justify the costs for this proposed rule
or for the alternative regulatory options considered (see section XIV.C
of this preamble for discussion of this finding and request for
comment).
Despite the Agency's science-based conclusion that perchlorate does
not occur in public drinking water systems across the nation ``with a
frequency and at levels of public health concern'' and that issuing an
NPDWR for perchlorate would not present a meaningful opportunity for
health risk reduction for persons served by PWSs, see SDWA section
1412(b)(1)(A), 42 U.S.C. 300g-1(b)(1)(A), the EPA is compelled by the
D.C. Circuit's decision in NRDC v. Regan to issue an NPDWR for
perchlorate.\3\ Absent the D.C. Circuit's decision, the Agency would
reject an NPDWR as an appropriate tool to address potential health
risks from perchlorate. The Agency would instead update the 2008
Interim Health Advisory and take other appropriate actions similar to
those conducted by the Agency in 2020. In this proposed rule, the
Agency has attempted to reduce burdens to the many systems that do not
have levels of perchlorate above the MCL but would nonetheless be
required to monitor for perchlorate by a final NPDWR for perchlorate.
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\3\ As the EPA recently explained in the Agency's announcement
of preliminary regulatory determinations for contaminants on the
fifth drinking water contaminant candidate list, the NRDC v. Regan
D.C. Circuit ruling has led to changes in the Agency's approach to
regulating contaminants. The EPA noted that the ``ruling present[ed]
a change to the EPA's understanding of the flexibilities afforded to
the agency under the SDWA,'' explaining that prior to the decision
``the EPA had understood that the agency could withdraw a positive
determination if, during the more-detailed analyses conducted during
the development of the proposed rule . . . the EPA determined that
the potential for health-risk reduction was less beneficial than
initially predicted'' (90 FR at 3820, USEPA, 2025a). In deciding
whether to regulate a contaminant under SDWA, the Agency will ``need
to be more certain of the potential for health-risk reduction
through regulation before making a determination to regulate a
contaminant'' and, to obtain that certainty, the Agency will need to
develop and ``consider preliminary health benefits analysis
information to support the finding that a positive determination
would provide a meaningful opportunity for health risk reduction if
the agency decides to regulate a contaminant under the SDWA'' (90 FR
at 3837, USEPA, 2025a).
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The EPA is proposing an MCLG for perchlorate in drinking water
based on the best available science (USEPA, 2025b) following the
Agency's current peer-reviewed systematic review methods (USEPA,
2022b), consistent with SDWA requirements, Executive Order 14303
Restoring Gold Standard Science (90 FR 22601) (see section V of this
preamble), and the EPA's human health risk assessment guidance and best
practices (e.g., USEPA, 2012b; USEPA, 2002b; USEPA, 2022b). The EPA
updated its 2019 health assessment to incorporate more recent health
effects literature and the EPA's peer-reviewed systematic review
methods (USEPA, 2022b), which were not available during the development
of the 2019 health assessment. An MCLG is the maximum level of a
contaminant in drinking water at which no known or anticipated adverse
effect on the health of persons would occur, allowing an adequate
margin of safety (SDWA section 1412(b)(4)(A), 42 U.S.C. 300g-
1(b)(4)(A)).
The EPA is proposing an MCLG of 20 [micro]g/L derived from a draft
reference dose of 1 [mu]g/kg/day. The proposed MCLG is the level of
perchlorate in drinking water expected to protect the population at
greater risk for adverse health effects following perchlorate exposure.
The population at greater risk is the offspring of iodine deficient,
hypothyroxinemic women exposed to perchlorate during their first
trimester of pregnancy. Hypothyroxinemia is characterized by normal
thyroid stimulating hormone (TSH) levels and thyroid hormone (free
thyroxine [fT4]) levels below the normal range. This MCLG protects
against a one point decrease in the mean IQ in the population at
greatest risk (the smallest IQ decrement that can be measured in an
individual; as measured in children at approximately 6-8 years in the
critical study). As this level is set for the population at greatest
risk, it in turn protects against adverse health effects following
perchlorate exposure in the general population, consistent with the
statutory definition of an MCLG. The EPA is also proposing an
enforceable MCL for perchlorate. An MCL is the maximum level allowed of
a contaminant in water which is delivered to any user of a PWS (SDWA
section 1401(3), 42 U.S.C. 300f(3)). The SDWA generally requires that
the EPA set the MCL ``as close to the maximum contaminant level goal as
is feasible'' (SDWA section 1412(b)(4)(B), 42 U.S.C. 300g-1(b)(4)(B)),
or, if the Administrator determines the health benefits of the MCL do
not justify the cost, at the level where the cost is justified by the
benefits (SDWA section 1412(b)(6)(A), 42 U.S.C. 300g-1(b)(6)). The EPA
is proposing to set an MCL of 20, 40, or 80 [micro]g/L, and seeking
comment on whether the Agency should consider any additional MCLs. As
explained below, although the EPA proposes that any of the proposed
MCLs would be feasible, the Administrator has determined that there is
no MCL at which the benefits of treatment at a limited number of
systems justify the costs of monitoring across systems where
perchlorate is not expected to occur at levels of concern.
The EPA is also proposing monitoring, reporting, and other
requirements for PWSs to meet the perchlorate MCL. Monitoring is a key
component of the NPDWR and assures that water systems affected by
perchlorate are identified and take action to be in compliance with the
MCL (see section X of this preamble for discussion of the proposed
monitoring and compliance requirements). The EPA is proposing
requirements for community water systems (CWSs) and non-transient non-
community water systems (NTNCWSs) to monitor for perchlorate in
drinking water where the monitoring frequency of a PWS depends on the
previous monitoring results. Because the EPA has determined that the
vast majority of water systems are not likely to have perchlorate
levels at the level of public health concern, the proposal includes
provisions that would attempt to reduce burden on both systems and
States compared to the standard monitoring requirements for other
regulated inorganic compounds (IOCs). This includes provisions that
would automatically reduce monitoring frequency for systems based on
initial sampling results, thereby reducing burden on States to make
individual system determinations. The EPA is also proposing the use of
previously collected data to satisfy initial monitoring requirements to
reduce burden on systems (see section X.A of this preamble for
additional discussion on the requirements for initial and reduced
monitoring).
Water systems with perchlorate levels that exceed the proposed MCL
would need to take action to comply with the MCL. Under the EPA's
proposal, these systems could install water treatment or
[[Page 402]]
consider options such as using a new uncontaminated water source (e.g.,
drilling a new well) or connecting to an uncontaminated water source.
Ion exchange, reverse osmosis, and biological treatment technologies
have been demonstrated to remove perchlorate from drinking water to
levels that would comply with the proposed MCL. These treatment
technologies can be installed at a water system's treatment plant.
Certified reverse osmosis point-of-use (POU) devices are also available
for small systems to reduce perchlorate levels below the MCL (see
section XII of this preamble for discussion on available treatment
technologies). See the Economic Analysis of the Proposed Perchlorate
National Primary Drinking Water Regulation (section 4.3, USEPA, 2025i)
for details on estimating water system costs. Water systems which
exceed the proposed MCL would also be required to conduct public
notification. The EPA is proposing that water systems issue Tier 1
public notification following an MCL exceedance based on the effect of
short-term exposure on the most sensitive population (the fetuses of
pregnant, hypothyroxinemic women with iodine deficiency in their first
trimester of pregnancy) identified from review of the available data
(see section XI.B of this preamble for more information on public
notification requirements).
In proposing a rule under the SDWA, the EPA must evaluate
quantifiable and nonquantifiable health risk reduction benefits and
costs in accordance with the statute's health risk reduction and cost
analysis (HRRCA) requirements (SDWA section 1412(b)(3)(C), 42 U.S.C.
300g-1(b)(3)(C)). This includes benefits and costs associated with
monitoring, reporting, and mitigation actions. The SDWA also requires
that the EPA determine whether the benefits of the proposed rule
justify the costs (SDWA section 1412(b)(4)(C), 42 U.S.C. 300g-
1(b)(4)(C)). In accordance with these requirements and considering the
best available science-based assessments, the Administrator is making a
determination in this preamble that the quantified and unquantifiable
benefits of the proposed perchlorate NPDWR do not justify the costs
(see section XIV of this preamble for additional discussion on the
HRRCA). This finding is the same conclusion reached by the
Administrator in the 2019 proposed drinking water rule for perchlorate
(84 FR 30555, USEPA, 2019a). The EPA is proposing requirements that
will attempt to reduce monitoring costs while identifying systems with
levels of perchlorate at or above the MCL; however, due to infrequent
perchlorate occurrence at levels of health concern, the vast majority
of the approximately 66,000 water systems that would be subject to the
rule will incur substantial administrative and monitoring costs with
limited or no corresponding public health benefit as a whole. The EPA
evaluated which entities would be affected by the rule, quantified
costs using available data and statistical models, and described
unquantifiable costs. The EPA also developed a qualitative summary of
benefits expected to result from the monitoring for perchlorate, and
the removal of perchlorate and potential co-occurring contaminants.
Public participation and consultations with key stakeholders are
critical in developing an implementable drinking water rule. The EPA
has engaged with stakeholders and consulted with entities such as the
National Drinking Water Advisory Council (NDWAC), water systems, and
State, Tribal, and local governments (see section XVI of this preamble
on EPA's Statutory and Executive Order reviews). The EPA is requesting
comment on this action, including the proposed NPDWR and MCLG and the
Administrator's determination that the benefits do not justify the
costs, and has identified specific areas where public input will be
helpful for the EPA in developing the final rule (see section XV of
this preamble for a discussion of topics highlighted by the EPA for
public comment).
II. Public Participation
A. Written Comments
Submit your comments, identified by Docket ID No. EPA-HQ-OW-2024-
0592, at https://www.regulations.gov (our preferred method), or the
other methods identified in the ADDRESSES section. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received to its public docket. Do not submit to the
EPA's docket at https://www.regulations.gov any information you
consider to be Confidential Business Information (CBI), Proprietary
Business Information (PBI), or other information whose disclosure is
restricted by statute. Multimedia submissions (audio, video, etc.) must
be accompanied by a written comment. The written comment is considered
the official comment and should include discussion of all points you
wish to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e., on the web,
cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the
full EPA public comment policy; information about CBI, PBI, or
multimedia submissions; and general guidance on making effective
comments.
B. Participation in Virtual Public Hearing
The EPA is hosting a virtual public hearing on February 19, 2026,
to receive public comment on the proposed requirements of the proposed
perchlorate NPDWR. The hearing will be held virtually from
approximately 1 p.m. to 4 p.m. eastern time. The EPA will begin pre-
registering speakers for the hearing upon publication of this document
in the Federal Register. To attend and/or register to speak at the
virtual hearing, please use the online registration form available at
https://www.epa.gov/sdwa/perchlorate-drinking-water. The last day to
pre-register to speak at the hearing will be February 12, 2026. On
February 16, 2026, the EPA will post a general agenda for the hearing
that will list pre-registered speakers in approximate, sequential order
at https://www.epa.gov/sdwa/perchlorate-drinking-water. The number of
online connections available for the hearing is limited and will be
offered on a first-come, first-served basis. To submit visual aids to
support your oral comment, please contact [email protected] for
guidelines and instructions by February 12, 2026.
Early registration is strongly encouraged to ensure proper
accommodations and adequate timing. The EPA will make every effort to
follow the schedule as closely as possible on the day of the hearing;
however, please plan for the hearing to run either ahead of schedule or
behind schedule. Please note that the public hearing may close early if
all business is finished.
The EPA encourages commenters to provide a written copy of their
oral testimony electronically by submitting it to the public docket at
https://www.regulations.gov, Docket ID: EPA-HQ-OW-2024-0592. Oral
comments will be time limited to maximize participation, which may
result in the full statement not being given during the virtual hearing
itself. Therefore, the EPA also recommends submitting the text of oral
comments as written comments to the rulemaking docket. The EPA will
also accept written comments submitted to the public docket, as
provided above, from persons
[[Page 403]]
not making an oral comment. Written statements and supporting
information submitted during the comment period will be considered with
the same weight as oral comments and supporting information presented
at the public hearing.
Please note that any updates made to any aspect of the hearing are
posted online at https://www.epa.gov/sdwa/perchlorate-drinking-water.
While the EPA expects the hearing to go forward as set forth above,
please monitor the Agency's website or contact [email protected]
to determine if there are any updates. The EPA does not intend to
publish a document in the Federal Register announcing updates about the
public virtual hearing.
If you require any accommodations for the day of the hearing, such
as language translation, captioning, or special accommodations, please
indicate this and describe your needs when you register. All requests
for accommodations should be submitted by February 12, 2026. Without
this one-week minimum advance notice, the EPA may not be able to
arrange accommodations. Please contact [email protected] with
any questions related to the virtual public hearing.
III. General Information
A. What is the EPA proposing?
Pursuant to its consent decree obligations and the D.C. Circuit's
decision in NRDC v. Regan, the EPA is proposing for public comment an
MCLG and an NPDWR for perchlorate in public drinking water supplies.
Specifically, the EPA is proposing a MCLG of 0.02 mg/L (20 [micro]g/L)
and is proposing and seeking comment on an enforceable MCL at 20, 40,
or 80 [micro]g/L, despite the Agency's science-based conclusion that
perchlorate does not occur in public drinking water systems at levels
of public health concern and that issuing an NPDWR for perchlorate
would not present a meaningful opportunity for health risk reduction
for persons served by PWSs, as required by the SDWA, and that there is
no MCL at which the benefits of treatment in a limited number of
systems justify the costs of monitoring nationwide. The EPA is also
proposing monitoring requirements for perchlorate under 40 CFR 141
subpart C, public notification requirements under 40 CFR 141 subpart Q,
and Consumer Confidence Report (CCR) requirements under 40 CFR 141
subpart O.
B. Does this action apply to me?
Entities that could potentially be affected by this proposed rule
include the following:
[GRAPHIC] [TIFF OMITTED] TP06JA26.000
This table is not intended to be exhaustive but rather provides a
guide for readers regarding entities likely to be regulated by this
action. Other types of entities not included could also be regulated.
To determine whether your entity is regulated by this action, please
read the full preamble and proposed rule.
As part of this notice for the proposed rule, ``State'' refers to
the agency of the State, Tribal, or territorial government that has
jurisdiction over PWSs consistent with the definition of ``State'' in
40 CFR 141.2. During any period when a State or Tribal government does
not have primacy enforcement responsibility pursuant to section 1413 of
SDWA, 42 U.S.C. 300g-2, the term ``State'' means the relevant Regional
Administrator of EPA. For questions regarding the applicability of this
action to a particular entity, consult the person listed in the FOR
FURTHER INFORMATION CONTACT section.
C. What is the Agency's authority for taking this action?
Section 1412(b)(1)(A) of SDWA requires the EPA to establish an
NPDWR for a contaminant when the Administrator has determined 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 with a frequency and at levels of public
health concern; and (3) where in the sole judgment of the
Administrator, regulation of such a contaminant presents a meaningful
opportunity for health risk reduction for persons served by PWSs. 42
U.S.C. 300g-1(b)(1)(A).
In 2020, based on the best available science regarding perchlorate
health effects and occurrence data, the EPA withdrew its 2011 final
determination to regulate perchlorate under SDWA section 1412(b)(1)(A),
42 U.S.C. 300g-1(b)(1)(A). In May 2023, the D.C. Circuit vacated the
EPA's withdrawal of the 2011 determination to regulate perchlorate
after holding that the EPA lacks authority under the SDWA to withdraw a
determination to regulate a contaminant. NRDC v. Regan, 67 F.4th 397.
As explained in this preamble, the EPA's scientific analyses and data
continue to indicate that perchlorate is not likely to occur with a
frequency and at levels of public health concern and therefore does not
meet the SDWA criteria for regulation. The EPA is nonetheless obligated
to propose this NPDWR pursuant to its consent decree obligations and
the D.C. Circuit's decision, which bars the Agency from finalizing an
action other than a NPDWR and MCLG even when the Agency determines that
the available
[[Page 404]]
evidence, including the best available scientific data, does not
support the statutory findings that are the prerequisite for regulation
of a contaminant.
D. What are the incremental costs and benefits of this action?
The incremental cost of this proposed rule is the difference
between the quantified costs that would be incurred if the proposed
rule were finalized and baseline conditions. The incremental benefits
of this proposed rule reflect the avoided future adverse health
outcomes attributable to perchlorate reduction due to actions
undertaken to comply with the proposed rule. For the proposed MCL of 20
[micro]g/L, the annualized incremental cost of the proposed rule in
2023 dollars is $16.1 million at a 3 percent discount rate and $18.9
million at a 7 percent discount rate. The monetized annualized
incremental benefit of the proposed rule in 2023 dollars is $8.3
million at a 3 percent discount rate and $1.6 million at a 7 percent
discount rate. Therefore, the monetized net annualized incremental
benefit is -$7.8 million at a 3 percent discount rate and -$17.3
million at a 7 percent discount rate.
For the proposed MCL of 40 [micro]g/L, the annualized incremental
cost of the proposed rule in 2023 dollars is $11.2 million at a 3
percent discount rate and $13.7 million at a 7 percent discount rate.
The monetized annualized incremental benefit of the proposed rule in
2023 dollars is $6.8 million at a 3 percent discount rate to $1.3
million at a 7 percent discount rate. Therefore, the monetized net
annualized incremental benefit is -$4.4 million at a 3 percent discount
rate to -$12.4 million at a 7 percent discount rate.
For the proposed MCL of 80 [micro]g/L, the annualized incremental
cost of the proposed rule in 2023 dollars is $8.6 million at a 3
percent discount rate and $10.9 million at a 7 percent discount rate.
The monetized annualized incremental benefit of the proposed rule in
2023 dollars is $5.3 million at a 3 percent discount rate to $1.0
million at a 7 percent discount rate. Therefore, the monetized net
annualized incremental benefit is -$3.3 million at a 3 percent discount
rate to -$9.9 million at a 7 percent discount rate. In addition, the
EPA expects there will be additional non-monetized benefits and costs
that result from the proposed action. Please see section XIV of this
preamble for details.
IV. Background
A. What is perchlorate?
Perchlorate is a negatively charged inorganic ion that is comprised
of one chlorine atom bound to four oxygen atoms
(ClO4-) and is both a naturally occurring and
manufactured chemical. It is formed naturally by photochemical
reactions with atmospheric ozone, after which it can be deposited in
soils and found within mineral deposits in certain geographical areas
(Bao and Gu, 2004; Michalski et al., 2004). In the United States,
perchlorate can accumulate in arid and semi-arid areas (Rao et al.,
2007). In the United States, perchlorate in the environment is also
associated with commercial fertilizers from Chilean saltpeter (mined
and imported from Chile's Atacama Desert), which are known to have
naturally high levels of perchlorate (USEPA, 2001).
Perchlorate is also produced synthetically and used in military and
industrial applications. It is primarily used as an oxidizer, in the
form of ammonium perchlorate, in solid fuels used to power rockets,
missiles, and fireworks (ATSDR, 2008). In 1994, U.S. production of
ammonium perchlorate was estimated at 22 million pounds; more recent
production data are not available (ATSDR, 2008). Historically, the
majority of perchlorate production took place at facilities in Nevada
and Utah (NDEP, 2013). Perchlorate salts are highly soluble in water,
and because perchlorate adheres poorly to mineral surfaces and organic
material, perchlorate is mobile in soil and aqueous environments
(ATSDR, 2008; USEPA, 2002a). The perchlorate ion is very stable and
inert to reduction (Urbansky, 2000). Under normal environmental
conditions in ground water and surface water, the ion may persist for
decades (Gullick et al., 2001). Additionally, trace amounts of
perchlorate can enter drinking water through improper handling and
degradation of hypochlorite solutions used for drinking water treatment
(AWWA/WaterRF, 2009).
For the general population, perchlorate exposure occurs mainly
through the ingestion of contaminated food and drinking water (USEPA,
2025b; ATSDR, 2008). Of the foods evaluated by the FDA total diet
study, 74 percent had at least one sample with detectable levels of
perchlorate (FDA, 2007; Murray et al., 2008). Perchlorate has also been
detected in drinking water supplies and tap water which indicates that
for those exposed in the general population, ingestion of water
containing perchlorate may be a significant exposure pathway. Other
potential perchlorate exposure sources include tobacco products
(Ellington et al., 2001), common household products such as bleach
(Gibbs et al., 1998), dietary supplements (Snyder et al., 2006),
ingestion of contaminated soil by children, and the use of signal
flares and fireworks. Occupational exposure at perchlorate production
facilities may occur via perchlorate dusts via inhalation or oral
routes (Gibbs et al., 1998).
B. Human Health Effects
The well-established mode of action (MOA) for perchlorate is
inhibition of iodide \4\ uptake in the thyroid gland by competitively
binding to the sodium-iodide symporter (NIS) (NRC, 2005; USEPA, 2013;
USEPA, 2019b). This decrease in iodide uptake results in a decrease in
the synthesis of two key thyroid hormones, triiodothyronine (T3) and
thyroxine (T4) since iodide is necessary for the synthesis of thyroid
hormones (NRC, 2005; USEPA, 2013; USEPA, 2019b; Blount et al., 2006;
Steinmaus et al., 2007; Steinmaus et al., 2013; Steinmaus et al., 2016;
McMullen et al., 2017; Knight et al., 2018). Decreased T3 and T4 levels
result in an increase in TSH levels, the hormone that acts on the
thyroid gland to stimulate iodide uptake to increase thyroid hormone
production (Blount et al., 2006; NRC, 2005; Steinmaus et al., 2013;
Steinmaus et al., 2016; USEPA, 2019). See the draft Health Effects TSD
for more information about perchlorate's mode of action (USEPA, 2025b).
