[Federal Register Volume 85, Number 140 (Tuesday, July 21, 2020)]
[Rules and Regulations]
[Pages 43990-44002]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-13462]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 141 and 142

[EPA-HQ-OW-2018-0780, EPA-HQ-OW-2008-0692, EPA-HQ-OW-2009-0297; FRL-
10011-21-OW]
RIN 2040-AF28


Drinking Water: Final Action on Perchlorate

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final action.

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SUMMARY: The Environmental Protection Agency (EPA) is announcing its 
withdrawal of the 2011 determination to regulate perchlorate in 
accordance with the Safe Drinking Water Act, (SDWA). On February 11, 
2011, the EPA published a Federal Register document in which the Agency 
determined that perchlorate met the SDWA's criteria for regulating a 
contaminant. On June 26, 2019, the EPA published a proposed national 
primary drinking water regulation (NPDWR) for perchlorate and requested 
public comments on multiple alternative actions, including the 
alternative of withdrawing the 2011 regulatory determination for 
perchlorate. The EPA received approximately 1,500 comments on the 
proposed rulemaking. The EPA has considered these public comments and 
based on the best available information the Agency is withdrawing the 
2011 regulatory determination and is making a final determination not 
to regulate perchlorate. The EPA has determined that perchlorate does 
not occur ``with a frequency and at levels of public health concern'' 
within the meaning of the SDWA. In addition, in the judgment of the EPA 
Administrator, regulation of perchlorate does not present a 
``meaningful opportunity for health risk reduction for persons served 
by public water systems.'' Accordingly, the EPA is

[[Page 43991]]

withdrawing its 2011 determination and is making a final determination 
not to regulate perchlorate, and therefore will not issue a NPDWR for 
perchlorate at this time.

DATES: For purposes of judicial review, the regulatory determination in 
this document is issued as of July 21, 2020.

FOR FURTHER INFORMATION CONTACT: Samuel Hernandez, Office of Ground 
Water and Drinking Water, Standards and Risk Management Division (Mail 
Code 4607M), Environmental Protection Agency, 1200 Pennsylvania Avenue 
NW, Washington, DC 20460; telephone number: (202) 564-1735; email 
address: [email protected].

SUPPLEMENTARY INFORMATION: This document is organized as follows:

I. General Information
    A. Does this action apply to me?
    B. How can I get copies of this document and other related 
information?
II. Background
    A. What is perchlorate?
    B. What is the purpose of this action?
    C. What is the EPA's statutory authority for this action?
    D. Statutory Framework and Perchlorate Regulatory History
III. Withdrawal of the 2011 Regulatory Determination and Final 
Determination Not To Regulate Perchlorate
    A. May perchlorate have an adverse effect on the health of 
persons?
    B. Is perchlorate known to occur or is there a substantial 
likelihood that perchlorate will occur in public water systems with 
a frequency and at levels of public health concern?
    C. Is there a meaningful opportunity for the reduction of health 
risks from perchlorate for persons served by public water systems?
    D. What is the EPA's final regulatory determination on 
perchlorate?
IV. Summary of Key Public Comments on Perchlorate
    A. SDWA Statutory Requirements and the EPA's Authority
    B. Health Effects Assessment
    C. Occurrence Analysis
V. Conclusion
VI. References

I. General Information

A. Does this action apply to me?

    This action will not impose any requirements on anyone. Instead, 
this action notifies interested parties of the EPA's withdrawal of the 
2011 regulatory determination for perchlorate and the final regulatory 
determination not to regulate perchlorate. Section IV of this document 
provides a summary of the key comments received on the June 26, 2019 
(84 FR 30524) proposed NPDWR for perchlorate (referred to hereinafter 
as ``the 2019 proposal'').

B. How can I get copies of this document and other related information?

    The EPA has established a docket for this action under Docket ID 
No. EPA-HQ-OW-2018-0780. Publicly available docket materials are 
available electronically at https://www.regulations.gov/docket?D=EPA-HQ-OW-2018-0780.

II. Background

A. What is perchlorate?

    Perchlorate is a negatively charged inorganic ion that is composed 
of one chlorine atom bound to four oxygen atoms (ClO4-), 
which is highly stable and mobile in the aqueous environment. 
Perchlorate comes from both natural and manmade sources. It is formed 
naturally via atmospheric processes and can be found within mineral 
deposits in certain geographical areas. It is also produced in the 
United States by industrial processes, and the most commonly produced 
compounds include ammonium perchlorate and potassium perchlorate used 
primarily as oxidizers in solid fuels to power rockets, missiles, and 
fireworks. Perchlorate can also result from the degradation of 
hypochlorite solutions used for water disinfection. The degradation 
into perchlorate occurs when hypochlorite solutions are improperly 
stored and handled. For the general population, most perchlorate 
exposure is through the ingestion of contaminated food or drinking 
water. Above certain levels, perchlorate can prevent the thyroid gland 
from getting enough iodine, which can affect thyroid hormone 
production. The consequences of insufficient thyroid hormone levels 
during human growth and development are well known. For pregnant women 
with low iodine levels, sufficient changes in thyroid hormone levels 
may cause changes in the child's brain development. In a 2005 report 
entitled ``Health Implications of Perchlorate Ingestion'', the National 
Research Council stated that: ``fetuses and preterm newborns constitute 
the most sensitive populations although infants and developing children 
are also considered sensitive populations'' (NRC, 2005). The existence 
of a quantifiable relationship between thyroid hormone changes and 
neurodevelopmental outcomes has strong support from the literature on 
the subject; however, not every study identifies an association between 
maternal thyroid hormone levels and the neurodevelopmental outcomes, 
and the state of the science on this relationship is constantly 
evolving.

B. What is the purpose of this action?

    The purpose of this action is to publish the EPA's notice to 
withdraw the 2011 regulatory determination, one of the alternative 
options in the 2019 proposal, and to issue a final determination not to 
regulate perchlorate in drinking water. This document presents the 
EPA's basis for this withdrawal and final regulatory determination, and 
the EPA's response to key issues raised by commenters in response to 
the 2019 proposal.

C. What is the EPA's statutory authority for this action?

    The SDWA sets forth three criteria that must be met for the EPA to 
issue a maximum contaminant level goal (MCLG) and promulgate a national 
primary drinking water regulation (NPDWR). Specifically, the 
Administrator must determine that (1) ``the contaminant may have an 
adverse effect on the health of persons''; (2) ``the contaminant is 
known to occur or there is a substantial likelihood that 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 such contaminant presents a meaningful 
opportunity for health risk reduction for persons served by public 
water systems'' (SDWA 1412(b)(1)(A)).
    SDWA 1412(b)(1)(B) sets out the process for the EPA to establish 
drinking water standards for an unregulated contaminant. As explained 
in more detail below, in 2011, the EPA issued a determination that 
perchlorate met the three statutory criteria outlined above and 
therefore should be regulated. Under the statute, a determination to 
regulate triggers a duty for the EPA to issue a proposed drinking water 
standard within two years and a final rule 18 months later (with the 
possibility of a 3 month extension). SDWA 1412(b)(1)(E). The EPA 
subsequently published a proposed drinking water standard for 
perchlorate, and alternatives including the withdrawal of the 2011 
regulatory determination, in 2019. The promulgation of a final drinking 
water standard would, when effective, require monitoring of public 
water supplies for the contaminant and treatment as necessary to meet 
the regulatory standard.
    The EPA has determined, based on reviewing data and analysis 
obtained since the issuance of the 2011 regulatory determination, that 
perchlorate does not meet the statutorily-prescribed criteria for 
regulation. As described in Sections III & VI of the 2019 proposal, the 
data

