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Rule2024-15807

National Primary Drinking Water Regulations; Announcement of the Results of EPA's Fourth Review of Existing Drinking Water Standards

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Published

July 23, 2024

Issuing agencies

Environmental Protection Agency

Abstract

The Safe Drinking Water Act (SDWA) requires the U.S. Environmental Protection Agency (EPA or the agency) to conduct a review every six years of existing national primary drinking water regulations (NPDWRs) and determine which, if any, are appropriate for revision. The purpose of the review, called the Six-Year Review, is to evaluate available information for regulated contaminants to determine if any new information on health effects, treatment technologies, analytical methods, occurrence, exposure, implementation, and/or other factors provides a basis to support a regulatory revision that would improve or strengthen public health protection. While EPA has recently completed several significant revisions to existing regulations and other regulatory revisions are currently underway, based on this periodic review of all NPDWRs, there are no additional candidates for regulatory revision at this time.

Full Text

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<title>Federal Register, Volume 89 Issue 141 (Tuesday, July 23, 2024)</title>
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[Federal Register Volume 89, Number 141 (Tuesday, July 23, 2024)]
[Rules and Regulations]
[Pages 59623-59645]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-15807]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 141

[EPA-HQ-OW-2023-0572; FRL 7946-01-OW]

National Primary Drinking Water Regulations; Announcement of the
Results of EPA's Fourth Review of Existing Drinking Water Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Results of regulatory review.

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SUMMARY: The Safe Drinking Water Act (SDWA) requires the U.S.
Environmental Protection Agency (EPA or the agency) to conduct a review
every six years of existing national primary drinking water regulations
(NPDWRs) and determine which, if any, are appropriate for revision. The
purpose of the review, called the Six-Year Review, is to evaluate
available information for regulated contaminants to determine if any
new information on health effects, treatment technologies, analytical
methods, occurrence, exposure, implementation, and/or other factors
provides a basis to support a regulatory revision that would improve or
strengthen public health protection. While EPA has recently completed
several significant revisions to existing regulations and other
regulatory revisions are currently underway, based on this periodic
review of all NPDWRs, there are no additional candidates for regulatory
revision at this time.

DATES: July 23, 2024.

ADDRESSES: EPA is not accepting public comment on the review results.

FOR FURTHER INFORMATION CONTACT: Samuel Hernandez, Environmental
Protection Agency, Office of Ground Water and Drinking Water, Standards
and Risk Management Division, (Mail Code 4607M), 1200 Pennsylvania
Avenue NW, Washington, DC 20460; telephone number: (202) 564-1735;
email address: <a href="/cdn-cgi/l/email-protection#81e9e4f3efe0efe5e4fbaff2e0ecf4e4edc1e4f1e0afe6eef7"><span class="__cf_email__" data-cfemail="8ae2eff8e4ebe4eeeff0a4f9ebe7ffefe6caeffaeba4ede5fc">[email&#160;protected]</span></a>.

SUPPLEMENTARY INFORMATION:
Abbreviations and acronyms: The following acronyms and
abbreviations are used throughout this document.

2,4-D--2,4-Dichlorophenoxyacetic acid
ADWR--Aircraft Drinking Water Rule
BAT--Best Available Technology
CFR--Code of Federal Regulations
CVOC--Carcinogenic Volatile Organic Contaminant
CWS--Community Water System
DBCP--1,2-Dibromo-3-Chloropropane
DBP--Disinfection Byproduct
DEHA--Di(2-ethylhexyl)adipate
DEHP--Di(2-ethylhexyl)phthalate
EPA--U.S. Environmental Protection Agency
EQL--Estimated Quantitation Level
FBRR--Filter Backwash Recycling Rule
GWR--Ground Water Rule
HAA5--Haloacetic Acids (five) (sum of monochloroacetic acid,
dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and
dibromoacetic acid)
ICR--Information Collection Request
IRIS--Integrated Risk Information System
LT2--Long-Term 2 Enhanced Surface Water Treatment Rule
MCLG--Maximum Contaminant Level Goal
MCL--Maximum Contaminant Level
MDBP--Microbial and Disinfection Byproduct
MDL--Method Detection Limit
MRDLG--Maximum Residual Disinfectant Level Goal
MRDL--Maximum Residual Disinfectant Level
MRL--Minimum Reporting Level
NAS--National Academy of Sciences
NCWS--Non-Community Water System
NDWAC--National Drinking Water Advisory Council
NPDWR--National Primary Drinking Water Regulations
NRC--National Research Council
NTP--National Toxicology Program
PCBs--Polychlorinated biphenyls
PCE--Tetrachloroethylene
PQL--Practical Quantitation Limit
PT--Proficiency Testing
PWS--Public Water System
RfD--Reference Dose
RSC--Relative Source Contribution
RTCR--Revised Total Coliform Rule
SDWA--Safe Drinking Water Act
SDWIS--Safe Drinking Water Information System
SWTR--Surface Water Treatment Rule
TCDD--Tetrachlorodibenzo-p-dioxin
TCE--Trichloroethylene
TCR--Total Coliform Rule
TNCWS--Transient Non-Community Water System
TTHM--Total Trihalomethanes (sum of four THMs: chloroform,
bromodichloromethane, dibromochloromethane, and bromoform)
TT--Treatment Technique
USGS--U.S. Geological Survey

Table of Contents

I. General Information
A. Does this action apply to me?
B. How can I get copies of this document and other related
information?
II. Statutory Requirements for the Six-Year Review
III. Regulations Included in the Six-Year Review 4
IV. EPA's Protocol for Reviewing the NPDWRs Included in This Action
A. What was EPA's review process?
B. How did EPA conduct the review of the NPDWRs?
1. Initial Review
2. Health Effects

[[Page 59624]]

3. Analytical Feasibility
4. Occurrence and Exposure Analysis
5. Treatment Feasibility
6. Risk-Balancing
7. Other NPDWR Revisions
V. Results of EPA's Review of NPDWRs
A. Overview of Six-Year Review 4 Results
B. Chemical Phase Rules/Radionuclides Rules
1. Key Review Outcomes
2. Summary of Review Results
3. Select NPDWRs with New Information Not Appropriate for
Revision
C. Microbial Contaminants Regulations
VI. References

I. General Information

A. Does this action apply to me?

This action itself does not impose any requirements on individual
people or entities. Instead, it notifies interested parties of EPA's
review of existing national primary drinking water regulations (NPDWRs)
and its conclusions about which of these NPDWRs may warrant regulatory
revisions at this time. The Six-Year Review is not a final regulatory
decision to revise or not revise an NPDWR, but rather a planning
process that involves more detailed analyses of factors relevant to
deciding whether a rulemaking to revise an NPDWR should be initiated.

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

1. Docket. EPA has established a docket for this action under
Docket ID No. EPA-HQ-OW-2023-0572. Publicly available docket materials
are available electronically on <a href="http://www.regulations.gov">www.regulations.gov</a> or in hard copy at
the EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution
Ave. NW, Washington, DC. The Docket Center's hours of operations are
8:30 a.m. to 4:30 p.m., Monday through Friday (except Federal
Holidays). For further information on the EPA Docket Center services
and the current status see: <a href="https://www.epa.gov/dockets">https://www.epa.gov/dockets</a>.
2. Electronic Access. You may access this Federal Register document
electronically from <a href="https://www.federalregister.gov">https://www.federalregister.gov</a>.

II. Statutory Requirements for the Six-Year Review

Under the Safe Drinking Water Act (SDWA), as amended in 1996, EPA
must periodically review existing NPDWRs and, if appropriate, revise
them. Section 1412(b)(9) of the SDWA states: ``The Administrator shall,
not less often than every six years, review and revise, as appropriate,
each national primary drinking water regulation promulgated under this
title. Any revision of a national primary drinking water regulation
shall be promulgated in accordance with this section, except that each
revision shall maintain, or provide for greater, protection of the
health of persons.''
Pursuant to the 1996 SDWA Amendments, EPA completed and published
the results of its first Six-Year Review (Six-Year Review 1) on July
18, 2003 (68 FR 42908, USEPA, 2003), the second Six-Year Review (Six-
Year Review 2) on March 29, 2010 (75 FR 15500, USEPA, 2010a) and the
third Six-Year Review (Six-Year Review 3) on January 11, 2017 (82 FR
3518, USEPA, 2017a).
During the Six-Year Review 1, EPA identified the Total Coliform
Rule (TCR) as a candidate for revision.\1\ In Six-Year Review 2, EPA
identified four NPDWRs corresponding to acrylamide, epichlorohydrin,
tetrachloroethylene (PCE), and trichloroethylene (TCE) as candidates
for revision. In Six-Year Review 3, eight NPDWRs were listed as
candidates for revision, including: chlorite, Cryptosporidium (under
SWTRs), Giardia lamblia, haloacetic acids (HAA5), heterotrophic
bacteria, Legionella, total trihalomethanes (TTHM), and viruses (under
SWTRs). EPA also announced that the NPDWRs for acrylamide and
epichlorohydrin were no longer candidates for revision due to low
opportunity for further reduction of public health risk through
regulatory revision (82 FR 3525, USEPA, 2017a).
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\1\ The NPDWRs apply to specific contaminants/parameters or
groups of contaminants. Historically, when issuing new or revised
standards for these contaminants/parameters, EPA has often grouped
the standards together in more general regulations, such as the
Total Coliform Rule, the Surface Water Treatment Rule or the Phase V
rules. In this action, however, for clarity, EPA discusses the
drinking water standards as they apply to each specific regulated
contaminant/parameter (or group of contaminants), not the more
general regulation in which the contaminant/parameter was regulated.
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In this document, EPA is announcing the results of the fourth Six-
Year Review (Six-Year Review 4). EPA's announcement of whether to
identify an NPDWR as a candidate for revision (pursuant to SDWA section
1412(b)(9)) is not a regulatory decision. Instead, announcing that an
NPDWR is a candidate for revision formally initiates a regulatory
process that involves more detailed analyses of health effects,
analytical constraints, treatment feasibility, occurrence, benefits,
costs, and other policy considerations relevant to informing an NPDWR
revision effort. The Six-Year Review results do not obligate the agency
to revise an NPDWR if EPA determines during the regulatory process that
revisions are no longer appropriate and discontinues further efforts to
revise the NPDWR. Similarly, when EPA announces that a particular NPDWR
has not been identified as a candidate for revision it means that the
agency has concluded that it is not appropriate for revision at this
time based on available information.
The criteria that EPA has applied to help identify when an NPDWR
might be considered as a ``candidate for revision'' are, at a minimum,
that the regulatory revision presents a meaningful opportunity to
improve the level of public health protection, and/or achieve cost
savings while maintaining or improving the level of public health
protection.

III. Regulations Included in the Six-Year Review 4

Table 1 of this document lists all 94 NPDWRs established to date.
The table also reports the maximum contaminant level goal (MCLG) and,
where applicable, the maximum contaminant level (MCL). The MCLG is
``set at the level at which no known or anticipated adverse effects on
the health of persons occur and which allows an adequate margin of
safety'' (SDWA section 1412(b)(4)). The MCL for each applicable NPDWR,
is the maximum permissible level of a contaminant in water delivered to
any user of a public water system (PWS) and generally ``is as close to
the maximum contaminant level goal as is feasible'' (SDWA section
1412(b)(4)(B)). If it is not ``economically or technically feasible to
ascertain the level of the contaminant,'' EPA can require the use of a
treatment technique (TT) in lieu of establishing an MCL. The treatment
technique(s) must prevent known or anticipated adverse health effects
``to the extent feasible'' (SDWA section 1412(b)(7)(A)).\2\ In the case
of disinfectants (e.g., chlorine, chloramines, chlorine dioxide), the
values reported in the table are not MCLGs and MCLs, but maximum
residual disinfectant level goals (MRDLGs) and maximum residual
disinfectant levels (MRDLs).
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\2\ Under limited circumstances, SDWA section 1412(b)(6)(A)
gives the Administrator the discretion to promulgate an MCL or TT
that is less stringent than the most protective feasible standard
that ``maximizes health risk reduction benefits at a cost that is
justified by the benefits.'' Similarly, SDWA section 1412(b)(5)
authorizes the Administrator to promulgate an MCL or TT that is less
stringent than the most protective feasible standard if the more
protective standard would increase the level of other contaminants
in drinking water or interfere with the efficacy of treatment
techniques or process used for compliance with other NPDWRs. Under
those circumstances, EPA is to promulgate feasible a MCL or TT rule
to ``minimize the oversall risk of adverse health effects'' while
avoiding an increase in health risks from other contaminants.

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[[Page 59625]]

As part of the fourth Six-Year Review, EPA did not consider
information after December 2021, unless otherwise noted. EPA identified
15 NPDWRs for which there has either been a recently completed, an
ongoing, or a pending regulatory action. EPA did not conduct a detailed
review of these 15 NPDWRs for the Six-Year Review 4. These include the
ongoing Lead & Copper rulemaking activities and the potential revisions
\3\ of the Microbial and Disinfection Byproduct Rules (MDBP). The MDBP
effort contemplates potential regulatory revisions for the NPDWRs
covering the following contaminants: (Bromate, Chloramines, Chlorine
Dioxide, Chlorine, Chlorite, Cryptosporidium, Giardia lamblia,
Haloacetic acids, Heterotrophic bacteria, Legionella, Total
Trihalomethanes, Turbidity, & Viruses).
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\3\ Additional information can be found at <a href="https://www.epa.gov/system/files/documents/2022-04/mdbp-rule-revisions-charge-to-the-ndwac.pdf">https://www.epa.gov/system/files/documents/2022-04/mdbp-rule-revisions-charge-to-the-ndwac.pdf</a>.
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The EPA did not include in this Six-Year Review cycle the recently
promulgated per-and polyfluoroalkyl substances (PFAS) regulations.\4\
The PFAS regulations, promulgated in April 2024, established 6 new
NPDWRs. The EPA anticipates that once the PFAS regulations go into
effect and sufficient information regarding compliance monitoring
becomes available, those NPDWRs will be subject to a more detailed
regulatory review under a future Six-Year Review cycle. This document
describes the detailed review of the remaining 73 NPDWRs. section IV of
this document describes the Six-Year Review 4 protocol, and section V
of this document describes the review results. Please see USEPA (2024a)
for more details.
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\4\ On April 26, 2024, the EPA promulgated legally enforceable
drinking water standards to address PFAS known to occur individually
and as mixtures in drinking water (89 FR 32532). The NPDWRs sets
limits for five individual PFAS: (perfluorooctanoic acid (PFOA),
perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid
(PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide
dimer acid (HFPO-DA, commonly known as GenX Chemicals)); and also
established a limit for mixtures of any two or more of the following
four PFAS: (PFNA, PFHxS, perfluorobutane sulfonic acid (PFBS), and
HFPO-DA).