Because thyroid hormones are essential for the development and
differentiation of the brain, changes in thyroid hormone levels in
pregnant women can cause permanent adverse neurodevelopmental effects
in their offspring (USEPA, 2025b). (USEPA, 2013; USEPA, 2019b; Korevaar
et al., 2016; Fan and Wu, 2016; Wang et al., 2016; Alexander et al.,
2017; Thompson et al., 2018). For example, decreased maternal T4 levels
during pregnancy, including in the hypothyroxinemic range, are
associated with intelligence quotient (IQ) decrements in offspring
(Alexander et al., 2017; Thompson et al., 2018; Wang et al., 2016;
USEPA, 2013; USEPA, 2019b). See the draft Health Effects TSD (USEPA,
2025b) and the Economic Analysis (USEPA, 2025i) for more information
about other potential health effects.
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\4\ For the purposes of this document, ``iodine'' will be used
to refer to dietary intake before entering the body. Once in the
body, ``iodide'' will be used to refer to the ionic form.
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[[Page 405]]
C. Statutory Framework and Regulatory History
1. Statutory Framework
The SDWA, the primary Federal law protecting tap water provided to
consumers by water systems across the country, was enacted in 1974 in
response to ``accumulating evidence that our drinking water contains
unsafe levels of a large variety of contaminants.'' Envtl. Def. Fund,
Inc. v. Costle, 578 F.2d 337, 339 (D.C. Cir. 1978). In passing the
SDWA, Congress intended to ensure ``that water supply systems serving
the public meet minimum national standards for protection of public
health'' (H.R. Rep. No. 93-1185, at 1 (1974)).
Congress amended the SDWA in 1996 to establish a stepwise process
for the EPA to identify unregulated contaminants and assess whether
they are appropriate for regulation under the Act (H.R. Rep. 104-
632(l), at 8 (1996); S. Rep. 104-169, at 2 (1995)). In contrast to
prior versions of the statute, which required the EPA to establish
regulations for an enumerated list of contaminants, Congress
established a ``flexible'' process to ensure that the EPA's
regulations, and the burdens imposed by those rules on water systems
nationwide, addressed contaminants that posed the most significant
health risks. See H.R. Rep. 104-632(l) at 8 (1996); S. Rep. 104-169 at
2 (1995). In the 1996 amendments, Congress required that once every
five years, the EPA must issue a list of no more than 30 unregulated
contaminants to be monitored by PWSs (SDWA section 1445(a)(2), 42
U.S.C. 300j-4(a)(2)). The EPA implements such monitoring through the
Unregulated Contaminant Monitoring Rule (UCMR), which collects data
from CWSs and NTNCWSs. In addition to prescribing a 5-year cycle of
monitoring to gather occurrence data on unregulated contaminants,
Congress also required the EPA to, every five years, publish a list of
contaminants that are known or anticipated to occur in PWSs and are not
currently subject to proposed or promulgated NPDWRs, known as the
Contaminant Candidate List (CCL) (SDWA section 1412(b)(1)(B)(i), 42
U.S.C. 300g-1(b)(1)(B)(i)). In accordance with Congress' revised
statutory framework, the EPA uses the CCL to identify priority
contaminants for regulatory decision-making and information collection.
The EPA included perchlorate on the first three CCLs, published in
1998, 2005, and 2009, respectively. The most recent, CCL 5, released in
November 2022 includes 81 contaminants and contaminant groups (87 FR
68060, USEPA, 2022a).
The EPA collects available data on a contaminant included on the
CCL to better understand its potential health effects and to determine
the levels at which it occurs in drinking water. SDWA section
1412(b)(1)(B)(ii), 42 U.S.C. 300g-1(b)(1)(B)(ii), requires that, every
five years, after considering public comment on a ``preliminary''
regulatory determination, the EPA must issue a determination to
regulate or not to regulate at least five contaminants on the CCL. 42
U.S.C. 300g-1(b)(1)(B)(ii). When making a determination to regulate a
contaminant in drinking water, SDWA section 1412(b)(1)(A), 42 U.S.C.
300g-1(b)(1)(A), requires that the EPA determine whether: (1) the
contaminant may have an adverse effect on the health of persons; (2)
the contaminant is known to occur or there is substantial likelihood
the contaminant will occur in public water systems with a frequency and
at levels of public health concern; and (3) in the sole judgment of the
Administrator, regulation of the contaminant presents a meaningful
opportunity for health risk reductions for persons served by public
water systems. 42 U.S.C. 300g-1(b)(1)(A). Pursuant to SDWA section
1412(b)(1)(B)(ii)(IV), a determination not to regulate is a reviewable
agency action. 42 U.S.C. 300g-1(b)(1)(B)(ii)(IV).
When the EPA determines not to regulate a contaminant because all
three statutory criteria at 1412(b)(1)(A) are not met, other non-
regulatory options are available for both the EPA and States to address
potential risks from unregulated contaminants. Such contaminants could
be included in subsequent CCLs for possible reevaluation based on new
data or included in future UCMRs. Further, SDWA section 1412(b)(1)(F),
42 U.S.C. 300g-1(b)(1)(F), expressly provides the EPA with authority to
``publish health advisories (which are not regulations) or take other
appropriate actions'' for contaminants not subject to any NPDWR. In
SDWA section 1414(e), 42 U.S.C. 300g-3(e), Congress also preserved
States' authority to promulgate State drinking water laws, providing
that nothing in the Act ``shall diminish any authority of a State . . .
to adopt or enforce any law . . . respecting drinking water regulations
or public water systems, but no such law shall relieve any person of
any requirement otherwise applicable under this [Act].''
A determination to regulate triggers a schedule for proposing and
finalizing a regulation setting a drinking water standard for the
contaminant. If the EPA finds that the contaminant meets the three
statutory criteria and finalizes a determination to regulate, the EPA
must issue a proposed NPDWR and MCLG within 24 months and publish and
promulgate a final NPDWR and MCLG within 18 months of the proposal
(SDWA section 1412(b)(1)(E), 42 U.S.C. 300g-1(b)(1)(E)) with the
possibility of a 9-month extension. Once the EPA decides to regulate a
contaminant, the statute lays out several steps that must be taken
before proposing an NPDWR, including developing a Health Risk Reduction
and Cost Analysis (HRRCA), which is an extensive cost, risk, and
benefit analysis that is subject to public comment (SDWA section
1412(b)(3)(C), 42 U.S.C. 300g-1(b)(3)(C)) and consulting with the SAB
(SDWA section 1412(e), 42 U.S.C. 300g-1(e)). Specifically, SDWA section
1412(e) requires that, ``prior to proposal of a maximum contaminant
level goal and national primary drinking water regulation,'' the EPA
must ``request comments from the Science Advisory Board.''
Prior to the D.C. Circuit's 2023 decision in NRDC v. Regan, the EPA
had long understood that the Agency could withdraw a section
1412(b)(1)(A), 42 U.S.C. 300g-1(b)(1)(A), final regulatory
determination if, during the more-detailed analyses required by the
statute during the subsequent development of a proposed NPDWR, the EPA
determined that the potential for health-risk reduction was less
beneficial than initially estimated. Based on the D.C. Circuit's
decision holding that the EPA cannot reevaluate the basis for a final
regulatory determination based on additional data obtained and analyzed
following that determination, the Agency has been forced to change its
approach to the regulatory determination process. As explained in the
EPA's January 2025 preliminary regulatory determinations for nine
contaminants on the CCL 5, the EPA will now ``need to consider
preliminary health benefits analysis information to support the finding
that a positive determination would provide a meaningful opportunity
for health risk reduction if the agency decides to regulate a
contaminant under the SDWA'' (90 FR at 3841, USEPA, 2025a). In other
words, the EPA will need to ensure it can satisfy the statutory
standards and prerequisite findings for a rulemaking before finalizing
a regulatory determination.
The SDWA requires that a proposed and final NPDWR must be
accompanied by the setting of an MCLG, which is a non-enforceable
health objective set at a level at which ``no known or anticipated
adverse effects on the health of persons occur and which allows an
adequate
[[Page 406]]
margin of safety'' (SDWA section 1412(b)(4)(A), 42 U.S.C. 300g-
1(b)(4)(A)). If the EPA is establishing an enforceable MCL in its
NPDWR, the SDWA generally requires that the EPA set the MCL ``as close
to the maximum contaminant level goal as is feasible'' (SDWA section
1412(b)(4)(B), 42 U.S.C. 300g-1(b)(4)(B)) or, if the Administrator
determines the benefits do not justify the cost, at the level where the
cost is justified by the benefits (SDWA section 1412(b)(6)(A), 42
U.S.C. 300g-1(b)(6)(A)) or when ``the Administrator finds that it is
not economically or technologically feasible to ascertain the level of
the contaminant'' (SDWA section 1412(b)(7), 42 U.S.C. 300g-1(b)(7)). In
those circumstances, the EPA may issue alternative standards (see
sections VII and XIV.A of this preamble for the EPA's evaluation of
alternative MCLs).
``Feasible'' is defined in SDWA section 1412(b)(4)(D), 42 U.S.C.
300g-1(b)(4)(D) as ``feasible with the use of the best technology,
treatment techniques and other means which the Administrator finds,
after examination for efficacy under field conditions and not solely
under laboratory conditions, are available (taking cost into
consideration).'' The technology, treatment techniques, or other means,
must have been tested beyond the laboratory under full-scale
conditions, but need not necessarily be in widespread, full-scale use.
Further, in selecting the best available technology, treatment
techniques, and other means, the EPA evaluates the ability of the
technology to reduce the level of the contaminant, and the
technological and economic feasibility of the technologies being
considered. The EPA has historically taken the position that
``feasibility'' is to be defined relative to what may reasonably be
afforded by large metropolitan or regional public water systems. (H.R.
Rep. No. 93-1185, at 6454, 6471(1974); see also S. Rep. No. 104-169, at
3 (1995) (feasibility is based on best available technology affordable
to ``large'' systems); City of Portland v. EPA, 507 F.3d 706 (D.C. Cir.
2007) (upholding the EPA's interpretation that ``feasible'' means
technically possible and affordable). As a result, the EPA historically
has not set different standards based solely on what is reasonably
afforded by small and medium systems. However, if the EPA cannot
identify any affordable technologies for a particular category of small
systems, the EPA must identify variance technologies that ``achieve the
maximum reduction or inactivation efficiency that is affordable'' and
protect public health (SDWA section 1412(b)(15)(A) and (b)(15)(B), 42
U.S.C. 300g-1(b)(15)(A), (B)).
Once a final NPDWR is in effect and an MCL has been established for
a contaminant, SDWA section 1414(c)(1)(A), 42 U.S.C. 300g-3(c)(1)(A),
requires PWSs to provide notice to the public if the water system fails
to comply with an applicable MCL. SDWA section 1414(c)(2), 42 U.S.C.
300g-3(c)(2), states that the Administrator ``shall by regulation . . .
prescribe the manner, frequency, form, and content for giving notice.''
SDWA section 1414(c)(2)(C), 42 U.S.C. 300g-3(c)(2), specifies
additional requirements related to public notice if the violation has
the potential to have serious adverse effects on human health as a
result of short-term exposure, including that it must ``be distributed
as soon as practicable, but not later than 24 hours'' after the PWS
learns of the violation or exceedance, and that the system must report
the violation to both the State and the Administrator within that same
time period.
SDWA section 1445(a), 42 U.S.C. 300j-4(a), provides that every
person subject to a requirement of SDWA or grantee \5\ shall establish
and maintain records, make reports, conduct monitoring, and provide
information to the Administrator as reasonably required by regulation
to assist the Administrator in establishing regulations under SDWA,
determining compliance with SDWA, administering any program of
financial assistance under SDWA, evaluating the health risks of
unregulated contaminants, and advising the public of such risks.
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\5\ SDWA section 1445(e), 42 U.S.C. 300j-4(e), defines
``grantee'' for purposes of section 1445 as ``any person who applies
for or receives financial assistance, by grant, contract, or loan
guarantee under this subchapter,'' and ``person'' is defined to
include a Federal agency.
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2. National Research Council Evaluation of Perchlorate (2005)
In 2005, the EPA and other Federal agencies asked the National
Research Council (NRC) to evaluate the human health effects of
perchlorate ingestion and to derive an oral reference dose (RfD), an
estimate of a daily exposure to humans that is likely to be without an
appreciable risk of adverse health effects. The NRC concluded that
perchlorate exposure inhibits the transport of iodide into the thyroid
by a protein molecule known as the sodium/iodide symporter (NIS), which
can lead to decreases in the two main thyroid hormone levels,
triiodothyronine (T3) and thyroxine (T4), and corresponding increases
in thyroid-stimulating hormone (TSH) levels (NRC, 2005). Additionally,
the NRC concluded that the most sensitive population to perchlorate
exposure is ``the fetuses of pregnant women who might have
hypothyroidism or iodide deficiency'' (NRC, 2005; p. 178). Following
the NRC's recommendations, the EPA issued an RfD of 0.7 [mu]g/kg/day
for perchlorate in 2005 (USEPA, 2005a). This value was based on a no-
observed-effect level (NOEL) \6\ of 7 [mu]g/kg/day, which was based on
a level identified for perchlorate's inhibition of radioactive iodine
uptake (RAIU), a measure of a precursor event which is considered
``non-adverse'' (USEPA, 2013), in a study (Greer et al., 2002) of
healthy adults and the application of a total uncertainty factor (UF)
of 10 to account for intraspecies variability.
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\6\ In the Integrated Risk Information System (IRIS) assessment
for perchlorate (2005a), the EPA used a NOEL (rather than a no-
observed-adverse-effect level or NOAEL) as the point of departure
because iodide uptake inhibition is not itself an adverse effect,
but a biochemical precursor.
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3. Regulatory Determination for Perchlorate
In October 2008, pursuant to SDWA section 1412(b)(1)(B), 42 U.S.C.
300g-1(b)(1)(B), the EPA issued a preliminary determination not to
regulate perchlorate in drinking water and requested public comment (73
FR 60262, USEPA, 2008a). Based on its evaluation of health and
occurrence data on perchlorate against the criteria in SDWA section
1412(b)(1)(A), 42 U.S.C. 300g-1(b)(1)(A), the EPA tentatively concluded
that, while perchlorate may have an adverse effect on the health of
persons at sufficient levels of exposure, an NPDWR would not provide a
meaningful opportunity to reduce health risk as required by the statute
(73 FR at 60265, USEPA, 2008a). Using pregnant women as the most
sensitive population for perchlorate exposure, the EPA derived and used
a health reference level (HRL) of 15 [micro]g/L using the Agency's RfD
of 0.7 [micro]g/kg/day as a level expected to be protective of all
populations (73 FR at 60267, USEPA, 2008a). Primarily using occurrence
data from UCMR 1, the EPA estimated that 0.8 percent of water systems
(serving approximately 2 million persons, of which approximately 1
million were female ``and thus might become pregnant at some point in
their lives'') had one or more detections with perchlorate levels above
the HRL (73 FR at 60267, USEPA, 2008a). The EPA further estimated that
900,000 people were served by the entry points (EPs) above the HRL
within those systems. At any one time, an estimated 1.4 percent
[[Page 407]]
of the general population served by the PWSs that detected perchlorate
above the HRL were pregnant women, based on the number of live births
as a percentage of the total U.S. population (73 FR at 60267, USEPA,
2008a). Thus, ``a best estimate of about 16,000 pregnant women (with a
high-end exposed estimate of 28,000 using the total system population)
could be exposed at levels exceeding the HRL at any given time'' (73 FR
at 60267, USEPA, 2008a). Based on the small percentage of PWSs where
drinking water detections were above the HRL, the EPA therefore
concluded there was not a meaningful opportunity for health risk
reduction through an NPDWR that would require monitoring and compliance
actions by all CWSs and NTNCWSs (73 FR at 60267, USEPA, 2008a).
In the October 2008 proposal, the EPA explicitly sought public
comment on the model that the Agency used to arrive at its HRL. The EPA
noted that ``[o]ne of the analyses that EPA considered for this
preliminary determination is a physiologically-based pharmacokinetic
(PBPK) model that predicts radioactive iodide uptake (RAIU) inhibition
in the thyroid for various sub-populations and drinking water
concentrations'' (73 FR at 60265, USEPA, 2008a). The EPA noted that the
Agency made adjustments to the model prior to considering it for the
preliminary regulatory determination, and that it would be appropriate
to have those adjustments peer-reviewed to ensure ``the model is
appropriate for use in assessing health outcomes associated with
perchlorate exposure'' (73 FR at 60265, USEPA, 2008a). The EPA stated
its intent to complete this review before publishing a final regulatory
determination.
In December 2008, the EPA issued an Interim Health Advisory for
perchlorate of 15 [micro]g/L, consistent with the derived HRL, to
assist State and local officials in addressing local contamination of
perchlorate in drinking water while the Agency conducted its evaluation
of the opportunity to reduce risks through an NPDWR (USEPA, 2008b).
Health advisories are non-enforceable and non-regulatory and provide
technical information to State agencies and other public health
officials on health effects, analytical methodologies, and treatment
technologies associated with drinking water contamination. Health
advisories help States, Tribes, and local governments inform the public
and determine whether local actions are needed to address public health
impacts in affected communities. For more details, see ``Interim
Drinking Water Health Advisory for Perchlorate'' (USEPA, 2008b). Prior
to the EPA issuing its Interim Health Advisory, two States established
their own perchlorate drinking water standards based on their own
state-level health effects evaluations. Massachusetts promulgated a
drinking water standard for perchlorate in 2006 and California
promulgated a drinking water standard for perchlorate in 2007.
In August 2009, the EPA published a supplemental request for public
comment on additional approaches for analyzing the data related to the
EPA's preliminary regulatory determination (74 FR 41883, USEPA, 2009a).
This request for public comment included alternative approaches to
deriving a level of health concern. In explaining the need for
additional public comment following the close of the comment period on
the 2008 preliminary regulatory determination, the EPA noted that the
comments that the Agency received ``underscore the complexity of the
scientific issues regarding the regulatory determination for
perchlorate in drinking water'' (74 FR at 41884, USEPA, 2009a). The EPA
noted that external peer reviewers of its PBPK model offered a number
of recommendations, including ``that the uncertainty inherent in the
modeling exercise should be made more transparent to the public'' (74
FR at 41885, USEPA, 2009a). Specifically, peer reviewers noted the
uncertainty due to ``the lack of human data for specific life stages
including pregnant women and their fetuses, lactating women and their
babies, and bottle-fed infants for which rat data were adapted'' (74 FR
at 41885, USEPA, 2009a). In the notice, the EPA requested comment on
whether the Agency should not use the PBPK model to inform the
selection of an HRL and should instead apply the NRC recommended RfD of
0.7 [micro]g/kg/day directly to exposures of other sensitive life
stages to derive potential alternative HRLs for 14 life stages,
including infants and children (74 FR at 41886, USEPA, 2009a). This
alternative approach responded to comments expressing concern about the
adequacy of the HRL for all sensitive life stages, including concerns
about higher exposure of infants to perchlorate and potential negative
health effects (74 FR at 41887, USEPA, 2009a). The EPA noted that some
of the life stage specific alternatives under consideration could
result in an HRL much lower than what was identified in the October
2008 notice and requested comment on the ``merits of the approach of .
. . deriving HRLs based on the RfD combined with the life stage
specific exposure data and whether there are other approaches that may
be useful for deriving HRLs'' (74 FR at 41889, USEPA, 2009a).
In February 2011, the EPA issued a final determination to regulate
perchlorate in drinking water under SDWA section 1412(b)(1)(B), 42
U.S.C. 300g-1(b)(1)(B), reversing course from the 2008 preliminary
determination not to regulate perchlorate (76 FR 7762, USEPA, 2011).
This determination considered the public comments from the October 2008
and August 2009 notices. In arriving at this determination, the EPA
assessed the public health impacts of perchlorate using the alternative
HRLs proposed in the August 2009 notice. Each of these potential HRLs
was much lower than the single HRL used to inform the 2008 preliminary
determination--4 [micro]g/L in the 2009 notice versus 15 [micro]g/L in
the 2008 notice--and, thus, the likelihood of perchlorate to occur at
levels of health concern was significantly higher in comparison to the
levels described in the October 2008 notice. The EPA explained that
``[g]iven the range of potential alternative HRLs, EPA has reversed its
October 2008 preliminary determination'' (76 FR at 7765, USEPA, 2011).
With respect to the PBPK model, the EPA ``decided that the model does
not directly bear on the current decision regarding the need for an
NPDWR for perchlorate,'' but stated that the EPA ``is continuing to
evaluate whether the model could be used in setting an NPDWR for
perchlorate'' (76 FR at 7767, USEPA, 2011).