[[Page 43992]]

and analysis in the record indicate that perchlorate does not occur in 
public water systems with a frequency and at levels of public health 
concern. Specifically, the peer-reviewed health effects analysis 
indicates that the estimated concentrations of perchlorate that may 
represent levels of public health concern (i.e., the proposed MCLG 
levels, 18-90 [micro]g/L) is higher than the concentration considered 
in issuance of the 2011 regulatory determination (1-47 [micro]g/L) 
(USEPA, 2019a). In addition, based on a re-evaluation of the nationally 
representative First Unregulated Contaminant Monitoring Rule (UCMR 1) 
data, the updated occurrence analysis shows that the frequency of 
occurrence of perchlorate in public water systems at levels exceeding 
any of the alternative proposed MCLGs (18 [micro]g/L-90 [micro]g/L) is 
significantly lower (0.03%-0.002%) than the frequency considered in the 
analysis for the 2011 regulatory determination (4%-0.39%) (USEPA, 
2019b). The EPA estimates that, even at the most stringent regulatory 
level considered in the 2019 proposal (18 [micro]g/L), not more than 15 
systems (0.03% of all water systems in the U.S. serving approximately 
620,000 people) would need to take action to reduce levels of 
perchlorate. Based on this information, the EPA determines that 
perchlorate does not occur in public water systems ``with a frequency 
and at levels of public health concern'' and thus does not meet the 
second criterion of the three required for regulation under the SDWA. 
In addition, while the third criterion is ``in the sole judgment of the 
Administrator,'' the small number of water systems with perchlorate 
levels greater than identified thresholds, and the correspondingly 
small population served, provides ample support for the EPA's 
conclusion that the regulation of perchlorate does not present a 
``meaningful opportunity for health risk reduction for persons served 
by public water systems,'' within the meaning of 1412(b)(1)(A)(iii). 
Accordingly, because perchlorate no longer meets the statutory criteria 
for regulation, the EPA does not have the authority to issue a MCLG or 
promulgate a NPDWR for perchlorate.
    While the EPA has not previously withdrawn a regulatory 
determination, the decision is supported by the legislative history 
underlying the 1996 amendments to the SDWA, which repealed the 
statutory requirement for the EPA to regulate an additional 25 
contaminants every 3 years and replaced it with the current requirement 
for the EPA to determine whether regulation is warranted for five 
contaminants every five years. In describing the need for such 
amendment, the legislative history points to the view expressed at the 
Committee Hearing that ``the current law is a one-size-fits-all 
program. It forces our water quality experts 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 (1995) at 12). This amendment reflected Congress' clear intent that 
the EPA prioritize actual health risks in determining whether to 
regulate any particular contaminant. See id at 12 (noting that the 
amendment ``repeals the requirement that the EPA regulate an additional 
25 contaminants every 3 years replacing it with a new selection process 
that gives the EPA the discretion to identify contaminants that warrant 
regulation in the future'').
    The EPA's decision to withdraw the regulatory determination is also 
consistent with Congress' direction to prioritize SDWA decisions based 
on the best available public health information. See 
1412(b)(1)(B)(ii)(II) (findings supporting a determination to regulate 
``shall be based on the best available public health information''); 
1412(b)(2)(A) (requiring that the EPA use ``the best available, peer-
reviewed science and supporting studies . . .'' in carrying out any 
actions under this section). Although the EPA determined in 2011 that 
perchlorate met the criteria for regulation, 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,'' 
are no longer accurate, and no longer support the Agency's 
prioritization of perchlorate for regulation. Accordingly, not only is 
the EPA not authorized to issue a MCLG or promulgate a NPDWR for 
perchlorate, but it would not be in the public interest for the EPA to 
do so.
    The EPA recognizes that the SDWA does not include a provision 
explicitly authorizing withdrawal of a regulatory determination. 
However, such authority is inherent in the authority to issue a 
regulatory determination under 1412(b)(1)(B)(ii)(II), particularly 
given the requirement that such determination be based on the ``best 
available public health information,'' as discussed above. Accordingly, 
the EPA must have the inherent authority to withdraw a regulatory 
determination if the underlying information changes between regulatory 
determination and promulgation. In light of Congress's concern that the 
EPA focus new contaminant regulations on priority health concerns, 
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 are available, especially when those data 
demonstrate that regulation of a new contaminant would not present a 
meaningful opportunity for health risk reduction.
    Moreover, the EPA notes that the statute specifically provides that 
a decision not to regulate a contaminant is a final Agency action 
subject to judicial review. SDWA 1412(b)(1)(B)(ii)(IV). Congress could 
have--but did not--specify the same with respect to determinations to 
regulate. Congress also did not explicitly prohibit the EPA from 
withdrawing or modifying a regulatory determination. Congress' silence 
with respect to determinations to regulate suggests that Congress 
intended that such a determination is not itself a final agency action, 
but rather a preliminary step in a decision-making process culminating 
in a NPDWR and thus subject to reconsideration based on new data and 
analysis considered during the 36 month promulgation process specified 
in the statute. Accordingly, reconsideration of this preliminary 
finding--and withdrawal of the determination based on subsequent 
analysis mandated for NPDWR development--is fully consistent with the 
statutory decision-making framework.

D. Statutory Framework and Perchlorate Regulatory History

    Section 1412(b)(1)(B)(i) of the SDWA requires the EPA to publish 
every five years a Contaminant Candidate List (CCL). The CCL is a list 
of drinking water contaminants that are known or anticipated to occur 
in public water systems and are not currently subject to federal 
drinking water regulations. The EPA uses the CCL to identify priority 
contaminants for regulatory decision-making and information collection. 
The placement of a substance on the CCL does not require that it be 
regulated under the SDWA. Contaminants listed on the CCL may require 
future regulation under the SDWA. The EPA included perchlorate on the 
first, second, and third CCLs published in 1998 (63 FR 10274, March 2, 
1998), 2005 (70 FR 9071, February 24, 2005), and 2009 (74 FR 51850, 
October 8, 2009).
    The EPA collects data on the CCL contaminants to better understand 
their potential health effects and to determine

[[Page 43993]]