Table 1--List of NPDWRs
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MCL or TT (mg/L) 2 3 Contaminants/ MCL or TT (mg/L) 2 3
Contaminants/parameters MCLG (mg/L) 1 3 parameters MCLG (mg/L) 1 3
--------------------------------------------------------------------------------------------------------------------------------------------------------
Acrylamide...................... 0...................... TT..................... Giardia lamblia 0...................... TT.
\4\.
Alachlor........................ 0...................... 0.002.................. Glyphosate........ 0.7.................... 0.7.
Alpha/photon emitters........... 0 (pCi/L).............. 15 (pCi/L)............. Haloacetic acids n/a \5\................ 0.060.
(HAA5).
Antimony........................ 0.006.................. 0.006.................. Heptachlor........ 0...................... 0.0004.
Arsenic......................... 0...................... 0.010.................. Heptachlor epoxide 0...................... 0.0002.
Asbestos........................ 7 (million fibers/L)... 7 (million fibers/L)... Heterotrophic n/a.................... TT.
bacteria \6\.
Atrazine........................ 0.003.................. 0.003.................. Hexachlorobenzene. 0...................... 0.001.
Barium.......................... 2...................... 2...................... Hexachlorocyclopen 0.05................... 0.05.
tadiene.
Benzene......................... 0...................... 0.005.................. Hexafluoropropylen 10 (ppt)............... 10 (ppt).
e oxide dimer
acid (HFPO-DA).
Benzo[a]pyrene.................. 0...................... 0.0002................. Lead.............. 0...................... TT.
Beryllium....................... 0.004.................. 0.004.................. Legionella........ 0...................... TT.
Beta/photon emitters............ 0 (millirems/yr)....... 4 (millirems/yr)....... Lindane........... 0.0002................. 0.0002.
Bromate......................... 0...................... 0.010.................. Mercury 0.002.................. 0.002.
(inorganic).
Cadmium......................... 0.005.................. 0.005.................. Methoxychlor...... 0.04................... 0.04.
Carbofuran...................... 0.04................... 0.04................... Monochlorobenzene 0.1.................... 0.1.
(Chlorobenzene).
Carbon tetrachloride............ 0...................... 0.005.................. Nitrate (as N).... 10..................... 10.
Chloramines (as Cl2)............ 4...................... 4.0.................... Nitrite (as N).... 1...................... 1.
Chlordane....................... 0...................... 0.002.................. Oxamyl (Vydate)... 0.2.................... 0.2.
Chlorine (as Cl2)............... 4...................... 4.0.................... Pentachlorophenol. 0...................... 0.001.
Chlorine dioxide (as ClO2)...... 0.8.................... 0.8.................... Perfluorohexane 10 (ppt)............... 10 (ppt).
sulfonic acid
(PFHxS).
Chlorite........................ 0.8.................... 1.0.................... Perfluorononanoic 10 (ppt)............... 10 (ppt).
acid (PFNA).
Chromium (total)................ 0.1.................... 0.1.................... Perfluorooctane 0 (ppt)................ 4.0 (ppt).
sulfonic acid
(PFOS).
Copper.......................... 1.3.................... TT..................... Perfluorooctanoic 0 (ppt)................ 4.0 (ppt).
acid (PFOA).
Cryptosporidium................. 0...................... TT..................... PFAS Mixture (HFPO- Hazard Index \12\ of 1. Hazard Index of 1.
DA, PFBS, PFHxS,
& PFNA).
Cyanide (as free cyanide)....... 0.2.................... 0.2.................... Picloram.......... 0.5.................... 0.5.
2,4-Dichlorophenoxyacetic acid 0.07................... 0.07................... Polychlorinated 0...................... 0.0005.
(2,4-D). biphenyls (PCBs).
Dalapon......................... 0.2.................... 0.2.................... Radium 226/228 0 (pCi/L).............. 5 (pCi/L).
(combined).
Di(2-ethylhexyl)adipate (DEHA).. 0.4.................... 0.4.................... Selenium.......... 0.05................... 0.05.
Di(2-ethylhexyl)phthalate (DEHP) 0...................... 0.006.................. Simazine.......... 0.004.................. 0.004.
1,2-Dibromo-3- chloropropane 0...................... 0.0002................. Styrene........... 0.1.................... 0.1.
(DBCP).
1,2-Dichlorobenzene (o- 0.6.................... 0.6.................... 2,3,7,8-TCDD 0...................... 3 x10 -8.
Dichlorobenzene). (Dioxin).
1,4-Dichlorobenzene (p- 0.075.................. 0.075.................. Tetrachloroethylen 0...................... 0.005.
Dichlorobenzene). e.
1,2-Dichloroethane (ethylene 0...................... 0.005.................. Thallium.......... 0.0005................. 0.002.
dichloride).
1,1-Dichloroethylene............ 0.007.................. 0.007.................. Toluene........... 1...................... 1.
cis-1,2-Dichloroethylene........ 0.07................... 0.07................... Total coliforms 7 n/a.................... TT.
8.
trans-1,2-Dichloroethylene...... 0.1.................... 0.1.................... Total n/a \9\................ 0.080.
Trihalomethanes
(TTHM).
Dichloromethane (methylene 0...................... 0.005.................. Toxaphene......... 0...................... 0.003.
chloride).
1,2-Dichloropropane............. 0...................... 0.005.................. 2,4,5-TP (Silvex). 0.05................... 0.05.
Dinoseb......................... 0.007.................. 0.007.................. 1,2,4- 0.07................... 0.07.
Trichlorobenzene.
Diquat.......................... 0.02................... 0.02................... 1,1,1- 0.2.................... 0.2.
Trichloroethane.
E. coli......................... 0...................... MCL,\10\ TT 8 11....... 1,1,2- 0.003.................. 0.005.
Trichloroethane.
Endothall....................... 0.1.................... 0.1.................... Trichloroethylene. 0...................... 0.005.
Endrin.......................... 0.002.................. 0.002.................. Turbidity \6\..... n/a.................... TT.
Epichlorohydrin................. 0...................... TT..................... Uranium........... 0...................... 0.030.
Ethylbenzene.................... 0.7.................... 0.7.................... Vinyl Chloride.... 0...................... 0.002.
Ethylene dibromide (EDB)........ 0...................... 0.00005................ Viruses........... 0...................... TT.
Fluoride........................ 4.0.................... 4.0.................... Xylenes (total)... 10..................... 10.
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\1\ MCLG: 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. Maximum contaminant level goals are nonenforceable health goals.

[[Page 59626]]

\2\ MCL: the maximum level allowed of a contaminant in water which is delivered to any user of a public water system. TT: any action, process, or
procedure required of the water system that leads to the reduction of the level of a contaminant in tap water that reaches the consumer.
\3\ Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million. For chlorine,
chloramines, and chlorine dioxide, values presented are MRDLG and MRDL.
\4\ The current preferred taxonomic name is Giardia duodenalis, with Giardia lamblia and Giardia intestinalis as synonymous names. However, Giardia
lamblia was the name used to establish the MCLG in 1989. Elsewhere in this document, this pathogen will be referred to as Giardia spp. or simply
Giardia unless discussing information on an individual species.
\5\ There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: dichloroacetic acid (zero), trichloroacetic acid
(0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group but have no MCLGs.
\6\ Includes indicators that are used in lieu of direct measurements (e.g., of heterotrophic bacteria, turbidity).
\7\ The Aircraft Drinking Water Rule (ADWR) 40 CFR part 141 subpart X, promulgated October 19, 2009, covers total coliforms and E. coli.
\8\ Under the RTCR, a PWS is required to conduct an assessment if it exceeded any of the TT triggers identified in 40 CFR 141.859(a). It is also
required to correct any sanitary defects found through the assessment. 40 CFR 141.859(c).
\9\ There is no MCLG for total trihalomethanes (TTHM). MCLGs for some of the individual contaminants are: bromodichloromethane (zero), bromoform (zero),
dibromochloromethane (0.06 mg/L), and chloroform (0.07 mg/L).
\10\ A PWS is in compliance with the E. coli MCL unless any of the conditions identified under 40 CFR 141.63(c) occur.
\11\ Under the GWR in 40 CFR 141.402, a ground water system that does not provide at least 4-log treatment of viruses and has a distribution system RTCR
sample that tests positive for total coliform is required to conduct triggered source water monitoring to evaluate whether the total coliform presence
in the distribution system is due to fecal contamination in the ground water source. The system must monitor for one of three State-specified fecal
indicators (i.e., E. coli, coliphage, or enterococci).
\12\ The Hazard Index is an approach that EPA uses to determine the health concerns associated with mixtures of certain PFAS in finished drinking water.
The Hazard Index is made up of a sum of fractions. Each fraction compares the level of each PFAS measured in the water to the associated health-based
water concentration.

IV. EPA's Protocol for Reviewing the NPDWRs Included in This Action

A. What was EPA's review process?

This section provides an overview of the process EPA used to review
the NPDWRs discussed in this document. The protocol document, ``EPA
Protocol for the Fourth Review of Existing National Primary Drinking
Water Regulations,'' contains a detailed description of the process the
agency used to review the NPDWRs (USEPA, 2024c). The foundation of this
protocol was developed for the Six-Year Review 1 based on the
recommendations of the National Drinking Water Advisory Council (NDWAC,
2000) and has undergone minor clarifications during each Six-Year
Review cycle (USEPA, 2024c). Figure 1 presents an overview of the Six-
Year Review protocol and the possible review outcomes.
The objective of the Six-Year Review process is to identify and
prioritize NPDWRs for possible regulatory revision. The two major
outcomes of the detailed review are either (1) the NPDWR is not
appropriate for revision and no action is necessary at this time or (2)
the NPDWR is a candidate for revision.
The reasons why EPA might list an NPDWR as ``not appropriate for
revision at this time'' could include:
<bullet> Recently completed, ongoing, or pending regulatory action:
The NPDWR was recently completed, is being reviewed under an ongoing
action, or is subject to a pending action.
<bullet> Ongoing or planned health effects assessment: The
contaminant or contaminants regulated by the NPDWR has an ongoing or
planned health effects assessment.
<bullet> No new information: EPA did not identify any new relevant
information for the contaminant since the last Six-Year Review that
indicates changes to the NPDWR may be appropriate.
<bullet> Data gaps/emerging information: New information indicates
a possible change to the MCLG and/or MCL but changes to the NPDWR are
not appropriate due to data gaps and emerging information that needs to
be evaluated.
<bullet> Low priority and/or no meaningful opportunity: New
information indicates a possible change to the MCLG and/or MCL but
changes to the NPDWR are not appropriate at this time due to one or
more of the following reasons: (1) possible changes present negligible
gains in public health protection; (2) possible changes present limited
opportunity for cost savings while maintaining the same or greater
level of health protection; and/or (3) possible changes are a low
priority because of competing workload priorities, limited return on
the administrative costs associated with rulemaking, and the burden on
states and the regulated community associated with implementing any
regulatory change that would result.
Alternatively, the reasons why an NPDWR could be listed as a
candidate for revision are that the regulatory revision presents a
meaningful opportunity to improve the level of public health
protection, and/or achieve cost savings while maintaining or improving
the level of public health protection.
Individual regulatory provisions that are evaluated as part of the
Six-Year Review process include: MCLG, MCL, MRDLG, MRDL, TT, best
available technology (BAT), and other requirements, such as monitoring
requirements.
For example, the microbial regulations include TT requirements
because no reliable, affordable, and technically feasible method is
available to measure the microbial contaminants covered by those
regulations. These TT requirements rely on the use of indicators that
can be measured in drinking water, such as detection of total coliforms
as an indicator of a potential pathway for pathogenic contamination in
the distribution system. As part of the Six-Year Review 4, EPA
evaluated new information related to the use of those indicators to
determine if a meaningful opportunity to improve the level of public
health protection exists. Results of EPA's review of the microbial
regulations are presented in section V of this document.
Basic Principles
EPA applied several basic principles to the Six-Year Review
process:
<bullet> The agency sought to avoid redundant review efforts.
Because EPA has reviewed information for certain NPDWRs as part of
recently completed, ongoing, or pending regulatory actions, these
NPDWRs were not subject to detailed review under the Six-Year Review
process.
<bullet> The agency does not believe it is appropriate to consider
revisions to NPDWRs for contaminants with an ongoing or planned health
effect assessment where the MCL is set equal to the MCLG or that were
set at the level at which health risk reduction benefits were maximized
at a cost justified by the benefits in accordance with SDWA section
1412(b)(6)(A)). This principle stems from the fact that any new health
effects assessment may affect the MCL via a change in the MCLG or the
assessment of the benefits associated with the MCL. EPA notes that
these NPDWRs are not appropriate for revision and no action is
necessary if the health effects assessment would not be completed
during the review cycle.
<bullet> In evaluating the potential for new information to affect
NPDWRs, EPA assumed no change to existing policies and procedures for
developing NPDWRs. For example, in determining whether new information
affected the feasibility of analytical methods for a contaminant, the
agency assumed no

[[Page 59627]]

change to current policies and procedures for calculating practical
quantitation limits.
<bullet> EPA may consider whether there is new public health risk
information to justify accelerating review and potential revision of a
particular NPDWR before the next review cycle.
Procedures
EPA also applied the following procedures in the review process:
<bullet> EPA considered new information from health effects
assessments that were completed by the information cutoff date.
Assessments completed after this cutoff date will be reviewed by EPA
during the next review cycle.
<bullet> During the review, EPA identified areas where relevant
information, which is needed to determine whether a revision to an
NPDWR may be appropriate, was either: inadequate, unavailable (i.e.,
data gaps), or emerging. To the extent EPA is able to fill data gaps or
fully evaluate the emerging information, the agency will consider the
information as part of the next review cycle.
<bullet> Finally, EPA assured that the scientific analyses
supporting the review were consistent with the agency's peer review
policy (USEPA, 2015a).
[GRAPHIC] [TIFF OMITTED] TR23JY24.000

B. How did EPA conduct the review of the NPDWRs?

The protocol for the Six-Year Review 4 is organized as a series of
questions to inform an assessment as to the appropriateness of revising
an NPDWR. These questions are logically ordered into a decision tree.
This section provides an overview of each of the review elements that
EPA considered for each NPDWR during the Six-Year Review 4, including
the following: initial review, health effects, analytical feasibility,
occurrence and exposure, treatment feasibility, risk balancing, and
other NPDWR revisions. The final review combines the findings from all
these review elements to recommend whether an NPDWR is a candidate for
revision. Further information about the review elements is described in
the protocol document (USEPA, 2024c). The results of the Six-Year
Review are presented in section V of this document.
1. Initial Review
EPA's initial review of all the contaminants included in the Six-
Year Review 4 involved a simple identification of the NPDWRs that have
either been recently completed or are being reviewed in an ongoing or
pending action since the publication of Six-Year Review 3. In addition,
the initial review also identified contaminants with ongoing health
effects assessments that have an MCL equal to the MCLG. Excluding such
contaminants from a more detailed review in the Six-Year Review 4
prevents duplicative agency efforts.
2. Health Effects
The principal objectives of the health effects review are to
identify: (1) contaminants for which a new health effects assessment
indicates that a change in the MCLG might be appropriate (e.g., because
of a change in cancer classification or a change in reference dose
(RfD)), and (2) contaminants for which new health effects information
indicates a need to initiate a new health effects assessment.
To meet the first objective, EPA reviewed the results of health
effects assessments completed since promulgation of each NPDWR. To meet
the second objective, the agency conducted a systematic literature
search, to capture more recently published peer-reviewed studies on
relevant health effects via the oral route

