Document ID: EPA-HQ-OW-2022-0114-0027
Agency: epa
Document Type: Proposed Rule
Title: Per- and Polyfluoroalkyl Substances National Primary Drinking Water Regulation
Posted Date: 2023-03-29T04:00Z

[Federal Register Volume 88, Number 60 (Wednesday, March 29, 2023)]
[Proposed Rules]
[Pages 18638-18754]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-05471]

[[Page 18637]]

Vol. 88

Wednesday,

No. 60

March 29, 2023

Part II

Environmental Protection Agency

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40 CFR Parts 141 and 142

PFAS National Primary Drinking Water Regulation Rulemaking; Proposed 
Rule

  Federal Register / Vol. 88, No. 60 / Wednesday, March 29, 2023 / 
Proposed Rules  

[[Page 18638]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 141 and 142

[EPA-HQ-OW-2022-0114; FRL 8543-01-OW]
RIN 2040-AG18

PFAS National Primary Drinking Water Regulation Rulemaking

AGENCY: Environmental Protection Agency (EPA).

ACTION: Preliminary regulatory determination and proposed rule; request 
for public comment; notice of public hearing.

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SUMMARY: The Environmental Protection Agency (EPA) is committed to 
using and advancing the best available science to tackle per- and 
polyfluoroalkyl substances (PFAS) pollution, protect public health, and 
harmonize policies that strengthen public health protections with 
infrastructure funding to help communities, especially disadvantaged 
communities, deliver safe drinking water. In March 2021, EPA issued a 
final regulatory determination to regulate perfluorooctanoic acid 
(PFOA) and perfluorooctane sulfonic acid (PFOS) as contaminants under 
Safe Drinking Water Act (SDWA). In this notice, EPA is issuing a 
preliminary regulatory determination to regulate perfluorohexane 
sulfonic acid (PFHxS), hexafluoropropylene oxide dimer acid (HFPO-DA) 
and its ammonium salt (also known as a GenX chemicals), 
perfluorononanoic acid (PFNA), and perfluorobutane sulfonic acid 
(PFBS), and mixtures of these PFAS as contaminants under SDWA. Through 
this action, EPA is also proposing a National Primary Drinking Water 
Regulation (NPDWR) and health-based Maximum Contaminant Level Goals 
(MCLG) for these four PFAS and their mixtures as well as for PFOA and 
PFOS. EPA is proposing to set the health-based value, the MCLG, for 
PFOA and PFOS at zero. Considering feasibility, including currently 
available analytical methods to measure and treat these chemicals in 
drinking water, EPA is proposing individual MCLs of 4.0 nanograms per 
liter (ng/L) or parts per trillion (ppt) for PFOA and PFOS. EPA is 
proposing to use a Hazard Index (HI) approach to protecting public 
health from mixtures of PFHxS, HFPO-DA and its ammonium salt, PFNA, and 
PFBS because of their known and additive toxic effects and occurrence 
and likely co-occurrence in drinking water. EPA is proposing an HI of 
1.0 as the MCLGs for these four PFAS and any mixture containing one or 
more of them because it represents a level at which no known or 
anticipated adverse effects on the health of persons is expected to 
occur and which allows for an adequate margin of safety. EPA has 
determined it is also feasible to set the MCLs for these four PFAS and 
for a mixture containing one or more of PFHxS, HFPO-DA and its ammonium 
salt, PFNA, PFBS as an HI of unitless 1.0. The Agency is requesting 
comment on this action, including this proposed NPDWR and MCLGs, and 
have identified specific areas where public input will be helpful for 
EPA in developing the final rule. In addition to seeking written input, 
the EPA will be holding a public hearing on May 4, 2023.

DATES: Comments must be received on or before May 30, 2023. Comments on 
the information collection provisions submitted to the Office of 
Management and Budget (OMB) under the Paperwork Reduction Act (PRA) are 
best assured of consideration by OMB if OMB receives a copy of your 
comments on or before April 28, 2023. Public hearing: EPA will hold a 
virtual public hearing on May 4, 2023, at https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas. Please refer to the SUPPLEMENTARY 
INFORMATION section for additional information on the public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OW-2022-0114 by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/ 
(our preferred method). Follow the online instructions for submitting 
comments.
     Mail: U.S. Environmental Protection Agency, EPA Docket 
Center, Office of Ground Water and Drinking Water Docket, Mail Code 
2822IT, 1200 Pennsylvania Avenue NW, Washington, DC 20460.
     Hand Delivery or Courier: EPA Docket Center, WJC West 
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. 
The Docket Center's hours of operations are 8:30 a.m. to 4:30 p.m., 
Monday through Friday (except Federal Holidays).
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the ``Public Participation'' 
heading of the SUPPLEMENTARY INFORMATION section of this document.

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

SUPPLEMENTARY INFORMATION: 

Executive Summary

    In March 2021, EPA issued a final regulatory determination to 
regulate perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic 
acid (PFOS) as contaminants under Safe Drinking Water Act (SDWA). EPA 
is issuing a preliminary regulatory determination to regulate 
perfluorohexane sulfonic acid (PFHxS), hexafluoropropylene oxide dimer 
acid (HFPO-DA) and its ammonium salt (also known as a GenX chemicals), 
perfluorononanoic acid (PFNA), and perfluorobutane sulfonic acid 
(PFBS), and mixtures of these PFAS as contaminants under SDWA (see 
section III of this preamble for additional discussion on EPA's 
preliminary regulatory determination). Through this action, EPA is also 
proposing a National Primary Drinking Water Regulation (NPDWR) and 
health-based Maximum Contaminant Level Goals (MCLG) for these four PFAS 
and their mixtures as well as for PFOA and PFOS. Exposure to these PFAS 
may cause adverse health effects, and all are likely to occur in 
drinking water.
    PFAS are a large family of synthetic chemicals that have been in 
use since the 1940s. Many of these compounds have unique physical and 
chemical properties that make them highly stable and resistant to 
degradation in the environment--colloquially termed ``forever 
chemicals.'' People can be exposed to PFAS through certain consumer 
products, occupational contact, and/or by consuming food and drinking 
water that contain PFAS (see section II.C of this preamble for 
additional discussion on PFAS chemistry, production, and uses). Current 
scientific evidence indicates that consuming water containing the PFAS 
covered in this proposed regulation above certain levels can result in 
harmful health effects. Depending on the individual PFAS, health 
effects can include negative impacts on fetal growth after exposure 
during pregnancy, on other aspects of development, reproduction, liver, 
thyroid, immune function, and/or the nervous system; and increased risk 
of cardiovascular and/or certain types of cancers, and other health 
impacts (see

[[Page 18639]]

section II.B and III.B of this preamble for additional discussion on 
health effects).
    This proposed PFAS drinking water regulation contains several key 
features. Based on a review of the best available health effects data, 
EPA is proposing MCLGs that address six PFAS. An MCLG is the maximum 
level of a contaminant in drinking water at which no known or 
anticipated adverse effect on the health of persons would occur, 
allowing an adequate margin of safety. A contaminant means any 
``physical, chemical or biological or radiological substance or matter 
in water.'' This proposal addresses contaminants and certain mixtures 
of contaminants. Through this action, EPA is also proposing enforceable 
standards which takes the form of maximum contaminant levels (MCLs) in 
this proposed regulation. An MCL is the maximum level allowed of a 
contaminant or a group of contaminants (i.e., mixture of contaminants) 
in water which is delivered to any user of a public water system (PWS). 
The SDWA generally requires EPA to set an MCL ``as close as feasible 
to'' the MCLG. EPA has also included monitoring, reporting, and other 
requirements to ensure regulated drinking water systems, known as a 
PWS, meet the PFAS limits in the regulation.
    Following a systematic review of available human epidemiological 
and animal toxicity studies, EPA has determined that PFOA and PFOS are 
likely to cause cancer (e.g., kidney and liver cancer) and that there 
is no dose below which either chemical is considered safe (see section 
IV.A and V.A through B of this preamble for additional discussion). 
Therefore, EPA is proposing to set the health-based value, the MCLG, 
for both of these contaminants at zero. Considering feasibility, 
including currently available analytical methods to measure and treat 
these chemicals in drinking water, EPA is proposing individual MCLs of 
4.0 nanograms per liter (ng/L) or parts per trillion (ppt) for PFOA and 
PFOS (see sections VI.C and VIII of this preamble for additional 
discussion on the MCLs and practical quantitation limits [PQLs]).
    Due to their widespread use and persistence, many PFAS are known to 
co-occur in drinking water and the environment--meaning that these 
compounds are often found together and in different combinations as 
mixtures (see section III.C and VII of this preamble for additional 
discussion on occurrence). PFAS disrupt signaling of multiple 
biological pathways resulting in common adverse effects on several 
biological systems and functions, including thyroid hormone levels, 
lipid synthesis and metabolism, development, and immune and liver 
function. Additionally, EPA's examination of health effects information 
found that exposure through drinking water to a mixture of PFAS can be 
assumed to act in a dose-additive manner (see sections III.B and IV.B 
of this preamble for additional discussion on mixture toxicity). This 
dose additivity means that low levels of multiple PFAS, that 
individually would not likely result in adverse health effects, when 
combined in a mixture are expected to result in adverse health effects. 
As a result, EPA is proposing to use a Hazard Index (HI) approach to 
protecting public health from mixtures of four PFAS: PFHxS, HFPO-DA and 
its ammonium salt (also known as GenX chemicals), PFNA, and PFBS 
because of their known and additive toxic effects and occurrence and 
likely co-occurrence in drinking water. PFOA and PFOS are being 
proposed for separate MCLs and not included in the HI because their 
individual proposed MCLGs are zero, and the level at which no known or 
anticipated adverse effects on the health of persons is expected to 
occur is well below current analytical quantitation levels. Based on 
our current understanding of health effects, this is not the case for 
the other covered PFAS. Because of the analytical limitations for PFOA 
and PFOS, the MCL for these two PFAS is set at the lowest feasible 
quantitation level and any exceedance of this limit requires action to 
protect public health, regardless of any mixture in which they are 
found. As a result, EPA is not proposing to include PFOA or PFOS in the 
HI.
    The HI is a commonly used risk management approach for mixtures of 
chemicals (USEPA, 1986a; 2000a). In this approach, a ratio called a 
hazard quotient (HQ) is calculated for each of the four PFAS (PFHxS, 
HFPO-DA and its ammonium salt (also known as GenX chemicals), PFNA, and 
PFBS) by dividing an exposure metric, in this case, the measured level 
of each of the four PFAS in drinking water, by a health reference value 
for that particular PFAS. For health reference values, in this 
proposal, EPA is using Health Based Water Concentration (HBWCs) as 
follows: 9.0 ppt for PFHxS, 10.0 ppt for HFPO-DA; 10.0 ppt for PFNA; 
and 2000 ppt for PFBS (USEPA, 2023a). The individual PFAS ratios (HQs) 
are then summed across the mixture to yield the HI. If the resulting HI 
is greater than one (1.0), then the exposure metric is greater than the 
health metric and potential risk is indicated. EPA's Science Advisory 
Board (SAB) opined that where the health endpoints of the chosen 
compounds are similar, it is reasonable to use an HI as ``a reasonable 
approach for estimating the potential aggregate health hazards 
associated with the occurrence of chemical mixtures in environmental 
media.'' (USEPA, 2022a). The HI provides an indication of overall 
potential risk of a mixture as well as individual PFAS that are 
potential drivers of risk (those PFAS(s) with high(er) ratios of 
exposure to health metrics) (USEPA, 2000a; see section IV.B and V.C of 
this preamble for additional discussion on the HI and its derivation). 
Therefore, EPA is proposing an HI of 1.0 as the MCLGs for these four 
PFAS and any mixture containing one or more of them because it 
represents a level at which no known or anticipated adverse effects on 
the health of persons is expected to occur and which allows for an 
adequate margin of safety. EPA has determined it is also feasible to 
set the MCLs for these four PFAS and for a mixture containing one or 
more of PFHxS, HFPO-DA and its ammonium salt, PFNA, PFBS as an HI of 
unitless 1.0 (see sections V.C and VI.B of this preamble for discussion 
of the HI MCLG and MCL, respectively).
    Monitoring is a core component of a NPDWR and assures that water 
systems are providing necessary public health protections (see section 
IX of this preamble for additional discussion on monitoring and 
compliance requirements). EPA is therefore proposing requirements for 
systems to monitor for PFOA, PFOS, PFHxS, HFPO-DA and its ammonium 
salt, PFNA, and PFBS in drinking water that build upon EPA's 
Standardized Monitoring Framework (SMF) for Synthetic Organic Compounds 
(SOCs) where the monitoring frequency for any PWS depends on previous 
monitoring results. This proposal includes flexibilities related to 
monitoring, including flexibilities for systems to use certain, 
previously collected data to satisfy initial monitoring requirements in 
this proposal as well as reduced monitoring requirements in certain 
circumstances (see section IX.E of this preamble for additional 
discussion on monitoring waivers).
    In summary, the proposed MCLs for PFOA and PFOS are 4 ng/L 
(individually), and the proposed MCL of an HI of 1.0 for any mixture 
containing PFHxS, HFPO-DA and its ammonium salt, PFNA, and/or PFBS. 
Water systems with PFAS levels that exceed the proposed MCLs would need 
to take action to provide safe and reliable drinking water. These 
systems may install water treatment or consider other

[[Page 18640]]

options such as using a new uncontaminated source water or connecting 
to an uncontaminated water system. Activated carbon, anion exchange 
(AIX) and high-pressure membrane technologies have all been 
demonstrated to remove PFAS, including PFOA, PFOS, PFHxS, HFPO-DA and 
its ammonium salt, PFNA, and PFBS, from drinking water systems. These 
treatment technologies can be installed at a water system's treatment 
plant and are also available through in-home filter options (see 
section XI of this preamble for additional discussion on available 
treatment technologies).
    As part of its health risk reduction and cost analysis, SDWA 
requires an evaluation of quantifiable and nonquantifiable health risk 
reduction benefits and costs. SDWA also requires that EPA considers 
quantifiable and nonquantifiable health risk reduction benefits from 
reductions in co-occurring contaminants. The SDWA also requires that 
EPA determine if the benefits of the proposed rule justify the costs. 
In accordance with these requirements, the EPA Administrator has 
determined that the quantified and nonquantifiable benefits of the 
proposed PFAS NPDWR justify the costs (see section XIII of this 
preamble for additional discussion on EPA's Health Risk Reduction and 
Cost Analysis [HRRCA]). Among other things, EPA evaluated which 
entities which would be affected by the rule, quantified costs using 
available data and statical models, and described unquantifiable costs. 
EPA also quantified benefits by estimating reduced cardiovascular 
events (e.g., heart attacks and strokes), developmental impacts to 
fetuses and infants, and reduced cases of kidney cancer. EPA has also 
quantified benefits by estimating reduced bladder cancer cases caused 
by reduced disinfection byproduct (DBP) formation in some systems that 
install treatment to meet the requirements of this rule. EPA has also 
developed a qualitative summary of benefits expected to result from the 
removal of regulated PFAS and additional co-removed PFAS contaminants.
    To help communities on the frontlines of PFAS contamination, the 
passage of the Infrastructure Investment and Jobs Act, also referred to 
as the Bipartisan Infrastructure Law (BIL), invests over $11.7 billion 
in the Drinking Water State Revolving Fund (SRF); $4 billion to the 
Drinking Water SRF for Emerging Contaminants; and $5 billion to Small, 
Underserved, and Disadvantaged Communities Grants. These funds will 
assist many disadvantaged communities, small systems, and others with 
the costs of installation of treatment when it might otherwise be cost-
challenging.
    Public participation and consultations with key stakeholders are 
critical in developing an implementable and public health protective 
rule. EPA has engaged with many stakeholders and consulted with 
entities such as the SAB, and the National Drinking Water Advisory 
Council (NDWAC) in developing this proposed rule (see section XV of 
this preamble on EPA's Statutory and Executive Order reviews). The 
Agency is requesting comment on this action, including this proposed 
NPDWR and MCLGs, and have identified specific areas where public input 
will be helpful for EPA in developing the final rule (see section XIV 
of this preamble on specific topics highlighted for public comment). In 
addition to seeking written input, EPA will be holding a public hearing 
on May 4th, 2023.

I. Public Participation

A. Written Comments

    Submit your comments, identified by Docket ID No. EPA-HQ-OW-2022-
0114, at https://www.regulations.gov (our preferred method), or the 
other methods identified in the ADDRESSES section. Once submitted, 
comments cannot be edited or removed from the docket. EPA may publish 
any comment received to its public docket. Do not submit to EPA's 
docket at https://www.regulations.gov any information you consider to 
be Confidential Business Information (CBI), Proprietary Business 
Information (PBI), or other information whose disclosure is restricted 
by statute. Multimedia submissions (audio, video, etc.) must be 
accompanied by a written comment. The written comment is considered the 
official comment and should include discussion of all points you wish 
to make. EPA will generally not consider comments or comment contents 
located outside of the primary submission (i.e., on the web, cloud, or 
other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the full EPA 
public comment policy; information about CBI, PBI, or multimedia 
submissions; and general guidance on making effective comments.

B. Participation in Virtual Public Hearing

    EPA will hold a public hearing on May 4th, 2023, to receive public 
comment and will present the proposed requirements of the draft NPDWR. 
The hearing will be held virtually from approximately 11 a.m. until 7 
p.m. eastern time. EPA will begin registering speakers for the hearing 
upon publication of this document in the Federal Register (FR). To 
attend and register to speak at the virtual hearing, please use the 
online registration form available at https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas. The last day to pre-register to speak 
at the hearing will be April 28, 2023. On May 3, 2023, EPA will post a 
general agenda for the hearing that will list pre-registered speakers 
in approximate order at: https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas. The number of online connections available for the 
hearing is limited and will be offered on a first- come, first-served 
basis. To submit visual aids to support your oral comment, please 
contact [email protected] for guidelines and instructions. Registration 
will remain open for the duration of the hearing itself for those 
wishing to provide oral comment during unscheduled testimony; however, 
early registration is strongly encouraged to ensure proper 
accommodations and adequate timing.
    EPA will make every effort to follow the schedule as closely as 
possible on the day of the hearing; however, please plan for the 
hearings to run either ahead of schedule or behind schedule. Please 
note that the public hearing may close early if all business is 
finished.
    EPA encourages commenters to provide EPA with a written copy of 
their oral testimony electronically by submitting it to the public 
docket at www.regulations.gov, Docket ID: EPA-HQ-OW-2022-0114. Oral 
comments will be time limited to allow for maximum participation, which 
may result in the full statement not being heard. Therefore, EPA also 
recommends submitting the text of your oral comments as written 
comments to the rulemaking docket. Any person not making an oral 
statement may also submit a written statement. Written statements and 
supporting information submitted during the comment period will be 
considered with the same weight as oral comments and supporting 
information presented at the public hearing.
    Please note that any updates made to any aspect of the hearing are 
posted online at https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas. While EPA expects the hearing to go forward as set 
forth above, please monitor our website or contact [email protected] to 
determine if there are any updates. EPA does not

[[Page 18641]]

intend to publish a document in the Federal Register announcing 
updates.
    If you require any accommodations such as language translation, 
captioning, or other special accommodations for the day of the hearing, 
please indicate this as a part of your registration and describe your 
needs by April 28, 2023. EPA may not be able to arrange accommodations 
without advance notice. Please contact [email protected] with any 
questions related to the public hearing.
    This proposed rule is organized as follows:

I. General Information
    A. What is EPA proposing?
    B. Does this action apply to me?
II. Background
    A. What are PFAS?
    B. Definitions
    C. Chemistry, Production and Uses
    D. Human Health Effects
    E. Statutory Authority
    F. Statutory Framework and PFAS Regulatory History
    G. Bipartisan Infrastructure Law
    H. EPA PFAS Strategic Roadmap
III. Preliminary Regulatory Determinations for Additional PFAS
    A. Agency Findings
    B. Statutory Criterion 1--Adverse Health Effects
    C. Statutory Criterion 2--Occurrence
    D. Statutory Criterion 3--Meaningful Opportunity
    E. EPA's Preliminary Regulatory Determination Summary for PFHxS, 
HFPO-DA, PFNA, and PFBS
    F. Request for Comment on EPA's Preliminary Regulatory 
Determination for PFHxS, HFPO-DA, PFNA, and PFBS
IV. Approaches to MCLG Derivation
    A. Approach to MCLG Derivation for Individual PFAS
    B. Approach to MCLG Derivation for a PFAS Mixture
V. Maximum Contaminant Level Goals
    A. PFOA
    B. PFOS
    C. PFAS Hazard Index: PFHxS, HFPO-DA, PFNA, and PFBS
VI. Maximum Contaminant Levels
    A. PFOA and PFOS
    B. PFAS Hazard Index: PFHxS, HFPO-DA, PFNA, and PFBS
    C. Reducing Public Health Risk by Protecting Against Dose 
Additive Noncancer Health Effects From PFAS
    D. Regulatory Alternatives
    E. MCL-Specific Requests for Comment
VII. Occurrence
    A. UCMR 3
    B. State Drinking Water Data
    C. Co-Occurrence
    D. Occurrence Relative to the Hazard Index
    E. Occurrence Model
    F. Combining State Data With Model Output To Estimate National 
Exceedance of Either MCLs or Hazard Index
VIII. Analytical Methods
    A. Practical Quantitation Levels (PQLs) for Regulated PFAS
IX. Monitoring and Compliance Requirements
    A. What are the monitoring requirements?
    B. How are PWS compliance and violations determined?
    C. Can systems use previously collected data to satisfy the 
initial monitoring requirement?
    D. Can systems composite samples?
    E. Can primacy agencies grant monitoring waivers?
    F. When must systems complete initial monitoring?
    G. What are the laboratory certification requirements?
X. Safe Drinking Water Act (SDWA) Right to Know Requirements
    A. What are the consumer confidence report requirements?
    B. What are the public notification (PN) requirements?
XI. Treatment Technologies
    A. What are the best available technologies?
    B. PFAS Co-Removal
    C. Management of Treatment Residuals
    D. What are Small System Compliance Technologies (SSCTs)?
XII. Rule Implementation and Enforcement
    A. What are the requirements for primacy?
    B. What are the primacy agency record keeping requirements?
    C. What are the primacy agency reporting requirements?
    D. Exemptions and Extensions
XIII. Health Risk Reduction and Cost Analysis
    A. Affected Entities and Major Data Sources Used To Develop the 
Baseline Water System Characterization
    B. Overview of the Cost-Benefit Model
    C. Method for Estimating Costs
    D. Method for Estimating Benefits
    E. Nonquantifiable Benefits of PFOA and PFOS Exposure Reduction
    F. Nonquantifiable Benefits of Removal of PFAS Included in the 
Proposed Regulation and Co-Removed PFAS
    G. Benefits Resulting From Disinfection By-Product Co-Removal
    H. Comparison of Costs and Benefits
    I. Quantified Uncertainties in the Economic Analysis
    J. Cost-Benefit Determination
XIV. Request for Comment on Proposed Rule
    Section III--Regulatory Determinations for Additional PFAS
    Section V--Maximum Contaminant Level Goals
    Section VI--Maximum Contaminant Levels
    Section VII--Occurrence
    Section IX--Monitoring and Compliance Requirements
    Section X--Safe Drinking Water Right to Know
    Section XI--Treatment Technologies
    Section XII--Rule Implementation and Enforcement
    Section XIII--HRRCA
    Section XV--Statutory and Executive Order Reviews
XV. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563 Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act of 1995
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Consultations With the Science Advisory Board, National 
Drinking Water Advisory Council, and the Secretary of Health and 
Human Services
XVI. References

I. General Information

A. What is EPA proposing?

    EPA is proposing for public comment a drinking water regulation 
that includes six PFAS. EPA is proposing to establish MCLGs and an 
NPDWR for these PFAS in public drinking water supplies. EPA proposes 
MCLGs for PFOA and PFOS at zero (0) and an enforceable MCL for PFOA and 
PFOS in drinking water at 4.0 ppt. Additionally, the Agency is 
requesting comment on a preliminary determination to regulate 
additional PFAS to include PFHxS, HFPO-DA \1\ (also known as and 
referred to as ``GenX Chemicals'' in this proposal), PFNA, and PFBS. 
Concurrent with this preliminary determination, EPA is proposing an HI 
of 1.0 as the MCLG and enforceable MCL to address individual and 
mixtures of these four contaminants where they occur in drinking water. 
EPA is proposing to calculate the HI as the sum total of component PFAS 
HQs, calculated by dividing the measured component PFAS concentration 
in water by the relevant HBWC. In this proposal, EPA is using HBWCs of 
9.0 ppt for PFHxS, 10.0 ppt

[[Page 18642]]

for HFPO-DA; 10.0 ppt for PFNA; and 2000 ppt for PFBS. The proposed 
approach to calculating the HI for this set of four PFAS compounds is 
designed to be protective against all adverse effects, not a single 
outcome/effect, and is a health protective decision aid for use in 
determining the level at which there are no adverse effects on the 
health of persons with an adequate margin of safety, thus is 
appropriate for MCLG development.
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    \1\ PFAS may exist in multiple forms, such as acids and organic 
or metal salts. Each of these forms may be listed as a separate 
entry in certain databases and have separate Chemical Abstract 
Service (CAS) Registry numbers. However, PFAS are expected to 
dissociate in water to their anionic form. For example, the term 
``GenX Chemicals'' acknowledges the ``acid'' and ``ammonium salt'' 
forms of HFPO-DA as two different chemicals. In water, though, these 
chemicals dissociate and therefore the resulting anion appears as a 
single analyte for the purposes of detection and quantitation. 
Please see ``definitions'' for more information. EPA notes that the 
chemical HFPO-DA is used in a processing aid technology developed by 
DuPont to make fluoropolymers without using PFOA. The chemicals 
associated with this process are commonly known as GenX Chemicals 
and the term is often used interchangeably for HFPO-DA along with 
its ammonium salt (USEPA, 2021b).
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    The requirements in this proposal that apply to (1) PFOA, (2) PFOS, 
and (3) PFHxS, HFPO-DA, PFNA, and PFBS and their mixtures are distinct 
and capable of operating independently.

B. Does this action apply to me?

    The preliminary regulatory determination to establish drinking 
water regulations for certain PFAS and their mixtures and the proposed 
regulation are proposals for public comment and are not requirements or 
regulations. Instead, this action notifies interested parties of the 
availability of information supporting the preliminary regulatory 
determinations for four PFAS and their mixtures, the development of the 
NPDWR for six PFAS, and proposed rule requirements for public comment. 
If EPA proceeds to a final regulatory determination and final 
regulation, once promulgated, this action will potentially affect the 
following:

------------------------------------------------------------------------
                                        Examples of potentially affected
               Category                             entities
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Public water systems \2\.............  Community water systems (CWSs);
                                        Non-transient, non-community
                                        water systems (NTNCWSs).
State and tribal agencies............  Agencies responsible for drinking
                                        water regulatory development and
                                        enforcement.
------------------------------------------------------------------------

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities that could be affected by this 
action once promulgated. To determine whether a facility or activities 
could be affected by this action, this proposed rule should be 
carefully examined. Questions regarding the applicability of this 
action to a particular entity may be directed to the person listed in 
the FOR FURTHER INFORMATION CONTACT section.
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    \2\ The term ``public water system'' means a system for the 
provision to the public of water for human consumption through pipes 
or other constructed conveyances, if such system has at least 
fifteen service connections or regularly serves at least twenty-five 
individuals. Such term includes (i) any collection, treatment, 
storage, and distribution facilities under control of the operator 
of such system and used primarily in connection with such system, 
and (ii) any collection or pretreatment storage facilities not under 
such control which are used primarily in connection with such 
system.
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II. Background

A. What are PFAS?

    PFAS are a large class of specialized synthetic chemicals that have 
been in use since the 1940s (USEPA, 2018a). This proposed regulation 
only applies to certain PFAS: PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and 
PFBS. People may potentially be exposed to these PFAS through certain 
consumer products such as textiles (e.g., seat covers, sail covers, 
weather protection (Janousek et al., 2019)), leather shoes as well as 
shoe polish/wax (Norden, 2013; Borg and Ivarsson, 2017), along with 
cooking/baking wares (Blom and Hanssen 2015; KEMI, 2015; Gl[uuml]ge et 
al., 2020), occupational contact, and/or by consuming food and drinking 
water that contain PFAS. Due to their widespread use, physicochemical 
properties, and prolonged persistence, many PFAS co-occur in exposure 
media (e.g., air, water, ice, sediment), and bioaccumulate in tissues 
and blood of aquatic as well as terrestrial organisms, including humans 
(Domingo and Nadal, 2019; Fromme et al., 2009). Industrial workers who 
are involved in manufacturing or processing fluoropolymers, or people 
who live or recreate near fluoropolymer facilities, may encounter 
greater exposures; particularly of PFOA, PFNA, as well as HFPO-DA. 
Firefighters as well as people who live near airfields or military 
bases may have especially higher exposure to PFHxS and PFBS due to the 
use of aqueous foam forming film as a fire suppressant. Pregnant and 
lactating women, as well as children, may be more sensitive to the 
harmful effects of certain PFAS, for example, PFOA, PFOS, PFNA, and 
PFBS. For example, studies indicate that PFOA and PFOS exposure above 
certain levels may result in adverse health effects, including 
developmental effects to fetuses during pregnancy or to breast- or 
formula-fed infants, cancer, immunological effects, among others 
(USEPA, 2023b; USEPA, 2023c). Other PFAS are also documented to result 
in a range of adverse health effects (USEPA, 2021a; USEPA, 2021b; 
ATSDR, 2021; NASEM 2022).
    Although most United States production of PFOS, PFOA, and PFNA, 
along with other long-chain PFAS, was phased out and then generally 
replaced by production of PFBS, PFHxS, HFPO-DA and other PFAS, EPA is 
aware of ongoing use of PFOS, PFOA, PFNA, and other long-chain PFAS. 
Domestic production and import of PFOA has been phased out in the 
United States by the companies participating in the 2010/2015 PFOA 
Stewardship Program. Small quantities of PFOA may be produced, 
imported, and used by companies not participating in the PFOA 
Stewardship Program and some uses of PFOS are ongoing (see 40 Code of 
Federal Regulations (CFR) Sec.  721.9582). EPA is also aware of ongoing 
use of the chemicals available from existing stocks or newly introduced 
via imports. Additionally, the environmental persistence of these 
chemicals and formation as degradation products from other compounds 
may still contribute to their release in the environment.

B. Definitions

    The six PFAS proposed for regulation and their relevant Chemical 
Abstract Service (CAS) registry numbers are:

 PFOA (C8F15CO2-; CAS: 45285-51-6)
 PFOS (C8F17SO3-; CAS: 45298-90-6)
 PFHxS (C6F13SO3-; CAS: 108427-53-8)
 HFPO-DA (C6F11O3-; CAS: 122499-17-6)
 PFNA (C9F17CO2-; CAS: 72007-68-2)
 PFBS (C4F9SO3-; CAS: 45187-15-3)

    These PFAS may exist in multiple forms, such as isomers or 
associated salts and each form may have a separate CAS Registry number 
or no CAS at all. Additionally, these compounds have various names 
under different classification systems. However, at environmentally 
relevant pHs, these PFAS are expected to dissociate in water to their 
anionic (negatively charged) forms. For instance, International Union 
of Pure and Applied Chemistry substance 2,3,3,3-tetrafluoro-2-
(heptafluoropropoxy) propanoate (CAS: 122499-17-6), also known as HFPO-
DA, is an anionic molecule which has an ammonium salt (CAS: 62037-80-
3), a conjugate acid (CAS: 13252-13-6), a potassium salt (CAS: 67118-
55-2), and an acyl fluoride precursor (CAS: 2062-98-8), among other 
variations. At environmentally relevant pHs these all dissociate into 
the propanoate/anion form (CAS: 122499-17-6). Each PFAS listed has 
multiple variants with differing chemical connectivity but the same 
molecular composition; these are known as

[[Page 18643]]

isomers. Commonly, the isomeric composition of PFAS is categorized as 
`linear,' consisting of an unbranched alkyl chain, or `branched,' 
encompassing a potentially diverse group of molecules including at 
least one, but potentially more offshoots from the linear molecule. 
While broadly similar, isomeric molecules may have differences in 
chemical properties. The proposed regulation covers all salts, isomers 
and derivatives of the chemicals listed, including derivatives other 
than the anionic form which might be created or identified.

C. Chemistry, Production and Uses

    PFAS are most commonly and widely used to make products resistant 
to water, heat, and stains. As a result, they are found in industrial 
and consumer products such as clothing, food packaging, cookware, 
cosmetics, carpeting, and fire-fighting foam (AAAS, 2020). Facilities 
associated with PFAS releases into the air, soil, and water include 
those for manufacturing, chemical as well as well as product production 
and military installations (USEPA, 2016a; USEPA, 2016b).
    The chemical structures of some PFAS cause them to repel water as 
well as oil, remain chemically and thermally stable, and exhibit 
surfactant properties. PFAS have strong, stable carbon-fluorine (C-F) 
bonds, making them resistant to hydrolysis, photolysis, microbial 
degradation, and metabolism (Ahrens, 2011; Beach et al., 2006; Buck et 
al., 2011). These properties are what make PFAS useful for commercial 
and industrial applications and purposes. However, these are also what 
make some PFAS extremely persistent in the human body and the 
environment (Calafat et al., 2007, 2019).
    PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS belong to a subset of 
PFAS known as perfluoroalkyl acids (PFAAs), all of which consist of a 
perfluorinated alkyl chain connected to an acidic headgroup. Humans are 
exposed to PFAS due to wide-ranging commercial and industrial 
applications along with long range migration from sources. The 
structure of these PFAS contribute to their persistence in the 
environment as well as their resistance to chemical, biological, and 
physical degradation processes.
    PFOA and PFOS are two of the most widely studied and longest used 
PFAS. These two compounds have been detected in up to 98 percent of 
human serum samples taken in biomonitoring studies that are 
representative of the U.S. general population; however, since PFOA and 
PFOS have been voluntarily phased out in the U.S., serum concentrations 
have been declining (CDC, 2019). The sole U.S. manufacturer of PFOS 
agreed to a voluntary phaseout in 2000, and the last reported 
production was in 2002 (USEPA, 2000b; USEPA, 2018b; USEPA, 2021c). PFOS 
has been used as a surfactant or emulsifier in firefighting foam, 
circuit board etching acids, alkaline cleaners, floor polish, and as a 
pesticide active ingredient for insect bait traps (HSBD, 2016). PFOA 
has been used as an emulsifier and surfactant in fluoropolymers (such 
as in the manufacturing of non-stick products like Teflon(copyright)), 
firefighting foams, cosmetics, grease and lubricants, paints, polishes, 
and adhesives (HSBD, 2016).
    PFNA was historically the second most used surfactant for emulsion 
polymerization (after PFOA) which was its main use (Buck et al., 2012). 
Fluorinated surfactants improve the physical properties of the polymer 
as well as improving the polymerization rate (Gl[uuml]ge et al., 2020). 
Fluoropolymers are used in many applications because of their unique 
physical properties such as resistance to high and low temperatures, 
resistance to chemical and environmental degradation, and nonstick 
characteristics. Fluoropolymers also have dielectric and fire-resistant 
properties that have a wide range of electrical and electronic 
applications, including architecture, fabrics, automotive uses, cabling 
materials, electronics, pharmaceutical and biotech manufacturing, and 
semiconductor manufacturing (Gardiner, 2014). Although drying processes 
can release the surfactants when manufacturing is complete, surfactant 
residues remain in the finished products (KEMI, 2015). Legacy stocks 
may still be used and products containing PFNA may still be produced 
internationally and imported to the U.S. (ATSDR, 2021).
    The voluntary phase out caused a shift to alternatives such as per- 
and polyfluoroalkyl ether carboxylic acids (PFECAs). The chemical HFPO-
DA is the most prevalent of these and is used in a processing aid 
technology developed by DuPont to make fluoropolymers without using 
PFOA. The chemicals associated with this process are commonly known as 
GenX Chemicals and the term is often used interchangeably for HFPO-DA 
along with its ammonium salt (USEPA, 2021b). The most common use for 
GenX Chemicals is for emulsion polymerization.
    Another alternative, PFBS, is mainly used as a water and stain 
repellent protection for leather, textiles, carpets, and porous hard 
surfaces, representing 25-50 tons/year of PFBS in mixtures (Norwegian 
Environment Agency, 2017). PFBS and related chemicals are also used in 
curatives for fluoroelastomers (Gl[uuml]ge et al., 2020). The curatives 
are used for manufacturing O-rings, seals, linings, protective 
clothing, cooking wares, and flame retardants (Norwegian Environment 
Agency, 2017; Blom and Hanssen, 2015).
    PFHxS is used in stain-resistant fabrics, fire-fighting foams, 
flame retardants, insecticides, and as a surfactant in industrial 
processes (Gl[uuml]ge et al., 2020). Additionally, particle 
accelerators including the Delphi Detector at Stanford University rely 
on liquid PFHxS (Gl[uuml]ge et al., 2020). PFHxS production, along with 
PFOS, was phased out in 2002 nationwide however, production continues 
in other countries and products containing PFHxS may be imported into 
the U.S. (USEPA, 2000c). Legacy stocks may also still be used.

D. Human Health Effects

    The publicly available landscape of human epidemiological and 
experimental animal-based exposure-effect data from repeat-dose studies 
across PFAS derive primarily from linear carboxylic and sulfonic acid 
species such as PFOA, PFOS, PFHxS, PFNA, and PFBS (ATSDR, 2021). Many 
other PFAS have preliminary human health effects data (Mahoney et al., 
2022) and some PFAS, such as PFBS and HFPO-DA, have sufficient data 
that has allowed EPA to derive toxicity values and publish toxicity 
assessments (USEPA, 2021a; USEPA, 2021b). The adverse health effects 
observed following oral exposure to such PFAS are significant and 
diverse and include (but are not limited to): cancer and effects on the 
liver (e.g., liver cell death), growth and development (e.g., low birth 
weight), hormone levels, kidney, immune system, lipid levels (e.g., 
high cholesterol), the nervous system, and reproduction. Please see 
sections III.B, IV, and V of this preamble for additional discussion on 
health considerations for the six PFAS EPA is proposing to regulate in 
this document.

E. Statutory Authority

    Section 1412(b)(1)(A) of SDWA requires EPA to establish NPDWRs for 
a contaminant where the Administrator determines that the contaminant: 
(1) may have an adverse effect on the health of persons; (2) is known 
to occur or there is a substantial likelihood that the contaminant will 
occur in PWSs with a frequency and at levels of public health concern; 
and (3) where in the sole

[[Page 18644]]

judgment of the Administrator, regulation of such contaminant presents 
a meaningful opportunity for health risk reduction for persons served 
by PWSs.

F. Statutory Framework and PFAS Regulatory History

    Section 1412(b)(1)(B)(i) of SDWA requires EPA to publish a 
Contaminant Candidate List (CCL) every five years. The CCL is a list of 
contaminants that are known or anticipated to occur in PWSs and are not 
currently subject to any proposed or promulgated NPDWRs. EPA uses the 
CCL to identify priority contaminants for regulatory decision-making 
(i.e., regulatory determinations), and information collection. 
Contaminants listed on the CCL may require future regulation under 
SDWA. EPA included PFOA and PFOS on the third and fourth CCLs published 
in 2009 (USEPA, 2009a) and 2016 (USEPA, 2016c). The Agency published 
the fifth CCL (CCL 5) earlier this year and it includes PFAS as a 
chemical group (USEPA, 2022b).
    EPA collects data on the CCL contaminants to better understand 
their potential health effects and to determine the levels at which 
they occur in PWSs. SDWA 1412(b)(1)(B)(ii) requires that, every five 
years and after considering public comments on a ``preliminary'' 
regulatory determination, EPA issue a final regulatory determination to 
regulate or not regulate at least five contaminants on each CCL. In 
addition, Section 1412(b)(1)(B)(ii)(III) authorizes EPA to make a 
determination to regulate a contaminant not listed on the CCL so long 
as the contaminant meets the three statutory criteria based on 
available public health information. SDWA 1412(b)(1)(B)(iii) requires 
that ``each document setting forth the determination for a contaminant 
under clause (ii) shall be available for public comment at such time as 
the determination is published.'' To implement these requirements, EPA 
issues preliminary regulatory determinations subject to public comment 
and then issues a final regulatory determination after consideration of 
public comment. For any contaminant that EPA determines meets the 
criteria for regulation under SDWA 1412(b)(1)(A), Section 1412(b)(1)(E) 
requires that EPA propose a NPDWR within two years and promulgate a 
final regulation within 18 months of the proposal (which may be 
extended by 9 additional months).
    EPA implements a monitoring program for unregulated contaminants 
under SDWA 1445(a)(2) which requires that once every five years, EPA 
issue a list of priority unregulated contaminants to be monitored by 
PWSs. This monitoring is implemented through the Unregulated 
Contaminant Monitoring Rule (UCMR), which collects data from CWSs and 
NTNCWSs. The first four UCMRs collected data from a census of large 
water systems (serving more than 10,000 people) and from a 
statistically representative sample of small water systems (serving 
10,000 or fewer people). Water system monitoring data for six PFAS were 
collected during the third UCMR (UCMR3) between 2013 to 2015. The fifth 
UCMR (UCMR5), published December 2021, requires sample collection and 
analysis for 29 PFAS to occur between 2023 and 2025 using analytical 
methods developed by EPA and consensus organizations. Section 2021 of 
America's Water Infrastructure Act of 2018 (AWIA) (Pub. L. 115-270) 
amended SDWA and specifies that, subject to the availability of EPA 
appropriations for such purpose and sufficient laboratory capacity, EPA 
must require all PWSs serving between 3,300 and 10,000 people to 
monitor and ensure that a nationally representative sample of systems 
serving fewer than 3,300 people monitor for the contaminants in UCMR 5 
and future UCMR cycles. All large water systems continue to be required 
to participate in the UCMR program. Section VII of this preamble 
provides additional discussion on PFAS occurrence. Additionally, while 
the UCMR 5 information will not be available to inform this proposal, 
EPA is proposing to consider the UCMR 5 data to support implementation 
of monitoring requirements under the proposed rule. Section IX of this 
preamble further discusses monitoring and compliance requirements.
    After careful consideration of public comments, EPA issued final 
regulatory determinations for contaminants on the fourth CCL in March 
of 2021 (USEPA, 2021d) which included determinations to regulate two 
contaminants, PFOA and PFOS, in drinking water. EPA found that PFOA and 
PFOS may have an adverse effect on the health of persons; that these 
contaminants are known to occur, or that there is a substantial 
likelihood that they will occur, in PWSs with a frequency and at levels 
that present a public health concern; and that regulation of PFOA and 
PFOS presents a meaningful opportunity for health risk reduction for 
persons served by PWSs. As discussed in the final Regulatory 
Determinations 4 Notice for CCL 4 contaminants (USEPA, 2021d) and EPA's 
PFAS Strategic Roadmap (USEPA, 2022c), the Agency has also evaluated 
additional PFAS chemicals for regulatory consideration as supported by 
the best available science. The Agency preliminarily finds that 
additional PFAS compounds also meet SDWA criteria for regulation. EPA's 
preliminary regulatory determination for these additional PFAS is 
discussed in section III of this preamble.
    Section 1412(b)(1)(E) provides that the Administrator may publish a 
proposed drinking water regulation concurrent ``with a determination to 
regulate.'' This provision authorizes a more expedited process by 
allowing EPA to make concurrent the regulatory determination and 
rulemaking processes. As a result, EPA interprets the reference to 
``determination to regulate'' in Section 1412(b)(1)(E) as referring to 
the regulatory process in 1412(b)(1)(B)(ii) that begins with a 
preliminary determination. Under this interpretation, Section 
1412(b)(1)(E) authorizes EPA to issue a preliminary determination to 
regulate a contaminant and a proposed NPDWR addressing that contaminant 
concurrently and request public comment at the same time. This allows 
EPA to act efficiently to issue a final determination to regulate 
concurrently with a final NPDWR to avoid delays to address contaminants 
that meet the statutory criteria. As a result, this proposal contains 
both a preliminary determination to regulate four PFAS contaminants and 
proposed regulations for those contaminants as well as the two PFAS 
contaminants (PFOA and PFOS) for which EPA has already issued a final 
Regulatory Determination. EPA developed a proposed MCLG and a proposed 
NPDWR for six PFAS compounds pursuant to the requirements under section 
1412(b)(1)(B) of SDWA. The proposed MCLGs and proposed NPDWR are 
discussed in more detail below.