the levels at which they occur in public water systems. SDWA 
1412(b)(1)(B)(ii) requires that, every five years, the EPA, after 
consideration of public comment, issue a determination of whether or 
not to regulate at least five contaminants on each CCL. For any 
contaminant that the EPA determines meets the criteria for regulation 
under SDWA 1412(b)(1)(E), the EPA must propose a NPDWR within two years 
and promulgate a final regulation within 18 months of the proposal 
(which may be extended by 9 additional months).
    As part of its responsibilities under the SDWA, the EPA implements 
section 1445(a)(2) (``Monitoring Program for Unregulated 
Contaminants''). This section requires that once every five years, the 
EPA issue a list of no more than 30 unregulated contaminants to be 
monitored by public water systems. This monitoring is implemented 
through the Unregulated Contaminant Monitoring Rule (UCMR), which 
collects data from community water systems and non-transient, non-
community water systems. The first four UCMRs collected data from a 
census of large water systems (serving more than 10,000 people) and 
from a statistically representative sample of small water systems. On 
September 17, 1999, the EPA published its first UCMR (64 FR 50556), 
which required all large systems and a representative sample of small 
systems to monitor for perchlorate and 25 other contaminants (USEPA, 
1999). Water system monitoring data for perchlorate were collected from 
2001 to 2005.
    The EPA and other federal agencies asked the National Research 
Council (NRC) to evaluate the health implications of perchlorate 
ingestion. In its 2005 report, the NRC concluded that perchlorate 
exposure inhibits the transport of iodide \1\ into the thyroid by a 
protein molecule known as the sodium/iodide symporter (NIS), which may 
lead to decreases in the production of two thyroid hormones, thyroxine 
(T3) and triiodothyronine (T4), and increases in the production of 
thyroid-stimulating hormone (TSH) (National Research Council (NRC), 
2005). Additionally, the NRC concluded that the most sensitive 
population to perchlorate exposure are ``the fetuses of pregnant women 
who might have hypothyroidism or iodide deficiency'' (p. 178). The EPA 
established a reference dose (RfD) consistent with the NRC's 
recommended RfD of 0.7 [micro]g/kg/day for perchlorate. The reference 
dose is an estimate of a human's daily exposure to perchlorate that is 
likely to be without an appreciable risk of adverse effects. This RfD 
was based on a study (Greer, Goodman, Pleus, & Greer, 2002) of 
perchlorate's inhibition of radioactive iodine uptake in healthy adults 
and the application of an uncertainty factor of 10 for intraspecies 
variability (USEPA, 2005a).
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    \1\ 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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    In October 2008, the EPA published a preliminary regulatory 
determination not to regulate perchlorate in drinking water and 
requested public comment (73 FR 60262, October 10, 2008). In that 
preliminary determination, the EPA found that perchlorate did not occur 
with a frequency and at levels of public health concern within the 
meaning of the SDWA, and that development of a regulation did not 
present a meaningful opportunity for health risk reduction for persons 
served by public water systems. In reaching this conclusion, the EPA 
derived and used a Health Reference Level (HRL) of 15 [mu]g/L based on 
the RfD of 0.7 [micro]g/kg/day and body weight and exposure information 
for pregnant women (USEPA, 2008a). Using the UCMR 1 occurrence data, 
the EPA estimated that less than 1% of drinking water systems (serving 
approximately 1 million people) had perchlorate levels above the HRL of 
15 [micro]g/L. Based on this information, the EPA found that 
perchlorate did not occur at a frequency and at levels of public health 
concern. The EPA also determined there was not a meaningful opportunity 
for a NPDWR for perchlorate to reduce health risks.
    In August 2009, the EPA published a supplemental request for 
comment with new analysis that derived potential alternative Health 
Reference Levels (HRLs) for 14 life stages, including infants and 
children. The analysis used the RfD of 0.7 [mu]g/kg/day and life stage-
specific bodyweight and exposure information, resulting in comparable 
perchlorate concentrations in drinking water, based on life stage, of 
between 1 [mu]g/l to 47 [mu]g/l (74 FR 41883; USEPA, 2009a).
    In February 11, 2011, the EPA published its determination to 
regulate perchlorate (76 FR 7762; USEPA, 2011) after careful 
consideration of public comments on the October 2008 and August 2009 
notices. The EPA found at that time that perchlorate may have an 
adverse effect on the health of persons; that it is known to occur, or 
that there is a substantial likelihood that it will occur, in public 
drinking water systems with a frequency and at levels that present a 
public health concern; and that regulation of perchlorate presented a 
meaningful opportunity for health risk reduction for persons served by 
public water systems. The EPA found that as many as 16 million people 
could potentially be exposed to perchlorate at levels of concern, up 
from 1 million people originally estimated in the 2008 notice.
    As a result of the determination, and as required by SDWA 
1412(b)(1)(E), the EPA initiated the process to develop a MCLG and a 
NPDWR for perchlorate.
    In September 2012, the U.S. Chamber of Commerce (the Chamber) 
submitted to the EPA a Request for Correction under the Information 
Quality Act regarding the EPA's regulatory determination.\2\ In the 
request, the Chamber claimed that the UCMR 1 data used in the EPA's 
occurrence analysis did not comply with data quality guidelines and 
were not representative of current conditions. In response to this 
request, the EPA reassessed the data and removed certain source water 
samples that could be paired with appropriate follow-up samples located 
at the entry point to the distribution system. The EPA also updated the 
UCMR 1 data in the analysis for systems in California and 
Massachusetts, using state compliance data to reflect current 
occurrence conditions after state regulatory limits for perchlorate 
were implemented. For more information on the Chamber's request and the 
EPA's response, see the Perchlorate Occurrence and Monitoring Report 
(USEPA, 2019b).
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    \2\ The U.S. Chamber of Commerce letter to the EPA and other 
corresponding records are available at https://www.epa.gov/quality/epa-information-quality-guidelines-requests-correction-and-requests-reconsideration#12004.
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    As required by section 1412(d) of the SDWA, as part of the NPDWR 
development process, the EPA requested comments from the Science 
Advisory Board (SAB) in 2012, seeking guidance on how best to consider 
and interpret the life stage information, the epidemiologic and 
biomonitoring data since the NRC report, physiologically-based 
pharmacokinetic (PBPK) analyses, and the totality of perchlorate health 
information to derive an MCLG for perchlorate. In May 2013, the SAB 
recommended that the EPA:
     Derive a perchlorate MCLG that addresses sensitive life 
stages through physiologically-based pharmacokinetic/pharmacodynamic 
modeling based upon its mode of action, rather than the default MCLG 
approach using the RfD and specific chemical exposure parameters;
     expand the modeling approach to account for thyroid 
hormone perturbations and potential adverse

[[Page 43994]]

neurodevelopmental outcomes from perchlorate exposure;
     utilize a mode-of-action framework for developing the MCLG 
that links the steps in the proposed mechanism leading from perchlorate 
exposure through iodide uptake inhibition--to thyroid hormone changes--
and finally to neurodevelopmental impacts; and
     ``[e]xtend 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''(SAB for the U.S. EPA, 
2013, p. 19).
    To address the SAB recommendations, the EPA revised an existing 
PBPK/PD model that describes the dynamics of perchlorate, iodide, and 
thyroid hormones in a woman during the third trimester of pregnancy 
(Lumen, Mattie, & Fisher, 2013; USEPA, 2009b). The EPA also created its 
own Biologically Based Dose Response (BBDR) models that included the 
additional sensitive life stages identified by the SAB, i.e., breast- 
and bottle-fed neonates and infants (SAB for the U.S. EPA, 2013, p. 
19).
    To determine whether the Agency had implemented the SAB 
recommendations for modeling thyroid hormone changes, the EPA convened 
an independent peer review panel to evaluate the BBDR models in January 
2017 (External Peer Reviewers for USEPA, 2017). The EPA considered the 
recommendations from the 2017 peer review and made necessary model 
revisions to increase the scientific rigor of the model and the 
modeling results, including extending the BBDR model to the first 
trimester and incorporating the TSH feedback mechanism.
    The EPA convened a second independent peer review panel in January 
2018 to evaluate the revisions to the BBDR model, including the 
transition from the third to the first trimester as the life stage of 
interest. The EPA also presented several approaches to link the thyroid 
hormone changes in a pregnant mother predicted by the BBDR model to 
neurodevelopmental effects using evidence from the epidemiological 
literature (External Peer Review for U.S. EPA, 2018).
    In response to a lawsuit brought to enforce the deadlines in SDWA 
1412(b)(1)(E) triggered by the 2011 regulatory determination for 
perchlorate, on October 18, 2016, the U.S. District Court for the 
Southern District of New York entered a consent decree, requiring the 
EPA to sign for publication a proposal for a MCLG and NPDWR for 
perchlorate in drinking water no later than October 31, 2018, and to 
sign for publication a final MCLG and NPDWR for perchlorate in drinking 
water no later than December 19, 2019. The deadline for the EPA to 
propose a MCLG and NPDWR for perchlorate in drinking water was later 
extended to May 28, 2019, and the date for signature of a final MCLG 
and NPDWR was extended to no later than June 19, 2020. The consent 
decree is available in the docket for this action.
    In compliance with the deadline established in the consent decree, 
on May 23, 2019, the EPA Administrator signed a proposed rulemaking 
document seeking public comment on a range of options regarding the 
regulation of perchlorate in public drinking water systems. The 
proposed rulemaking document was published in the Federal Register on 
June 26, 2019. 84 FR 30524. The EPA proposed a NPDWR for perchlorate 
with an MCL and MCLG of 56 [micro]g/L. The proposed MCLG of 56 
[micro]g/L was based on avoiding an estimated 2 point IQ decrement 
associated with exposure to perchlorate in drinking water during the 
most sensitive life stage (the fetus) within a specific segment of the 
population (iodine deficient pregnant women).
    The EPA also requested comment on two alternative MCL/MCLG values 
of 18 [micro]g/L and 90 [micro]g/L. These alternatives were based upon 
avoiding an estimated 1 point and 3 point IQ decrement respectively, 
associated with perchlorate exposure. Additionally, the EPA requested 
comment on whether the 2011 regulatory determination should be 
withdrawn, based on new information including updated occurrence data 
on perchlorate in drinking water and new analysis of the concentration 
of perchlorate in drinking water that represents a level of health 
concern.