[[Page 59628]]

of exposure for the general population as well as sensitive
subpopulations including children. The results of the literature search
were used to survey the health effects literature that has become
available since the previous review cycle, identify any emerging issues
for a contaminant, and identify data gaps to inform future health
assessment nominations.
3. Analytical Feasibility
When establishing an NPDWR, EPA identifies a practical quantitation
limit (PQL), which is the lowest achievable level of analytical
quantitation during routine laboratory operating conditions within
specified limits of precision and accuracy (50 FR 46880, USEPA, 1985).
EPA has a separate process in place to approve new analytical methods
for drinking water contaminants; therefore, review and approval of
potential new methods is outside the scope of the Six-Year Review
protocol. EPA recognizes, however, that the approval and adoption in
recent years of new and/or improved analytical methods may enable
laboratories to quantify contaminants at lower levels than was possible
when NPDWRs were originally promulgated. This ability of laboratories
to measure a contaminant at lower levels could affect its PQL, the
value at which an MCL is set when it is limited by analytical
feasibility. Therefore, the Six-Year Review process includes an
examination of whether there have been changes in analytical
feasibility that could possibly change the PQL for the subset of the
NPDWRs that reach this stage of the review.
To determine if changes in analytical feasibility could possibly
support changes to PQLs, EPA relied primarily on two approaches to
develop estimated quantitation levels (EQLs), which are based on either
(1) minimum reporting levels (MRLs) obtained as part of the Six-Year
Review 4 Information Collection Request (ICR), or (2) method detection
limits (MDLs) from EPA-approved laboratory protocols.
An MRL is the lowest level or contaminant concentration that a
laboratory can reliably achieve within specified limits of precision
and accuracy under routine laboratory operating conditions using a
given method. The MRL values provide direct evidence from actual
monitoring results about whether quantitation below the PQL using
current analytical methods is feasible. An MDL is a measure of
analytical sensitivity, representing the minimum reported concentration
that can be distinguished from blank results with 99 percent
confidence. MDLs have been used in the past to derive PQLs for
regulated contaminants.
EPA used the EQL as a threshold for occurrence analysis to help the
agency assess for a meaningful opportunity to improve public health
protection. It should be noted, however, that the use of an EQL does
not necessarily indicate the agency's intention to promulgate a revised
MCL based on the new PQL. Any change in the PQL for a contaminant could
be part of future rulemaking efforts if EPA decides to initiate a
regulatory revision for the contaminant.
4. Occurrence and Exposure Analysis
EPA conducted the occurrence and exposure analysis in conjunction
with other review elements to determine if an NPDWR revision would
provide a meaningful opportunity to improve public health by:
<bullet> estimating the extent of contaminant occurrence, i.e., the
number of PWSs in which contaminants occur at levels of interest
(health-effects-based thresholds or analytical method limits), and;
<bullet> evaluating the number of people potentially exposed to
contaminants at these levels.
To evaluate national contaminant occurrence under the Six-Year
Review 4, EPA reviewed data from the Six-Year Review 4 ICR database
(SYR 4 ICR database) and other relevant sources. EPA collected SDWA
compliance monitoring data and treatment technique information through
use of an ICR (84 FR 58381, USEPA, 2019). EPA requested that states, as
well as Tribes and territories with primacy voluntarily submit their
compliance monitoring data and treatment technique information for
regulated contaminants in PWSs. Specifically, EPA requested the
submission of compliance monitoring data, treatment technique
information, and related details collected between January 2012 and
December 2019 for regulated contaminants and related parameters (e.g.,
water quality indicators). Forty-six states plus 13 other jurisdictions
(Washington, DC, territories, and Tribes) provided data. The assembled
data constitute the largest, most comprehensive set of drinking water
compliance monitoring data and treatment technique information ever
compiled and analyzed by EPA to inform decision making, containing
almost 71 million analytical records from approximately 140,000 PWSs,
serving approximately 301 million people nationally. Through extensive
data management efforts, quality assurance evaluations, and
communications with state data management staff, EPA established the
SYR 4 ICR dataset (USEPA, 2019). The number of states and PWSs
represented in the dataset varies across contaminants because of
variability in state data submissions and contaminant monitoring
schedules. EPA considers that these data are of sufficient quality to
inform an understanding of the national occurrence of regulated
contaminants and related parameters. Details of the data management and
data quality assurance evaluations are available in the supporting
document (USEPA, 2024d). The resulting database is available online on
the Six-Year Review website at <a href="https://www.epa.gov/dwsixyearreview">https://www.epa.gov/dwsixyearreview</a>.
5. Treatment Feasibility
An NPDWR either identifies an MCL or establishes enforceable TT
requirements. When promulgating an MCL or enforceable treatment
technique requirements, to determine feasibility, EPA identifies the
best technology, treatment techniques, and other means which EPA finds,
after examination for efficacy under field conditions and not solely
under laboratory conditions, are available (taking cost into
consideration). When promulgating an MCL, EPA also lists the
technology, treatment techniques, or other means which are feasible for
purposes of meeting the MCL. EPA reviews treatment feasibility to
ascertain if available technologies meet BAT criteria for a
hypothetical more stringent MCL, or if new information demonstrates an
opportunity to improve public health protection through revision of an
NPDWR TT requirement.
To be a BAT, the treatment technology must meet several criteria
such as having demonstrated consistent removal of the target
contaminant under field conditions. Although treatment feasibility and
analytical feasibility are considered together in evaluating the
technical feasibility requirement for an MCL, historically, treatment
feasibility has not been a limiting factor for MCLs. The result of this
review element is a determination of whether treatment feasibility
would pose a limitation to revising an MCL or provide an opportunity to
revise the NPDWR TT requirement.
6. Risk-Balancing
EPA reviews the risk-balancing analysis underlying some NPDWRs to
examine how a potential regulatory revision would address tradeoffs in
risks associated with different contaminants. Under this review, EPA
considers whether a change to an MCL and/or TT

[[Page 59629]]

will increase the public health risk posed by one or more contaminants,
and, if so, the agency considers revisions that will balance overall
risks. This review element is relevant only to the NPDWRs included in
the microbial and disinfection byproduct (MDBP) rules, which were
promulgated to address the need for risk-balancing between microbial
and disinfection byproduct (DBP) requirements, and among differing
types of DBPs. NPDWRs for microbials and disinfectants and DBPs were
not reviewed during Six-Year Review 4 due to ongoing regulatory action
initiated by Six-Year Review 3.
7. Other NPDWR Revisions
In addition to possible revisions to MCLGs, MCLs, and TTs, EPA
evaluated whether other revisions are needed to other regulatory
provisions in NPDWRs, such as monitoring and system reporting
requirements. EPA focused this review element on issues that were not
already being addressed through alternative mechanisms, such as a
recently completed, ongoing, or pending regulatory action. EPA also
reviewed implementation-related NPDWR concerns that were ``ready'' for
rulemaking--that is, the problem to be resolved had been clearly
identified, along with specific options to address the problem that
could be shown to either clearly improve the level of public health
protection or represent a meaningful opportunity for achieving cost
savings while maintaining the same level of public health protection.
The result of this review element is a determination regarding whether
EPA should consider revisions to the monitoring and/or reporting
requirements of an NPDWR.

V. Results of EPA's Review of NPDWRs

A. Overview of Six-Year Review 4 Results

Table 2 of this document, lists the results of EPA's review of the
88 NPDWRs assessed during Six-Year Review 4, along with the principal
rationale for the review outcomes. Table 2 includes the 15 NPDWRs that
have ongoing or pending regulatory actions.

Table 2--Summary of Six-Year Review 4 Results
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
Outcome Regulated contaminants
----------------------------------------------------------------------------------------------------------------
Not Appropriate for Revision at Recently completed, ongoing or pending Bromate........... Haloacetic acids
this Time. regulatory action. Chloramines (as (HAA5).
Cl2). Heterotrophic
Chlorine Dioxide bacteria.
(as ClO2). Lead.
Chlorine (as Cl2). Legionella.
Chlorite.......... Total
Copper............ Trihalomethanes
Cryptosporidium (TTHM).
(IE, LT1) \1\. Turbidity.
Giardia lamblia... Viruses (SWTR, IE,
LT1).\1\
----------------------------------------------------------------------------------------------------------------
Not Appropriate for Revision at Health effects assessment in process Alpha/photon Mercury
this Time. or contaminant nominated for health emitters. (inorganic).
assessment. Arsenic........... Polychlorinated
Beta/photon biphenyls (PCBs).
emitters. Radium 226/228
Chromium (total).. (combined).
Ethylbenzene...... Uranium.
-------------------------------------------------------------------------------
No new information, NPDWR remains Asbestos.......... trans-1,2-
appropriate after review. Benzo(a)pyrene.... Dichloroethylene.
Chlorobenzene..... Dinoseb.
Dalapon........... E. coli.
Di(2- Endrin.
ethylhexyl)adipat Ethylene
e (DEHA). dibromide.
Di(2- 2,4,5-TP (Silvex).
ethylhexyl)phthal
ate (DEHP).
1,2-Dibromo-3-
chloropropane
(DBCP).
-------------------------------------------------------------------------------
New information, Low priority and/ Acrylamide........ Heptachlor.
but no revision or no meaningful Alachlor.......... Heptachlor
recommended opportunity. Antimony.......... Epoxide.
because . . . Atrazine.......... Hexachlorobenzene.
Barium............ Hexachlorocyclopen
Benzene........... tadiene.
Lindane.
Methoxychlor.
Beryllium......... Oxamyl (Vydate).
Cadmium........... Pentachlorophenol.
Carbofuran........ Picloram.
Carbon Selenium.
Tetrachloride. Simazine.
Chlordane......... Styrene.
Cryptosporidium Tetrachloroethylen
(LT2) \1\. e (PCE).
1,2- Thallium.
Dichlorobenzene. 1,2,4-
1,4- Trichlorobenzene.
Dichlorobenzene. 1,1,1-
1,2-Dichloroethane Trichloroethane.
1,1- 1,1,2-
Dichloroethylene. Trichloroethane.
cis-1,2- Toluene.
Dichloroethylene.
Dichloromethane...
2,4- Total Coliform.
Dichlorophenoxyac Toxaphene.
etic acid (2,4-D). Trichloroethylene
1,2-Dichoropropane (TCE).
Dioxin (2,3,7,8- Vinyl Chloride.
TCDD). Xylenes.
Diquat............
Endothall.........
Epichlorohydrin...
Glyphosate........
-----------------------------------------------------------
Emerging Cyanide (as free Nitrate.
information and/ cyanide). Nitrite.
or data gaps. Fluoride..........
----------------------------------------------------------------------------------------------------------------
Candidate for Revision.......... New information.
None.
----------------------------------------------------------------------------------------------------------------
\1\ Regulation abbreviations: Aircraft Drinking Water Rule (ADWR), Ground Water Rule (GWR), Revised Total
Coliform Rule (RTCR), Surface Water Treatment Rule (SWTR), Interim Enhanced Surface Water Treatment Rule (IE),
Long Term 1 Enhanced Surface Water Treatment Rule (LT1), and Long Term 2 Enhanced Surface Water Treatment Rule
(LT2).

[[Page 59630]]

EPA has identified no appropriate candidates for revision at this
time.
EPA's Office of Ground Water and Drinking Water is currently
engaged in several ongoing and potential regulatory actions, in
addition to being involved in the efforts to successfully implement
recently promulgated rules including:
<bullet> Developing a proposal to revise the Microbial and
Disinfection By-Product Rules, including eight NPDWRs listed as
candidates for revision in Six-Year Review 3 (85 FR 61680, USEPA,
2020a).
<bullet> On December 6, 2023, EPA published the proposed rule
``National Primary Drinking Water for Lead and Copper: Improvements''
(88 FR 84878, USEPA, 2023a).
<bullet> In January 2024, EPA announced its commitment to
promulgate a National Primary Drinking Water Regulation for Perchlorate
by May 2027.\5\
---------------------------------------------------------------------------

\5\ Additional information can be found at <a href="https://www.epa.gov/sdwa/perchlorate-drinking-water">https://www.epa.gov/sdwa/perchlorate-drinking-water</a>.
---------------------------------------------------------------------------

<bullet> On April 26, 2024, EPA published the PFAS final rule
``PFAS National Primary Drinking Water Regulation'' (89 FR 32532,
USEPA, 2024a).
<bullet> On May 24, 2024, EPA published the final rule ``National
Primary Drinking Water Regulations: Consumer Confidence Reports'' (89
FR 45980, USEPA, 2024b).
Therefore, when evaluating the review results described in sections
V.B and V.C of this document, EPA also considered competing workloads
and potential diversion of resources from these other planned, ongoing,
and pending higher priority efforts within the drinking water office.

B. Chemical Phase Rules/Radionuclides Rules

The NPDWRs for chemical contaminants, collectively called the Phase
Rules, were promulgated between 1987 and 1992, following the 1986 SDWA
amendments. In December 2000, EPA promulgated final radionuclide
regulations, which had been issued as interim rules in July 1976.
1. Key Review Outcomes
EPA has decided that it is not appropriate at this time to revise
any of the NPDWRs covered under the Phase or Radionuclides Rules (Table
2 of this document). These NPDWRs were determined not to be candidates
for revision for one or more of the following reasons:
<bullet> ongoing/pending regulatory action warrants waiting for
further review;
<bullet> no new information was identified to suggest possible
changes in MCLG/MCL;
<bullet> new information did not present a meaningful opportunity
for health risk reduction or cost savings while maintaining/improving
public health protection;
<bullet> emerging information and/or data gaps create substantial
uncertainty.
In addition, EPA is announcing that the NPDWRs for
trichloroethylene (TCE) and tetrachloroethylene (PCE) are no longer
candidates for revision at this time. In March 2010, as an outcome of
the second cycle of Six-Year Review, EPA listed the TCE and PCE NPDWRs
as candidates for revision (75 FR 15500, USEPA, 2010a). TCE and PCE
were not reviewed under Six-Year Review 3 because regulatory revisions
were being considered as part of plans to address regulated and
unregulated Carcinogenic Volatile Organic Contaminants (cVOCs) in a
group rule (75 FR 3525, January 21, 2010; 82 FR 3531, USEPA, 2017a).
However, after evaluating currently available information for both of
these chemicals, the EPA concludes that these NPDWRS are not
appropriate for revision at this time because minimal reductions in
health risks would be associated with any revisions to these
regulations. Given resource limitations, competing workload priorities,
and administrative costs and burden to states to adopt any regulatory
changes associated with rulemakings, as well as limited potential
health benefits, these NPDWRs are considered a low priority and are no
longer candidates for revision at this time.
Section V.B.2 of this document describes the results of the review
organized by each review element. Section V.B.3 of this document
includes a description of the new information gathered by EPA for
select contaminants that EPA determined are not candidates for revision
at this time due to emerging information or data gaps or no meaningful
opportunity for health risk reduction. The contaminants discussed in
detail in section V.B.3 of this document are cyanide, fluoride,
nitrate, nitrite, TCE, and PCE.
Review results organized by contaminant for the Chemical Phase and
Radionuclides Rules can be found in the ``Chemical Contaminant
Summaries for the Fourth Six-Year Review of National Primary Drinking
Water Regulations'' (USEPA, 2024e).
2. Summary of Review Results
Initial Review
After conducting the initial review, as described in section IV.B.1
of this document, EPA identified two chemical contaminants (lead and
copper) with NPDWRs that were considered as part of a recently
completed action, and which are also currently part of an ongoing or
pending regulatory action. EPA published the Lead and Copper Rule
Revisions in January 2021 and published the proposed Lead and Copper
Rule Improvements on December 6, 2023. EPA did not evaluate lead and
copper in Six-Year Review 4 because such effort would be redundant with
these recent and ongoing rulemakings. EPA also identified contaminants
with ongoing or planned EPA health effects assessments. As of December
31, 2021, nine chemical or radiological contaminants reviewed had
ongoing or planned formal EPA health effects assessments. Table 3 of
this document below lists the contaminants with ongoing or planned EPA
assessments at the time of the Six-Year Review 4 cutoff date and the
current status of those reviews. EPA did not conduct a detailed review
of these nine chemical and radiological contaminants under Six-Year
Review 4.