In 2011, the EPA concluded that up to 16 million people could be at
risk of exposure to perchlorate at levels of health concern, rather
than the 2 million people described in the October 2008 notice. While
the 2011 regulatory determination did not include an estimate of the
number of pregnant women potentially affected, applying the 1.4 percent
of live births per year used in the 2008 notice results in 224,000
pregnant women (the most sensitive population identified) affected
compared to the 28,000 estimated in 2008. Based on the lower HRL and
related greater occurrence estimates, the EPA determined that
perchlorate met the three statutory criteria for regulating a
contaminant, finding that perchlorate may have an adverse effect on the
health of persons; that perchlorate is known to occur or there is a
substantial likelihood that perchlorate will occur in PWSs with a
frequency and at levels of public health concern; and that in the sole
judgment of the Administrator, regulation of perchlorate in drinking
water systems presents a meaningful
[[Page 408]]
opportunity for health risk reduction for persons served by PWSs (76 FR
7762, USEPA, 2011).
4. Recommendations From the EPA's Science Advisory Board
Following the 2011 determination to regulate perchlorate, as
required by SDWA section 1412(e), 42 U.S.C. 300g-1(e), the EPA
requested comment from the SAB prior to the proposal of an NPDWR and
MCLG (77 FR 31847, USEPA, 2012a). Specifically, the EPA asked for
advice from the SAB on how to best consider and interpret life stage
information and PBPK analyses, as well as data that post-dated the 2005
NRC health effects assessment for perchlorate which had informed the
Agency's 2011 regulatory determination.
In response and based on the available science, in 2013 the SAB
recommended that the EPA:
``. . . Derive an MCLG for perchlorate . . . us[ing] a
mode of action approach and physiologically-based pharmacokinetic/
pharmacodynamic iodide uptake inhibition (PBPK/PD-IUI) modeling to
integrate this information . . . PBPK/PD-IUI modeling provides a more
rigorous tool to integrate the totality of information available on
perchlorate, and this approach may better address different life stage
susceptibilities to perchlorate than the default MCLG approach''
(USEPA, 2013, p. 1-2); and
``Extend the [BBDR] model expeditiously to . . . provide a
key tool for linking early events with subsequent events as reported in
the scientific and clinical literature on iodide deficiency, changes in
thyroid hormone levels, and their relationship to neurodevelopmental
outcomes during sensitive early life stages'' (USEPA, 2013, p. 19).
The SAB's recommended framework incorporates the endpoint of iodide
uptake inhibition that was the basis for the NRC and the EPA Integrated
Risk Information System (IRIS) RfD (USEPA, 2005a) into a broader and
more comprehensive framework that links perchlorate exposure to adverse
neurodevelopmental outcomes. The framework also focuses on the
decreases in fT4 levels associated with maternal hypothyroxinemia and
subsequent adverse neurodevelopmental health effects rather than the
changes in both fT4 and TSH associated with hypothyroidism.
Specifically, the SAB noted that while the 2005 NRC assessment
``concluded that the first adverse effect in the continuum of effects
from perchlorate exposure would be hypothyroidism,'' the SAB found that
``hypothyroxinemia (i.e., low levels of thyroid hormone) is a more
appropriate indicator of the potential adverse health effects than the
more pronounced decreases in thyroid hormone associated with
hypothyroidism'' (USEPA, 2013). Furthermore, the SAB recommended that
the EPA consider the available data on potential adverse health effects
(i.e., neurodevelopmental outcomes) from thyroid hormone-level
perturbations (USEPA, 2013) because such thyroid hormone perturbations
do not need to be caused by perchlorate exposure to be relevant for
inclusion in the model.
5. Implementing the SAB Recommendations--Biologically Based-Dose
Response (BBDR) Modeling Approach (2017-2019)
Based on the SAB's recommendations (USEPA, 2013) and input from two
independent peer-review panels in 2017 (USEPA, 2017) and 2018 (USEPA,
2018), the EPA developed a two-step biologically based-dose response
(BBDR) modeling approach that relates thyroid hormone effects,
specifically fT4 levels, after perchlorate exposure in pregnant women
to adverse neurodevelopmental outcomes in children (see Figure 1
below). The new model allowed the EPA to estimate adverse
neurodevelopmental outcomes from different levels of perchlorate
exposure, unlike the NRC reference dose relied upon in the EPA's 2011
regulatory determination, which measured a ``precursor, non-adverse
effect'' for perchlorate based on iodide uptake inhibition (USEPA,
2013). In the first step of the BBDR modeling approach, the BBDR model
estimates serum fT4 levels in iodine-deficient pregnant women in the
first trimester. In the second step, the maternal ft4 levels are
related to neurodevelopmental health effects in the offspring.
Specifically, the BBDR model's serum fT4 results are integrated with
data from an epidemiological study evaluating the impact of maternal
thyroid hormone levels and offspring neurodevelopmental outcomes. This
modeling approach was used to inform the MCLG for perchlorate in the
2019 rule proposal. Additional details on model development can be
found in the EPA's Technical Support Document: Deriving a Maximum
Contaminant Level Goal for Perchlorate in Drinking Water (hereafter
referred to as the ``2019 TSD'') (USEPA, 2019b) and the accompanying
Proposed Approaches to Inform the Derivation of a Maximum Contaminant
Level Goal for Perchlorate in Drinking Water Volumes 1-3 (hereafter
referred to as the ``Approaches Report'') (USEPA, 2019c; USEPA, 2019d;
USEPA, 2019e).
[GRAPHIC] [TIFF OMITTED] TP06JA26.001
In the 2019 TSD, the EPA used this BBDR modeling approach to derive
a noncancer toxicity value for perchlorate (USEPA, 2019b). To inform
the second step of the BBDR model and consistent with the SAB
recommendation that the EPA ``consider available data on potential
adverse health effects (neurodevelopmental outcomes) due to thyroid
hormone level perturbations regardless of the cause of those
perturbations'' (USEPA, 2013), the EPA
[[Page 409]]
evaluated 71 epidemiological studies that investigated the association
between maternal thyroid hormone levels and neurodevelopmental
outcomes. Given the well-established MOA (see section IV.B of this
preamble), the recommendations of the SAB, and the large volume of
scientific literature investigating this association, other health
outcomes were not evaluated at that time (USEPA, 2019b). Of the studies
evaluated in the 2019 TSD, five studies were selected for dose response
assessment and ultimately data from Korevaar et al. (2016) was selected
to inform the BBDR modeling approach because it had sufficient
quantitative data for modeling (3,600 usable mother/child data pairs),
appropriately addressed confounding variables, and assessed an adverse
neurodevelopmental endpoint of decreased IQ in children (USEPA, 2019b).
The other studies identified did not provide one or more of those
features. The EPA solicited comments from external peer reviewers on
its analysis of Korevaar et al. (2016) and whether better studies or
strategies were available (no major changes were recommended).
Additional details on study selection for the 2019 health assessment
can be found in the 2019 TSD (USEPA, 2019b), the Approaches Report
(USEPA, 2019c; USEPA, 2019d; USEPA, 2019e), and corresponding external
peer review (USEPA, 2018).
6. 2019 Proposed Perchlorate NPDWR
In 2016, while the EPA was finalizing the BBDR model, the NRDC
filed a complaint in the U.S. District Court for the Southern District
of New York alleging that the EPA had failed to meet the statutory
deadline for proposing and finalizing an NPDWR for perchlorate. The
parties resolved the deadline suit by entering into a consent decree
requiring the Agency propose an NPDWR and MCLG for perchlorate in 2018
and finalize an NPDWR and MCLG for perchlorate no later than December
19, 2019. Those deadlines were later extended to 2019 for proposal,
with a final NPDWR and MCLG by June 19, 2020, to allow the Agency time
to complete and incorporate feedback from the peer-review of the BBDR
model as well as to complete the statutorily required health and risk
reduction analysis.
On June 26, 2019, the EPA proposed an NPDWR and MCLG for
perchlorate (84 FR 30524, USEPA, 2019a). The EPA proposed to establish
an enforceable MCL and a MCLG at 56 [micro]g/L and requested public
comment on two alternative MCL and MCLG values of 18 [micro]g/L and 90
[micro]g/L.\7\ As part of the rulemaking, the EPA conducted a new
analysis of health effects information from perchlorate exposure based
on the SAB's recommendation and using the BBDR modeling approach
explained above, as well as a new analysis of perchlorate occurrence in
PWSs. Based on these new analyses, the EPA solicited comment on the
alternative option of withdrawing the 2011 regulatory determination (84
FR at 30557, USEPA, 2019a). Specifically, the EPA explained that its
recent findings on occurrence and health effects using the SAB-
recommended BBDR modeling approach ``suggest that perchlorate does not
occur in public water systems with a frequency and at levels of public
health concern'' and further ``suggest that the regulation of
perchlorate does not present a meaningful opportunity for risk
reduction for persons served by public water systems,'' as required for
a positive regulatory determination by SDWA section 1412(b)(1)(A), 42
U.S.C. 300g-1(b)(1)(A) (84 FR at 30557, USEPA, 2019a). The EPA found
that, even at an MCL of 18 [micro]g/L (the lowest alternative MCL),
similar to the Agency's finding in the 2008 preliminary regulatory
determination based on a health reference level of 15 [micro]g/L, there
would be very few PWSs that would exceed the regulatory threshold. The
EPA noted examples of prior instances where the Agency had determined
that there was not a meaningful opportunity for risk reduction from
exposure to a contaminant that was more prevalent in systems than
perchlorate.
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\7\ These three different proposed MCLG values of 18, 56, and 90
[micro]g/L corresponded, respectively, to the level of perchlorate
in drinking water expected to protect against a one, two, and three-
point IQ decrement in the most sensitive life stage identified.
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7. 2020 Final Action on Perchlorate and Litigation
On July 21, 2020, after reviewing the public input received on the
proposed perchlorate NPDWR as well as data obtained and analyses
conducted since 2011, the EPA took final action to withdraw the 2011
determination to regulate (85 FR 43990, USEPA, 2020a). The EPA
explained that its peer-reviewed health effects analysis indicated that
the concentrations of perchlorate estimated to present levels of public
health concern were higher than the health reference levels that the
Agency considered in the 2011 regulatory determination. Re-evaluating
occurrence data based on the 2019 proposed MCLG range (18-90 [micro]g/
L), the EPA also found that the occurrence of perchlorate in PWSs
exceeding those levels was significantly lower than the frequency
considered in the 2011 regulatory determination analysis (0.03%-0.002%
in 2020 versus 4%-0.39% in 2011) (85 FR at 43993, USEPA, 2020a). Based
on that information, the EPA determined that perchlorate does not occur
in PWSs ``with a frequency and at levels of public health concern'' as
required by SDWA section 1412(b)(1)(A)(ii), 42 U.S.C. 300g-
1(b)(1)(A)(ii). The EPA further found that the national regulation of
perchlorate did not present a ``meaningful opportunity for health risk
reduction for persons served by public water systems'' within the
meaning of SDWA section 1412(b)(1)(A)(iii), 42 U.S.C. 300g-
1(b)(1)(A)(iii). Thus, because two of the three required statutory
factors for a positive regulatory determination were not met, the EPA
withdrew the determination to regulate rather than proceeding with a
final NPDWR and MCLG.
In the preamble to the withdrawal action, the EPA explained that,
while it had not previously had occasion to withdraw a regulatory
determination under the 1996 amendments, its decision to do so was
supported by the statutory text and structure of SDWA as well as
relevant legislative history. Indeed, the perchlorate regulation
determination was the first such determination to regulate a
contaminant that the Agency had issued through the new regulatory
determination process codified in 1996. The EPA explained that its
decision to withdraw the 2011 regulatory determination was consistent
with Congress' direction to apply its regulatory authorities and
prioritize SDWA regulations based on the best available public health
information, citing to SDWA section 1412(b)(1)(B)(ii)(II), 42 U.S.C.
300g-1(b)(1)(B)(ii)(II) (findings supporting a determination to
regulate ``shall be based on the best available public health
information'') and SDWA section 1412(b)(3)(A), 42 U.S.C. 300g-
1(b)(3)(A) (requiring the use of ``the best available, peer-reviewed
science and supporting studies conducted in accordance with sound and
objective scientific practices'' in taking actions, including
regulatory determinations, under section 1412). The EPA explained that,
while it recognized that SDWA does not include a provision explicitly
authorizing the withdrawal of a regulatory determination, Congress
could not have intended that the EPA's regulatory decision-making ``be
hamstrung by older data when newer, more accurate scientific and public
health data . . . demonstrate that regulation of a new
[[Page 410]]
contaminant would not present a meaningful opportunity for health risk
reduction'' (85 FR at 43992, USEPA, 2020a). Further, the EPA noted that
SDWA section 1412(b)(1)(B)(ii)(IV), 42 U.S.C. 300g-1(b)(1)(B)(ii)(IV),
specifically provides that a decision not to regulate a contaminant is
a final Agency action subject to judicial review, but Congress did not
specify the same with respect to determinations to regulate (85 FR at
43992, USEPA, 2020a).
With respect to SDWA's legislative history, the EPA noted that in
1996, Congress repealed the statutory requirement for the EPA to
regulate an additional 25 contaminants every three years and replaced
it with the current requirement for the EPA to determine whether
regulation is warranted for five contaminants every five years. This
change was animated by concerns heard by Congress that, under SDWA's
initial 25 contaminant paradigm, the EPA's water quality experts were
forced ``to spend scarce resources searching for dangers that often do
not exist rather than identifying and removing real health risks from
our drinking water'' (S. Rep. 104-169 at 12 (1995)).
In its 2020 action, the EPA concluded that ``new data and analysis
developed by the Agency as part of the 2019 proposal demonstrate that
the occurrence and health effects information used as the basis for the
2011 determination no longer constitute `best available information' ''
as required by SDWA section 1412, 42 U.S.C. 300g-1, and further, that
the Agency's 2011 findings were ``no longer accurate, and no longer
support the Agency's prioritization of perchlorate for regulation'' (85
FR at 43992). The Agency found that the EPA was thus no longer
authorized by the statute to promulgate an NPDWR for perchlorate, and
further, that it would not be in the public interest to do so.
NRDC filed a petition for review of the EPA's 2020 withdrawal
action before the D.C. Circuit. In May 2023, the D.C. Circuit vacated
and remanded the EPA's July 2020 withdrawal of its determination to
issue a drinking water regulation for perchlorate in NRDC v. Regan. The
panel majority held that SDWA requires that the EPA must proceed to
regulate after making a determination to regulate a contaminant.
Specifically, the panel majority focused on the language in SDWA
section 1412(b)(1)(E), 42 U.S.C. 300g-1(b)(1)(E), providing that
``[f]or each contaminant that the Administrator determines to
regulate'' the Administrator ``shall publish'' an NPDWR and MCLG in
accordance with the statutory timelines. 67 F.4th at 401-02. Relying on
the use of the term ``shall'' in this provision, the panel majority
found that the Agency lacked authority to withdraw its determination to
regulate. Id. at 402. The court rejected the EPA's argument that the
statute and general principles of administrative law provided the EPA
with implicit authority to revisit a positive regulatory determination,
which the Agency noted is not a final, reviewable Agency action under
the statute. Instead, the panel majority found that Congress had
limited the EPA's discretion to reconsider positive determinations by
providing that the EPA ``shall publish'' a proposed rule and MCLG after
issuing a positive regulatory determination. Id. at 402-03.
The panel majority posited that, while new science between a
determination to regulate and issuance of an NPDWR would not justify
revisiting the regulatory determination, ``EPA can--and must--account
for those changes when setting the appropriate regulatory level.'' Id.
at 403.
One panel member concurred in the judgment only and disagreed with
the majority's holding that the EPA cannot withdraw a regulatory
determination based on new scientific evidence, noting her view that,
where the ``agency had not yet proposed and promulgated a final
regulation when it made a new finding that the best available, peer
reviewed science no longer supported its prior regulatory
determination'' the EPA ``may appropriately reverse a decision to
regulate based on a change in scientific evidence, after engaging in
notice-and-comment procedures.'' Id. at 410 (Pan, J., concurring in the
judgment).
As explained in sections V and VIII of this preamble the EPA has
accounted for the latest science and occurrence data in proposing this
NPDWR and MCLG. However, despite the data continuing to show low
perchlorate occurrence levels and the costs associated with
establishing an NPDWR outweighing the anticipated public health
benefits, the EPA is precluded by the D.C. Circuit's decision in NRDC
v. Regan from reconsidering whether national regulation of perchlorate
is supported by the statute.
Following the D.C. Circuit's vacatur of the 2020 withdrawal action,
the parties modified the consent decree with new deadlines for the
Agency to propose and finalize an NPDWR for perchlorate. Pursuant to
the revised consent decree, as further revised in November 2025, the
EPA is required to propose an NPDWR and MCLG for perchlorate by January
2, 2026, and sign a final NPDWR and MCLG for perchlorate by May 21,
2027 (NRDC v. EPA, No. 2:16-cv-01251 (S.D.N.Y.), Dkt. No. 110 (Nov. 21,
2025)). Today's action is in accordance with the revised consent
decree.
V. 2025 Health Effects Assessment for Perchlorate
The EPA is requesting public comment on the 2025 draft health
effects TSD for perchlorate (USEPA, 2025b), included in the docket for
this rulemaking.
A. Consistency of the EPA's Systematic Review Principles and Process
for Developing Human Health Assessments With Executive Order 14303
Restoring Gold Standard Science
The EPA's 2025 draft health effects TSD (USEPA, 2025b) for
perchlorate was developed using the Agency's peer-reviewed systematic
review methods to identify, evaluate, and use the best available
science (USEPA, 2022b). Systematic review is a structured and
documented process for identifying, selecting, assessing, and
summarizing the findings of studies relevant to the human health
assessment goals and scope. The health assessment development process
based on systematic review is consistent with SDWA requirements,
Executive Order 14303 Restoring Gold Standard Science (90 FR 22601, May
29, 2025), and the EPA's human health risk assessment guidance and best
practices (e.g., USEPA, 2012b; USEPA, 2002b; USEPA, 2022b). The EPA's
2025 draft health effects TSD for perchlorate is consistent with all
nine tenets of Gold Standard Science (Section 3, 90 FR 22601).
1. Reproducible
Reproducibility is one of the key principles of systematic review.
The thorough documentation required at all steps of systematic review
enables reproducibility of the assessment conclusions by the scientific
community and the public. The 2025 draft health effects TSD for
perchlorate (USEPA, 2025b) followed the EPA's systematic review methods
(USEPA, 2022b), ensuring reproducibility through extensive
documentation of the methods and results (e.g., see sections 4, 5, 6 in
the 2025 draft TSD and sections A.1.3 to A.1.9 in Appendix A) (USEPA,
2025b).
2. Transparent
Like reproducibility, transparency is a core principle of
systematic review. The 2025 draft health effects TSD (USEPA, 2025b)
contains extensive documentation of every step in the
[[Page 411]]
EPA's assessment development process. Examples include a description of
literature search terms and the study relevancy screening criteria
(section A.1.3; Tables A-3 and A-5) and study evaluation results, which
are publicly available via the Health Assessment Workspace
Collaborative (HAWC) perchlorate page (https://hawc.epa.gov/assessment/100500419/).
3. Communicative of Error and Uncertainty
Transparent documentation of all systematic review and assessment
development steps leads to clear communication of error and
uncertainties. The 2025 draft health effects TSD includes lengthy
discussions of potential errors and uncertainties related to reference
dose derivation (section 5.2.5.1), the epidemiological evidence base
(section 7.2.1), and other potentially sensitive populations (section
7.2.3) (USEPA, 2025b).
4. Collaborative and Interdisciplinary
The EPA systematic review process requires technical experts from
multiple scientific fields, such as epidemiology and toxicology, to
ensure a comprehensive evaluation of the health effects information and
development of conclusions. This collaborative and interdisciplinary
approach strengthens the scientific rigor of resulting health
assessments. The 2025 draft health effects TSD was developed by a team
of systematic review experts, epidemiologists, toxicologists, public
health experts, and statistical modelers (see Acknowledgements section
USEPA, 2025b).
5. Skeptical of its Findings and Assumptions
The EPA's systematic review steps of evaluating the potential bias
of individual studies, following an evidence determination framework,
and documenting uncertainties support this tenet. The in-depth
evaluation of individual studies leads to a rigorous evidence
determination/integration process and allows for robust
characterization of data gaps and limitations, thus increasing
confidence in overall assessment conclusions. For example, see methods
outlined in section A.1.6 with results reported throughout section 4
(USEPA, 2025b).
6. Structured for Falsifiability of Hypotheses
Systematic review steps consistent with this tenet include the
identification and use of studies agnostic of results, evaluation of
studies for potential bias, evidence determination and integration, and
clear documentation of uncertainties. Systematic review steps allow for
falsifiability of hypotheses by first using criteria agnostic to study
results to identify all relevant studies (e.g., see section A.1.3 in
USEPA, 2025b). All relevant studies were independently evaluated by
multiple scientists for potential bias and received a confidence rating
following a pre-defined study evaluation framework which was agnostic
to study results (see section 3.4.1.3 and section A.1.6 in USEPA,
2025b).
7. Subject to Unbiased Peer Review
During the EPA's systematic review process, studies are identified
from peer-reviewed literature databases agnostic of results. In the
2025 draft health effects TSD for perchlorate, the process for
identifying and incorporating peer-reviewed studies into the assessment
is transparently documented (see literature identification in section
3.4.1.1 and literature screening in section 3.4.1.2 (USEPA, 2025b)).