III. Withdrawal of the 2011 Regulatory Determination and Final 
Determination Not To Regulate Perchlorate

    In determining whether to regulate a particular contaminant, the 
EPA must follow the criteria mandated by the 1996 SDWA Amendments. 
Specifically, in order to issue a MCLG and NPDWR for perchlorate, the 
EPA must determine that perchlorate ``may have an adverse effect on the 
health of persons,'' that perchlorate occurs at ``a frequency and at 
levels of public health concern'' in public water systems, and that 
regulation of perchlorate in drinking water systems ``presents a 
meaningful opportunity for health risk reduction for persons served by 
public water systems.'' SDWA 1412(b)(1)(A). In preparing the 2019 
proposal for perchlorate, the EPA updated and improved information on 
the levels of public health concern and the frequency and levels of 
perchlorate in public water systems. The following is the EPA's 
reassessment of the regulatory determination criteria applied to the 
best available health science and occurrence data for perchlorate.

A. May perchlorate have an adverse effect on the health of persons?

    Yes, perchlorate may have adverse health effects above certain 
exposure levels. The perchlorate anion is biologically significant 
specifically with respect to the functioning of the thyroid gland. 
Above certain exposure levels, perchlorate can interfere with the 
normal functioning of the thyroid gland by inhibiting the transport of 
iodide into the thyroid, resulting in a deficiency of iodide in the 
thyroid. Perchlorate inhibits (or blocks) iodide transport into the 
thyroid by chemically competing with iodide, which has a similar shape 
and electric charge. The transfer of iodide from the blood into the 
thyroid is an essential step in the synthesis of thyroid hormones. 
Thyroid hormones play an important role in the regulation of metabolic 
processes throughout the body and are also critical to developing 
fetuses and infants, especially for brain development. Because the 
developing fetus depends on an adequate supply of maternal thyroid 
hormones for its central nervous system development during the first 
and second trimester of pregnancy, iodide uptake inhibition from 
perchlorate exposure has been identified as a concern in connection 
with increasing risk of neurodevelopmental impairment in fetuses of 
pregnant women with low dietary iodine. Poor iodide uptake and 
subsequent impairment of the thyroid function in pregnant and lactating 
women have been linked to delayed development and decreased learning 
capability in their infants and children (NRC, 2005). There is 
scientific evidence to support that perchlorate can reduce iodide 
uptake and therefore alter the level of thyroid hormones. There is also 
scientific evidence that changes in thyroid hormone levels in a 
pregnant woman may be linked to changes in the neurodevelopment of her 
offspring. The existence of a quantifiable relationship between thyroid 
hormone changes and neurodevelopmental outcomes has strong support from 
the literature on the subject; however, not every study identifies an 
association between maternal thyroid hormone levels and the 
neurodevelopmental outcomes and

[[Page 43995]]

the state of the science on this relationship is constantly evolving.
    Therefore, the EPA continues to find that perchlorate may have an 
adverse effect on the health of persons above certain exposure levels 
based on its ability to interfere with thyroid hormone production.

B. Is perchlorate known to occur or is there a substantial likelihood 
that perchlorate will occur in public water systems with a frequency 
and at levels of public health concern?

    The EPA has determined that perchlorate does not occur with a 
frequency and at levels of public health concern in public water 
systems. The EPA has made this determination by comparing the best 
available data on the occurrence of perchlorate in public water systems 
with potential MCLGs for perchlorate.
    In past regulatory determinations, the EPA has identified HRLs as 
benchmarks against which the EPA compares the concentration of a 
contaminant found in public water systems to determine whether it 
occurs at levels of public health concern. For the 2011 regulatory 
determination, the EPA identified potential alternative HRL values 
ranging from 1 to 47 [micro]g/L for 14 different life stages. These 
HRLs were not final decisions about the level of perchlorate in 
drinking water that is without adverse effects. For the 2019 proposal, 
the EPA derived three potential MCLGs for perchlorate of 18, 56, and 90 
[mu]g/L for the most sensitive life stage using the best available peer 
reviewed science in accordance with the SDWA. After considering public 
comment, the EPA used these potential MCLGs as the levels of public 
health concern in assessing the frequency of occurrence of perchlorate 
in this regulatory determination. These MCLGs were set at levels to 
avoid estimated IQ decrements of 1, 2, and 3 points respectively in the 
most sensitive life stage, the children of hypothyroxinemic women with 
low iodine intake. The EPA proposed an MCLG of 56 [mu]g/L and 
alternative MCLG values of 18 and 90 [mu]g/L.
    The rationale used in deriving the numerical values is presented in 
greater detail in the EPA technical support document entitled 
``Deriving a Maximum Contaminant Level Goal for Perchlorate in Drinking 
Water'' (USEPA, 2019a).
    The EPA compared these potential MCLG values with the updated 
perchlorate UCMR 1 occurrence data set. A comprehensive description of 
the perchlorate occurrence data is presented in Section VI of the 2019 
proposal. It is also available in the ``Perchlorate Occurrence and 
Monitoring Report'' (USEPA, 2019a).
    The occurrence data for perchlorate were collected from 3,865 PWSs 
between 2001 and 2005 under the UCMR 1. In the 2019 proposal, the EPA 
modified the UCMR 1 data set in response to concerns raised by 
stakeholders regarding the data quality and to represent current 
conditions in California and Massachusetts, which have enacted 
perchlorate regulations since the UCMR 1 data were collected. 
Massachusetts promulgated a drinking water standard for perchlorate of 
2 [mu]g/L in 2006 (MassDEP, 2006), and California promulgated a 
drinking water standard of 6 [mu]g/L in 2007 (California Department of 
Public Health, 2007). Systems in these states are now required to keep 
perchlorate levels in drinking water below their state limits. As 
discussed below, the EPA finds that perchlorate levels in drinking 
water and sources of drinking water have decreased since the UCMR 1 
data collection. The main factors contributing to the decrease in 
perchlorate levels are the promulgation of drinking water regulations 
for perchlorate in California and Massachusetts and the ongoing 
remediation efforts in the state of Nevada to address perchlorate 
contamination in groundwater adjacent to the lower Colorado River 
upstream of Lake Mead.
    To update the occurrence data for systems sampled during UCMR 1 
from California and Massachusetts, the EPA identified all systems and 
corresponding entry points which had reported perchlorate detections in 
UCMR 1. Once the systems and entry points with detections were 
appropriately identified, the EPA then used publicly available 
California and Massachusetts monitoring data for perchlorate, to 
replace the original UCMR1 data with more recent data where available 
(Perchlorate Occurrence and Monitoring Report, USEPA, 2019b).
    The EPA has determined that the UCMR 1 data with these updates are 
the best available data collected in accordance with accepted methods 
regarding the frequency and level of perchlorate nationally. The UCMR 1 
data are from a census of the large water systems (serving more than 
10,000 people) and a statistically representative sample of small water 
systems that provides the best available, national assessment of 
perchlorate occurrence in drinking water.
    The EPA used entry point maximum measurements to estimate potential 
baseline occurrence and exposure at levels that exceed the potential 
MCLG thresholds. The maximum measurements indicate highest perchlorate 
levels reported in at least one quarterly sample from surface water 
systems and at least one semi-annual sample from ground water systems.