Table 3--Six-Year Review Chemical/Radiological Contaminants With Ongoing
or Planned EPA Health Assessments
------------------------------------------------------------------------
Chemical/radionuclide Status \1\
------------------------------------------------------------------------
Alpha/photon emitters......... EPA Office of Air and Radiation (OAR) is
conducting a review of alpha and beta
photon emitters. Additional information
about this effort can be found at in
the Federal Register (87 FR 15988,
USEPA, 2022a) or at: <a href="https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209">https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209</a>.
Arsenic....................... Inorganic arsenic is being assessed by
the EPA IRIS Program. The assessment
status can be found at: <a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=278">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=278</a>.
Beta/photon emitters.......... EPA/OAR is conducting a review of alpha
and beta photon emitters. Additional
information about this effort can be
found at in the Federal Register (87 FR
15988, USEPA, 2022a) or at: <a href="https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209">https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209</a>.

[[Page 59631]]

Chromium VI (as part of total Chromium VI is being assessed by the EPA
Cr). IRIS Program. The assessment status can
be found at: <a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=144">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=144</a>.
Ethylbenzene.................. Ethylbenzene is being assessed by the
EPA IRIS Program. The assessment status
can be found at: <a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=51">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=51</a>.
Mercury....................... Inorganic Mercury Salts is being
assessed by the EPA IRIS Program. The
Assessment status can be found at:
<a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1522">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=1522</a>.
PCBs.......................... PCBs are being assessed by the EPA IRIS
Program. The assessment status can be
found at: <a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=294">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=294</a>.
Radium 226/228................ EPA/OAR is conducting a review of
radium. Additional information about
this effort can be found at in the
Federal Register (87 FR 15988, USEPA,
2022a) or at: <a href="https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209">https://sab.epa.gov/ords/sab/r/sab_apex/sab_bkup/advisoryactivitydetail?p18_id=2616&clear=18&session=8694491614209</a>.
Uranium....................... Uranium is being assessed by the EPA
IRIS Program. The assessment status can
be found at: <a href="https://iris.epa.gov/ChemicalLanding/&substance_nmbr=259">https://iris.epa.gov/ChemicalLanding/&substance_nmbr=259</a>.
------------------------------------------------------------------------
\1\ Additional information on the status of EPA IRIS Program assessments
can be found in the EPA IRIS Program Outlooks at <a href="https://www.epa.gov/iris/iris-program-outlook">https://www.epa.gov/iris/iris-program-outlook</a>.

Regarding the ongoing health assessment for Chromium VI (hexavalent
chromium), on October 20, 2022 the EPA published its draft ``IRIS
Toxicological Review of Hexavalent Chromium [Cr(IV)]'' (87 FR 63774,
USEPA, 2022b). This draft health effects assessment, which includes a
comprehensive evaluation of potential health effects, preliminarily
categorizes hexavalent chromium as likely carcinogenic to humans via
the oral exposure pathway. The final IRIS assessment was not available
as of the publication of this document and for consideration as part of
Six-Year Review 4. When this human health assessment is final, EPA will
carefully review the conclusions and consider all relevant information
to determine whether the NPDWR for chromium is a candidate for
revision.
After the initial review was completed, EPA identified 71 chemical
and radiological NPDWRs that were appropriate for detailed review.
Health Effects
The principal objectives of the health effects assessment review
were to identify: (1) contaminants for which a new health effects
assessment indicates that a change in MCLG might be appropriate (e.g.,
because of a change in cancer classification or an RfD), and (2)
contaminants for which the agency has identified new health effects
information suggesting a need to initiate a new health effects
assessment. For chemicals that were not excluded due to an ongoing or
planned health effects assessment by EPA, a more detailed review was
undertaken. Of the chemicals that underwent a more detailed review, EPA
identified 29 contaminants for which an updated RfD and/or the cancer
risk assessment (from oral exposure) or new relevant non-EPA
assessments might support a change to the MCLG. These 29 chemicals were
further evaluated as part of the Six-Year Review 4 to determine whether
they were candidates for regulatory revision. Table 4 of this document
lists the chemicals with available new health effects information and
the sources of the relevant new information. As shown in this table, 15
chemical contaminants have information that could support a lower MCLG,
and 14 contaminants have new information that could support a higher
MCLG.

Table 4--Chemicals With New Health Assessments That Could Support a
Change in MCLG
------------------------------------------------------------------------
Chemical Relevant new assessment
------------------------------------------------------------------------
15 Contaminants with Potential to Decrease the MCLG
------------------------------------------------------------------------
Antimony............................... CalEPA, 2016.
Cadmium................................ ATSDR, 2012.
Carbofuran............................. USEPA OPP, 2008.
Cyanide................................ USEPA IRIS, 2010b.
cis-1,2-Dichloroethylene............... USEPA IRIS, 2010c.
Endothall.............................. USEPA OPP, 2015b.
Fluoride............................... USEPA OW, 2010d.
Hexachlorocyclopentadiene.............. USEPA IRIS, 2001.
Methoxychlor........................... CalEPA, 2010a.
Oxamyl................................. USEPA OPP, 2017b.
Selenium............................... ATSDR, 2003.
Styrene................................ CalEPA, 2010b.
Toluene................................ Health Canada, 2014.
1,2,4-Trichlorobenzene................. USEPA PPRTV, 2009a.
Xylenes................................ Health Canada, 2014.
------------------------------------------------------------------------
14 Contaminants with Potential to Increase the MCLG
------------------------------------------------------------------------
Alachlor............................... USEPA OPP, 2007a.
Atrazine............................... USEPA OPP, 2018a.
Barium................................. USEPA IRIS, 2005.
Beryllium.............................. USEPA IRIS, 1998.
2,4-Dichlorophenoxy-acetic acid (2,4-D) USEPA OPP, 2017c.
1,2-Dichlorobenzene.................... ATSDR, 2006.
1,4-Dichlorobenzene.................... ATSDR, 2006.

[[Page 59632]]

1,1-Dichloroethylene................... USEPA IRIS, 2002.
Diquat................................. USEPA OPP, 2020b.
Glyphosate............................. USEPA OPP, 2017d.
Lindane................................ USEPA OPP, 2004.
Picloram............................... USEPA OPP, 2020c.
Simazine............................... USEPA OPP, 2018b.
1,1,1-Trichloroethane.................. USEPA IRIS, 2007b.
------------------------------------------------------------------------

Details of the health effects assessment review of the chemical and
radiological contaminants are documented in the ``Results of the Health
Effects Assessment for the Fourth Six-Year Review of Existing Chemical
and Radionuclide National Primary Drinking Water Standards'' (USEPA,
2024f).
Analytical Feasibility
EPA performed analytical feasibility analyses for the contaminants
that reached this portion of the review. These contaminants included
the 15 chemical contaminants identified under the health effects
assessment review as having potential for a lower MCLG. EPA evaluated
whether there were any analytical limitations to lowering the MCL to
the potential MCLG. EPA also evaluated an additional 22 contaminants
with MCLs higher than the current MCLGs due to analytical limitations
at the time of rule promulgation. The document ``Analytical Feasibility
Support Document for the Fourth Six-Year Review of National Primary
Drinking Water Regulations: Chemical Phase and Radionuclides Rules''
(USEPA, 2024g) describes the process EPA used to evaluate whether
changes in PQL are possible in those instances where the MCL may be
limited by analytical feasibility.
Table 5 of this document shows the outcomes of EPA's analytical
feasibility review for two general categories of drinking water
contaminants: (1) contaminants where health effects assessments
indicate potential for lower MCLGs, and (2) contaminants where existing
MCLs were limited by analytical feasibility at the time of promulgation
and new information indicates a potential to reduce the PQL.
<bullet> A health effects assessment indicates potential for lower
MCLG. This category includes the 15 contaminants identified in the
health effects review as having potential for a lower MCLG. EPA
reviewed the available information to determine if analytical
feasibility could limit the potential for MCL revisions. The current
PQL is not a limiting factor for seven of the 15 contaminants
identified by the health effects review as potential candidates for
lower MCLGs (cis-1,2-dichloroethylene, fluoride,
hexachlorocyclopentadiene, oxamyl, selenium, toluene, and xylenes). For
the remaining eight contaminants, the current PQL is higher than the
potential new MCLG, so EPA evaluated whether there is an opportunity to
lower the PQL. The evaluations indicated that all but one contaminant
(antimony) have potential for a lower PQL, although not to the
potential MCLG. Consequently, analytical feasibility may limit
potential MCL revisions for the remaining seven contaminants (Table 5
of this document).
<bullet> Existing MCLs are based on analytical feasibility. This
category includes 22 contaminants with existing MCLs that are greater
than the associated MCLGs due to analytical constraints at the time of
rule promulgation. Two of the contaminants (thallium and 1,1,2-
trichloroethane) are non-carcinogenic and have a non-zero MCLG, and the
remaining 20 contaminants are carcinogens with MCLGs equal to zero. EPA
evaluated whether the PQL could be lowered for each of these
contaminants. The evaluations indicated that all but five
(benzo[a]pyrene, DBCP, DEHP, ethylene dibromide, PCBs) of the 22
contaminants evaluated have potential for a lower PQL (Table 5 of this
document).
Where analytical feasibility evaluations indicated the potential
for a PQL reduction, Table 5 of this document lists the type of data
that support this conclusion. The types of data considered include
laboratory proficiency tests (PT), method detection limits (MDL) from
EPA-approved methods, and minimum reporting level (MRL) from the SYR 4
ICR dataset. The methods to evaluate each of these data types to
identify potential to reduce PQLs are described in the analytical
feasibility support document (USEPA, 2024g). Where the evaluations
indicated that the current PQL remained appropriate, Table 5 shows of
this document ``Data do not support PQL reduction.'' EPA found
information supporting potentially lower MCLs for 31 out of 37
contaminants evaluated.

[[Page 59633]]

Table 5--Analytical Feasibility Reassessment Results
------------------------------------------------------------------------
Analytical feasibility
Current PQL reassessment result
Contaminant ([micro]g/L) (and source of new
information) \1\
------------------------------------------------------------------------
15 Contaminants Identified Under the Health Effects Review as Having
Potential for Lower MCLG
------------------------------------------------------------------------
Antimony....................... 6 Data do not support PQL
reduction.
Cadmium........................ 2 PQL reduction supported
(MDL, MRL).
Carbofuran..................... 7 PQL reduction supported
(MDL).
Cis-1,2-dichloroethylene....... 5 PQL not limiting.
Cyanide........................ 100 PQL reduction supported
(MDL).
Endothall...................... 90 PQL reduction supported
(MDL, MRL).
Fluoride....................... 500 PQL not limiting.
Hexachlorocyclopentadiene...... 1 PQL not limiting.
Methoxychlor................... 10 PQL reduction supported
(MDL, MRL, PT).
Oxamyl......................... 20 PQL not limiting.
Selenium....................... 10 PQL not limiting.
Styrene........................ 5 PQL reduction supported
(MDL, MRL, PT).
Toluene........................ 5 PQL not limiting.
Xylenes........................ 5 PQL not limiting.
1,2,4-Trichlorobenzene......... 5 PQL reduction supported
(MDL, MRL, PT).
------------------------------------------------------------------------
22 Contaminants with MCLs Limited by Analytical Feasibility and Higher
than MCLGs
------------------------------------------------------------------------
Benzene........................ 5 PQL reduction supported
(MDL, MRL, PT).
Benzo[a]pyrene................. 0.2 Data do not support PQL
reduction.
Carbon tetrachloride........... 5 PQL reduction supported
(MDL, MRL, PT).
Chlordane...................... 2 PQL reduction supported
(MDL).
1,2-Dibromo-3-chloropropane 0.2 Data do not support PQL
(DBCP). reduction.
1,2-Dichloroethane............. 5 PQL reduction supported
(MDL, MRL, PT).
Dichloromethane................ 5 PQL reduction supported
(MDL, MRL, PT).
1,2-Dichloropropane............ 5 PQL reduction supported
(MDL, MRL, PT).
Di(2-ethylhexyl)phthalate 5 Data do not support PQL
(DEHP). reduction.
Ethylene dibromide............. 0.05 Data do not support PQL
reduction.
Heptachlor..................... 0.4 PQL reduction supported
(MDL).
Heptachlor epoxide............. 0.2 PQL reduction supported
(MDL).
Hexachlorobenzene.............. 1 PQL reduction supported
(MDL, MRL).
Pentachlorophenol.............. 1 PQL reduction supported
(MDL).
PCBs........................... 0.5 Data do not support PQL
reduction.
2,3,7,8-TCDD (dioxin).......... 0.00003 PQL reduction supported
(MRL).
Tetrachloroethylene............ 5 PQL reduction supported
(MDL, MRL).
Thallium....................... 2 PQL reduction supported
(MRL).
Toxaphene...................... 3 PQL reduction supported
(MRL, PT).
1,1,2-Trichloroethane.......... 5 PQL reduction supported
(MDL, MRL, PT).
Trichloroethylene.............. 5 PQL reduction supported
(MDL, MRL, PT).
Vinyl chloride................. 2 PQL reduction supported
(MDL, MRL, PT).
------------------------------------------------------------------------
\1\ The information source codes refer to the method detection limit
(MDL), minimum reporting level (MRL), and proficiency testing (PT)
data analyses. See USEPA (2024g) for further information.

Occurrence and Exposure
Using the SYR 4 ICR database, EPA conducted an assessment to
evaluate national occurrence of regulated contaminants and estimate the
potential population exposed to these contaminants. The details of the
current chemical occurrence analysis are documented in the ``Analysis
of Regulated Contaminant Occurrence Data from Public Water Systems in
Support of the Fourth Six-Year Review of National Primary Drinking
Water Regulations: Chemical Phase Rules and Radionuclides Rules''
(USEPA, 2024h). Based on quantitative benchmarks which were identified
in the health effects and analytical feasibility analyses, EPA
conducted the occurrence and exposure analysis for 31 contaminants.
This analysis shows that 27 of the 31 contaminants assessed rarely
occur at levels above the identified benchmark (e.g., potential MCLG or
PQL). For these 27 contaminants, monitoring results only exceeded
benchmarks in a very small percentage (i.e., less than 0.5 percent) of
systems, which serve a very small percentage of the population,
indicating that revisions to NPDWRs are unlikely to provide a
meaningful opportunity to improve public health protection at the
national level. Therefore, these 27 contaminants were not further
considered as candidates for regulatory revision. The other four
contaminants (cyanide, fluoride, TCE, and PCE) occurred at rates
ranging from 0.57 to 9.1 percent of systems within the SYR 4 ICR
dataset and 3.4 to 6.3 percent of the population served by those
systems. Additional considerations for cyanide, fluoride, TCE, and PCE
are discussed in section V.B.3 of this document. Table 6 of this
document lists the numerical benchmarks used to conduct the occurrence
analysis, the total number of systems with mean concentrations
exceeding a benchmark, and the estimated population served by those
systems. These average concentration-based evaluations are intended to
inform the Six-Year Review, not to assess compliance with regulatory
standards.