G. Bipartisan Infrastructure Law

    The Agency notes that the passage of the Infrastructure Investment 
and Jobs Act, also referred to as the BIL, invests over $11.7 billion 
in the Drinking Water SRF; $4 billion to the Drinking Water SRF for 
Emerging Contaminants; and $5 billion to Small, Underserved, and 
Disadvantaged Communities Grants. These funds will assist many 
disadvantaged communities, small systems, and others with the costs of 
installation of treatment when it might otherwise be cost-challenging. 
These funds can also be used to address emerging contaminants like PFAS 
in drinking water through actions such as technical assistance, water 
quality testing, and contractor training, which will allow communities 
supplemental funding to meet their obligations under

[[Page 18645]]

this proposed regulation and help ensure protection from PFAS 
contamination of drinking water.

H. EPA PFAS Strategic Roadmap

    In October 2021, EPA published the PFAS Strategic Roadmap that 
outlined the Agency's plan to ``further the science and research, to 
restrict these dangerous chemicals from getting into the environment, 
and to immediately move to remediate the problem in communities across 
the country'' (USEPA, 2022c). Described in the Roadmap are key 
commitments the Agency made toward addressing these contaminants in the 
environment. With this proposal, EPA is delivering on a key commitment 
in the Roadmap to ``establish a National Primary Drinking Water 
Regulation'' for proposal and is working toward promulgating the final 
NPDWR in Fall of 2023.

III. Preliminary Regulatory Determinations for Additional PFAS

    Since 2021 when EPA determined to regulate two PFAS contaminants, 
PFOA and PFOS, EPA has evaluated additional PFAS compounds for 
regulatory consideration and has preliminarily determined that an 
additional four individual PFAS and mixtures of these PFAS meet SDWA 
criteria for regulation. Section 1401(6) defines the term 
``contaminant'' to mean ``any physical, chemical or biological or 
radiological substance or matter in water.'' A mixture of two or more 
``contaminants'' qualifies as a ``contaminant'' because the mixture 
itself is ``any physical, chemical or biological or radiological 
substance or matter in water.'' (emphasis added). Therefore, pursuant 
to the provisions outlined in Section 1412(b)(1)(A) and 1412(b)(1)(B) 
of SDWA, the Agency is making a preliminary determination to regulate 
PFHxS, HFPO-DA, PFNA, and PFBS in drinking water, and mixtures of these 
PFAS contaminants. PFHxS, HFPO-DA, PFNA, and PFBS, and mixtures of 
these PFAS, are known to cause adverse human health effects; there is 
substantial likelihood that they will occur and co-occur in PWSs with a 
frequency and at levels of public health concern, particularly when 
considering them in a mixture; and in the sole judgment of the 
Administrator, regulation of PFHxS, HFPO-DA, PFNA, PFBS and mixtures of 
these PFAS present a meaningful opportunity for health risk reductions 
for people served by PWSs. This section describes the best available 
science and information used by the Agency to support this preliminary 
Regulatory Determination. The proposed MCLG and enforceable standard 
for these four PFAS and mixtures of these PFAS are discussed further in 
sections V to VI of this preamble.

A. Agency Findings

    To support the Agency's preliminary Regulatory Determination, EPA 
examined health effects information from available peer reviewed human 
health assessments as well as drinking water monitoring data collected 
as part of the UCMR 3 and state-led monitoring efforts. EPA finds that 
oral exposure to PFHxS, HFPO-DA, PFNA, and PFBS may individually and in 
a mixture each result in adverse health effects, including disrupting 
multiple biological pathways that result in common adverse effects on 
several biological systems including the endocrine, cardiovascular, 
developmental, immune, and hepatic systems (USEPA, 2023a). PFAS, 
including PFHxS, HFPO-DA, PFNA, and PFBS and their mixtures are 
anticipated to affect common target organs, tissues, or systems to 
produce dose-additive effects from co-exposures. Additionally, based on 
the Agency's evaluation of the best-available science, EPA finds that 
PFHxS, HFPO-DA, PFNA, and PFBS each have a substantial likelihood to 
occur in finished drinking water and that these PFAS are also likely to 
co-occur as mixtures and result in increased exposure above levels of 
health concern. Therefore, given this high occurrence and co-occurrence 
likelihood and that adverse health effects arise as a result of both 
these PFAS individually and as mixtures, the Agency is preliminarily 
determining that PFHxS, HFPO-DA, PFNA, and PFBS and their mixtures may 
have adverse human health effects; there is a substantial likelihood 
that PFHxS, HFPO-DA, PFNA, PFBS and mixtures of these PFAS, will occur 
and co-occur in PWSs with a frequency and at levels of public health 
concern; and in the sole judgment of the Administrator, regulation of 
PFHxS, HFPO-DA, PFNA, and PFBS, and their mixtures, presents a 
meaningful opportunity for health risk reductions for persons served by 
PWSs.

B. Statutory Criterion 1--Adverse Health Effects

    The Agency finds that PFHxS, HFPO-DA, PFNA, PFBS and their mixtures 
may have an adverse effect on the health of persons. Discussion related 
to health effects for each of the four PFAS is below. For this 
proposal, the Agency is developing HBWCs for PFHxS, HFPO-DA, PFNA and 
PFBS, defined as a level protective of health effects over a lifetime 
of exposure, including sensitive populations and life stages. Each of 
the four HBWCs is used in this proposal to evaluate occurrence data and 
the likelihood of potential risk to human health to justify the 
agency's preliminary regulatory determinations for PFHxS, HFPO-DA, PFNA 
and PFBS. The chemical-specific HBWCs are also used to assess the 
potential human health risk associated with mixtures of the four PFAS 
in drinking water using the HI approach. Additional details on the HBWC 
for PFHxS, HFPO-DA, PFNA and PFBS are found in section IV of this 
preamble. More information supporting EPA's preliminary regulatory 
determination relating to adverse health effects for these PFAS and the 
HI approach for mixtures is available in section V of this preamble.
1. PFHxS
    Toxicity studies of oral PFHxS exposure in animals have reported 
adverse health effects on the liver, thyroid, and development (ATSDR, 
2021). EPA has not yet classified the carcinogenicity of PFHxS. For a 
detailed discussion on adverse effects of oral exposure to PFHxS, 
please see ATSDR (2021) and USEPA (2023a).
    The HBWC for PFHxS is derived using a chronic reference value based 
on an Agency For Toxic Substances And Disease Registry (ATSDR) 
intermediate-duration oral Minimal Risk Level, which was based on 
thyroid effects seen in male rats after oral PFHxS exposure (ATSDR, 
2021). The most sensitive non-cancer effect observed was thyroid 
follicular epithelial hypertrophy/hyperplasia in parental male rats 
exposed to PFHxS for 42-44 days, identified in the critical 
developmental toxicity study selected by ATSDR (no observed adverse 
effect level (NOAEL) of 1 mg/kg/day) (Butenhoff et al., 2009; ATSDR, 
2021). To derive the intermediate-duration Minimal Risk Level for 
PFHxS, ATSDR calculated a human equivalent dose (HED) of 0.0047 mg/kg/
day from the NOAEL of 1 mg/kg/day identified in the principal study. 
Then, ATSDR applied a total uncertainty factor (UF)/modifying factor 
(MF) of 300X (10X UF for intraspecies variability, 3X UF for 
interspecies differences, and a 10X MF for database deficiencies) to 
yield an intermediate-duration oral Minimal Risk Level of 0.00002 mg/
kg/day (ATSDR, 2021). Per Agency guidance (USEPA, 2002), to calculate 
the HBWC, EPA applied an additional UF of 10 to adjust for subchronic-
to-chronic duration (UFS) because the effect was not in a 
developmental life stage (i.e., thyroid follicular epithelial 
hypertrophy/hyperplasia in parental male rats). The

[[Page 18646]]

resulting chronic reference value was 0.000002 mg/kg/day.
    No sensitive population or life stage was identified for 
bodyweight-adjusted drinking water intake (DWI-BW) selection for PFHxS 
because the critical effect on which the ATSDR Minimal Risk Level was 
based (thyroid alterations) was observed in adult male rats. Since this 
exposure life stage does not correspond to a sensitive population or 
life stage, a DWI-BW for adults within the general population (0.034 L/
kg/day; 90th percentile direct and indirect consumption of community 
water, consumer-only two-day average, adults 21 years and older) was 
selected for HBWC derivation (USEPA, 2019a).
    EPA calculated the HBWC for PFHxS using a relative source 
contribution (RSC) of 0.20. This means that 20% of the exposure--equal 
to the chronic reference value--is allocated to drinking water, and the 
remaining 80% is attributed to all other potential exposure sources. 
This was based on EPA's determination that the available data on PFHxS 
exposure routes and sources did not permit quantitative 
characterization of PFHxS exposure. In such cases, an RSC of 0.20 is 
typically used (USEPA, 2000c). See U.S.EPA (2023a) for complete details 
on the RSC determination for PFHxS.
    As further described in USEPA (2023a) and section V of this 
preamble below, the HBWC for PFHxS is calculated to be 9.0 ppt. This 
HBWC of 9.0 ppt is also used as the health reference level (HRL) for 
this preliminary regulatory determination.
2. HFPO-DA
    EPA's 2021 Human Health Toxicity Assessment for GenX Chemicals 
describes potential health effects associated with oral exposure to 
HFPO-DA (USEPA, 2021b). Toxicity studies in animals indicate that 
exposures to HFPO-DA may result in adverse health effects, including 
liver and kidney toxicity and immune system, hematological, 
reproductive, and developmental effects (USEPA, 2021b). There is 
Suggestive Evidence of Carcinogenic Potential of oral exposure to HFPO-
DA in humans, but the available data are insufficient to derive a 
cancer risk concentration in water for HFPO-DA. For a detailed 
discussion on adverse effects of oral exposure to HFPO-DA, please see 
USEPA (2021b).
    EPA's noncancer HBWC for HFPO-DA is derived from a reference dose 
(RfD) that is based on liver effects observed following oral exposure 
of mice to HFPO-DA (USEPA, 2021b). The most sensitive noncancer effect 
observed was a constellation of liver lesions in parental female mice 
exposed to HFPO-DA by gavage for 53-64 days, identified in the critical 
reproductive/developmental toxicity study selected by EPA (NOAEL of 0.1 
mg/kg/day) (DuPont, 2010; USEPA, 2021b). To develop the chronic RfD for 
HFPO-DA, EPA derived an HED of 0.01 mg/kg/day from the NOAEL of 0.1 mg/
kg/day identified in the principal study. EPA then applied a composite 
UF of 3,000 (i.e., 10X for intraspecies variability, 3X for 
interspecies differences, 10X for extrapolation from a subchronic to a 
chronic dosing duration, and 10X for database deficiencies) to yield 
the chronic RfD (USEPA, 2021b).
    To select an appropriate DWI-BW for use in derivation of the 
noncancer HBWC values for HFPO-DA, EPA considered the HFPO-DA exposure 
interval used in the oral reproductive/developmental toxicity study in 
mice that was the basis for chronic RfD derivation (the critical 
study). In this study, parental female mice were dosed from pre-mating 
through lactation, corresponding to three potentially sensitive human 
adult life stages that may represent critical windows of exposure for 
HFPO-DA: women of childbearing age, pregnant women, and lactating women 
(Table 3-63 in USEPA, 2019a). Of these three, the DWI-BW for lactating 
women (0.0469 L/kg/day) is anticipated to be protective of the other 
two sensitive life stages. Therefore, EPA used the DWI-BW for lactating 
women to calculate the HBWC for the proposed regulation, which is also 
used for the HRL for the preliminary regulatory determination.
    The HBWC value for HFPO-DA was calculated using an RSC of 0.20. 
This means that 20% of the exposure--equal to the RfD--is allocated to 
drinking water, and the remaining 80% is attributed to all other 
potential exposure sources (USEPA, 2022d). Selection of this RSC was 
based on EPA's determination that the available exposure data for HFPO-
DA did not enable a quantitative characterization of relative HFPO-DA 
exposure sources and routes. In such cases, an RSC of 0.20 is typically 
used (USEPA, 2000c).
    As further described in USEPA (2023a) and USEPA (2022d), the HBWC 
for HFPO-DA is calculated to be 10.0 ppt. This value is consistent with 
EPA's 2022 drinking water health advisory for HFPO-DA (USEPA, 2022d), 
but was derived from EPA's 2021 Human Health Toxicity Assessment for 
HFPO-DA (USEPA, 2021b). This HBWC of 10 ppt is also used as the HRL for 
this preliminary Regulatory Determination for HFPO-DA.
3. PFNA
    Animal toxicity studies have reported adverse health effects, 
specifically on development, reproduction, immune function, and the 
liver, after oral exposure to PFNA (ATSDR, 2021). EPA has not yet 
classified the carcinogenicity of PFNA. For a detailed discussion on 
adverse effects of oral exposure to PFNA, please see ATSDR (2021) and 
USEPA (2023a).
    The HBWC for PFNA is derived using a chronic reference value based 
on an ATSDR intermediate-duration oral Minimal Risk Level, which was 
based on developmental effects seen in mice after oral PFHxS exposure 
(ATSDR, 2021). The most sensitive non-cancer effects were decreased 
body weight (BW) gain and developmental delays (i.e., delayed eye 
opening, preputial separation, and vaginal opening) in mice born to 
mothers that were gavaged with PFNA from gestational days (GD) 1-17, 
with continued exposure through lactation and monitoring until 
postnatal day (PND) 287, identified in the critical developmental 
toxicity study selected by ATSDR (NOAEL of 1 mg/kg/day) (Das et al., 
2015; ATSDR, 2021). To derive the intermediate-duration Minimal Risk 
Level, ATSDR calculated an HED of 0.001 mg/kg/day from the NOAEL of 1 
mg/kg/day identified in the principal study. Then, ATSDR applied a 
total UF/MF of 300X (total UF of 30X and a MF of 10X for database 
deficiencies) to yield an intermediate-duration Minimal Risk Level of 
0.000003 mg/kg/day. EPA did not apply an additional UF to adjust for 
subchronic-to-chronic duration (i.e., UFS) to calculate the 
chronic reference value because the critical effects were observed 
during a developmental life stage (USEPA, 2002). The chronic reference 
value of 0.000003 mg/kg/day was used to derive the HBWC for PFNA.
    Based on the life stages of exposure in the principal study from 
which the intermediate-duration Minimal Risk Level was derived (i.e., 
during gestation and lactation), EPA identified three potentially 
sensitive life stages that may represent critical windows of exposure 
for PFNA: women of childbearing age (13 to < 50 years), pregnant women, 
and lactating women (Table 3-63 in USEPA, 2019a). The DWI-BW for 
lactating women (0.0469 L/kg/day; 90th percentile direct and indirect 
consumption of community water, consumer-only two-day average) was 
selected to calculate the HBWC for PFNA because it is the highest of 
the three DWI-BWs and is anticipated to be protective of the other two 
sensitive life stages.

[[Page 18647]]

    EPA calculated the HBWC for PFNA using an RSC of 0.20. This means 
that 20% of the exposure--equal to the chronic reference value--is 
allocated to drinking water, and the remaining 80% is attributed to all 
other potential exposure sources. This was based on EPA's determination 
that the available data on PFNA exposure routes and sources did not 
permit quantitative characterization of PFNA exposure. In such cases, 
an RSC of 0.20 is typically used (USEPA, 2000c). See USEPA (2023a) for 
complete details on the RSC determination for PFNA.
    As further described in USEPA (2023a), the HBWC for PFNA is 
calculated to be 100 ppt. This HBWC of 10.0 ppt is also used as the HRL 
for this preliminary Regulatory Determination for PFNA.
4. PFBS
    EPA's 2021 PFBS Toxicity Assessment describe potential health 
effects associated with oral PFBS exposure (USEPA, 2021a). Toxicity 
studies of oral PFBS exposures in animals have reported adverse health 
effects on development, as well as the thyroid and kidneys (USEPA, 
2021a). Human and animal studies evaluated other health effects 
following PFBS exposure including effects on the immune, reproductive, 
and hepatic systems and lipid and lipoprotein homeostasis, but the 
evidence was determined to be equivocal (USEPA, 2021a). No studies 
evaluating the carcinogenicity of PFBS in humans or animals were 
identified. EPA concluded that there is ``Inadequate Information to 
Assess Carcinogenic Potential'' for PFBS and K+PFBS by any route of 
exposure. For a detailed discussion on adverse effects of oral exposure 
to PFBS, please see USEPA (2021a).
    EPA's noncancer HBWC for PFBS is derived from a chronic RfD that is 
based on thyroid effects observed following gestational exposure of 
mice to K+PFBS (USEPA, 2021a; USEPA, 2022e). The most sensitive non-
cancer effect observed was decreased serum total thyroxine (T4) in 
newborn (PND 1) mice gestationally exposed to K+PFBS from GD 1-20, 
identified in the critical developmental toxicity study selected by EPA 
(benchmark dose lower confidence limit HED or BMDLHED) of 0.095 mg/kg/
day) (Feng et al., 2017; USEPA, 2021a). To develop the chronic RfD for 
PFBS, EPA applied a composite UF of 300 (i.e., 10X for intraspecies 
uncertainty factor (UFH), 3X for interspecies uncertainty 
factor (UFA), and 10X for database uncertainty factor 
(UFD)) to yield a value of 0.0003 mg/kg/day (USEPA, 2021a).
    To select an appropriate DWI-BW for use in deriving the noncancer 
HBWC value, EPA considered the PFBS exposure interval used in the 
developmental toxicity study in mice that was the basis for chronic RfD 
derivation. In this study, pregnant mice were exposed throughout 
gestation, which is relevant to two human adult life stages: women of 
child-bearing age who may be or become pregnant, and pregnant women and 
their developing embryo or fetus (Table 3-63 in USEPA, 2019a). Of these 
two, EPA selected the DWI-BW for women of child-bearing age (0.0354 L/
kg/day) to derive the noncancer HBWC for PFBS because it was higher and 
therefore more health-protective (USEPA, 2022e).
    The HBWC value for PFBS was calculated using an RSC of 0.20. This 
means that 20% of the exposure--equal to the RfD--is allocated to 
drinking water, and the remaining 80% is attributed to all other 
potential exposure sources (USEPA, 2022e). This was based on EPA's 
determination that the available data on PFBS exposure routes and 
sources did not enable a quantitative characterization of PFBS 
exposure. In such cases, an RSC of 0.20 is typically used (USEPA, 
2000c).
    As further described in USEPA (2022e), the HBWC for PFBS is 
calculated to be 2000 ppt. This value is consistent with EPA's 2022 
drinking water health advisory for PFBS (USEPA, 2022d), but was derived 
from EPA's 2021 PFBS Toxicity Assessment (USEPA, 2021a). This HBWC of 
2000 ppt is also used as the HRL for this preliminary Regulatory 
Determination for PFBS.
5. Mixtures of PFHxS, HFPO-DA, PFNA, and PFBS
    PFAAs, including PFHxS, HFPO-DA, PFNA, and PFBS, disrupt signaling 
of multiple biological pathways resulting in common adverse effects on 
several biological systems including thyroid hormone levels, lipid 
synthesis and metabolism, as well as on development, and immune and 
liver function (ATSDR, 2021; EFSA, 2018, 2020; USEPA, 2023a).
    Studies with PFAS and other classes of chemicals support the health 
protective assumption that a mixture of chemicals with similar observed 
effects should be assumed to also act in a dose additive manner unless 
data demonstrate otherwise (USEPA, 2023d). Dose additivity means that 
each of the component chemicals in the mixture (in this case, PFHxS, 
HFPO-DA, PFNA, and PFBS) behaves as a concentration or dilution of 
every other chemical in the mixture differing only in relative toxicity 
(USEPA, 2000a). See additional discussion of PFAS dose additivity in 
Section V.C of this preamble.

C. Statutory Criterion 2--Occurrence

    With this proposal, EPA is preliminarily determining that PFHxS, 
HFPO-DA, PFNA, and PFBS, both individually and as mixtures of these 
PFAS, meet SDWA's second statutory criterion for regulatory 
determination: there is a substantial likelihood that the contaminants 
will occur and co-occur with a frequency and at levels of public health 
concern in PWSs based on EPA's evaluation of the best available 
occurrence information. EPA is seeking public comment on whether 
additional data or studies exist which EPA should consider that support 
or do not support this preliminary determination.
    EPA has made its preliminary determination based on the most 
recent, publicly available data, which includes UCMR 3 data and more 
recent PFAS drinking water data collected by several states. Informed 
by these data, EPA determined that there is a substantial likelihood 
PFHxS, HFPO-DA, PFNA, and PFBS will occur and co-occur with a frequency 
of public health concern. Additionally, when determining that there is 
a substantial likelihood these PFAS will occur at levels of public 
health concern, EPA considered both the occurrence concentration levels 
for each contaminant individually, as well as their collective co-
occurrence and corresponding dose additive health effects from co-
exposures. Furthermore, the Agency notes that it does not have a 
bright-line threshold for occurrence in drinking water that triggers 
whether a contaminant is of public health concern. A determination of 
public health concern involves consideration of a number of factors, 
some of which include the level at which the contaminant is found in 
drinking water, the frequency at which the contaminant is found and at 
which it co-occurs with other contaminants, whether there is an 
sustained upward trend that these contaminant will occur at a frequency 
and at levels of public health concern, the geographic distribution 
(national, regional, or local occurrence), the impacted population, 
health effect(s), the potency of the contaminant, other possible 
sources of exposure, and potential impacts on sensitive populations or 
lifestages. Given the many possible combinations of factors, a simple 
threshold is not viable and is a highly contaminant-specific decision 
that takes into consideration multiple factors.
    UCMR 3 monitoring occurred between 2013 and 2015 for PFHxS,

[[Page 18648]]

PFNA, and PFBS. HFPO-DA were not monitored for as part of the UCMR 3. 
Under the UCMR 3, 36,972 samples from 4,920 PWSs were analyzed for 
PFHxS, PFNA, and PFBS. The minimum reporting levels (MRLs) for PFHxS, 
PFNA, and PFBS were 30 ppt, 20 ppt, and 90 ppt, respectively. EPA notes 
that these UCMR 3 MRLs are higher than those utilized within the 
majority of state monitoring data and for the upcoming UCMR 5. A total 
of 233 samples and 70 systems serving a total population of 
approximately 6.7 million people had reported detections (greater than 
or equal to the MRL) of at least one of the three compounds. Moreover, 
the large majority of these UCMR 3 reported detections were found at 
concentrations at or above levels of public health concern as described 
previously in section III.B of this preamble and below within this 
section. USEPA (2023e) presents sample and system level summaries of 
the results for the individual contaminants. More information 
supporting EPA's regulatory determination relating to the occurrence of 
these PFAS and their mixtures is included in section VII.A. of this 
preamble.
    EPA has also collected more recent finished drinking water data 
from 23 states who have made their data publicly available as of August 
2021 (USEPA, 2023e). EPA used this cutoff date to allow the Agency to 
conduct thorough analyses of the state information. EPA further refined 
this dataset based on representativeness and reporting limitations, 
resulting in detailed technical analyses using a subset of the 
available state data (i.e., all 23 states' data were not included 
within the detailed technical analyses). For example, a few states only 
reported results as a combination of analytes which was not conducive 
for analyzing PFAS. In general, the state data which were more recently 
collected using newer analytical methods that have lower reporting 
limits than those under UCMR 3 show widespread occurrence of PFOA, 
PFOS, PFHxS, PFNA, and PFBS in multiple geographic locations. These 
data also show that there is a substantial likelihood that these PFAS 
occur at concentrations below UCMR 3 reporting limits. Furthermore, 
these data include results for more PFAS than were included in the UCMR 
3, including HFPO-DA, and show that PFHxS, HFPO-DA, PFNA, and PFBS, and 
mixtures of these PFAS, occur and co-occur at levels of public health 
concern as they are measured at concentrations above their respective 
individual HRLs or, when considering their dose additive impacts, 
exceed these levels. The Agency notes that the data vary in terms of 
quantity and coverage, including that some of these available data are 
from targeted or site-specific sampling efforts (i.e., monitoring 
specifically in areas of known or potential contamination) and thus may 
be expected to have higher detection rates or not be representative of 
levels found in all PWSs within the state.
    Tables 1 and 2 below show the percent of samples with state 
reported detections of PFHxS, HFPO-DA, PFNA, and PFBS, and the 
percentage of monitored systems with detections of PFHxS, HFPO-DA, 
PFNA, and PFBS, respectively, across the non-targeted or non-site 
specific (i.e., monitoring not conducted specifically in areas of known 
or potential contamination) state finished water monitoring data.
    EPA notes that different states utilized various reporting 
thresholds or limits when presenting their data, and for some states 
there were no clearly defined limits publicly provided. Further, the 
limits often varied within the data for each state depending on the 
specific analyte, as well as the laboratory analyzing the data. When 
conducting data analyses, EPA incorporated individual state-specific 
reporting limits where possible. In some cases, states reported data at 
concentrations below EPA's proposed rule trigger level for reduced 
compliance monitoring frequency and/or PQLs described in sections 
VIII.A., IX.A., and IX.B of this preamble. However, to present the best 
available occurrence data, EPA collected and evaluated the data based 
on the information as reported directly by the states. EPA also notes, 
and as described in further detail in section VIII.A. of this preamble, 
some laboratories are able to detect and measure the PFAS addressed in 
this document at lower concentrations than EPA's proposed rule trigger 
level and PQLs which account for differences in the capability of 
laboratories across the country. As such, EPA believes this data can 
reasonably support EPA's evaluation of PFOA, PFOS, PFHxS, HFPO-DA, 
PFNA, and PFBS occurrence and co-occurrence in drinking water. Specific 
details on state data reporting thresholds are available in Table 1 
within USEPA (2023e).

 Table 1--Non-Targeted State PFAS Finished Water Data--Summary of Samples With State Reported Detections \1\ of
                                         PFHxS, HFPO-DA, PFNA, and PFBS
----------------------------------------------------------------------------------------------------------------
                      State                         PFHxS  (%)       PFNA  (%)       PFBS  (%)     HFPO-DA  (%)
----------------------------------------------------------------------------------------------------------------
Colorado........................................            10.8             0.9            11.0             0.2
Illinois........................................             5.1             0.2             7.8             0.0
Kentucky........................................             8.6             2.5            12.3            13.6
Massachusetts...................................            31.9             4.6            35.5             0.0
Michigan........................................             2.9             0.1             5.2            0.04
New Hampshire...................................            16.6             3.3            31.4             3.8
New Jersey......................................            24.7             8.0            24.9             N/A
North Dakota....................................             1.6             0.0             0.0             0.0
Ohio............................................             5.8             0.3             4.7             0.1
South Carolina..................................            13.5             2.1            38.3             6.0
Vermont.........................................             2.2             1.7             4.8             0.2
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.

[[Page 18649]]

   Table 2--Non-Targeted State PFAS Finished Water Data--Summary of Monitored Systems With State Reported \1\
                                  Detections of PFHxS, HFPO-DA, PFNA, and PFBS
----------------------------------------------------------------------------------------------------------------
                      State                         PFHxS  (%)       PFNA  (%)       PFBS  (%)     HFPO-DA  (%)
----------------------------------------------------------------------------------------------------------------
Colorado........................................            13.4             1.0            13.4             0.3
Illinois........................................             4.3             0.2             6.6             0.0
Kentucky........................................             8.6             2.5            12.3            13.6
Massachusetts...................................            30.2             8.4            39.4             0.0
Michigan........................................             3.0             0.2             5.3             0.1
New Hampshire...................................            22.5             5.5            37.9             5.1
New Jersey......................................            32.6            13.3            34.0             N/A
North Dakota....................................             1.6             0.0             0.0             0.0
Ohio............................................             2.2             0.3             2.4             0.1
South Carolina..................................            20.0             6.1            56.0            10.9
Vermont.........................................             1.6             1.3             5.2             0.5
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.

    As shown in Tables 1 and 2, all states except one report sample and 
system detections for at least three of the four PFAS. For those states 
that reported detections, the percentage of samples and systems where 
these PFAS were found ranged from 0.1 to 38.3 percent and 0.1 to 56.0 
percent, respectively. While these percentages show occurrence 
variability across states, several of these states demonstrate a 
significant number of samples (e.g., detections of PFHxS in 31.9 
percent of Massachusetts samples) and systems (e.g., detections of 
HFPO-DA in 13.9 percent of monitored systems in Kentucky) with some or 
all of the four PFAS, which supports the Agency's preliminary 
determination that there is a substantial likelihood these PFAS and 
their mixtures occur and co-occur with a frequency of public health 
concern. Specific discussion related to occurrence for each of the four 
PFAS is below.
1. PFHxS
    The occurrence data presented above, throughout section VII. of 
this preamble and discussed in the USEPA (2023e) support the Agency's 
preliminary determination that there is a substantial likelihood PFHxS 
occurs with a frequency and at levels of public health concern in 
drinking water systems across the United States. PFHxS was found under 
UCMR 3 in approximately 1.1% of systems using an MRL of 30 ppt. All 
UCMR 3 reported values are greater than the HRL of 9.0 ppt. 
Additionally, through analysis of available non-targeted state data all 
states in Tables 1 and 2 had reported detections of PFHxS within 1.6 to 
32.6 percent of their systems and reported concentrations ranging from 
0.46 to 310 ppt with median sample concentrations ranging from 2.14 to 
11.3 ppt. Results from targeted state monitoring data of PFHxS are also 
consistent with non-targeted state data. For example, California 
reported 29.2 percent of monitored systems found PFHxS, where 
concentrations ranged from 1.1 to 140.0 ppt. Therefore, in addition to 
the UCMR 3 results, these state data reflect PFHxS at frequencies and 
levels of public health concern. EPA also evaluated PFHxS in a national 
occurrence model that has been developed and utilized to estimate 
national-scale PFAS occurrence for four PFAS that were included in UCMR 
3 (Cadwallader et al., 2022). The model and results are described in 
section VII.E of this preamble. Hundreds of systems serving millions of 
people were estimated to have mean concentrations exceeding the PFHxS 
HRL (9.0 ppt). Further supporting this preliminary determination, PFAS 
have dose additive impacts and PFHxS co-occurs in mixtures with other 
PFAS, including PFOA, PFOS, HFPO-DA, PFNA, and PFBS. More information 
on PFHxS co-occurrence is available in section VII.C. and VII.D. of 
this preamble.
2. HFPO-DA
    The occurrence data presented above, throughout section VII of this 
preamble, and discussed in the USEPA (2023e) support the Agency's 
preliminary determination that there is a substantial likelihood HFPO-
DA occur with a frequency and at levels of public health concern in 
drinking water systems across the United States. Through analysis of 
available non-targeted state data over half of the states in Tables 1 
and 2 had state reported detections of HFPO-DA within 0.1 to 13.6 
percent of their systems. State reported sample results were also 
reported above the HRL of 10.0 ppt with sample results ranging from 1.7 
to 29.7 ppt and median sample results ranging from 1.7 to 9.7 ppt. 
Additionally, targeted state monitoring in North Carolina which 
conducted sampling across six finished drinking water sites where 438 
samples showed HFPO-DA ranging from 9.2 to 1100 ppt, with a median 
concentration of 40 ppt. Therefore, these state data demonstrate 
concentrations of HFPO-DA at levels of public health concern. Further 
supporting this preliminary determination, PFAS have dose additive 
impacts and HFPO-DA occur in mixtures with other PFAS, including PFOA, 
PFOS, PFHxS, PFNA, and PFBS. More information on HFPO-DA co-occurrence 
is available in section VII.C. and VII.D. of this preamble.
3. PFNA
    The occurrence data presented above, throughout section VII of this 
preamble, and discussed in USEPA (2023e) support the Agency's 
preliminary determination that there is a substantial likelihood PFNA 
occurs with a frequency and at levels of public health concern in 
drinking water systems across the United States. PFNA was found under 
UCMR 3 using an MRL of 20 ppt. Thus, all UCMR 3 reported detections are 
greater than the HRL of 10.0 ppt. Additionally, through analysis of 
available non-targeted state data all states except one in Tables 1 and 
2 had state reported detections of PFNA within 0.2 to 13.3 percent of 
their systems, and state reported sample results ranging from 0.25 to 
94.2 ppt with median sample results range from 2.1 to 7.46 ppt. 
Targeted state monitoring data of PFNA are also consistent with non-
targeted state data; for example, Pennsylvania reported 5.8 percent of 
monitored systems found PFNA, where concentrations ranged from 1.8 to 
18.1 ppt. Thus, in addition to the UCMR 3 results, these state data 
also reflect PFNA concentrations at levels of public health concern. 
Further supporting this preliminary

[[Page 18650]]

determination, PFAS have dose additive impacts and PFNA co-occurs in 
mixtures with other PFAS, including PFOA, PFOS, PFHxS, HFPO-DA, and 
PFBS. More information on PFNA co-occurrence is available in section 
VII.C. and VII.D. of this preamble.
4. PFBS
    The occurrence data presented above, throughout section VII of this 
preamble, and discussed in USEPA (2023e) support the Agency's 
preliminary determination that there is a substantial likelihood PFBS 
occurs with a frequency and at levels of public health concern in 
drinking water systems across the United States. PFBS was found under 
UCMR 3 using an MRL of 90 ppt. Additionally, through analysis of 
available non-targeted state data all states except one in Tables 1 and 
2 had state reported detections of PFBS within 2.4 to 56 percent of 
their systems, with four states finding PFBS in over 34 percent of 
their systems. Furthermore, PFBS occurred at a greater frequency in all 
but one state than the other three PFAS. State reported sample results 
ranged from 1 to 310 ppt with median sample results ranging from 1.99 
to 7.26 ppt. Targeted state monitoring data of PFBS are consistent with 
non-targeted state data. Maryland reported 51.5 percent of monitored 
systems found PFBS, where concentrations ranged from 1.01 to 21.29 ppt. 
Further supporting this preliminary determination, PFAS have dose 
additive impacts and PFBS occurs in mixtures with other PFAS, including 
PFOA, PFOS, PFHxS, HFPO-DA, and PFNA. Moreover, given the considerable 
prevalence of PFBS in state data reviewed by EPA and frequency in which 
it has been shown to have other PFAS co-occurring with it, PFBS may 
serve as an indicator of broad contamination of other PFAS. Those other 
PFAS are also likely dose additive to PFBS and other PFAS being 
proposed for regulation. EPA notes that PFBS concentrations do not 
exceed their HRL of 2000 ppt when considered in isolation; however, 
when considering dose additivity and the elevated frequency to which 
PFBS occurrence has been observed over time, EPA has determined that 
PFBS is an important component of regulated PFAS mixtures and because 
of their pervasiveness, there is a substantial likelihood of its 
occurrence with a frequency and at levels of public health concern. 
More information on PFBS co-occurrence is available in section VII.C. 
and VII.D. of this preamble. Based on the occurrence and co-occurrence 
information above and throughout section VII of this preamble, EPA has 
preliminarily determined that there is substantial likelihood PFBS 
occurs with a considerable frequency and at levels of public health 
concern.
5. Preliminary Occurrence Determination for PFHxS, HFPO-DA, PFNA, and 
PFBS
    Through the information presented within this section and in USEPA 
(2023e), along with the co-occurrence information presented in section 
VII.C. and VII.D. of this preamble, EPA's evaluation of the UCMR 3 data 
and state data collected more recently demonstrates that as analytical 
methods improved, monitoring has increased, and minimum reporting 
thresholds are lowered, there is a sustained upward trend that there is 
a substantial likelihood that these contaminants will occur and co-
occur at a frequency and at levels of public health concern. The UCMR 3 
results showed there were over 6.5 million people served by PWSs that 
had reported detections of PFHxS, PFNA, and PFBS, with many of the 
detections for PFHxS and PFNA above the HRLs. EPA's evaluation of 
monitoring data from multiple states that was primarily gathered 
following the UCMR 3 using improved analytical methods that could 
measure more PFAS at lower concentrations found that there is even 
greater demonstrated occurrence and co-occurrence of these PFAS, as 
well as for HFPO-DA, at significantly greater frequencies and at levels 
of public health concern. EPA anticipates that national monitoring with 
newer analytical methods capable of quantifying PFAS occurrence to 
lower levels, significant occurrence and co-occurrence of these PFAS 
are likely to be observed.
    EPA notes that it focused the evaluation of the state data on the 
non-targeted monitoring efforts from 12 states, given that these types 
of monitoring efforts are likely to be more representative of PFHxS, 
HFPO-DA, PFNA, and PFBS occurrence as they are not specifically 
conducted in areas of known or potential contamination. In these 12 
states, there were reported detections of PFHxS, HFPO-DA, PFNA, or 
PFBS, with nearly all states reporting detections of at least three of 
these four PFAS. EPA considered the targeted state data separately 
since a higher rate of detections may occur as a result of specifically 
looking in areas of suspected or known contamination. For the 
additional targeted state data that EPA analyzed, EPA also found that 
these states reported detections at systems serving millions of 
additional people, as well as at levels of public health concern, 
particularly when considering PFAS mixtures and dose additive impacts. 
State data detection frequency and concentration results vary for 
PFHxS, HFPO-DA, PFNA, and PFBS, both between these four different PFAS 
and across different states, with some states showing much higher 
reported detections and concentrations of these PFAS when compared to 
other states. However, given the overall results, this demonstrates the 
substantial likelihood that these PFAS and their mixtures will occur at 
frequencies and levels of public health concern, and where these PFAS 
have been monitored they are very commonly found. Furthermore, EPA 
notes that as described in section VII.C.1. of this preamble, when 
evaluating only a subset of the available state data representing non-
targeted monitoring, that one or more of PFHxS, HFPO-DA, PFNA, and PFBS 
were reported in approximately 13.9 percent of monitored systems; if 
these results were extrapolated to the nation, one or more of these 
four PFAS would be detectable in over 9,000 PWSs. Moreover, as shown in 
section VII.C.2. of this preamble, PFHxS, HFPO-DA, PFNA, and PFBS 
generally co-occur with each other, as well as with PFOA and PFOS, 
supporting that there is substantial likelihood that these PFAS will 
co-occur in mixtures with dose additive impacts. For all of these 
reasons, EPA has determined that there is sufficient occurrence 
information available to support this preliminary determination that 
there is a substantial likelihood that PFHxS, HFPO-DA, PFNA, and PFBS 
will occur at frequencies and levels of public health concern.

D. Statutory Criterion 3--Meaningful Opportunity

    EPA has preliminarily determined that regulation of PFHxS, HFPO-DA, 
PFNA, and PFBS, both individually and in a mixture, presents a 
meaningful opportunity for health risk reduction for persons served by 
PWSs. EPA has made this preliminary determination after evaluating 
health, occurrence, treatment, and other related information against 
the three SDWA statutory criteria including consideration of the 
following for the four PFAS and their mixtures:
     PFHxS, HFPO-DA, PFNA, and PFBS, individually and in a 
mixture, may cause adverse human health effects on several biological 
systems including the endocrine, cardiovascular, developmental, immune, 
and hepatic systems. Additionally, these four PFAS, as well as other 
PFAS, are likely to

[[Page 18651]]

produce dose-additive effects from co-exposures.
     The substantial likelihood that PFHxS, HFPO-DA, PFNA, and 
PFBS, individually occur and co-occur together at frequencies and 
levels of public health concern in PWSs as discussed in section III of 
this preamble above and in section VII of this preamble, and the 
corresponding significant populations served by these water systems.
     PFHxS, HFPO-DA, PFNA, and PFBS, individually and in a 
mixture, are expected to be environmentally persistent.
     Validated EPA-approved measurement methods are available 
to measure PFHxS, HFPO-DA, PFNA, and PFBS, individually and in 
mixtures. See section VIII of this preamble for further discussion.
     Treatment technologies are available to remove PFHxS, 
HFPO-DA, PFNA, and PFBS, and mixtures of these contaminants, from 
drinking water. See section XI of this preamble for further discussion.
     Regulating PFHxS, HFPO-DA, PFNA, and PFBS, in addition to 
PFOA and PFOS, is anticipated to reduce the overall public health risk 
from all other PFAS that co-occur and are co-removed. Their regulation 
is anticipated to provide public health protection at the majority of 
known sites with PFAS-impacted drinking water.
     There are achievable steps to manage drinking water that 
can be taken to reduce risk.
    Due to the environmental persistence of these chemicals, there is 
potential for toxicity at environmentally relevant concentrations as 
studies show it can take years for many PFAS to leave the human body 
(NIEHS, 2020). See section III of this preamble above and section V of 
this preamble for discussion about the human health effects of PFHxS, 
HFPO-DA, PFNA, and PFBS.
    Data from both the UCMR 3 and state monitoring efforts demonstrates 
occurrence or likely occurrence and co-occurrence of PFHxS, HFPO-DA, 
PFNA, and PFBS, and their mixtures, at frequencies and levels of public 
health concern. Under UCMR 3, 1.4% of systems serving approximately 6.7 
million people had reported detections (greater than or equal to their 
MRLs) of PFHxS, PFNA, and PFBS of at least one of the three compounds. 
Additionally, based on the available state monitoring data presented 
earlier in this section, in the 11 states shown in Table 2 that 
conducted non-targeted sampling of the four PFAS, monitored systems 
that reported detections of PFHxS, HFPO-DA, PFNA, and PFBS serve 
approximate populations of 8.3 million, 1.8 million, 2.6 million, and 
8.8 million people, respectively. Further, as demonstrated in the UCMR 
3 and state data, concentrations of these PFAS, as well as PFOA and 
PFOS, and their mixtures co-occur at levels of public health concern as 
described in more detail in section VII.C. and VII.D. of this preamble 
and USEPA (2023e).
    Analytical methods are available to measure PFHxS, HFPO-DA, PFNA, 
and PFBS in drinking water. EPA has published two multi-laboratory 
validated drinking water methods for individually measuring PFHxS, 
HFPO-DA, PFNA, and PFBS: EPA Method 537.1 which measures 18 PFAS and 
EPA Method 533 which measures 25 PFAS. There are 14 PFAS which overlap 
between methods and both methods measure PFOA and PFOS). Additional 
discussion on analytical methods can be found in section VIII of this 
preamble.
    EPA's analysis, summarized in section XI of this preamble, found 
there are available technologies capable of reducing PFHxS, HFPO-DA, 
PFNA, and PFBS. These technologies include granular activated carbon 
(GAC), AIX resins, reverse osmosis (RO), and nanofiltration (NF). See 
discussion in section XI of this preamble for information about these 
treatment technologies. Due to the inherent nature of sorptive and 
high-pressure membrane technologies such as these, treatment 
technologies that remove PFHxS, HFPO-DA, PFNA, and PFBS and their 
mixtures also have been documented to co-remove other PFAS 
(S[ouml]reng[aring]rd et al., 2020; McCleaf et al., 2017; Mastropietro 
et al., 2021). Furthermore, as described in section VII of this 
preamble, PFHxS, HFPO-DA, PFNA, and PFBS also co-occur with PFAS for 
which the Agency is not currently making a preliminary regulatory 
determination. Many of these other emergent co-occurring PFAS are 
likely to also pose hazards to public health and the environment 
(Mahoney et al., 2022). Therefore, based on EPA's findings that PFHxS, 
HFPO-DA, PFNA, and PFBS have a substantial likelihood to co-occur in 
drinking water with other PFAS and treating for PFHxS, HFPO-DA, PFNA, 
and PFBS is anticipated to result in removing these and other PFAS, 
regulation of PFHxS, HFPO-DA, PFNA, PFBS (as well as PFOA and PFOS) 
also presents a meaningful opportunity to reduce the overall public 
health risk from all other PFAS that co-occur and are co-removed with 
PFHxS, HFPO-DA, PFNA, and PFBS.
    With the ability to monitor for PFAS, identify contaminated 
drinking water sources and contaminated finished drinking water, and 
reduce PFAS exposure through management of drinking water, EPA has 
identified meaningful and achievable actions that can be taken to 
reduce the human health risk of PFAS.
    EPA is preliminarily determining that regulation of PFHxS, HFPO-DA, 
PFNA, and PFBS presents a meaningful opportunity for health risk 
reduction for persons served by PWSs.