The foundational science linking perchlorate exposure to
neurodevelopmental effects, i.e., the two-step modeling approach, is
based on the peer-reviewed literature and underwent multiple
independent external peer review processes, including by the SAB
(USEPA, 2013) and two independent peer review panels in 2017 (USEPA,
2017) and 2018 (USEPA, 2018).
8. Accepting of Negative Results as Positive Outcomes
The EPA's systematic review method for identifying literature is
agnostic to results. Specifically, the EPA identifies studies based on
the analysis of health effects following exposure to a chemical of
interest and not based on study results (i.e., studies reporting null
findings or significant findings are considered). In addition, negative
results from studies are included during study evaluation, evidence
determination and integration, and uncertainty characterization. In the
2025 draft health effects TSD, the evidence integration process
(section A.1.9 in USEPA, 2025b) included consideration of negative or
inconsistent results and applied the appropriate evidence determination
in such cases (i.e., evidence inadequate). Following this process, two
of the three health outcomes (i.e., cardiovascular and neurological
effects) were determined to have inadequate evidence (USEPA, 2025b).
9. Without Conflicts of Interest
Throughout the EPA's structured systematic review process there are
steps to ensure that the development of the health assessment is
without conflicts of interest. Specific steps include study
identification from peer-reviewed literature databases, transparent
documentation of the systematic review process and results, use of
studies agnostic of results, and evaluation of studies for potential
bias. For example, the 2025 draft health effects TSD relied on publicly
available peer-reviewed literature databases queried as part of
systematic review (sections 3.4.1.1 and A.1.4.2 in USEPA, 2025b). The
use of peer-reviewed literature minimizes the potential for conflicts
of interest because peer-reviewed scientific journals require a
conflict of interest (COI) statement by authors and reviewers to ensure
research integrity, transparency, and to alert readers to potential
biases. In unusual circumstances when journal articles have not met
some COI requirements, the EPA may require additional independent peer
review of scientific journal articles to meet Information Quality
guideline requirements for COI (see Final Information Quality Bulletin
for Peer Review) (OMB, 2005).
B. Systematic Reviews of the Perchlorate Health Effects Literature
The EPA must ensure that the MCLG is based on the best available
science, and accordingly, must account for changes in science after it
makes its determination to regulate but before it proposes the NPDWR
(SDWA section 1412(b)(3)(A), 42 U.S.C. 300g-1(b)(3)(A)). Accordingly,
the 2025 draft health effects TSD describes the results of two fit-for-
purpose systematic reviews performed according to the Agency's peer-
reviewed systematic review methods described above (USEPA, 2022b) to
identify the best available science, including studies published since
the 2019 TSD, to inform the perchlorate oral RfD and MCLG. The first
systematic review was designed to identify human epidemiological and
animal toxicological data relevant to oral perchlorate exposure and
health effects in four major health outcome categories (endocrine,
neurological, cardiovascular, and cancer). The second systematic review
was designed to identify studies of the relationship between decreased
maternal T4 levels, which reflect in utero thyroid levels, and
neurodevelopmental health effects in offspring that had the potential
to be used in the BBDR modeling approach
[[Page 412]]
that was used in the 2019 TSD to derive the RfD (USEPA, 2019b; USEPA,
2019c), consistent with recommendations from the SAB (USEPA, 2013).
From the results of the first systematic review, the EPA concluded
that the available evidence indicates (likely) \8\ that oral
perchlorate exposure is likely to cause adverse endocrine, including
thyroid, effects in humans, consistent with the well-established MOA
for perchlorate (NRC, 2005; USEPA, 2013; USEPA, 2019b). The EPA also
concluded that the evidence is inadequate to assess whether perchlorate
exposure may directly cause either nervous system or cardiovascular
effects in humans. Based on the epidemiology and toxicology studies of
cancer effects identified in the first literature search and systematic
review and in accordance with the Guidelines for Carcinogen Risk
Assessment (USEPA, 2005b), the EPA maintains the conclusion that
perchlorate is Not Likely to Be Carcinogenic to Humans. As such, the
EPA did not perform a cancer dose-response assessment for perchlorate
and did not derive an MCLG based on cancer effects (see section 4.1.4
of the 2025 draft health effects TSD for information on the
carcinogenicity assessment for perchlorate). Informed by these 2024
perchlorate health hazard systematic review results, the EPA maintained
the 2-step BBDR modeling approach used in 2019 (see section IV of this
preamble).
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\8\ The EPA's Staff Handbook for Developing IRIS Assessments
(USEPA, 2022b) describes terminology for evidence integration
judgments based on reviewing the weight of evidence for each health
outcome. The evidence integration judgement terms are either
evidence demonstrates, evidence indicates (likely), evidence
suggests, evidence inadequate, or strong evidence supports no
effect.
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After evaluating the relevant literature identified in the second
systematic review, Korevaar et al. (2016), the study that the EPA
previously selected in 2019 (USEPA, 2019b), was selected as the
critical study because it remains the best available study to inform
the relationship between maternal fT4 levels and neurodevelopmental
outcomes in children. See the 2025 draft health effects TSD (USEPA,
2025b) for more information about the systematic reviews.
C. Draft Oral Noncancer Reference Dose Derivation
In deriving an RfD in the 2019 proposed NPDWR, the EPA selected a 2
percent decrement in the mean population level IQ as the benchmark
response (BMR), among evaluations of a 1 percent, 2 percent, and 3
percent BMR (USEPA, 2019b). IQ is on a 100-point scale; therefore, a 2
percent decrease in the mean population level IQ corresponds to a 2-
point decrease in IQ. For this NPDWR, after considering BMRs of 1
percent and 2 percent for the adverse neurodevelopmental endpoint, the
EPA is selecting a BMR of 1 percent decrement in the mean population
IQ, consistent with the EPA's Benchmark Dose Technical Guidance (USEPA,
2012b) which describes several considerations. The selected BMR of 1
percent is supported by the biological significance and severity of the
decreased IQ health effect, the observable range of the health effects
data identified (i.e., decreases in IQ scores), and the statistical
power of the critical study selected (Korevaar et al., 2016). This
decision to select a 1 percent BMR is consistent with the EPA's
Benchmark Dose Modeling Technical Guidance regarding epidemiology data
which states that ``a BMR of 1% has typically been used for quantal
human data from epidemiology studies'' (USEPA, 2012b). While a BMR
below 1 percent was considered, benchmark dose modeling was not
performed because the EPA guidance (USEPA, 2012b; USEPA, 2002a) does
not provide recommendations for modeling below a 1 percent BMR, IQ is
measured and reported in integer/whole numbers (typically expressed in
ranges of intellectual capacity), and a BMR below 1 percent is below
the observable range of the data identified. See section 5.2.4 of the
2025 draft health effects TSD for more information (USEPA, 2025b).
Based on the 2-step BBDR model and the BMR of 1 percent decrease in
the mean population level IQ, the EPA derived a point of departure
(POD) of 3.1 [mu]g/kg/day as described in the 2025 draft health effects
TSD (USEPA, 2025b). Consistent with the recommendations presented in
the EPA's peer-reviewed human health risk assessment methods for
developing toxicity values (USEPA, 2002a), the Agency applied a total
uncertainty factor (UF) of 3 to the human-equivalent POD to account for
variation in sensitivity among the human population. The same total UF
value of 3 was used in the 2019 TSD for perchlorate (USEPA, 2019b).
From this POD and total UF, the EPA derived a draft RfD of 1 [mu]g/
kg/day, after rounding to one significant figure according to Agency
best practice (APHA, 1992; Brinker and Wolf, 1984; USEPA, 2000a). As
the critical effect of perchlorate is a developmental endpoint that can
result from a short-term exposure during critical periods of
development, the overall draft RfD for perchlorate is applicable to
both short-term and chronic exposure scenarios (USEPA, 1991).
VI. Maximum Contaminant Level Goal
Section 1412(a)(3) of the SDWA requires the EPA to propose an MCLG
simultaneously with the NPDWR. The MCLG is defined in SDWA section
1412(b)(4)(A), 42 U.S.C. 300g-1(b)(4)(A), as ``the level at which no
known or anticipated adverse effects on the health of persons occurs
and which allows an adequate margin of safety.'' Consistent with SDWA
section 1412(b)(3)(C)(i)(V), 42 U.S.C. 300g-1(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.'' Accordingly, the EPA reviewed the available information
to identify the most sensitive population(s) to derive the MCLG.
Consistent with SAB recommendations (USEPA 2013) and peer review, the
EPA is proposing an MCLG that is based on protecting the offspring of
hypothyroxinemic pregnant women in their first trimester with low-
iodine intake levels. The inputs for a noncancer MCLG include an oral
noncancer toxicity value (i.e., an RfD), body weight-adjusted drinking
water intake (DWI-BW), and a relative source contribution (RSC).
[GRAPHIC] [TIFF OMITTED] TP06JA26.002
[[Page 413]]
As described in section V of this preamble, the EPA derived a draft
RfD of 1 [mu]g/kg/day. Given the most sensitive life stage identified,
fetuses of iodine-deficient, hypothyroxinemic pregnant women in their
first trimester, the EPA selected the DWI-BW corresponding to females
of reproductive age, 13 to <50 years (0.0354 L/kg/day), who may be
pregnant or become pregnant, to calculate the proposed MCLG for
perchlorate (USEPA, 2019f) (see section 6.1 of the 2025 draft health
effects TSD for more information about exposure factor selection
(USEPA, 2025b)). In alignment with the EPA guidance for substances with
one non-water exposure route and no other standards, guidance, or
criteria, the RSC was calculated as a proportion of the difference
between the RfD and exposure to perchlorate attributable to food and
other sources (USEPA, 2000b). The EPA calculated an RSC of 80 percent
based on the draft RfD of 0.001 mg/kg/day (1 [mu]g/kg/day) (see section
6.2 of the 2025 draft health effects TSD for more information about the
RSC derivation (USEPA, 2025b)).
Calculating the MCLG based on these input values, described above,
results in a proposed MCLG for perchlorate in drinking water of 0.02
mg/L, after rounding to one significant figure following Agency best
practice (APHA, 1992; Brinker and Wolf, 1984; USEPA, 2000a).
[GRAPHIC] [TIFF OMITTED] TP06JA26.003
Rounded to 1 significant figure:
Proposed MCLG = 0.020 mg/L
The proposed MCLG of 0.02 mg/L (20 [mu]g/L) is a level in drinking
water expected to protect against the lowest IQ decrement that can be
accurately estimated. Specifically, the EPA derived the proposed MCLG
using an RfD that was based on a BMR of a 1-point IQ decrement in the
population at greater risk to adverse health effects following
perchlorate exposure (the offspring of iodine-deficient,
hypothyroxinemic pregnant women in their first trimester), and which in
turn protects against adverse health effects following perchlorate
exposure in the general population.
In this notice, the EPA is clarifying the role the 1 percent, or 1-
point, decrement in IQ plays in the derivation of the MCLG for
perchlorate. See NRDC v. Regan, 67 F.4th at 411, n.2 (Pan, J.,
concurring) (asserting that ``[t]he proposed MCLGs are the levels of
perchlorate associated with decreases in IQ of one'' point) (emphasis
in original). In deriving the reference dose, the EPA selected a 1
percent benchmark response for decreased IQ in the most sensitive life
stage: the offspring of iodine-deficient, hypothyroxinemic mothers in
their first trimester of pregnancy. Following EPA guidance for human
health risk assessment, the EPA first calculated a POD dose of
perchlorate to determine the level of perchlorate exposure at the BMR.
Specifically, the POD is the level of perchlorate exposure in first
trimester pregnant women associated with a BMR of 1-point decrement in
offspring IQ. Here, the POD is 3.1 [mu]g/kg/day. By applying
uncertainty factors (UFs) to the POD, the EPA derived a draft RfD,
which is ``an estimate (with uncertainty spanning perhaps an order of
magnitude) of a daily oral exposure to the human population (including
sensitive subgroups) that is likely to be without an appreciable risk
of deleterious effects during a lifetime'' (USEPA, 2002b) (emphasis
added). The proposed MCLG, the drinking water concentration, was then
derived from the draft RfD, the oral dose, of 1 [mu]g/kg/day,
approximately three times lower than the POD dose of perchlorate. The
SDWA requires that the MCLG be the level at which there are no known or
anticipated adverse effects to human health with an adequate margin of
safety. Therefore, perchlorate exposure via drinking water at or below
the MCLG to iodine-deficient, hypothyroxinemic pregnant women in their
first trimester should be understood as protecting against a 1-point IQ
decrement in their offspring, which is expected to be protective of
other life stages and populations as well.
As explained in this section, the proposed MCLG allows for an
adequate margin of safety through the derivation of the RfD which
included selection of the most sensitive endpoint in the most sensitive
population, selection of the 1 percent BMR, and application of
uncertainty factors and the RSC. The Agency seeks comment on the
proposed MCLG value of 20 [micro]g/L and the methodology used to derive
the value as described in this section, including whether the Agency
should instead consider using a BMR of 2 percent or 3 percent to derive
the RfD (see section XV of this preamble for more information).
VII. Maximum Contaminant Level
Under section 1412(b)(4)(B) of the SDWA, the EPA generally must
establish an MCL as close to the MCLG as feasible. The EPA evaluated
available analytical methods to determine the lowest concentration at
which perchlorate can be measured and evaluated the treatment
technologies for perchlorate that have been examined under field
conditions (USEPA, 2025c; USEPA, 2025d). These field studies, as
discussed in section XII.A of this preamble, demonstrated that three
different treatment technologies (ion exchange, biological treatment,
and reverse osmosis) are capable of high removal efficiency of
perchlorate at a reasonable cost basis for large systems. The EPA
determined that setting an MCL equal to 20 [micro]g/L, 40 [micro]g/L,
80 [micro]g/L, or higher values would be feasible given that the
approved analytical method for perchlorate for UCMR 1 had a minimum
reporting level (MRL) of 4.0 [micro]g/L (USEPA, 1999; USEPA, 2000c) and
that available, adequately tested, and reasonably cost-affordable
treatment technologies can treat to concentrations below 20 [micro]g/L
(USEPA, 2025d). Additionally, more recently approved analytical methods
for perchlorate have lower MRLs (see section IX of this preamble).
Based on this evaluation of analytical methods and treatment
technologies, the EPA determined that the proposed MCL of 20 [micro]g/L
is the closest feasible level to the MCLG.
When proposing an MCL, the EPA must publish and seek public comment
on the HRRCA for the proposed MCL and each alternative MCL considered
(SDWA section 1412(b)(3)(C)(i), 42 U.S.C. 300g-1(b)(3)(C)(i)),
including: the quantifiable and nonquantifiable health risk reduction
benefits attributable to MCL compliance; the quantifiable and
nonquantifiable health risk reduction benefits of reduced exposure to
co-occurring contaminants attributable to MCL compliance; the
quantifiable and nonquantifiable costs of MCL compliance; the
incremental costs and benefits of each alternative MCL; the effects of
the contaminant on the general population and sensitive populations
likely to be at greater risk of any adverse health risks posed by
compliance; and other factors such as data quality and uncertainty. The
EPA provides this
[[Page 414]]
information in section XIV in this preamble and in more detail in the
Economic Analysis for the Proposed Perchlorate National Primary
Drinking Water Regulation (USEPA, 2025i) available in the docket for
the proposed rule.
As the occurrence analysis in section VIII of this preamble
demonstrates, there is infrequent occurrence of perchlorate at or above
20 [micro]g/L. In addition to evaluating the benefits and costs of the
proposed MCL of 20 [micro]g/L (the level as close as feasible to the
MCLG), the EPA evaluated benefits and costs of alternative proposed
MCLs to determine whether a higher MCL (i.e., 40 [micro]g/L or 80
[micro]g/L) would maximize health risk reduction benefits at a cost
that is justified by the benefits. These levels represent a doubling
and quadrupling of the 20 [micro]g/L level and are therefore reasonable
levels at which to analyze the relationship between costs and benefits
and trends in the relationship between costs and benefits. However, the
EPA found that benefits did not justify the costs at any of these
levels. The EPA found that costs decrease as the MCL increases because
fewer water systems are expected to exceed the MCL and would not be
required to incur treatment costs to reduce perchlorate drinking water
concentrations. As a result, quantified benefits decrease, but not at
the same rate as the costs, leading to quantified net benefits that
grow closer to positive at 40 [micro]g/L and 80 [micro]g/L,
respectively (see section XIV.C of this preamble for discussion). For
this reason, notwithstanding the finding that no MCL would result in
benefits that are justified by the costs under SDWA section
1412(b)(6)(A), 42 U.S.C. 300g-1(b)(6)(A), the Agency is proposing and
seeking comment on setting the MCL at 20 [micro]g/L, 40 [micro]g/L, or
80 [micro]g/L. The Agency is requesting comment on the three proposed
MCLs and any other alternative MCL higher than the MCLG. See section XV
of this preamble for more information. For the purposes of this
proposal, the EPA is including the three proposed MCLs (i.e., 20
[micro]g/L, 40 [micro]g/L, or 80 [micro]g/L) in the proposed regulatory
text in Table 1 to paragraph (b) of 40 CFR 141.51, Table 1 to paragraph
(b) of 40 CFR 141.62, and under the entries for ``Perchlorate'' in
Appendix A to Subpart O of Part 141 and Appendix A to subpart Q of Part
141. Upon promulgation of a final rule, only one MCL will be included
in the regulatory text.
In implementing SDWA section 1412, 42 U.S.C. 300g-1, the EPA must
use the best available, peer-reviewed science and supporting studies,
taking into consideration the quality of the information and the
uncertainties in the benefit-cost analysis (SDWA section 1412(b)(3), 42
U.S.C. 300g-1(b)(3)). The following sections, as well as the health
effects discussion in sections V and VI of this preamble and the 2025
draft health effects TSD (USEPA, 2025b), document the science and
studies that the EPA relied upon to develop estimates of benefits and
costs and to understand the impact of uncertainty on the Agency's
analysis.
VIII. Occurrence
The EPA relied on data from UCMR 1 and compliance data from States
that have elected to regulate perchlorate in drinking water to evaluate
the occurrence of perchlorate. The EPA combined data from both UCMR 1
and State compliance monitoring into a Bayesian hierarchical model,
which allows the utilization of all suitable observed data available,
including quantifiable detections and non-detects (i.e., samples with
no reported value), to produce probabilistic exposure estimates for
perchlorate. The EPA used a similar statistical approach to evaluating
occurrence data in the per- and polyfluoroalkyl substances (PFAS) NPDWR
rulemaking (89 FR 32532, USEPA, 2024a) as well as for arsenic and
Cryptosporidium parvum (USEPA, 2000d; USEPA, 2006). The data and
occurrence model informed estimates of the number of water systems and
the associated population expected to be exposed to levels of
perchlorate which would potentially exceed the proposed MCLs and
require the water systems to take action under the proposed rule. The
EPA estimates the mean number of systems that would exceed 20 [micro]g/
L in a single round of sampling to be 103 systems out of 66,320
community and non-transient non-community water systems. Please see the
Perchlorate Occurrence and Monitoring Report for the Perchlorate
National Primary Drinking Water Regulation (USEPA, 2025e) for a full
analysis and discussion of perchlorate occurrence.
IX. Analytical Methods
The EPA is proposing analytical methods for water systems to comply
with the MCL. SDWA section 1401(1)(D), 42 U.S.C. 300f(1)(D), requires
that an NPDWR ``contains criteria and procedures to assure a supply of
drinking water which dependably complies with such [MCLs]; including
accepted methods for quality control and testing procedures to ensure
compliance with such levels.'' SDWA section 1412(b)(4)(B), 42 U.S.C.
300g-1(b)(4)(B), also directs the EPA to set a contaminant's MCL as
close to its MCLG as is ``feasible'', the definition of which includes
an evaluation of the feasibility of performing chemical analysis of the
contaminant at standard drinking water laboratories.
To comply with these requirements, the EPA considers method
performance under relevant laboratory conditions, their likelihood of
utilization among certified drinking water laboratories, and the
associated analytical costs. The EPA has developed five analytical
methods for the identification and quantification of perchlorate in
drinking water that meet these criteria. The proposed EPA methods for
perchlorate are method numbers 314.0, 314.1, 314.2, 331.0, and 332.0. A
detailed description of these methods is presented in section 6 of the
Perchlorate Occurrence and Monitoring Report for the Perchlorate
National Primary Drinking Water Regulation (USEPA, 2025e).
X. Monitoring and Compliance Requirements
A. Proposed Monitoring Requirements
The EPA is proposing to require all CWSs and NTNCWSs to monitor for
perchlorate. The EPA is proposing to amend 40 CFR 141.23(c) to
incorporate monitoring requirements for perchlorate with a monitoring
protocol based on the EPA's Standardized Monitoring Framework (SMF) for
IOCs. Under the SMF for IOCs, the monitoring frequency for a PWS is
dependent on previous monitoring results, source water type, and
whether a monitoring waiver has been granted. The SMF follows 9-year
compliance cycles divided into three 3-year periods. Water systems are
generally required to monitor for contaminants at least once every
compliance cycle.