                     Table 1--Perchlorate Occurrence and Exposure (Updated UCMR 1 Data Set)
----------------------------------------------------------------------------------------------------------------
                                                                             Percent of U.S.
                                      Entry points with    Water systems      water systems
Threshold concentration ([micro]g/L)   detections above   with detections    with detections   Population served
                                          threshold       above threshold    above threshold
                                                                                (percent)
----------------------------------------------------------------------------------------------------------------
18 [micro]g/L.......................                 17                 15               0.03            620,560
56 [micro]g/L.......................                  2                  2              0.004             32,432
90 [micro]g/L.......................                  1                  1              0.002             25,972
----------------------------------------------------------------------------------------------------------------

    Table 1 presents the number and percentage of water systems that 
reported perchlorate at levels exceeding the three proposed MCLG 
threshold concentrations. In summary, the updated perchlorate 
occurrence information suggests that at an MCLG of 18 [micro]g/L, there 
would be 15 systems (0.03% of all water systems in the U.S.) that would 
exceed the threshold, at an MCLG of 56 [micro]g/L, two systems (0.004% 
of all water systems in the U.S.) would exceed the threshold, and 
finally one system would exceed the MCLG threshold of 90 [micro]g/L. 
Based on the analysis of drinking water occurrence presented in the 
2019 proposal and the data summarized in Table 1 and the range of 
potential MCLGs, the EPA concludes that perchlorate does not occur with 
a frequency and at levels of

[[Page 43996]]

public health concern in public water systems.
    The EPA notes that in 2008, the EPA stated in its preliminary 
regulatory determination that perchlorate did not occur with a 
frequency and at levels of public health concern in public water 
systems based upon the health effects and occurrence information 
available at that time, which indicated that 0.8% of public water 
system had perchlorate at levels exceeding the HRL of 15 mg/L. The EPA 
also stated that there was not a meaningful opportunity for a NPDWR to 
reduce health risks based upon the estimates at that time that 0.9 
million people had perchlorate levels above the HRL. The EPA further 
notes that the Agency has previously determined CCL1 and CCL2 
contaminants did not occur with frequency at levels of public health 
concern when the percentage of water systems exceeding the HRL were 
greater than the frequency of perchlorate occurrence level at the 
proposed MCL (0.004% of all water systems in the U.S.). For example, in 
2003 the EPA determined that aldrin did not occur with a frequency and 
at levels of public health concern based upon data that showed 0.2% of 
water systems had aldrin at levels greater than the HRL. The EPA also 
concluded that there was not a meaningful opportunity for health risk 
reduction for persons served through a drinking water regulation based 
on this occurrence data and the estimate that these systems above the 
HRL served approximately 1 million people (USEPA, 2003). In 2008 the 
EPA determined that DCPA Mono- and Di-Acid degradates did not occur 
with a frequency and at levels of public health concern based on data 
that showed 0.03% of water systems exceeded the HRL. The EPA also 
concluded that there was not a meaningful opportunity for health risk 
reduction through a drinking water regulation based on this occurrence 
data and the estimate that these systems above the HRL served 
approximately 100,000 people (USEPA, 2008b).
    While the EPA has made its conclusion that perchlorate does not 
occur at a frequency and at levels of public health concern in public 
water systems based on the updated UCMR 1 data in Table 1 above, the 
EPA also sought to find additional information about the perchlorate 
levels at the 15 water systems that had at least one reported result 
greater than 18 [micro]g/L in the updated UCMR 1 data. The EPA found 
that perchlorate levels have been reduced at many of these water 
systems. Although these water systems were not required to take actions 
to reduce perchlorate in drinking water, many had conducted additional 
monitoring for perchlorate and found decreased levels or had taken 
mitigation efforts to address perchlorate, confirming the EPA's 
conclusion described above. The status of each of these systems is 
described in Table 2 below and confirms the Agency's conclusion that is 
based upon the information in Table 1.

              Table 2--Update on Systems With Perchlorate Levels Above 18 [micro]g/L in the UCMR 1
----------------------------------------------------------------------------------------------------------------
                                                                 Range of UCMR 1
               State                       System name        results ([micro]g/L)     Update on mitigation and
                                                                       **             levels of perchlorate \++\
----------------------------------------------------------------------------------------------------------------
Florida............................  Sebring Water.........  ND-70.................  The EPA contacted the
                                                                                      Sebring system in January
                                                                                      2020. Operations personnel
                                                                                      indicated that no follow-
                                                                                      up/updated monitoring data
                                                                                      for perchlorate are
                                                                                      available.
Florida............................  Manatee County          ND-30.................  Researchers contacted the
                                      Utilities Dept.                                 system to identify the
                                                                                      source of perchlorate.
                                                                                      System personnel
                                                                                      attributed the sole
                                                                                      perchlorate detection
                                                                                      under UCMR 1 to analytical
                                                                                      error. System personnel
                                                                                      indicated that three other
                                                                                      quarterly samples
                                                                                      collected under UCMR 1 as
                                                                                      well as other subsequent
                                                                                      perchlorate sampling
                                                                                      efforts were non-detect.
                                                                                      Source: AWWA (2008).
Georgia............................  Oconee Co.--            38 (single sample)....  Researchers contacted the
                                      Watkinsville.                                   system and found that a
                                                                                      perchlorate contaminated
                                                                                      well was removed from
                                                                                      service in 2003. The
                                                                                      system indicates that
                                                                                      perchlorate is no longer
                                                                                      detected. Source: Luis et
                                                                                      al. (2019).
Louisiana..........................  St. Charles Water       ND-24.................  The EPA was not able to
                                      District 1 East Bank.                           identify updated data on
                                                                                      perchlorate levels for
                                                                                      this system.
Maryland...........................  City of Aberdeen......  ND-19.................  The system's 2018 Consumer
                                                                                      Confidence Report (CCR)
                                                                                      indicates that perchlorate
                                                                                      was not detected.
                                                                                      According to the Maryland
                                                                                      Department of Environment,
                                                                                      perchlorate was not
                                                                                      detected in this system in
                                                                                      2019. In addition,
                                                                                      researchers contacted the
                                                                                      system and found that
                                                                                      there has been no
                                                                                      detection of perchlorate
                                                                                      since treatment was
                                                                                      installed in 2009. Source:
                                                                                      Luis et al. (2019).
Maryland...........................  Chapel Hill--Aberdeen   ND-20.................  The EPA contacted the
                                      Proving Grounds.                                Chapel Hill System in
                                                                                      January 2020. Water system
                                                                                      personnel indicate that
                                                                                      the Chapel Hill WTP was
                                                                                      taken off-line and was
                                                                                      replaced with a new
                                                                                      treatment plant and five
                                                                                      new production wells. The
                                                                                      new treatment plant
                                                                                      started operations on
                                                                                      January 27, 2020. System
                                                                                      personnel also indicate
                                                                                      that monitoring was
                                                                                      conducted in November 2019
                                                                                      and perchlorate was not
                                                                                      detected in either the
                                                                                      source well water or the
                                                                                      finished water. In
                                                                                      addition, according to the
                                                                                      Maryland Department of
                                                                                      Environment, perchlorate
                                                                                      was not detected in this
                                                                                      system in 2019.

[[Page 43997]]

 
Mississippi........................  Hilldale Water          ND-20.................  The EPA contacted the
                                      District.                                       Hilldale System in January
                                                                                      2020. Water system
                                                                                      personnel indicated that
                                                                                      no follow-up/updated
                                                                                      monitoring data for
                                                                                      perchlorate are available.
New Mexico.........................  Deming Municipal Water  15-20.................  Data from the EPA's SDWIS/
                                      System.                                         FED database indicates
                                                                                      that the entry point that
                                                                                      reported detections in
                                                                                      UCMR 1 (Well #3) is now
                                                                                      inactive (i.e., the
                                                                                      contaminated source is no
                                                                                      longer in use).
Nevada.............................  City of Henderson.....  6-23..................  Researchers report that the
                                                                                      perchlorate levels
                                                                                      described in the system's
                                                                                      CCR ranged from non-detect
                                                                                      to 9.7 [micro]g/L. Source:
                                                                                      AWWA (2008).
Ohio...............................  Fairfield City PWS....  6-27..................  The EPA contacted the
                                                                                      Fairfield City System in
                                                                                      January 2020. Water system
                                                                                      personnel indicated that
                                                                                      follow-up monitoring was
                                                                                      conducted after UCMR 1,
                                                                                      between 2002 and 2004. The
                                                                                      Ohio EPA provided copies
                                                                                      of the follow-up
                                                                                      monitoring results which
                                                                                      indicate that results at
                                                                                      the entry point ranged
                                                                                      from non-detect to 13
                                                                                      [micro]g/L.
Ohio...............................  Hecla Water             ND-32.................  The EPA contacted the Hecla
                                      Association--Plant                              Water Association System
                                      PWS.                                            in January 2020. Water
                                                                                      system personnel indicated
                                                                                      that that no follow-up/
                                                                                      updated monitoring data
                                                                                      for perchlorate are
                                                                                      available.
Oklahoma...........................  Enid..................  ND-30.................  The EPA reviewed Oklahoma's
                                                                                      monitoring data and did
                                                                                      not find any monitoring
                                                                                      results reported for
                                                                                      perchlorate.
Pennsylvania.......................  Meadville Area Water    ND-33.................  The EPA contacted the
                                      Authority.                                      Meadville System in
                                                                                      January 2020. Water system
                                                                                      personnel indicated that
                                                                                      no follow-up/updated
                                                                                      monitoring data for
                                                                                      perchlorate are available.
Puerto Rico........................  Utuado Urbano.........  ND-420................  The EPA contacted the
                                                                                      Puerto Rico Aqueduct and
                                                                                      Sewer Authority (PRASA) in
                                                                                      January 2019. PRASA
                                                                                      personnel indicated that
                                                                                      no updated monitoring data
                                                                                      for perchlorate are
                                                                                      available. NOTE: The PRASA
                                                                                      personnel stated that the
                                                                                      Utuado water system was
                                                                                      significantly impacted by
                                                                                      Hurricane Maria and that
                                                                                      monitoring records from
                                                                                      years prior to 2017 were
                                                                                      lost.
Texas..............................  City of Levelland.....  ND-32.................  Researchers found that a
                                                                                      water storage tank was the
                                                                                      source of perchlorate
                                                                                      contamination. The wells
                                                                                      feeding the tank were
                                                                                      tested by the state and
                                                                                      perchlorate was not
                                                                                      detected. The water tank
                                                                                      was shut off from service.
                                                                                      Source: Luis et al.
                                                                                      (2019).
----------------------------------------------------------------------------------------------------------------
**Values have been rounded. ND describes a sampling event where perchlorate was not detected at or above the
  UCMR 1 minimum reporting level of 4 [micro]g/L. UCMR 1 results collected between 2001 and 2005.
++To obtain updated data and/or information regarding perchlorate levels, the EPA reviewed Consumer Confidence
  Reports and other publicly available data, as well as published studies. In addition, the EPA contacted some
  water systems for information about current perchlorate levels. (USEPA, 2020a)