E. EPA's Preliminary Regulatory Determination Summary for PFHxS, HFPO-
DA, PFNA, and PFBS

    The statute provides EPA significant discretion when making a 
preliminary determination under Section 1412(b)(1)(A). This decision to 
make a preliminary regulatory determination for PFHxS, HFPO-DA, PFNA 
and PFBS and their mixtures is based on consideration of the evidence 
supporting the factors individually and as a whole.
    EPA's preliminary determination that PFHxS, HFPO-DA, PFNA, and PFBS 
``may have an adverse effect on the health of persons'' is strongly 
supported by numerous studies where multiple health effects are 
demonstrated following exposure. EPA's preliminary determination 
regarding occurrence is supported by evidence documenting the trend 
demonstrated first by the UCMR 3 data and then subsequent state 
occurrence data that measured occurrence of the four PFAS has increased 
with more widespread monitoring primarily using EPA approved methods 
that have, lower reporting thresholds. The statute contemplates that 
there may be instances where exact occurrence may not be ``known'' and 
in these instances EPA need only demonstrate that that it has a basis 
to determine that there is a ``substantial likelihood that the 
contaminant will occur.'' Additional nationwide monitoring data will be 
conducted between 2023-2025 under the UCMR 5. This data will serve to 
demonstrate whether the four PFAS are known to occur, however, EPA has 
sufficient evidence now to support a preliminary determination there is 
a substantial likelihood that these PFAS will occur frequently and at 
concentrations where they are likely to exceed their respective HRLs 
based on the increased occurrence trends documented by available 
information. This finding is further supported by available dose 
additive impacts and co-occurrence information that demonstrates that 
there is a substantial likelihood that these PFAS co-occur in PWSs with 
a frequency and at levels of public health concern at hundreds of 
systems serving millions of people.

[[Page 18652]]

Finally, EPA's preliminary determination that regulating these four 
PFAS presents a meaningful opportunity for health risks reductions is 
strongly supported by numerous bases, including the potential adverse 
human health effects and potential for exposure and co-exposure of 
these PFAS, and the availability of both analytical methods to measure 
and treatment technologies to remove these contaminants in drinking 
water.
    After considering these factors individually and together, EPA has 
preliminarily determined that now is the appropriate time to exercise 
its discretion under the statute to regulate the four PFAS and their 
mixtures as contaminants under SDWA. EPA recognizes the public health 
burden of PFHxS, HFPO-DA, PFNA, and PFBS, as well as PFOA, PFOS, and 
other PFAS, a public urgency to reduce PFAS concentrations in drinking 
water, and that the proposed regulation provides a mechanism to reduce 
these PFAS expeditiously and efficiently for regulated utilities, 
States, and Tribes. Furthermore, in addition to making this preliminary 
regulatory determination, EPA is concurrently proposing an NPDWR to 
include all four of these PFAS, in part to allow utilities to consider 
these PFAS specifically as they design systems to remove PFAS and to 
ensure that they are reducing these PFAS in their drinking water as 
effectively and quickly as feasible, maximizing the protection of 
drinking water for the American public.

F. Request for Comment on EPA's Preliminary Regulatory Determination 
for PFHxS, HFPO-DA, PFNA, and PFBS

    EPA specifically requests comment on its preliminary regulatory 
determination for PFHxS, HFPO-DA, PFNA, and PFBS and their mixtures. In 
particular, EPA requests comment on whether there is additional health 
information the Agency should consider as to whether PFHxS, HFPO-DA, 
PFNA, and PFBS and their mixtures may have an adverse effect on the 
health of persons. EPA also requests comment on whether there are other 
peer-reviewed health or toxicity assessments for other PFAS the Agency 
should consider as part of this action. Additionally, EPA requests 
comment on additional occurrence data the Agency should consider 
regarding its decision that PFHxS, HFPO-DA, PFNA, and PFBS and their 
mixtures occur or are substantially likely to occur in PWSs with a 
frequency and at levels of public health concern. EPA also requests 
public comment on its evaluation that regulation of PFHxS, HFPO-DA, 
PFNA, and PFBS and their mixtures, in addition to PFOA and PFOS, will 
provide protection from PFAS that will not be regulated as part of this 
proposed PFAS NPDWR.

IV. Approaches to MCLG Derivation

    Section 1412(a)(3) of the SDWA requires the Administrator of the 
EPA to propose a MCLG simultaneously with the NPDWR. The MCLG is set, 
as defined in Section 1412(b)(4)(A), at ``the level at which no known 
or anticipated adverse effects on the health of persons occur and which 
allows an adequate margin of safety''. Consistent with SDWA 
1412(b)(3)(C)(i)(V), in developing the MCLG, EPA considers ``the 
effects of the contaminant on the general population and on groups 
within the general population such as infants, children, pregnant 
women, the elderly, individuals with a history of serious illness, or 
other subpopulations that are identified as likely to be at greater 
risk of adverse health effects due to exposure to contaminants in 
drinking water than the general population.'' Other factors considered 
in determining MCLGs include health effects data on drinking water 
contaminants and potential sources of exposure other than drinking 
water. MCLGs are not regulatory levels and are not enforceable.
    EPA is proposing individual MCLGs for two PFAS (PFOA and PFOS; see 
USEPA, 2023b; USEPA, 2023c) and a separate MCLG to account for dose 
additive noncancer effects for a mixture of four PFAS (PFHxS, HFPO-DA, 
PFNA, and PFBS; see USEPA, 2023d). The derivation of the proposed MCLG 
for the mixture is based on an HI approach (USEPA, 2023a).
    The SAB, discussed further in section XV.K.1. of this preamble 
below, supported many of EPA's conclusions presented in the PFOA and 
PFOS MCLG approaches, mixtures framework, and economics benefits 
documents including health effects and economic benefits analyses 
(USEPA, 2022a). Regarding the Proposed Approaches to the Derivation of 
Draft MCLGs for PFOA and PFOS (USEPA, 2021e; USEPA, 2021f), SAB agreed 
with the selection of the UFs used in deriving the noncancer RfDs, 
supported the selection of an RSC of 20%, and agreed with the 
``likely'' designation for PFOA carcinogenicity.
    The SAB commented that EPA should ``focus on those health outcomes 
that have been concluded to have the strongest evidence'' and 
``consider multiple human and animal studies for a variety of endpoints 
in different populations so as to provide convergent evidence that is 
more reliable than any single study or health endpoint in isolation.'' 
EPA applied these recommendations when deriving points of departure and 
selecting critical studies used for toxicity value development in the 
MCLG documents for PFOA and PFOS (USEPA, 2023b; USEPA, 2023c). 
Specifically, EPA focused on the five health outcomes with the 
strongest weight of evidence--liver, immune, cardiovascular, 
developmental, and cancer--during quantitative analyses.
    However, the SAB had a number of consensus recommendations and 
identified ``methodological concerns in the draft MCLG documents for 
PFOA and PFOS.'' EPA has addressed these concerns by providing 
additional clarity and transparency on the systematic literature review 
process and expanding the systematic review steps included in the 
health effects assessment. The systematic review protocols, which were 
developed to be consistent with EPA's Office of Research and 
Development (ORD) Integrated Risk Information System (IRIS) Staff 
Handbook (USEPA, 2022f), are available in the Appendices of the MCLG 
documents for PFOA and PFOS (USEPA, 2023b; USEPA, 2023c). In order to 
base the MCLG derivation on the best available science, EPA has updated 
the draft MCLG documents to reflect the results of conducting an update 
to the literature search and performing new evaluations of models, 
methods, and data. More information is available in section XV.K.1. of 
this preamble.
    EPA expects to conduct a final literature search update before the 
final rule is promulgated. The SAB input has made this product more 
scientifically sound and ensures that it reflects the best available 
science. The updated supporting information can be found in the MCLG 
documents for PFOA and PFOS (USEPA, 2023b; USEPA, 2023c).

A. Approach to MCLG Derivation for Individual PFAS

    To establish the MCLG, EPA assesses the peer reviewed science 
examining cancer and noncancer health effects associated with oral 
exposure to the contaminant. For linear carcinogenic contaminants, 
where there is a proportional relationship between dose and 
carcinogenicity at low concentrations, EPA has a long-standing practice 
of establishing the MCLG at zero (see USEPA, 1998a; USEPA, 2000d; 
USEPA, 2001). For nonlinear carcinogenic contaminants, contaminants 
that are suggestive carcinogens, and non-carcinogenic contaminants, EPA 
typically establishes the MCLG based on an RfD. An RfD is an estimate 
of a daily exposure to the

[[Page 18653]]

human population (including sensitive populations) that is likely to be 
without an appreciable risk of deleterious effects during a lifetime. A 
nonlinear carcinogen is a chemical agent for which the associated 
cancer response does not increase in direct proportion to the exposure 
level and for which there is scientific evidence demonstrating a 
threshold level of exposure below which there is no appreciable cancer 
risk.
    The MCLG is derived depending on the noncancer and cancer evidence 
for a particular contaminant. Establishing the MCLG for a chemical has 
historically been accomplished in one of three ways depending upon a 
three-category classification approach (USEPA, 1985; USEPA, 1991a). The 
categories are based on the available evidence of carcinogenicity after 
exposure via ingestion. The starting point in categorizing a chemical 
is through assigning a cancer descriptor using EPA's current Guidelines 
for Carcinogen Risk Assessment (USEPA, 2005). The 2005 Guidelines 
replaced the prior alphanumeric groupings although the basis for the 
classifications is similar. In prior rulemakings, the Agency typically 
placed Group A, B1, and B2 contaminants into Category I, Group C into 
Category II, and Group D and E into Category III based on the Agency's 
previous cancer classification guidelines (i.e., Guidelines for 
Carcinogen Risk Assessment, published in 51 FR 33992, September 24, 
1986 (USEPA, 1986b) and the 1999 draft revised final guidelines (USEPA, 
1999):
     Category I chemicals have ``strong evidence [of 
carcinogenicity] considering weight of evidence, pharmacokinetics, and 
exposure'' (USEPA, 1985; USEPA, 1991a). EPA's 2005 Cancer descriptors 
associated with this category are: ``Carcinogenic to Humans'' or 
``Likely to be Carcinogenic to Humans'' (USEPA, 2005). EPA's policy 
under SDWA is to set MCLGs for Category I chemicals at zero, based on 
the principle that there is no known threshold for carcinogenicity 
(USEPA, 1985; USEPA, 1991a; USEPA, 2016d). In cases when there is 
sufficient evidence to determine a nonlinear cancer mode of action 
(MOA), the MCLG is based on the RfD approach described below.
     Category II chemicals have ``limited evidence [of 
carcinogenicity] considering weight of evidence, pharmacokinetics, and 
exposure'' (USEPA, 1985; USEPA, 1991a). EPA's 2005 Cancer descriptor 
associated with this category is: ``Suggestive Evidence of Carcinogenic 
Potential'' (USEPA, 2005). The MCLG for Category II contaminants is 
based on noncancer effects (USEPA, 1985; USEPA, 1991a) as described 
below.
     Category III chemicals have ``inadequate or no animal 
evidence [of carcinogenicity]'' (USEPA, 1985; USEPA, 1991a). EPA's 2005 
Cancer descriptors associated with this category are: ``Inadequate 
Information to Assess Carcinogenic Potential'' and ``Not Likely to Be 
Carcinogenic to Humans'' (USEPA, 2005). The MCLG for Category III 
contaminants is based on noncancer effects as described below.
    For chemicals exhibiting a noncancer threshold for toxic effects 
(e.g., Category II or III; e.g., see USEPA, 1985 and USEPA, 1991a) and 
nonlinear carcinogens (e.g., see USEPA, 2006a), EPA establishes the 
MCLG based on a toxicity value, typically an RfD, but similar toxicity 
values may also be used when they represent the best available science 
(e.g., ATSDR Minimal Risk Level). A noncancer MCLG is designed to be 
protective of noncancer effects over a lifetime of exposure with an 
adequate margin of safety, including for sensitive populations and life 
stages, consistent with SDWA 1412(b)(3)(C)(i)(V) and 1412(b)(4)(A). The 
calculation of a noncancer MCLG includes an oral toxicity reference 
value such as an RfD (or Minimal Risk Level), DWI-BW, and RSC as 
presented in the equation below:
[GRAPHIC] [TIFF OMITTED] TP29MR23.060

Where:

RfD \3\ = reference dose--an estimate (with uncertainty spanning 
perhaps an order of magnitude) of a daily oral exposure of the human 
population to a substance that is likely to be without an 
appreciable risk of deleterious effects during a lifetime. The RfD 
is equal to a point-of-departure (POD) divided by a composite UF.
---------------------------------------------------------------------------

    \3\ A reference dose (RfD) is an estimate of the amount of a 
chemical a person can ingest daily over a lifetime (chronic RfD) or 
less (subchronic RfD) that is unlikely to lead to adverse health 
effects in humans.
---------------------------------------------------------------------------

DWI-BW = An exposure factor in the form of the 90th percentile DWI-
BW for the identified population or life stage, in units of liters 
of water consumed per kilogram BW per day (L/kg/day). The DWI-BW 
considers both direct and indirect consumption of drinking water 
(indirect water consumption encompasses water added in the 
preparation of foods or beverages, such as tea or coffee). Chapter 3 
of EPA's Exposure Factors Handbook (USEPA, 2019a) provides DWI-BWs 
for various populations or life stages within the general population 
for which there are publicly available, peer-reviewed data such as 
National Health and Nutrition Examination Survey (NHANES) data.
RSC = relative source contribution--the percentage of the total 
exposure attributed to drinking water sources (USEPA, 2000c), with 
the remainder of the exposure allocated to all other routes or 
sources.

    EPA established internal protocols for the systematic review steps 
of literature search, Population, Exposure, Comparator, and Outcomes 
(PECO) development, literature screening, study quality evaluation, and 
data extraction prior to conducting the systematic review for PFOA and 
PFOS. However, EPA recognizes that while components of the protocols 
were included in the November 2021 draft Proposed Approaches documents 
(USEPA, 2021e; USEPA, 2021f), the protocols were only partially 
described in those documents. EPA has incorporated detailed, 
transparent, and complete protocols for all steps of the systematic 
review process into the Proposed MCLG documents (USEPA, 2023b; USEPA, 
2023c). Additionally, the protocols and methods have been updated and 
expanded based on SAB recommendations to improve the transparency of 
the process used to derive the MCLGs for PFOA and PFOS and to be 
consistent with the ORD Staff Handbook for Developing IRIS Assessments 
(USEPA, 2022f). For additional details of EPA's systematic review 
methods, see USEPA (2023b, 2023c; Chapter 2 and Appendix A).
    EPA evaluated strengths and limitations of each study to determine 
an overall classification of high, medium, low, or uninformative with 
respect to confidence in the quality and reliability of the study (this 
was done for each endpoint evaluated in each study). High, medium, and 
low confidence studies were prioritized for qualitative assessments, 
while only high and medium confidence studies were prioritized for 
quantitative assessments. Within each health outcome, the evidence from 
epidemiology and animal toxicity studies was synthesized. For noncancer 
health outcomes, the animal toxicological and epidemiological evidence 
for each health outcome was classified as either robust, moderate, 
slight, indeterminate, or compelling evidence of no effect. The weight 
of evidence for each health outcome across all available evidence 
(i.e., epidemiology, animal toxicity, and mechanistic studies) was 
classified as either evidence demonstrates, evidence indicates 
(likely), evidence suggests, evidence inadequate, or strong evidence 
supports no effect. To characterize the weight of evidence for cancer 
effects,

[[Page 18654]]

EPA followed recommendations of the Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005). Further description of the methods used to 
make these determinations for PFOA and PFOS is provided in USEPA 
(2023b; 2023c). Consistent with the recommendations of the SAB and to 
ensure that the rule reflects the best available science, EPA continues 
to evaluate the literature using systematic review methods.
    The approach to select the DWI-BW and RSC for MCLG derivation 
includes a step to identify sensitive population(s) or life stage(s) 
(i.e., populations or life stages that may be more susceptible or 
sensitive to a chemical exposure) by considering the available data for 
the contaminant, including the adverse health effects reported in the 
toxicity study on which the RfD was based (known as the critical effect 
within the critical or principal study). Although data gaps can 
complicate identification of the most sensitive population (e.g., not 
all windows or life stages of exposure or health outcomes may have been 
assessed in available studies), the critical effect and POD that form 
the basis for the RfD (or Minimal Risk Level) can provide some 
information about sensitive populations because the critical effect is 
typically observed within the low dose range among the available data. 
Evaluation of the critical study, including the exposure window or 
interval, may identify a sensitive population or life stage (e.g., 
pregnant women, formula-fed infants, lactating women). In such cases, 
EPA can select the corresponding DWI-BW for that sensitive population 
or life stage from the Exposure Factors Handbook (USEPA, 2019a) to 
derive the MCLG. In the absence of information indicating a sensitive 
population or life stage, the DWI-BW corresponding to the general 
population may be selected for use in MCLG derivation.
    To account for potential aggregate risk from exposures and exposure 
pathways other than oral ingestion of drinking water, EPA applies an 
RSC when calculating MCLGs to ensure that total exposure to a 
contaminant does not exceed the daily exposure associated with the 
toxicity value, consistent with USEPA (2000c) and long-standing EPA 
methodology for establishing drinking water MCLGs and NPDWRs. The RSC 
represents the proportion of an individual's total exposure to a 
contaminant that is attributed to drinking water ingestion (directly or 
indirectly in beverages like coffee, tea, or soup, as well as from 
transfer to dietary items prepared with drinking water) relative to 
other exposure pathways. The remainder of the exposure equal to the RfD 
(or Minimal Risk Level) is allocated to other potential exposure 
sources (USEPA, 2000c). The purpose of the RSC is to ensure that the 
level of a contaminant (e.g., MCLG), when combined with other 
identified potential sources of exposure for the population of concern, 
will not result in exposures that exceed the RfD (or Minimal Risk 
Level) (USEPA, 2000c).
    To determine the RSC, EPA follows the Exposure Decision Tree for 
Defining Proposed RfD (or POD/UF) Apportionment in EPA's Methodology 
for Deriving Ambient Water Quality Criteria for the Protection of Human 
Health (USEPA, 2000c). EPA considers whether there are significant 
known or potential uses/sources of the contaminant other than drinking 
water, the adequacy of data and strength of evidence available for each 
relevant exposure medium and pathway, and whether adequate information 
on each exposure source is available to quantitatively characterize the 
exposure profile. The RSC is developed to reflect the exposure to the 
general population or a sensitive population within the general 
population. When exposure data are available for multiple sensitive 
populations or life stages, the most health-protective RSC is selected. 
In the absence of adequate data to quantitatively characterize exposure 
to a contaminant, EPA typically selects an RSC of 20 percent (0.2). 
When scientific data demonstrating that sources and routes of exposure 
other than drinking water are not anticipated for a specific pollutant, 
the RSC can be raised as high as 80 percent based on the available 
data, thereby allocating the remaining 20 percent to other potential 
exposure sources (USEPA, 2000c).

B. Approach to MCLG Derivation for a PFAS Mixture

    There has been a lot of work evaluating parameters that best inform 
the combining of PFAS components identified in environmental matrices 
into mixtures analyses. Indeed, there is currently no consensus on 
whether or how PFAS should be combined for risk assessment purposes. 
EPA considered several approaches to account for dose additive 
noncancer effects associated with PFHxS, HFPO-DA, PFNA, and PFBS in 
mixtures. PFAS can affect multiple human health endpoints and differ in 
their impact (i.e., potency of effect) on target organs/systems. PFAS 
disrupt signaling of multiple biological pathways resulting in common 
adverse effects on several biological systems and functions, including 
thyroid hormone levels, lipid synthesis and metabolism, development, 
and immune and liver function (ATSDR, 2021; EFSA, 2018, 2020; EPA, 
2023d). For example, one PFAS may be most toxic to the liver, and 
another may be most toxic to the thyroid but both chemicals affect the 
liver and the thyroid. Other chemicals regulated as groups operate 
through a common MOA and predominately affect one human health 
endpoint. This supports a flexible data-driven approach that 
facilitates the evaluation of multiple health endpoints, such as the 
HI.
    EPA is proposing to establish an MCLG for a mixture of chemicals 
that are expected to impact multiple endpoints. SDWA requires the 
agency to establish a health-based MCLG set at, ``a level at which no 
known or anticipated adverse effects on the health of persons occur and 
which allow for an adequate margin of safety. EPA's SAB opined that 
where the health endpoints of the chosen compounds are similar, ``the 
HI methodology is a reasonable approach for estimating the potential 
aggregate health hazards associated with the occurrence of chemical 
mixtures in environmental media. The HI is an approach based on dose 
additivity (DA) that has been validated and used by EPA'' (USEPA, 
2022a). This proposal is based on the Agency's finding that the general 
HI approach is the most efficient and effective approach for 
establishing an MCLG for PFAS mixtures consistent with the statutory 
requirement described above. This finding is based on the level of 
protection afforded by both the HBWCs for the individual PFAS as 
components of a mixture and the resulting HI itself, which provides an 
added margin of safety with respect to potential health hazards of 
mixtures of these PFAS. An HI greater than 1.0 is generally regarded as 
an indicator of potential adverse health risks associated with exposure 
to the mixture (USEPA, 1986a; USEPA, 1991b; USEPA, 2000a). A HI less 
than or equal to 1.0 is generally regarded as having no appreciable 
risk (USEPA, 1986a; USEPA, 1991b; USEPA, 2000a). The proposed MCLG is 
based on using this HI of 1.0, and the HBWCs of each mixture component, 
which in turn is based on its respective health-based reference value 
(RfV; RfD or MRL). Because the RfV represents an estimate at which no 
appreciable risk of deleterious effects exists (USEPA, 1986a, 1991a, 
2000a), the use of the HBWCs means that the HI of 1.0 will ensure that 
there are no known or anticipated effects on the health of persons and 
allow for an adequate

[[Page 18655]]

margin of safety. In addition, the resulting HI adds an additional 
margin of safety for mixtures of the four PFAS, to address the 
potential for additive toxicity where the contaminants co-occur and the 
HBWCs for the individual components are less than 1.0. The Agency 
therefore proposes the general HI approach as the basis for the MCLG, 
and because treatment to this level is also feasible, the MCL for these 
PFAS, (see additional discussion in section VI of this preamble) and 
welcomes public comment on its findings.
    EPA considered the two main types of HI approaches: (1) the general 
HI which allows for component chemicals in the mixture to have 
different health effects or endpoints as the basis for the component 
chemical reference values (e.g., RfDs), and (2) the target-organ 
specific HI which relies on reference values based on the same organ or 
organ system (e.g., liver-, thyroid-, or developmental-specific). The 
general HI approach is based on the overall RfD which is protective of 
all effects for a given chemical, and thus is a more health protective 
indicator of risk. The target-organ specific HI approach produces a 
less health protective estimate of risk than the general HI when a 
contaminant impacts multiple organs because the range of potential 
effects has been scoped to a specific target organ, which may be one of 
the less potent effects or for which there may be significant currently 
unquantified effects. Additionally, a target-organ specific HI approach 
relies on toxicity values aggregated by the ``same'' target organ 
endpoint/effect, and the absence of information about a specific 
endpoint may result in the contaminant not being adequately considered 
in a target-organ specific approach, and thus, underestimating 
potential health risk. A target-organ specific HI can only be performed 
for those PFAS for which a health effect specific RfD is calculated. 
For example, for some PFAS a given health effect might be poorly 
characterized or not studied at all, or, as a function of dose may be 
one of the less(er) potent effects in the profile of toxicity for that 
particular PFAS. Another limitation is that so many PFAS lack human 
epidemiological or experimental animal hazard and dose-response 
information across a broad(er) effect range thus limiting derivation of 
target-organ specific values. A similar, effect/endpoint-specific 
method called the relative potency factor (RPF) approach, which 
represents the relative difference in potency of an effect/endpoint 
between an index chemical and other members of the mixture, was also 
considered. (Further background on all of these approaches, plus 
illustrative examples, and a discussion of the advantages and 
challenges associated with each approach can be found in Section 5 and 
6 in USEPA, 2023d).
    EPA also considered setting individual MCLGs instead of and in 
addition to using a mixtures-based approach for PFHxS, HFPO-DA, PFNA, 
and/or PFBS in mixtures. EPA ultimately selected the general HI 
approach for establishing an MCLG for these four PFAS, as described in 
greater detail below, because it provides the most health protective 
endpoint for multiple PFAS in a mixture to ensure there would be no 
known or anticipated adverse effects on the health of persons. EPA also 
considered a target-specific HI or RPF approach but, because of 
information gaps, EPA may not be able to ensure that the MCLG is 
sufficiently health protective. If the Agency only established an 
individual MCLG, the Agency would not provide any protection against 
dose-additivity from regulated co-occurring PFAS. EPA is seeking 
comments on the merits and drawbacks of each of the approaches 
described above. As discussed later in this proposal, EPA is also 
seeking comment on whether to set MCLGs for the individual PFAS in 
addition to or instead of setting them for the mixture.
    EPA is proposing use of the general HI approach. Although EPA's SAB 
opined that it is reasonable to use a HI for evaluation of mixtures of 
PFAS in drinking water for situations where the profile of health 
effects of the chosen compounds share similarity in one or more effect 
domains, the SAB emphasized that using a HI in the context of 
developing regulations for PFAS should not be directly interpreted as a 
quantitative estimate of mixture risk. Rather the SAB agreed that the 
HI can be used as an indicator of potential health risk(s) associated 
with exposure to mixtures of PFAS; see discussion in USEPA (2023d) and 
Section V of this preamble for further information. EPA addresses the 
full range of responses to SAB comments in a response to comment 
document; that document is included in the docket for this action 
(USEPA, 2023f).
    EPA proposes that the general HI is the most appropriate and 
justified approach for considering PFAS mixtures in this rulemaking 
because of the level of protection afforded for the evaluation of 
chemicals with diverse (but in many cases shared) health endpoints. 
SDWA requires the agency to establish a MCLG set at, ``a level at which 
no known or anticipated adverse effects on the health of persons occur 
and which allow for an adequate margin of safety.'' In this context, 
EPA has made a reasonable policy choice for regulating a mixture of 
chemicals that are expected to adversely impact multiple health 
endpoints. Because mixture component chemical HBWCs are based on 
overall lowest RfDs across candidate critical effects, the approach is 
protective against all health effects across component chemicals and 
therefore meets the statutory requirements of establishing an MCLG 
under SDWA. Basing the mixture MCLG on overall RfDs ensures that there 
are no known or anticipated effects, and using the HI adds an 
appropriate margin of safety for a class of contaminants that have been 
shown to co-occur and evidence suggests that they may have dose 
additive toxicity. Conversely, by definition, a target-organ specific 
(e.g., liver-, thyroid-, or developmental-specific) HI or RPF approach 
would not be protective of all health effects across the four PFAS 
proposed for regulation with the mixture MCLG.
    Use of the general HI approach over the target-organ specific HI 
for these four PFAS is supported by EPA guidance (EPA, 2000a) and 
available health assessments and toxicity values (overall RfDs). 
Target-organ specific reference values and RPFs are not currently 
available for HFPO-DA, PFBS, PFHxS, and PFNA.
    EPA's protocol for MCLG development for the mixture of PFHxS, HFPO-
DA, PFNA, and PFBS follows existing Agency guidance, policies, and 
procedures related to the three key inputs (i.e., RfD/Minimal Risk 
Level, DWI-BW, and RSC) and longstanding Agency mixtures guidance 
(USEPA, 1986a; USEPA, 2000a) to address dose additive health effects. 
First, EPA identifies or derives a HBWC, calculated using the MCLG 
equation above, for each of the four individual PFAS in the mixture. 
More information on HBWCs for PFHxS, HFPO-DA, PFNA, and PFBS is 
available in section III.B of this preamble. Peer reviewed, publicly 
available assessments for PFHxS (ATSDR, 2021), HFPO-DA (USEPA, 2021b), 
PFNA (ATSDR, 2021), and PFBS (USEPA, 2021a) provide the chronic 
reference values (RfD, adjusted Minimal Risk Level) used to calculate 
the HBWCs for these four PFAS. The DWI-BW and RSC for each of the four 
PFAS are determined as described using the processes described for 
individual PFAS (Section IV.A of this preamble). Briefly, the DWI-BW 
for each of the four PFAS is selected from the EPA Exposure Factors 
Handbook (USEPA, 2019a), taking into account the relevant

[[Page 18656]]

sensitive population(s) or life stage(s). RSCs are determined based on 
a literature review of potential exposure sources of the four PFAS and 
using the Exposure Decision Tree approach (USEPA, 2000c).
    The HI is based on an assumption of dose addition (DA) among the 
mixture components (Svendsgaard and Hertzberg, 1994; USEPA, 2000a). An 
important aspect of the proposed `general HI' approach is that it is 
based on the availability of a reference value regardless of the 
critical effect for each mixture component. Unlike a target-organ 
specific Hazard Index which is typically based on either shared mode-
of-action or shared health outcome of mixture components, the general 
HI is based on a non-cancer reference value (RfD or Minimal Risk Level) 
for the critical (usually the most sensitive) effect of each component 
(USEPA, 2000a; USEPA, 1989). Importantly, while many PFAS share some 
common target organs/health outcomes such as liver toxicity, the 
potency--and in some cases, even the overall most sensitive target 
organ--differs among PFAS. As an example, the most sensitive organ to 
HFPO-DA is the liver while the most sensitive organ to PFBS is the 
thyroid. Integrating the overall RfDs for each mixture PFAS in the 
calculation of component HQs and a corresponding mixture HI, regardless 
of the critical (most sensitive) effect, ensures health protection 
under an assumption of dose additivity. The alternative may 
underestimate potential health risk(s) associated with exposure to a 
PFAS mixture as a given effect-specific HI might entail the use of 
target-organ specific reference values that are not protective of 
effects at a given mixture component's corresponding overall RfD. 
Further, effect-specific RfDs are not typically derived for chemicals 
beyond the critical effect for the overall RfD which might prohibit the 
inclusion of a chemical in a target-organ specific HI. Recognizing the 
various nuances to the HI approach, EPA welcomes public comment.
    In the HI approach, an HQ is calculated as the ratio of human 
exposure (E) to a health-based reference value (RfV) for each mixture 
component chemical (i) (USEPA, 1986a). The HI involves the use of RfVs 
for each PFAS mixture component (in this case, PFHxS, HFPO-DA, PFNA, 
and PFBS), which have been selected based on sensitive health outcomes 
that are protective of all other adverse health effects observed after 
exposure to the individual PFAS. Thus, this approach, which protects 
against all adverse effects, not only a single adverse outcome/effect 
(e.g., as would be the case using other mixture approaches such as the 
target-organ specific HI or RPF approach), is a health protective risk 
indicator and appropriate for MCLG development. The HI is unitless; in 
the HI formula, E and the RfV must be in the same units. For example, 
if E is the oral intake rate (mg/kg/day), then the RfV could be the RfD 
or Minimal Risk Level, which have the same units. Alternatively, the 
exposure metric can be a media-specific metric such as a measured water 
concentration (e.g., nanograms per liter or ng/L) and the RfV can be an 
HBWC (e.g., ng/L). The component chemical HQs are then summed across 
the mixture to yield the HI. A mixture HI exceeding 1.0 indicates that 
the exposure metric is greater than the toxicity metric and there is 
potential concern for a given environmental medium or site, in this 
case, drinking water served to consumers from a PWS. The HI provides an 
indication of: (1) concern for the overall mixture and (2) potential 
driver PFAS (i.e., those PFAS with high[er] HQs). The HI accounts for 
differences in toxicity among the mixture component chemicals rather 
than weighting them all equally. For a detailed discussion of PFAS dose 
additivity and the HI approach, see the PFAS Mixtures Framework (USEPA, 
2023d). The HI is calculated through the following equation:
[GRAPHIC] [TIFF OMITTED] TP29MR23.061

Where:

HI = Hazard Index
HQi = Hazard Quotient for chemical i
Ei = Exposure, i.e., dose (mg/kg/day) or occurrence 
concentration, such as in drinking water (mg/L), for chemical i
RfVi = Reference value (e.g., oral RfD or Minimal Risk 
Level) [mg/kg/day], or corresponding HBWC; e.g., such as an MCLG for 
chemical i (in milligrams per liter or mg/L)

V. Maximum Contaminant Level Goals

A. PFOA

1. Carcinogenicity Assessment and Cancer Slope Factor (CSF) Derivation
a. Summary of Cancer Health Effects
    The carcinogenicity of PFOA has been observed in both human 
epidemiological and animal toxicity studies. The evidence in high and 
medium confidence epidemiological studies is primarily based on the 
incidence of kidney and testicular cancer, as well as some medium 
quality studies providing limited evidence of breast cancer associated 
with exposure to PFOA. Other cancer types have been observed in human 
studies, although the evidence for these is largely from low confidence 
studies. The evidence of carcinogenicity in animal models was observed 
in three medium or high quality chronic oral animal studies in adult 
Sprague-Dawley rats which identified neoplastic lesions in the liver, 
pancreas, and testes after PFOA exposure.
    Since publication of the 2016 PFOA Health Effects Support Document 
(HESD) (USEPA, 2016e), the evidence supporting the carcinogenicity of 
PFOA has been strengthened by additional published studies. In 
particular, the evidence of kidney cancer from highly exposed community 
studies (Vieira et al., 2013; Barry et al., 2013) is now supported by 
new evidence of renal cell carcinoma (RCC) from a nested case-control 
study in the general population (Shearer et al., 2021). In animal 
models, the evidence of multi-site tumorigenesis reported in two 
chronic bioassays in rats (Butenhoff et al., 2012a; Biegel et al., 
2001) is now supported by new evidence from a third chronic bioassay in 
rats that also reports multi-site tumorigenesis (NTP, 2020).
    The available evidence indicates that PFOA has carcinogenic 
potential in humans and at least one animal species. A plausible, 
though not definitively causal, association between human exposure to 
PFOA and kidney and testicular cancers in the general population and 
highly exposed populations is supported by the available evidence. As 
stated in the Guidelines for Carcinogen Risk Assessment (USEPA, 2005), 
``an inference of causality is strengthened when a pattern of elevated 
risks is observed across several independent studies.'' Two medium 
confidence studies in independent populations provide evidence of an 
association between elevated PFOA serum concentrations and kidney 
cancer (Shearer et al., 2021; Vieira et al., 2013), while two studies 
from the same cohort provide evidence of an association between 
testicular cancer and elevated PFOA serum concentrations (Vieira et 
al., 2013; Barry et al., 2013). A recent National Academies of Science, 
Engineering, and Mathematics report on PFAS similarly ``concluded that 
there is sufficient evidence for an association between PFAS and kidney 
cancer'' (NASEM, 2022). The evidence of carcinogenicity in animals is 
from three studies in rats of the same strain. The results from these 
studies provide evidence of increased incidence of three tumor types 
(Leydig cell tumors (LCTs), pancreatic acinar cell tumors (PACTs),

[[Page 18657]]

and hepatocellular adenomas) in males administered diets dosed with 
PFOA. Importantly, site concordance is not always assumed between 
humans and animal models; agents observed to produce tumors may do so 
at the same or different sites in humans and animals, as appears to be 
the case for PFOA (USEPA, 2005).
b. CSF Derivation
    When a chemical is a linear carcinogen, a value that numerically 
describes the relationship between the dose of a chemical and the risk 
of cancer, is calculated. This is known as a cancer slope factor (CSF). 
The CSF is the cancer risk (i.e., proportion affected) per unit of dose 
(USEPA, 2005). In addition to reevaluating the CSF previously derived 
and described in the 2016 HESD (USEPA, 2016e) based on LCTs in male 
rats observed by Butenhoff et al. (2012a), EPA derived CSFs for 
combined hepatocellular adenomas and carcinomas and pancreatic acinar 
cell adenomas in male rats observed by NTP (2020) and kidney cancer in 
humans reported by Shearer et al. (2021) and Vieira et al. (2013). EPA 
focused on the CSFs derived from the epidemiological data consistent 
with the EPA ORD handbook which states ``when both laboratory animal 
data and human data with sufficient information to perform exposure-
response modeling are available, human data are generally preferred for 
the derivation of toxicity values'' (USEPA, 2022f).
    EPA selected the critical effect of RCCs in human males reported by 
Shearer et al. (2021) as the basis of the CSF for PFOA. Shearer et al. 
(2021) is a multi-center case-control epidemiological study nested 
within the National Cancer Institute's (NCI) Prostate, Lung, 
Colorectal, and Ovarian Screening Trial (PLCO) with median PFOA levels 
relevant to the general U.S. population. The PLCO is a randomized 
clinical trial of the use of serum biomarkers for cancer screening. The 
cases in Shearer et al. (2021) included all the participants in the 
screening arm of the PLCO trial who were newly diagnosed with RCC 
during the follow-up period (N = 326) and all cases were 
histopathologically confirmed. Controls were selected among 
participants in the PLCO trial screening arm based on those who had 
never had RCC and were individually matched to the RCC cases by age at 
enrollment, sex, race/ethnicity, study center, and year of blood draw. 
Additionally, analyses conducted by the authors accounted for numerous 
confounders, including the potential for confounding by other PFAS. 
Study design advantages of the Shearer et al. (2021) compared with the 
Vieira et al. (2013) include specificity in the health outcome 
considered (RCC vs. any kidney cancer), the type of exposure assessment 
(serum biomarker vs. modeled exposure), source population (multi-center 
vs. Ohio and West Virginia regions), and study size (324 cases and 324 
matched controls vs. 59 cases and 7,585 registry-based controls). The 
resulting CSF is 0.0293 (ng/kg/day)-\1\.
    Selection of RCCs as the critical effect is supported by similar 
findings from other studies of a highly exposed community (Barry et 
al., 2013; Vieira et al., 2013), an occupational kidney cancer 
mortality study (Steenland and Woskie, 2012), as well as a meta-
analysis of epidemiological literature that concluded that there was an 
increased risk of kidney tumors correlated with increased PFOA serum 
concentrations (Bartell et al., 2021). Further discussion of the 
rationale for endpoint and study selection and descriptions of the 
modeling methods are described in USEPA (2023b).
2. Assessment of Noncancer Health Effects and Reference Dose (RfD) 
Derivation
    The Agency has also considered noncancer effects in its assessment 
of the best available science to derive the MCLG. As described in USEPA 
(2023b), there is evidence from both human epidemiological and animal 
toxicological studies that oral PFOA exposure may result in adverse 
health effects across many health outcomes, including but not limited 
to: immune, hepatic, developmental, cardiovascular, reproductive, and 
endocrine outcomes. As recommended by the SAB (USEPA, 2022a), EPA has 
largely focused its systematic literature review, health outcome 
synthesis, and toxicity value derivation efforts ``on those health 
outcomes that have been concluded to have the strongest evidence, 
including the liver disease, immune system dysfunction, serum lipid 
aberration, impaired fetal growth, and cancer.'' Conclusions regarding 
the four noncancer adverse health outcome categories (i.e., judgements 
for human, animal, and integrated evidence streams (USEPA, 2023b)) are 
described in the subsections below. Descriptions of studies and the 
basis for conclusions about the non-prioritized health outcomes are 
described in USEPA (2023b).
a. Summary of Noncancer Health Effects
    EPA determined that the evidence indicates that oral PFOA exposure 
is associated with adverse hepatic effects based on the study quality 
evaluation, evidence synthesis and evidence integration of the relevant 
human epidemiological and animal toxicity studies. There is moderate 
evidence from epidemiological studies supporting an association between 
PFOA exposure and hepatic outcomes such as elevated serum liver enzymes 
indicative of hepatic damage. Overall, there is consistent evidence of 
a positive association between PFOA serum concentrations and alanine 
aminotransferase (ALT), a liver enzyme marker. The evidence of hepatic 
effects in humans was supported by robust evidence of hepatic effects 
resulting from PFOA exposure in animal studies. Several studies provide 
comprehensive histopathological reports of non-neoplastic hepatic 
lesions (e.g., hepatocellular death and necrosis) in PFOA-treated 
rodents, as well as increases in serum liver enzymes similar to the 
trends observed in humans.
    EPA determined that the evidence indicates that oral PFOA exposure 
is associated with adverse immunological effects based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal toxicity studies. There is 
moderate evidence from epidemiological studies supporting an 
association between PFOA and immune outcomes such as immunosuppression. 
Overall, there is consistent evidence of an association between PFOA 
serum concentrations and developmental immune effects (i.e., reduced 
antibody response to vaccination in children). Associations between 
PFOA and other immune system effects (e.g., hypersensitivity and 
autoimmune disease) were mixed. The evidence for developmental 
immunological effects in humans was supported by moderate evidence of 
immunotoxicity resulting from PFOA exposure in animal studies. Studies 
report varying manifestations of immune system effects including 
altered immune cell populations and altered spleen and thymus 
cellularity and weight. PFOA treatment resulted in reduced globulin and 
immunoglobulin levels in animals that are consistent with the decreased 
antibody response seen in human populations (i.e., the observed animal 
and human study health outcomes are both indicators of 
immunosuppression).
    EPA determined that the evidence indicates that oral PFOA exposure 
is associated with adverse developmental effects based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal

[[Page 18658]]

toxicity studies. There is moderate evidence from epidemiological 
studies supporting an association between PFOA and developmental 
outcomes such as fetal growth. Overall, there is consistent evidence of 
a relationship between PFOA concentrations and low birth weight. 
Associations between PFOA and other developmental effects (e.g., 
postnatal growth, fetal loss, and birth defects) were mixed. The 
evidence for developmental effects in humans was supported by robust 
evidence of developmental toxicity resulting from PFOA exposure in 
animal studies. Several studies in rodents provide evidence of 
decreased fetal and pup weight due to gestational PFOA exposure, 
consistent with the evidence of low birth weight in humans. Other pre- 
and post-natal effects observed in animal models include decreased 
offspring survival and developmental delays (e.g., delayed eye 
opening).
    EPA determined that the evidence indicates that oral PFOA exposure 
is associated with adverse cardiovascular effects based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal toxicity studies. There is 
moderate evidence from epidemiological studies supporting an 
association between PFOA and cardiovascular outcomes such as 
alterations in serum lipids. Overall, there is consistent evidence of 
positive relationships between PFOA serum concentrations and serum 
total cholesterol, low-density lipoproteins, and triglycerides. There 
is also limited evidence of positive associations of PFOA with blood 
pressure and hypertension among adult populations. The evidence for 
cardiovascular effects in humans was supported by moderate evidence of 
cardiovascular effects resulting from PFOA exposure in animal studies. 
Several studies in rodents provide evidence of alterations in serum 
total cholesterol and triglycerides, though the effect direction varied 
with dose. Regardless, these effects indicate a disruption in lipid 
metabolism resulting from PFOA treatment, consistent with the 
alterations in serum lipids observed in humans.
b. RfD Derivation
    The databases for the four prioritized health outcomes were 
evaluated further for identification of medium and high confidence 
studies and endpoints to select for dose-response modeling. EPA 
prioritized endpoints with the strongest overall weight of evidence 
based on human and animal evidence for POD derivation. Specifically, 
EPA focused the dose response assessment on the health outcomes where 
the evidence indicated that PFOA causes health effects in humans under 
relevant exposure circumstances. The focus of this Federal Register 
Notice (FRN) is on epidemiological studies for the four prioritized 
health outcomes for which studies meeting this consideration were 
available, as human data are generally preferred ``when both laboratory 
animal data and human data with sufficient information to perform 
exposure-response modeling are available'' (USEPA, 2023b). EPA presents 
PODs and candidate RfDs for animal studies, as well as other health 
outcomes determined to have sufficient strength of evidence and studies 
suitable for dose-response modeling in USEPA (2023b).
    EPA identified four candidate critical effects across the four 
prioritized health outcomes, all of which were represented by several 
candidate critical studies. These candidate critical effects are 
decreased antibody production in response to vaccinations (immune), low 
birth weight (developmental), increased serum total cholesterol 
(cardiovascular), and elevated ALT (hepatic). As described in the 
following paragraphs and in further detail in USEPA (2023b), EPA 
selected studies from each health outcome to proceed with candidate RfD 
derivation. For all selected candidate RfDs, the composite UF was 10 
(10x for intraspecies variability). The candidate RfDs are presented in 
Table 3.
    Two medium confidence studies were considered for POD derivation 
for the decreased antibody production in response to various 
vaccinations in children Budtz-J[oslash]rgensen and Grandjean (2018); 
and Timmerman et al. (2021). These candidate studies offer a variety of 
PFOA exposure measures across various populations and various 
vaccinations. Budtz-J[oslash]rgensen and Grandjean (2018) investigated 
anti-tetanus and anti-diphtheria responses in Faroese children aged 5-7 
and Timmerman et al. (2021) investigated anti-tetanus and anti-
diphtheria responses in Greenlandic children aged 7-12. Though the 
Timmerman et al. (2021) study is also a medium confidence study, the 
study by Budtz-J[oslash]rgensen and Grandjean (2018) has two additional 
features that strengthen the confidence in this RfD: (1) the response 
reported by this study was more precise in that it reached statistical 
significance, and (2) the analysis considered co-exposures of other 
PFAS. The RfD for anti-tetanus response in 7-year-old Faroese children 
and anti-diphtheria response in 7-year-old Faroese children, both from 
Budtz-J[oslash]rgensen and Grandjean (2018) were ultimately selected 
for the immune outcome as they are the same and have no distinguishing 
characteristics that would facilitate selection of one over the other.
    Six high confidence studies (Chu et al., 2020; Govarts et al., 
2016; Sagiv et al., 2018; Starling et al., 2017; Wikstr[ouml]m et al., 
2020; Yao et al., 2021) reported decreased birth weight in infants 
whose mothers were exposed to PFOA. These candidate studies offer a 
variety of PFOA exposure measures across the fetal and neonatal window. 
All six studies reported their exposure metric in units of ng/mL and 
reported the [beta] coefficients per ng/mL or ln(ng/mL), along with 95% 
confidence intervals (CIs), estimated from linear regression models. Of 
the six individual studies, Sagiv et al. (2018) and Wikstr[ouml]m et 
al. (2020) assessed maternal PFOA serum concentrations primarily or 
exclusively in the first trimester, minimizing concerns surrounding 
bias due to pregnancy-related hemodynamic effects. Therefore, the RfDs 
from these two studies were considered further for candidate RfD 
selection. Both were high confidence prospective cohort studies with 
many study strengths including sufficient study sensitivity and largely 
sound methodological approaches, analysis, and design, as well as no 
evidence of bias. The RfD from Wikstr[ouml]m et al. (2020) was 
ultimately selected for the developmental outcome as it was the lowest 
candidate RfD from these two studies.
    Three medium confidence studies were considered for POD derivation 
for the cholesterol endpoint (Dong et al., 2019; Lin et al., 2019; 
Steenland et al., 2009). These candidate studies offer a variety of 
PFOA exposure measures across various populations. Dong et al. (2019) 
investigated the NHANES population (2003-2014), while Steenland et al. 
(2009) investigated effects in a high-exposure community (the C8 Health 
Project study population). Lin et al. (2019) collected data from 
prediabetic adults from the Diabetes Prevention Program (DPP) and DPP 
Outcomes Study at baseline (1996-1999). Of the three studies, Dong et 
al. (2019) and Steenland et al. (2009) exclude those prescribed 
cholesterol medication, minimizing concerns surrounding confounding due 
to the medical intervention altering serum total cholesterol levels. 
Additionally, Dong et al. (2019) reported measured serum total 
cholesterol whereas Steenland et al. (2009) reported regression 
coefficients as the response variable. Since EPA prefers dose response 
modeling of endpoint data, the RfD from Dong et al. (2019) was selected 
for the cardiovascular outcome, as there

[[Page 18659]]

is increased confidence in the modeling results from this study.
    Four medium confidence studies were selected as candidates for POD 
derivation for the ALT endpoint (Gallo et al., 2012; Darrow et al., 
2016; Nian et al., 2019; Lin et al., 2010). The two largest studies of 
PFOA and ALT in adults are Gallo et al. (2012) and Darrow et al. 
(2016), both conducted in over 30,000 adults from the C8 Study. Gallo 
et al. (2012) reported measured serum ALT levels, unlike Darrow et al. 
(2016) which reported a modeled regression coefficient as the response 
variable. Another difference between the two studies is reflected in 
exposure assessment: Gallo et al. (2012) includes measured PFOA serum 
concentrations, while Darrow et al. (2016) based PFOA exposure on 
modeled PFOA serum levels. Two additional studies (Lin et al., 2010; 
Nian et al., 2019) were considered by EPA for POD derivation because 
they reported significant associations in general populations in the 
U.S and a high exposed population in China, respectively. Nian et al. 
(2019) examined a large population of adults in Shenyang (one of the 
largest fluoropolymer manufacturing centers in China) part of the 
Isomers of C8 Health Project. In an NHANES adult population, Lin et al. 
(2010) observed elevated ALT levels per log-unit increase in PFOA. 
While this is a large nationally representative population, several 
methodological limitations, including lack of clarity about base of 
logarithmic transformation applied to PFOA concentrations in regression 
models and the choice to model ALT as an untransformed variable 
preclude its use for POD derivation. While both Nian et al. (2019) and 
Gallo et al. (2012) provide measured PFOA serum concentrations and a 
measure of serum ALT levels, the RfD for increased ALT from Gallo et 
al. (2012) was ultimately selected for the hepatic outcome as it was 
conducted in a community exposed predominately to PFOA whereas Nian et 
al. (2019) was in a community exposed predominately to PFOS, which 
reduces concerns about confounding from other PFAS.

  Table 3--Candidate Reference Doses for PFOA for the Four Prioritized
                             Health Outcomes
------------------------------------------------------------------------
                                   Measurement of      Candidate RfD \1\
       Study reference         exposure and endpoint      (mg/kg/day)
------------------------------------------------------------------------
                                 Immune
------------------------------------------------------------------------
Budtz-J[oslash]rgensen and     PFOA at age five                 3 x 10-
 Grandjean, 2018.               years and anti-
                                tetanus antibody
                                concentrations at
                                age seven years.
Budtz-J[oslash]rgensen and     PFOA at age five                 3 x 10-
 Grandjean, 2018.               years on anti-
                                diphtheria antibody
                                concentrations at
                                age seven years.
Timmerman et al., 2021.......  PFOA and anti-tetanus         3 x 10-\8\
                                antibody
                                concentrations at
                                ages 7-10 years.
Timmerman et al., 2021.......  PFOA and anti-                2 x 10-\8\
                                diphtheria antibody
                                concentrations at
                                ages 7-10 years.
------------------------------------------------------------------------
                              Developmental
------------------------------------------------------------------------
Sagiv et al., 2018...........  PFOA in first                 1 x 10-\7\
                                trimester and
                                decreased birth
                                weight.
Wikstr[ouml]m et al., 2020...  PFOA in first and                3 x 10-
                                second trimesters
                                and decreased birth
                                weight.
------------------------------------------------------------------------
                             Cardiovascular
------------------------------------------------------------------------
Dong et al., 2019............  Increased serum total            3 x 10-
                                cholesterol.
Steenland et al., 2009.......  Increased serum total         5 x 10-\8\
                                cholesterol.
------------------------------------------------------------------------
                                 Hepatic
------------------------------------------------------------------------
Gallo et al., 2012...........  Increased serum ALT..            2 x 10-
Darrow et al., 2016..........  Increased serum ALT..         8 x 10-\7\
Nian et al., 2019............  Increased serum ALT..         5 x 10-\8\
------------------------------------------------------------------------
Notes:
\1\ RfDs are rounded to 1 significant digit.
Bolded values indicate selected health outcome-specific RfDs.

    The available evidence indicates there are effects across immune, 
developmental, cardiovascular, and hepatic organ systems at the same or 
approximately the same level of PFOA exposure. Candidate RfDs within 
the immune, developmental, and cardiovascular outcomes are the same 
value (i.e., 3 x 10-8 mg/kg/day). Therefore, EPA has selected an 
overall RfD for PFOA of 3 x 10-8 mg/kg/day. The immune, developmental 
and cholesterol RfDs and serve as co-critical effects and are 
protective of effects that may occur in sensitive populations (i.e., 
infants and children), as well as hepatic effects that may result from 
PFOA exposure.
c. MCLG Derivation
    Consistent with the Guidelines for Carcinogen Risk Assessment 
(USEPA, 2005), EPA reviewed the weight of the evidence and determined 
that PFOA is Likely to Be Carcinogenic to Humans, as ``the evidence is 
adequate to demonstrate carcinogenic potential to humans but does not 
reach the weight of evidence for the descriptor Carcinogenic to 
Humans.'' This determination is based on the evidence of kidney and 
testicular cancer in humans and LCTs, pancreatic acinar cell tumors, 
and hepatocellular adenomas in rats as described in USEPA (2023b).
    Consistent with the statutory definition of MCLG, EPA establishes 
MCLGs of zero for carcinogens classified as Carcinogenic to Humans or 
Likely to be Carcinogenic to Humans where there is insufficient 
information to determine that a carcinogen has a threshold dose below 
which no carcinogenic effects have been observed. In this situation, 
EPA takes a health protective approach of assuming that there is no 
such threshold and that carcinogenic effects should therefore be 
extrapolated linearly to zero. This approach ensures that the MCLG is 
set at a level where there are no anticipated adverse health effects 
with a margin of safety. This is the linear default extrapolation

[[Page 18660]]

approach. Here, EPA has determined that PFOA is Likely to be 
Carcinogenic to Humans based on sufficient evidence of carcinogenicity 
in humans and animals and has also determined that a linear default 
extrapolation approach is appropriate as there is no evidence 
demonstrating a threshold level of exposure below which there is no 
appreciable cancer risk (USEPA, 2005) and therefore, it is assumed that 
there is no known threshold for carcinogenicity (USEPA, 2016d). Based 
upon a consideration of the best available peer reviewed science and a 
consideration of an adequate margin of safety, EPA proposes a MCLG of 
zero for PFOA in drinking water.
    EPA is seeking comment on the derivation of the proposed MCLG for 
PFOA and its determination that PFOA is Likely to be Carcinogenic to 
Humans and whether the proposed MCLG is set at the level at which there 
are no adverse effects to the health of persons and which provides an 
adequate margin of safety. EPA is also seeking comment on its 
assessment of the noncancer effects associated with exposure to PFOA 
and the toxicity values described in USEPA (2023b).

B. PFOS

1. Carcinogenicity Assessment and CSF Derivation
a. Summary of Cancer Health Effects
    Several medium and high confidence human epidemiological studies 
and one high confidence animal chronic cancer bioassay comprise the 
evidence database for the carcinogenicity of PFOS. The available 
epidemiology studies reported elevated risk of bladder, prostate, 
kidney, and breast cancers after chronic PFOS exposure. While there are 
reports of cancer incidence from epidemiological studies, the study 
designs, analyses, and mixed results preclude a definitive conclusion 
about the relationship between PFOS exposure and cancer outcomes in 
humans. The one high confidence animal chronic cancer bioassay study 
provides evidence of multi-site tumorigenesis in both male and female 
rats.
    While the epidemiological evidence of associations between PFOS and 
cancer found mixed results across tumor types, the available study 
findings support a plausible correlation between PFOS exposure and 
carcinogenicity in humans. The single chronic cancer bioassay performed 
in rats is positive for multi-site and -sex tumorigenesis (Thomford, 
2002; Butenhoff et al., 2012b). In this study, statistically 
significant increases in the incidences of hepatocellular adenomas or 
combined hepatocellular adenomas and carcinomas were observed in both 
male and female rats. There was also a statistically significant dose-
response trend of these tumors in both sexes. As described in USEPA 
(2023c), the available mechanistic evidence is consistent with multiple 
potential MOAs for this tumor type; therefore, the hepatocellular 
tumors observed by Thomford (2002)/Butenhoff et al. (2012b) may be 
relevant to humans. In addition to hepatocellular tumors, Thomford 
(2002)/Butenhoff et al. (2012b) reported increased incidences of 
pancreatic islet cell tumors with a statistically significant dose-
dependent positive trend, as well as modest increases in the incidence 
of thyroid follicular cell tumors. The findings of multiple tumor types 
provide additional support for potential multi-site tumorigenesis 
resulting from PFOS exposure. Structural similarities between PFOS and 
PFOA add to the weight of evidence for carcinogenicity of PFOS. 
Notably, a similar set of noncancer effects have been observed after 
exposure to either PFOA or PFOS in humans and animal studies including 
similarities in hepatic, developmental, immunological, cardiovascular, 
and endocrine effects.
    Under the Guidelines for Carcinogen Risk Assessment (USEPA, 2005), 
EPA reviewed the weight of the evidence and determined that PFOS is 
Likely to Be Carcinogenic to Humans, as ``the evidence is adequate to 
demonstrate carcinogenic potential to humans but does not reach the 
weight of evidence for the descriptor Carcinogenic to Humans.'' As 
described in USEPA (2023c), EPA determined that the available data for 
PFOS surpass many of the descriptions for the descriptor of Suggestive 
Evidence of Carcinogenic Potential.
b. CSF Derivation
    The Thomford (2002)/Butenhoff et al. (2012b) chronic cancer study 
in male and female rats is of high confidence and provides multi-dose 
tumor incidence findings that are suitable for dose-response modeling 
and subsequent CSF derivation. As described in USEPA (2023c), EPA 
derived PODs and candidate CSFs for three endpoints reported by this 
study: hepatocellular adenomas in male rats; combined hepatocellular 
adenomas and carcinomas in female rats; and pancreatic islet cell 
carcinomas in male rats.
    EPA selected the hepatocellular adenomas and carcinomas in female 
rats reported by Thomford (2002)/Butenhoff et al. (2012b) as the basis 
of the CSF for PFOS because there was a statistically significant 
increase in tumor incidence in the highest dose group, a trend of 
increased incidence with increasing PFOS concentrations across dose 
groups, and it was the most health-protective value. The resulting CSF 
is 39.5 (mg/kg/day)-1. Selection of hepatocellular adenomas and 
carcinomas in female rats is supported by statistically significant 
increases in hepatocellular tumor incidence in the high dose group as 
well as a statistically significant trend of this response observed in 
the male rats. The critical effect of pancreatic islet cell carcinomas 
was not selected as the basis of the CSF because the response of the 
high dose group was not statistically different from the control group, 
though the trend of response across dose groups was statistically 
significant. Further discussion on the rationale for endpoint selection 
and descriptions of the modeling methods are described in USEPA 
(2023c).
    In support of the selection of hepatocellular tumors as the basis 
of the CSF for PFOS, a recently published study (Goodrich et al., 2022) 
reports associations between hepatocellular carcinomas and PFOS serum 
concentrations in humans. These findings provide further support for 
both MOA conclusions in USEPA (2023c) and the ``Likely to Be 
Carcinogenic to Humans'' designation. This study was published after 
the systematic literature review cutoff date for the proposed MCLG for 
PFOS (USEPA, 2023c), therefore EPA requests comment on the Goodrich et 
al. (2022) study and whether it supports EPA's ``Likely to Be 
Carcinogenic to Humans'' designation.
2. Assessment of Noncancer Health Effects and Reference Dose (RfD) 
Derivation
    The Agency has also considered noncancer effects in its assessment 
of the best available science to derive the MCLG. As described in USEPA 
(2023c), there is evidence from both human epidemiological and animal 
toxicological studies that oral PFOS exposure may result in adverse 
health effects across many health outcomes, including but not limited 
to immune, hepatic, developmental, cardiovascular, nervous system, and 
endocrine outcomes. As recommended by the SAB (USEPA, 2022a), EPA has 
focused its systematic literature review, health outcome synthesis, and 
toxicity value derivation efforts ``on those health outcomes that have 
been concluded to have the strongest evidence, including

[[Page 18661]]

the liver disease, immune system dysfunction, serum lipid aberration, 
impaired fetal growth, and cancer.'' Conclusions regarding the four 
noncancer adverse health outcome categories (i.e., judgements for 
human, animal, and integrated evidence streams (USEPA, 2022f)) are 
described in the subsections below. Descriptions and conclusions about 
the non-priority health outcomes are described in USEPA (2023c).
a. Summary of Noncancer Health Effects
    EPA determined that the evidence indicates that oral PFOS exposure 
is associated with adverse hepatic effects based on the study quality 
evaluation, evidence synthesis and evidence integration of the relevant 
human epidemiological and animal toxicity studies. Specifically, there 
is moderate evidence from epidemiological studies supporting an 
association between PFOS exposure and hepatic outcomes such as elevated 
serum liver enzymes indicative of hepatic damage. Overall, there is 
consistent evidence of a positive association between PFOS serum 
concentrations and ALT, a liver enzyme marker. The evidence of hepatic 
effects in humans was supported by robust evidence of hepatotoxicity 
resulting from PFOS exposure in animal studies. Studies in rodents 
observed several manifestations of hepatic toxicity including 
histopathological reports of non-neoplastic hepatic lesions (e.g., 
hepatic necrosis and inflammation) and increases in serum liver enzymes 
similar to the trends observed in humans.
    EPA determined that the evidence indicates that oral PFOS exposure 
is associated with adverse immunological effects based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal toxicity studies. There is 
moderate evidence from epidemiological studies supporting an 
association between PFOS and immune outcomes such immunosuppression. 
Overall, there is generally consistent evidence of an association 
between PFOS serum concentrations and reduced antibody response to 
vaccination in children. Associations between PFOS and other immune 
system effects (e.g., hypersensitivity and asthma) were mixed. The 
evidence for immunological effects in humans was supported by moderate 
evidence of immunotoxicity resulting from PFOS exposure in animal 
studies. Studies in rodents report immune system effects including 
altered activity of plaque-forming cells and natural killer cells, 
altered spleen and thymus cellularity, and bone marrow hypocellularity 
and extramedullary hematopoiesis. The alterations in plaque-forming and 
natural killer cells in animals are consistent with the decreased 
antibody response seen in human populations (i.e., the observed animal 
and human study health outcomes are both indicators of 
immunosuppression).
    EPA determined that the evidence indicates that oral PFOS exposure 
is associated with adverse developmental effects, based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal toxicity studies. There is 
moderate evidence from epidemiological studies supporting an 
association between PFOS and developmental outcomes such as fetal 
growth and gestational duration. Overall, there is consistent evidence 
of a relationship between PFOS concentrations and low birth weight, 
preterm birth, and gestational age. Associations between PFOS and 
postnatal growth were inconsistent while there was limited evidence for 
other developmental effects (e.g., fetal loss and birth defects). The 
evidence for developmental effects in humans was supported by moderate 
evidence of developmental toxicity resulting from PFOS exposure in 
animal studies. Several studies in rodents provide evidence of 
decreased fetal and pup weight due to gestational PFOS exposure, 
consistent with the evidence of low birth weight in humans. Decreased 
maternal BW was also observed. Other pre- and post-natal effects 
observed in animal models include increased offspring mortality, 
skeletal and soft tissue effects, and developmental delays (e.g., 
delayed eye opening). However, some studies reported no indications of 
developmental toxicity.
    EPA determined that the evidence indicates that oral PFOS exposure 
is associated with adverse cardiovascular effects, based on the study 
quality evaluation, evidence synthesis and evidence integration of the 
relevant human epidemiological and animal toxicity studies. There is 
moderate evidence from epidemiological studies supporting an 
association between PFOS and cardiovascular outcomes such as 
alterations in serum lipids. Overall, there is consistent evidence of 
positive relationships between PFOS serum concentrations and serum 
total cholesterol and low-density lipoproteins. There is also evidence 
of positive associations of PFOS with blood pressure and hypertension 
in adults. The evidence for cardiovascular effects in humans was 
supported by moderate evidence of cardiovascular effects resulting from 
PFOS exposure in animal studies. Several studies in rodents provide 
evidence of alterations in serum total cholesterol and triglycerides, 
though the effect direction varied with dose. Regardless, these effects 
indicate a disruption in lipid metabolism resulting from PFOS 
treatment, consistent with the alterations in serum lipids observed in 
humans.
b. RfD Derivation
    The databases for the four prioritized health outcomes were 
evaluated further for identification of medium and high confidence 
studies and endpoints to select for dose-response modeling. EPA 
prioritized endpoints with the strongest overall weight of evidence 
based on human and animal evidence for POD derivation. Specifically, 
EPA focused the dose response assessment on the health outcomes where 
the evidence indicated that PFOS causes health effects in humans under 
relevant exposure circumstances. The focus of this FRN is on 
epidemiological studies for the four prioritized health outcomes for 
which studies meeting this consideration were available, as human data 
are generally preferred ``when both laboratory animal data and human 
data with sufficient information to perform exposure-response modeling 
are available'' (USEPA, 2022f). EPA presents PODs and candidate RfDs 
for animal studies, as well as other health outcomes determined to have 
sufficient strength of evidence and studies suitable for dose-response 
modeling in USEPA (2023c).
    EPA identified four candidate critical effects across the four 
prioritized health outcomes, all of which were represented by several 
candidate critical studies. These candidate critical effects are 
decreased antibody production in response to vaccinations (immune), low 
birth weight (developmental), increased serum total cholesterol 
(cardiovascular), and elevated ALT (hepatic). As described in the 
following paragraphs and in further detail in USEPA (2023c), EPA 
selected studies from each health outcome to proceed with candidate RfD 
derivation. For all selected candidate RfDs, presented in Table 4, the 
composite UF was 10 (10x for intraspecies variability).
    Two medium confidence studies were considered for POD derivation 
for the decreased antibody production in response to various 
vaccinations in children Budtz-J[oslash]rgensen and Grandjean (2018) 
and Timmerman et al. (2021). These candidate studies offer a variety

[[Page 18662]]

of PFOS exposure measures across various populations and various 
vaccinations. Budtz-J[oslash]rgensen and Grandjean (2018) investigated 
anti-tetanus and anti-diphtheria responses in Faroese children aged 5-7 
and Timmerman et al. (2021) investigated anti-tetanus and anti-
diphtheria responses in Greenlandic children aged 7-12. Though the 
Timmerman et al. (2021) study is also a medium confidence study, the 
study by Budtz-J[oslash]rgensen and Grandjean (2018) has two features 
that strengthen the results: (1) the response reported by this study 
reached statistical significance, and (2) the analysis considered co-
exposures of other PFAS. The RfD for anti-diphtheria response in 7-
year-old Faroese children from Budtz-J[oslash]rgensen and Grandjean 
(2018) was ultimately selected for the immune outcome because the 
response reported by this study reached statistical significance, this 
analysis considered co-exposures of other PFAS, and it was the more 
health-protective of the two vaccine-specific responses reported by 
Budtz-J[oslash]rgensen and Grandjean (2018).
    Six high confidence studies (Chu et al., 2020; Sagiv et al., 2018; 
Starling et al., 2017; Wikstr[ouml]m et al., 2020; Darrow et al., 2013; 
Yao et al., 2021) reported decreased birth weight in infants whose 
mothers were exposed to PFOS. These candidate studies offer a variety 
of PFOS exposure measures across the fetal and neonatal window. All six 
studies reported their exposure metric in units of ng/mL and reported 
the [beta] coefficients per ng/mL or ln(ng/mL), along with 95% CIs, 
estimated from linear regression models. Of the six individual studies, 
Sagiv et al. (2018) and Wikstr[ouml]m et al. (2020) assessed maternal 
PFOS serum concentrations primarily or exclusively in the first 
trimester, minimizing concerns surrounding bias due to pregnancy-
related hemodynamic effects. Therefore, the RfDs from these two studies 
were considered further for candidate RfD selection. Both were high 
confidence prospective cohort studies with many study strengths 
including sufficient study sensitivity and largely sound methodological 
approaches, analysis, and design, as well as no evidence of bias. The 
RfD from Wikstr[ouml]m et al. (2020) was ultimately selected for the 
developmental outcome as it was the lowest candidate RfD from these two 
studies.
    Three medium confidence studies were considered for POD derivation 
for the cholesterol endpoint (Dong et al., 2019; Lin et al., 2019; 
Steenland et al., 2009). These candidate studies offer a variety of 
PFOS exposure measures across various populations. Dong et al. (2019) 
investigated the NHANES population (2003-2014), while Steenland et al. 
(2009) investigated effects in a high-exposure community (the C8 Health 
Project study population). Lin et al. (2019) collected data from 
prediabetic adults from the DPP and DPP Outcomes Study at baseline 
(1996-1999). Of the three studies, Dong et al. (2019) and Steenland et 
al. (2009) exclude those prescribed cholesterol medication, minimizing 
concerns surrounding confounding due to the medical intervention 
altering serum total cholesterol levels. Additionally, Dong et al. 
(2019) reported measured serum total cholesterol whereas Steenland et 
al. (2009) reported modeled regression coefficients as the response 
variable. Since EPA prefers dose response modeling of measured data, 
the RfD from Dong et al. (2019) was selected for cardiovascular 
endpoint as there is increased confidence in the modeling from this 
study.
    Three medium confidence studies were selected as candidates for POD 
derivation for the ALT endpoint (Gallo et al., 2012; Nian et al., 2019; 
Lin et al., 2010). The largest study of PFOS and ALT in adults is Gallo 
et al. (2012), conducted in over 30,000 adults from the C8 Study 
Project. Two additional studies (Lin et al., 2010; Nian et al., 2019) 
were considered by EPA for POD derivation because they reported 
significant associations in general populations in the U.S and a high 
exposed population in China, respectively. Nian et al. (2019) examined 
a large population of adults in Shenyang (one of the largest 
fluoropolymer manufacturing centers in China) part of the Isomers of C8 
Health Project. In an NHANES adult population, Lin et al. (2010) 
observed elevated ALT levels per log-unit increase in PFOS. While this 
is a large nationally representative population, several methodological 
limitations, including lack of clarity about base of logarithmic 
transformation applied to PFOS concentrations in regression models and 
the choice to model ALT as an untransformed variable preclude its use 
for POD derivation. The RfD from Nian et al., 2019 was ultimately 
selected for the hepatic outcome as PFOS was the predominating PFAS in 
this study which reduces concern about potential confounding by other 
PFAS.

  Table 4--Candidate Reference Doses for PFOS for the Four Prioritized
                             Health Outcomes
------------------------------------------------------------------------
                                                       Candidate RfD \1\
            Study                     Endpoint            (mg/kg/day)
------------------------------------------------------------------------
                                 Immune
------------------------------------------------------------------------
Budtz-J[oslash]rgensen and     PFOS at age five              3 x 10-\7\
 Grandjean, 2018.               years and anti-
                                tetanus antibody
                                concentrations at
                                age seven years.
Budtz-J[oslash]rgensen and     PFOS at age five                 2 x 10-
 Grandjean, 2018.               years on anti-
                                diphtheria antibody
                                concentrations at
                                age seven years.
Timmerman et al., 2021.......  PFOS and anti-tetanus         2 x 10-\7\
                                antibody
                                concentrations at
                                ages 7-10 years.
Timmerman et al., 2021.......  PFOS and anti-                1 x 10-\7\
                                diphtheria antibody
                                concentrations at
                                ages 7-10 years.
------------------------------------------------------------------------
                              Developmental
------------------------------------------------------------------------
Sagiv et al., 2018...........  PFOS in first                 6 x 10-\7\
                                trimester and
                                decreased birth
                                weight.
Wikstr[ouml]m et al., 2020...  PFOS in first and                1 x 10-
                                second trimesters
                                and decreased birth
                                weight.
------------------------------------------------------------------------
                             Cardiovascular
------------------------------------------------------------------------
Dong et al., 2019............  Increased serum total            1 x 10-
                                cholesterol.
Steenland et al., 2009.......  Increased serum total         1 x 10-\7\
                                cholesterol.
------------------------------------------------------------------------
                                 Hepatic
------------------------------------------------------------------------
Gallo et al., 2012...........  Increased serum ALT..         7 x 10-\7\

[[Page 18663]]

 
Nian et al., 2019............  Increased serum ALT..            2 x 10-
------------------------------------------------------------------------
Notes:
\1\ RfDs are rounded to 1 significant digit.
Bolded values indicate selected health outcome-specific RfDs.

    The available evidence indicates there are effects across immune, 
developmental, cardiovascular, and hepatic organ systems at the same or 
approximately the same level of PFOS exposure. Candidate RfDs within 
the developmental and cardiovascular outcomes are the same value (i.e., 
1 x 10-7 mg/kg/day). Therefore, EPA has selected an overall RfD for 
PFOS of 1 x 10-7 mg/kg/day. The developmental and cholesterol RfDs 
serve as co-critical effects and are protective of immune and hepatic 
effects that may result from PFOS exposure.
c. MCLG Derivation
    Consistent with the Guidelines for Carcinogen Risk Assessment 
(USEPA, 2005), EPA reviewed the weight of the evidence and determined 
that PFOS is Likely to Be Carcinogenic to Humans, as ``the evidence is 
adequate to demonstrate carcinogenic potential to humans but does not 
reach the weight of evidence for the descriptor Carcinogenic to 
Humans.'' This determination is based on the evidence of hepatocellular 
tumors in male and female rats, pancreatic islet cell carcinomas in 
male rats, and mixed but plausible evidence of bladder, prostate, 
kidney, and breast cancers in humans. As previously noted, the results 
provided by one chronic cancer bioassay in rats exceeds the descriptor 
of Suggestive Evidence of Carcinogenic Potential as it provides 
evidence of multi-site and multi-sex tumorigenesis (Thomford, 2002; 
Butenhoff et al., 2012b).
    Consistent with the statutory definition of MCLG, EPA establishes 
MCLGs of zero for carcinogens classified as Carcinogenic to Humans or 
Likely to be Carcinogenic to Humans, described in Section V.A. of this 
preamble above as the linear default extrapolation approach. EPA has 
determined that PFOS is Likely to be Carcinogenic to Humans based on 
sufficient evidence of carcinogenicity in humans and animals and has 
also determined that a linear default extrapolation approach is 
appropriate as there is no evidence demonstrating a threshold level of 
exposure below which there is no appreciable cancer risk (USEPA, 2005) 
and therefore, it is assumed that there is no known threshold for 
carcinogenicity (USEPA, 2016d). Based upon a consideration of the best 
available peer reviewed science and a consideration of an adequate 
margin of safety, EPA proposes a MCLG of zero for PFOS in drinking 
water.
    EPA is seeking comment on the derivation of the proposed MCLG for 
PFOS, its determination that PFOS is Likely to be Carcinogenic to 
Humans and whether the proposed MCLG is set at the level at which there 
are no adverse effects to the health of persons and which provides an 
adequate margin of safety. EPA is also seeking comment on its 
assessment of the noncancer effects associated with exposure to PFOS 
and the toxicity values described in USEPA (2023c).

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

1. Background
    Although it would be optimal to leverage whole mixture data for 
human health risk assessment, such data for PFAS and other chemicals 
are extremely rare, particularly at component-chemical (i.e., 
individual PFAS) proportions consistent with environmental mixtures. As 
such, mixtures assessment commonly relies upon integration of toxicity 
information for the individual component chemicals that co-occur in 
environmental media. In order to assess the potential health risks 
associated with PFAS mixtures, EPA has developed a Framework for 
Estimating Noncancer Health Risks Associated with Mixtures of Per- and 
Polyfluoroalkyl Substances (PFAS) (``PFAS Mixtures Framework'') (USEPA, 
2023d), based on existing EPA mixtures guidelines and guidance (USEPA, 
1986a, 2000a). The PFAS Mixtures Framework describes a flexible 
approach that facilitates practical component-based mixtures evaluation 
of two or more PFAS based on dose additivity. Studies with PFAS and 
other classes of chemicals support the assumption that a mixture of 
chemicals with similar apical effects should be assumed to also act in 
a dose additive manner unless data demonstrate otherwise. This health 
protective assumption for PFAS mixture assessment was supported by the 
SAB in their recent review of the draft PFAS Mixtures Framework (USEPA, 
2022a). All of the approaches described in the PFAS Mixtures Framework, 
including the HI approach (Section III of this preamble), involve 
integrating dose-response metrics that have been scaled based on the 
potency of each PFAS in the mixture. As discussed in section XV of this 
preamble, the SAB has reviewed the PFAS Mixtures Framework, and 
concluded that the approaches in that document, including the HI 
approach, are scientifically robust and defensible for assessing dose 
additive effects from co-occurring PFAS (USEPA, 2022a).
    The MOA is considered a key determinant of chemical toxicity. It 
describes key changes in cellular interaction that may lead to 
functional or anatomical changes. Toxicants are classified by their 
type of toxic actions. Yet, because PFAS are an emerging chemical class 
of note for toxicological evaluations and human health risk assessment, 
MOA data may be limited or not available at all for many PFAS. 
Component-based approaches for assessing risks of PFAS mixtures are 
focused on evaluation of similarity of toxicity endpoint/effect rather 
than similarity in MOA, consistent with EPA mixtures guidance (USEPA, 
2000a). Precedents of prior research conducted on mixtures of various 
chemical classes with common key events and adverse outcomes support 
the use of dose additive models for estimating mixture-based effects, 
even in instances where chemicals with disparate molecular initiating 
events were included. Thus, in the absence of detailed characterization 
of molecular mechanisms for most PFAS, it is considered a reasonable 
health-protective assumption, consistent with the statute's admonition 
to ensure an adequate margin of safety (1412(b)(4)(A)), that PFAS which 
can be demonstrated to share one or more key events or adverse outcomes 
will produce dose-additive effects from co-exposure (USEPA, 2022c, 
2023a). This assumption of dose additivity and the HI approach was 
supported by the SAB in its review of the draft PFAS Mixtures

[[Page 18664]]

Framework (USEPA, 2022a). For a detailed description of the evidence 
supporting dose additivity for PFOA, PFOS, and other PFAS, see the 
revised PFAS Mixtures Framework (USEPA, 2023d).
    Following EPA's data-driven approach for component-based mixtures 
assessment based on dose additivity (i.e., see Figure 4-1 in USEPA, 
2023d), the Agency selected the HI approach for MCLG development to 
ensure the Agency is protecting against dose additive risk from 
mixtures of PFHxS, HFPO-DA, PFNA, and PFBS. While a single PFAS may 
occur in concentrations below where EPA might establish an individual 
MCLG, PFAS tend to co-occur (see discussion in sections III.C and VII 
of this preamble). Hence, there are some situations where setting an 
MCLG while only considering the concentration of an individual PFAS 
without considering the dose additive effects that would occur from 
other PFAS that may be present in a mixture may not provide a 
sufficiently protective MCLG with an adequate margin of safety. For 
this proposed rule, in addition to the PFOA and PFOS assessments 
discussed above, peer reviewed, publicly available assessments with 
final toxicity values (i.e., RfDs, Minimal Risk Levels) are available 
for HFPO-DA (USEPA, 2021b), PFBS (USEPA, 2021a), PFNA (ATSDR, 2021), 
and PFHxS (ATSDR, 2021). These toxicity values (along with DWI-BW and 
RSC) are used to derive the HBWCs for the HI approach for PFHxS, HFPO-
DA, PFNA, and PFBS. EPA is seeking comment on derivation of the HBWCs 
for each of the four PFAS considered as part of the HI. See discussion 
in section VI.C of this preamble as to why EPA is not proposing to 
include PFOA and PFOS in the HI MCLG at this time.
    As discussed previously in this document, the Agency is proposing 
the general HI as the most appropriate and justified approach for 
considering PFAS mixtures in this rulemaking because of the level of 
protection afforded for diverse endpoints. SDWA requires the Agency to 
establish a health-based MCLG set at, ``a level at which no known or 
anticipated adverse effects on the health of persons occur and which 
allow for an adequate margin of safety.'' The Safe Drinking Water Act 
defines the term ``contaminant'' very broadly to mean any ``physical, 
chemical, biological, or radiological substance or matter in water 
(SDWA 1401 4(A)(ii)(C)(6)).'' In this context, this proposal addresses 
contaminants and certain mixtures of contaminants. A mixture of two or 
more ``contaminants'' qualifies as a ``contaminant'' because the 
mixture itself is ``any physical, chemical or biological or 
radiological substance or matter in water.'' (emphasis added). EPA has 
a long-standing history of regulating contaminants in this manner 
(i.e., as contaminant groups or mixtures). For instance, the TTHM Rule 
(U.S. EPA, 1979) EPA regulated total trihalomethanes as a group due to 
their concurrent formation during the chlorination of drinking water; 
EPA stating that the four regulated THMs were ``also indicative of the 
presence of a host of other halogenated and oxidized, potentially 
harmful byproducts of the chlorination process that are concurrently 
formed in even larger quantities but which cannot be characterized 
chemically'' (USEPA, 1979). In the Stage I and II Disinfection 
Byproduct (DBPs) Rules, EPA regulates a second group of DBPs, in this 
instance setting regulatory standards for a group of five haloacetic 
acids (HAA5) (USEPA, 1998a; 2006a). A third example is EPA's regulation 
of radionuclides, where, among other things, EPA regulates 
radionuclides mixtures for gross alpha radiation that account for both 
natural and man-made alpha emitters as a group rather than individually 
(USEPA, 2000d). In summary, EPA has the statutory authority to regulate 
groups and/or mixtures of contaminants, EPA has a history of regulating 
groups and mixtures of contaminants that have improved public health 
protection, and EPA has made a reasonable policy choice for 
establishing an MCLG for a mixture of chemicals that are expected to 
impact multiple endpoints. Because mixture component chemical HBWCs are 
based on overall (i.e., not target-organ specific) RfDs, the approach 
is protective against all health effects across component chemicals and 
therefore meets the statutory requirements of establishing an MCLG 
under SDWA. Basing the mixture MCLG on overall RfDs ensures that there 
are no known or anticipated effects, and using the HI adds an 
appropriate margin of safety for a class of contaminants that have been 
shown to co-occur and evidence indicates that they have additive 
toxicity.
2. PFAS Mixture MCLG Derivation
    To account for dose additive noncancer effects associated with 
PFHxS, HFPO-DA, PFNA, and PFBS, EPA is proposing an MCLG for the 
mixture of these four PFAS based on the HI approach (USEPA, 2023a). As 
described in Section IV of this preamble, a mixture HI can be 
calculated when HBWCs for a set of PFAS are available or can be 
calculated. The health effects information including relevant studies 
mentioned in this section are summarized from USEPA (2023a) and are 
also described in Section III of this preamble.
    There is currently no EPA RfD available for PFHxS; however, EPA's 
IRIS program is developing a human health toxicity assessment for PFHxS 
(expected to undergo public comment and external peer review in 2023). 
The HBWC for PFHxS is derived using an ATSDR intermediate-duration oral 
Minimal Risk Level based on thyroid effects seen in male rats after 
oral PFHxS exposure (ATSDR, 2021; USEPA, 2023a). ATSDR calculated an 
HED of 0.0047 mg/kg/day and applied a combined UF/MF factor of 300X 
(total UF of 30X and a MF of 10X for database deficiencies) to yield an 
intermediate-duration oral Minimal Risk Level of 2E-05 mg/kg/day 
(ATSDR, 2021). To calculate the HBWC, EPA applied an additional UF of 
10 to adjust for subchronic-to-chronic duration, per Agency guidance 
(USEPA, 2002), because the effect is not in a developmental population 
(i.e., thyroid follicular epithelial hypertrophy/hyperplasia in 
parental male rats). The resulting chronic reference value for use in 
HBWC calculation was 2E-06 mg/kg/day. EPA selected a DWI-BW for adults 
within the general population (0.034 L/kg/day) and applied an RSC of 20 
percent (USEPA, 2022c). The resulting HBWC for PFHxS is 9 ng/L (ppt) 
(USEPA, 2022c).
    Like EPA's drinking water health advisory for HFPO-DA and its 
ammonium salt (USEPA, 2022d), the HBWC that the agency is using for the 
HI MCLG was derived from the agency's 2021 human health toxicity 
assessment, specifically the chronic RfD of 3E-06 mg/kg/day based on 
liver effects observed following oral exposure of mice to HFPO-DA 
(USEPA, 2021b). EPA selected a DWI-BW for lactating women (0.0469 L/kg/
day) and applied an RSC of 20 percent (USEPA, 2023a) to calculate the 
HBWC for HFPO-DA. The HBWC for HFPO-DA is 10 ng/L (ppt) (USEPA, 2023a).
    There is currently no EPA RfD available for PFNA; however, EPA's 
IRIS program is developing a human health toxicity assessment for PFNA. 
The HBWC for PFNA is derived using an ATSDR intermediate-duration oral 
Minimal Risk Level that was based on developmental effects seen in mice 
after oral PFNA exposure (ATSDR, 2021; USEPA, 2023a). ATSDR calculated 
an HED of 0.001 mg/kg/day and applied a combined UF/MF factor of 300X 
(total UF of 30X and a MF of 10X for database

[[Page 18665]]

deficiencies) to yield an intermediate-duration oral Minimal Risk Level 
of 3E-06 mg/kg/day (ATSDR, 2021). EPA did not apply an additional UF to 
adjust for subchronic-to-chronic duration for PFNA because the critical 
effects were observed during a developmental life stage (USEPA, 2002). 
EPA used the chronic reference value of 3E-06 mg/kg/day to calculate 
the HBWC for PFNA. EPA selected a DWI-BW for lactating women (0.0469 L/
kg/day) and applied an RSC of 20 percent (USEPA, 2023a). The resulting 
HBWC for PFNA is 10 ng/L (ppt) (USEPA, 2023a).
    Like EPA's drinking water health advisory for PFBS (USEPA, 2022e), 
the HBWC that the agency is using for the HI MCLG was derived from the 
agency's 2021 human health toxicity assessment, specifically the 
chronic RfD of 3E-04 mg/kg/day based on thyroid effects observed seen 
in newborn mice born to mothers that had been orally exposed to PFBS 
throughout gestation (USEPA, 2021a; 2023a). EPA selected a DWI-BW for 
women of child-bearing age (0.0354 L/kg/day) and applied an RSC of 20 
percent (USEPA, 2023a) to calculate the HBWC for PFBS. The HBWC for 
PFBS is 2,000 ng/L (ppt) (USEPA, 2023a).
    As described above, the HBWCs for PFHxS, HFPO-DA, PFNA, and PFBS 
are 9, 10, 10, and 2000 ppt respectively (see Section III.A of this 
preamble, as well as in USEPA (2022c)). HQs are calculated by dividing 
the measured component PFAS concentration in water (e.g., expressed as 
ppt) by the relevant HBWC (e.g., expressed as ppt), as shown in the 
equation below. Component HQs are then summed across the PFAS mixture 
to yield the PFAS mixture HI MCLG. Thus, the HI accounts for 
differences in toxicity among the mixture component chemicals rather 
than weighting them all equally in the mixture. A PFAS mixture HI 
greater than 1.0 indicates an exceedance of the health protective level 
and indicates potential human health risk for noncancer effects from 
the PFAS mixture in water. For more details on this approach, please 
see USEPA (2023a). The proposed mixture HI MCLG for PFHxS, HFPO-DA, 
PFNA, and PFBS is as follows:
[GRAPHIC] [TIFF OMITTED] TP29MR23.062

Where:

[PFASwater] = the measured component PFAS concentration 
in water and
[PFASHBWC] = the HBWC of a component PFAS.