The EPA is proposing that all ground water systems serving greater
than 10,000 persons and all surface water systems \9\ be initially
required to monitor each entry point to the distribution system
quarterly within a 12-month period for perchlorate prior to the rule
compliance date. The EPA is proposing that ground water systems serving
10,000 people or fewer be initially required to monitor twice within a
12-month period, and that the second of these samples should be
collected five to seven months after the first sample. Water systems
would be required to complete this initial monitoring by the rule
compliance date (see section XIII.A of this preamble for additional
details about the rule
[[Page 415]]
compliance date). The EPA is proposing that States may allow systems to
use previously acquired monitoring data to satisfy the initial
monitoring requirements (see section X.E of this preamble for
discussion of historical data).
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\9\ All ground water under the direct influence of surface water
(GWUDI) systems are treated as surface water systems.
---------------------------------------------------------------------------
The monitoring requirements for IOCs under 40 CFR 141.23(c) provide
that the State may reduce a system's monitoring frequency from
quarterly to annually (surface water systems) or triennially (ground
water systems) if the State determines the system is ``reliably and
consistently'' below the MCL.\10\ The EPA is aware that there can be
significant administrative burden on the State to make these
determinations, particularly for many systems simultaneously (USEPA,
2025f). The analysis of perchlorate occurrence data indicates that
virtually all systems would have initial perchlorate sample
concentrations below any of the proposed MCLs (see section VIII of this
preamble for information about perchlorate occurrence). Therefore, the
EPA anticipates that, for most systems, rule implementation will only
require monitoring and no other action, imposing costs and burden with
limited public health benefit. While the EPA explored requirements to
limit monitoring only to systems that are likely to have perchlorate,
the Agency could not determine a reliable basis to support such an
approach. Instead, the EPA is proposing requirements that would require
all CWSs and NTNCWSs to monitor for perchlorate but would also reduce
costs and burden compared to the monitoring requirements for other
IOCs.
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\10\ The term ``Reliably and Consistently below the MCL'' means
that the State has enough confidence that future sampling results
will be sufficiently below the MCL to justify reducing the quarterly
monitoring frequency. At a minimum, all individual samples should be
below the MCL. Systems with widely varying analytical results or
analytical results that are just below the MCL would not meet this
criterion (USEPA, 1992).
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In response to stakeholder feedback (USEPA, 2025f) and in an effort
to reduce burden on systems and States, the EPA is proposing a binning
approach in 40 CFR 141.23(c)(10)(iii) based on the initial monitoring
samples collected prior to the rule compliance date to reduce
monitoring frequency without States making a ``reliably and
consistently'' determination for each system. Based on the initial
monitoring samples, if all sample concentrations at an entry point are
at or below 4.0 [micro]g/L, the system would automatically start at a
monitoring frequency of once every nine years after the rule compliance
date at that entry point. The EPA is proposing 4.0 [micro]g/L as the
level for automatic reduction to nine-year monitoring because it was
the MRL for perchlorate established during UCMR 1. While the EPA is
aware that capabilities have improved since UCMR 1 and that labs can
quantify lower levels depending on the method used (see section IX of
this preamble), the Agency is selecting 4.0 [micro]g/L as the threshold
for determining an automatic reduced monitoring frequency to ensure
water systems nationally can reduce their monitoring frequency as
appropriate. The EPA anticipates that a system with all initial
monitoring results at or below 4.0 [micro]g/L at an entry point is
unlikely to exceed the perchlorate MCL and is proposing for the system
to reduce to monitoring once a compliance cycle (nine years) at that
entry point. This approach would allow a water system to reduce to
nine-year monitoring sooner compared to the standard monitoring
framework waiver process for IOCs. Additionally, the EPA is proposing
that States may require more frequent sampling (40 CFR
141.23(c)(10)(iv)) to account for situations where automatic reduced
monitoring to once every nine years may not be appropriate (e.g.,
presence of known sources of perchlorate, high variability in initial
sample results). If any of the sample concentrations are greater than
4.0 [micro]g/L but all are below or equal to the MCL, the system would
be required to sample at an annual (surface water system) or triennial
(ground water system) frequency starting at the rule compliance date.
If the system has any samples greater than the MCL, the system would be
required to conduct quarterly monitoring starting at the rule
compliance date. This approach would effectively stagger system
monitoring frequencies at the compliance date and help reduce burden on
both systems and States. The EPA is proposing that this automatic
reduction be based only on the results of the initial monitoring
samples collected prior to the rule compliance date (including samples
collected between January 1, 2021, and the publication date of the
final rule that satisfy initial monitoring requirements. See section
X.E of this preamble for more information). At the compliance date,
systems would continue to monitor at those established frequencies and
could then reduce their monitoring frequency as applicable consistent
with the SMF for IOCs. For example, a system that was required to
remain on quarterly monitoring after the compliance date could reduce
to annual or triennial monitoring if the State determines the system is
``reliably and consistently'' below the MCL and the system has
collected at least two quarterly samples (ground water) or at least
four quarterly samples (surface water) in accordance with 40 CFR
141.23(c)(8). Likewise, systems that automatically qualify for annual
or triennial monitoring after initial sampling would be eligible to
apply to the State for a monitoring waiver to reduce to sampling once
every nine years following the procedures in 40 CFR 141.23(c)(3)-(6) as
described in section X.B of this preamble. The EPA is requesting
comment on this automatic monitoring approach, including the thresholds
used for binning, in section XV of this preamble. The EPA is also
requesting comment on whether a trigger value higher than 4 [micro]g/L,
such as one half of the MCL, should be used for an automatic reduction
to nine year monitoring. Once compliance monitoring begins, any system
on reduced monitoring that exceeds the MCL would be required to begin
quarterly monitoring at that sampling point.
B. Can States grant monitoring waivers?
In addition to the proposed automatic monitoring frequency
reduction based on initial sampling, the EPA is proposing to allow
water systems to apply to the State for a monitoring waiver for
perchlorate if the conditions described in 40 CFR 141.23(c)(3)-(6) are
met. In contrast to the automatic reductions, a water system must apply
to the State for a waiver based on several rounds of compliance
sampling. If a State approves the waiver request, the State must
provide the waiver in writing and the sampling frequency must be no
less frequent than once every compliance cycle (i.e., nine years). A
State may grant a waiver for surface water systems after three rounds
of annual monitoring with results less than the MCL and for ground
water systems after conducting three rounds of triennial monitoring
with results less than the MCL (40 CFR 141.23(c)(4)). Systems on
quarterly monitoring must first reduce to annual or triennial sampling
following a determination by the State that the system is ``reliably
and consistently'' below the MCL and conduct at least three rounds of
annual or triennial monitoring before applying for a waiver. At a
minimum, one sample must be collected during the time that the waiver
is effective, and the term during which the waiver is effective cannot
exceed one compliance cycle (nine years) (40 CFR 141.23(c)(3)).
[[Page 416]]
C. How are system MCL violations determined?
The EPA is proposing that violations of the perchlorate MCL be
determined based on the average of a compliance sample and confirmation
sample consistent with 40 CFR 141.23(i)(3). Compliance with the
perchlorate MCL would be determined based on one sample if the sample
is at or below the MCL. If a sample exceeds the perchlorate MCL, the
water system would be required to collect a confirmation sample.
Compliance with the MCL would then be determined based on the average
value of the initial and confirmation samples. Because the MCLG has one
significant figure and the proposed MCL is set equal to the MCLG,
sample results would be rounded to one significant figure prior to
being evaluated against the MCL. The EPA is proposing this compliance
calculation instead of a running annual average approach used for many
other IOCs because of the short period of time corresponding to the
sensitive exposure window (i.e., first trimester of pregnancy) for the
selected critical health effect underlying the RfD and MCLG.
The EPA is proposing for water systems to collect the confirmation
sample within five calendar days following the system's receipt of the
notification of the analytical result of the first sample. The EPA
considers that this timeframe is appropriate given the short period of
time (i.e., first trimester of pregnancy) associated with the critical
health effect underlying the MCLG. The EPA is also seeking comment on
whether the Agency should require a shorter timeframe for collecting a
confirmation sample (e.g., three days) or a longer time frame (e.g.,
the two week timeframe States may require for other IOCs under 40 CFR
141.23(f)(1)) due to challenges systems may face challenges in
reviewing results and collecting confirmation samples due to staff
scheduling and resource availability (for more information, see section
XV of this preamble).
D. When must systems complete initial monitoring?
The EPA is proposing that water systems complete initial monitoring
in anticipation of the rule compliance date (see session XII.A of this
preamble for a discussion on the compliance date). Under SDWA section
1412(b)(10), 42 U.S.C. 300g-1(b)(10), NPDWRs generally take effect
three years after the date of promulgation of the final rule or any
amendment thereto. The initial monitoring results would be used to
determine the actions systems will need to take after the compliance
date for the MCL is in effect. For a small percentage of systems, that
data will inform whether the system needs to take actions to reduce
perchlorate to levels below the MCL. The initial monitoring data will
be used to determine the compliance monitoring frequency after the
rule's compliance dates are in effect. The EPA estimates that after the
initial monitoring period, the majority of systems would conduct
monitoring once every nine years (40 CFR 141.23(c)(10)(iii)(A)). To
satisfy initial monitoring requirements, ground water systems serving
more than 10,000 persons and all surface water systems would be
required to collect four samples at each entry point to the
distribution system over four consecutive quarters before the rule
compliance date goes into effect. Ground water systems serving 10,000
people or fewer would be required to collect two samples within a 12-
month period five to seven months apart at each entry point before the
rule compliance date goes into effect.
E. Can systems use previously collected data to satisfy the initial
monitoring requirements?
The EPA is proposing that States can allow systems to use
perchlorate data collected after January 1, 2021, to satisfy the
initial monitoring requirements. To satisfy the initial monitoring
requirements in 40 CFR 141.23(c)(10)(i)-(ii), a system with historical
monitoring data for an entry point to the distribution system could use
monitoring data obtained from between January 1, 2021, to the
compliance date to comply with the initial monitoring requirements at
that entry point. Systems would be required to either have collected
the same number of samples as required for initial monitoring (i.e.,
two or four depending on system size and type) or have data collected
under a State monitoring requirement. The EPA is proposing this
provision to account for systems that are already monitoring for
perchlorate, including in States with perchlorate drinking water
requirements. For example, some systems have years of annual or
triennial perchlorate monitoring data demonstrating perchlorate levels
far below the proposed MCL. The EPA does not intend for these systems
to restart at quarterly monitoring provided the State approves the use
of previously collected data. The EPA is proposing a cut-off date of
approximately six years prior to the beginning of the initial
monitoring period (January 1, 2021). This is to ensure that recent data
are being used to determine if a system is required to conduct
quarterly sampling during the initial monitoring period. While the EPA
is aware of systems that may have conducted sampling earlier than the
cut-off date, such as part of UCMR 1 sampling, the Agency is concerned
that older data may not capture current conditions. The EPA is seeking
comment in section XI of this preamble on alternative cut-off dates for
application of previously collected data.
F. Can systems composite samples?
40 CFR 141.23(a)(4) provides that the State may reduce the total
number of samples which must be analyzed by allowing the use of
compositing. Composite sampling is an approach in which equal volumes
of water from multiple samples (maximum of five) are combined and
analyzed as a mixture. The reported concentration from the analysis
reflects the average of the concentrations from the contributing entry
points. Composite sampling can reduce costs because a single composite
sample is analyzed instead of individual samples. However, if the
concentration of the composite sample is greater than or equal to the
MCL divided by the number of samples analyzed, the water system is
required to take a follow-up sample at each sampling point included in
the composite and analyze each sample separately. For example, at a
proposed MCL of 20 [micro]g/L, a five-sample composite would trigger
follow-up sampling at each entry point included in the composite sample
with a perchlorate concentration of 4 [micro]g/L or greater. Under the
proposal, the provisions in 40 CFR 141.23(a)(4) would apply to
perchlorate. The EPA expects that many water systems will have
perchlorate concentrations far below the MCL. Compositing is one
potential method for systems to further reduce their monitoring and
analytical costs.
XI. SDWA Right To Know Requirements
A. What are the proposed consumer confidence report requirements?
The 1996 Right to Know provisions of the SDWA (section 1414(c)(4))
require all community water systems (CWSs) to provide their customers
at least once a year with a Consumer Confidence Report (CCR) in
accordance with the CCR Rule requirements in 40 CFR 141 subpart O. The
CCR is a drinking water quality report that summarizes the state of the
water system's drinking water supply. The CCR must include information
about the water system, sources of water, detected contaminants,
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compliance with drinking water rules, as well as other information. The
EPA revised the CCR Rule in 2024 (89 FR 45980, USEPA, 2024b) in
response to the America's Water Infrastructure Act of 2018 in an effort
to improve the readability, clarity, and understandability of CCRs as
well as the accuracy of the information presented, improve risk
communication in CCRs, incorporate electronic delivery options, provide
supplemental information regarding lead levels and control efforts, and
require systems who serve 10,000 or more persons to provide CCRs to
customers biannually (twice per year). Under this proposal, CWSs would
be required to report perchlorate information in their CCR. As with
other detected regulated contaminants, this information would include
the MCL, MCLG, range of detected levels, highest detected level used to
determine compliance, and likely sources of the perchlorate. If there
is a violation of the MCL, the report must also include information
about the violation, potential adverse health effects of perchlorate,
and actions taken by the system to address the violation. The EPA is
proposing mandatory health effects language for perchlorate consistent
with the Agency's health assessment of perchlorate (see sections IV.B
and V of this preamble for details about perchlorate health effects and
the EPA's health effects assessment). This proposed language for the
CCR would be listed in appendix A to subpart O of part 141. This is the
same health effects language that would be required in public
notification, as specified in appendix B to subpart Q of part 141 (see
section XI.B of this preamble for discussion). Please see the CCR Rule
(40 CFR part 141, subpart O) for more information on what must be
reported in the CCR.
B. What are the proposed public notification requirements?
The EPA promulgated a Public Notification (PN) Rule in 40 CFR part
141, subpart Q in 2000 (65 FR 26035, USEPA, 2000e). This PN Rule
implements SDWA section 1414(c)(1) and (2), 42 U.S.C. 300g-3(c)(1),
(2). The PN Rule ensures that consumers will know if there is an issue
with their drinking water and alerts consumers if there is risk to
public health. Under the PN Rule, water systems must notify customers
of any failure of the water system to comply with an MCL, a prescribed
treatment technique, or failure to perform required water quality
monitoring, or testing procedures; any variance or exemption the system
has been granted, or failure to comply with the requirements of any
schedule set under a variance or exemption; or reporting and
recordkeeping violations under subpart Y; and certain specified
situations such as the occurrence of a waterborne disease outbreak or
emergency and the availability of unregulated contaminant monitoring
data (see 40 CFR 141.201, table 1). There are three tiers of PN defined
in 40 CFR 141.201(b) to take into account the seriousness of the
violation or situation and any potential adverse health effects that
may be involved. The EPA is proposing revisions to 40 CFR 141.202 to
comply with the PN requirements of the proposed perchlorate rulemaking.
Additionally, the EPA is proposing mandatory health effects language in
appendix A of subpart Q for perchlorate consistent with the Agency's
health assessment of perchlorate (see section V of this preamble for
details about the health effects assessment). This is the same health
effects language that would be required in the CCR (see section XI.A of
this preamble for discussion).
All PWSs must give public notice for all violations of NPDWRs and
for other situations under the requirements of 40 CFR 141.201. Under
this proposal, violations of the perchlorate MCL would be designated as
Tier 1 and as such, PWSs would be required to comply with 40 CFR
141.202. Based on the available evidence, the most sensitive adverse
health effect of perchlorate exposure is decreased IQ, a developmental
health outcome that can result from short-term exposure during critical
periods of development (described in section V of this preamble). The
offspring of iodine-deficient pregnant women in their first trimester
are the most sensitive population identified for the decreased IQ
health outcome. The EPA is proposing Tier 1 PN for a perchlorate MCL
exceedance. Because the first trimester of pregnancy is a short
exposure window, the EPA finds it appropriate to require Tier 1 PN so
that the most sensitive population identified can change behaviors to
reduce the risk of exposure to perchlorate. Additionally, timely
notification could benefit a larger portion of the water system
population than just pregnant women with iodine deficiency in their
first trimester. For example, public notification could benefit females
of reproductive age (13 to <50 years of age) who may become pregnant,
which make up a considerable proportion (24.6 percent) of the overall
U.S. population (U.S. Census Bureau, 2024a; U.S. Census Bureau 2024b).
Stakeholders have expressed the importance of timely notification and
transparency in communicating with consumers due to the adverse health
end point of perchlorate exposure (USEPA, 2025g). Conversely, the EPA
is aware that water systems may face implementation challenges in
complying with Tier 1 PN compared to complying with Tier 2 PN. Water
systems have expressed capacity challenges with complying with Tier 1
PN, as well as the potential to erode public trust in drinking water
due to a potential for increased notices on drinking water violations
(USEPA, 2025g). The EPA requests public comment on the selection of
Tier 1 PN rather than Tier 2 PN for an MCL exceedance for the proposed
rulemaking. See section XV of this preamble for more information. The
EPA is also proposing PN requirements for perchlorate monitoring and
procedure violations. Specifically, the EPA is proposing to require
Tier 3 PN for perchlorate monitoring and testing procedure violations,
which is consistent with other IOCs.
XII. Treatment Technologies
Systems that exceed the proposed perchlorate MCL would need to
adopt new treatment or another strategy to reduce perchlorate to a
level that meets the MCL. When the EPA establishes an MCL for a
drinking water contaminant, SDWA section 1412(b)(4)(E)(i), 42 U.S.C.
300g-1(b)(4)(E)(i), requires the Agency to ``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). Water systems are not required
to implement BATs for rule compliance. Rather, these BATs are used by
States to establish conditions for source water variances under SDWA
section 1415(a), 42 U.S.C. 300g-4(a). Furthermore, SDWA section
1412(b)(4)(E)(ii), 42 U.S.C. 300g-1(b)(4)(E)(ii), requires the Agency
to identify small system compliance technologies (SSCTs), which are
more affordable treatment technologies, or other means that can achieve
compliance with the MCL (or treatment technique, where applicable). The
lack of an affordable SSCT for a contaminant triggers certain
additional procedures which can result in States issuing small system
variances under SDWA section 1412(e), 42 U.S.C. 300g-1(e). The Agency
is requesting comment on the treatment technologies discussed in this
section.
A. Best Available Technologies
The EPA identifies BATs as those meeting the following criteria:
(1) capability of a high removal efficiency,
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(2) history of full-scale operation, (3) general geographic
applicability, (4) compatibility with other water treatment processes,
(5) ability to bring all the water in a system into compliance, and (6)
reasonable cost basis for large and medium water systems. The Agency is
proposing to list the following technologies as BATs for removal of
perchlorate from drinking water based on its review of the treatment
and cost literature (USEPA, 2025c; USEPA, 2025d):
Ion exchange;
Biological treatment; and
Reverse osmosis.
Non-treatment options might also be used for compliance in lieu of
installing and operating treatment technologies. These include blending
existing water sources, replacing a perchlorate-contaminated source of
drinking water with a new source (e.g., a new well), and purchasing
compliant water from another system. See the Best Available
Technologies and Small System Compliance Technologies for the
Perchlorate National Primary Drinking Water Regulation (USEPA, 2025c)
for details on each proposed BAT and non-treatment option.
B. Small System Compliance Technologies
The EPA is proposing the SSCTs shown in Exhibit 1. The table shows
which of the BATs listed in section XII.A of this preamble are also
affordable for each small system size category listed in section
1412(b)(4)(E)(ii) of SDWA. The Agency identified these technologies
based on an analysis of treatment effectiveness and affordability
(USEPA, 2025c).
[GRAPHIC] [TIFF OMITTED] TP06JA26.004
The SSCTs listed in Exhibit 1 include a point-of-use (POU) version
of reverse osmosis in addition to ion exchange, biological treatment,
and reverse osmosis. The POU reverse osmosis technology can be used by
small systems to comply with the proposed MCL and, therefore, meets the
effectiveness requirement for an SSCT. The EPA is not aware of any
point-of-entry (POE) devices certified for perchlorate removal or any
POU devices certified for perchlorate removal using technologies other
than reverse osmosis (such as using ion exchange).
The EPA identified the SSCT using the affordability criteria
methodology it developed for drinking water rules (USEPA, 1998b). The
EPA also conducted supplemental analyses using alternative metrics used
in recent drinking water regulations (89 FR 32532, USEPA, 2024a) and
recommended by stakeholders, such as the SAB and NDWAC (88 FR 18688,
USEPA, 2023), to demonstrate the potential affordability implications
of the proposed rule on the determination of affordable technologies
for small systems in a national-level analysis. See section 6 in Best
Available Technologies and Small System Compliance Technologies for the
Perchlorate National Primary Drinking Water Regulation (USEPA, 2025c)
for discussion of the affordability analyses and the methodology used.
While the EPA has found that the proposed treatment technologies
are affordable for small systems nationally, the Agency recognizes that
individual water systems may face resource challenges. As discussed in
section XIII.E of this preamble, States that have adopted the 1998
Variance and Exemptions Regulation (USEPA, 1998e) may grant exemptions
to individual water systems from any requirement respecting an MCL
under SDWA section 1416(a), 42 U.S.C. 300g-5(a), including for reasons
due to economic factors. The EPA is committed to providing technical
assistance to water systems in complying with NPDWRs. A range of
resources are available under the EPA's Water Technical Assistance
(WaterTA) programs and initiatives, including for small systems (USEPA,
2025h) that may help alleviate some of the burden on small systems
complying with the NPDWR for perchlorate.