[[Page 59634]]

Table 6--Occurrence and Potential Exposure Analysis for Chemical NPDWRs
----------------------------------------------------------------------------------------------------------------
Number (and Population served by
percentage) of systems with a mean
Current MCL Benchmark \1\ systems with a concentration higher
Contaminant (ug/L) (ug/L) mean concentration than benchmark (and
\2\ higher than percentage of total
benchmark population)
----------------------------------------------------------------------------------------------------------------
Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG
----------------------------------------------------------------------------------------------------------------
Cadmium............................... 5 1 182 (0.36%) 430,823 (0.16%)
Carbofuran............................ 40 5 \3\ 7 (0.02%) \3\ 49,409 (0.02%)
Cyanide............................... 200 50 328 (0.85%) 8,134,220 (3.43%)
cis-1,2-Dichloroethylene.............. 70 10 7 (0.01%) 42,215 (0.02%)
Endothall............................. 100 50 0 0
Fluoride \4\.......................... 4,000 900 4,479 (9.05%) 17,058,830 (6.30%)
Hexachlorocyclopentadiene............. 50 40 0 0
Methoxychlor.......................... 40 1 1 (<0.01%) 22,536 (0.01%)
Oxamyl................................ 200 9 \3\ 7 (0.02%) \3\ 52,677 (0.02%)
Selenium.............................. 50 30 91 (0.18%) 84,988 (0.03%)
Styrene............................... 100 0.5 89 (0.17%) 27,473 (0.01%)
Toluene............................... 1,000 60 14 (0.03%) 5,256 (<0.01%)
1,2,4-Trichlorobenzene................ 70 0.5 15 (0.03%) 126,201 (0.05%)
Xylenes (total)....................... 10,000 80 23 (0.05%) 34,728 (0.01%)
----------------------------------------------------------------------------------------------------------------
Contaminants with MCLs Higher than MCLGs (Limited by Analytical Feasibility)
----------------------------------------------------------------------------------------------------------------
Benzene............................... 5 0.5 83 (0.16%) 319,633 (0.12%)
Carbon tetrachloride.................. 5 0.5 90 (0.17%) 766,891 (0.28%)
Chlordane............................. 2 1 1 (<0.01%) 240 (<0.01%)
1,2-Dichloroethane.................... 5 0.5 60 (0.11%) 181,041 (0.07%)
Dichloromethane....................... 5 0.5 215 (0.41%) 360,289 (0.13%)
1,2-Dichloropropane................... 5 0.5 41 (0.08%) 34,800 (0.01%)
Heptachlor............................ 0.4 0.1 1 (<0.01%) 900 (<0.01%)
Heptachlor epoxide.................... 0.2 0.1 3 (0.01%) 32,710 (0.01%)
Hexachlorobenzene..................... 1 0.1 6 (0.02%) 17,278 (0.01%)
Pentachlorophenol..................... 1 0.9 0 0
2,3,7,8-TCDD (dioxin)................. 0.00003 0.000005 7 (0.11%) 2,311 (<0.01%)
Tetrachloroethylene (PCE)............. 5 0.5 432 (0.83%) 15,811,810 (5.76%)
Thallium.............................. 2 1 71 (0.14%) 57,541 (0.02%)
Toxaphene............................. 3 1 2 (0.01%) 335 (<0.01%)
1,1,2-Trichloroethane................. 5 3 2 (<0.01%) 50 (<0.01%)
Trichloroethylene (TCE)............... 5 0.5 297 (0.57%) 12,755,926 (4.65%)
Vinyl chloride........................ 2 0.5 24 (0.05%) 307,275 (0.11%)
----------------------------------------------------------------------------------------------------------------
\1\ Benchmark screening levels were set to either potential maximum contaminant level goals (MCLGs) or estimated
quantitation levels (EQLs), depending on the contaminant. For more information see USEPA (2024g).
\2\ Results are based on long-term means generated by substituting one-half the MRL for each non-detection
record. For results based on substituting the value of the full MRL or zero see USEPA (2024h).
\3\ Oxamyl and carbofuran have health endpoints associated with acute exposure and are not appropriate for long-
term mean estimates. Results show the number of systems with at least one detection exceeding the benchmark.
\4\ Estimates represent naturally occurring fluoride concentrations. Quality assurance steps were taken to
exclude samples from fluoridated water systems. See USEPA (2024i) for details.

In addition, EPA performed a source water occurrence analysis for
the 15 chemical contaminants in which updated health effects
assessments indicated the possibility to increase (i.e., render less
stringent) the MCLG values. EPA conducted this analysis to assess for
meaningful opportunity to achieve cost savings while maintaining or
improving the level of public health protection. The data available to
characterize contaminant occurrence was limited because a comprehensive
dataset to characterize drinking water source quality is not available.
Data from the U.S. Geological Survey (USGS) National Water Quality
Assessment program and the U.S. Department of Agriculture Pesticide
Data Program water monitoring survey provide useful insights into
potential contaminant occurrence in source water. The analysis of the
available contaminant occurrence data for potential drinking water
sources indicated relatively low contaminant occurrence in the
concentration ranges of interest, and consequently, no meaningful
opportunity for system cost savings by increasing the MCLG and MCL for
these 15 contaminants. The results of this analysis were documented in
``Occurrence Analysis for Potential Source Waters for the Fourth Six-
Year Review of National Primary Drinking Water Regulations'' (USEPA,
2024j).
Treatment Feasibility
Currently, all of the MCLs for chemical and radiological
contaminants are either (1) set equal to the MCLGs, (2) limited by
analytical feasibility, or (3) set at the level at which health risk
reduction benefits were maximized at a cost justified by the benefits;
none are currently limited by treatment feasibility. EPA considers
treatment feasibility after identifying contaminants with the potential
to lower the MCLG/MCL that constitute a meaningful opportunity to
improve public health. No such contaminants were identified in the
occurrence and exposure analysis described above.
Treatment techniques were promulgated for two of the chemical and
radiological contaminants that were subject to a detailed review in
Six-Year Review 4. Acrylamide and epichlorohydrin occur in drinking
water as treatment impurities and are primarily introduced as residuals
in polymers and copolymers used for water treatment. There are no
standardized analytical methods for their measurement in water; instead
of sampling, water systems must certify to the State in writing that
they use products meeting the specifications in the NPDWR. To evaluate
the potential to revise the NPDWRs for these contaminants, EPA obtained
data from

[[Page 59635]]

NSF on analyses for approval of products against NSF/ANSI Standard 60,
which are based on EPA's regulation. NSF certification data shows that
manufactured products contain acrylamide and epichlorohydrin impurity
levels far below the current regulatory standard. Specifically, the
mean residual acrylamide concentration of certified products is one-
fifth of the current regulatory level and the 90th percentile is one-
half. There were no samples with detections of residual
epichlorohydrin. The available data indicates that the majority of
tested products already pose lower health risks than required under the
current TT, and therefore, revisions are a low priority. EPA is not
listing acrylamide and epichlorohydrin as candidates for revision at
this time. See USEPA (2024k) for details.
Other Regulatory Revisions
In addition to possible revisions to MCLGs, MCLs, and TTs, as a
part of the Six-Year Review 4, EPA considered whether other regulatory
revisions to NPDWRs are needed to address implementation issues, such
as revisions to monitoring and system reporting requirements. EPA used
the protocol to evaluate which implementation issues to consider
(USEPA, 2024c). EPA's protocol focused on items that were not already
being addressed, or had not yet been addressed, through alternative
mechanisms (e.g., as a part of a recent or ongoing rulemaking).
EPA compiled information on implementation-related issues
associated with the Chemical Phase Rules. EPA also identified
unresolved implementation issues and concerns from previous Six-Year
Reviews. The complete list of implementation issues related to the
Phase and Radionuclides Rules is presented in ``Consideration of Other
Regulatory Revisions in Support of the Fourth Six-Year Review of the
National Primary Drinking Water Regulations: Chemical Phase Rules and
Radionuclides Rules'' (USEPA, 2024l).
The agency focused on the following five implementation issues in
the Six-Year Review 4:

<bullet> Use of an alternative MCL for nitrate in Noncommunity Water
Systems (NCWSs)
<bullet> Frequency of nitrate monitoring in Transient Noncommunity
Water Systems (TNCWS)
<bullet> Frequency of nitrite monitoring
<bullet> Total nitrate-nitrogen plus nitrite-nitrogen MCL
<bullet> Total cyanide screening for free cyanide
Table 7 of this document provides a brief description of the five
issues and identified potential ways of addressing them. Please see
section V.B.3. of this document for a discussion of these contaminants
and their review outcomes. Please see USEPA (2024l) for a more detailed
description and estimated scope of these issues.

Table 7--Chemical Rule Implementation Issues Identified That Fall Within
the Scope of an NPDWR Review
------------------------------------------------------------------------
Implementation issue Description of issue
------------------------------------------------------------------------
Nitrate Alternative MCL in Non-community Water EPA evaluated the
Systems. possibility of
removing or further
restricting the
options for some
NCWSs to use an
alternative nitrate-
nitrogen MCL of up
to 20 mg/L. The
nitrate-nitrogen
MCL specified for
PWSs in 40 CFR
141.62 is 10 mg/L
and is based on the
critical health
endpoint of
methemoglobinemia
in children under
six months of age.
40 CFR 141.11
provides States the
discretion to use
an alternative MCL
of 20 mg/L for non-
community water
systems (NCWS).
This alternative
MCL is allowed
under certain
conditions--includi
ng that water would
be unavailable to
children under six
months of age.
Monitoring
requirements for
nitrate-nitrogen
are specified in
the introductory
text to 40 CFR
141.23, which
states that ``Non-
transient, non-
community water
systems shall
conduct monitoring
to determine
compliance with the
maximum contaminant
levels specified in
Sec. 141.62 in
accordance with
this section.
Transient, non-
community water
systems (TNCWS)
shall conduct
monitoring to
determine
compliance with the
nitrate and nitrite
MCL in Sec. Sec.
141.11 and 141.62
(as appropriate) in
accordance with
this section.''
Potential concerns
with the current
rule provisions
were identified as:
<bullet> The
alternative MCL
does not address
any nitrate-
induced health
concerns beyond
methemoglobinemi
a and
<bullet> While
Sec. 141.11
allows the use
of the
alternative MCL
by all eligible
NCWS, Sec.
141.23 implies
that only TNCWS,
a subcategory of
NCWS, are
eligible to use
the alternative
MCL.
To determine the
scope of this
issue, the agency
reviewed state
drinking water
regulations and
analyzed SYR 4 ICR
nitrate compliance
data and identified
nominal application
of the alternative
nitrate MCL by
NCWSs. In addition,
the nitrate and
nitrite human
health assessments
are currently being
evaluated by the
EPA IRIS program.
An updated
assessment could
inform the
potential health
effects of nitrate
exposure to levels
between 10 and 20
mg/L on adult
populations. EPA
will consider all
available and
updated human
health assessments
as it conducts
future cycles of
the six-year
review.
Nitrate Monitoring Frequency in Transient Currently, community
Noncommunity Water Systems. water systems
(CWSs) and NTNCWSs
are required to
monitor for nitrate
quarterly if a
sample is greater
than or equal to 50
percent of the
nitrate MCL (Sec.
141.23). TNCWSs are
required to monitor
for nitrate
annually (Sec.
141.23(d)(4)). In
the preamble to the
1991 final Phase II
rule, the agency
describes TNCWSs as
being subject to
the quarterly
monitoring
requirement stating
that ``EPA has
decided to retain
the 50 percent
trigger for
increased nitrate
monitoring in the
case of nitrate and
also to extend this
requirement to
TWSs'' (56 FR 3566,
USEPA, 1991).
EPA notes the
conflict between
the regulatory text
and the preamble.
To evaluate whether
it may be
appropriate to
revise the nitrate
NPDWR, the agency
analyzed compliance
monitoring data
collected under the
SYR 4 ICR. EPA
found that while
the majority of
TNCWSs that
reported detections
equal or greater
than 50 percent of
the nitrate MCL did
not conduct
quarterly
monitoring
afterward, the
number of these
systems appears
relatively small.
Due to the limited
scope of this
issue, EPA is not
revising the
monitoring
requirements at
this time but will
consider monitoring
requirements if
NPDWRs are revised
in the future.

[[Page 59636]]

Nitrite Monitoring Frequency...................... According to 40 CFR
141.23(e)(1), all
PWSs were required
to monitor for
nitrite once
between January 1,
1993, and December
31, 1995. If this
initial sample was
less than 50
percent of the MCL
(10 mg/L), systems
``shall monitor at
the frequency
specified by the
State``. Though the
nitrite monitoring
frequency is not
explicitly stated
in the CFR, EPA's
guidance provides
that this frequency
should be at least
once every 9-year
compliance cycle
(USEPA, 2020d). EPA
is aware that some
States may not
require systems to
conduct routine
nitrite monitoring
when sample results
are less than 50
percent of the MCL.
Because sample
results below the
MCL are not
reported to EPA,
the scope of this
issue is uncertain.
To address this
uncertainty, EPA
analyzed State
regulations and
nitrite compliance
monitoring data to
characterize the
frequency of
nitrite monitoring.
Results indicated
that a majority of
systems monitored
for nitrite at
least once during
the last 9-year
compliance cycle
(2011-2019). EPA
intends to work
with States to
encourage more
systems to sample
for nitrite at
least once during
each 9-year
compliance cycle.
Total Nitrate and Nitrite Analysis for Nitrate MCL In 40 CFR 141.62,
Monitoring. the MCL for nitrate
is specified as 10
mg/L and the MCL
for total nitrate
and nitrite is also
specified as 10 mg/
L. Sampling and
analytical
requirements as
specified in 40 CFR
141.23, however,
only included
nitrate and left
total nitrate and
nitrite monitoring
up to the
discretion of
States. Using Safe
Drinking Water
Information System
(SDWIS) compliance
data, EPA is aware
that at least half
of the States allow
total nitrate/
nitrite analysis to
determine
compliance with the
nitrate MCL.
To characterize
monitoring
practices for the
nitrate MCL, the
Agency analyzed Six-
Year Review 4
compliance
monitoring data for
both nitrate and
total nitrate/
nitrite. This
evaluation aims to
serve as a baseline
to assess nitrate
monitoring
practices in the
future, in response
to the 2020 EPA
guidance outlining
best practices when
using total nitrate/
nitrite analysis
for monitoring
compliance with the
nitrate MCL. EPA is
not revising the
monitoring
requirements at
this time but will
consider monitoring
requirements in
Sec. 141.23 if
NPDWRs are revised
in the future, to
incorporate best
practices similar
to those described
in recent guidance
(USEPA, 2020e).
------------------------------------------------------------------------