    For example, if each of the four PFAS are measured at their 
respective proposed PQLs described in section VIII.A. of this preamble, 
the HI calculation would be as follows:
[GRAPHIC] [TIFF OMITTED] TP29MR23.063

    In this scenario, while none of the individual PFAS contaminants 
exceed their relative HBWC, when considered in the HI, the sum of the 
four PFAS in the HI exceeds 1.0, and therefore is higher than the MCLG. 
In the following example, if only PFNA and PFHxS were measured at 8 ppt 
each, while also below their individual HWBCs, the two would sum to an 
exceedance of the HI.
[GRAPHIC] [TIFF OMITTED] TP29MR23.064

[[Page 18666]]

    In a final example, if only a single PFAS, PFHxS were reported 
above its PQL, but that value was 20, this would also result in an HI 
higher than 1.0.
[GRAPHIC] [TIFF OMITTED] TP29MR23.065

    EPA requests comment on significant figure use when calculating 
both the HI MCLG and the MCL (see discussion in section VI of this 
preamble). EPA has set the HI MCLG and MCL using two significant 
figures (i.e., 1.0). EPA requests comment on the proposed use of two 
significant figures for the MCLG when considering underlying health 
information and for the MCL when considering the precision of the 
analytical methods.
    In conclusion, while current weight of evidence suggests that PFAS 
vary in their precise structure and function, exposure to different 
PFAS can result in similar health effects. As a result, PFAS exposures 
are likely to result in dose-additive effects (ATSDR, 2021; USEPA, 
2023a) and therefore the assumption of dose-additivity is reasonable. 
While individual PFAS can pose a potential risk to human health if the 
exposure level exceeds the chemical-specific toxicity value (RfD or 
Minimal Risk Level) (i.e., individual PFAS HQ >1.0), mixtures of PFAS 
can result in dose additive health effects when lower individual 
concentrations of PFAS are present in that mixture. For example, if the 
individual HQs for PFHxS, HFPO-DA, PFNA, and PFBS were each 0.9 that 
would indicate that the measured concentration of each PFAS in drinking 
water is below the level of appreciable risk (recall that an RfV, such 
as an oral RfD, represents an estimate at which no appreciable risk of 
deleterious effects exists). However, the overall HI for that mixture 
would be 3.6 (i.e., sum of four HQs of 0.9). An HI of 3.6 means that 
the total measured concentration of PFAS is 3.6 times the level 
associated with potential health risks. Thus, setting an MCLG while 
only considering the concentration of an individual PFAS without 
considering the dose additive effects from other PFAS in a mixture 
would not provide a sufficiently protective MCLG with an adequate 
margin of safety. In order to account for dose additive noncancer 
effects associated with co-occurring PFAS and PFAS in mixtures, to 
protect against health impacts from likely multi-chemical exposures of 
PFHxS, HFPO-DA, PFNA, and PFBS, with an adequate margin of safety, the 
Agency is proposing to use of the HI approach, a commonly used 
component-based mixture risk assessment method, for the MCLG for these 
four PFAS (USEPA, 2022). Consistent with the statutory requirement 
under 1412(b)(4)(A), establishing the MCLG for PFHxS, HFPO-DA, PFNA, 
and PFBS at an HI = 1.0 ensures that MCLG is set at a level where there 
are no known or anticipated adverse effect on the health of persons and 
ensuring an adequate margin of safety.

VI. Maximum Contaminant Level

    Under section 1412(b)(4)(B) of SDWA, EPA must generally establish 
an enforceable MCL as close to the MCLG as is feasible, taking costs 
into consideration. The Agency evaluates feasibility according to 
several factors including the availability of analytical methods 
capable of measuring the targeted compounds in drinking water and 
examining available treatment technologies capable of contaminant 
removal examined under laboratory and field conditions.

A. PFOA and PFOS

    The Agency evaluated available analytical methods to determine the 
lowest concentration at which PFOA and PFOS can reliably be measured in 
finished drinking water. There are two analytical methods approved by 
EPA for analyzing PFAS regulated under this proposed rule, USEPA 
Methods 537.1 and 533. In this evaluation, EPA determined that 4.0 ppt 
is the lowest concentration that PFOA and PFOS can be reliably 
quantified within specific limits of precision and accuracy during 
routine laboratory operating conditions. EPA has historically called 
this level the ``practical quantitation level,'' also known as a PQL 
(USEPA, 1987). Under UCMR5, EPA published MRLs of 4.0 ppt each for PFOA 
and PFOS (USEPA, 2022g). As described in the UCMR 5 rulemaking, this 
reporting level is the minimum quantitation level that, with 95 percent 
confidence, can be achieved by capable analysts at 75 percent or more 
of the laboratories using a specified analytical method (i.e., Method 
533 and 537.1, discussed in more detail in section VIII of this 
preamble). Based on the multi-laboratory data acquired for the UCMR 5 
rule, EPA has defined the PQL for PFOA and PFOS to be equal to the UCMR 
5 MRL of 0.0000040 mg/L or 4.0 ppt. This quantitation level provides an 
allowance for the degree of measurement precision and accuracy that EPA 
estimates can be achieved across laboratories nationwide. Furthermore, 
the PQLs provide for consistency in data quality from a diverse group 
of laboratories across the country and provide routine performance 
goals that many laboratories must strive to achieve. The agency must 
have a high degree of confidence in the quantified result as it may 
compel utilities to make potentially costly compliance decisions in 
order to comply with the MCL. Please see section VIII of this preamble 
for more information on analytical methods for PFAS and a detailed 
discussion of the PQL and other levels below this quantitation level 
that may be appropriate for screening values.
    EPA has promulgated and successfully implemented NPDWRs with MCLs 
equal to the contaminant PQLs. In 1987, EPA finalized the Phase I 
Volatile Organic Compounds (VOC) rule (USEPA, 1987), where the agency 
set the MCL at the PQL for benzene, carbon tetrachloride, p-
dichlorobenzene, trichloroethylene, vinyl chloride, 1,1,1-
trichloroethane, 1,1-dichloroethylene and 1,2-dichloroethane. In that 
rule, EPA set the PQL at a level consistent with what was then the 
``general rule of five to ten times the [method detection limit] MDL.'' 
While some commenters at the time stated they believed implementation 
would be challenging, EPA notes that those rules have been

[[Page 18667]]

implemented successfully and provided an incentive for laboratories to 
improve analytical capabilities and reduce method quantitation and 
detection limits.
    EPA requests comment on whether setting the MCL at the PQLs for 
PFOA and PFOS is similarly implementable and feasible. As in the 1987 
rule, EPA recognizes that quantitation of the contaminants can be 
achieved between the MDL (e.g., see Method 537.1, section 9.2.8) and 
the PQL, albeit not necessarily with the same precision and accuracy 
that is possible at and above the PQL. Measuring PFOA and PFOS results 
below the PQLs may not be achievable from all laboratories and may not 
have the same precision as higher-level measurements, nor does EPA 
believe it is appropriate to make potentially costly compliance 
decisions based on such lower-level measurements. Nonetheless, the 
ability to know that PFOA and PFOS may be present within a certain 
range at these low concentrations (i.e., below the PQLs) can be used to 
inform decisions for already installed treatment (e.g., a utility can 
evaluate when break though is most likely to occur or is imminent) and 
to judge appropriate monitoring frequency. In addition, further support 
for considering measurement levels below PQL, and the demonstrated 
capability of laboratories to support screening at these lower levels, 
was found within laboratory calibration standard data submitted as part 
of the UCMR 5 Laboratory Approval Program.\4\ These data revealed that 
49 of the 54 laboratories seeking EPA approval included a lowest PFAS 
calibration standard level at 1 ppt or lower, with the median lowest 
calibration level among all laboratories at 0.5 ppt. Therefore, for 
almost all laboratories, the proposed PQLs for PFOA and PFOS of 4.0 ppt 
are at least 4 times greater than the lowest calibration standard. This 
suggests the overwhelming majority of laboratories with the necessary 
instrumentation to support PFAS monitoring have the capability to 
provide screening measurement results above the proposed trigger level 
of \1/3\ of the MCL (i.e., 1.3 ppt for PFOS or PFOS). Hence, a utility 
may use the lower-level measurements as a warning that they may be 
nearing the PFOA and PFOS MCLs of 4.0 ppt prior to exceeding them and 
can make informed treatment decisions about managing their systems 
(e.g., replacing GAC). For more information on the proposed trigger 
level, please see sections VIII and IX of this preamble. EPA requests 
comment on implementation challenges and considerations for setting the 
MCL at the PQLs for PFOA and PFOS, including on the costs and benefits 
related to this approach.
---------------------------------------------------------------------------

    \4\ Instrument calibration for the approved methods is defined 
by analyzing a set of at least five standard solutions spanning a 
20-fold concentration range, in which the lowest concentration must 
be at or below the quantitation level. Calibration standards below 
the quantitation level must meet defined precision requirements. The 
resulting calibration curve is validated by measuring standard 
solutions of known concentration prepared from commercially 
available reference materials. Calibration is confirmed at multiple 
points, including by performing an initial calibration and initial 
demonstration of capability prior to analysis, through the addition 
of internal and surrogate standards, and by incorporating continuous 
calibration check samples into the analysis routine.
---------------------------------------------------------------------------

    Additionally, consistent with EPA's SMF for many drinking water 
contaminants, EPA is proposing to utilize a running annual average 
approach to calculate compliance with this proposed rule. As a result, 
a single occurrence of PFOA or PFOS that is slightly above the proposed 
MCLs would not result in an MCL violation, assuming other quarterly 
samples remain below the MCLs. For example, if a system had a sample 
result of PFOA at 5.0 ppt and the remaining quarter sample results were 
all 2.0 ppt each, the system would not be violation. In addition, when 
calculating the running annual averages, if a sample result is less 
than the PQL for the monitored PFAS, EPA is also proposing to use zero 
to calculate the average for compliance purposes. For further 
discussion on monitoring and compliance, please see section IX of this 
preamble. Hence, while EPA believes utilities should endeavor for all 
samples to remain below the MCL, the proposed rule allows for temporal 
fluctuations in concentrations that may occur because of unexpected 
events such as premature PFOA and PFOS breakthrough or temporary 
increased source water concentrations. This extra buffer provides the 
utilities additional operational safety margins in the event of minor 
management or treatment issues. As an alternative, and as described in 
more detail in section IX of this preamble, when calculating the 
running annual averages, rather than using zero for sample results less 
than the PQL, EPA seeks comment on instead using the proposed rule 
trigger levels (i.e., 1.3 ppt for PFOA and PFOS) in the case where PFAS 
are detected but below their proposed PQLs. This would have the 
potential to be more protective in the long run than counting sampling 
results below the PQL as zero and provide PWSs greater forewarning that 
their results may exceed the MCLs.
    EPA anticipates there would not be sufficient laboratory capacity 
if the quantitation level were set at a level below 4.0 ppt. The 
rigorous laboratory certification and quality assurance/quality control 
(QA/QC) procedures could limit the number of laboratories that can 
achieve lower quantitation levels and many water systems would not be 
able to secure the services of laboratories that are capable of 
consistently providing precise and accurate quantitation of 
concentrations of PFOA and PFOS at levels lower than 4.0 ppt. The 
Agency has determined that high confidence in the accuracy of 
analytical results is necessary to demonstrate that any treatment 
technologies are effectively reducing levels of PFOA and PFOS to the 
levels as close as feasible to the proposed MCLGs for these 
contaminants. To achieve this intended purpose, the Agency is proposing 
to establish the MCLs for PFOA and PFOS at this PQL of 4.0 ppt.
    While EPA anticipates potential laboratory capacity issues if the 
Agency were to propose MCLs below 4.0 ppt, EPA believes there will be 
sufficient laboratory capacity with the MCLs set at 4.0 ppt. As of 
September 2022, as a part of the UCMR 5 laboratory approval program, 
fifty-four (54) laboratories submitted applications to EPA for approval 
to analyze PFOA and PFOS to quantification limits of 4.0 ppt using EPA 
Method 533. Each of these 54 laboratories had acquired the analytical 
equipment necessary to run both EPA Method 533 and 537.1 and 
laboratories are required to achieve and demonstrate they can meet the 
PFOA and PFOS PQLs of 4.0 ppt to receive EPA Method 533 approval. EPA 
received strong interest from a significant number of laboratories 
seeking UCMR 5 laboratory approval, demonstrating there is effective 
laboratory capacity to support the program. The commercial market for 
PFAS analysis is likely to remain strong and, in fact, grow as more 
laboratories develop the technical capability further enhancing lab 
capacity to analyze PFAS for drinking water rule compliance purposes. 
The various State regulatory monitoring programs established in recent 
years for PFAS incorporate laboratory certification/accreditation 
programs that further elevate commercial laboratory interest and expand 
laboratory capacity. Additionally, because EPA is proposing to allow 
the use of existing PFAS monitoring data to meet the initial monitoring 
requirements of this proposed rule where available (see section IX of 
this preamble for further discussion), EPA anticipates the sudden spike 
in laboratory demands that could

[[Page 18668]]

otherwise accompany a proposed rule such as this will instead be 
distributed during the initial rule implementation timeframe. EPA 
requests comment on the underlying assumptions that sufficient 
laboratory capacity will be available with the MCLs set at 4.0 ppt; 
that demand will be sufficiently distributed during rule implementation 
to allow for laboratory capacity; and on the cost estimates related to 
these assumptions.
    SDWA 1412(b)(4)(d) defines feasibility as, ``feasible with the use 
of the best technology, treatment techniques and other means which the 
Administrator finds, after examination for efficacy under field 
conditions and not solely under laboratory conditions, are available 
(taking cost into consideration).'' Further, Section 1412(b)(4)(E) of 
SDWA requires identification of technologies, referred to as best 
available technologies (BATs) ``which the Administrator finds to be 
feasible for purposes of meeting [the MCL].'' As described in section 
XI.A. of this preamble, the Agency identifies the BATs as those meeting 
certain criteria including: (1) The capability of a high removal 
efficiency; (2) a history of full-scale operation; (3) general 
geographic applicability; (4) reasonable cost based on large and 
metropolitan water systems; (5) reasonable service life; (6) 
compatibility with other water treatment processes; and (7) the ability 
to bring all the water in a system into compliance. In section XI of 
this preamble, EPA evaluated treatment technologies for the removal of 
PFOA and PFOS that would meet these criteria and determined there are 
multiple technologies (i.e., GAC, AIX, RO, and NF) that are both 
available and have reliably demonstrated PFAS removal efficiencies that 
may exceed >99 percent and can achieve concentrations less than the 
proposed MCLs for PFOA and PFOS. Based on its evaluation, the Agency 
proposes to determine that it is feasible to treat PFOA and PFOS to 4.0 
ppt because multiple treatment technologies are effective and available 
and there are methods available to reliably quantify PFOA and PFOS at 
4.0 ppt. For more information about treatment technologies, please see 
section XI of this preamble. For more information about available 
analytical methods, please see section VIII of this preamble.
    For purposes of its proposed feasibility determination, EPA also 
considered costs when setting the MCLs for PFOA and PFOS at 4.0 ppt and 
that analysis supports a finding that 4.0 ppt represents the level of 
what is ``feasible'' under the standard of Section 1412(b)(4)(D). Based 
on legislative history (A Legislative History of the Safe Drinking 
Water Act, Committee Print, 97th Cong., 2d Sess. (1982) at 550), EPA 
interprets ``taking cost into consideration'' in Section 1412(b)(4)(D) 
to be limited to ``reasonable cost based on large and metropolitan 
water systems.'' EPA has determined that 4.0 ppt represents what is 
achievable for BATs given the standard of ``reasonable cost based on 
large and metropolitan water systems.'' As discussed in section XII of 
this preamble, EPA evaluated quantifiable and nonquantifiable costs for 
MCLs for PFOA and PFOS at 4.0, 5.0, and 10.0 ppt. As part of that 
evaluation, EPA considered capital, operational, administrative, 
monitoring, and other costs. In addition to estimating national level 
costs associated with the proposed rule and potential regulatory 
alternatives, EPA assessed PWS level costs, costs to small systems, and 
costs at the household level. For more information about EPA's cost 
estimates, please see Best Available Technologies and Small System 
Compliance Technologies Per- and Polyfluoroalkyl Substances (PFAS) in 
Drinking Water (USEPA, 2023g). EPA considered these cost analyses, in 
addition to analytical methods, quantitation levels, and treatment 
technologies in coming to its proposed finding that MCLs of 4.0 ppt for 
PFOA and PFOS represents levels that are as close as feasible to the 
MCLGs. EPA seeks comment on its PFOA and PFOS evaluation of feasibility 
for the proposal, including analytical measurement and treatment 
capability, as well as reasonable costs, as defined by SDWA.

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

    To protect against the potential for dose additive health impacts 
from likely multi-chemical exposures when they occur as mixtures in 
drinking water, EPA is proposing an MCL for mixtures of PFHxS, HFPO-DA, 
PFNA, and PFBS expressed as an HI. An HI is the sum of HQs from 
multiple substances. HQs are the ratio of potential exposure to a 
substance and the level at which no health effects are expected. EPA is 
proposing the MCL for mixtures of PFHxS, HFPO-DA, PFNA, and PFBS as 
equal to the MCLG: as proposed, the HI must be equal to or less than 
1.0. SDWA section 1401(3) defines an MCL as the ``maximum permissible 
level of a contaminant in water which is delivered to any user of a 
public water system.'' This approach, as proposed, sets a permissible 
level for the contaminant mixture (i.e., a resulting PFAS mixture HI 
greater than 1.0 indicates an exceedance of the health protective level 
and indicates potential human health risk for noncancer effects from 
the PFAS mixture in water). If there is only one contaminant PFAS 
present, the HI approach in practice also sets a permissible level for 
the individual contaminant through the use of its respective HBWC (see 
example and discussion in section V.C2 of this preamble). As discussed 
below in this section (section VI.D. of this preamble) and in section 
XIII of this preamble, the Agency is also inviting comment on whether 
establishing a traditional MCLG and MCL for PFHxS, HFPO-DA, PFNA, and 
PFBS instead of or in addition to the HI approach would change public 
health protection, improve clarity for the rule, or change costs.
    EPA asked the SAB for advice on using an HI approach as an option 
for PFAS mixture assessment under an assumption of dose additivity. 
Consistent with EPA Guidance (e.g., USEPA, 2000a; USEPA, 1989) the HI 
is used here as a decision aid, and determination of dose additivity 
among chemicals is relaxed from the level of common MOA to common 
target organ(s)/health outcome(s). Per SAB's suggestion, EPA outlines 
here the validity of, and procedures for, calculating the HI given a 
mixture such as this one that includes PFAS with varying levels of 
available information across health outcomes.
    Consistent with advice from the SAB, EPA considers it an 
appropriately health protective approach to assume dose additivity for 
PFAS co-occurring in mixtures as they share similar profiles of health 
effect domains (e.g., liver, thyroid, developmental, etc.). EPA's 
analysis of finished water monitoring data demonstrates that PFAS often 
have a substantial likelihood to co-occur in mixtures (see section 
III.D of this preamble). While PFAS are well documented to co-occur, 
the exact chemical composition is often site-specific in nature (i.e., 
each location of PFAS mixture is influenced by different environmental 
point and diffuse sources that results in a unique PFAS profile) 
(Banzhaf et al., 2017). Yet, EPA finds that PFHxS, HFPO-DA, PFNA, and 
PFBS often co-occur in mixtures in drinking water, including with other 
PFAS (USEPA, 2023e). To protect against the potential for dose additive 
health impacts from likely multi-chemical exposures of PFHxS, HFPO-DA, 
PFNA, and PFBS when they occur as mixtures in drinking water, the 
Agency is proposing to use the HI approach. Both EPA's recent PFAS 
mixture's framework (USEPA, 2023d), and SAB's review of the prior draft 
of

[[Page 18669]]

this document discuss the strengths and limitations associated with 
using an HI approach as the basis for evaluating potential health risks 
associated with exposure to mixtures of PFAS, and consideration as a 
metric to inform health-based decision-making for regulatory purposes 
(USEPA, 2022a). For a full discussion of the strengths and limitations 
identified during SAB's review and how EPA responded, please see USEPA, 
2022a and 2023f. The HI approach is used regularly by EPA (and States) 
to inform potential health risks of chemical mixtures associated with 
contaminated sites/locations under the Comprehensive Environmental 
Response, Compensation, and Liability Act (CERCLA)/the Superfund 
Amendments and Reauthorization Act (SARA); as such, the application of 
the HI approach under a regulatory purview is not novel for the Agency 
though this is the first use of an HI approach for a SDWA National 
Primary Drinking Water Regulation.
    EPA is proposing an MCL based on a HI composed of the four PFAS for 
which there are validated EPA methods for measurement and treatment, 
evidence of co-occurrence, the potential for similar health effects, 
and the availability of finalized peer reviewed toxicity values to use 
in generating the HI. For this proposal, those PFAS are PFHxS, HFPO-DA, 
PFNA, and PFBS. The MCL for mixtures of PFHxS, HFPO-DA, PFNA, and PFBS 
would be an HI = 1.0. In this proposal, the HBWCs that EPA uses to 
calculate the HI are proposed to be 9.0 ppt for PFHxS; 10.0 ppt for 
HFPO-DA; 10.0 ppt for PFNA; and 2000 ppt for PFBS (USEPA, 2023a). To 
calculate the proposed HI, regulated PWSs would be required to monitor 
to determine the concentrations of PFHxS, HFPO-DA, PFNA, and PFBS in 
their finished drinking water. See section IX of this preamble for 
proposed requirements related to monitoring and determining compliance. 
See equation below for calculation of the PFHxS, HFPO-DA, PFNA, and 
PFBS HI MCL:
[GRAPHIC] [TIFF OMITTED] TP29MR23.066

Where:

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

    See discussion in section IV of this preamble above for how EPA 
derived these values for these contaminants.
    As described in section VI.A. of this preamble for PFOA and PFOS, 
the Agency has similarly considered feasibility as defined by SDWA 
1412(b)(4)(D) for PFHxS, HFPO-DA, PFNA, and PFBS. The Agency has 
determined that there are validated analytical methods that can measure 
below the HBWC for each of these PFAS. Additionally, as discussed 
above, the Agency proposes to determine that it is feasible to treat 
each of these PFAS to below their PQL (between 3.0-5.0 ppt) and it is 
feasible to treat these PFAS to below their PQLs individually and as a 
group. When identifying BATs, EPA evaluated the same factors as defined 
previously in Section VI.A. and in Section XI.A. of this preamble and 
has found the same technologies identified for PFOA and PFOS are also 
both available and have reliably demonstrated PFAS removal efficiencies 
that may exceed >99 percent and achieve concentrations less than the 
proposed HI MCL for PFHxS, HFPO-DA, PFNA, and PFBS.
    As described in section VI.A. of this preamble for PFOA and PFOS, 
the Agency similarly considered costs as part of its proposed 
feasibility determination for PFHxS, HFPO-DA, PFNA, and PFBS and 
setting the HI MCL at 1.0. EPA's analysis supports a finding that an HI 
of 1.0 is ``feasible'' under standard of SDWA 1412(b)(4)(D) because it 
is achievable for BATs given the standard of ``reasonable cost based on 
large and metropolitan water systems.'' For more information about 
EPA's cost estimates, please see Best Available Technologies and Small 
System Compliance Technologies Per- and Polyfluoroalkyl Substances 
(PFAS) in Drinking Water (USEPA, 2023g; USEPA, 2023h). EPA considered 
these cost analyses, in addition to analytical methods, quantitation 
levels, and treatment technologies in coming to its proposal that an HI 
MCL of 1.0 for PFHxS, HFPO-DA, PFNA, and PFBS represents a level that 
is as close as feasible to the MCLG. EPA seeks comment on its 
evaluation of feasibility for the proposed HI MCL finding, including 
analytical measurement and treatment capability, as well as reasonable 
costs, as defined by SDWA.

C. Reducing Public Health Risk by Protecting Against Dose Additive 
Noncancer Health Effects From PFAS

    As described above, PFOA and PFOS are demonstrated to have the 
potential for adverse health effects at low levels of exposure. The 
level at which no known or anticipated adverse effects on the health of 
persons would occur is well below current analytical quantitation level 
for PFOA and PFOS. To ensure maximum public health protection for these 
contaminants, the statute generally requires that exposure be driven to 
the lowest feasible concentration.
    Because of the analytical limitations discussed in the preceding 
section VI.A of this preamble, EPA is not proposing to include PFOA and 
PFOS in the HI. The only feasible way to represent PFOA and PFOS in the 
HI approach would be to only consider values for PFOA and PFOS at or 
above the PQL of 4.0 ppt. As a result, any measured concentration above 
4.0 ppt for PFOA and PFOS would result in an exceedance of the HI of 
1.0. Therefore, regulating PFOA and PFOS under a HI approach would not 
add any meaningful health protection over setting an individual MCL for 
these PFAS. Additionally, EPA believes that adding PFOA or PFOS to the 
HI could increase potential compliance challenges with the rule as 
there could be confusion created by how to consider screening level 
values above detection but below quantitation (see additional 
discussion in section VIII of the preamble for discussion on screening 
and trigger levels). Therefore, EPA is proposing to set MCLs for PFOA 
and PFOS individually and not part of the HI.
    Some PFAS (such as PFHxS, HFPO-DA, PFNA, and PFBS) have HBWCs at 
thresholds higher than current analytical quantitation levels. As a 
result of assuming dose-additivity, PFHxS, HFPO-DA, PFNA, and PFBS

[[Page 18670]]

may have individual detectable or quantifiable concentrations below 
their individual HBWCs, but their combined concentrations can be above 
levels of health concern. As proposed, the HI MCL provides a protective 
approach to avoiding these potential health risks associated with 
mixtures of PFAS that are below the public health goals individually, 
yet exceed the PFAS mixture limit (i.e., HI MCL = 1.0). Separating PFOA 
and PFOS away from a HI approach is not meant to ignore the potential 
dose additive health impacts for these compounds in mixtures. As 
described in the preceding paragraph, EPA is not including PFOA and 
PFOS as part of the HI approach because the Agency believes doing so 
would not add meaningful health protection over setting an individual 
MCL for these PFAS.
    EPA recognizes that some PFAS such as PFOA, PFOS, and PFNA have 
been voluntarily phased out of production and replaced in the United 
States so their relative concentrations in source waters may decrease 
over time. However, other PFAS that have been shown to also cause 
adverse health effects (e.g., perfluorobutanoic acid [PFBA], PFBS, 
HFPO-DA) may increase in concentration as their production, use, and 
discharges into source water continues. The HI framework is designed to 
inform protection of human health for any source water PFAS, with 
available human health assessment values, still in production and use. 
Under the HI approach, additional PFAS can be added over time once more 
information on health effects, analytics, exposure and/or treatment 
becomes available, and merits additional regulation as determined by 
EPA. As such, this approach provides a framework for Federal and State 
public health agencies to consider using to address other PFAS in the 
future as needed.

D. Regulatory Alternatives

    As discussed in section VI.A of this preamble above, EPA proposes 
to determine that it is feasible to set MCLs for PFOA and PFOS at 4.0 
ppt each and that the level is as close as feasible to the MCLGs. As 
discussed in Section VI.B of this preamble, EPA proposes to determine 
it is feasible to set an MCL for mixtures of PFHxS, HFPO-DA, PFNA, and 
PFBS as a HI = 1.0 which is the same level as the MCLG.
    In section XIII of this preamble, the HRRCA section of this 
proposal, EPA is presenting estimated costs and benefits of regulatory 
alternatives for PFOA and PFOS of MCLs at 4.0, 5.0 ppt and 10.0 ppt. 
Quantified costs and benefits for the proposed option and alternative 
options considered are summarized in section XIII.H of this preamble, 
specifically tables 66-69. Tables 70-71 summarize the non-quantified 
benefits and costs and assess the potential impact of non-quantifiable 
benefits and costs on the overall benefits and costs estimate. 
Establishing only MCLs at 4.0 ppt for PFOA and PFOS instead of the 
proposed rule (MCLs at 4.0 ppt for PFOA and PFOS and the HI) would 
result in a reduction of $16 million in quantified costs and $17 
million in quantified benefits at the 3% discount level and $27 million 
in quantified costs and $13 million in quantified benefits at the 7% 
discount level. Establishing MCLs at 5.0 ppt for PFOA and PFOS instead 
of 4.0 ppt would result in a reduction of $145 million in quantified 
costs and $169 million in quantified benefits at the 3% discount level 
and $235 million in quantified costs and $122 million in quantified 
benefits at the 7% discount level. Establishing MCLs at 10.0 ppt for 
PFOA and PFOS instead of 5.0 ppt would result in a reduction of $318 
million in quantified costs and $462 million in quantified benefits at 
the 3% discount level and $511 million in quantified costs and $337 
million in quantified benefits at the 7% discount level. EPA notes that 
there would also be commensurate reduction in the nonquantifiable 
benefits and costs among these options. As discussed elsewhere in this 
proposal, the nonquantifiable benefits are anticipated to be 
significant. EPA evaluated these regulatory alternatives in its HRRCA, 
discussed in Section XIII of this preamble below and is requesting 
comment on these alternatives.
    EPA considered an MCL of 5.0 ppt for PFOA and PFOS because it is 25 
percent above the PQL of 4.0 ppt. A commenter in EPA's outreach 
consultations for this regulation suggested the Agency consider a 
buffer of approximately 20 percent if the MCL is close to the 
quantitation level because water systems operate with a margin of 
safety and plan for performance that maintains water quality below 
quantitation levels. Therefore, in this commenter's opinion, having an 
increased buffer between the PQL and the MCL may allow utilities to 
manage treatment technology performance more efficiently because 
utilities typically aim to achieve lower than the MCL to avoid a 
violation. With the MCL at the PQL, the commenter believes that 
utilities would not have the early warning that they may exceed the MCL 
prior to doing so. EPA disagrees that utilities would not have early 
warning prior to exceeding the MCL; see discussion above in section 
VI.A of this preamble for more information. For results between the 
detection limit and the PQL, EPA has determined that utilities would be 
able to reliably conclude analyte presence, though this detection is 
less precise regarding specific concentration. Knowledge regarding the 
presence of PFOA and PFAS at concentrations below PQLs can inform 
decisions related to monitoring frequency and existing treatment. EPA 
requests comment on this approach.
    EPA also considered the MCL of 10.0 ppt to evaluate the national 
costs and benefits and whether the expected reduction in costs would 
change EPA's determination of the level at which the benefits would 
justify the costs. See SDWA Section 1412(b)(6)(A). The Agency notes 
that this regulatory alternative level is consistent with State-enacted 
MCLs for certain PFAS (NYDOH, 2020). Because there is significant 
expected occurrence of PFOA and PFOS between 4.0 ppt and 10.0 ppt, 
raising the MCL from 4.0 to 10.0 would be expected to significantly 
decrease the number of utilities that must take action to manage PFOA 
and PFOS concentrations in their finished drinking water. However, it 
would also result in millions of Americans continuing to be exposed to 
levels that have the potential for harmful levels of PFOA and PFOS that 
can feasibly be removed through treatment, thereby decreasing the 
quantified and non-quantified benefits delivered by this proposed 
regulation. Furthermore, since EPA has found proposed PFOA and PFOS 
MCLs of 4.0 ppt to be feasible, the Agency must set the MCL as close to 
the MCLG as feasible, the Administrator determined the costs were 
justified by the benefits at a PFOA and PFOS proposed MCL at 4.0 (see 
discussion in section XIII of this preamble), and setting the PFOA and 
PFOS MCLs at 10.0 ppt would not reduce PFOA and PFOS exposure risks for 
millions of Americans to the extent feasible, EPA preliminarily 
determined that proposing PFOA and PFOS MCLs at 10.0 ppt would not be 
appropriate or justifiable under the SDWA statutory criteria.
    EPA also considered the traditional approach of establishing 
individual MCLGs and MCLs for PFHxS, HFPO-DA, PFNA, and PFBS in lieu of 
or in addition to separate rule language for the HI approach. As noted 
earlier, this action includes a preliminary determination to regulate 
these additional PFAS and their mixtures. EPA's proposed HI approach 
addresses both the particular PFAS and their mixtures. If EPA does not 
finalize a

[[Page 18671]]

regulatory determination for mixtures of these PFAS, then a more 
traditional approach may be warranted. Under this alternative, the 
proposed MCLG and MCL for PFHxS would be 9.0 ppt; for HFPO-DA the MCLG 
and MCL would be 10 ppt; for PFNA the MCLG and MCL would be 10 ppt; and 
for PFBS the MCLG and MCL would be 2000 ppt (i.e., 2.0x103 or 2.0e+3). 
As discussed in section XIII of this preamble, EPA has not separately 
presented changes in quantified costs and benefits for these 
approaches. If EPA adds individual MCLs in addition to using the HI 
approach, EPA anticipates there will be no change in costs and benefits 
relative to the proposed rule (i.e., the same number of systems will 
incur identical costs to the proposed option and the same benefits will 
be realized). EPA has not separately quantified the benefits and costs 
for the approach to regulate PFHxS, PFNA, PFBS, and HFPO-DA with 
individual MCLs instead of the HI. However, EPA expects both the costs 
and benefits would be reduced under this approach as fewer systems may 
be triggered into treatment and its associated costs. Additionally, 
systems that exceed one or more of the individual MCLs will treat to a 
less stringent and public health-protective standard. Furthermore, 
while EPA recognized that regulating these PFAS with individual MCLs 
and MCLGs might be simpler to implement for some states or operators, 
if EPA were to regulate these PFAS individually and not under the HI 
MCL approach, it would not provide equivalent protection against 
potential dose additive impacts for these PFAS, nor would it establish 
a framework to consider potential dose additive impacts for future PFAS 
components or groups as EPA develops a better understanding of the 
adverse health effects of other PFAS. The Agency is requesting comment 
on whether establishing a traditional MCLG and MCL for PFHxS, HFPO-DA, 
PFNA, and PFBS instead of or in addition to the HI approach would 
change public health protection, improve clarity of the rule, or change 
costs.
    EPA also considered an alternative regulatory construct of 
establishing both MCLGs and MCLs for these four PFAS in addition to 
separate rule language for the HI MCL. Hence, these four PFAS would 
expressly be subject to two MCLs: the individual MCLs and the HI MCL 
for the mixture. However, this approach has the potential to function 
the same as the proposed rule because a system cannot have MCL 
violations of an individually regulated PFAS without also exceeding the 
HI MCL. EPA considered this approach because it may improve the ability 
to communicate about PFAS risks with PWSs and the public, while still 
providing the important benefit of protection against dose additive 
impacts from these PFAS with the HI approach, as well as building a 
potential framework for considering future PFAS regulation. Moreover, 
this approach may improve the ability to communicate about PFAS 
concentrations and their relative importance with operators and the 
public although there may be challenges in risk communication with 
respect to those small number of facilities that would not exceed an 
individual MCL but would exceed the HI MCL.
    While EPA evaluated these regulatory alternatives, EPA proposal is 
based upon its proposed finding that an MCL of 4.0 ppt for PFOA and 
PFOS and an HI of 1.0 for PFHxS, HFPO-DA, PFNA, and PFBS are feasible 
because treatment technologies are available that treat to below these 
levels and there are analytical methods that can reliably quantify at 
these levels (See discussion above in Section VI.A and Section VIII of 
this preamble). Additionally, EPA determined that the benefits justify 
the costs with the current rule's proposed MCLs of 4.0 ppt and an HI of 
1.0 for PFHxS, HFPO-DA, PFNA, and PFBS.
    When proposing an MCL, EPA must publish, and seek public comment 
on, the HRRCA for the proposed MCL and each alternative standard 
considered under paragraphs 5 and 6(a) of Section 1412(b) (SDWA Section 
1412(b)(3)(C)(i)), including:
     the quantifiable and nonquantifiable health risk reduction 
benefits attributable to MCL compliance;
     the quantifiable and nonquantifiable health risk reduction 
benefits of reduced exposure to co-occurring contaminants attributable 
to MCL compliance;
     the quantifiable and nonquantifiable costs of MCL 
compliance including monitoring, treatment, and other costs;
     the incremental costs and benefits of each alternative 
MCL;
     the effects of the contaminant on the general population 
and sensitive subpopulations likely to be at greater risk of exposure; 
and
    any adverse health risks posed by compliance; and
     other factors such as data quality and uncertainty.
    EPA provides this information in section XIII in this preamble. EPA 
must base its action on the best available, peer-reviewed science and 
supporting studies, taking into consideration the quality of the 
information and the uncertainties in the benefit-cost analysis (SDWA 
Section 1412(b)(3)). The following sections, as well as the health 
effects discussion in sections IV and V of this preamble document the 
science and studies that EPA relied upon to develop estimates of 
benefits and costs and understand the impact of uncertainty on the 
Agency's analysis.

E. MCL-Specific Requests for Comment

    EPA specifically requests comment on its proposal to set MCLs at 
4.0 ppt for PFOA and PFOS and whether 4.0 ppt is the lowest PQL that 
can be achieved by laboratories nationwide. EPA also requests comment 
on implementation challenges and considerations for setting the MCL at 
the PQLs for PFOA and PFOS. EPA requests comment on its evaluation of 
feasibility under SDWA for the proposed PFOA and PFOS MCLs and the 
proposed HI MCL. EPA also requests comment on using an HI approach for 
PFHxS, HFPO-DA, PFNA, and PFBS. Additionally, EPA requests comment on 
its decision to establish stand-alone MCLs for PFOA and PFOS in lieu of 
including them in the HI approach. Finally, EPA specifically requests 
comment on whether establishing a traditional MCLG and MCL for each of 
the following: PFHxS, HFPO-DA, PFNA, and PFBS instead of or in addition 
to the HI approach would change public health protection or improve 
clarity of the rule; or change anticipated costs.

VII. Occurrence

    EPA relied on multiple data sources, including UCMR 3 and state 
finished water data to evaluate the occurrence and probability of co-
occurrence of PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS. EPA also 
incorporated both the UCMR 3 and some state data into a Bayesian 
hierarchical model which supported exposure estimates for select PFAS 
at lower levels than were measured under UCMR 3. EPA has utilized 
similar statistical approaches in past regulatory actions to inform its 
decision making, particularly where a contaminant's occurrence is 
infrequent or at low concentrations (USEPA, 2006b). The specific 
modeling framework used to inform this regulatory action is based on 
the peer-reviewed model published in Cadwallader et al. (2022). 
Collectively, these data and the occurrence model informed estimates of 
the number of

[[Page 18672]]

water systems (and associated population) expected to be exposed to 
levels of PFOA and PFOS which would potentially exceed the proposed and 
alternative MCLs, and to levels of PFHxS, HFPO-DA, PFNA, and PFBS that 
would potentially exceed the HI.
    EPA relied on the UCMR 3 as the primary source of nationwide 
occurrence data to inform the occurrence model's exposure estimates for 
four PFAS: PFOA, PFOS, perfluoroheptanoic acid (PFHpA), and PFHxS. 
Additionally, as described in the final regulatory determination for 
PFOA and PFOS (USEPA, 2021d), EPA has also considered and evaluated 
publicly-available state finished water PFAS monitoring data, including 
data on PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS.

A. UCMR 3

    As discussed in section III.B. of this preamble, UCMR 3 monitoring 
occurred between 2013 and 2015 and is currently the best nationally 
representative finished water dataset for any PFAS, including PFOA, 
PFOS, PFNA, PFBS, and PFHxS. Under UCMR 3, 36,972 samples from 4,920 
PWSs were analyzed for these five PFAS.
    PFOA was found above the UCMR 3 MRL (20 ppt) in 379 samples at 117 
systems serving a population of approximately 7.6 million people 
located in 28 states, tribes, or U.S. territories. PFOS was found in 
292 samples at 95 systems above the UCMR 3 MRL (40 ppt). These systems 
serve a population of approximately 10.4 million people located in 28 
states, tribes, or U.S. territories. PFHxS was found above the UCMR 3 
MRL (30 ppt) in 207 samples at 55 systems that serve a population of 
approximately 5.7 million located in 25 states, tribes, and U.S. 
territories. PFBS was found in 19 samples at 8 systems above the UCMR 3 
MRL (90 ppt). These systems serve a population of approximately 350,000 
people located in 5 states, tribes, and U.S. territories. Lastly, PFNA 
was found above the UCMR 3 MRL (20 ppt) in 19 samples at 14 systems 
serving a population of approximately 526,000 people located in 7 
states, tribes, and U.S. territories.

B. State Drinking Water Data

    As discussed in section III.B of this preamble, the Agency has 
supplemented its UCMR 3 data with more recent data collected by states 
who have made their data publicly available. In general, the large 
majority of these more recent state data were collected using newer 
EPA-approved analytical methods and state results reflect lower 
reporting limits than those in the UCMR 3. State results show continued 
occurrence of PFOA, PFOS, PFHxS, PFBS, and PFNA in multiple geographic 
locations. These data also show these PFAS occur at lower 
concentrations and significantly greater frequencies than were measured 
under the UCMR 3. Furthermore, these data include results for more PFAS 
than were included in the UCMR 3, including HFPO-DA.
    EPA evaluated publicly available monitoring data from the following 
23 states: Alabama, Arizona, California, Colorado, Delaware, George, 
Illinois, Kentucky, Maine, Massachusetts, Maryland, Michigan, Missouri, 
New Hampshire, New Mexico, New Jersey, North Carolina, North Dakota, 
Ohio, Pennsylvania, Rhode Island, South Carolina, and Vermont. The data 
EPA used in its analyses were collected from public state websites 
through August 2021, but represent sampling conducted on or before May 
2021.
    The available data are varied in terms of quantity as well as 
coverage, and some are from targeted sampling efforts (i.e., monitoring 
in areas of known or potential PFAS contamination) so may not be 
representative of levels found in all PWSs within the state or 
represent occurrence in other states. EPA further refined this dataset 
based on representativeness and reporting limitations, resulting in 
detailed technical analyses using a subset of the available state data 
(i.e., all 23 states' data were not included within the detailed 
technical analyses). USEPA (2023e) presents a comprehensive discussion 
of all the available state PFAS drinking water occurrence data.
    Tables 5 and 6 in this section demonstrate the number and percent 
of samples with PFOA and PFOS state reported detections, and the number 
and percent of monitored systems with PFOA and PFOS state reported 
detections, respectively, for the non-targeted state finished water 
monitoring data. Section III.B. of this preamble describes the state 
reported finished water occurrence data for PFHxS, HFPO-DA, PFNA, and 
PFBS data.
    Different states utilized various reporting thresholds when 
presenting their data, and for some states there were no clearly 
defined limits. Further, the limits often varied within the data for 
each state depending on the specific analyte, as well as the laboratory 
analyzing the data. In some cases, states reported data at 
concentrations below EPA's proposed rule trigger level and/or PQLs in 
this document. However, to present the best available occurrence 
information, EPA collected and evaluated the data based on the 
information as reported directly by the states. When conducting data 
analyses, EPA incorporated individual state-specific reporting limits 
where possible. Specific details on state data reporting thresholds are 
available in USEPA (2023e).