XIII. Rule Implementation and Enforcement
A. Compliance Date
In accordance with SDWA section 1412(b)(10), 42 U.S.C. 300g-
1(b)(10), the EPA is proposing setting the compliance date three years
after the date of publication of the final rule. The EPA is proposing
that water systems complete all initial monitoring by the compliance
date as described in section X.D of this preamble. Water systems would
start compliance monitoring on a schedule based on initial monitoring
and comply with the MCL starting on the rule compliance date.
Similarly, water systems exceeding the MCL after the rule compliance
date would be required to take actions to reduce their perchlorate
levels below the MCL and conduct public notification (see section XI.B
of this preamble for discussion of PN requirements). The EPA is aware
that the proposed compliance date falls in the middle of the first
period of the fifth cycle of the SMF (USEPA, 2020c). The EPA
acknowledges that this timing may pose logistical challenges for
systems and States to align perchlorate monitoring frequencies with
existing schedules for other IOCs. The EPA is seeking comment in
section XV of this preamble on the compliance date for the proposed
rule, including whether it is practicable for the EPA to require water
systems to comply with the requirements sooner than three years after
publication of the final rule. Please also see section XIII.E of this
preamble
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for a discussion of extensions and exemptions.
B. Primacy Requirements
While the EPA retains independent enforcement authority under the
SDWA, the Agency may authorize States, Territories, and Tribes to
assume primary enforcement responsibility (``primacy''; primacy
agencies are also referred to as ``States'' in this preamble) to
implement the NPDWRs under SDWA section 1413(a)(1), 42 U.S.C. 300g-
2)(a)(1), when the EPA has determined, among other conditions, that the
State has adopted regulations that are no less stringent than the
promulgated NPDWR. This section describes the regulations and other
procedures and policies primacy entities would be required to adopt, or
have in place, to implement the proposed perchlorate rule, if
finalized. States must continue to meet all other conditions of primacy
in 40 CFR part 142. SDWA section 1413, 42 U.S.C. 300g-2, establishes
requirements that primacy entities (States, territories, or Tribes)
must meet to maintain 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 SDWA section
1412(a) and (b), 42 U.S.C. 300g-1(a), (b); (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, 42 U.S.C. 300g-4, 5; and (5) adopting and being capable
of implementing an adequate plan for the provision of safe drinking
water under emergency situations. 40 CFR part 142 sets out the specific
program implementation requirements for States to obtain primacy for
the Public Water Supply Supervision Program, as authorized under SDWA
section 1413, 42 U.S.C. 300g-2.
To implement the perchlorate rule, States would be required to
adopt revisions at least as stringent as the proposed provisions in 40
CFR 141.6 (Effective Dates); 40 CFR 141.23 (Inorganic chemical sampling
and analytical requirements); 40 CFR 141.51 (Maximum contaminant level
goals for inorganic contaminants); 40 CFR 141.60 (Effective Dates); 40
CFR 141.62 (Maximum contaminant levels for inorganic contaminants);
appendix A to subpart O ([Consumer Confidence Report] Regulated
contaminants); appendix A to subpart Q (NPDWR violations and other
situations requiring public notice); appendix B to subpart Q (Standard
health effects language for public notification); and 40 CFR 142.62
(Variances and exemptions from the maximum contaminant levels for
organic and inorganic contaminants). Under 40 CFR 142.12(b), all
primacy States/Territories/Tribes would be required to submit a revised
program to the EPA for approval within two years of promulgation of any
final perchlorate NPDWR and could request an extension of up to two
years in certain circumstances. Existing special primacy requirements
in 40 CFR 142.16(e) and (k) would also apply to States that adopt the
perchlorate NPDWR. The EPA is not proposing updates to these
provisions. These include requirements for States to submit as part of
its primacy revision application package a monitoring plan enforceable
under State law for the initial monitoring period by which the State
will assure all systems complete the required initial monitoring within
the regulatory deadlines (40 CFR142.16(e)(2)). If a State chooses to
allow waivers for perchlorate in accordance with 40 CFR 141.23(c), the
State shall also include in its primacy revision application package a
description of the procedures and criteria it will use to review waiver
applications and issue waiver determinations (40 CFR 142.16(e)(1)).
Additionally, States must explain their initial monitoring schedules,
how these monitoring schedules ensure that PWSs and sources comply with
the MCL and monitoring requirements, and the time frame in which new
systems will be required to demonstrate compliance with the MCL (40 CFR
142.16(k)).
The EPA must approve or deny State primacy applications within 90
days after determining that the State submission to the EPA is complete
and final (40 CFR 142.12(d)(3)(i); SDWA section 1413(b)(2), 42 U.S.C.
300g-2(b)(2)). In some cases, a State submitting a primacy application
to adopt an NPDWR has primary enforcement authority for a new
regulation while the EPA's decision on the primacy application is
pending (SDWA section 1413(c), 42 U.S.C. 300g-2(c)); this can occur
when the State meets the criteria for interim primacy (see 40 CFR
142.12(e)).
C. State Recordkeeping Requirements
The current regulations in 40 CFR 142.14 require States with
primary enforcement responsibility (i.e., primacy) 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 EPA is not proposing any changes to the State
recordkeeping requirements and existing requirements would apply to
perchlorate as with any other regulated contaminant.
D. State Reporting Requirements
Currently, States must report information under 40 CFR 142.15
regarding violations, variances and exemptions, enforcement actions and
general operations of State public water supply programs to the EPA.
The EPA is not proposing any changes to the State reporting
requirements and existing requirements would apply to perchlorate as
with any other regulated contaminant. However, the perchlorate MCL,
when final, could result in a greater frequency of reporting by certain
States. See discussion of Paperwork Reduction Act compliance in section
XVI.C for more information.
E. Exemptions and Extensions
SDWA section 1412(b)(10), 42 U.S.C. 300g-1(b)(10), grants the EPA
or the State (in the case of an individual water system) the authority
to allow up to two additional years to comply with an MCL if the
Administrator or State (in the case of an individual system) determines
that additional time is necessary for capital improvements. As noted in
section XIII.A of this preamble, the EPA is proposing to set the
compliance date three years after the date of publication of the final
rule. The EPA is not proposing a two-year extension nationwide because
the EPA has not determined that an additional two years is necessary
for water systems nationwide to make capital improvements to comply
with the rule. While the EPA is aware that some systems may face
challenges in complying with the proposed requirements, the EPA's
analyses indicate that few systems nationwide would exceed the MCL and
be required to take action under the rule. However, the EPA notes that
SDWA section 1412(b)(10) allows States to make these extension
determinations on an individual system basis.
In addition, under SDWA section 1416, 42 U.S.C. 300g-5, the EPA or
States may grant an exemption for PWSs meeting specified criteria that
provides an additional period for compliance not to exceed three years
beyond the time period provided by SDWA section 1412(b)(10). Under SDWA
section 1416(a), 42 U.S.C. 300g-5(a), a State may exempt any PWSs
within the State's jurisdiction from any
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requirement respecting an MCL. States may grant an exemption upon
finding that: ``(1) due to compelling factors (which may include
economic factors, including qualification of the public water system as
a system serving a disadvantaged community pursuant to section
1452(d)), the public water system is unable to comply with such
contaminant level or treatment technique requirement, or to implement
measures to develop an alternative source of water supply, (2) the
public water system was in operation on the effective date of such
contaminant level or treatment technique requirement, a system that was
not in operation by that date, only if no reasonable alternative source
of drinking water is available to such new system, (3) the granting of
the exemption will not result in an unreasonable risk to health, and
(4) management or restructuring changes (or both) cannot reasonably be
made that will result in compliance with this title or, if compliance
cannot be achieved, improve the quality of the drinking water.''
In addition, SDWA section 1416(b)(2)(C), 42 U.S.C. 300g-5(b)(2)(C),
gives States the authority to grant up to three additional two-year
period exemptions to systems serving 3,300 people or fewer that need
financial assistance for necessary improvements, not to exceed a total
of six years provided that the system establishes that it is taking all
practicable steps to meet the requirements.
F. Funding and Technical Assistance Availability
As subject to appropriations, there are funding sources available
to water systems and States to assist with complying with a final
perchlorate NPDWR. Funding is available under the Drinking Water State
Revolving Fund (DWSRF). These funds could be used to assist systems
with completing initial monitoring and reduce perchlorate in drinking
water. Additionally, there are EPA grant programs that provide
technical assistance and funding to assist PWSs in meeting SDWA
requirements (USEPA, 2025h). A range of resources are also available
under the EPA's Water Technical Assistance (WaterTA) programs and
initiatives (USEPA, 2025h) to help communities assess water challenges
and implement solutions, build system capacity, and develop application
materials to access water infrastructure funding.
XIV. Health Risk Reduction and Cost Analysis
Section 1412(b)(3)(C)(i), 42 U.S.C. 300g-1(b)(3)(C)(i), of the SDWA
requires the EPA to prepare a Health Risk Reduction and Cost Analysis
(HRRCA) in support of any NPDWR that includes an MCL. The prescribed
HRRCA requirements include:
(I) 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 as the result of treatment to
comply with each level;
(II) 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;
(III) Quantifiable and nonquantifiable costs for which there is a
factual basis in the rulemaking record to conclude that such costs are
likely to occur solely as a result of compliance with the MCL,
including monitoring, treatment, and other costs, and excluding costs
resulting from compliance with other proposed or promulgated
regulations;
(IV) Incremental costs and benefits associated with each
alternative MCL considered;
(V) 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 sub-populations 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;
(VI) Any increased health risk that may occur as the result of
compliance, including risks associated with co-occurring contaminants;
and
(VII) Other relevant factors, including the quality and extent of
the information, the uncertainties in the analysis, and factors with
respect to the degree and nature of the risk.
The complete HRRCA for the proposed NPDWR, Economic Analysis for
the Proposed Perchlorate National Primary Drinking Water Regulation
(USEPA, 2025i), is hereafter referred to as the ``Economic Analysis''
and can be found in the docket for the proposed rule.
In this analysis, the EPA assumes any final perchlorate NPDWR will
be promulgated in 2027 consistent with the deadline in the consent
decree. The Agency estimated the benefits and costs over a 35-year
period of analysis. The 35-year window was selected to capture the
discounted benefits and costs of the rule over multiple compliance
cycles. Note in the regulatory analysis baseline, the EPA accounts for
California and Massachusetts, which have promulgated perchlorate
drinking water standards. Hence, the estimated proposed perchlorate
NPDWR costs will not double count treatment and monitoring costs
already required by California and Massachusetts. See section 3 of the
Economic Analysis for a summary of the entities that would be affected
by the proposed rule and a list of key data sources used to develop the
EPA's baseline characterization of water systems.
Relying on data specific to the proposed rule, the EPA used
SafeWater Cost Benefit Model (CBX) to estimate benefits and costs
associated with the proposed perchlorate NPDWR. The EPA estimated the
costs associated with monitoring, administrative requirements, and
treatment compliance actions (USEPA, 2025i). The EPA calculated the
incremental costs incurred by PWSs, which includes CWSs and NTNCWSs,
and the costs to States to implement and enforce the proposed NPDWR.
See section 4 in the Economic Analysis for the cost associated with the
proposed rule.
The EPA quantitatively assesses and qualitatively discusses health
endpoints associated with exposure to perchlorate. The monetized
benefits evaluated include reductions in human health risks associated
with IQ loss in offspring from reduced exposure by iodine deficient,
hypothyroxinemic pregnant women in their first trimester to perchlorate
in drinking water. The EPA was not able to quantify or monetize other
potential benefits, including those related to other reported health
effects associated with perchlorate exposure such as cardiovascular
disease, hypothyroidism, additional neurodevelopmental endpoints such
as ADHD, reduced iodine uptake, or benefits accruing from removal of
co-occurring contaminants and the value of information. See section 5
in the Economic Analysis for the quantified and unquantifiable
benefits.
A. Comparison of Benefits and Costs
Included here are estimates of total quantified annualized benefits
and costs for the proposed option and regulatory alternatives
considered as well as considerations for the nonquantifiable benefits
and costs. The incremental cost is the difference between the
quantified costs that will be incurred if the proposed rule is
finalized and the baseline. Incremental benefits reflect the avoided
future adverse health outcomes (i.e., avoided total IQ point
decrements) attributable to perchlorate reduction due
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to actions undertaken to comply with the proposed rule.
Exhibit 2 provides the incremental quantified benefits and costs of
the proposed rule at a 3 and 7 percent discount rate in 2023 dollars.
The estimates are the expected (mean) values and the 5th and 95th
percentile estimates from the uncertainty distribution produced by
SafeWater CBX. These distributions reflect the joint effect of multiple
sources of variability and uncertainty for quantified costs and
benefits. See sections 4.2 and 5.2.5 in the Economic Analysis (USEPA,
2025i) for further discussion on how SafeWater CBX incorporates
variability and uncertainty into model estimates. As shown in Exhibit
2, the annualized quantified incremental net benefits (benefits minus
costs) are -$7.8 million at a 3 percent discount rate and -$17.3
million at a 7 percent discount rate. The uncertainty range for the net
quantified benefits is -$15.3 million to $4.2 million at a 3 percent
discount rate and -$22.9 million to -$13.5 million at a 7 percent
discount rate. The EPA also evaluated the proposed MCLs that are higher
than the proposed MCLG (i.e., 40 [micro]g/L, 80 [micro]g/L). The
results are shown in Exhibits 3 and 4, respectively.
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The Administrator has determined that the benefits do not justify
the costs at any of the evaluated MCL options. The total net benefits
are higher for the higher proposed MCLs evaluated, but remain negative.
However, the improvement is not as significant as would generally be
expected for a doubling and quadrupling of the MCL. This is because
monitoring and administrative costs comprise a higher proportion of
total rule costs than is typical for an NPDWR, amounting to about half
of the total cost, given the low occurrence of perchlorate at levels of
concern in PWSs. Because monitoring costs are a significant portion of
the total cost and CWSs and NTNCWSs would be required to conduct
initial monitoring regardless of the MCL, there
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is limited opportunity to improve net benefits by increasing the MCL.
Benefits accrue when systems are required to take actions to reduce
perchlorate exposure (i.e., installing and operating treatment, public
notification, including information in the CCR). Increasing the MCL
would decrease the number of systems required to take actions, thus
reducing both treatment costs and benefits while monitoring and
administrative costs would remain similar across the MCL options.
Additionally, the uncertainty range for net benefits for 40 [micro]g/L
is -$9.9 million to $6.1 million at a 3 percent discount rate and -
$16.2 million to -$10.3 million at a 7 percent discount rate. The
uncertainty range for net benefits for 80 [micro]g/L is -$7.3 million
to $6.9 million at a 3 percent discount rate and -$12.0 million to -
$8.4 at a 7 percent discount rate. Therefore, there is no significant
difference between the uncertainty range at 20 [micro]g/L and the
higher evaluated levels. See section 6 in the Economic Analysis for a
summary of the benefits and costs that are quantified and
nonquantifiable under the proposed rule. The EPA notes there are
uncertainties in the estimates, however there are no nonquantifiable
costs associated with the analysis. Therefore, net benefits have a
downward bias since benefits are underestimated when compared to costs.
B. Uncertainty Analysis
The EPA provides discussions regarding several sources of
uncertainty. In the Economic Analysis the summary of limitations and
uncertainties and their potential effects can be found in section 3.4
for the baseline, in section 4.8 for the cost analysis and section
5.2.4 for the benefit assessment (USEPA, 2025i). 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 benefit or cost analysis.
The EPA provides the potential direction of the impact on the estimates
where possible but does not prioritize the entries with respect to the
impact magnitude.
C. Benefit-Cost Determination
SDWA section 1412(b)(4)(C), 42 U.S.C. 300g-1(b)(4)(C), requires
that, 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 SDWA section
1412(b)(3)(C), 42 U.S.C. 300g-1(b)(3)(C). For the proposed perchlorate
NPDWR, the Administrator has determined the quantified and
nonquantifiable benefits do not justify the costs given the significant
percentage of total costs due to monitoring and administrative costs
that are not expected to yield any significant health benefits.
Sections 4 through 6 in the Economic Analysis summarize the
quantified and nonquantifiable benefits and costs of this proposed rule
analysis. As indicated in section I of this preamble, the proposed rule
would impose significant monitoring and administrative cost burdens on
PWSs and States. Due to the infrequent occurrence of perchlorate at
levels of health concern, only a small subset of these systems is
expected to exceed even an MCL as close to the MCLG as feasible (20
[micro]g/L) and would be required to take action to reduce perchlorate
levels in their drinking water. Therefore, few systems are expected to
experience health benefits from reduced levels of perchlorate and the
associated reduced health risk compared to the number of systems
required to incur monitoring and administrative costs.
Under these circumstances, section 1412(b)(6)(A) of SDWA states
``the Administrator may, after notice and opportunity for public
comment, promulgate a maximum contaminant level for the contaminant
that maximizes health risk reduction benefits at a cost that is
justified by the benefits.'' The EPA evaluated higher alternative
proposed MCLs of 40 [micro]g/L and 80 [micro]g/L to determine whether
there is a level where benefits were maximized at a cost justified by
the benefits in accordance with SDWA section 1412(b)(6)(A), 42 U.S.C.
300g-1(b)(6)(A), (see Exhibits 3 and 4). Because fewer systems are
expected to exceed the higher proposed MCLs, not many systems would
need to treat for perchlorate. Therefore, the higher potential MCLs
would result in lower treatment costs, but would also result in lower
health benefits. In addition, raising the MCL does not significantly
increase the number of systems that would be eligible to reduce their
monitoring frequency and the associated monitoring costs (see section
4.1.1 of the Economic Analysis (USEPA, 2025i) for more details). Thus,
monitoring and administrative costs remain consistent at the higher
potential MCLs even with the proposed approach to monitoring, which is
intended to promote flexibility and reduce costs within permissible
bounds. Net benefits increase at the higher potential MCLs, but at a
slow rate due to fewer systems being required to take action to reduce
perchlorate levels in their drinking water yet remain negative overall.
Therefore, based on the significant percentage of total cost due to
monitoring, the consistent monitoring and administrative costs across
MCLs, and fewer benefits at higher potential MCLs, the Administrator
finds the benefits of an NPDWR at the higher potential MCLs evaluated
also would not justify the rule costs.
The EPA is unable to estimate nonquantifiable benefits, however the
EPA expects nonquantifiable benefits to follow the same pattern as
quantified benefits--there are fewer benefits as the number of systems
required to take action to reduce perchlorate in their drinking water
decreases. The EPA is unable to estimate the magnitude of these
benefits and at what levels they would occur. Thus, the EPA has
determined the nonquantifiable benefits combined with the quantifiable
benefits do not justify the costs at any of the MCLs evaluated.
Notwithstanding the Administrator's determination the benefits
would not justify the cost at any of the MCLs evaluated, the EPA is
proposing and seeking comment on MCLs of 20 [micro]g/L, 40 [micro]g/L,
or 80 [micro]g/L. As explained in section IV, the EPA is precluded from
reconsidering whether a NPDWR and MCLG for perchlorate are supported by
the statute and withdrawing the underlying regulatory determination in
light of the D.C. Circuit's 2023 opinion in NRDC v. Regan. A proposed
MCL of 20 [micro]g/L is feasible and is equal to the proposed MCLG,
there are no analytical or treatment feasibility constraints at that
level, and the monitoring and administrative costs are largely
unaffected by the MCL selected. The costs decrease at a faster rate
than the benefits as the MCL increases, resulting in a smaller gap
between benefits and costs at 40 [micro]g/L and 80 [micro]g/L as
compared to 20 [micro]g/L. This results in net benefits that are closer
to positive at these higher levels. This may indicate that one of these
proposed MCLs is more appropriate than the proposed MCL of 20 [micro]g/
L; however, the Administrator has determined the benefits are not
justified by the costs at any of these levels, and the EPA is not aware
of a level at which net benefits are close enough to positive to
support an MCL under the relevant statutory provision. The EPA is
seeking comment on the determination that benefits do not justify the
costs for the proposed MCL as close to the MCLG as feasible (20
[micro]g/L) made in accordance with SDWA section 1412(b)(4)(C), 42
U.S.C. 300g-1(b)(4)(C), and seeks comment and any supporting data or
information on the proposed MCLs of 40 [micro]g/L, 80 [micro]g/L, and
any other alternative MCL higher than the MCLG.
[[Page 424]]
XV. Request for Comment on Proposed Rule
The EPA is requesting comment on all aspects of this proposed NPDWR
for perchlorate. Comments are most helpful when accompanied by specific
examples and supporting data. The EPA specifically requests comments,
information, and data on the following topics:
General Matters
1. The EPA requests comment on ways that the proposed perchlorate
NPDWR could be simplified and ways that burden, including paperwork and
other administrative burden, could be reduced without affecting the
ability of the rule to prevent known or anticipated adverse health
effects.
2. The EPA requests comment on ways to further reduce burden on
small water systems, including flexibilities for monitoring and
compliance dates.
3. The EPA is seeking comment on the compliance date for the
proposed rule, including whether it is practicable for the EPA to
require water systems to comply with the requirements sooner than three
years after publication of the final rule.