C. Is there a meaningful opportunity for the reduction of health risks 
from perchlorate for persons served by public water systems?

    The EPA's analysis presented in the 2019 proposal demonstrates that 
a NPDWR for perchlorate does not present a meaningful opportunity for 
health risk reduction for persons served by public water systems. As 
discussed above, the EPA found that perchlorate occurs with very low 
frequency at levels of public health concern. Based on updated UCMR 1 
occurrence information, there were 15 water systems (0.03% of all water 
systems in the U.S.) that detected perchlorate in drinking water above 
the lowest proposed alternative MCLG of 18 [micro]g/L, and only 1 
system had a detection above the proposed alternative MCLG of 90 
[micro]g/L. Specifically, Table 1 presents the population served by 
PWSs that were monitored under UCMR 1 for which the highest reported 
perchlorate concentration was greater than the identified thresholds. 
The EPA estimates \3\ that the number of people who may be potentially 
consuming water containing perchlorate at levels that could exceed the 
levels of concern for perchlorate could range between 26,000 and 
620,000.
---------------------------------------------------------------------------

    \3\ The values shown in Table 1 are based on the revised UCMR 1 
data. The EPA also applied statistical sampling weights to the small 
systems results to extrapolate to national results. There was one 
small system included in the statistical sample stratum which had a 
perchlorate measurement exceeding 18 [micro]g/L. Accordingly, the 
EPA estimates that approximately 41,000 small system customers may 
be exposed to perchlorate greater than 18 [micro]g/L.
---------------------------------------------------------------------------

    The small number of water systems with perchlorate levels greater 
than identified thresholds, and the correspondingly small population 
served, provides ample support for the EPA's conclusion that the 
regulation of perchlorate does not present a ``meaningful opportunity 
for health risk reduction for persons served by public water systems,'' 
within the meaning of SDWA 1412(b)(1)(A)(iii).
    While the EPA does not believe that a national primary drinking 
water regulation presents a meaningful opportunity for health risk 
reduction, the Agency remains committed to

[[Page 43998]]

working with States and communities in addressing perchlorate 
contamination of drinking water. For example, the EPA has issued a 
document entitled ``Perchlorate Recommendations for Public Water 
Systems'' which provides recommendations for actions that systems may 
take if there are concerns about perchlorate (USEPA, 2020b). The 
document outlines steps public systems can take to address perchlorate 
in drinking water, including testing, installing treatment equipment, 
and communication with customers.
    Although a cost benefit analysis is not one of the three SDWA 
criteria for making a regulatory determination, the EPA also considered 
the findings of the Health Risk Reduction and Cost Analysis (HRRCA, 
USEPA 2019c) as additional information confirming the appropriateness 
of the withdrawal of the regulatory determination. The HRRCA for 
perchlorate (which was presented in the 2019 proposal) provides a 
unique set of economic data indicators that are not available for 
regulatory determinations because the HRRCA is required for a proposed 
NPDWR under SDWA 1412(b)(3)(C), but is not required to support a 
regulatory determination. Accordingly, because the EPA initially 
determined that perchlorate met the criteria for regulation and began 
the regulatory analysis process, the HRRCA was available with respect 
to perchlorate at this stage in the SDWA process, and the Agency 
considered this comprehensive economic analysis in informing its 
decision to withdraw the regulatory determination.
    Specifically, the HRRCA provides a description of the potential 
benefits and costs of a drinking water regulation for perchlorate. For 
all potential regulatory levels considered for perchlorate (18, 56, and 
90 [micro]g/L), the total costs associated with establishing a 
regulation (ranging from $9.5 to $18.0 million across discount rates 
and levels) were substantially higher than the potential range of 
benefits (ranging from $0.3 to $3.7 million) (USEPA, 2019c). The 
infrequent occurrence of perchlorate at levels of health concern 
imposes high monitoring and administrative cost burdens on public water 
systems and the states, while having little impact on health risk 
reductions and the associated low estimates of benefits. The EPA is not 
finalizing the HRRCA for this final action nor is the EPA conducting an 
analysis in accordance with the Regulatory Flexibility Act because the 
Agency is not promulgating a final regulation.
    Based on a comparison of costs and benefits estimated at the three 
potential regulatory levels, the EPA determined in the 2019 proposal 
that the benefits of establishing a drinking water regulation for 
perchlorate do not justify the potential costs.
    A drinking water regulation for perchlorate would impose 
significant burdens on states and water systems, mainly associated with 
requirements for monitoring, including initial monitoring and long-term 
monitoring for over 60,000 systems (see Section VIII of the 2019 
proposal for more information), but would result in very few systems 
having to take action to reduce perchlorate levels. It is of paramount 
importance that water systems (particularly medium, small, and 
economically distressed systems) focus their limited resources on 
actions that ensure compliance with existing NPDWRs and maintain their 
technical, managerial, and financial capacity to improve system 
operations and the quality of water being provided to their customers, 
rather than spending resources monitoring for contaminants that are 
unlikely to occur.

D. What is the EPA's final regulatory determination on perchlorate?

    Based on the EPA's analysis of the best available public health 
information, and after careful review and consideration of public 
comments on the June 2019 proposal, the Agency is withdrawing its 2011 
determination and is making a final determination not to regulate 
perchlorate. Accordingly, the EPA will not issue a NPDWR for 
perchlorate at this time. While the EPA has found that perchlorate may 
have an adverse effect on human health above certain exposure levels, 
based on the analysis presented in this document and supporting record, 
the EPA has determined that perchlorate does not occur in public water 
systems with a frequency and at levels of public health concern and 
that regulation of perchlorate does not present a meaningful 
opportunity to reduce health risks for persons served by public water 
systems. This conclusion is based on the best available peer reviewed 
science and data collected in accordance with accepted methods on 
perchlorate health effects and occurrence.

IV. Summary of Key Public Comments on Perchlorate

    The EPA received approximately 1,500 comments from individuals or 
organizations on the June 2019 proposal. This section briefly discusses 
the key technical issues raised by commenters and the EPA's response. 
Comments are also addressed in the ``Comment Response Document for the 
Final Regulatory Action for Perchlorate'' (USEPA, 2020c) available at 
http://www.regulations.gov (Docket ID No. EPA-HQ-OW-2018-0780).