Table 5--Non-Targeted State PFOS and PFOA Finished Water Data--Summary of Samples With State Reported Detections
                                                       \1\
----------------------------------------------------------------------------------------------------------------
                                            PFOS samples       PFOS state       PFOA samples       PFOA state
                                             with state     reported  sample     with state     reported  sample
                  State                       reported           percent          reported           percent
                                             detections         detection        detections        detections
----------------------------------------------------------------------------------------------------------------
Alabama \2\.............................               140               N/A                80               N/A
Colorado................................                60              10.3                54               9.3
Illinois................................                55               5.2                56               5.3
Kentucky................................                33              40.7                24              29.6
Massachusetts...........................               441              49.1               506              66.5
Michigan................................                70               2.5               103               3.6
New Hampshire...........................               495              27.1             1,010              55.3
New Jersey..............................             3,512              37.2             4,379              46.4
North Dakota............................                 0               0.0                 0               0.0
Ohio....................................                93               4.9                93               4.9
South Carolina..........................                88              57.9                82              53.9

[[Page 18673]]

 
Vermont.................................                87               6.9               109               8.7
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.
\2\ Only reported detections.

 Table 6--Non-Targeted State PFOS and PFOA Finished Water Data--Summary of Monitored Systems With State Reported
                                                 Detections \1\
----------------------------------------------------------------------------------------------------------------
                                                               PFOS state                          PFOA state
                                           PFOS  monitored      reported       PFOA  monitored      reported
                  State                     systems with        monitored       systems with        monitored
                                           state reported    system percent    state reported    system percent
                                             detections         detection        detections        detections
----------------------------------------------------------------------------------------------------------------
Alabama \2\.............................                49               N/A                28               N/A
Colorado................................                50              12.6                45              11.3
Illinois................................                36               5.5                32               4.9
Kentucky................................                33              40.7                24              29.6
Massachusetts...........................               107              47.3               126              55.5
Michigan................................                55               2.6                82               3.8
New Hampshire...........................               189              33.8               310              55.4
New Jersey..............................               494              45.9               564              52.4
North Dakota............................                 0               0.0                 0               0.0
Ohio....................................                29               2.0                32               2.2
South Carolina..........................                42              82.4                40              78.4
Vermont.................................                35               6.3                44               7.9
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.
\2\ Only reported detections.

    As illustrated in Tables 5 and 6, there is a wide range in PFOA and 
PFOS results between states, however in nearly half of states that 
conducted non-targeted monitoring, more than 25 percent of the 
monitored systems found PFOA and/or PFOS. Additionally, considering all 
states in Tables 5 and 6, PFOA detected concentrations ranged from 0.51 
to 153 ppt with a range of median detected concentrations from 1.98 to 
9.4 ppt, and PFOS detected concentrations ranged from 0.5 to 350 ppt 
with a range of median detected concentrations from 3 to 11.9 ppt.
    Monitoring data for PFOA and PFOS from states that conducted 
targeted sampling efforts, including California, Maryland, and 
Pennsylvania, demonstrate results consistent with the non-targeted 
state monitoring. For example, in Pennsylvania, 26.3 and 24.9 percent 
of monitored systems found PFOA and PFOS, respectively, with reported 
concentrations of PFOA ranging from 1.7 to 59.6 ppt and PFOS ranging 
from 1.8 to 94 ppt. California reported 26.2 and 29.9 percent of 
monitored systems found PFOA and PFOS, respectively, including reported 
concentrations of PFOA ranging from 0.9 to 120 ppt and reported 
concentrations of PFOS from 0.4 to 250 ppt. In Maryland, PFOA and PFOS 
were found in 57.6 and 39.4 percent of systems monitored, respectively, 
with reported concentrations of PFOA ranging from 1.02 to 23.98 ppt and 
reported concentrations of PFOS ranging from 2.05 to 235 ppt.
    As discussed above in section VI of this preamble, EPA is proposing 
individual MCLs of 4.0 ppt for PFOA and PFOS, and an HI level of 1.0 
for PFHxS, PFNA, PFBS, and HFPO-DA. EPA also evaluated occurrence for 
the regulatory alternatives discussed in section VI of this preamble 
including alternative MCLs for PFOA and PFOS of 5.0 ppt and 10.0 ppt. 
Table 7, Table 8, and Table 9 demonstrate, based on available state 
data, the total state reported number and percentages of monitored 
systems that exceed these proposed and alternative MCL values across 
the non-targeted state finished water monitoring data.

 Table 7--Non-Targeted State PFOS and PFOA Finished Water Data--Summary of Monitored Systems With State Reported
                                            Detections \1\ >=4.0 ppt
----------------------------------------------------------------------------------------------------------------
                                                               PFOS state                          PFOA state
                                           PFOS  monitored      reported       PFOA  monitored      reported
                  State                     systems with        monitored       systems with        monitored
                                           state reported    systems percent   state reported    systems percent
                                             detections         detection        detections         detection
----------------------------------------------------------------------------------------------------------------
Alabama \2\.............................                37               N/A                19               N/A
Colorado................................                22               5.5                18               4.5
Illinois................................                17               2.6                16               2.5
Kentucky................................                 4               4.9                 9              11.1

[[Page 18674]]

 
Massachusetts...........................                72              31.9                90              39.6
Michigan................................                15               0.7                24               1.1
New Hampshire...........................               107              19.1               210              37.5
New Jersey..............................               315              29.3               411              38.2
North Dakota............................                 0               0.0                 0               0.0
Ohio....................................                29               2.0                32               2.2
South Carolina..........................                27              52.9                30              58.8
Vermont.................................                16               2.9                24               4.3
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.
\2\ Only reported detections.

 Table 8--Non-Targeted State PFOS and PFOA Finished Water Data--Summary of Monitored Systems With State Reported
                                            Detections \1\ >=5.0 ppt
----------------------------------------------------------------------------------------------------------------
                                                               PFOS state                          PFOA state
                                           PFOS  monitored      reported       PFOA  monitored      reported
                  State                     systems with        monitored       systems with        monitored
                                           state reported    systems percent   state reported    systems percent
                                             detections         detection        detections         detection
----------------------------------------------------------------------------------------------------------------
Alabama \2\.............................                31               N/A                15               N/A
Colorado................................                16               4.0                14               3.5
Illinois................................                12               1.8                11               1.7
Kentucky................................                 3               3.7                 4               4.9
Massachusetts...........................                64              28.3                83              36.6
Michigan................................                12               0.6                17               0.8
New Hampshire...........................                86              15.4               186              33.2
New Jersey..............................               272              25.3               363              33.7
North Dakota............................                 0               0.0                 0               0.0
Ohio....................................                29               2.0                32               2.2
South Carolina..........................                25              49.0                25              49.0
Vermont.................................                13              2.33                16               2.9
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.
\2\ Only reported detections.

 Table 9--Non-Targeted State PFOS and PFOA Finished Water Data--Summary of Monitored Systems With State Reported
                                            Detections \1\ >=10.0 ppt
----------------------------------------------------------------------------------------------------------------
                                                               PFOS state                          PFOA state
                                           PFOS  monitored      reported       PFOA  monitored      reported
                  State                     systems with        monitored       systems with        monitored
                                           state reported    systems percent   state reported    systems percent
                                             detections         detection        detections         detection
----------------------------------------------------------------------------------------------------------------
Alabama \2\.............................                23               N/A                 8               N/A
Colorado................................                 3               0.8                 2               0.5
Illinois................................                 3               0.5                 6               0.9
Kentucky................................                 1               1.2                 1               1.2
Massachusetts...........................                32              14.2                32              14.1
Michigan................................                 6               0.3                 7               0.3
New Hampshire...........................                39               7.0                83              14.8
New Jersey..............................               133              12.4               189              17.6
North Dakota............................                 0               0.0                 0               0.0
Ohio....................................                20               1.4                15               1.0
South Carolina..........................                 3               5.9                 3               5.9
Vermont.................................                 4               0.7                 7               1.3
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Detections determined by individual state reported limits which are not defined consistently across all
  states.
\2\ Only reported detections.

    Based on the available state data evaluated and presented in Table 
7, Table 8, and Table 9, within 12 states that conducted non-targeted 
monitoring there are 661 systems that show exceedances of the proposed 
PFOS MCL

[[Page 18675]]

of 4.0 ppt and 883 systems with exceedances of the proposed PFOA MCL of 
4.0 ppt. These systems serve populations of approximately 8.8 and 10.5 
million people, respectively. As expected, the number of systems 
exceeding either of the proposed alternative MCLs decreases as the 
values are higher, however, even at the highest alternative PFOS and 
PFOA MCL values of 10.0 ppt, would still be 267 and 353 systems with 
exceedances, serving populations of approximately 3.7 and 4.4 million 
people, respectively.
    Monitoring data for PFOA and PFOS from states that conducted 
targeted sampling efforts shows additional systems that would exceed 
the proposed and alternative MCLs. For example, in California, Maine, 
Maryland, and Pennsylvania, 23.4 percent (25 PWSs), 30.4 percent (7 
PWSs), 22.7 percent (15 PWSs), and 19.3 percent (66 PWSs) of monitored 
systems exceeded the proposed PFOS MCL of 4.0 ppt, respectively, and 
20.6 percent (22 PWSs), 21.7 percent (5 PWSs), 25.8 percent (17 PWSs), 
and 21.1 percent (72 PWSs) of monitored systems exceeded the proposed 
PFOA MCL of 4.0 ppt, respectively. While these frequencies may be 
anticipated given the sampling locations, within only these four states 
that conducted limited, targeted monitoring, the monitored systems 
exceeding the proposed PFOS MCL and proposed PFOA MCL serve significant 
populations of approximately 4.6 million people and approximately 4.4 
million people, respectively.

C. Co-Occurrence

    While the discussions in sections III.B, VII.A. and VII.B of this 
preamble describe how PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS occur 
individually, PFAS have been documented to co-occur in finished 
drinking water (Adamson et al., 2017; Cadwallader et al., 2022; Guelfo 
and Adamson, 2018). As discussed in section VI of this preamble, EPA is 
proposing regulation of four PFAS including PFHxS, HFPO-DA, PFNA, and 
PFBS (collectively referred to as ``HI PFAS'') as part of an HI 
approach. Sampling results in the aggregated state dataset were 
examined to determine the extent to which the HI PFAS occurred with 
each other as well as with PFOA and/or PFOS. This involved considering 
the observed occurrence in terms of grouping (i.e., groups of HI PFAS 
and ``PFOS or PFOA'') as well as pairwise by means of odds ratios. For 
the group assessment, the aggregated state dataset was limited to 
samples from non-targeted monitoring efforts where at least one HI PFAS 
was analyzed and PFOS and PFOA were analyzed sufficiently to determine 
whether one was present.
1. Groupwise Chemical Co-Occurrence
    Table 10 shows the distribution of systems and samples according to 
whether states report detections for any HI PFAS (PFHxS, HFPO-DA, PFNA 
and PFBS) and whether they also reported detections of PFOS or PFOA. 
USEPA (2023e) provides additional information for this analysis.

 Table 10--Non-Targeted State PFAS Finished Water Data--Samples and Systems Binned According to Whether PFOS or
                    PFOA Were Reported by States and Whether Additional HI PFAS Were Reported
----------------------------------------------------------------------------------------------------------------
                                        No PFOS or PFOA reported            PFOS or PFOA reported
                                  ----------------------------------------------------------------------
               Type                                    At least one                       At least one    Total
                                      No HI PFAS         HI PFAS         No HI PFAS         HI PFAS       count
                                       reported          reported         reported          reported
----------------------------------------------------------------------------------------------------------------
Samples..........................    12,704 (65.2%)       357 (1.8%)     3,380 (17.3%)    3,041 (15.6%)   19,482
Systems..........................     5,560 (78.8%)       196 (2.8%)        516 (7.3%)      784 (11.1%)    7,056
----------------------------------------------------------------------------------------------------------------

    Considering eligible samples and systems within the aggregated 
state dataset, states reported detections of either PFOS, PFOA, or one 
or more HI PFAS in 34.8 percent (6,778 of 19,482) of samples and 21.2 
percent (1,496 of 7,056) of systems. When any PFAS (among PFOA, PFOS, 
and the HI PFAS) were reported detected, at least one HI PFAS was also 
reported in 50.1 percent (3,398 of 6,778) of samples and at 65.5 
percent (980 of 1,496) of systems. Further, among samples and systems 
that reported detections of PFOS or PFOA, at least one HI PFAS was 
detected in 47.4 percent (3,041 of 6,421) of samples and at 60.3 
percent (784 of 1,300) of systems. This demonstrated strong co-
occurrence of HI PFAS with PFOA and PFOS and a substantial likelihood 
(over 50 percent) of at least one HI PFAS being present at systems with 
reported detections of PFOS or PFOA. Overall, one or more HI PFAS were 
reported at about 13.9 percent (980 of 7,056) of systems included in 
the aggregated state dataset of non-targeted monitoring. If this 
percentage were extrapolated to the nation, one or more HI PFAS would 
be at detectable levels in over 9,000 systems. Table 11 shows the 
distribution of systems in a similar manner but provides a breakdown by 
state and includes only systems that monitored for either three or four 
of the HI PFAS.

 Table 11--Non-Targeted State PFAS Finished Water Data--Systems That Sampled for 3 or 4 HI PFAS Binned According
         to Whether PFOS or PFOA Were Reported and Whether Any Additional HI PFAS Were Reported by State
----------------------------------------------------------------------------------------------------------------
                                        No PFOA/S detected                    PFOA/S detected             Total
             State             ------------------------------------------------------------------------  system
                                  No HI detected     HI detected      No HI detected     HI detected      count
----------------------------------------------------------------------------------------------------------------
CO............................        270 (68.0%)        26 (6.5%)          11 (2.8%)       90 (22.7%)       397
IL............................        582 (89.7%)        22 (3.4%)          15 (2.3%)        30 (4.6%)       649
KY............................         37 (52.9%)         2 (2.9%)         16 (22.9%)       15 (21.4%)        70
MA............................         60 (35.5%)         2 (1.2%)          12 (7.1%)       95 (56.2%)       169
MI............................      1,969 (91.5%)        82 (3.8%)          43 (2.0%)        58 (2.7%)     2,152
ND............................           49 (98%)         1 (2.0%)           0 (0.0%)         0 (0.0%)        50
NH............................         60 (43.2%)         2 (1.4%)         34 (24.5%)       43 (30.9%)       139
NJ............................        225 (36.3%)         7 (1.1%)        127 (20.5%)      261 (42.1%)       620

[[Page 18676]]

 
OH............................      1,397 (94.5%)        31 (2.1%)          25 (1.7%)        26 (1.8%)     1,479
SC............................         10 (22.2%)         1 (2.2%)         10 (22.2%)       24 (53.3%)        45
VT............................        488 (87.6%)        15 (2.7%)          31 (5.6%)        23 (4.1%)       557
----------------------------------------------------------------------------------------------------------------

    The percentage of systems included in Table 11 that reported 
detections of any HI PFAS ranged from 2.0 to 57.4 percent of systems 
when broken down by state, with six states exceeding 20 percent of 
systems. The percentage of systems that reported detections of any PFAS 
ranged from 2.0 to 77.8 percent. Many systems and/or samples that were 
included in the aggregated state dataset did not monitor for all four 
HI PFAS. It is possible that more systems would have detected HI PFAS 
if they had monitored for all four HI PFAS. Additionally, as 
demonstrated in Table 11, when PFOA and/or PFOS were reported, at least 
one of the HI PFAS chemicals were also frequently reported. Table 12 
presents system counts for systems where PFOS or PFOA were detected 
according to (a) how many HI PFAS were monitored and (b) how many HI 
PFAS were reported to be detected.

 Table 12--Non-Targeted State PFAS Finished Water Data--System Counts According to HI PFAS Analyzed and Reported Present for Systems Where PFOS and PFOA
                                                                      Were Reported
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                               HI reported present
                          HI analyzed                           --------------------------------------------------------------------------------  Total
                                                                        0               1               2               3               4
--------------------------------------------------------------------------------------------------------------------------------------------------------
1..............................................................     143 (70.1%)      61 (29.9%)  ..............  ..............  ..............      204
2..............................................................      49 (45.8%)      41 (38.3%)      17 (15.9%)  ..............  ..............      107
3..............................................................     153 (34.7%)      95 (21.5%)     137 (31.1%)      56 (12.7%)  ..............      441
4..............................................................     171 (31.2%)     135 (24.6%)     179 (32.7%)      61 (11.1%)        2 (0.4%)      548
                                                                ----------------------------------------------------------------------------------------
    Total......................................................             516             332             333             117               2  .......
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Among systems that reported detections of PFOS and/or PFOA, the 
fraction of systems that also reported detections of any HI PFAS tended 
to increase as systems monitored for more of the HI PFAS. At systems 
monitoring for a single HI PFAS, 29.9 percent reported a detection at 
some point during sampling. This increased to 68.8 percent of systems 
reporting detections of at least one HI PFAS when monitoring for all 
four HI PFAS. Not only did the fraction of systems reporting detections 
of any HI PFAS increase as the number of HI PFAS increased, so did the 
number of HI PFAS that were reported. When three or four HI PFAS were 
monitored, over 40 percent of systems reported detections of two to 
three of the HI PFAS. Thus, if PFOS or PFOA are reported, there is a 
reasonable likelihood that multiple HI PFAS would be present as well.
2. Pairwise Chemical Co-Occurrence
    In addition to considering the co-occurrence of six PFAS as two 
groups, EPA conducted a pairwise analysis to further explore co-
occurrence relationships. Table 13 shows the calculated system-level 
odds ratios for every unique pair of PFAS chemicals evaluated. The 
equation for calculating odds ratios is symmetrical. Because of this, 
in a given row it does not matter which chemical is ``Chemical A'' and 
which is ``Chemical B.'' Additional information on odds ratios may be 
found in USEPA (2023e) and a brief explanation is described following 
Table 13.

  Table 13--Non-Targeted State PFAS Finished Water Data--System-Level Counts of Pairwise Chemical Occurrence and Odds Ratios Calculated From Aggregated
                                                 State Dataset PFAS Samples for PFOS, PFOA, and HI PFAS
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                   Chems A  and B    Only Chem B     Only Chem A    Neither Chem
                Chem A                            Chem B              reported        reported        reported        reported      Odds ratio  [95% CI]
--------------------------------------------------------------------------------------------------------------------------------------------------------
HFPO-DA...............................  PFBS.....................              10             452              10           5,116        11.3 [4.8-26.7]
HFPO-DA...............................  PFHxS....................               2             339              18           5,229          1.7 [0.4-6.7]
HFPO-DA...............................  PFNA.....................               2              77              18           5,491         7.9 [2.0-31.4]
HFPO-DA...............................  PFOA.....................              16             438               4           5,129      46.8 [16.3-134.1]
HFPO-DA...............................  PFOS.....................              14             399               6           5,168       30.2 [11.9-76.5]
PFBS..................................  PFHxS....................             433             133             261           5,501       68.6 [54.5-86.5]
PFBS..................................  PFNA.....................             135              33             560           5,601       40.9 [27.7-60.4]
PFBS..................................  PFOA.....................             517             360             178           5,273       42.5 [34.8-52.0]
PFBS..................................  PFOS.....................             503             278             192           5,355       50.5 [41.1-62.0]
PFHxS.................................  PFNA.....................             150              38             473           5,939       49.6 [34.3-71.6]
PFHxS.................................  PFOA.....................             510             466             113           5,510       53.4 [42.6-66.9]
PFHxS.................................  PFOS.....................             507             353             116           5,623       69.6 [55.4-87.6]

[[Page 18677]]

 
PFNA..................................  PFOA.....................             236             934              15           5,871      98.9 [58.7-166.5]
PFNA..................................  PFOS.....................             234             789              17           6,016     105.0 [64.1-171.9]
PFOA..................................  PFOS.....................             893             130             277           5,756    142.7 [114.5-177.9]
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Odds ratios reflect the change in the odds of detecting one 
chemical (e.g., Chemical A) given that the second chemical (e.g., 
Chemical B) is known to be present compared to the odds of detecting if 
the second chemical is not present. For example, as shown in Table 13, 
the point estimate of 142.7 for the odds ratio between PFOA and PFOS 
indicates that the odds of detecting PFOA after knowing that PFOS has 
been observed are 142.7 times what the odds would have been if PFOS was 
not observed, and vice versa. For every pair of chemicals, except for 
HFPO-DA and PFHxS, both the point estimate and 95 percent CI were above 
1, indicating significant increases in the likelihood of detecting one 
chemical if the other is present. For HFPO-DA and PFHxS, 1 fell within 
the 95 percent CI, and thus the odds ratio was not determined to be 
statistically significantly different from 1.
    Both as a group and as individual chemicals, the HI PFAS had a 
higher likelihood of being reported if PFOS or PFOA were present. 
PFHxS, HFPO-DA, PFNA and PFBS (the individual HI PFAS) are demonstrated 
to generally co-occur with each other, as well. As such, these data 
support that there is a substantial likelihood PFHxS, HFPO-DA, PFNA, 
and PFBS co-occur with a frequency of public health concern in drinking 
water systems.

D. Occurrence Relative to the Hazard Index

    EPA analyzed the available state data in comparison to the proposed 
HI MCL of 1.0 to evaluate the co-occurrence of PFHxS, HFPO-DA, PFNA, 
and PFBS. Table 14 presents the total number and percentage of 
monitored systems that exceeded the proposed HI MCL based on state 
reported HI PFAS detections for the states that conducted non-targeted 
monitoring and that sampled all four HI PFAS as a part of their overall 
monitoring efforts. EPA notes that for equivalent comparison purposes 
Table 14 only accounts for samples that included reported values 
(including non-detects) of all four HI PFAS. As shown within the table, 
the majority of states evaluated had monitored systems exceed the 
proposed HI MCL, ranging from 0.72 to 7.41 percent of total monitored 
systems.

 Table 14--Non-Targeted State PFAS Finished Water Data--Summary of Total
  Number and Percent of Monitored Systems Exceeding the HI With Samples
                Containing Reported Values of All HI PFAS
------------------------------------------------------------------------
                                 Total monitored
            State              systems > proposed    Percent  systems >
                                    HI of 1.0        proposed  HI of 1.0
------------------------------------------------------------------------
Colorado....................                     5                  1.26
Illinois....................                    10                  1.54
Kentucky....................                     6                  7.41
Massachusetts...............                     8                  6.40
Michigan....................                    14                  0.65
New Hampshire...............                     4                  2.99
North Dakota................                     0                  0.00
Ohio........................                    25                  1.69
South Carolina..............                     0                  0.00
Vermont.....................                     4                  0.72
------------------------------------------------------------------------

    Further evaluating the available state data related to the proposed 
HI MCL of 1.0, Table 15 presents the total number of systems and 
associated populations served that exceed the proposed HI of 1.0 based 
on state reported HI PFAS detections for the same states shown in Table 
15. However, in this case, EPA also analyzed the same non-targeted 
state data adding in additional samples even if those samples did not 
contain reported values (including non-detects) for all four HI PFAS 
(i.e., exceeding the HI based on only one to three HI PFAS with 
reported values included within a sample). Moreover, while these states 
did monitor for all four HI PFAS as a part of their overall monitoring, 
in a subset of those states some samples did not include reported data 
on all four HI PFAS (i.e., values of one or more of the HI PFAS were 
not reported as non-detect, rather no value was reported). This 
analysis, presented in Table 15, shows an increase in the number of 
monitored systems exceeding the proposed HI of 1.0 and demonstrates 
prevalence of these PFAS at levels of concern, even when all four PFAS 
may not be included within a sample.

[[Page 18678]]

 Table 15--Non-Targeted State PFAS Finished Water Data--Summary of Total
   Monitored Systems Exceeding the HI With Samples Containing Reported
                     Values of Any Number of HI PFAS
------------------------------------------------------------------------
                                 Total monitored
            State              systems > proposed     Population served
                                    HI of 1.0
------------------------------------------------------------------------
Colorado....................                     5                 5,429
Illinois....................                    10               107,461
Kentucky....................                     6               103,315
Massachusetts...............                    19               302,482
Michigan....................                    14               221,484
New Hampshire...............                    25                36,463
North Dakota................                     0                     0
Ohio........................                    25               234,834
South Carolina..............                     0                     0
Vermont.....................                     4                   410
------------------------------------------------------------------------

    Combining the non-targeted monitoring results shown previously with 
targeted state monitoring conducted for all four HI PFAS showed at 
least 917 samples from 157 PWSs in 15 states that exceed the proposed 
HI of 1.0 for PFHxS, HFPO-DA, PFNA, and PFBS. These systems serve 
approximately 3.08 million people. Additionally, data from New Jersey, 
which conducted non-targeted monitoring but did not conduct any 
monitoring that included all four HI PFAS, showed an additional 243 
samples within 57 systems serving a total population of approximately 
1.43 million people exceeding the proposed HI of 1.0 based solely upon 
the reported detections of three of the four HI PFAS (i.e., PFHxS, 
PFNA, and PFBS). USEPA (2023e) presents a detailed discussion on state 
PFAS monitoring information. More information on occurrence in state 
monitoring is available in section III.B. of this preamble.
    In summary, the finished water data collected under both non-
targeted and targeted state monitoring efforts from 22 states showed 
there are at least 1,007 PWSs serving a total population of 
approximately 15.3 million people that have at least one result 
exceeding the proposed PFOA MCL of 4.0 ppt. In those same 22 states, 
there are also at least 805 PWSs serving a total population of 
approximately 13.6 million people that have at least one result 
exceeding the proposed PFOS MCL of 4.0 ppt. Related to the proposed HI, 
finished water data collected under both non-targeted and targeted 
state monitoring efforts in 16 states showed there are at least 214 
systems serving a total population of approximately 4.5 million people 
that exceed the proposed HI value of 1.0 for PFHxS, HFPO-DA, PFNA, and 
PFBS. USEPA (2023e) presents a detailed discussion on state PFAS 
monitoring information. Additionally, EPA is aware that since the data 
were collected some of these states may have updated data available and 
that additional states have or intend to conduct monitoring of finished 
drinking water, such as New York and Virginia. EPA will consider, and 
as appropriate, analyze additional data submitted in response to this 
proposal to inform future regulatory decision making.

E. Occurrence Model

    A Bayesian hierarchical occurrence model was developed to explore 
national occurrence of the four PFAS that were most frequently detected 
in the UCMR 3: PFOS, PFOA, PFHxS, and PFHpA. While PFNA and PFBS were 
included in the UCMR 3 as well, they lacked sufficient reported values 
above the UCMR 3 MRLs to be incorporated into the model. The model has 
been peer reviewed and is described extensively in Cadwallader et al. 
(2022). Briefly, inputs to the model include the UCMR 3 dataset as well 
as subsequent data in publicly available state datasets that were 
collected at PWSs that took part in the UCMR 3. 23,130 analytical 
results from state datasets were used to supplement the UCMR 3. These 
results were derived from 17 state datasets. The objective of the model 
was to enable national estimates of PFAS occurrence by using available 
UCMR 3 and state data to inform occurrence distributions both within 
and across PWSs. Note that while PFHpA was included in the model 
because of its UCMR 3 occurrence data availability, EPA is not 
proposing to regulate it in this document.
    The model uses Markov chain Monte Carlo (MCMC) and the assumption 
of lognormality in PFAS chemical occurrence. After log-transforming all 
available data, system-level means (where each system has a mean 
concentration for each chemical) were assumed to be distributed 
multivariate normally. Further, within-system occurrence was assumed to 
be distributed normally for each chemical. Since system-level means are 
distributed multivariate normally, correlation between estimated 
system-level means across chemicals could also be assessed. The 
assumption of lognormality as well as the incorporation of state data 
with lower reporting limits allowed the model to generate reasonable 
estimates for PFAS occurrence at levels below the UCMR 3 MRLs. EPA has 
used similar hierarchical statistical models to inform regulatory 
decision making in the past, such as for development of the NPDWR for 
Arsenic and Cryptosporidium parvum (USEPA, 2006b; USEPA, 2000e).
    After the model was fit with available data from PWSs that were 
included in the UCMR 3, it was used to simulate occurrence at an 
inventory of active CWS and NTNCWS extracted from the Safe Drinking 
Water Information System (SDWIS). System-level means for non-UCMR 3 
systems were simulated by sampling from the multivariate normal 
distribution of system-level means that was produced during the model 
fitting process. For systems that were included in the UCMR 3, the 
fitted system-level mean was used directly. Using population data 
retrieved from SDWIS, the total number of systems with system-level 
mean concentrations of each chemical, as well as their associated 
population served, could be estimated. The median estimate and the 90 
percent credible interval are shown for the systems with system-level 
means at or above various PFAS concentrations in Table 16 and the 
population served by those systems in Table 17.

[[Page 18679]]

  Table 16--National Occurrence Model Estimate--Estimated Number of Systems With System-Level Means at or Above
                                             Various Concentrations
----------------------------------------------------------------------------------------------------------------
            Concentration  (ppt)                PFHxS  [90% CI]         PFOA  [90% CI]         PFOS  [90% CI]
----------------------------------------------------------------------------------------------------------------
4.0........................................    1,697 [1,053-2,702]    1,987 [1,338-3,016]    3,427 [2,326-4,900]
5.0........................................      1,232 [745-2,009]      1,351 [903-2,083]    2,593 [1,737-3,770]
10.0.......................................          417 [241-730]          349 [223-577]        986 [627-1,531]
----------------------------------------------------------------------------------------------------------------

 Table 17--National Occurrence Model Estimate--Estimated Population Served by Systems With System-Level Means at
                                         or Above Various Concentrations
----------------------------------------------------------------------------------------------------------------
    Concentration  (ppt)            PFHxS  [90% CI]             PFOA  [90% CI]              PFOS  [90% CI]
----------------------------------------------------------------------------------------------------------------
4.0.........................                  18,641,000                  28,051,000                  30,627,000
                                 [15,669,000-21,693,000]     [24,966,000-33,071,000]     [27,407,000-35,665,000]
5.0.........................                  14,092,000                  20,844,000                  24,405,000
                                 [11,129,000-16,887,000]     [18,193,000-24,239,000]     [21,611,000-28,440,000]
10.0........................                   4,608,000                   7,111,000                  10,561,000
                                   [3,432,000-7,262,000]       [5,566,000-9,335,000]      [7,858,000-12,866,000]
----------------------------------------------------------------------------------------------------------------

    For PFOA, PFOS, and PFHxS, thousands of systems were estimated to 
have mean concentrations over the lowest thresholds (i.e., 4.0 and 5.0 
ppt) presented in Tables 16 and 17 with the total population served 
estimated to be in the tens of millions. The populations shown here 
represent the entire populations served by systems estimated to have 
system-level means over the various thresholds. It is likely that 
different subpopulations would be exposed to different mean PFAS 
concentrations if multiple source waters are used.
    In addition to the estimates of individual chemical occurrence, the 
multivariate normal distribution of system-level means allowed the 
model to provide insight on estimated co-occurrence. Untransformed 
estimates of system-level means were assessed for correlation across 
each unique pair of the four modeled chemicals included in the model. 
Estimates of the Pearson correlation coefficient are shown in Table 18. 
The Pearson correlation coefficient serves as an indicator of the 
strength of the linear relationship between two variables and may range 
from -1 to 1. Positive values indicate a positive relationship (i.e., 
as one variable increases, so does the other).

 Table 18--National Occurrence Model Estimate--Median Estimated Pearson
  Correlation Coefficient and 90% Credible Interval Among System-Level
                                  Means
------------------------------------------------------------------------
                                                    Pearson correlation
                  Chemical pair                    coefficient  [90% CI]
------------------------------------------------------------------------
PFOS-PFOA........................................       0.71 [0.60-0.79]
PFOS-PFHpA.......................................       0.69 [0.57-0.78]
PFOS-PFHxS.......................................       0.85 [0.74-0.92]
PFOA-PFHpA.......................................       0.85 [0.80-0.89]
PFOA-PFHxS.......................................       0.55 [0.41-0.65]
PFHpA-PFHxS......................................       0.62 [0.47-0.72]
------------------------------------------------------------------------

    EPA considered a moderate strength correlation as greater than 0.5 
and a strong correlation as greater than 0.7. Each point estimate of 
correlation coefficients between two chemicals was above the threshold 
for a moderate strength correlation. The carboxylic acids (PFOA-PFHpA) 
and sulfonic acids (PFOS-PFHxS) had the highest estimated correlation 
strengths, with both the point estimate and the 90% credible interval 
above 0.7. PFOS-PFOA and PFOS-PFHpA had similar point estimates and 90% 
credible interval ranges, spanning the moderate-to-strong correlation 
range. Both PFOA-PFHxS and PFHpA-PFHxS had the bulk of their posterior 
distributions fall in the range of a moderate strength correlation. 
Thus, the model predicted significant positive relationships among 
system-level means of all four chemicals that were included. These 
results support the co-occurrence discussion presented in section VII.C 
of this preamble that indicated extensive co-occurrence of PFOA, PFOS, 
and the HI PFAS observed in state datasets from both groupwise and 
pairwise chemical perspectives.

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

    In order to broadly estimate the number of systems that would be 
impacted by the proposed regulation, including MCLs of 4.0 ppt for PFOA 
and PFOS alongside an HI of 1.0 for PFHxS, HFPO-DA, PFNA, and PFBS, 
findings from non-targeted monitoring in state datasets were combined 
with model estimates. Specific details on the methodology can be found 
in USEPA (2023e). Briefly, information collected from non-targeted 
state datasets included the fractions of systems that reported a 
measurement at or above the UCMR 5 MRL for a given analyte and an 
empirical cumulative distribution function (eCDF) consisting of system-
level maximum observed concentrations of that chemical at these 
systems. The UCMR 5 MRLs for HFPO-DA, PFNA, and PFBS are equivalent to 
5.0 ppt, 4.0 ppt, and 3.0 ppt, respectively (USEPA, 2021e). This 
applies the assumption that

[[Page 18680]]

the fraction of systems that observed HFPO-DA, PFNA, and PFBS at or 
above UCMR 5 MRLs and the maximum concentrations observed at those 
systems are reasonably representative of the nation.
    The model was used to simulate entry point-level concentrations of 
the four modeled PFAS (PFOA, PFOS, PFHpA, and PFHxS) under the 
assumption that within-system concentrations are lognormally 
distributed (a common assumption for drinking water contaminants, see 
(Cadwallader et al. (2022)) and that variability in concentrations is 
entirely across entry points (thus a given entry point is assumed to 
have a constant concentration) For each system, the maximum estimated 
entry point PFOA or PFOS concentration was selected to determine 
whether the system exceeded either of the proposed MCLs of 4.0 ppt. The 
entry point with the maximum concentration is the point that determines 
whether a system has an entry point that is above an MCL. Estimates of 
the system-level maximum for PFHxS were also selected for the HI 
calculation. The maximum value of the sum of the four modeled PFAS at 
each system was selected and used as a basis for determining which 
systems would receive superimposed concentrations of the three 
remaining HI chemicals (HFPO-DA, PFNA, and PFBS). This approach was 
selected due to the extensive observed co-occurrence of PFAS in the 
UCMR 3, state data, and modeled estimates.
    Multiple methods of system selection were used that reflected 
different degrees of co-occurrence. The chemical concentration that was 
applied to selected systems were randomly sampled from the eCDF for 
each chemical. Based on the model output, this assumes that system-
level maximums for HFPO-DA, PFNA, and PFBS would occur at the same 
location within a system. Substantial co-occurrence among PFAS was 
observed in the model output, state datasets, and the UCMR 3 dataset. 
Combination of system-level maximums independently pulled from chemical 
eCDFs is a reasonable simplifying assumption given this co-occurrence. 
This is particularly true given that the systems selected for each 
chemical are not necessarily the same and in most cases were 
probability-weighted. Estimates of the range of systems impacted were 
developed by taking Q5 and Q95 estimates for each method. The low end 
of the range was taken as the lowest Q5 estimate across methods, 
rounded down, while the high end of the range was taken as the highest 
Q95 estimate across methods, rounded up. This was also done for the 
total population served by these systems.
    The resulting range of systems estimated to be impacted by the 
proposed regulation of an MCL of 4.0 ppt for PFOA and PFOS and an HI of 
1.0 for a mixture of PFHxS, HFPO-DA, PFNA, and PFBS was 3,400-6,300 
systems serving a total population of 70-94 million people. Among these 
systems, 100-500 were estimated to be systems exceeding the HI for 
PFHxS, HFPO-DA, PFNA, and PFBS that had not already exceeded the MCLs 
for PFOA and/or PFOS. The total population served by these systems was 
estimated to be 0.6 to 6.3 million people.
    In summary, using the MCMC occurrence model, EPA estimated baseline 
occurrence to derive occurrence and exposure estimates for the proposed 
MCLs for PFOA and PFOS, as well as alternative MCLs. EPA then used 
these modeled estimates to inform the costs and benefits determination 
as described in section XIII of this preamble. Here and in section XIII 
of this preamble, EPA requests comment on the number of systems 
estimated to solely exceed the HI (but not the PFOA or PFOS MCLs) 
according to the approach outlined in USEPA (2023e).

VIII. Analytical Methods

    EPA developed the following liquid chromatography/tandem mass 
spectrometry (LC/MS/MS) analytical methods to quantitatively monitor 
drinking water for targeted PFAS: EPA Method 533 (USEPA, 2019b) and EPA 
Method 537.1, Version 2.0 (USEPA, 2009b; USEPA, 2020a). All six PFAS 
proposed for regulation can be measured by both EPA Methods 533 and 
537.1 and both methods are acceptable for meeting the monitoring 
requirements of this regulation.
    EPA Method 533 monitors for 25 select PFAS, including PFOA, PFOS, 
PFHxS, HFPO-DA, PFNA, and PFBS, with published measurement accuracy and 
precision data for PFOA in reagent water, finished ground water, and 
finished surface water. For further details about the procedures for 
this analytical method, please see Method 533: Determination of Per- 
and Polyfluoroalkyl Substances in Drinking Water by Isotope Dilution 
Anion Exchange Solid Phase Extraction and Liquid Chromatography/Tandem 
Mass Spectrometry (USEPA, 2019b).
    EPA Method 537.1 (an update to EPA Method 537), monitors for 18 
select PFAS, including PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS, with 
published measurement accuracy and precision data for PFOA in reagent 
water, finished ground water, and finished surface water. For further 
details about the procedures for this analytical method, please see 
Method 537.1, Version 2.0, Determination of Selected Per- and 
Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase 
Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/
MS) (USEPA, 2020a).

A. Practical Quantitation Levels (PQLs) for Regulated PFAS

    As described in section VI of this preamble, a PQL is defined as 
the ``lowest concentration of an analyte that can be reliably measured 
within specified limits of precision and accuracy during routine 
laboratory operating conditions'' (USEPA, 1985). EPA uses the PQL to 
estimate or evaluate the minimum, reliable quantitation level that most 
laboratories can be expected to meet during day-to-day operations. The 
basis for setting PQLs is (1) quantitation, (2) precision and accuracy, 
(3) normal operations of a laboratory, and (4) the fundamental need (in 
the compliance monitoring program) to have a sufficient number of 
laboratories available to conduct the analyses. For the PFAS regulated 
in this proposal, EPA is proposing the following PQLs outlined in Table 
19:

                    Table 19--PQLs for Regulated PFAS
------------------------------------------------------------------------
                                                                  PQL
                         Contaminant                             (ppt)
------------------------------------------------------------------------
PFOA.........................................................        4.0
PFOS.........................................................        4.0
HFPO-DA......................................................        5.0
PFHxS........................................................        3.0
PFNA.........................................................        4.0
PFBS.........................................................        3.0
------------------------------------------------------------------------

    Drinking water analytical laboratories have different performance 
capabilities dependent upon their instrumentation (manufacturer, age, 
usage, routine maintenance, operating configuration, etc.) and analyst 
experience. Some laboratories will effectively generate accurate, 
precise, quantifiable results at lower concentrations than others. 
Organizations that collect data need to establish data quality 
objectives (DQOs) to meet the needs of their program. These DQOs should 
consider establishing reasonable quantitation levels that laboratories 
can routinely meet. Establishing a quantitation level that is too low 
may result in recurring QC failures that will necessitate repeating 
sample analyses, increase

[[Page 18681]]

costs, and potentially reduce laboratory capacity. Establishing a 
quantitation level that is too high may result in important lower-
concentration results not being quantitated.
    EPA's approach to establishing DQOs within the UCMR program serves 
as an example. EPA established MRLs for UCMR 5, finalized in December 
2021, and requires laboratories approved to analyze UCMR samples to 
demonstrate that they can make quality measurements at or below the 
established MRLs. EPA calculated the UCMR 5 MRLs using quantitation-
limit data from multiple laboratories participating in an MRL-setting 
study. An MRL is set after a statistical determination that 75% of 
laboratories will be able to meet that level with a 95% CI (USEPA, 
2022g). The UCMR 5 MRLs are not intended to represent the lowest 
achievable measurement level an individual laboratory may achieve. As 
noted above, these MRLs are derived using the quantitation level 
results from multiple laboratories participating in an analytical study 
and account for differences in the capability of laboratories across 
the country.
    For UCMR 5, EPA calculated and published the following multi-
laboratory MRLs for the PFAS addressed in this proposed rule: PFOA: 
0.004 [micro]g/L (4.0 ppt); PFOS: 0.004 [micro]g/L (4.0 ppt); PFHxS: 
0.003 [micro]g/L (3.0 ppt); HFPO-DA: 0.005 [micro]g/L (5.0 ppt); PFNA: 
0.004 [micro]g/L (4.0 ppt); PFBS: 0.003 [micro]g/L (3.0 ppt). Based on 
the multi-laboratory data acquired for the UCMR 5 rule, EPA has defined 
the PQL for PFAS addressed in this proposed rule to be equal to the 
UCMR 5 MRL (see Table 19, above).
    Some laboratories are capable of measuring the PFAS addressed in 
this proposed rule at lower concentrations. Indeed, EPA received some 
public comments prior to developing the final UCMR 5 recommending lower 
MRLs than those that were ultimately promulgated (USEPA, 2022g). 
However, after reviewing the data from laboratories that participated 
in the MRL-setting study for UCMR 5, EPA concluded that the MRLs set in 
that rule represented ``lowest feasible'' levels for a national 
measurement program. Based on laboratory performance in EPA's UCMR 5 
Laboratory Approval Program, during 2021-2022, EPA believes that the 
UCMR 5 MRLs are appropriate for using as PQL for this proposed 
rulemaking. EPA recognizes that as more laboratories upgrade their 
instrumentation and gain more experience analyzing drinking water 
samples for PFAS, more laboratories may become capable of 
quantitatively measuring PFAS at lower concentrations.
    While the values below the PQL will not be used to calculate 
compliance with the proposed MCLs under this proposed rule (see 
discussion above in Section VI of this preamble), values lower than the 
PQL are achievable by individual laboratories, and therefore lower 
levels can be used for purposes of screening and to determine 
compliance monitoring frequency. EPA is proposing the use of a rule 
trigger level for less frequent compliance monitoring under certain 
circumstances in which systems can demonstrate PFAS concentrations in 
finished drinking water are below:
     one-third of the MCLs for PFOA and PFOS, i.e., 1.3 ppt; 
and
     one-third of the HI MCL for the HI PFAS (PFHxS, HFPO-DA, 
PFNA, and PFBS), i.e., 0.33.
    Based on laboratory calibration standard data submitted as part of 
the UCMR 5 Laboratory Approval Program, described in more detail in 
section VI.A. of this preamble, EPA maintains that laboratories are 
capable of screening to this level. For additional discussion on this 
rule trigger level and monitoring requirements for this proposal, 
please see sections VI.A. and IX of this preamble.