4. The EPA is seeking comment on whether the Agency should provide
an additional two-year nationwide extension to the compliance date for
water systems to make capital improvements to comply with the rule.
5. The EPA is seeking comment on potential implementation
challenges associated with the proposed perchlorate regulation that the
Agency should consider, specifically for small systems.
6. The EPA is seeking comment on the consistency of the proposed
rule and all supporting documents with the Agency's guidelines on risk
characterization and Executive Order 14303, ``Restoring Gold Standard
Science.''
Maximum Contaminant Level Goal
1. The EPA is seeking comment on the quality and rigor of the
scientific review, evaluation, and use of epidemiological studies that
investigated the association between maternal thyroid hormone level and
neurodevelopmental outcomes.
2. The EPA is seeking comment on the adequacy and uncertainties of
the derivation of the perchlorate reference dose, including on the
health effects assessment and the BBDR model developed by the EPA to
estimate thyroid hormone level decreases due to perchlorate exposure to
hypothyroxinemic pregnant women in their first trimester with low
iodine intake, and model parameters. Several input parameters are
selected in the BBDR model to reflect a well-characterized sensitive
population. These parameters include: a weak TSH feedback loop
(pTSH=0.398), low iodine intake level (75 [mu]g/d), low baseline
maternal fT4 (10th percentile, 6.7 p.m.), and the first trimester of
pregnancy (13th gestational week). The rationale for the inputs and
underlying assumptions are described in section 5.2 of the 2025 draft
health effects TSD (USEPA, 2025b) and also in the 2019 TSD (USEPA,
2019a) and the Approaches Report (USEPA,2019c, 2019d). The EPA seeks
comment on the appropriateness of the selected model input values and
the underlying assumptions and whether alternative values should be
utilized for the purposes of deriving the MCLG. Specifically, the
Agency seeks comment on whether a weak TSH feedback response
constitutes a reasonable factor for the characterization of the
sensitive population. The Agency also seeks comment on the
appropriateness of the applied pTSH value of 0.398 to represent a
significantly weakened TSH feedback response, as well as alternative
pTSH values that could be selected instead (e.g., 1 to represent the
median TSH feedback response), for deriving the MCLG.
3. The EPA is seeking comment on the proposed MCLG of 20 [micro]g/L
and the methodology and science policy choices used to derive the
value, including whether the Agency should use a BMR of 2 or 3 percent
instead of 1 percent.
Maximum Contaminant Level
1. The EPA seeks comment on the three proposed MCLs of 20 [micro]g/
L, 40 [micro]g/L, 80 [micro]g/L, and any other alternative MCL higher
than the MCLG.
2. The EPA requests comment on the Agency's determination that the
proposed MCL of 20 [micro]g/L is the closest feasible level to the
MCLG.
3. The EPA requests comment on whether the Agency should promulgate
one of the other proposed MCLs of 40 [micro]g/L or 80 [micro]g/L, or
any MCL higher than the MCLG and any data or information that support
that any of the alternative proposed levels are the level at which the
health risk reductions are maximized at a cost justified by the
benefits.
4.The EPA specifically seeks comment on what MCL, if any, the
Agency may appropriately set consistent with the statute where, as
here, the low occurrence rate of a contaminant at levels of concern
mean that benefits are not justified by the costs at any MCL, including
when unquantifiable benefits and uncertainty are reasonably taken into
account.
Occurrence
1. The EPA is seeking comment on additional data sources on the
levels of perchlorate in drinking water.
2. The EPA is seeking comment on the adequacy of the underlying
assumptions and analysis of occurrence information, including data and
methods, used to estimate perchlorate concentrations at levels below
quantified detection. (section VIII of this preamble and Perchlorate
Occurrence and Monitoring Report for the Perchlorate National Primary
Drinking Water Regulation (USEPA, 2025e)).
3. The EPA requests comment on the method used and the estimated
number of systems likely to exceed the proposed MCL.
Monitoring
1. The EPA is seeking comment on potential implementation
challenges associated with the proposed monitoring and compliance
schedule (section X of this preamble), including the proposed
monitoring framework and public notification.
2. The EPA is seeking comment on the proposed requirement for all
CWSs and NTNCWSs to conduct initial monitoring prior to the rule
compliance date and on the required number of samples. Specifically,
the EPA is requesting comment on the proposed monitoring flexibility
for ground water systems serving 10,000 or fewer people to collect two
samples at each entry point to the distribution system instead of four
samples to satisfy initial monitoring requirements.
3. The EPA is seeking comment on its proposal to allow water
systems to use historical data to satisfy the initial monitoring
requirements, whether the EPA should specify an earlier or later cut-
off date than January 1, 2021, and whether the EPA should specify
additional factors or conditions for water systems to use this
provision.
4. The EPA is seeking comment on the proposed provision to allow
water systems to automatically reduce monitoring frequency without
State approval based on the results of the initial monitoring samples,
including the thresholds used (i.e., 4.0 [micro]g/L, proposed MCL) and
allowable frequencies (i.e., annual, triennial, nine-year). The EPA is
also requesting comment on using a threshold of one half of the MCL to
automatically reduce monitoring frequency. The EPA is also requesting
comment on the proposed
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provision allowing States to specify a more frequent monitoring
schedule.
5. The EPA is seeking comment on its proposal for water systems to
follow the monitoring frequencies and waiver provisions in 40 CFR
141.23 for IOCs after systems are binned into their monitoring
frequencies based on initial monitoring.
6. The EPA is seeking comment on the proposed compliance
calculation for an MCL exceedance. Specifically, whether the EPA should
base an exceedance of the MCL on the average of an initial sample and
confirmation sample instead of a running annual average. The EPA is
also requesting comment on its proposal that water systems would be
required to collect a follow-up sample within 5 days of the initial
sample or whether the EPA should require a shorter (e.g., three days)
or longer (e.g., 10 days) timeframe.
Public Notification and CCR
1. The EPA is seeking comment on the proposed requirement for Tier
1 public notification (PN) following an exceedance of the perchlorate
MCL as well as comment and supporting information on whether Tier 2 PN
should be required instead (section XI.B of this preamble).
2. The EPA is seeking comment on the accuracy and clarity of the
proposed mandatory health effects language for perchlorate proposed in
appendix A to subpart Q.
3. The EPA is seeking comment on the accuracy and clarity of the
proposed required language describing sources of perchlorate in
appendix A to subpart O.
Treatment Technologies
1. The EPA is seeking comment on the costs and availability of the
treatment technologies and non-treatment options for perchlorate
removal, including comments on the WBS model assumptions (section XII
of this preamble; Technologies and Costs for Treating Perchlorate-
Contaminated Waters for the Perchlorate National Primary Drinking Water
Regulation (USEPA, 2025d)). Specifically, the EPA seeks comment on the
assumption that any system exceeding the MCL could design and operate
systems to produce finished water concentrations that are 80 percent of
the MCL as a safety factor to avoid future exceedances.
2. The EPA is seeking any relevant data or information about the
effectiveness of the treatment technologies and non-treatment options
for perchlorate removal, specifically any relevant data on the impact
of competing ions on the bed life of perchlorate-selective resins
(section XII of this preamble and Best Available Technologies and Small
System Compliance Technologies for the Perchlorate National Primary
Drinking Water Regulation (USEPA, 2025c)). Additionally, the EPA is
seeking comment on the use of different measures of household income in
the SSCT affordability analysis and supplemental analysis (section 7.12
of the Economic Analysis of the Proposed Perchlorate National Primary
Drinking Water Regulation (USEPA, 2025i)).
3. The EPA is seeking comment on any additional information on
treatment technologies to remove perchlorate that are not identified in
the proposed rule and have been shown to reduce perchlorate levels to
the proposed MCL (section XII of this preamble and Best Available
Technologies and Small System Compliance Technologies for the
Perchlorate National Primary Drinking Water Regulation (USEPA, 2025c)
and Technologies and Costs for Treating Perchlorate-Contaminated Waters
for the Perchlorate National Primary Drinking Water Regulation (USEPA,
2025d)).
Health Risk Reduction Cost Analysis
1. The EPA is seeking comment on the adequacy of the underlying
estimates, assumptions, and analysis used to estimate costs and
benefits and describe unquantified costs and benefits (section XIV of
this preamble and Economic Analysis of the Proposed Perchlorate
National Primary Drinking Water Regulation (USEPA, 2025i).
Specifically, the EPA is seeking comment on additional data and
approaches to quantify the unquantified benefits in this action, and on
the unit costs used to estimate rule costs for PWSs and States.
Additionally, the EPA is seeking comment on the cost estimates for
small water systems (section XVI.D of this preamble and section 7.4 of
the Economic Analysis of the Proposed Perchlorate National Primary
Drinking Water Regulation (USEPA, 2025i)).
2. The EPA is seeking comment upon whether there are costs to PWSs
and States that are not quantified in section 4 of the Economic
Analysis of the Proposed Perchlorate National Primary Drinking Water
Regulation (USEPA, 2025i).
3. The EPA is seeking comment on the Administrator's finding in
accordance with SDWA section 1412(b)(4)(C), 42 U.S.C. 300g-1(b)(4)(C),
that the benefits of setting the proposed MCL at 20 [micro]g/L, 40
[micro]g/L, or 80 [micro]g/L for perchlorate do not justify the costs,
the information that supports that determination as described in
section XIV of this preamble, and the proposal to adopt one of these
MCLs notwithstanding this finding.
4. The EPA is seeking comment and information on other approaches
for identifying an MCL for which benefits justify the costs. The EPA is
also seeking comment on the Agency's conclusion that no alternative MCL
would ``maximize health risk reduction benefits at a cost that is
justified by the benefits'' and the analysis used to arrive at that
conclusion.
XVI. 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 13563: Improving Regulation and Regulatory Review
This action is an economically significant regulatory action under
Executive Order 12866 that was submitted to the Office of Management
and Budget (OMB) for review. Any changes made in response to E.O. 12866
review have been documented in the docket. The EPA prepared an analysis
of the potential benefits and costs associated with this action. At the
most stringent proposed MCL of 20 [micro]g/L, the annualized national
costs of the rule at a 3 percent discount rate ($2023) are $16.1
million and at a 7 percent discount rate ($2023) are $18.9 million. At
the most stringent proposed MCL of 20 [micro]g/L the annualized
national benefits at a 3 percent discount rate ($2023) are $8.3 million
and at a 7 percent discount rate ($2023) are $1.6 million. This
analysis, the Economic Analysis (USEPA, 2025i), is available in the
docket and is summarized in section XIV of this preamble. One year of
the proposed rule period of analysis would result in an undiscounted
impact greater than $100 million ($100.4 million).
B. Executive Order 14192: Unleashing Prosperity Through Deregulation
This action is expected to be an Executive Order 14192 regulatory
action. Details on the estimated costs of this proposed rule can be
found in the EPA's analysis of the potential costs and benefits
associated with this action.
C. Paperwork Reduction Act (PRA)
The information collection activities in this proposed rule have
been submitted for approval to the OMB under the PRA. The Information
Collection Request (ICR) document that the EPA prepared has been
assigned
[[Page 426]]
EPA ICR number XXXX.XX. You can find a copy of the ICR in the docket
for this rule, and it is briefly summarized here.
The burden includes the time needed to conduct State and water
system activities during the first three years after promulgation, as
described in section 4 of the Economic Analysis (USEPA, 2025i). The
paperwork burden associated with this proposed rule consists of the
burden imposed on systems to read and understand the perchlorate rule
as well as the burden associated with certain new collections of
information. Specifically, PWSs will have to assign personnel and
devote resources to implement the rule, including collecting or
compiling initial water samples and submitting this monitoring data to
the State. In addition, PWSs will need to attend training sessions and
receive technical assistance from their State during implementation of
the perchlorate rule.
Likewise, the paperwork burden for States include reading and
understanding the perchlorate rule. States will have to adopt the NPDWR
and develop programs to implement the rule. This may result in States
modifying or updating their data systems while implementing the
perchlorate rule. States will also have to provide staff with training
and technical assistance as well as provide water systems with training
and technical assistance for implementation of the perchlorate rule.
The information collected under this ICR is critical to States and
other authorized entities that have been granted primacy (i.e., primary
enforcement authority) for the perchlorate rule. These authorized
entities are responsible for overseeing the perchlorate rule
implementation by certain PWSs within their jurisdiction. States would
utilize these data to determine compliance. The collected information
is also necessary for PWSs. PWSs would use these data to demonstrate
compliance, communicate water quality information to consumers served
by the water system and, if needed, assess treatment options, and
operate and maintain installed treatment equipment. States would also
be required to report a subset of these data to the EPA. The EPA would
utilize the information to protect public health by ensuring compliance
with the perchlorate rule, measuring progress toward meeting the
perchlorate rule's goals, and evaluating the appropriateness of State
implementation activities. No confidential information would be
collected as a result of this ICR.
Respondents/affected entities: Respondents would include owners and
operators of public water systems who must report to their State, and
States who must report to the Federal Government.
Respondent's obligation to respond: The collection requirements are
mandatory under sections 1401(1)(D), 1445(a)(1)(A), and 1413(a)(3) of
SDWA.
Estimated number of respondents: 61,343; includes 56 primacy
agencies and 61,287 public water systems.
Frequency of response: For the first three years after the proposed
rule is published, the majority of the responses are required once.
Total estimated burden: 650,564 hours (per year). Burden is defined
at 5 CFR 1320.3(b).
Total estimated cost: $36,282,282 (per year), includes $8,771,558
annualized capital and operation and maintenance costs.
An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of 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.
Submit your comments on the Agency's need for this information, the
accuracy of the provided burden estimates, and any suggested methods
for minimizing respondent burden to the EPA using the Docket ID (EPA-
HQ-OW-2024-0592). The EPA will respond to any ICR-related comments in
the final rule. You may also send your ICR-related comments to OMB's
Office of Information and Regulatory Affairs using the interface at
www.reginfo.gov/public/do/PRAMain. Find this particular information
collection by selecting ``Currently under Review--Open for Public
Comments'' or by using the search function. OMB must receive comments
no later than February 5, 2026.
D. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the Regulatory
Flexibility Act (RFA).
The small entities subject to the requirements of this action are
water systems serving 10,000 persons 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 (63 FR at
7620, USEPA, 1998c), requested public comment, consulted with the Small
Business Administration (SBA), and finalized the alternative definition
in the Agency's CCR regulation (63 FR 44524, USEPA, 1998d). As stated
in the 1998 CCR rule (USEPA, 1998d), the alternative definition would
apply to all future drinking water regulations. The EPA used the
Federal Safe Drinking Water Information System (SDWIS/Federal) data
from the fourth quarter of 2023 to identify approximately 62,000 small
PWSs that may be impacted by the proposed perchlorate rule. These water
systems include approximately 45,000 CWSs that serve year-round
residents and approximately 17,000 NTNCWSs that serve the same persons
at least six months per year (e.g., a water system that is an office
park or church).
The Agency has determined that none of the proposed MCLs of 20
[micro]g/L, 40 [micro]g/L, or 80 [micro]g/L would result in annual
costs that exceed 1 percent of revenue for a substantial number of
small systems affected by the proposed perchlorate rule. There are
61,721 CWSs and NTNCWSs serving 10,000 or fewer people that would be
required to conduct perchlorate monitoring. The EPA estimates
approximately 80 small systems would incur costs to reduce the levels
of perchlorate in drinking water (see section 7.4.1 of the Economic
Analysis, USEPA, 2025i). Impacts on small entities are described in
more detail in section 7.4 of the Economic Analysis (USEPA, 2025i).
Under the proposed rule, the EPA also estimates approximately 6,279
small CWSs (14 percent of small CWSs) could incur annual costs greater
than 1 percent of annual revenue, and approximately 580 small CWSs (1
percent of small CWSs) could incur annual costs greater than 3 percent
of annual revenue. The EPA estimated annual revenue using each system's
average daily flow and the average revenue per thousand gallons
delivered from the 2006 Community Water System Survey (USEPA, 2009b).
These revenue estimates were then inflated to 2023 dollars using the
Gross Domestic Product (GDP) implicit price deflator. See section 7.4.3
in the Economic Analysis (USEPA, 2025i) for further discussion.
E. Unfunded Mandates Reform Act (UMRA)
This action does not contain an unfunded mandate of $100 million
(adjusted annually for inflation) or more (in 1995 dollars) as
described in UMRA, 2 U.S.C. 1531-1538. The action imposes minimal
enforceable duty on any State, local, or Tribal governments or the
private sector. Based on the cost estimates in section XIV of this
preamble, the EPA determined that the costs involved in this action are
[[Page 427]]
estimated to not exceed $187 million in 2024 dollars ($100 million in
1995 dollars adjusted for inflation using the GDP implicit price
deflator) or more in any one year. 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. See section XVI.F of this
preamble for details of this consultation. The EPA encourages small
entities to provide comment during the public comment period.
F. Executive Order 13132: Federalism
The EPA has concluded that this action does not have federalism
implications. However, this proposed rule may be of significant
interest to States and local governments. Consistent with the EPA's
policy to promote communications between the EPA and state and local
governments, the EPA consulted with representatives of state and local
governments early in the process of developing the proposed perchlorate
NPDWR to permit them to have meaningful and timely input into its
development. Annual costs are estimated to range from $16.1 million at
a 3 percent discount rate to $18.9 million at a 7 percent discount
rate, with $11.1 million to $12.6 million annually accruing to public
entities. On January 16, 2025, the EPA held a Federalism consultation
through a virtual meeting. The EPA invited the following national
organizations representing State and local officials to that meeting:
the National Governor's 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 Council of State
Governments, County Executives of America, and the Environmental
Council of the States. The EPA also invited the Association of State
Drinking Water Administrators, the Association of Metropolitan Water
Agencies, the National Rural Water Association, the American Water
Works Association, the Association of State and Territorial Health
Officials, the National Association of County and City Health
Officials, the American Public Works Association, the Association of
Clean Water Administrators, the Western States Water Council, the
African American Mayors Association, the National Association of State
Attorneys General, and the Western Governors' Association to
participate in the meeting. Representatives from 10 organizations
participated in the meeting. The EPA also provided the members of the
various associations an opportunity to provide input during follow-up
meetings. The EPA did not receive any requests for additional meetings.
In addition to input received during the meeting on January 16,
2025, the EPA provided an opportunity to receive written input within
60 days after the date of that meeting. A summary report of the views
expressed during the federalism consultation meeting and written
submissions is available in the Docket (EPA-HQ-OW-2024-0592).
G. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
The EPA has concluded that this proposed rule may have Tribal
implications because it may impose substantial direct compliance costs
on Tribal governments and the Federal Government will not provide the
funds necessary to pay those costs. The EPA has identified 1,026 water
systems serving Tribal communities, 91 Federally-owned, that may be
subject to the proposed rule. They would bear an estimated total
annualized cost of $122,000 at a 3 percent discount rate ($148,000 at 7
percent) to implement this rule as proposed. Estimated average
annualized cost per system ranges from $119 at a 3 percent discount
rate to $144 at a 7 percent discount rate.
The EPA consulted with Federally recognized Tribal officials early
in the process of developing this action to permit them to have
meaningful and timely input into its development. Between December 30,
2024, and February 28, 2025, the EPA conducted consultations with
Federally recognized Tribes, which included two national webinars with
interested Tribes on January 14 and 15, 2025, to request input and
provide rulemaking information to interested parties. A meeting summary
report is available on the docket for public inspection (USEPA, 2025j).
The EPA notes that 996 of the 1,026 Tribal systems identified by the
Agency as subject to the proposed rule are small systems. Due to the
health risks associated with perchlorate, capital expenditures needed
for compliance with the rule would be eligible for Federal funding
sources, specifically the DWSRF. In the spirit of Executive Order
13175, and consistent with the EPA policy to promote communications
between the EPA and Tribal governments, the EPA specifically solicits
additional comment on this proposed rule from Tribal officials.
H. Executive Order 13045: Protection of Children From Environmental
Health Risks 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 Executive Order 13045
because it is a significant regulatory action under section 3(f)(1) of
Executive Order 12866, and the EPA believes that the environmental
health or safety risk addressed by this action may have a
disproportionate effect on children. The EPA believes the environmental
health or safety risks addressed by this action may have a
disproportionate effect on children due to the most sensitive adverse
health effect of perchlorate exposure being decreased IQ effects in the
offspring of iodine-deficient, hypothyroxinemic pregnant women exposed
to perchlorate during the first trimester. Accordingly, we have
evaluated the environmental health or safety effects of perchlorate on
children. The results of this evaluation are contained in the draft
health effects support document for perchlorate (USEPA, 2025b).
The EPA is proposing setting the MCL at 20 [micro]g/L, 40 [micro]g/
L, or 80 [micro]g/L. The EPA recognizes that setting the MCL at 40
[micro]g/L, 80 [micro]g/L, or any higher level may result in lower
implementation costs. Any MCL selected at or above the MCLG would tend
to reduce adverse health effects in some children that had been exposed
during their mother's first trimester of pregnancy through drinking
water from PWSs that would be required to treat under a final NPDWR.
Furthermore, the EPA's Policy on Children's Health also applies to
this action. Information on how the Policy was applied is available
under section IV.B of this preamble.
I. Executive Order 132311: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
This action is not a ``significant energy action'' because it is
not likely to have significant adverse effect on the supply,
distribution, or use of energy. This determination is based on the
following analysis.