A. SDWA Statutory Requirements and the EPA's Authority

    The EPA received comments stating that the Agency should promulgate 
an MCLG and MCL for perchlorate and comments stating that the Agency 
should not promulgate a regulation. After considering these comments, 
the EPA has re-evaluated perchlorate in accordance with SDWA 
1412(b)(1)(A), which requires that the Agency promulgate a NPDWR if (i) 
the contaminant may have an adverse effect on the health of persons; 
(ii) the contaminant is known to occur or there is a substantial 
likelihood that the contaminant will occur in public water systems with 
a frequency and at levels of public health concern; and (iii) in the 
sole judgment of the Administrator, regulation of such contaminant 
presents a meaningful opportunity for health risk reduction for persons 
served by public water systems.
    The EPA has determined, based upon the best available peer reviewed 
science and data collected in accordance with accepted methods, that 
perchlorate does not occur at a frequency and at levels of public 
health concern, and that regulation of perchlorate does not present a 
meaningful opportunity for health risk reduction. Because perchlorate 
does not meet the statutory criteria for regulation, the EPA lacks the 
authority to issue a MCLG or NPDWR for perchlorate, and, is therefore 
withdrawing its 2011 regulatory determination and issuing this final 
determination not to regulate perchlorate. For more information 
regarding the EPA's statutory authority to withdraw its regulatory 
determination, see Section II.C above.

B. Health Effects Assessment

Health Effects/MCLG Derivation
    The EPA received comments indicating that the Agency should utilize 
different approaches to derive the MCLG for perchlorate including 
approaches that some states used to develop their perchlorate advisory 
levels or drinking water standards. The EPA considered a number of 
alternative approaches to develop the MCLG for perchlorate and in 
accordance with SDWA 1412(e), the Agency sought recommendations from 
the Science Advisory Board. The EPA derived the proposed MCLG for 
perchlorate based on the approach recommended by the Science Advisory 
Board (SAB) (SAB for

[[Page 43999]]

the U.S. EPA, 2013). The SAB recommended that ``the EPA derive a 
perchlorate MCLG that addresses sensitive life stages through 
physiologically-based pharmacokinetic/pharmacodynamic modeling based 
upon its mode of action rather than the default MCLG approach using the 
RfD and specific chemical exposure parameters.'' The EPA has 
implemented these recommendations and has obtained two independent peer 
reviews of the analysis. These peer reviewers stated that: ``[o]verall, 
the panel agreed that the EPA and its collaborators have prepared a 
highly innovative state-of-the-science set of quantitative tools to 
evaluate neurodevelopmental effects that could arise from drinking 
water exposure to perchlorate. While there is always room for 
improvement of the models, with limited additional work to address the 
committee's comments below, the current models are fit-for-purpose to 
determine an MCLG'' (External Peer Reviewers for USEPA, 2018, p. 2).
    The EPA received comments indicating that the most sensitive life 
stages were not selected and/or considered in the Agency's approach. 
The EPA disagrees. Gestational exposure to perchlorate during 
neurodevelopment is the most sensitive time period. The NRC concluded 
that the population most sensitive to perchlorate exposure are ``the 
fetuses of pregnant women who might have hypothyroidism or iodide 
deficiency'' (p. 178, NRC 2005). In addition, there is clear evidence 
that disrupted maternal thyroid hormone levels during gestation can 
impact neurodevelopment later in life (Alexander et al., 2017; Costeira 
et al., 2011; Endendijk et al., 2017; Ghassabian, Bongers-Schokking, 
Henrichs, Jaddoe, & Visser, 2011; Glinoer & Delange, 2000; Glinoer & 
Rovet, 2009; Gyllenberg et al., 2016; Henrichs et al., 2010; Korevaar 
et al., 2016; Morreale de Escobar, Obreg[oacute]n, & Escobar del Rey, 
2004; Noten et al., 2015; Pop et al., 2003, 1999; SAB for the U.S. EPA, 
2013; Thompson et al., 2018; van Mil et al., 2012; Wang et al., 2016; 
Zoeller & Rovet, 2004; Zoeller et al., 2007). The available data 
demonstrate that the fetus of the first trimester pregnant mother, when 
compared to other life-stages, experiences the greatest impact from the 
same dose of perchlorate, which is described in detail in Section 6 of 
the document ``Deriving a Maximum Contaminant Level Goal for 
Perchlorate in Drinking Water'' (USEPA, 2019a). Some commenters 
suggested that the bottle-fed infant is a more sensitive life-stage. 
The EPA disagrees. As described in the January 2017 Peer Review Report 
on the original Biologically Based Dose Response (BBDR) model, the 
bottle-fed infant's thyroid hormone levels were not impacted by doses 
of perchlorate up to 20 [micro]g/day (External Peer Reviewers for 
USEPA, 2017). This lack of any impact is due primarily to the iodine in 
the formula, which offsets the impact of perchlorate on the thyroid.
    The EPA received comments advocating for the use of the population-
based approach evaluating the shift in the proportion of a population 
that would fall below a hypothyroxinemic cut point under a perchlorate 
exposure scenario. The EPA chose to develop the MCLG using dose-
response functions from the epidemiological literature to estimate 
neurodevelopmental impacts in the offspring of pregnant women exposed 
to perchlorate. The EPA selected this proposed approach because it is 
consistent with the SDWA's definition of a MCLG to avoid adverse health 
effects and because it is most consistent with the SAB recommendations. 
In addition, given that thyroid hormone levels vary by reference 
population and that there is not a defined threshold for the 
concentration of fT4 representing hypothyroxinemia makes the 
population-based approach less desirable than the approach selected 
(USEPA, 2018).
End Point Selection/Basis
    The EPA received comments regarding the magnitude of an IQ change 
which should be used in deriving the MCLG. The EPA's proposed MCLG was 
based upon avoiding a 2% change in IQ in the most sensitive life stage, 
and the EPA also requested comment on alternative options for the MCLG 
that would respectively avoid 1% or 3% change in IQ in the most 
sensitive life stage. Many comments stated that the EPA should at most 
consider a 1% IQ change. However, several commenters stated that a 3% 
change is too small to have a meaningful impact and suggested that the 
EPA consider a higher IQ percent change.
    The EPA uses a variety of science policy approaches to select 
points of departure for developing regulatory values. For instance, in 
noncancer risk assessment, the EPA often uses a percentage change in 
value. When assessing toxicological data, a 10% extra risk (for 
discrete data), or a 1 standard deviation (i.e., 15 IQ points) change 
from the mean (for continuous data) is often used (USEPA, 2012). A 
smaller response to inform a POD has been applied when using 
epidemiological literature, because there is an inherently more direct 
relationship between the study results and the exposure context and 
health endpoint.
    Given the difficulty in identifying a response below which no 
adverse impact occurs when considering a continuous outcome in the 
human population, the EPA looked to its Benchmark Dose Guidance (2012) 
for insight regarding a starting point. Specifically, ``[a] BMR of 1% 
has typically been used for quantal human data from epidemiology 
studies'' (p. 21, USEPA, 2012). For the specific context of setting an 
MCLG for perchlorate, the EPA evaluated the level of perchlorate in 
water associated with a 1% decrease, a 2% decrease, and a 3 percent 
decrease in the mean population IQ (i.e., 1, 2 and 3 IQ points).
    In evaluating the frequency and level of occurrence of perchlorate 
in drinking water, the EPA has found that perchlorate does not occur 
with frequency even at the lowest alternative MCLG of 18 [micro]g/L, 
which is based upon avoiding a 1% change in IQ in the most sensitive 
life stage.
    The EPA received comments that the proposed MCLG did not 
incorporate an adequate margin of safety to comply with the SDWA. The 
EPA disagrees that it failed to use an adequate margin of safety. The 
EPA's assessment focused upon the most sensitive subset of the 
population, specifically offspring whose mothers had low (75 [micro]g/
day) iodine intake and were hypothyroxinemic (fT4 in the lowest 10th 
percentile of the population). In addition, to account for 
uncertainties and to ensure that the most sensitive subset of the 
population is protected with an adequate margin of safety, a 3-fold 
uncertainty factor was applied to the proposed MCLG calculation (USEPA, 
2019a). More discussion on the uncertainty factor is presented below, 
in the section entitled ``Consideration of Uncertainties.''
    The EPA received some comments stating that the selection of the 
study for informing the relationship between maternal hormone levels 
(fT4) and IQ was inadequately described. Other comments supported the 
EPA's study selection. The EPA concludes that selection of the Korevaar 
et al. (2016) study is appropriate because that study provides the most 
robust data available with a clear measure of neurodevelopment that can 
be expressed as a function of changing maternal fT4 exposure, which is 
necessary to the development of the model.