IX. Monitoring and Compliance Requirements

A. What are the monitoring requirements?

    EPA is proposing requirements for CWS and NTNCWSs to monitor for 
certain PFAS. The Agency is proposing to amend 40 CFR part 141 by 
adding a new subpart to incorporate the regulated PFAS discussed in 
this preamble. Under this new subpart, PWSs must sample entry points to 
the distribution system using a monitoring regime based on EPA's SMF 
for SOCs. Under the SMF for SOCs, the monitoring frequency for a PWS is 
dependent on previous monitoring results, among other things (USEPA, 
2004). EPA is proposing that, consistent with the SMF for SOCs, 
groundwater systems serving greater than 10,000 and all surface water 
systems are initially required to monitor quarterly within a 12-month 
period for regulated PFAS. To provide additional flexibilities for 
small groundwater systems, EPA is also proposing and taking comment on 
a modification to the SMF for SOCs in that groundwater systems serving 
10,000 or fewer are initially required to only monitor twice for 
regulated PFAS within a 12-month period, each sample at least 90 days 
apart. In this proposal, all systems would be allowed to use previously 
acquired monitoring data to satisfy the initial monitoring requirements 
(see subsection (C) of this preamble below for additional details about 
using previously acquired monitoring data to satisfy initial monitoring 
requirements). Based on the SMF, EPA is also proposing that based upon 
the initial monitoring results, primacy agencies would be able to 
reduce compliance monitoring frequency for a system to once or twice 
every three years (depending on system size) if the monitoring results 
are below the rule trigger level (defined below).
    EPA is proposing that water systems will conduct compliance 
monitoring to demonstrate that finished drinking water does not exceed 
the MCLs for regulated PFAS. Water systems must show the primacy agency 
that the contaminant is not present in the drinking water supply or, if 
present, it does not exceed the proposed MCLs for regulated PFAS. For 
compliance monitoring frequency purposes only, EPA is proposing a rule 
trigger level of one-third the MCLs (1.3 ppt for PFOA and PFOS and 0.33 
for HI PFAS (PFHxS, HFPO-DA, PFNA, and PFBS)). As such, EPA is 
proposing amendments for a new subpart to include the following term to 
describe the circumstances in which water systems may be eligible for 
reduced monitoring for PFOA and PFOS and the HI PFAS if below this:
     Rule Trigger Level: One-third of the MCLs for regulated 
PFAS, i.e., 1.3 ppt for PFOA and PFOS and 0.33 for PFAS regulated by 
the HI (PFHxS, HFPO-DA, PFNA, and PFBS).
    For more information, including the basis of the rule trigger 
level, please see sections VI.A. and VIII.A. of this preamble.
    EPA notes that for some proposed regulated PFAS, the values used to 
determine reduced monitoring may be below their PQLs (e.g., PFOA and 
PFOS at 1.3 ppt when the PQL is 4.0 ppt). For purposes of screening to 
determine monitoring frequency, however, EPA has sufficient confidence 
that while measurements below the PQL may be slightly less precise and 
accurate, they are achievable by individual laboratories and 
appropriate for this intended purpose. EPA requests comment on this 
finding regarding feasibility of the proposed MCLs and more generally 
on laboratory capacity. As noted earlier, EPA anticipates laboratories 
will be able to adjust to demand (including possible price effects), 
which the Agency anticipates will be distributed across the 
implementation period. Further, at the proposed rule trigger level, the 
measurement is primarily useful in determining whether the contaminant 
is

[[Page 18682]]

present in a sample and for evaluating monitoring flexibilities, rather 
than to determine its specific concentration. EPA has set these values 
below the MCLs to allow systems the opportunity to reduce their 
monitoring schedule and burden, while minimizing the chance of random 
normal variation resulting in a single sample close to, but below the 
MCLs, when the ``true'' annual average value would be above the MCL. 
For additional discussion on PQL, please see section VII of this 
preamble. Systems below the rule trigger level would be required to 
conduct compliance monitoring according to the following schedule:
     Systems that do not detect regulated PFAS in their systems 
at or above the rule trigger level (1.3 ppt for PFOA and PFOS and 0.33 
for the HI PFAS (PFHxS, HFPO-DA, PFNA, and PFBS)), and that serve 3,300 
or fewer customers will be required to analyze one sample for all 
regulated PFAS per three-year compliance period at each entry point to 
the distribution system (EPTDS) that does not meet or exceed the rule 
trigger level.
     Systems that do not detect regulated PFAS in their systems 
at or above the rule trigger level (1.3 ppt for PFOA and PFOS and 0.33 
for the HI PFAS (PFHxS, HFPO-DA, PFNA, and PFBS), and that serve a 
population of greater than 3,300 will be required to analyze two 
samples for all regulated PFAS at least 90 days apart in one calendar 
year per three-year compliance period at each EPTDS that does not meet 
or exceed the rule trigger level.
    If a water system is not below the rule trigger level for regulated 
PFAS at a given EPTDS, it will be required to monitor for all regulated 
PFAS quarterly at that EPTDS. Systems monitoring less frequently than 
quarterly whose sample result is at or exceeds the rule trigger level 
must also begin quarterly sampling at the EPTDS where regulated PFAS 
were observed at or above the trigger level. In either case, the 
primacy agency may allow a system to move to a reduced monitoring 
frequency when the primacy agency determines that the system is below 
the rule trigger level and reliably and consistently below the MCL. 
However, primacy agencies cannot determine that the system is below the 
rule trigger level and reliably and consistently below the MCL until at 
least four consecutive quarters of quarterly monitoring have occurred. 
EPA notes that, as described above, systems may have EPTDS within a 
system on different compliance monitoring schedules depending on 
monitoring results.
    In this document, EPA requests comment on the reduced monitoring 
approach the Agency is proposing which will save resources for many 
lower-risk water systems. First, EPA is requesting comment on the 
allowance of a water system to potentially have each EPTDS on a 
different compliance monitoring schedule based on specific entry point 
sampling results (i.e., some EPTDS being sampled quarterly and other 
EPTDS sampled only once or twice during each three-year compliance 
period), and if instead, compliance monitoring frequency should be 
consistent across all of the system's sampling points. EPA is also 
requesting comment on establishing the proposed rule trigger level 
values of 1.3 ppt for PFOA and PFOS and 0.33 for the PFAS regulated by 
the HI (PFHxS, HFPO-DA, PFNA, and PFBS). EPA is seeking comment on 
establishing the trigger level at other levels, specifically 
alternative values of 2.0 ppt for PFOA and PFOS and 0.50 for the HI 
PFAS. EPA notes that adjusting the trigger levels to 2.0 ppt for PFOA 
and PFOS and 0.50 for the HI PFAS would result in a considerable number 
of additional water systems significantly reducing their monitoring 
frequency from at least four times each year to once or twice every 
three years. EPA also notes that the higher trigger may provide 
slightly less assurance of the water systems' current regulated PFAS 
levels as a result of the more intermittent monitoring. EPA is seeking 
comment on the merits and drawbacks of these higher trigger levels 
compared to those proposed in this document.

B. How are PWS compliance and violations determined?

    Consistent with existing rules for determining compliance with 
NPDWRs, EPA is proposing that compliance with this rule will be 
determined based on the analytical results obtained at each sampling 
point. For systems monitoring quarterly, compliance with the proposed 
MCLs for regulated PFAS will be determined by running annual averages 
at the sampling point. Systems monitoring less frequently whose sample 
result(s) are at or exceed the rule trigger level must revert to 
quarterly sampling at each EPTDS where the trigger level is met or 
exceeded for all regulated PFAS in the next quarter, with the triggered 
sample result being used for the first quarter of monitoring in 
calculating the running annual average.
    A running annual average is an average of sample analytical results 
for samples taken at a particular monitoring location during the 
previous four consecutive quarters. If a system takes more than one 
compliance sample during each quarter at a particular monitoring 
location, the system must average all samples taken in the quarter at 
that location to determine the quarterly averages to be used in 
calculating the running annual averages. Conversely, if a system does 
not collect required samples for a quarter, the running annual average 
will be based on the total number of samples collected for the quarters 
in which sampling was conducted. A system will not be considered in 
violation of an MCL until it has completed one year of quarterly 
sampling, except in the case where, if a quarterly sampling result will 
cause the running annual averages to exceed an MCL at any sampling 
point (i.e., the analytical result is greater than four times the MCL). 
In that case, the system is out of compliance with the MCL immediately.
    When calculating the running annual averages, if a sample result is 
less than the PQL for the monitored PFAS, EPA is proposing to use zero 
to calculate the average for compliance purposes. For example, if a 
system has sample results for PFOA that are 2.0, 1.5, 5.0, and 1.5 ppt 
for their last four quarters at a sample location, the values used to 
calculate the running annual average would be 0.0, 0.0, 5.0, and 0.0 
with a resulting PFOA running annual average of 1.3 ppt. As described 
in sections VI and VIII of this preamble, EPA is proposing that values 
below the PQL will not be used to determine compliance with the 
proposed MCLs as these PQLs are the lowest concentration of analyte 
that can be reliably measured within specified limits of precision and 
accuracy during routine laboratory conditions. As such, quantifying 
concentrations below the PQL for compliance purposes may decrease the 
precision and accuracy of the measured value and may not be achievable 
for some individual laboratories. In this document, EPA is requesting 
comment on whether EPA should consider an alternative approach when 
calculating the running annual averages for compliance. Specifically, 
in the case where a regulated PFAS is detected but below its proposed 
PQL, that the proposed rule trigger level (1.3 ppt for PFOA and PFOS 
and 0.33 of each of the HI PFAS PQLs (i.e., PFHxS=1.0, HFPO-DA=1.7, 
PFNA=1.3, and PFBS=1.0)) be used as the value in calculating the 
running annual average for compliance purposes. While this approach may 
be more complicated to implement than using zero when below the PQL, it 
is largely consistent with EPA's NPDWRs related to other SOCs and has 
the

[[Page 18683]]

potential to slightly increase the public health protection provided by 
this proposed regulation.

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

    As proposed, systems would be allowed to use previously collected 
monitoring data to satisfy the initial monitoring requirements. In 
general, a system with appropriate historical monitoring data for each 
distribution system entry point, collected using EPA Methods 533 or 
537.1 as part of UCMR 5 or a state-level or other appropriate 
monitoring campaign, could use that monitoring data to satisfy initial 
monitoring requirements.
    EPA is proposing that systems with previously acquired monitoring 
data from UCMR 5 will not be required to conduct separate initial 
monitoring for regulated PFAS. To satisfy the initial monitoring 
requirements for these systems using UCMR 5 data, data collected after 
January 1st, 2023, can be used for entry point samples.
    While EPA expects most systems serving 3,300 or greater will have 
UCMR 5 data, EPA is also proposing that systems with previously 
acquired monitoring data from outside UCMR 5, including State-led or 
other appropriate occurrence monitoring using EPA methods 533 or 537.1 
will also not be required to conduct separate initial monitoring for 
regulated PFAS. This addition may allow systems serving fewer than 
3,300 to satisfy the initial monitoring requirements. Data collected 
after January 1st, 2023, can be used for entry point samples. Data 
collected between January 1st, 2019, and December 31, 2022, may also be 
used if it is below the proposed rule trigger level of 1.3 ppt for PFOA 
and PFOS and an HI of 0.33 for PFHxS, HFPO-DA, PFNA, and PFBS. The 
additional analytical requirement for older data is to ensure the use 
of these data is adequately representative of current water quality 
conditions. If systems have multiple years of data, the most recent 
data must be used.

D. Can systems composite samples?

    40 CFR 141.24 subpart C describes instances where primacy agencies 
may reduce the samples a system must analyze by allowing samples to be 
composited. Composite sampling is an approach in which equal volumes of 
water from multiple entry points are combined into a single container 
and analyzed as a mixture. The reported concentration from the analysis 
of the composite sample therefore reflects the average of the analyte 
concentrations from the contributing entry points. Composite sampling 
can potentially reduce analytical costs because the number of required 
analyses is reduced by combining multiple samples into one and 
analyzing the composited sample. However, based on comments EPA 
received in consulting with state regulators and small business 
entities (operators of small PWSs), PFAS are ubiquitous in the 
environment at low concentrations which necessitates robust laboratory 
analytical precision at these low concentrations. For example, 
incidental contamination from or adherence to surface laboratory 
equipment may artificially lower contaminant concentrations or result 
in false negatives. Additionally, PFAS are demonstrated to be 
ubiquitous in the environment such that the risk for false positives 
may increase when combining samples for composite analysis. Based on 
these potential implementation issues, EPA is proposing a deviation 
from the SMF for SOCs by not allowing samples to be composited.

E. Can primacy agencies grant monitoring waivers?

    40 CFR 141.24 Subpart C describes instances where the primacy 
agency may grant waivers predicated on proximity of the system to 
contaminant sources (i.e., susceptibility to contamination) and 
previous uses of the contaminant within the watershed (including 
transport, storage, or disposal). Based on EPA's consultation with 
state regulators and operators of small PWSs, the Agency believes that 
due to the ubiquity, environmental persistence, and transport abilities 
of PFAS, granting waivers based on these conditions would be 
challenging, therefore EPA is not incorporating this flexibility as a 
part of these proposed monitoring requirements. However, in this 
proposal, EPA is considering and taking comment on waivers based on 
sampling results. Specifically, EPA is requesting comment on whether 
water systems should be permitted to apply to the primacy agency for a 
monitoring waiver of up to 9-years (one full compliance cycle) for 
these proposed PFAS if after at least one year of quarterly sampling 
the results are below the rule trigger level of one-third of the MCLs, 
or for systems that may be monitoring less frequently than quarterly if 
at least two consecutive three year-compliance period sample results 
are below the rule trigger level. Additionally, EPA is requesting 
comment on allowing similar monitoring waivers to be granted based on 
previously acquired monitoring data as described above in subsection 
(C) of this preamble. In either case, systems with a monitoring waiver 
would be required to take at least one sample per nine-year compliance 
cycle in order to maintain or renew an existing waiver. Furthermore, 
EPA is seeking comment on the identification of possible alternatives 
to traditional vulnerability assessments that should be considered to 
identify systems as low risk and potential eligibility for monitoring 
waivers.

F. When must systems complete initial monitoring?

    Pursuant to Section 1412(b)(10), this proposed rule would require 
compliance three years after promulgation. To satisfy initial 
monitoring requirements and demonstrate rule compliance, within the 
three years following rule promulgation, groundwater systems serving a 
population greater than 10,000 and all surface water systems will be 
required to demonstrate their baseline concentrations using data from 
four quarterly samples collected over a one-year period. Groundwater 
systems serving a population 10,000 or fewer may collect two quarterly 
samples at least 90 days apart over a one-year period for the purpose 
of initial monitoring, rather than collecting four quarterly samples. 
Additionally, as described earlier in this section (subsection C of 
this preamble), EPA is proposing that systems with appropriate, 
previously acquired monitoring data from UCMR 5, state-led, or other 
applicable monitoring programs using EPA Methods 533 or 537.1, will not 
be required to conduct separate initial monitoring for regulated PFAS. 
As such, given the advantageous timing of UCMR 5 monitoring data for 
all systems serving greater than 3,300 and the availability of 
historical monitoring data that many small systems serving 3,300 or 
fewer may utilize from state-level monitoring programs, EPA notes this 
proposed allowance will offer significant burden reduction for these 
systems and sufficient timing to take necessary actions and ensure rule 
compliance. For systems that may not have available data and/or choose 
to conduct additional monitoring, as proposed in this document, EPA 
would encourage those systems to conduct their initial monitoring as 
soon as practicable following rule promulgation to allow for actions 
that may need to be taken based on monitoring results and to certify 
rule compliance. The Agency seeks comment on EPA's proposed initial 
monitoring timeframe, particularly for NTNCWS or all systems serving 
3,300 or fewer.

[[Page 18684]]

G. What are the laboratory certification requirements?

    EPA is proposing that laboratories demonstrate their ability to 
achieve the precision and detection limits necessary to meet the 
objectives of this regulation. The proposal would require laboratories 
to analyze performance evaluation (PE) samples every year in order to 
achieve and maintain certification.

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

A. What are the Consumer Confidence Report requirements?

    A CWS must prepare and deliver to its customers an annual Consumer 
Confidence Report (CCR) in accordance with requirements in 40 CFR 141 
Subpart O. A CCR provides customers with information about their local 
drinking water quality as well as information regarding the water 
system compliance with drinking water regulations. Under this proposal 
CWSs would be required to report detected PFAS in their CCR; 
specifically, PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS, and the HI 
for the mixtures of PFHxS, HFPO-DA, PFNA, and PFBS.

B. What are the public notification (PN) requirements?

    As part of SDWA, the Public Notification (PN) rule ensures that 
consumers will know if there is a problem with their drinking water. 
Notices alert consumers if there is risk to public health. They also 
notify customers: If the water does not meet drinking water standards; 
if the water system fails to test its water; if the system has been 
granted a variance (use of less costly technology); or if the system 
has been granted an exemption (more time to comply with a new 
regulation).
    All PWSs must give the public notice for all violations of NPDWRs 
and for other situations. Under this proposal, EPA is proposing that 
violations of the three MCLs in the proposal would be designated as 
Tier 2 and as such, PWSs would be required to comply with 40 CFR 
141.203. Per 40 CFR 141.203(b)(1), notification of an MCL violation 
should be provided as soon as practicable but no later than 30 days 
after the system learns of the violation.

XI. Treatment Technologies

    Water systems with PFAS levels that exceed the MCLs proposed would 
need to take action to provide drinking water which meets the NPDWR by 
the compliance dates established in the rule when final. For example, 
systems may install water treatment or consider other options such as 
source remediation or connecting to an uncontaminated water system. 
While conventional treatment technologies are unable to remove PFOS, 
PFOA, PFNA, PFHxS, PFBS, or HFPO-DA to levels protective of public 
health (McCleaf et al., 2017), there are technologies currently 
available that effectively remove these and other PFAS.
    Section 1412(b)(4)(E) of SDWA requires that the Agency ``list the 
technology, treatment techniques, and other means which the 
Administrator finds to be feasible for purposes of meeting [the MCL],'' 
which are referred to as BATs. These BATs are used by states to 
establish conditions for source water variances under Section 1415(a). 
Section 1412(b)(4)(E)(ii) also requires that the Agency identify small 
system compliance technologies (SSCTs), which are affordable treatment 
technologies, or other means that can achieve compliance with the MCL 
(or treatment technique [TT], where applicable).

A. What are the best available technologies?

    The Agency identifies the BATs as those meeting the following 
criteria: (1) The capability of a high removal efficiency; (2) a 
history of full-scale operation; (3) general geographic applicability; 
(4) reasonable cost based on large and metropolitan water systems; (5) 
reasonable service life; (6) compatibility with other water treatment 
processes; and (7) the ability to bring all the water in a system into 
compliance. The Agency is proposing the following technologies as BAT 
for PFAS removal from drinking water based its review of the treatment 
and cost literature (USEPA, 2023g):

 GAC
 AIX
 High pressure membranes (RO and NF)

    Operationally, GAC and AIX are sorptive processes meaning a process 
where one substance becomes attached to another. Sorption is typically 
composed of absorption where one substance is incorporated into 
another, adsorption where one substance is incorporated onto another, 
or ion exchange (IX) where an aqueous ion (the contaminant) is traded 
for a different less dangerous ion (typically chloride in AIX) on an 
insoluble matrix. Sorptive processes pour feed water through a vessel 
filled with a sorbent known as a contactor. The operation continues 
until the sorbent no longer effectively removes the target contaminant; 
this is when the contaminant ``breaks through'' the treatment process. 
At this point, the sorbent must be disposed then replaced or 
regenerated. The length of time until the sorbent must be replaced or 
regenerated is known as bed life and is a critical factor in the cost 
effectiveness of sorptive technology. One bed life measurement is the 
water volume that can be treated before breakthrough and is measured in 
bed volumes (BV). BVs are how many times the sorbent (i.e., media) can 
be filled in the bed in which the sorbent resides before contaminant 
breakthrough. EPA estimates GAC treatment will be sufficiently 
available to support cost-effective compliance with this proposed 
regulation, and requests comment on whether additional guidance on 
applicable circumstances for GAC treatment is needed.
    High pressure membranes are a separation process where feed water 
is split into two streams across a membrane. One stream has few 
contaminants or other solutes left in it and is known as permeate or 
produced water. The other stream contains the concentrated contaminant 
and other solutes which is known as concentrate, brine, retentate, or 
reject water. Membrane flux is how much permeate is produced for a 
given surface area and time; different system configurations operating 
at the same flux produce differing quantities of finished water. This 
means that membrane systems with differing configurations cannot be 
directly compared based on flux. Flux can be reduced during membrane 
fouling which is where things accumulate on or in the membrane. Fouling 
can require membrane cleaning and replacement or operational changes.
    There are also non-treatment options which may be used for 
compliance such as replacing a PFAS-contaminated drinking water source 
with a new uncontaminated source (e.g., a new well), or purchasing 
compliant water from another system. Conventional and most advanced 
water treatment methods are ineffective at removing PFAS (Rahman et 
al., 2014). Further information on the proposed BATs is provided below.
1. Granular Activated Carbon
    GAC is a separation process where contaminants become attached to 
specially treated carbon with a high surface area. The GAC 
manufacturing process can accept any highly carbonaceous material as an 
input such as bituminous coal, lignite coal, peat, wood, coconut 
shells, and peach pits. Activation is predominantly a thermal process, 
although it may also be a chemical process, that creates as well as

[[Page 18685]]

enlarges pores generating a porous structure with a large surface area 
per unit mass. Literature suggests that the primary mechanisms of 
adsorption include both hydrophobic and electrostatic interactions 
(Ateia et al., 2019). In addition to removing PFAS, GAC can remove 
contaminants including taste and odor compounds, natural organic matter 
(NOM), VOCs, SOCs, DBP precursors, and radon. Organic compounds with 
high molecular weights are also readily adsorbable.
    Demonstrated PFAS removal efficiencies can exceed >99 percent and 
can achieve concentrations less than 4 ng/L (Forrester and Bostardi, 
2019; Zeng et al., 2020; Westreich et al., 2018; Belkouteb et al., 
2020; Woodard et al., 2017; and Hopkins et al., 2018). During the 
operation, carbon is removed from the system periodically, for disposal 
or regeneration, based on treatment objectives. Several factors affect 
bed life, including the presence of competing contaminants such as 
nitrate and the carbon type used. Most studies found that natural or 
dissolved organic matter (NOM/DOM) interferes with PFAS sorption, in 
general, and its presence dramatically lowers treatment efficacy 
(McNamara et al., 2018; Pramanik et al., 2015; Yu et al., 2012). The 
lowered treatment effectiveness was found to be less pronounced for 
HFPO-DA than for perfluoroalkyl carboxylic acid (PFCA) C7 and above for 
GAC (Park et al., 2020).
    Reactivation is a process that removes organic compounds from 
adsorption sites on GAC enabling reuse. Although different methods are 
available for GAC reactivation, the process most commonly involves high 
temperature thermal treatment in a specialized facility such as a 
multiple hearth furnace or rotary kiln (Matthis and Carr, 2018; USEPA, 
2023g). Reactivated carbon can become totally exhausted with other 
contaminants not removed during reactivation and must be replaced. 
However, for GAC, the loss of approximately 10 percent of the media due 
to abrasion within the reactivation process can result in a somewhat 
steady state for performance as new GAC is added each time to replace 
the lost GAC. Systems may decide to dispose of GAC (i.e., operate on a 
`throw-away' basis) instead of reactivating the media. GAC can be a 
cost-effective treatment option despite needing to dispose of 
contaminated carbon.
2. Anion Exchange
    AIX is a separation process where an anion in the aqueous phase is 
exchanged for an ion attached to an exchange resin. Similar to GAC, AIX 
uses contactors. These contactors, however, are filled with a bed of 
beads or gel known as resin instead of carbon. As feed water moves 
through the resin, an anionic contaminant, such as PFAS exchanges, for 
an anion, typically chloride, on the resin. For PFAS compounds, vendors 
generally recommend using PFAS-selective resins (Boodoo, 2018; Boodoo 
et al., 2019; Lombardo et al., 2018; Woodard et al., 2017). AIX may 
also have a beneficial effect by removing other undesirable anions from 
the treated water such as nitrate or sulfate.
    Demonstrated PFAS removal efficiencies may be >99 percent and can 
achieve concentrations less than 4 ng/L (Dixit et al., 2021; Dixit et 
al., 2020; Zeng et al., 2020; Liu, 2017; Kumarasamy et al., 2020; 
Arevalo et al., 2014; and Yan et al., 2020). The operation continues 
until enough of the resin's available IX sites have ions from the feed 
water and the resin no longer effectively removes the target 
contaminant, also known as ``breaks through.'' At this point, the resin 
must be disposed and replaced or regenerated. The length of time until 
resin must be replaced or regenerated is known as bed life and is a 
critical factor in the cost effectiveness of IX as a treatment 
technology. Several factors affect bed life, including the presence of 
competing ions such as nitrate and the resin type used.
    Conventional regeneration solutions are not generally effective for 
restoring the capacity of PFAS-selective resins (Liu and Sun, 2021). 
Regeneration may be possible using organic solvents (Boodoo, 2018; 
Zaggia et al., 2016) or proprietary methods (Woodard et al., 2017). 
These alternative regeneration practices are generally practical or 
cost-effective only with very high influent concentrations, such as in 
remediation settings. Therefore, in drinking water applications using 
PFAS-selective resin, vendors recommend a single-use approach where the 
spent resin is disposed and replaced with fresh resin (Boodoo, 2018; 
Lombardo et al., 2018). Exhausted resin must be disposed; due to the 
difficulties mentioned earlier and vendor recommendation, resins are 
often operated on a `throw-away' basis. This operational mode avoids 
generating spent regenerant liquid residuals. AIX can be a cost-
effective treatment option.
3. High Pressure Membranes (RO and NF)
    RO and NF are membrane separation processes where water is forced 
through a membrane at greater than osmotic pressure. The water that 
transverses the membrane is known as permeate or produce water, and has 
few solutes left in it; the remaining water is known as concentrate, 
brine, retentate, or reject water and forms a waste stream with 
concentrated solutes. NF has a less dense active layer than RO, which 
enables lower operating pressures but also makes it less effective at 
removing contaminants. In drinking water treatment, these membranes are 
most often used in a spiral-wound configuration that consists of 
several membrane envelopes, layered with feed spacers, and rolled 
together in and around a central collection tube. Feed pressures for NF 
membranes are typically in the range of 50 to 150 pounds per square 
inch (psi). Feed pressures for RO membranes are in the range of 125 to 
300 psi in low pressure applications (such as PFAS removal) but can be 
as high as 1,200 psi in applications such as seawater desalination 
(USEPA, 2023d). RO may remove other contaminants including arsenic and 
chromium-VI.
    RO and NF may achieve PFAS removal >99 percent (Lipp et al., 2010; 
Horst et al., 2018; Liu et al., 2021; Dickenson and Higgins, 2016; 
Steinle-Darling et al., 2008; Boonya-Atichart et al., 2016; Appleman et 
al., 2014; Thompson et al., 2011; CDM Smith, 2018; Dickenson and 
Higgins, 2016; and Dowbiggin et al., 2021). While water quality affects 
process design (e.g., recovery rate, cleaning frequency, and 
antiscalant selection), it has relatively little effect on PFAS removal 
percent. High pressure membranes generate a relatively large 
concentrate stream, which will contain PFAS as well as other rejected 
dissolved species, which will require disposal or additional treatment. 
The large concentrate stream also means less treated water is available 
for distribution (e.g., 70 to 85 percent of source water), which is a 
disadvantage for systems with limited water supply.

B. PFAS Co-Removal

    AIX and GAC are effective at removing PFAS and there is generally a 
linear relationship between PFAS chain length and removal efficiency 
shifted by functional group (McCleaf et al., 2017; S[ouml]reng[aring]rd 
et al., 2020). Perfluoroalkyl sulfonates (PFSA), such as PFOS, are 
removed with greater efficiency than the corresponding PFCA, such as 
PFOA, of the same carbon backbone length (Appleman et al., 2014; Du et 
al., 2014; Eschauzier et al., 2012; Ochoa-Herrera and Sierra-Alvarez, 
2008; Zaggia et al., 2016). Generally, for a given water type and 
concentration, a PFSA is removed

[[Page 18686]]

about as well as a PFCA which has two more fully perfluorinated carbons 
in its backbone. For example, PFHxS (six carbon backbone and a sulfonic 
acid functional group) is removed about as well as PFOA (eight carbon 
backbone and a carboxylate head) and perfluorohexanoic acid (PFHxA) 
(six carbon backbone with a carboxylate head) is removed approximately 
as well as PFBS (four carbon backbone and a sulfonic acid functional 
group). Additionally, the compounds with longer carbon chain displayed 
a smaller percentage decrease in average removal efficiency over time 
(McCleaf et al., 2017).
    The three technologies discussed above have all been demonstrated 
to be effective in removing all six PFAS proposed for regulation as 
part of this rulemaking. As discussed in section VII.C. of this 
preamble, PFAS have been shown to co-occur. Hence, where the six PFAS 
being regulated today occur in concentrations above their respective 
regulatory standards there is also an increased probability of other 
unregulated PFAS being present. Further, since these same technologies 
also remove other long-chain and higher carbon/higher molecular weight 
PFAS EPA expects this rulemaking will provide additional public health 
benefits and protection by removing unregulated PFAS that may have 
adverse health effects. While EPA has not quantified those benefits as 
part of this rulemaking, the Agency believes these important secondary 
benefits further enhance public protection offered by this proposed 
regulation.

C. Management of Treatment Residuals

    As part of EPA's BAT evaluation, the Agency assesses the 
availability of studies of full-scale treatment of residuals that fully 
characterize residual waste streams and disposal options. At present, 
the most likely management option for spent material containing PFAS is 
reactivation for GAC and incineration for spent IX resin. For disposal 
of RO/NF membrane concentrate, most systems use surface water discharge 
or discharge to sanitary sewer. The large volume of residuals is a 
well-known obstacle to adoption of membrane separation technology in 
general. For more information on current residuals management 
practices, see Best Available Technologies and Small System Compliance 
Technologies for Per- and Polyfluoroalkyl Substances (PFAS) in Drinking 
Water (USEPA, 2023g) or Managing and Treating Per- and Polyfluoroalkyl 
Substances (PFAS) in Membrane Concentrates (Tow et al., 2021).
    EPA recognizes that future actions through several statutory 
authorities other than SDWA may have direct or indirect implications 
for drinking water treatment facilities and some actions may prevent or 
reduce PFAS entering drinking water sources. EPA is addressing PFAS 
through statutory authorities including the CERCLA, Resource 
Conservation and Recovery Act (RCRA), Toxic Substances Control Act 
(TSCA), Clean Water Act, Clean Air Act, and Emergency Planning and 
Community Right-to-Know Act (EPCRA). For example, as part of EPA's PFAS 
Strategic Roadmap, EPA proposed certain PFAS be designated as CERCLA 
hazardous substances to require reporting of PFOA and PFOS releases, 
enhance the availability of data, and ensure agencies can recover 
cleanup costs (USEPA, 2022c). In the Strategic Roadmap, EPA has also 
committed to expanding research on and accelerating the deployment of 
emerging PFAS treatment, remediation, destruction, disposal, and 
control technologies (USEPA, 2022c). EPA's 2020 Interim Guidance on the 
Destruction and Disposal of Perfluoroalkyl and Polyfluoroalkyl 
Substances and Materials Containing Perfluoroalkyl and Polyfluoroalkyl 
Substances outlines the current state of the science on techniques and 
treatments that may be used to destroy or dispose of PFAS (USEPA, 
2020b). In accordance with EPA's PFAS Strategic Roadmap, EPA 
anticipates releasing an updated version of the Guidance in 2023. As 
part of this rulemaking, EPA considered that in drinking water 
treatment, large volumes of spent GAC and ion exchange resin must be 
removed which does not lend itself to on-site storage over time. The 
disposal options identified in the Interim Guidance (USEPA, 2020b) are 
landfill disposal and thermal treatment.
    Stakeholders have expressed concern to EPA that a hazardous 
substance designation for certain PFAS may limit their disposal options 
for drinking water treatment residuals (e.g., spent media, concentrated 
waste streams) and/or potentially increase costs. Although EPA 
anticipates that designating chemicals as hazardous substances under 
CERCLA generally should not result in limits on for disposal of PFAS 
drinking water treatment residuals, EPA has estimated the treatment 
costs for systems both with the use of hazardous waste disposal and 
non-hazardous disposal options to assess the effects of potentially 
increased disposal costs. Specifically, EPA assessed the potential 
impact on PWS treatment costs associated with hazardous residual 
management requirements in a sensitivity analysis on the proposed 
option. Relative to the national analysis for the proposed option 
assuming non-hazardous disposal, the hazardous waste disposal 
assumption would increase PWS costs by 4% ($30 million annually) at the 
3% discount rate and 5% ($61 million annually) at the 7% discount rate 
should spent media need to be disposed of as hazardous waste in the 
future because of separate EPA or State regulatory action. EPA's 
sensitivity analysis demonstrates that potential hazardous waste 
disposal requirements may increase PWS treatment costs marginally, 
however the increase in PWS costs are not significant enough to change 
the determination that benefits of the rulemaking justify the costs. 
These estimates are discussed in greater detail in the HRRCA section of 
this proposed rulemaking and in Appendix N of the Economic Analysis 
(USEPA, 2023i). These costs are limited to the disposal of the PFAS 
contaminated residuals and wastes. Results for small systems are 
presented in Section D of this preamble below. EPA is seeking public 
input related to PFAS treatment residual disposal in Section XIV of 
this preamble.

D. What are small system compliance technologies (SSCTs)?

    EPA is proposing the SSCTs shown in Table 20. The table shows which 
of the BATs listed above are also affordable for each small system size 
category listed in Section 1412(b)(4)(E)(ii) of SDWA. The Agency 
identified these technologies based on an analysis of treatment 
effectiveness and affordability.

                                    Table 20--Proposed SSCTs for PFAS Removal
----------------------------------------------------------------------------------------------------------------
   System size  (population                                                                      Point of use
           served)                     GAC                   IX                 RO/NF           (POU) RO/NF \1\
----------------------------------------------------------------------------------------------------------------
25-500.......................  Yes................  Yes................  No.................  Yes.
501-3,300....................  Yes................  Yes................  No.................  Yes.

[[Page 18687]]

 
3,301-10,000.................  Yes................  Yes................  Yes................  not applicable.\2\
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ POU RO is not currently listed as a compliance option because the regulatory options under consideration
  require treatment to concentrations below the current NSF International/American National Standards Institute
  (NSF/ANSI) certification standard for POU device removal of PFAS. However, POU treatment is reasonably
  anticipated to become a compliance option for small systems in the future if NSF/ANSI or other independent
  third-party certification organizations develop a new certification standard that mirrors EPA's proposed
  regulatory standard. The affordability conclusions presented here reflect the costs of devices certified under
  the current standard, not a future standard, which may change dependent on future device design.
\2\ EPA's work breakdown structure (WBS) model for POU treatment does not cover systems larger than 3,300 people
  (greater than 1 million gallons per day [MGD] design flow), because implementing and maintaining a large-scale
  POU program is likely to be impractical.

    The operating principle for POU RO devices is the same as 
centralized RO: Steric exclusion and electrostatic repulsion of ions 
from the charged membrane surface. In addition to a RO membrane for 
dissolved ion removal, POU RO devices often have a sediment pre-filter 
and a carbon filter in front of the RO membrane, a 3- to 5-gallon 
treated water storage tank, and a carbon filter between the tank and 
the tap.
    EPA identified SSCTs using the affordability criteria methodology 
developed for drinking water rules (USEPA, 1998b). The analysis method 
is a comparison of estimated incremental household costs for PFAS 
treatment to an expenditure margin, which is the difference between 
baseline household water costs and a threshold equal to 2.5% of median 
household income (MHI). Table 21 shows the expenditure margins derived 
for the analysis. These margins show the cap on affordable incremental 
annual expenditures.

                          Table 21--Expenditure Margins for SSCT Affordability Analysis
----------------------------------------------------------------------------------------------------------------
                                                              Affordability    Baseline water      Expenditure
     System size  (population served)           MHI \1\       threshold \2\       cost \3\           margin
                                                         A      B = 2.5% x A                 C           D = B-C
----------------------------------------------------------------------------------------------------------------
25-500....................................         $55,377            $1,384              $507              $877
501-3,300.................................          53,596             1,340               587               753
3,301-10,000..............................          58,717             1,468               613               855
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ MHI based on U.S. Census Bureau's American Community Survey five-year estimates (United States Census
  Bureau, 2010) stated in 2010 dollars, adjusted to 2020 dollars using the Consumer Price Index (CPI) (for all
  items) for areas under 2.5 million persons.
\2\ Affordability threshold equals 2.5 percent of MHI.
\3\ Household water costs derived from 2006 Community Water System Survey (USEPA, 2009c), based on residential
  revenue per connection within each size category, adjusted to 2020 dollars based on the CPI for All Urban
  Consumers: Water and Sewer and Trash Collection Services in U.S. City Average.

    Table 21 shows the estimates of per-household costs by treatment 
technology and size category generated using the treatment cost method 
described in section XII.B of this preamble as well as Best Available 
Technologies and Small System Compliance Technologies for Perchlorate 
in Drinking Water (USEPA, 2019c) and Technologies and Costs for 
Treating Perchlorate-Contaminated Waters (USEPA, 2018c). Based on the 
results presented in Table 22, EPA identified candidate technologies 
available for which costs do not exceed the corresponding expenditure 
margin and, therefore, meet the SSCT affordability criterion. As such, 
EPA has determined that affordable SSCTs are available, and the Agency 
is not proposing any variance technologies.

                      Table 22--Total Annual Cost per Household for Candidate Technologies
----------------------------------------------------------------------------------------------------------------
   System size  (population
            served)                    GAC                 IX               RO/NF             POU RO/NF \1\
----------------------------------------------------------------------------------------------------------------
25-500........................  $395 to $727.....  $376 to $645.....  $3,711 to $4,676.  $317 to $326.
501-3,300.....................  $139 to $332.....  $133 to $235.....  $608 to $1,169...  $299 to $300.
3,301-10,000..................  $136 to $329.....  $121 to $218.....  $326 to $462.....  not applicable.\2\
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ POU RO is not currently a compliance option because the regulatory options under consideration require
  treatment to concentrations below the current NSF/ANSI certification standard for POU device removal of PFAS.
  However, POU treatment is reasonably anticipated to become a compliance option for small systems in the future
  if NSF/ANSI or other independent third-party certification organizations develop a new certification standard
  that mirrors EPA's proposed regulatory standard. Costs presented here reflect the costs of devices certified
  under the current testing standard, not a future standard, which may change dependent on future device design.
\2\ EPA's WBS model for POU treatment does not cover systems larger than 3,300 people (greater than 1 MGD design
  flow), because implementing and maintaining a large-scale POU program is likely to be impractical.

[[Page 18688]]

    The results discussed above assume management of spent GAC and 
spent IX resin using current typical management practices (reactivation 
for GAC and incineration for resin). EPA is in the process of proposing 
some PFAS be designated as hazardous substances under CERCLA and listed 
as hazardous constituents under RCRA. If finalized, neither of these 
actions should result in limiting disposal options and how PFAS 
containing waste, including spent GAC or resin, is required to be 
managed. However, waste management facilities may, at their own 
discretion, refuse to accept PFAS-containing materials or drinking 
water treatment operations may choose to send spent GAC and resin 
containing PFAS to facilities permitted to treat and/or dispose of 
hazardous wastes. To consider the implications of this possibility, EPA 
has developed an assessment of the current unit costs for disposing 
spent treatment materials and the costs associated with their disposal 
as hazardous waste. Table 23 shows the resulting cost per household if 
systems dispose of these residuals as hazardous waste. Although costs 
would increase somewhat compared to if they do not treat the spent 
media as hazardous waste, those increases are not significant enough to 
change the conclusions about affordability.

   Table 23--Total Annual Cost per Household Assuming Hazardous Waste
                    Disposal for Spent GAC and Resin
------------------------------------------------------------------------
   System size  (population
           served)                    GAC                   IX
------------------------------------------------------------------------
25-500.......................  $417 to $827....  $397 to $678.
501-3,300....................  $149 to $368....  $138 to $243.
3,301-10,000.................  $146 to $360....  $124 to $222.
------------------------------------------------------------------------

    In addition to the required analysis for small system 
affordability, EPA having received a number of recommendations from the 
SAB, the NDWAC, and other stakeholders, is exploring the use of 
alternative expenditure margins and other potential changes to the 
national level affordability methodology to better understand the cost 
impacts of new standards on low income and disadvantaged households 
served by small drinking water systems. The Agency conducted 
supplemental affordability analyses using alternative metrics suggested 
to EPA by stakeholders to demonstrate the potential affordability 
implications of the proposed NPDWR on the determination of affordable 
technologies for small systems at the national level of analysis.
    As required under the 1996 amendments to SDWA, EPA lists treatment 
technologies for small systems that are affordable and that achieve 
compliance with the regulatory standard. As part of its affordability 
analysis for the proposed PFAS rule, EPA determined that there are 
several affordable treatment technologies for small systems, including 
GAC, IX, RO, and POU RO.\5\ EPA is seeking public comment on the 
national level analysis of affordability of SSCTs and specifically on 
the potential methodologies presented. EPA's national small system 
affordability determination can be found in Section 9.12.1 of the EA. 
EPA's supplementary affordability analyses can be found in Section 
9.12.2 of the EA. EPA is also seeking comment on whether there are 
additional technologies which are viable for PFAS removal to the 
proposed MCLs as well as any additional costs which may be associated 
with non-treatment options such as water rights procurement. Finally, 
EPA is seeking comment on the benefits from using treatment 
technologies (such as reverse osmosis and GAC) that have been 
demonstrated to co-remove other types of contaminants found in drinking 
water and whether employing these treatment technologies are sound 
strategies to address PFAS and other regulated or unregulated 
contaminants that may co-occur in drinking water.
---------------------------------------------------------------------------

    \5\ POU RO is not currently a compliance option because the 
regulatory options under consideration require treatment to 
concentrations below 70 ppt total of PFOA and PFOS, the current 
certification standard for POU devices. However, POU treatment is 
anticipated to become a compliance option for small systems in the 
future should NSF/ANSI or another accredited third-party 
certification entity develop a new certification standard that 
mirrors (or is demonstrated to treat to concentrations lower than) 
EPA's proposed regulatory standard. The affordability conclusions 
for POU RO should be considered preliminary because they reflect the 
costs of devices certified under the current standard, not a future 
standard.
---------------------------------------------------------------------------

    Following finalization of the PFAS NPDWR, EPA will work with 
primacy agencies to provide assistance to support implementation of the 
rule. EPA requests comment on the type of assistance that would help 
small public water systems identify laboratories that can perform the 
required monitoring, evaluate treatment technologies and determine the 
most appropriate way to dispose of PFAS contaminated residuals and 
waste the systems may generate when implementing the rule.