The first consideration is whether the proposed rule would
adversely affect the supply of energy. The proposed rule does not
regulate power generation,
[[Page 428]]
either directly or indirectly. The public and private water systems
that the proposed rule regulates do not generate power. Further, the
cost increases borne by customers of water utilities as a result of the
proposed rule are a low percentage of the total cost of water, except
for a few water systems that might install treatment technologies and
would likely spread that cost over their customer base. In sum, the
proposed rule does not regulate the supply of energy, does not
generally regulate the utilities that supply energy, and is unlikely to
affect significantly the customer base of energy suppliers. Thus, the
proposed rule would not translate into adverse effects on the supply of
energy.
The second consideration is whether the proposed rule would
adversely affect the distribution of energy. The proposed rule does not
regulate any aspect of energy distribution. The water systems that are
regulated by the proposed rule already have electrical service. At the
proposed MCL of 20 [micro]g/L, approximately 100 systems may require
incremental power to operate new treatment processes. At the proposed
MCLs of 40 [micro]g/L and 80 [micro]g/L, the number of systems
decreases to approximately 60 systems and 20 systems, respectively, and
the number would decrease further at any higher MCL. The increase in
peak electricity demand at water utilities is negligible. Therefore,
the EPA estimates that the existing connections are adequate and that
the proposed rule has no discernable adverse effect on energy
distribution.
The third consideration is whether the proposed rule would
adversely affect the use of energy. Because only approxiately100
systems are expected to add treatment technologies that use electrical
power at an MCL of 20 [micro]g/L and fewer at MCLs of 40 [micro]g/L, 80
[micro]g/L, or any higher level, this potential impact on sector demand
or overall national demand for power is negligible. Based on its
analysis of these considerations, the EPA has concluded that the
proposed rule is not likely to have a significant adverse effect on the
supply, distribution, or use of energy.
J. National Technology Transfer and Advancement Act (NTTAA)
This action involves technical standards. The EPA proposes to use
voluntary consensus standards that would require monitoring for
perchlorate and analysis of the samples obtained from monitoring based
on required methods. The EPA proposed five analytical methods for the
identification and quantification of perchlorate in drinking water. EPA
Methods 314.0, 314.1, 314.2, 331.0, and 332.0 incorporate quality
control criteria which allow accurate quantitation of perchlorate.
Additional information about the analytical methods is available in
section IX 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. The EPA also maintains a Water Docket
phone number available to call at (202) 566-2426, Monday-Friday,
8:30am-5:00pm.
The EPA's monitoring and sampling protocols generally include
voluntary consensus standards developed by agencies such as ASTM
International, Standard Methods and other such bodies wherever the EPA
deems these methodologies appropriate for compliance monitoring. The
EPA welcomes comments on this aspect of the proposed rulemaking and,
specifically, invites the public to identify potentially applicable
voluntary consensus standards and to explain why such standards should
be used in this regulation. The Director of the Federal Register
approved the voluntary consensus standards incorporated by reference in
40 CFR 141.23 of the proposed regulatory text as of April 11, 2007.
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 Safe
Drinking Water Act (SDWA), the Agency consulted with the National
Drinking Water Advisory Council (NDWAC or the Council); the Secretary
of Health and Human Services (HHS); and with the EPA Science Advisory
Board (SAB). The EPA consulted with NDWAC during the Council's January
10, 2025 meeting. A summary of the NDWAC recommendations is available
in the National Drinking Water Advisory Council, Public Meeting on the
Proposed Perchlorate National Primary Drinking Water Regulation
National Drinking Water Advisory Council (NDWAC) Summary (USEPA, 2025g)
and is in the docket for this proposed rule (EPA-HQ-OW-2024-0592). The
EPA carefully considered NDWAC recommendations during the development
of the proposed perchlorate NPDWR.
On May 29, 2012, the EPA sought guidance from the EPA's SAB on how
best to consider and interpret life stage information, epidemiological
and biomonitoring data since the publication of the National Research
Council 2005 report, the Agency's physiologically-based pharmacokinetic
(PBPK) analyses, and the totality of perchlorate health information to
derive a Maximum Contaminant Level Goal (MCLG) for perchlorate (USEPA,
2012b; NRC, 2005). On May 29, 2013, the EPA received significant input
from the SAB, summarized in the report, SAB Advice on Approaches to
Derive a Maximum Contaminant Level Goal for Perchlorate (USEPA, 2013).
To address SAB recommendations, the EPA collaborated with Food and
Drug Administration (FDA) scientists to develop PBPK/pharmacodynamic
(PD), or biologically based dose-response (BBDR), models that
incorporate all available health related information on perchlorate to
estimate changes in thyroid hormones in sensitive life stages exposed
to different dietary iodine and perchlorate levels (USEPA 2017). As
recommended by the SAB, the EPA developed these models based upon
perchlorate's mode of action (i.e., iodide uptake inhibition by the
thyroid) (USEPA, 2013). Additional details are in section IV.B of this
preamble and in the 2025 draft health effects TSD located in the docket
for this proposed rule (USEPA, 2025b).
In accordance with SAB recommendations, the EPA developed a two-
step approach to integrate BBDR model results with data on
neurodevelopmental outcomes from epidemiological studies, this approach
allowed the Agency to link maternal thyroid hormone levels as a result
of low iodine intake and perchlorate exposure, to derive an MCLG that
directly addresses the most sensitive life stage identified (USEPA,
2013).
In August 2025, the EPA initiated a consultation with the
Department of Health and Human Services (HHS) and the consultation was
held November18, 2025. During the consultation the EPA provided
information to HHS officials on the draft proposed perchlorate
regulation and considered HHS input as part of interagency review
described in section XVI.A of this preamble.
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USEPA. (2020a). Drinking Water: Final Action on Perchlorate. Federal
Register. 85 FR 43990. July 21, 2020.
USEPA. (2020b). Reductions of Perchlorate in Drinking Water. EPA
815-F-20-002. https://www.epa.gov/sites/default/files/2020-05/documents/perchlorate_reductions_5.14.20.pdf.
USEPA. (2020c). The Standardized Monitoring Framework: A Quick
Reference Guide. EPA 816-F-20-002. May 2020.
USEPA. (2022a). Drinking Water Contaminant Candidate List 5--Final.
Federal Register. 87 FR 68060. November 14, 2022.
USEPA. (2022b). ORD staff handbook for developing IRIS assessments.
EPA600R22268. Washington, DC: U.S. Environmental Protection Agency,
Office of Research and Development, Center for Public Health and
Environmental Assessment. https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=356370.
USEPA. (2023). PFAS National Primary Drinking Water Regulation
Rulemaking. Proposed Rule. Federal Register. 88 FR 18638. March 29,
2023.
USEPA. (2024a). PFAS National Primary Drinking Water Regulation.
Final Rule. Federal Register. 89 FR 32532. April 26, 2024.
USEPA. (2024b). National Primary Drinking Water Regulations:
Consumer Confidence Report. Final Rule. Federal Register. 89 FR
45980. May 24, 2024.
USEPA. (2025a). Announcement of Preliminary Regulatory
Determinations for Contaminants on the Fifth Drinking Water
Contaminant Candidate List. Federal Register. 90 FR 3830. January
15, 2025.
USEPA. (2025b). Draft Health Effects Technical Support Document:
Deriving a Reference Dose and Maximum Contaminant Level Goal for
Perchlorate in Drinking Water. EPA 815-D-25-001.
USEPA. (2025c). Best Available Technologies and Small System
Compliance Technologies for the Perchlorate National Primary
Drinking Water Regulation. EPA 815-R-25-005.
USEPA. (2025d). Technologies and Costs for Treating Perchlorate-
Contaminated Waters for the Perchlorate National Primary Drinking
Water Regulation. EPA 815-R-25-004.
USEPA. (2025e). Perchlorate Occurrence and Monitoring Report for the
Perchlorate National Primary Drinking Water Regulation. EPA 815-R-
25-006.
USEPA. (2025f). Federalism Consultation Report for the Perchlorate
National Primary Drinking Water Regulation.
USEPA. (2025g) Proposed Perchlorate National Primary Drinking Water
Regulation National Drinking Water Advisory Council (NDWAC) Meeting
Summary.
USEPA. (2025h). EPA Water TA: A Summary of Providers, Programs, and
Initiatives. EPA 830-F-25-001. January 2025.
USEPA. (2025i). Economic Analysis for the Proposed Perchlorate
National Primary Drinking Water Regulation. EPA 815-R-25-007.
USEPA. (2025j). Tribal Consultation Report for the Perchlorate
National Primary Drinking Water Regulation.
Urbansky, E.T. (2000). Quantitation of Perchlorate Ion: Practices
and Advances Applied to the Analysis of Common Matrices. Critical
Reviews in Analytical Chemistry. 30(4): 311-343.
van Mil, N.H., Steegers-Theunissen, R.P., Bongers-Schokking, J.J.,
et al. (2012). Maternal hypothyroxinemia during pregnancy and growth
of the fetal and infant head. Reproductive Sciences, 19: 1315-1322.
10.1177/1933719112450338.
Wang, P., Gao, J., Zhao, S., et al. (2016). Maternal Thyroxine
Levels During Pregnancy and Outcomes of Cognitive Development in
Children. Mol Neurobiol, 53: 2241-2248. 10.1007/s12035-015-9189-z.
List of Subjects
40 CFR Part 141
Environmental protection, Chemicals, Incorporation by reference,
Indians--lands, Intergovernmental relations, Monitoring and analytical
requirements, National primary drinking water regulation, Perchlorate,
Reporting and recordkeeping requirements, Water supply.
40 CFR Part 142
Environmental protection, Administrative practice and procedure,
Chemicals, Indians--lands, Intergovernmental relations, Monitoring and
analytical requirements, National primary drinking water regulation,
Perchlorate, Reporting and recordkeeping requirements, Water supply.
Lee Zeldin,
Administrator.
For the reasons set forth in the preamble, EPA proposes to amend 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. 141.6 by revising paragraph (a) and adding paragraph (m)
to read as follows:
Sec. 141.6 Effective dates.
(a) Except as provided in paragraphs (b) through (m) of this
section the regulations set forth in this part take effect on June 24,
1977.
* * * * *
(m) The regulations contained in the revisions to Sec. Sec.
141.23(a)(4)(i), 141.23(a)(5), 141.23(c), 141.23(f)(3)-(4),
141.23(i)(3) 141.23(k)(1)-(3), 141.23(k)(3)(ii), 141.51(b),
141.60(b)(5), 141.62(b), 141.62(c), 141.62(e), appendix A to subpart O
(the consumer confidence rule) and appendices A and B to subpart Q (the
public notification rule) are effective for the purposes of compliance
on [INSERT DATE 3 YEARS AFTER DATE OF PUBLICATION OF FINAL RULE IN THE
FEDERAL REGISTER].
* * * * *
0
3. Amend Sec. 141.23 by:
0
a. Revising and republishing Table 1 to paragraph (a)(4)(i);
0
b. Revising and republishing paragraph (a)(5);
0
c. Revising and republishing the introductory text of paragraph (c);
0
d. Adding paragraph (c)(10);
0
e. Revising and republishing paragraph (f)(3);
0
f. Adding paragraph (f)(4); and
0
g. Revising and republishing paragraph (h)(3), Table 2 to paragraph
(k)(1), Table 3 to paragraph (k)(2), and Table 4 to paragraph
(k)(3)(ii).
The revisions and additions read as follows:
Sec. 141.23 Inorganic chemical sampling and analytical requirements.
* * * * *
(a) * * *
(4) * * *
(i) * * *
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* * * * *
(5) The frequency of monitoring for asbestos shall be in accordance
with paragraph (b) of this section: the frequency of monitoring for
antimony, arsenic, barium, beryllium, cadmium, chromium, cyanide,
fluoride, mercury, nickel, perchlorate, selenium and thallium shall be
in accordance with paragraph (c) of this section; the frequency of
monitoring for nitrate shall be in accordance with paragraph (d) of
this section; and the frequency of monitoring for nitrite shall be in
accordance with paragraph (e) of this section.
* * * * *
(c) The frequency of monitoring conducted to determine compliance
with the maximum contaminant levels in Sec. 141.62 for antimony,
arsenic, barium, beryllium, cadmium, chromium, cyanide, fluoride,
mercury, nickel, perchlorate, selenium and thallium shall be as
follows:
* * * * *
(10) Community water systems and non-transient non-community water
systems must conduct monitoring for perchlorate as follows:
(i) All ground water systems serving greater than 10,000 persons
without acceptable historic data and all surface water systems without
acceptable historic data, as defined in paragraph (c)(10)(v), must
collect four initial consecutive quarterly samples at all sampling
points by [INSERT DATE 3 YEARS AFTER DATE OF PUBLICATION OF FINAL RULE
IN THE FEDERAL REGISTER].
(ii) Ground water systems serving 10,000 persons or fewer without
acceptable historic data, as defined in paragraph (c)(10)(v), must
collect two initial samples between five and seven months apart at all
sampling points by [INSERT DATE 3 YEARS AFTER DATE OF PUBLICATION OF
FINAL RULE IN THE FEDERAL REGISTER].
(iii) Based on the initial monitoring results in paragraphs
(c)(10)(i) and (ii) of this section, at the start of the monitoring
period that begins on [INSERT DATE 3 YEARS AFTER DATE OF PUBLICATION OF
FINAL RULE IN THE FEDERAL REGISTER], systems must monitor at the
following frequencies at sampling points approved by the State and any
further increase or reduction in sampling frequency is in accordance
with paragraphs (c)(1) through (9) of this section:
(A) Any system with all initial samples at or below 4.0 [micro]g/L
at a sampling point shall take one sample at that sampling point during
each compliance cycle (i.e., nine years).
(B) Surface water systems with all initial samples at or below the
MCL and any above 4.0 [micro]g/L at a sampling point, shall take one
sample annually at the sampling point.
(C) Ground water systems with all initial samples at or below the
MCL and any above 4.0 [micro]g/L at a sampling point shall take one
sample at that sampling point during each compliance period (i.e.,
three years).
(D) Any system with an initial monitoring result above the MCL
shall monitor quarterly at that sampling point.
(iv) States may increase the frequency of sampling in paragraph
(c)(10)(iii) of this section.
(v) States may accept historical data by a water system to satisfy
the initial monitoring requirements if systems use monitoring data for
a sampling point using the same number of samples specified in
paragraphs (c)(10)(i) and (ii) of this section, or data that was
collected under a state monitoring requirement, collected between
January 1, 2021 and [INSERT DATE OF PUBLICATION OF THE FINAL RULE IN
THE FEDERAL REGISTER] to satisfy the initial monitoring requirements
for that sampling point.
* * * * *
(f) * * *
(3) Where the results of sampling for perchlorate indicate an
exceedance of the maximum contaminant level, the systems must take a
confirmation sample within five days of the system's receipt of
notification of the analytical results of the first sample.
(4) If a State-required confirmation sample is taken for any
contaminant, then the results of the initial and
[[Page 433]]
confirmation sample shall be averaged. The resulting average shall be
used to determine the system's compliance in accordance with paragraph
(i) of this section. States have the discretion to delete results of
obvious sampling errors.
* * * * *
(i) * * *
(3) Compliance with the maximum contaminant levels for nitrate,
nitrite, and perchlorate is determined based on one sample if the
levels of these contaminants are below the MCLs. If the level of
perchlorate exceeds the MCL in the initial sample, a confirmation
sample is required in accordance with paragraph (f)(3) of this section,
and compliance shall be based on the average of the initial and
confirmation sample. If the levels of nitrate and/or nitrite exceed the
MCLs in the initial sample, a confirmation sample is required in
accordance with paragraph (f)(2) of this section, and compliance shall
be determined based on the average of the initial and confirmation
samples.
* * * * *
(k) * * *
(1) Analysis for the following contaminants shall be conducted in
accordance with the methods in the following table, or the alternative
methods listed in appendix A to subpart C of this part, or their
equivalent as determined by EPA. Criteria for analyzing arsenic,
barium, beryllium, cadmium, calcium, chromium, copper, lead, nickel,
selenium, sodium, and thallium with digestion or directly without
digestion, and other analytical test procedures are contained in
Technical Notes on Drinking Water Methods, EPA-600/R-94-173, October
1994. This document is available from the National Service Center for
Environmental Publications (NSCEP), P.O. Box 42419, Cincinnati, OH
45242-0419 or http://www.epa.gov/nscep/.
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The approved compliance methods for determining perchlorate in
drinking water listed in table 1 to paragraph (k) of this section, are
incorporated by reference. The Director of the Federal Register
approves this incorporation by reference in accordance with 5 U.S.C.
552(a) and 1 CFR part 51. Copies of the material incorporated by
reference in this paragraph (k) may be inspected at EPA's Drinking
Water Docket, 1301 Constitution Avenue NW, EPA West, Room 3334,
Washington, DC 20460 (Telephone: 202-566-2426); or at the National
Archives and Records Administration (NARA). For information on the
availability of this material at NARA, call 202-741-6030, or go to:
http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
* * * * *
(2) Sample collection for antimony, arsenic, asbestos, barium,
beryllium, cadmium, chromium, cyanide, fluoride, mercury, nickel,
nitrate, nitrite, perchlorate, selenium, and thallium under this
section shall be conducted using the sample preservation, container,
and maximum holding time procedures specified in the table below:
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(3) Analysis under this section shall only be conducted by
laboratories that have been certified by EPA or the State. Laboratories
may conduct sample analysis under provisional certification until
January 1, 1996. To receive certification to conduct analyses for
antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium,
cyanide, fluoride, mercury, nickel, nitrate, nitrite, perchlorate,
selenium, and thallium, the laboratory must: * * *
(ii) * * *
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* * * * *
0
4. Amend Sec. 141.51 by revising table 1 to paragraph (b) by adding in
alphabetical order, an entry for ``Perchlorate'', to read as follows:
Sec. 141.51 Maximum contaminant level goals for inorganic
contaminants.
* * * * *
(b) * * *
[GRAPHIC] [TIFF OMITTED] TP06JA26.022
* * * * *
0
5. Amend Sec. 141.60 by adding paragraph (b)(5) to read as follows:
Sec. 141.60 Effective Dates.
* * * * *
(b) * * *
(5) The effective date for Sec. 141.62(b)(17) is [DATE OF
PUBLICATION OF FINAL RULE IN THE Federal Register].
* * * * *
0
6. Amend Sec. 141.62 by:
0
a. In Table 1 to paragraph (b), adding in numerical order the entries
for ``(17)'';
0
b. In Table 1 to paragraph (c), adding an entry for ``Perchlorate'' in
alphabetical order, and an entry ``14 = Biological Treatment'' under
the undesignated heading entitled ``Key to BATs''; and
0
c. Adding paragraph (e).
Sec. 141.62 Maximum contaminant levels for inorganic contaminants.
* * * * *
(b) * * *
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(c) * * *
[[Page 439]]
[GRAPHIC] [TIFF OMITTED] TP06JA26.015
* * * * *
Key to BATs in Table
* * * * *
5 = Ion Exchange
* * * * *
7 = Reverse Osmosis
* * * * *
14 = Biological Treatment
* * * * *
(e) The Administrator, pursuant to section 1412 of the Act, hereby
identifies in the following table the affordable technology, treatment
technique, or other means available to systems serving 10,000 persons
or fewer for achieving compliance with the maximum contaminant level
for perchlorate:
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0
7. Amend appendix A to subpart O of part 141 under the heading
``Inorganic contaminants'' by adding an entry for ``Perchlorate'' in
alphabetical order to read as follows:
[[Page 441]]
Appendix A to Subpart O of Part 141--Regulated Contaminants
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* * * * *
0
8. Amend appendix A to subpart Q of part 141, under ``B. Inorganic
Chemicals (IOCs)'', by adding an entry for ``Perchlorate'' in
alphabetical order to read as follows:
[[Page 442]]
Appendix A to Subpart Q of Part 141--NPDWR Violations and Other
Situations Requiring Public Notice 1
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Appendix A--Endnotes
* * * * *
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.
* * * * *
0
9. Amend appendix B to subpart Q of part 141 by adding under ``C.
Inorganic Chemicals (IOCs)'', an entry for ``Perchlorate'' in
alphabetical order to read as follows:
[[Page 443]]
Appendix B to Subpart Q of Part 141--Standard Health Effects Language
for Public Notification
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Appendix B--Endnotes
* * * * *
1. MCLG--Maximum contaminant level goal.
2. MCL--Maximum contaminant level.
* * * * *
PART 142--NATIONAL PRIMARY DRINKING WATER REGULATIONS
IMPLEMENTATION
0
10. 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
11. Amend table 1 to paragraph (b) in Sec. 142.62 by adding an entry
for ``Perchlorate'' in alphabetical order, and an entry ``13 =
Biological Treatment'' under the undesignated heading entitled ``Key to
BATs'' to read as follows:
Sec. 142.62 Variances and exemptions from the maximum contaminant
levels for organic and inorganic chemicals.
* * * * *
(b) * * *
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[GRAPHIC] [TIFF OMITTED] TP06JA26.020
* * * * *
Key to BATs in Table
* * * * *
5 = Ion Exchange
* * * * *
7 = Reverse Osmosis
* * * * *
13 = Biological Treatment
* * * * *
[FR Doc. 2026-00021 Filed 1-5-26; 8:45 am]
BILLING CODE 6560-50-C