[[Page 44000]]

BBDR and PBPK Models
    The EPA received comments indicating that the BBDR model was not 
transparent, scientifically valid, or based on robust data. The EPA 
disagrees. The model represents the best available peer reviewed 
science and uses the best available data to inform a MCLG for 
perchlorate. The EPA disagrees with the suggestion that there is a 
significant lack of transparency with respect to the assumptions 
related to the BBDR model. Appendix A of the EPA's Proposed MCLG 
Approaches report outlines the justification for all assumptions used 
in the development of the BBDR model (USEPA, 2019a). The EPA also 
disagrees with the assertion that the BBDR model is far too uncertain 
to be relied upon as the basis for the derivation of the RfD. The EPA 
has used the best available science to calibrate the pharmacokinetic 
aspects of the BBDR model. The development of the BBDR model was in 
response to SAB recommendations, and a model was deemed to be a more 
refined approach to estimating a dose-response relationship between 
perchlorate exposure and maternal fT4 than anything that was available 
in the current scientific literature. The EPA disputes the claim that 
the BBDR model is not scientifically valid, as the Agency conducted a 
peer review of the approach proposed and the reviewers concluded that 
the approach was ``fit for purpose'' to inform a MCLG for perchlorate 
(External Peer Reviewers for U.S. EPA, 2018, p. 2).
Consideration of Uncertainties
    The EPA received comments on the Agency's use of Uncertainty 
factors (UFs); with most commenters suggesting that the EPA should 
consider a higher UF for inter-individual variability. The EPA 
thoroughly considered the application of UFs when deriving the RfDs and 
followed guidance presented in ``A review of the reference dose and 
reference concentration processes'' (USEPA, 2002). The EPA concluded 
that the UFs are adequately justified, and subsequently no changes have 
been made. Justification for each of the UFs can be found in Section 11 
of the Agency's MCLG Derivation report (USEPA, 2019a).
    The EPA selected a UF of 3 for inter-individual variability, 
because the Agency specifically modeled groups within the population 
that are identified as likely to be at greater risk of the adverse 
effects from perchlorate in drinking water (i.e., the fetus of the 
iodide deficient pregnant mother). The EPA selected model parameters to 
account for the most sensitive individuals in that group (i.e., muted 
TSH feedback, low fT4 values, low-iodine intake). As discussed in the 
MCLG Derivation report, the EPA has attempted to select the most 
appropriate inputs to protect the most sensitive population with an 
adequate margin of safety (USEPA, 2019a). The EPA has determined that 
the selection of a UF of 3 for inter-individual variability is 
justified. As described in the MCLG Derivation report, because the 
output from the BBDR model is specific to the sensitive population, the 
EPA concluded that the UF of 3 is appropriate. In regard to variation 
in sensitivity among the members of the human population (i.e., inter-
individual variability), section 4.4.5.3 of the EPA guidance ``A review 
of the reference dose and reference concentration process'' (USEPA, 
2002) document states, ``In general, the Technical Panel reaffirms the 
importance of this UF, recommending that reduction of the intraspecies 
UF from a default of 10 be considered only if data are sufficiently 
representative of the exposure/dose-response data for the most 
susceptible subpopulation(s). Similar to the interspecies UF, the 
intraspecies UF can be considered to consist of both a toxicokinetic 
and toxicodynamic portion (i.e. 10[caret]0.5 each)'' (USEPA, 2002). 
Given that the BBDR model significantly accounts for differences within 
the human population, the full UF of 10 is not warranted.
    One commenter suggested using a UF greater than 1 to account for 
the extrapolation of the lowest-observed adverse effect level (LOAEL) 
to the no-observed-adverse-effect-level (NOAEL). LOAELs and NOAELs were 
not identified or used by the EPA in its assessment because the Agency 
employed a sophisticated BBDR modeling approach, which was coupled with 
extrapolation to changes in IQ using linear regression, to determine a 
POD that would not be expected to represent an adverse effect. 
Therefore, a UF of 1 is appropriate. Other commenters suggested 
incorporating UFs for database deficiencies. Based on the findings of 
the NRC report, the EPA has previously concluded that this UF was not 
needed for deficiencies in the perchlorate database (NRC, 2005; USEPA, 
2005a). The EPA determined that a UF of 1 to account for database 
deficiencies is still appropriate, given that the comprehensiveness of 
the perchlorate database has only increased since 2005.
Health Advisory
    Several commenters suggest that the EPA should withdraw the 2011 
determination to regulate perchlorate and instead issue an updated 
health advisory for perchlorate. The EPA issued an interim health 
advisory level for perchlorate in 2008. Health advisories provide 
information on contaminants that can cause human health effects and are 
known or anticipated to occur in drinking water. The EPA's health 
advisories are non-enforceable and non-regulatory and provide technical 
information to state agencies on health effects, analytical 
methodologies, and treatment technologies associated with drinking 
water contamination. State and local public health officials have the 
discretion to use the perchlorate health advisory as they deem 
necessary. The EPA will consider updating the 2008 perchlorate health 
advisory in the future.

C. Occurrence Analysis

    The EPA received comments suggesting that the revised UCMR 1 data 
did not provide an adequate estimate of the perchlorate occurrence in 
drinking water systems. Some commenters indicated that the age of the 
collected data rendered the occurrence analysis obsolete and 
overestimated, because it no longer captures current lower 
contamination conditions that have been achieved due to mitigation 
measures taken in the Colorado River Basin. Other commenters criticized 
the EPA for replacing UCMR 1 data for systems located in the States of 
California and Massachusetts with more recent state compliance data for 
perchlorate.
    The EPA recognizes that changes in perchlorate levels (increasing 
or decreasing) may have occurred in water systems since the UCMR 1 
samples were collected between 2001 to 2005. The EPA updated the UCMR 1 
data set to improve its accuracy in representing the current conditions 
for states that have enacted perchlorate regulations since the UCMR 1 
monitoring was conducted. As outlined in the June 26, 2019 proposal, 
the EPA updated occurrence data for California and Massachusetts with 
current compliance data as reported by the states. Systems from these 
two states that were sampled during the UCMR 1 and that had reported 
perchlorate detections were updated with more recently measured values 
taken from current compliance monitoring data from Consumer Confidence 
Reports and state-level perchlorate compliance monitoring data

[[Page 44001]]

to match corresponding water systems and entry points.
    The EPA has determined that the updated UCMR 1 data are the best 
available data collected in accordance with accepted methods on the 
frequency and level of perchlorate occurrence in drinking water on a 
national scale.

V. Conclusion

    With this withdrawal of the 2011 perchlorate regulatory 
determination and final determination not to regulate perchlorate, the 
EPA announces that there will be no NPDWR for perchlorate at this time. 
The EPA could consider re-listing perchlorate on the CCL and could 
proceed to regulation in the future if the occurrence or health risk 
information changes. As with other unregulated contaminants, the EPA 
will consider addressing limited instances of elevated levels of 
perchlorate by working with the affected system and state, as 
appropriate.

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List of Subjects

40 CFR Part 141

    Environmental protection, Administrative practice and procedure, 
Chemicals, Indians--lands, Intergovernmental relations, Radiation 
protection, Reporting and recordkeeping requirements, Water supply.

40 CFR Part 142

    Environmental protection, Administrative practice and procedure, 
Chemicals, Indians--lands, Radiation protection, Reporting and 
recordkeeping requirements, Water supply.

Andrew Wheeler,
Administrator.
[FR Doc. 2020-13462 Filed 7-20-20; 8:45 am]
BILLING CODE 6560-50-P