3. Select NPDWRs With New Information Not Appropriate for Revision
The NPDWRs discussed in this section had new information
identified, but EPA has determined they are not appropriate for
revision at this time due to: (1) data gaps or emerging information
that are necessary for EPA to evaluate as part of a review or; (2) new
information that suggests low or no meaningful opportunity to provide
greater public health protection. Examples of data gaps and emerging
information identified during the review include an analytical
monitoring challenge, a compliance reporting limitation, and an
anticipated health effects assessment being developed by another U.S.
Federal Agency. Specific details about the data gaps and emerging
information identified during the review for on cyanide, fluoride,
nitrate, nitrite, TCE, and PCE are provided below.
Cyanide
EPA published the current MCL and MCLG of 0.2 mg/L (200 [micro]g/L)
for free cyanide on July 17, 1992 (57 FR 31776, USEPA, 1992). In 2010,
EPA published an IRIS assessment (USEPA, 2010b), which identified a new
reproductive health effect endpoint that supports decreasing the MCLG
from 200 [micro]g/L to 4 [micro]g/L. Analytical feasibility information
identified in Six-Year Review 3 and Six-Year Review 4 supports a PQL
reduction to as low as 50 [micro]g/L. In Six-Year Review 3, cyanide was
listed as ``low priority'' due to low occurrence at levels below the
current MCL. Analysis of Six-Year Review 4 occurrence data identified
greater occurrence with 328 systems serving 8.1 million people with
mean concentrations above 50 [micro]g/L (see Table 6 of this document).
However, occurrence was limited to few states (USEPA, 2024h). EPA
considered these occurrence results and the potential for a meaningful
opportunity to improve the level of public health protection.
Two analytical monitoring challenges complicate interpretation of
the occurrence data. As described in section V.B.2 of this document, an
analytical artifact created by ascorbic acid pretreatment of drinking
water samples, which had been disinfected with chloramines, can result
in false positives for free cyanide (USEPA, 2020f). An EPA guidance
document (USEPA, 2020f) identified solutions to address this analytical
challenge, but the general awareness of the availability of this
guidance is uncertain. Second, EPA is aware that some systems analyze
samples for total cyanide, and if the results are lower than the MCL,
these systems report the total cyanide results as free cyanide. Systems
may achieve cost savings by analyzing samples for total cyanide;
however, using results for total cyanide instead of free cyanide could
potentially overestimate the actual occurrence of free cyanide. Free
and total cyanide results cannot be distinguished in the Six-Year
Review 4 ICR dataset because the Safe Drinking Water Information System
(SDWIS) State-version that many primacy agencies use to manage SDWA
compliance monitoring data does not have an analyte code for total
cyanide. Because the numerical benchmark used for occurrence is
significantly lower than the current cyanide MCL, some of the reported
concentrations may be for total cyanide. Therefore, the Six-Year Review
4 occurrence analysis likely overestimates free cyanide occurrence. For
these reasons, EPA does not believe it is appropriate to list the
cyanide NPDWR as a candidate for revision at this time. EPA intends to
help address these data gaps by continuing to disseminate the 2020
guidance on analytical methods for cyanide and may consider an
additional analyte code for total cyanide in the SDWIS reporting
system. Further discussion of the cyanide monitoring issues can be
found in USEPA (2024h).
Fluoride
EPA published the MCL and MCLG of 4.0 mg/L for fluoride on April 2,
1986 (51 FR 11396, USEPA, 1986) based on the critical health endpoint
of crippling skeletal fluorosis. EPA also established a secondary MCL/
MCLG at 2.0 mg/L to protect against cosmetically objectionable dental
fluorosis

[[Page 59637]]

(discoloration and/or pitting of teeth). Certain drinking water systems
may choose to fluoridate finished water as a public health protection
measure for reducing the incidence of cavities. The U.S. Public Health
Service (PHS) recommendation for the optimal community water
fluoridation level is 0.7 mg/L (U.S. Department of Health and Human
Services, 2015). The decision to fluoridate a community water supply is
made by the state or local municipalities and is not required by EPA or
any other federal entity. Fluoride is also added to various consumer
products, such as toothpaste and mouthwash.
EPA has reviewed the NPDWR for fluoride in prior Six-Year Reviews.
As a result of Six-Year Review 1, EPA requested that the National
Research Council (NRC) of the National Academies of Sciences (NAS)
conduct a review of the health and exposure data on orally ingested
fluoride. In 2006, the NRC published the results of its review and
concluded that severe dental fluorosis can be an adverse health effect
(NRC, 2006). The NRC report recommended that EPA develop a dose-
response assessment for severe dental fluorosis as the critical health
endpoint and update an assessment of fluoride exposure from all
sources.
In 2010, EPA published Dose Response Analysis for Noncancer Effects
(USEPA, 2010d), which was considered under Six-Year Review 3. For more
information, please see Appendix C of the Six-Year Review 3 Health
Effects Assessment for Existing Chemical and Radionuclide National
Primary Drinking Water Regulations--Summary Report (USEPA, 2016). In
Six-Year Review 3, EPA did not recommend the fluoride NPDWR for
revisions citing limited agency resources, prioritization of other
contaminants, ongoing health effects research, and other factors that
were anticipated to reduce the U.S. population's exposure to fluoride
via drinking water (82 FR 3531, USEPA, 2017a). In Six-Year Review 4,
EPA again considered the 2010 EPA assessment to derive a lower
potential MCLG of 0.9 mg/L. Review results are provided in section
V.B.2. of this document.
Available published literature on other health effect categories
including neurotoxicity and behavior, reproduction and development,
endocrine effects, and cancer were reviewed in the EPA assessment
(USEPA, 2010d). However, based on the review of the available
literature at the time, EPA determined that the data for these other
health effects associated with fluoride exposure were insufficient to
support their selection as critical effects for potential MCLG
derivation (USEPA, 2010d). EPA is aware of ongoing efforts by the
National Toxicology Program (NTP) to conduct a systematic review and
meta-analysis of the published literature on developmental
neurotoxicity for fluoride. In May 2023, NTP released the Draft ``NTP
Monograph on the State of the Science Concerning Fluoride Exposure and
Neurodevelopmental and Cognitive Health Effects: A Systematic Review''
(NTP, 2023); however, the NTP systematic review and meta-analysis are
not health assessments that could be used to directly inform the
derivation of a potential MCLG. Due to emerging research published on
developmental neurotoxicity after fluoride exposure coupled with
competing workloads and other ongoing high priority actions (see
section V.A of this document.), EPA has decided that the fluoride NPDWR
is not a candidate for revision at this time. In addition, the NTP has
not made a final decision about the report's developmental
neurotoxicity systematic review conclusions and has not formally
released a final report. Following publication of the final NTP report,
EPA will consider the systematic review and meta-analysis conclusions
regarding developmental neurotoxicity to inform the agency's future
development of a health effects assessment for fluoride. See USEPA
(2024f) Appendix B for more information.
Nitrate and Nitrite
EPA published the MCLs and MCLGs for nitrate (10 mg/L) and nitrite
(1 mg/L) based on the critical endpoint of methemoglobinemia (blue baby
syndrome) on January 30, 1991 (56 FR 3526, USEPA, 1991). Nitrate and
nitrite were not reviewed in detail under Six-Year Review 3 due to
ongoing IRIS assessments at that time. Although the development of the
IRIS assessment for nitrate and nitrite was suspended in December 2018,
EPA has restarted development of their health assessment for nitrate
and nitrite as indicated in the October 2023 IRIS Program Outlook. The
agency recently released the ``Protocol for the Nitrate and Nitrite
IRIS Assessment (Oral)'' for public comment on November 9, 2023 (88 FR
77310, USEPA, 2023b). EPA plans to evaluate whether a revision of the
nitrate and nitrite NPDWRs is appropriate, once the final IRIS
assessment is available.
Trichloroethylene (TCE) and Tetrachloroethylene (PCE)
The NPDWR for TCE was published on July 8, 1987 (52 FR 25690,
USEPA, 1987) and the NPDWR for PCE was published on January 30, 1991
(56 FR 3526, USEPA, 1991). Both TCE and PCE are classified as
carcinogens and have MCLGs and MCLs of zero and 5 [micro]g/L,
respectively. The MCLs were based on analytical feasibility at the time
of rule promulgation. TCE and PCE were both listed as candidates for
revision in Six-Year Review 2, based on updated analytical feasibility,
treatment, and occurrence information.
In 2011, EPA announced plans to address a group of regulated and
unregulated carcinogenic volatile organic contaminants (cVOCs) in a
single regulatory effort. The eight regulated contaminants that were
evaluated for the cVOCs group regulation included benzene, carbon
tetrachloride, 1,2-dichloroethane, 1,2-dichloropropane,
dichloromethane, PCE, TCE, and vinyl chloride. In Six-Year Review 3,
these contaminants were categorized under recent, ongoing, or planned
regulatory action and were not reviewed. The cVOC group regulation was
not promulgated, as a result these eight contaminants were reviewed
again during Six-Year Review 4. EPA has determined that TCE and PCE are
no longer candidates for revision at this time based on updated
information.
In Six-Year Review 2, EPA assessed analytical information that
supported reducing the PQL and evaluated occurrence for TCE and PCE at
0.5 [micro]g/L. As shown in Tables 5 and 6 of this document, EPA
identified information in Six-Year Review 4 that again supported
assessing occurrence at that level. The average TCE concentration
exceeded 0.5 [micro]g/L in 297 systems, representing 0.57 percent of
the systems assessed nationwide and serving approximately 13 million
people. Similarly, the average PCE concentration exceeded 0.5 [micro]g/
L in 432 systems, which represent 0.83 percent of the approximately
50,000 PWSs assessed nationwide and serve approximately 16 million
people. These occurrence results are consistent with the Six-Year
Review 2 estimates (75 FR 15500, March 29, 2010, USEPA, 2010a).
The most recent final IRIS assessments for TCE (USEPA, 2011) and
PCE (USEPA, 2012) were completed after the Six-Year Review 2 results
were published and have been selected as the health assessments
relevant to chronic toxicity for TCE and PCE in Six-Year Review 4
(USEPA, 2024f). The updated IRIS assessments maintained the
classification of ``carcinogenic to humans,'' and therefore do not
support a change to the MCLGs of zero for either TCE or PCE. Based on
the Six-Year Review 4 occurrence estimates described above, EPA
considered if there was a potential for an increase in

[[Page 59638]]

human health protection at the lower identified level. To evaluate this
potential, EPA examined the cancer risk level associated with the
current MCLs (5 [micro]g/L) and the screening level (0.5 [micro]g/L)
using updated occurrence and health effects information from Six-Year
Review 4. The cancer risk levels at the current MCLs for TCE and PCE
are 1 x 10<SUP>-5</SUP> (USEPA, 2011) and 3.0 x 10<SUP>-7</SUP> (USEPA,
2012), respectively. These cancer risk levels correspond to excess
lifetime cancer cases of 10 and 0.3 cases per million people,
respectively. At the screening level of 0.5 [micro]g/L, the risk per
million people would be 1 case for TCE and 0.03 cases for PCE. The
implied number of baseline cancer cases over a 70-year exposure period
is unlikely to exceed 120 total cases for TCE and 5 total cases for
PCE. This corresponds to annual averages of 1.7 and 0.07 cases for TCE
and PCE, respectively. This new information identified since Six-Year
Review 2 indicates that revising the MCLs for either TCE or PCE would
result in relatively small health risk reductions among the exposed
population and would divert significant resources from other planned
and ongoing work. Therefore, EPA has determined that TCE and PCE are
considered ``low priority'' and are no longer candidates for revision.

C. Microbial Contaminants Regulations

As discussed in section III of this document, the initial review
branch of the review protocol identifies NPDWRs that have recently been
recently competed or are being reviewed in ongoing or pending
regulatory actions. Excluding such contaminants from a more detailed
review in the Six-Year Review 4 prevents duplicative Agency efforts.
Based on the initial review and considering the ongoing rulemaking
activities for the Microbial and Disinfection Byproduct Rules, EPA did
not perform a more detailed review for the Surface Water Treatment Rule
(SWTR), the Interim Enhanced Surface Water Treatment Rule (IESWTR), the
Long-Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), and the
Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules.
The following microbial contaminant regulations were subject to a more
detailed review for the Six-Year Review 4:

<bullet> Revised Total Coliform Rule (RTCR)
<bullet> Long Term 2 Enhanced Surface Water Treatment Rule (LT2)
<bullet> Ground Water Rule (GWR)
<bullet> Aircraft Drinking Water Rule (ADWR)
<bullet> Filter Backwash Recycling Rule (FBRR)

Background information on each of the microbial contaminant
regulations is presented in the subsequent sections. EPA is conducting
its first detailed review of the RTCR and the ADWR as part of the Six-
Year Review. The RTCR and the ADWR were excluded from a detailed review
in Six Year Review 3 because they were promulgated in 2013 and 2009,
respectively.
These microbial contaminants regulations establish treatment
technique (TT) requirements in lieu of MCLs, except in the RTCR, EPA
also established an MCL for Escherichia coli (E. coli) and TT
requirements for total coliform. In accordance with the Six-Year Review
Protocol, during the six-year review process, EPA assesses whether new
health risk, analytical methods, or treatment information indicate
possible TT revision. For the RTCR, the regulatory review determines
whether new information indicates potential revision to the MCL for E.
coli.
The elements of the RTCR, LT2, GWR, and ADWR regulations that were
reviewed for Six-Year Review 4 were: health effects, analytical
feasibility, occurrence and exposure, and treatment feasibility. For
the RTCR, LT2, GWR, and ADWR regulations, the EPA did not find any new
relevant information as it relates to analytical feasibility. For all
the other elements reviewed a summary of the findings is included in
the subsequent sections. In addition, detailed information about the
review is provided in the ``Six-Year Review 4 Technical Support
Document for Microbial Contaminant Regulations'' (USEPA, 2024m).
At this time, none of the reviewed microbial contaminant rules are
being identified as a candidate for regulatory revision.
1. Revised Total Coliform Rule
Background
EPA promulgated the Revised Total Coliform Rule (RTCR), a revision
to the Total Coliform Rule, on February 13, 2013 (78 FR 10269, USEPA,
2013). The Total Coliform Rule (TCR) was promulgated on June 29, 1989
(54 FR 27544, USEPA, 1989). The purpose of the revision was to increase
public health protection through the reduction of potential entry
pathways for fecal contamination into distribution systems. The TCR
required all public water systems (PWSs) to monitor for the presence of
total coliforms and Escherichia coli (E. coli)) in the distribution
system at a frequency dependent on the size (population served by) of
the system. Under the TCR, a maximum contaminant level (MCL) was
established based on the presence or absence of total coliforms with
the intent to address contamination that could enter into distribution
systems. The RTCR revised the TCR to eliminate the MCL for total
coliforms and established an MCLG and MCL for E. coli of zero. The RTCR
also requires PWSs that have an indication of coliform contamination
(e.g., as a result of total coliform positive samples, E. coli MCL
violations or performance failure) to find and assess the problem,
identify sanitary defects and take corrective action. There are two
levels of assessments (i.e., Level 1 and Level 2) based on the severity
or frequency of the problem.
Summary of Review Results
Information available for national occurrence and exposure
indicates that both routine total coliform and E. coli positive rates
have decreased after the implementation of RTCR. EPA concludes that no
regulatory revisions to the RTCR are appropriate at this time based on
the review of available information.
Health Effects
Collier et al. (2021) estimated the collective U.S. disease burden
attributable to over a dozen waterborne illnesses from infectious
pathogens found in the distribution system (vibriosis,
campylobacteriosis, cryptosporidiosis, giardiasis, Legionnaire's
disease, salmonellosis, shigellosis, infections by non-tuberculous
mycobacteria (NTM), norovirus, Shiga-toxin-producing E. coli, otitis
externa, pneumonia, and septicemia). These researchers estimated the
total disease burden at approximately 7.15 million cases annually, with
an estimated 118,000 hospitalizations and 6,630 deaths. In this
analysis, waterborne disease is understood to include gastrointestinal,
respiratory, and systemic disease attributable to both drinking-water
and non-drinking-water exposure. From further evaluation of this
study's cases, Gerdes et al. (2023) determined 1.13 million of these
illnesses were attributable to drinking water. According to the
estimates presented in these studies, the opportunistic pathogens
(Legionella, Nontuberculous Mycobacteria (NTM), and Pseudomonas) impose
a greater public health burden than the fecal pathogens. Of the
estimated 7.15 million infectious waterborne illnesses in 2014 in the
United States, drinking water exposure caused 40 percent of
hospitalizations and 50 percent of deaths.

[[Page 59639]]

Occurrence and Exposure
To evaluate potential pathogenic contamination in distribution
systems EPA analyzed national compliance monitoring data from the SYR 4
ICR dataset (USEPA, 2019. EPA assessed the trends that may be
associated with the implementation of the RTCR and found a
statistically significant decline for total coliform positive results
from years of 2014-2015 to 2018-2019 (i.e., before and after the
implementation of RTCR respectively). The result suggests that the
presence of these indicator organisms in the distribution system was
declining. The trend of declining positive total coliform results was
observed across different types of public water systems, water sources
(ground water versus surface water), and system sizes (small versus
large). With respect to the fecal contamination indicator E. coli, the
observed decreasing trend was not supported by a statistical test of
significance. EPA also found that the absolute number of E. coli
positives were low, suggesting that the treatment techniques are
effective (USEPA, 2024m).
Treatment Feasibility
In this section as part of Six-Year Review process, EPA evaluated
new information about tools and treatment techniques. Since the major
treatment technique requirements under the RTCR are assessments
followed by corrective actions (if total coliform and/or E. coli are
detected), EPA evaluated the effectiveness of such requirements by
comparing total coliform and E. coli positive rates after completion of
either Level 1 or Level 2 assessments (USEPA, 2024m).
EPA found about an 80 percent decrease in both routine total
coliform and E. coli positive rates, two months after completion of
RTCR assessments for systems having a monthly monitoring schedule.
These analytical results and newly compiled information suggest
that the ``find and fix'' approach prescribed under the provisions of
assessments and corrective action within RTCR appears to work as
intended for reducing the microbial occurrence in distribution systems
and may be improving public health protection from microbial risks (as
indicated by a substantial drop of the total coliform and E. coli
positive rates following completion of corrective actions to respond to
assessments).
2. Long Term 2 Enhanced Surface Water Treatment Rule
Background
EPA promulgated the Long Term 2 Enhanced Surface Water Treatment
Rule, hereafter referred to as ``LT2'', on January 5, 2006 (71 FR 654,
USEPA, 2006a). The LT2 applies to all PWSs that use surface water or
ground water under the direct influence of surface water. The LT2
builds upon the IESWTR and the LT1 by improving control of microbial
pathogens and by focusing on systems with elevated Cryptosporidium
contamination risk. The purposes of the LT2 are to protect public
health from illness arising from exposure to Cryptosporidium and other
microbial pathogens in drinking water and to prevent significant
increases in risks that might occur when systems implement drinking
water disinfection byproduct rules.
Key provisions in the LT2 include: source water monitoring for
Cryptosporidium (with a screening procedure to reduce monitoring costs
for small systems); risk-targeted Cryptosporidium treatment by filtered
systems with the highest source water Cryptosporidium levels;
inactivation of Cryptosporidium by all unfiltered systems; criteria for
the use of Cryptosporidium treatment and control processes; and
covering or treating uncovered finished water storage facilities.
The LT2 requires PWSs using surface water or ground water under the
direct influence of surface water to monitor their source waters for
Cryptosporidium and/or E. coli to identify additional treatment
requirements. PWSs must monitor their source water (i.e., the influent
water entering the treatment plant) over two different timeframes
(defined as Round 1 and Round 2) to determine the occurrence of
Cryptosporidium. Monitoring results determine the extent of
Cryptosporidium treatment requirements under the LT2. According to the
LT2 rule requirements, all PWSs were to complete Round 2 by 2021. To
reduce monitoring costs, small filtered PWSs (serving fewer than 10,000
people) which initially monitor for E. coli for one year as a screening
analysis, are required to monitor for Cryptosporidium only if their E.
coli levels exceed specified trigger values. Small filtered PWSs that
exceed the E. coli trigger, as well as small unfiltered PWSs, must
monitor for Cryptosporidium for one or two years, depending on the
sampling frequency. The LT2 also requires all unfiltered PWSs to
provide at least 2 to 3-log (i.e., 99 to 99.9 percent) inactivation of
Cryptosporidium. Further, under the LT2, unfiltered PWSs must achieve
their overall inactivation requirements (including Giardia lamblia and
virus inactivation as established by earlier regulations) using a
minimum of two disinfectants.
Under the LT2, PWSs with uncovered finished water reservoirs
(UCFWR) must either cover the storage facility or treat the water
leaving the storage facility to achieve inactivation and/or removal of
4-log virus, 3-log Giardia lamblia and 2-log Cryptosporidium using a
protocol approved by the state (USEPA, 2006a). Most finished water
reservoirs for surface water systems are covered. All PWSs with UCFWRs
are under administrative orders or compliance agreements to cover or
treat their UCFWR.
Summary of Review Results
From a review of the literature on Cryptosporidium health effects,
EPA concludes that there is no new health information to suggest a need
to modify the LT2. In addition, EPA determined that no regulatory
revisions to the microbial toolbox options are appropriate at this
time. During Six-Year Review 4, EPA did not consider disinfection
profiling information since EPA is evaluating overall filtration and
disinfection requirements in the SWTRs as part of the on-going
consideration of potential revisions to the MDBP rules. For more
information regarding EPA's review of treatment feasibility see the
``Six-Year Review 4 Technical Support Document for Microbial
Contaminant Regulations'' (USEPA, 2024m).
Health Effects
Since 1995, cryptosporidiosis has been a nationally notifiable
disease, meaning healthcare providers and laboratories that diagnose
cases of laboratory-confirmed cryptosporidiosis are required to report
cases to their local or state health departments, which in turn report
the cases to CDC. Since 2012, there have been four reported outbreaks
of cryptosporidiosis from public water systems to CDC. The four
outbreaks together resulted in a total of 201 recorded illnesses, 2
hospitalizations, and no deaths (CDC, 2022). Although cryptosporidiosis
is a nationally notifiable disease, additional outbreaks may go
unreported to CDC or may have been recorded as of uncertain causes. In
addition, since CDC's National Outbreak Reporting System is
specifically focused on outbreaks, it does not capture rates of endemic
disease of cryptosporidiosis from drinking water.

[[Page 59640]]

Occurrence and Exposure
Based on the LT2 source water monitoring results, filtered systems
were classified in one of four risk categories (Bins 1-4) to determine
additional treatment needed. Systems in Bin 1 are not required to
provide additional Cryptosporidium treatment. Systems in Bins 2-4 must
achieve 1.0-2.5 log of treatment (i.e., 90 to 99.7 percent reduction
for Cryptosporidium) over and above that provided by conventional
treatment, depending on the Cryptosporidium concentrations. Filtered
PWSs must meet the additional Cryptosporidium treatment requirements in
Bins 2, 3, or 4 by selecting one or more technologies from the
microbial toolbox to ensure source water protection and management,
and/or Cryptosporidium removal or inactivation. All unfiltered water
systems must provide at least 99 or 99.9 percent (2 or 3-log)
inactivation of Cryptosporidium, depending on their monitoring results.
All filtered systems that provide 5.5 log treatment for Cryptosporidium
are exempt from monitoring and subsequent bin classification.
Six years after the initial bin classification following a first
round of monitoring, filtered systems were required to conduct a second
round of monitoring. Round 2 monitoring began in 2015. Round 2
monitoring was implemented to understand year-to-year variability for
occurrence of Cryptosporidium. The difference observed between
occurrence at the time of the ICR Supplemental Surveys and the LT2
Round 1 monitoring indicates year-to-year variability (USEPA, 2017a).
Limited occurrence data for Cryptosporidium was available to EPA in
response to the SYR 4 ICR since fewer than 1 percent of the
Cryptosporidium monitoring records provided actual concentration levels
with units of oocysts/L; however, the data about system binning for
about 300 PWSs serving populations larger than 10,000 was provided.
Those data indicate that the percentage of PWSs potentially moving to
an ``action bin'' based on Round 2 monitoring would not be
substantially higher than the percentage estimated based on modeling
conducted during the LT2 review included as part of the Six-Year Review
3, thus suggesting no change to the review decision made under Six-Year
Review 3.
Treatment Feasibility
The LT2 includes a variety of treatment and control options,
collectively termed the ``microbial toolbox,'' that PWSs can implement
to comply with the LT2's additional Cryptosporidium treatment
requirements. Most options in the microbial toolbox carry prescribed
credits toward Cryptosporidium treatment and control requirements. The
LT2 Toolbox Guidance Manual (USEPA, 2010e) provides guidance on how to
apply the toolbox options.
For the Six-Year Review 4, EPA reviewed additional research into
the relationship between ultraviolet light (UV) dose and log
inactivation. Some studies showed the same log inactivation at UV doses
lower than those reported in previous EPA guidance, and other studies
showed log inactivation at UV doses higher than those contained in the
guidance. Since there is not a consensus of log inactivation at levels
significantly lower than EPA prior published guidance, EPA concludes
that the new information does not support changes to the UV dose table.
EPA also reviewed new information pertaining to technologies, which
have not been included in the existing LT2 toolbox guidance manual, and
which may be effective for the removal or inactivation of protozoa
including Cryptosporidium. In addition, EPA also reviewed new
technologies that water systems may be employing to improve treatment
performance for complying with the MDBP rules, e.g., turbo coagulation
and powdered activated carbon. Initiatives by states and EPA's Area
Wide Optimization Program were evaluated as well. EPA found that this
new information appears insufficient to develop quantification criteria
for inactivation and removal credit for Cryptosporidium.
3. Ground Water Rule
Background
EPA promulgated the Ground Water Rule (GWR) in 2006 (71 FR 65574,
USEPA, 2006b) to provide protection against microbial pathogens in PWSs
using ground water sources. The rule establishes a risk-based approach
to target undisinfected ground water systems that are vulnerable to
fecal contamination. In addition to the protection provided by the RTCR
and GWR monitoring requirements, systems that do not disinfect are also
protected by the sanitary survey provisions of the GWR and the
treatment technique provisions of the RTCR.
The GWR required compliance beginning December 1, 2009. Since the
triggered source water monitoring provision was built upon the
compliance monitoring results of total coliform and E. coli under the
TCR and later RTCR, implementation of the GWR was not yet completed for
the period of time covered by the Six-Year Review 3 ICR (2006-2011).
The RTCR was promulgated in 2013 and became effective on April 1, 2016.
EPA expected that implementation of the RTCR might impact the percent
of ground water systems that would be triggered into source water
monitoring and taking any corrective actions under the GWR. Therefore,
the effects of the GWR and the RTCR implementation in addressing
vulnerable ground water systems were not reviewed during the Six-Year
Review 3 process.
Summary of Review Results
The information considered during this review suggest that
microbial pathogens have been detected in untreated ground water
samples which show no presence of fecal indicators, however these
studies are limited in quantity and the prevalence of endemic disease
from microbial contamination of untreated ground water cannot be well
characterized with the available information (USEPA, 2024m). Additional
and more robust studies are needed to further understand the magnitude
of the issue. EPA concludes that no regulatory revisions to the GWR are
appropriate at this time.
Health Effects
Waterborne pathogens can cause mild to severe illnesses (Wallender
et al., 2014). These illnesses may include; acute gastrointestinal
illness (AGI) with diarrhea, abdominal pain/discomfort, nausea,
vomiting, conjunctivitis, aseptic meningitis, and hand-foot-and-mouth
disease. Infections from some waterborne pathogens (e.g.,
Campylobacter) may cause long-term implications, such as reactive
arthritis, Guillain-Barr[eacute] syndrome, and irritable bowel syndrome
(Keithlin et al., 2014). Other more severe illnesses include hemolytic
uremic syndrome (HUS) (kidney failure), hepatitis, and bloody diarrhea
(WHO, 2004).
Some studies have indicated that waterborne pathogens such as
adenovirus, enteroviruses, hepatitis A, norovirus, rotavirus,
Salmonella, Giardia, Cryptosporidium, and Shigella have been found in
untreated ground water samples (Borchardt et al., 2012; Wallender et
al., 2014; Stokdyk et al., 2020).
Human enteric viruses have been detected in drinking water free of
bacterial indicators, such as total coliform. With total coliform
detections rates similar to the average rate for

[[Page 59641]]

undisinfected community PWSs in the U.S, Borchardt et al. (2012)
estimated a six to 22 percent attributable risk for enteric illness
from viruses present in the communities' drinking water. In another
study, Burch et al. (2022) found that noncommunity wells had higher
infection risk than community wells. Burch et al. (2022) found the
annual risk was relatively high for all pathogens combined in the
study, while the average daily doses for individual pathogens were low,
indicating that significant risk results from sporadic pathogen
exposure. Studies by Fout et al. (2017) and Stokdyk et al. (2020) found
that total coliform (and other indicators like E. coli, somatic phage,
HF183, and Bacteroidales-like HumM2) tend to have high specificity,
meaning that absence of the indicator provides relatively strong
assurance that water is free of viral and other pathogens, but also
have low sensitivity, meaning that presence of the indicator does not
necessarily predict presence of pathogens.
Occurrence and Exposure
Similar to the RTCR, EPA examined the national compliance
monitoring data collected for the Six-Year Review 4 to understand how
total coliform and E. coli, indicators of contamination behaved before
and after implementation of the GWR, as well as understanding how level
of contamination for high risk undisinfected ground water systems have
changed.
As noted, GWR monitoring is based on initial monitoring under the
RTCR. If a system has a positive total coliform sample (based on
routine coliform monitoring under the RTCR), the system must test that
sample for the presence of E. coli. Under the GWR, ground water systems
that do not provide at least 4-log treatment of viruses and are
notified of a routine positive total coliform sample collected under
RTCR must collect and analyze at least one source water sample for E.
coli or other fecal indicators from each ground water source (well)
within 24 hours. If the triggered source water sample has a positive
for E. coli the ground water systems must take corrective action. EPA
conducted a distribution system total coliform/E. coli data exploration
and analysis effort to identify findings that could inform the risk
reduction of the fully implemented GWR, as well as characterize high
risk systems.
The national average total coliform and E. coli rates (i.e., total
number of positives divided by total number of samples) before and
after implementation of the GWR were calculated using Six-Year Review 3
and Six-Year Review 4 datasets. The analytical results were grouped by
system sizes and disinfection status (i.e., disinfecting versus and
undisinfected). The period of analysis was from 2007-2008 (before the
GWR was implemented) to 2014-2015 (after the completed implementation
of the first round of sanitary surveys under the GWR). The total
coliform rates across different system categories decreased, suggesting
that there may be less pathogenic contamination pathways and so
potentially less microbial exposure, corresponding to the period when
the GWR was being implemented. This downward change is supported by a
statistical significance test. The declining count of the fecal
contamination indicator, E. coli was not supported by a test of
statistical significance. Yet numbers of E. coli positives were
consistently low, which may indicate low exposure to fecal
contamination.
EPA performed a more specific analysis using a statistical model
focused on the most vulnerable water systems, the undisinfected ground
water systems. EPA conducted statistical modeling focused on
examination of total coliform levels in small ground water systems to
account for their infrequent sampling and relatively low level of
monitoring observations compared to larger systems that monitor more
frequently.
There are approximately 45,000 undisinfected ground water systems
associated with total coliform records collected and less than 1
percent population among the population served by the public community
water systems in the U.S. (based on SYR 4 ICR data). Most undisinfected
ground water systems serve small permanent populations or transient
populations.
EPA found that the smallest systems (serving a population fewer
than 1,001) have higher median total coliform rates than undisinfected
larger systems. In addition, the analysis indicates that median
occurrence rates for many undisinfected transient systems may have
fallen, from four to three percent total coliform detection rate from
2011 to 2019. Another finding from the statistical modeling is that the
number of non-community systems that have high total coliform
detections in the systems serving fewer than 1,001 people has remained
roughly the same, about 7,000 undisinfected ground water systems, when
running a comparison using Six-Year Review 3 and Six-Year Review 4 ICR
data with a threshold of five percent rate of total coliform positive
detections, which is the threshold that triggers a Level 1 Assessment
in the RTCR. For statistical analysis of E. coli detection rates, there
was not sufficient data to make estimates of averages and numbers of
systems exceeding high levels.
Two implications of these modelling results should be noted as it
relates to estimating potential exposure and occurrence. One is that
the non-community systems serving fewer than 1,001 have total coliform
positive rates around two to four percent, while a study of 14
community systems served by untreated ground water in Wisconsin found
that a total coliform positive rate of 2.3 percent was associated AGI
burden (Borchardt et al, 2012). EPA concludes, however, that studies
indicating microbial disease burden at total coliform positive levels
found in high-risk systems are limited in number as mentioned in the
Health Effects section, as well as in geographic scope. Another
implication from the results of this statistical analysis is that the
remaining systems with very high total coliform rates could suggest
compliance challenges among small ground water systems.
In addition to evaluating trends with indicators under RTCR to
evaluate protection for vulnerable ground water systems, EPA also
considered the results from the GWR requirement for triggered source
water sampling. The sample results indicate that there is a small
percent of positive source water E. coli detections ranging from 0.76
percent to 1.99 percent of E. coli samples for non-community systems
which are primarily undisinfected systems, and 250 out of 270 of source
water E. coli detections were associated with undisinfected systems
serving fewer than 500 people. The other fecal indicators, coliphage
and enterococci were used very infrequently, and data was insufficient
to evaluate. Low incidence of fecal indicators may indicate low
exposure to fecal contamination among undisinfected ground water
systems.
Treatment Feasibility
Per treatment technique requirements under the GWR, there are two
scenarios that trigger ground water systems to take corrective actions:
(1) positive results of the triggered source water monitoring, and (2)
significant deficiencies found during Sanitary Survey (EPA was not able
to assess sanitary surveys directly given data limitations). EPA
evaluated whether treatment was improving under the GWR by using the
RTCR occurrence analysis data to consider total coliform rates before
and after the GWR was implemented.

[[Page 59642]]

EPA developed a systematic approach to identify disinfection status
of ground water systems for each of the years included in the Six-Year
Review ICR datasets and found that the percentage of ground water
systems that were disinfecting had increased consistently from 2007-
2008 (before the GWR was implemented) to 2014-2015. This finding of an
increasing number of systems disinfecting could be attributable to
systems taking corrective actions to address positive results after
triggered source water monitoring. The analytical results presented in
the ``Six-Year Review 4 Technical Support Document for Microbial
Contaminant Regulations'' (USEPA, 2024m) also indicate that
disinfecting ground water systems had substantially lower total
coliform positive rates than undisinfected ground water systems. In
addition, EPA also observed that the total coliform positive rates
decreased after completion of the first round of sanitary surveys under
the GWR among ground water systems.
4. Aircraft Drinking Water Rule
Background
EPA promulgated the Aircraft Drinking Water Rule (ADWR) on October
19, 2009 (74 FR 53590, USEPA, 2009b). The primary purpose of the ADWR
is to ensure that safe and reliable drinking water is provided to
aircraft passengers and crew. This entails providing air carriers with
a feasible way to comply with SDWA and NPDWRs. The existing NPDWRs were
designed for traditional, stationary public water systems not mobile
aircraft water systems that are operationally different. For example,
aircraft fly to multiple destinations throughout the course of any
given day and may board drinking water from sources at any of these
destinations. Aircraft board water from airport watering points via
temporary connections. Aircraft drinking water safety depends on a
number of factors including the quality of the water that is boarded
from these multiple sources, the care used to board the water, and the
operation and maintenance of the onboard water system and the water
transfer equipment.
The ADWR's provisions protect against disease-causing
microbiological contaminants through the required development and
implementation of aircraft water system operations and maintenance
plans. The ADWR's provisions include: routine disinfection and flushing
of the water system, air carrier training requirements for key
personnel, and periodic sampling of the onboard drinking water, as well
as self-inspections of each aircraft water system and immediate
notification of passengers and crew when violations or specific
situations occur.
Summary of Review Results
The ADWR is a unique rule within the context of the SDWA. This rule
applies only to aircraft engaged in interstate commerce with onboard
systems that provide water for human consumption through pipes. These
aircraft water systems board finished water for human consumption and
regularly serve an average of at least twenty-five individuals daily,
at least 60 days out of the year. Human consumption includes water for
drinking, hand washing, food preparation, and oral hygiene. From a
review of available technical information within the scope of the
review, EPA concludes that there is no new information to suggest that
regulatory revisions to the ADWR are appropriate at this time.
Health Effects
Limited new literature is available on the presence of microbial
pathogens in aircraft drinking water. Handschuh et al. (2015) found
that long-haul flights were significantly poorer in terms of microbial
water quality than short haul flights. A follow-up study by Handschuh
et al. (2017) demonstrated that there is a diversity of microorganisms
within the aircraft drinking water supply chain.
Other studies have also found microbial contaminants present in
aircraft drinking water, including Pseudomonas aeruginosa, enterococci,
clostridia, and Salmonella (WHO, 2009; Schaeffer et al., 2012).
Tracking an illness back to contaminated water served on an aircraft
presents a technical challenge. Most disease incubation periods are
longer than the duration of a flight, and even if it is possible to
determine that a disease was incurred in air travel, it may be
difficult to determine if the route of transmission was from beverages,
food, or close proximity of people, and to determine whether
transmission happened on board the aircraft or at an air terminal.
Occurrence and Exposure
The Aircraft Reporting and Compliance System (ARCS) is used to
facilitate the reporting of aircraft water system data under the ADWR.
Air carriers subject to the ADWR must report to EPA about their
inventory of aircraft water system fleet; the date the operations and
maintenance plan was developed; the date the coliform sampling plan was
developed; the date the aircraft water system sampling plan(s) was
incorporated into the aircraft water system Operations and Maintenance
plan; the date the Operations and Maintenance plan(s) was incorporated
into the U.S. Federal Aviation Administration (FAA) accepted air
carrier Operation and Maintenance program; the frequency for routine
disinfection and flushing, and the corresponding routine total coliform
sampling frequency; and the date for routine disinfection and flushing,
routine coliform sampling dates and results, and corrective actions
(when applicable).
For Six-Year Review 4, EPA downloaded and reviewed compliance
monitoring data available in ARCS as of May 2021. Approximately 140,000
records of aircraft water systems compliance monitoring data for total
coliform and E. coli samples were available in ARCS from February 2011
through May 2021, including results reported for more than 70 different
makes/models of aircraft. These results were used to characterize the
positivity rates of total coliform and E. coli in aircraft water
systems on an annual basis for the years that data were available
(2011-2021) and for the subset of years 2012 through 2019. This
approach removes potentially confounding considerations associated with
evaluating data for calendar year 2020 when a large number of aircraft
PWS were inactive due to COVID-19, as well as years 2011 and 2021 for
which the ARCS data evaluated represents partial years.
Monitoring data broken down by year for the years 2012-2019 shows
an average annual total coliform positivity rate of 5.46 percent, with
a median of 5.63 percent, a minimum of 3.76 percent and a maximum of
7.03 percent. The total coliform positivity rate decreased on an annual
basis from 2012-2019. The average E. coli positivity rate was 0.26
percent, and the median rate was also 0.26 percent, with a minimum of
0.17 percent and a maximum of 0.33 percent. The E. coli positivity rate
also decreased on an annual basis.
Treatment Feasibility
Under the ADWR, air carriers routinely disinfect and flush aircraft
water systems at the frequency recommended by the water system
manufacturer or, if not specified by the manufacturer, they may choose
from one of four options. If corrective disinfection and flushing is
chosen or required, air carriers follow the procedures in their O&M
plans. Unscheduled flight disruptions to

[[Page 59643]]

perform corrective disinfection and flushing can be minimized by
shutting off the water or preventing the flow of water to the taps.
Before allowing unrestricted access to the aircraft water system, a
complete set of follow-up samples must be collected and submitted for
analysis after the disinfection and flushing event if triggered by a
total coliform-positive sample and must be reported as total coliform-
negative if triggered by an E. coli-positive sample. One study was
identified that examined the effectiveness of disinfection and flushing
procedures to prevent coliform persistence in aircraft water systems
(Szabo et al., 2019). That study showed that coliforms were not
persistent on the aircraft plumbing surfaces, and coliforms were not
detected after disinfection and flushing. However, it noted an
exception for the aerator installed in the lavatory faucet which was
coliform positive after disinfection with ozone and mixed oxidants;
disinfection with glycolic acid and quaternary ammonia showed no
detectable coliforms on aerators after 30 minutes of soaking in the
disinfectants.
Each aircraft water system must be inspected by the air carrier at
least every 5 years according to the procedures in their O&M plans. At
a minimum, the self-inspection procedures for an aircraft water system
must include inspection of the storage tank, distribution system,
supplemental treatment, fixtures, valves, and backflow prevention
devices. Any deficiencies detected must be addressed, and any
deficiency that is unresolved within 90 days of identification of the
deficiency must be reported to EPA.
5. Filter Backwash Recycling Rule
EPA promulgated the Filter Backwash Recycling Rule (FBRR) on June
8, 2001 (66 FR 31086, USEPA, 2001a). The rule aimed to increase public
health protection by addressing microbial contaminant risks associated
with filter backwash recycling practices. The rule required certain
systems to return recycled filter backwash water, sludge thickener
supernatant, and liquids from dewatering processes to a location in the
system such that all filtration processes of a system are employed, or
at an alternate location if approved by the State. In addition, the
rule required systems that employ conventional filtration or direct
filtration to notify States of their recycling practices by June 8,
2004, and after then to keep and retain records on file about their
recycle flows for subsequent review and evaluation by the State. There
are no ongoing monitoring requirements associated with the FBBR.
EPA reviewed available State data collected under the ICR; however,
the EPA did not identify any new and relevant information that would
indicate that revisions to the NPDWR at this time are appropriate.

VI. References

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USEPA. 2020e. Use of Total Nitrate and Nitrite Analysis for
Compliance Determinations with the Nitrate Maximum Contaminant Level
(WSG 213). November 30, 2020. <a href="https://www.epa.gov/sites/default/files/2021-01/documents/wsg_213_nitrate_wsg_11-30-2020_signed_508-compliantfinal.pdf">https://www.epa.gov/sites/default/files/2021-01/documents/wsg_213_nitrate_wsg_11-30-2020_signed_508-compliantfinal.pdf</a>.
USEPA. 2020f. Clarification of Free and Total Cyanide Analysis for
Safe Drinking Water Act (SDWA) Compliance Revision 1.0. EPA 815-B-
20-004. June 2020.
USEPA. 2022a. Request for Nominations for the Science Advisory Board
Radionuclide Cancer Risk Coefficients Review Panel. 87 FR 15988.
March 21, 2022.
USEPA. 2022b. Availability of the Draft IRIS Toxicological Review of
Hexavalent Chromium. 87 FR 63774. October 10, 2022.
USEPA. 2023a. National Primary Drinking Water Regulations for Lead
and Copper: Improvements (LCRI). 88 FR 84878. December 6, 2023.
USEPA. 2023b. Availability of the Protocol for the Nitrate and
Nitrite IRIS Assessment (Oral). 88 FR 77310. November 9, 2023.
USEPA. 2024a. PFAS National Primary Drinking Water Regulation. 89 FR
32532. April 26, 2024.
USEPA. 2024b. National Primary Drinking Water Regulations: Consumer
Confidence Report Rule Revisions. 89 FR 45980. May 24, 2024.
USEPA. 2024c. EPA Protocol for the Fourth Review of Existing
National Primary Drinking Water Regulations. EPA 815-R-24-018.
USEPA. 2024d. Data Management and Quality Assurance/Quality Control
Process for the Fourth Six-Year Review Information Collection
Request Dataset. EPA 815-R-24-017.
USEPA. 2024e. Chemical Contaminant Summaries for the Fourth Six-Year
Review of Existing National Primary Drinking Water Regulations. EPA
815-S-24-002.
USEPA. 2024f. Results of the Health Effects Assessment for the
Fourth Six-Year Review of Existing Chemical and Radionuclide
National Primary Drinking Water Standards. EPA 815-R-24-020.
USEPA. 2024g. Analytical Feasibility Support Document for the Fourth
Six-Year Review of National Primary Drinking Water Regulations. EPA
815-R-24-015.
USEPA. 2024h. Analysis of Regulated Contaminant Occurrence Data from
Public Water Systems in Support of the Fourth Six-Year Review of
National Primary Drinking Water Regulations: Chemical Phase and
Radionuclides Rules. EPA 815-R-24-014.
USEPA. 2024i. Review of Fluoride Occurrence for the Fourth Six-Year
Review. EPA 815-R-24-021.
USEPA. 2024j. Occurrence Analysis for Potential Source Waters for
the Fourth Six-Year Review of National Primary Drinking Water
Regulations. EPA 815-R-24-019.
USEPA. 2024k. Support Document for the Fourth Six-Year Review of
Drinking Water Regulations for Acrylamide and Epichlorohydrin. EPA
815-R-24-023.
USEPA. 2024l. Consideration of Other Regulatory Revisions in Support
of the Fourth Six-Year Review of the National Primary Drinking Water
Regulations: Chemical Phase Rules and Radionuclides Rule. EPA 815-R-
24-016.
USEPA. 2024m. Six-Year Review 4 Technical Support Document for
Microbial Contaminant Regulations. EPA 815-R-24-022.
Wallender, E.K., E.C. Ailes, J.S. Yoder, V.A. Roberts, and J.M.
Brunkard. 2014. Contributing factors to disease outbreaks associated
with untreated groundwater. Ground Water. 52(6): 886-97.
World Health Organization (WHO). 2004. Guidelines for Drinking-Water
Quality, Third Edition. Volume 1: Recommendations. <a href="https://www.who.int/publications/i/item/9789241547611">https://www.who.int/publications/i/item/9789241547611</a>.
WHO. 2009. Guide to hygiene and sanitation in aviation, 3rd edition.
<a href="https://www.who.int/publications/i/item/9789241547772">https://www.who.int/publications/i/item/9789241547772</a>.

Michael S. Regan,
Administrator.
[FR Doc. 2024-15807 Filed 7-22-24; 8:45 am]
BILLING CODE 6560-50-P

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