XII. Rule Implementation and Enforcement

A. What are the requirements for primacy?

    This section describes the regulations, procedures, and policies 
primacy entities must adopt, or have in place, to implement the PFAS 
rule, when it is final. States, Territories, and Tribes must continue 
to meet all other conditions of primacy in 40 CFR part 142. Section 
1413 of SDWA establishes requirements that primacy entities (States or 
Indian Tribes) must meet to maintain primary enforcement responsibility 
(primacy) for its PWSs. These include:
     Adopting drinking water regulations that are no less 
stringent than Federal NPDWRs in effect under sections 1412(a) and 
1412(b) of the Act;
     Adopting and implementing adequate procedures for 
enforcement;
     Keeping records and making reports available on activities 
that EPA requires by regulations;
     Issuing variances and exemptions (if allowed by the State) 
under conditions no less stringent than allowed by SDWA Sections 1415 
and 1416; and
     Adopting and being capable of implementing an adequate 
plan for the provision of safe drinking water under emergency 
situations.
    40 CFR part 142 sets out the specific program implementation 
requirements for States to obtain primacy for the Public Water System 
Supervision (PWSS) Program, as authorized under 1413 of the Act.
    Under 40 CFR 142.12(b), all primacy States/territories/tribes would 
be required to submit a revised program to

[[Page 18689]]

EPA for approval within two years of promulgation of any final PFAS 
NPDWR or could request an extension of up to two years in certain 
circumstances. To be approved for a program revision, primacy States/
territories/tribes would be required to adopt revisions at least as 
stringent as the revised PFAS-related provisions in 40 CFR 141.6 
(Effective Dates); 40 CFR 141.900 subpart Z (Control of Per- and 
Polyfluoroalkyl Substances); 40 CFR 141.50 (Maximum Contaminant Level 
Goals for organic contaminants); 40 CFR 141.60 (Maximum Contaminant 
Levels for organic contaminants); appendix A to subpart O ([Consumer 
Confidence Report] Regulated contaminants); Appendix A to Subpart Q 
((NPDWR violations and other situations requiring public notice); 
Appendix B to Subpart Q (Standard health effects language for public 
notification); 40 CFR 142.62 (Variances and exemptions from the MCLs 
for organic and inorganic contaminants); and 40 CFR 142.16 (Primary 
Enforcement Responsibility).

B. What are the primacy agency record keeping requirements?

    The current regulations in 40 CFR 142.14 require primacy agencies 
to keep records of analytical results to determine compliance, system 
inventories, sanitary surveys, state approvals, vulnerability and 
waiver determinations, monitoring requirements, monitoring frequency 
decisions, enforcement actions, and the issuance of variances and 
exemptions. If primacy agencies grant monitoring waivers, they must 
record monitoring results that are below the rule trigger level in 
order to ensure systems are eligible for reduced monitoring schedules 
(for additional discussion on the rule trigger level and monitoring 
waivers, please see sections VIII and IX of this preamble). The primacy 
agency record keeping requirements remain unchanged and would apply to 
PFAS as with any other regulated contaminant.

C. What are the primacy agency reporting requirements?

    Currently, primacy agencies must report to EPA information under 40 
CFR 142.15 regarding violations, variances and exemptions, enforcement 
actions, and general operations of State PWS programs. These reporting 
requirements remain unchanged and would apply to PFAS as with any other 
regulated contaminant. However, the proposed PFAS MCLs, when final, 
could result in a greater frequency of reporting by certain primacy 
agencies. See discussion of PRA compliance in Section XV of this 
preamble for more information.

D. Exemptions and Extensions

    In accordance with SDWA Sec.  1412(b)(10), a state or EPA may grant 
an extension of up to two additional years to comply with an NPDWR's 
MCL(s) if the state or EPA determines an individual system needs 
additional time for capital improvements. At this time, EPA does not 
intend to provide a two-year extension nationwide. However, States may 
provide such an extension on an individual system basis. Where a State 
or EPA chooses to provide such an extension, the system would have up 
to five years from the rule's promulgation date to meet the MCLs. In 
addition, under SDWA Sec.  1416, EPA or primacy Agencies may grant an 
exemption for systems meeting specified criteria that provides an 
additional period for compliance not to exceed 3 years beyond the time 
period provided by Section 1412(b)(10). Under SDWA Sec.  1416(a), a 
State which has primary enforcement responsibility may exempt any 
public water system within the State's jurisdiction from any 
requirement respecting a MCL of any applicable NPDWR upon a finding 
that:
     Due to compelling factors (which may include economic 
factors, including qualification of the public water system as a system 
serving a disadvantaged community pursuant to section 300j-12(d) of 
this title), the public water system is unable to comply with such 
contaminant level or treatment technique requirement, or to implement 
measures to develop an alternative source of water supply,
     The public water system was in operation on the effective 
date of such contaminant level or treatment technique requirement, or, 
for a system that was not in operation by that date, only if no 
reasonable alternative source of drinking water is available to such 
new system,
     The granting of the exemption will not result in an 
unreasonable risk to health; and
     Management or restructuring changes (or both) cannot 
reasonably be made that will result in compliance with this subchapter, 
or if compliance cannot be achieved, improve the quality of the 
drinking water.
    In addition, SDWA Sec.  1416(b)(2)(C) also allows for a small 
system that does not serve a population of more than 3,300 and which 
needs financial assistance for the necessary improvements to receive up 
to three additional two-year exemptions, not to exceed a total of six 
years provided that the system establishes that it is taking all 
practicable steps to meet the requirements. In total, this means that 
some systems could potentially exceed the MCLs' numerical standards for 
up to 14 years after the rule promulgation date (or approximately 2037/
2038). EPA is seeking comment as to whether there are specific 
conditions that should be mandated for systems to be eligible for 
exemptions under 1416 to ensure that they are only used in rare 
circumstances where there are no other viable alternatives and what 
those conditions would be. EPA has established requirements for EPA 
issuance of these exemptions in 40 CFR 142 subpart F but could consider 
amending these requirements or establishing requirements for State 
exemptions.

XIII. Health Risk Reduction and Cost Analysis

    This section summarizes the HRRCA for the proposed NPDWR for PFAS, 
which is written in compliance with SDWA section 1412(b)(3)(C). Section 
1412(b)(3)(C)(i) lists the analytical elements required in a HRRCA 
applicable to a NPDWR that includes an MCL. The prescribed HRRCA 
elements include:
    (1) Quantifiable and nonquantifiable health risk reduction 
benefits;
    (2) quantifiable and nonquantifiable health risk reduction benefits 
from reductions in co-occurring contaminants;
    (3) quantifiable and nonquantifiable costs that are likely to occur 
solely as a result of compliance;
    (4) incremental costs and benefits of rule options;
    (5) effects of the contaminant on the general population and 
sensitive subpopulations including infants, children, pregnant women, 
the elderly, and individuals with a history of serious illness;
    (6) any increased health risks that may occur as a result of 
compliance, including risks associated with co-occurring contaminants; 
and
    (7) other relevant factors such as uncertainties in the analysis 
and factors with respect to the degree and nature of the risk.
    Based on this analysis and pursuant to Section 1412(b)(4)(C) of 
SDWA, the Administrator has determined that the quantified and 
nonquantifiable benefits of the proposed regulation justify the costs. 
The complete HRRCA for the proposed NPDWR, Economic Analysis for the 
Proposed PFAS Rule, is hereafter referred to as the ``Economic 
Analysis,'' and can be found in the docket at USEPA (2023j).
    For purposes of this Economic Analysis, EPA assumes that the NPDWR

[[Page 18690]]

will be promulgated by the end of 2023. This analysis follows the 
standard NPDWR compliance schedule with regulatory requirements taking 
effect three years after the date on which the regulation is 
promulgated. If EPA issues a final NPDWR for PFAS by the end of 2023, 
EPA assumes actions to comply with the rule, including installation of 
treatment technologies, will occur by 2026. Based on an assumed mean 
human lifespan of 80 years, EPA evaluates costs and benefits under the 
proposed rule through the year 2104. EPA selected this period of 
analysis to capture health effects from chronic illnesses that are 
typically experienced later in life (i.e., cardiovascular disease [CVD] 
and cancer). EPA annualized the future estimated streams of costs and 
benefits symmetrically over this same period of analysis. Capital costs 
for installation of treatment technologies are spread over the useful 
life of the technologies. EPA does not capture effects of compliance 
with the proposed rule after the end of the period of analysis. Costs 
and benefits discussed in this section are presented as annualized 
present values in 2021 dollars. EPA determined the present value of 
these costs using discount rates of 3 and 7 percent, which are discount 
rates prescribed by the (OMB Circular A-4, 2003).
    Estimates of PFAS occurrence used for cost-benefit modeling rely on 
a Bayesian hierarchical estimation model of national PFAS occurrence in 
drinking water (Cadwallader et al., 2022) discussed in Section VII.E. 
of this preamble above. The model was fitted using sample data from 
systems participating in PFAS sampling under UCMR 3 and included 
systems serving over 10,000 customers, as well as a subset of 800 
smaller systems. A best-fit model was selected using sample data to 
define occurrence and co-occurrence of PFOA, PFOS, PFHpA, and PFHxS in 
water systems stratified by system size and incorporating variations 
within and among systems. Sample data were derived from state-level 
datasets as well as from UCMR 3. For more information on EPA's 
occurrence model, please see Section VII.E. of this preamble and USEPA 
(2023e).
    In the Economic Analysis, EPA analyzes the costs and benefits of 
the proposed rule, as well as several regulatory alternatives. EPA 
analyzed the costs and benefits of setting individual MCLs for PFOA and 
PFOS at 4.0 ppt, 5.0 ppt, and 10.0 ppt, referred to as Option 1a, 
Option 1b, and Option1c, respectively. EPA assessed these options in 
the Economic Analysis to understand the impact of less stringent PFOA 
and PFOS MCLs, and the Agency is asking for comment on these 
assessments in the Economic Analysis. The Agency is also inviting 
comment on whether establishing a traditional MCLG and MCL for PFHxS, 
HFPO-DA, PFNA, and PFBS instead of or in addition to the HI approach 
would change public health protection, improve clarity of the rule, or 
change costs. EPA has not separately presented changes in quantified 
costs and benefits for these approaches. If EPA adds individual MCLs in 
addition to using the HI approach, EPA anticipates there will be no 
change in costs and benefits relative to the proposed rule (i.e., the 
same number of systems will incur identical costs to the proposed 
option and the same benefits will be realized). EPA has not separately 
quantified the benefits and costs for the alternative approach to 
regulate PFHxS, PFNA, PFBS, and HFPO-DA with individual MCLs instead of 
the HI. However, EPA expects both the costs and benefits would be 
reduced under this approach as fewer systems may be triggered into 
treatment and its associated costs. Additionally, systems that exceed 
one or more of the individual MCLs will treat to a less stringent and 
public health-protective standard. Furthermore, under the proposed 
option, PWSs are required to treat based on the combined occurrence of 
PFAS included in the HI which considers the known and additive toxic 
effects and occurrence and likely co-occurrence of PFAS compounds in 
the HI, providing more public health protection compared to an 
individual MCL approach.
    Section A summarizes the entities which would be affected by the 
rule and provides a list of key data sources used to develop EPA's 
baseline water system characterization. Section B provides an overview 
of the cost-benefit model used to estimate the national costs and 
benefits of the proposed rule. Section C summarizes the methods EPA 
used to estimate costs associated with the proposed rule. Section D 
summarizes the methods EPA used to estimate quantified benefits 
associated with the proposed rule. Section E provides a summary of the 
nonquantifiable benefits associated with reductions in exposure to both 
PFOA and PFOS. Section F provides a qualitative summary of benefits 
expected to result from the removal of PFAS included in the HI 
component of the proposed regulation and additional co-removed PFAS 
contaminants. Section G summarizes benefits expected to result from 
DBPs co-removal. Section H provides a comparison of cost and benefit 
estimates. Section I summarizes and discusses key uncertainties in the 
cost and benefit analyses. Quantified costs and benefits for the 
proposed option and alternative options considered are summarized in 
section H, specifically Tables 66-69. Tables 70-71 summarizes the non-
quantified B-Cs and assess the potential impact of non-quantifiable 
benefits and costs on the overall B-C estimate. Finally, Section J 
presents the Administrator's cost-benefit determination for the 
proposed rule.

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

    The entities potentially affected by the proposed PFAS regulation 
are primacy agencies and PWSs. PWSs subject to the proposed rule 
requirements are either CWSs or NTNCWSs. These water systems can be 
publicly or privately owned. PWSs subject to the rule would be required 
to meet the MCL and comply with monitoring and reporting requirements. 
Primacy agencies would be required to adopt and enforce the drinking 
water standard as well as the monitoring and reporting requirements.
    Both PWSs and primacy agencies are expected to incur costs, 
including administrative costs, monitoring and reporting costs, and--in 
a limited number of cases--anticipated costs to reduce PFAS levels in 
drinking water to meet this proposed NPDWR using treatment or 
nontreatment options. Section C of this preamble below summarizes the 
method EPA used to estimate these costs.
    The systems that reduce PFAS concentrations will reduce associated 
health risks. EPA developed methods to estimate the potential benefits 
of reduced PFAS exposure among the service populations of systems with 
PFAS levels exceeding the proposed drinking water standard. Section B 
of this preamble below summarizes this method used to estimate these 
benefits.
    In its Guidelines for Preparing Economic Analyses, EPA 
characterizes the ``baseline'' as a reference point that reflects the 
world without the proposed regulation (USEPA, 2010). It is the starting 
point for estimating the potential benefits and costs of the proposed 
PFAS NPDWR. EPA used a variety of data sources to develop the baseline 
drinking water system characterization for the regulatory analysis. 
Table 24 lists the major data sources and the baseline data derived 
from them. Additional detailed descriptions of these data sources and 
how they were used in the characterization of baseline conditions

[[Page 18691]]

can be found in the Chapter 4 of USEPA (2023j).

      Table 24--Data Sources Used To Develop Baseline Water System
                            Characterization
------------------------------------------------------------------------
         Data source             Baseline data derived from the source
------------------------------------------------------------------------
SDWIS/Federal version fourth    Water System Inventory: PWS
 quarter 2021 Q4 ``frozen''     inventory, including system unique
 dataset \1\.                   identifier, population served, number of
                                service connections, source water type,
                                and system type.
                                Population and Households
                                Served: PWS population served.
                                Treatment Plant
                                Characterization: Number of unique
                                treatment plant facilities per system,
                                which are used as a proxy for entry
                                points when UCMR 3 sampling site data
                                are not available.
UCMR 3 (USEPA, 2017).........   Treatment Plant
                                Characterization: Number of unique entry
                                point sampling sites, which are used as
                                a proxy for entry points.
                                Treatment Plant
                                Characterization: PFAS concentration
                                data collected as part of UCMR 3.
Independent state sampling      Treatment Plant
 programs.                      Characterization: PFAS concentration
                                data collected by states. These data
                                supplemented the occurrence modeling for
                                systems included in UCMR 3.
Six-Year Review 4 Information   Treatment Plant
 Collection Request (SYR4       Characterization: Total organic carbon
 ICR) Occurrence Dataset        (TOC).
 (2012-2019).
Geometries and                  Treatment Plant
 Characteristics of Public      Characterization: Design and average
 Water Systems (USEPA, 2000f).  daily flow per system.
2006 Community Water System     Public Water System Labor Rates:
 Survey (CWSS; USEPA, 2009c).   PWS labor rates.
------------------------------------------------------------------------
Notes:
\1\ Contains information extracted on January 14, 2022.

B. Overview of the Cost-Benefit Model

    EPA's existing SafeWater Cost Benefit Model (CBX) was designed to 
calculate the costs and benefits associated with setting a new or 
revised MCL. Since the proposed PFAS rule simultaneously regulates 
multiple PFAS contaminants, EPA developed a new model version called 
the SafeWater Multi-Contaminant Benefit Cost Model (MCBC) to 
efficiently handle more than one contaminant. SafeWater MCBC, allows 
for inputs that include differing mixtures of contaminants based on 
available occurrence data as well as multiple regulatory thresholds. 
The model structure allows for assignment of compliance technology or 
technologies that achieve all regulatory requirements and estimates 
costs and benefits associated with multiple PFAS contaminant 
reductions. SafeWater MCBC is designed to model co-occurrence, 
sampling, treatment, and administrative costs, and simultaneous 
contaminants reductions and resultant benefits. The modifications to 
the SafeWater model are consistent with the methodology that was 
developed in the single MCL SafeWater CBX Beta version that was peer 
reviewed. More detail on the modifications to the SafeWater model can 
be found in Section 5.2 of EPA's economic analysis.
    The costs incurred by a PWS depend on water system characteristics; 
SDWIS/Fed provides information on PWS characteristics that typically 
define PWS categories, or strata, for which EPA has develops cost 
estimates in rulemakings, including system type (CWS, NTNCWS), number 
of people served by the PWS, the PWS's primary raw water source (ground 
water or surface water), the PWS's ownership type (public or private), 
and PWS state.
    Because EPA does not have complete PWS-specific data across the 
approximately 49,000 CWSs and 17,000 NTNCWSs in SDWIS/Fed for many of 
the baseline and compliance characteristics necessary to estimate costs 
and benefits, such as design and average daily flow rates, water 
quality characteristics, treatment in-place, and labor rates, EPA 
adopted a ``model PWS'' approach. SafeWater MCBC creates model PWSs by 
combining the PWS-specific data available in SDWIS/Fed with data on 
baseline and compliance characteristics available at the PWS category 
level. In some cases, the categorical data are simple point estimates. 
In this case, every model PWS in a category is assigned the same value. 
In other cases, where more robust data representing system variability 
are available, the category-level data include a distribution of 
potential values. In the case of distributional information, SafeWater 
MCBC assigns each model PWS a value sampled from the distribution. 
These distributions are assumed to be independent.
    For a list of PWS characteristics that impact model PWS compliance 
costs, please see Chapter 5 of USEPA (2023j). These data include 
inventory data specific to each system and categorical data for which 
randomly assigned values are based on distributions that vary by 
category (e.g., ground water and surface water TOC distributions or 
compliance forecast distributions that vary by system size category).
    Once model PWSs are created and assigned baseline and compliance 
characteristics, SafeWater MCBC estimates the quantified costs and 
benefits of compliance for each model PWS under the proposed rule. 
Because of this model PWS approach, SafeWater MCBC does not output any 
results at the PWS level. Instead, the outputs are cost and benefit 
estimates for 36 PWS categories, or strata. Each PWS category is 
defined by system type (CWS and NTNCWS), primary water source (ground 
or surface), and size category. Note EPA does not report state specific 
strata although state location is utilized in the SafeWater MCBC model 
(e.g., current state level regulatory limits on PFAS in drinking 
water). The detailed output across these strata can be found in the 
Chapter 5 of USEPA (2023j).
    For each PWS category, the model then calculates summary statistics 
that describe the costs and benefits associated with the proposed rule 
compliance. These summary statistics include total quantified costs of 
the proposed regulatory requirement, total quantified benefits of the 
proposed regulatory requirement, the variability in PWS-level costs 
(e.g., 5th and 95th percentile system costs), and the variability in 
household-level costs.

C. Method for Estimating Costs

    This section summarizes the cost elements and estimates total cost 
of compliance for the proposed PFAS NPDWR discounted at 3 and 7 
percent. EPA estimated the costs associated with

[[Page 18692]]

monitoring, administrative requirements, and both treatment and non-
treatment compliance actions associated with the proposed rule (USEPA, 
2023j).
1. Public Water System (PWS) Costs
a. PWS Treatment and Non-Treatment Compliance Costs
    EPA estimated costs associated with engineering, installing, 
operating, and maintaining PFAS removal treatment technologies, 
including treatment media replacement and spent media destruction or 
disposal, as well as non-treatment actions that some PWSs may take in 
lieu of treatment, such as constructing new wells in an uncontaminated 
aquifer or interconnecting with and purchasing water from a neighboring 
PWS. EPA used SafeWater MCBC to apply costs for one of the treatment 
technologies or non-treatment alternatives at each entry point in a PWS 
estimated to be out of compliance with the proposed rule. For each 
affected entry point, SafeWater MCBC selected from among the compliance 
alternatives using a decision tree procedure, described in more detail 
in USEPA (2023g) and (2023h). Next, the model estimated the cost of the 
chosen compliance alternative using outputs from EPA's WBS cost 
estimating models.
    Specifically, EPA used cost equations generated from the following 
models (USEPA, 2023h):
     the GAC WBS model (USEPA, 2021g);
     the PFAS-selective IX WBS model (USEPA, 2021h);
     the centralized RO/NF WBS model (USEPA, 2021i); and
     the non-treatment WBS model (USEPA, 2021j).
    The Technologies and Costs (T&C) document (USEPA, 2023h) provides a 
comprehensive discussion of each of the treatment technologies, their 
effectiveness, and the WBS cost models as well as the equations used to 
calculate treatment costs. In total, there are nearly 3,500 individual 
cost equations across the categories of capital and operation and 
maintenance (O&M) cost, water source, component level, flow, bed life 
(for GAC and IX), residuals management scenarios (for GAC and IX), and 
design type (for GAC).
b. Decision Tree for Technology Selection
    For entry points at which baseline PFAS concentrations exceed 
regulatory thresholds, the decision tree selects a treatment technology 
or non-treatment alternative using a two-step process that both:
     Determines whether to include or exclude each alternative 
from consideration given the entry point's characteristics and the 
regulatory option selected, and
     Selects from among the alternatives that remain viable 
based on percentage distributions derived, in part, from data on recent 
PWS actions in response to PFAS contamination.
    Inputs to the decision tree include the following:
     Influent concentrations of individual PFAS contaminants in 
ppt;
     Entry point design flow in MGD;
     TOC influent to the new treatment process in mg/L.
    EPA relied on information from the national PFAS occurrence model 
to inform influent PFAS concentrations. EPA relied on Geometries and 
Characteristics of Public Water Supplies (USEPA, 2000f) and SDWIS 
inventory information to derive entry point design flow. SafeWater MCBC 
selects influent TOC using the distribution shown below in Table 25.

        Table 25--Frequency Distribution To Estimate Influent TOC
                                [In mg/L]
------------------------------------------------------------------------
            Percentile                Surface water       Ground water
------------------------------------------------------------------------
0.05..............................               0.65               0.35
0.15..............................                1.1               0.48
0.25..............................               1.38                0.5
0.35..............................                1.6                0.5
0.45..............................               1.85               0.58
0.5...............................               1.97               0.69
0.55..............................               2.14               0.75
0.65..............................               2.54                  1
0.75..............................               3.04               1.39
0.85..............................               3.63               2.01
0.95..............................               4.81                3.8
------------------------------------------------------------------------
Source: EPA's analysis of TOC concentrations in the SYR4 ICR database.

    Step 1 of the decision tree uses these inputs to determine whether 
to include or exclude each treatment alternative from consideration in 
the compliance forecast. For the treatment technologies (GAC, IX, and 
RO/NF), this determination is based on estimates of each technology's 
performance given available data about influent water quality and the 
regulatory option under consideration.
    EPA assumes a small number of PWSs may be able to take non-
treatment actions in lieu of treatment. The viability of non-treatment 
actions is likely to depend on the quantity of water being replaced. 
Therefore, the decision tree considers non-treatment only for entry 
points with design flows less than or equal to 3.536 MGD. EPA's WBS 
model for non-treatment does not generate costs for flows greater than 
this value, so the decision tree excludes non-treatment actions from 
consideration above this flow. EPA estimates approximately 2% of 
systems of this size will develop new wells and approximately 6-7% of 
systems will elect to interconnect with another system to achieve 
compliance.
    Step 2 of the decision tree selects a compliance alternative for 
each entry point from among the alternatives that remain in 
consideration after Step 1. Table 26 shows the initial compliance 
forecast that is the starting point for this step. The percentages in 
Table 26 consider data presented in the T&C document (USEPA, 2023h) on 
actions PWSs have taken in response to PFAS contamination.
    To date, the majority of PWSs for which data are available have 
installed GAC (USEPA, 2023h). The data in USEPA (2023h) suggest that an 
increasing share of PWSs have selected IX in response to PFAS since the 
first full-scale system treated with PFAS-selective IX in 2017. EPA 
expects this trend to continue, so the initial percentages include 
adjustments to

[[Page 18693]]

account for this expectation. In addition, the performance of GAC is 
affected by the presence of TOC, as further described in the cost 
chapter of the Economic Analysis (USEPA, 2023j). Accordingly, the table 
includes adjusted distributions for systems with higher influent TOC.
    The list of compliance alternatives in Table 26 does not include 
POU RO for small systems. At this time, EPA is not including POU RO in 
the national cost estimates because the regulatory options under 
consideration require treatment to concentrations below 70 ppt PFOA and 
PFOS summed, the current certification standard for POU devices. 
Therefore, the decision tree excludes POU RO from consideration and 
proportionally redistributes the percentages among the other 
alternatives.

                                                          Table 26--Initial Compliance Forecast
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Design flow less than  1 MGD   Design flow 1 to less than  10   Design flow greater than  or
                                                         --------------------------------               MGD                       equal to 10 MGD
                                                                                         ---------------------------------------------------------------
                 Compliance alternative                   TOC  less than   TOC  greater   TOC  less than   TOC  greater   TOC  less than   TOC  greater
                                                           or  equal to   than  1.5 mg/L   or  equal to   than  1.5 mg/L   or  equal to   than  1.5 mg/L
                                                           1.5 mg/L  (%)        (%)        1.5 mg/L  (%)        (%)        1.5 mg/L  (%)        (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
GAC.....................................................              75              57              77              50              85              50
PFAS-selective IX.......................................              11              29              10              37              10              45
Central RO/NF...........................................               5               5               5               5               5               5
Interconnection.........................................               7               7               6               6               0               0
New Wells...............................................               2               2               2               2               0               0
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: EPA's analysis of TOC concentrations in the SYR4 ICR database.
Note: EPA is not including POU RO in the national cost estimates for the proposed rule because the regulatory options under consideration require
  treatment to concentrations below 70 ppt PFOA and PFOS summed, the current certification standard for POU devices. Therefore, the decision tree
  excludes POU RO from consideration and proportionally redistributes the percentages among the other alternatives.

    If all the compliance alternatives remain in consideration after 
Step 1, the decision tree uses the forecast shown in Table 26 above. If 
Step 1 eliminated on one or more of the alternatives, the decision tree 
proportionally redistributes the percentages among the remaining 
alternatives and uses the redistributed percentages.
    EPA's approach to estimating GAC and IX performance under the 
proposed option and all alternatives considered is discussed in detail 
within the cost chapter of the Economic Analysis (USEPA, 2023j).
c. Work Breakdown Structure Models
    The WBS models are spreadsheet-based engineering models for 
individual treatment technologies, linked to a central database of 
component unit costs. EPA developed the WBS model approach as part of 
an effort to address recommendations made by the Technology Design 
Panel (TDP), which convened in 1997 to review the Agency's methods for 
estimating drinking water compliance costs (USEPA, 1997). The TDP 
consisted of nationally recognized drinking water experts from EPA, 
water treatment consulting companies, public as well as private water 
utilities along with suppliers, equipment vendors, and Federal along 
with State regulators in addition to cost estimating professionals.
    In general, the WBS approach involves breaking a process down into 
discrete components for the purpose of estimating unit costs. The WBS 
models represent improvements over past cost estimating methods by 
increasing comprehensiveness, flexibility, and transparency. By 
adopting a WBS-based approach to identify the components that should be 
included in a cost analysis, the models produce a more comprehensive 
assessment of the capital and operating requirements for a treatment 
system.
    Each WBS model contains the work breakdown for a particular 
treatment process and preprogrammed engineering criteria and equations 
that estimate equipment requirements for user-specified design 
requirements (e.g., system size and influent water quality). Each model 
also provides unit and total cost information by component (e.g., 
individual items of capital equipment) and totals the individual 
component costs to obtain a direct capital cost. Additionally, the 
models estimate add-on costs (e.g., permits and land acquisition), 
indirect capital costs, and annual O&M costs, thereby producing a 
complete compliance cost estimate.
    Primary inputs common to all the WBS models include design flow and 
average daily flow in MGD. Each WBS model has default designs (input 
sets) that correspond to specified categories of flow, but the models 
can generate designs for many other combinations of flows. To estimate 
costs for PFAS compliance, EPA fit cost curves to the WBS estimates 
across a range of flow rates, which is described in Chapter 5 of the 
Economic Analysis (USEPA, 2023j).
    Another input common to all the WBS models is ``component level'' 
or ``cost level.'' This input drives the selection of materials for 
items of equipment that can be constructed of different materials. For 
example, a low-cost system might include fiberglass pressure vessels 
and polyvinyl chloride (PVC) piping. A high-cost system might include 
stainless steel pressure vessels and stainless-steel piping. The 
component level input also drives other model assumptions that can 
affect the total cost of the system, such as building quality and 
heating and cooling. The component level input has three possible 
values: low cost, mid cost, and high cost. The components used in each 
of the estimated component/cost levels provide the treatment efficacy 
needed to meet the regulatory requirements. Note that the level of 
component (e.g., plastic versus resin or stainless-steel piping and 
vessels) may impact the capital replacement rate but does not interfere 
with treatment efficacy. EPA estimates the three levels of cost because 
it has found that the choice of materials associated with the 
installation of new treatment equipment often varies across drinking 
water systems. These systems may, for example, choose to balance 
capital cost with staff familiarity with certain materials and existing 
treatment infrastructure. Given this experience, EPA models the 
potential variability in treatment cost based on the three component/
cost levels. To estimate costs for PFAS treatment, EPA generated 
separate cost equations for each of the

[[Page 18694]]

three component levels, thus creating a range of cost estimates for use 
in national compliance cost estimates. EPA requests comment on the 
range of component levels assumed and the range of estimated PFAS 
treatment costs.
    The third input common to all the WBS models is system automation, 
which allows the design of treatment systems that are operated manually 
or with varying degrees of automation (i.e., with control systems that 
reduce the need for operator intervention). Cost equations for system 
automation are described in Chapter 5 of the Economic Analysis (USEPA, 
2023j).
    The WBS models generate cost estimates that include a consistent 
set of capital, add-on, indirect, and O&M costs. Table 27 below 
identified these cost elements, which are common to all the WBS models 
and included in the cost estimates below. As described below and 
summarized in Tables 28-31 the WBS models also include technology-
specific cost elements. The documentation for the WBS models provide 
more information on the methods and assumptions in the WBS models to 
estimate the costs for both the technology-specific and common cost 
elements (USEPA, 2021g; USEPA, 2021h; USEPA, 2021i; and USEPA, 2021j). 
WBS model accuracy is described in Chapter 5 of the Economic Analysis 
(USEPA, 2023j).

           Table 27--Cost Elements Included in All WBS Models
------------------------------------------------------------------------
         Cost category                     Components included
------------------------------------------------------------------------
Direct Capital Costs..........   Technology-specific equipment
                                 (e.g., vessels, basins, pumps,
                                 treatment media, piping, valves).
                                 Instrumentation and system
                                 controls.
                                 Buildings.
                                 Residuals management equipment.
Add-on Costs..................   Land.
                                 Permits.
                                 Pilot testing.
Indirect Capital Costs........   Mobilization and
                                 demobilization.
                                 Architectural fees for
                                 treatment building.
                                 Equipment delivery,
                                 installation, and contractor's overhead
                                 and profit.
                                 Sitework.
                                 Yard piping.
                                 Geotechnical.
                                 Standby power.
                                 Electrical infrastructure.
                                 Process engineering.
                                 Contingency.
                                 Miscellaneous allowance.
                                 Legal, fiscal, and
                                 administrative.
                                 Sales tax.
                                 Financing during construction.
                                 Construction management.
O&M Costs: Technology-specific   Operator labor for technology-
                                 specific tasks (e.g., managing backwash
                                 and media replacement).
                                 Materials for O&M of technology-
                                 specific equipment.
                                 Technology-specific chemical
                                 usage.
                                 Replacement of technology-
                                 specific equipment that occurs on an
                                 annual basis (e.g., treatment media).
                                 Energy for operation of
                                 technology-specific equipment (e.g.,
                                 mixers).
O&M Costs: Labor..............   Operator labor for O&M of
                                 process equipment.
                                 Operator labor for building
                                 maintenance.
                                 Managerial and clerical labor.
O&M Costs: Materials..........   Materials for maintenance of
                                 booster or influent pumps.
                                 Materials for building
                                 maintenance.
O&M Costs: Energy.............   Energy for operation of booster
                                 or influent pumps.
                                 Energy for lighting,
                                 ventilation, cooling, and heating.
O&M Costs: Residuals..........   Residuals management operator
                                 labor, materials, and energy.
                                 Residuals disposal and
                                 discharge costs.
------------------------------------------------------------------------

    The GAC model can generate costs for two types of design:
     Pressure designs where the GAC bed is contained in 
stainless steel, carbon steel, or fiberglass pressure vessel;
     Gravity designs where the GAC bed is contained in open 
concrete basins.
    Table 28 shows the technology-specific capital equipment and O&M 
requirements included in the GAC model. These items are in addition to 
the common WBS cost elements listed in the Cost Elements Included in 
All WBS Models table above.

  Table 28--Technology-Specific Cost Elements Included in the GAC Model
------------------------------------------------------------------------
         Cost category                  Major components included
------------------------------------------------------------------------
Direct Capital Costs..........   Booster pumps for influent
                                 water.
                                 Contactors (either pressure
                                 vessels or concrete basins) that
                                 contain the GAC bed.
                                 Tanks and pumps for backwashing
                                 the contactors.
                                 GAC transfer and storage
                                 equipment.
                                 Spent GAC reactivation
                                 facilities (if on-site reactivation is
                                 selected).
                                 Associated piping, valves, and
                                 instrumentation.

[[Page 18695]]

 
O&M Costs: Labor..............   Operator labor for contactor
                                 maintenance (for gravity GAC designs).
                                 Operator labor for managing
                                 backwash events.
                                 Operator labor for backwash
                                 pump maintenance (if backwash occurs
                                 weekly or more frequently).
                                 Operator labor for GAC transfer
                                 and replacement.
O&M Costs: Materials..........   Materials for contactor
                                 maintenance (accounts for vessel
                                 relining in pressure designs, because
                                 GAC can be corrosive, and for concrete
                                 and underdrain maintenance in gravity
                                 designs).
                                 Materials for backwash pump
                                 maintenance (if backwash occurs weekly
                                 or more frequently).
                                 Replacement virgin GAC (loss
                                 replacement only if reactivation is
                                 selected).
O&M Costs: Energy.............   Operating energy for backwash
                                 pumps.
O&M Costs: Residuals..........   Discharge fees for spent
                                 backwash.
                                 Fees for reactivating spent GAC
                                 (if off-site reactivation is selected).
                                 Labor, materials, energy, and
                                 natural gas for regeneration facility
                                 (if on-site reactivation is selected).
                                 Disposal of spent GAC (if
                                 disposal is selected).
------------------------------------------------------------------------

    For small systems (less than 1 MGD) using pressure designs, the GAC 
model assumes the use of package treatment systems that are pre-
assembled in a factory, mounted on a skid, and transported to the site. 
The model estimates costs for package systems by costing all individual 
equipment line items (e.g., vessels, interconnecting piping and valves, 
instrumentation, and system controls) in the same manner as custom-
engineered systems. This approach is based on vendor practices of 
partially engineering these types of package plants for specific 
systems (e.g., selecting vessel size to meet flow and treatment 
criteria). The model applies a variant set of design inputs and 
assumptions that are intended to simulate the use of a package plant 
and that reduce the size and cost of the treatment system. USEPA 
(2021g) provides complete details on the variant design assumptions 
used for package plants.
    To generate the GAC cost equations, EPA used the following key 
inputs in the GAC model:
     For pressure designs, two vessels in series with a minimum 
total empty bed contact time (EBCT) of 20 minutes;
     For gravity designs, contactors in parallel with a minimum 
total EBCT of 20 minutes; and
     Bed life varying over a range from 5,000 to 150,000 BV.
    EPA generated separate cost equations for two spent GAC management 
scenarios:
     Off-site reactivation under current RCRA non-hazardous 
waste regulations
     Off-site disposal as a hazardous waste and replacement 
with virgin GAC (i.e., single use operation).
    The T&C document (USEPA, 2023h) provides a comprehensive discussion 
of these and other key inputs and assumptions.
    Table 29 shows the technology-specific capital equipment and O&M 
requirements included in the PFAS selective IX model. These items are 
in addition to the common WBS cost elements listed in the Cost Elements 
Included in All WBS Models table above.

    Table 29--Technology-Specific Cost Elements Included in the PFAS-
                           Selective IX Model
------------------------------------------------------------------------
         Cost category                  Major components included
------------------------------------------------------------------------
Direct Capital Costs..........   Booster pumps for influent
                                 water.
                                 Pre-treatment cartridge
                                 filters.
                                 Pressure vessels that contain
                                 the resin bed.
                                 Tanks and pumps for initial
                                 rinse and (optionally) backwash of the
                                 resin bed.
                                 Tanks (with secondary
                                 containment), pumps and mixers for
                                 delivering sodium hydroxide for use in
                                 post-treatment corrosion control
                                 (optional).
                                 Associated piping, valves, and
                                 instrumentation.
O&M Costs: Labor..............   Operator labor for pre-
                                 treatment filters.
                                 Operator labor for managing
                                 backwash/rinse events.
                                 Operator labor for backwash
                                 pump maintenance (only if backwash
                                 occurs weekly or more frequently).
                                 Operator labor for resin
                                 replacement.
O&M Costs: Materials..........   Replacement cartridges for pre-
                                 treatment filters.
                                 Materials for backwash pump
                                 maintenance (only if backwash occurs
                                 weekly or more frequently).
                                 Chemical usage (if post-
                                 treatment corrosion control is
                                 selected).
                                 Replacement virgin PFAS-
                                 selective resin.
O&M Costs: Energy.............   Operating energy for backwash/
                                 rinse pumps.
O&M Costs: Residuals..........   Disposal of spent cartridge
                                 filters.
                                 Discharge fees for spent
                                 backwash/rinse.
                                 Disposal of spent resin.
------------------------------------------------------------------------

    For small systems (less than 1 MGD), the PFAS-selective IX model 
assumes the use of package treatment systems that are pre-assembled in 
a factory, mounted on a skid, and transported to the site. The IX model 
estimates costs for package systems using an approach similar to that 
described for the GAC model, applying a variant set of inputs and 
assumptions that reduce the size and cost of the treatment system. 
USEPA (2021j) provides complete details on the variant design 
assumptions used for IX package plants.
    To generate the IX cost equations, EPA used the following key 
inputs in the PFAS-selective IX model:
     Two vessels in series with a minimum total EBCT of 6 
minutes.
     Bed life varying over a range from 20,000 to 440,000 BV.

[[Page 18696]]

    EPA generated separate cost equations for two spent resin 
management scenarios:
     Spent resin managed as non-hazardous and sent off-site for 
incineration.
     Spent resin managed as hazardous and sent off-site for 
incineration.
    The T&C document (USEPA, 2023h) provides a comprehensive discussion 
of these and other key inputs and assumptions.
    Table 30 shows the technology-specific capital equipment and O&M 
requirements included in the model for RO/NF (USEPA, 2021i). These 
items are in addition to the common WBS cost elements listed in listed 
in the Cost Elements Included in All WBS Models table above.

 Table 30--Technology-Specific Cost Elements Included in the RO/NF Model
------------------------------------------------------------------------
         Cost category                  Major components included
------------------------------------------------------------------------
Direct Capital Costs..........   High-pressure pumps for
                                 influent water and (optionally)
                                 interstage pressure boost.
                                 Pre-treatment cartridge
                                 filters.
                                 Tanks, pumps, and mixers for
                                 pretreatment chemicals.
                                 Pressure vessels, membrane
                                 elements, piping, connectors, and steel
                                 structure for the membrane racks.
                                 Valves for concentrate control
                                 and (optionally) per-stage throttle.
                                 Tanks, pumps, screens,
                                 cartridge filters, and heaters for
                                 membrane cleaning.
                                 Equipment, including dedicated
                                 concentrate discharge piping, for
                                 managing RO/NF concentrate and spent
                                 cleaning chemicals.
                                 Associated pipes, valves, and
                                 instrumentation.
O&M Costs: Labor..............   Operator labor for pre-
                                 treatment filters.
                                 Operator labor for routine O&M
                                 of membrane units.
                                 Operator labor to maintain
                                 membrane cleaning equipment.
O&M Costs: Materials..........   Replacement cartridges for pre-
                                 treatment filters.
                                 Chemical usage for
                                 pretreatment.
                                 Maintenance materials for pre-
                                 treatment, membrane process, and
                                 cleaning equipment.
                                 Replacement membrane elements.
                                 Chemical usage for cleaning.
O&M Costs: Energy.............   Energy for high-pressure
                                 pumping.
O&M Costs: Residuals..........   Disposal costs for spent
                                 cartridge filters and membrane
                                 elements.
------------------------------------------------------------------------

    The RO/NF model includes three default ground waters and three 
default surface waters, ranging from high to low quality (i.e., from 
low to high total dissolved solids and scaling potential). To generate 
the cost equations, EPA used the model's default high-quality influent 
water parameters to reflect the incremental cost of removing PFAS from 
otherwise potable water. EPA used the following additional key inputs 
and assumptions:
     For systems larger than approximately 0.5 MGD, target 
recovery rates of 80 percent for ground water and 85 percent for 
surface water.
     Target recovery rates of 70 to 75 percent for smaller 
systems.
     Flux rates of 19 gallons per square foot per day (gfd) for 
ground water and 15 to 16 gfd for surface water.
     Direct discharge of RO/NF concentrate to a permitted 
outfall on a non-potable water body (e.g., ocean or brackish estuary) 
via 10,000 feet of buried dedicated piping.
    The T&C document (USEPA, 2023h) provides a comprehensive discussion 
of these and other key inputs and assumptions.
    USEPA (2021j) provides a complete description of the engineering 
design process used by the WBS model for nontreatment actions. The 
model can estimate costs for two nontreatment alternatives: 
interconnection with another system and drilling new wells to replace a 
contaminated source. Table 31 below shows the technology-specific 
capital equipment and O&M requirements included in the model for each 
alternative.

    Table 31--Technology-Specific Cost Elements Included in the Non-
                             Treatment Model
------------------------------------------------------------------------
                                    Major components    Major components
          Cost category               included for      included for new
                                     interconnection         wells
------------------------------------------------------------------------
Direct Capital Costs.............   Booster     Well
                                    pumps or pressure   casing, screens,
                                    reducing valves     and plugs.
                                    (depending on       Well
                                    pressure at         installation
                                    supply source).     costs including
                                    Concrete    drilling,
                                    vaults (buried)     development,
                                    for booster pumps   gravel pack, and
                                    or pressure         surface seals.
                                    reducing valves.    Well
                                                pumps.
                                    Interconnecting     Piping
                                    piping (buried)     (buried) and
                                    and valves.         valves to
                                                        connect the new
                                                        well to the
                                                        system.
O&M Costs: Labor.................   Operator    Operator
                                    labor for O&M of    labor for
                                    booster pumps or    operating and
                                    pressure reducing   maintaining well
                                    valves (depending   pumps and
                                    on pressure at      valves.
                                    supply source)
                                    and
                                    interconnecting
                                    valves.
O&M Costs: Materials.............   Cost of    
                                    purchased water.    Materials for
                                    Materials   maintaining well
                                    for maintaining     pumps.
                                    booster pumps (if
                                    required by
                                    pressure at
                                    supply source).
O&M Costs: Energy................   Energy      Energy
                                    for operating       for operating
                                    booster pumps (if   well pumps.
                                    required by
                                    pressure at
                                    supply source).
------------------------------------------------------------------------

    To generate the cost equations, EPA used the following key inputs 
in the non-treatment model for interconnection:
     An interconnection distance of 10,000 feet;

[[Page 18697]]

     Minimal differences in pressure between the supplier and 
the purchasing system, so that neither booster pumps nor pressure 
reducing valves are needed;
     An average cost of purchased water of $3.00 per thousand 
gallons in 2020 dollars.
    For new wells, EPA used the following key inputs:
     A maximum well capacity of 500 gallons per minute (gpm), 
such that one new well is installed per 500 gpm of water production 
capacity required;
     A well depth of 250 feet;
     500 feet of distance between the new wells and the 
distribution system.
    The T&C document (USEPA, 2023h) provides a comprehensive discussion 
of these and other key inputs and assumptions.
d. Incremental Treatment Costs
    EPA has estimated the national level costs of the proposed rule 
associated with PFOA, PFOS, and PFHxS. Given the available occurrence 
data for the other compounds in the proposed rule (PFNA, HFPO-DA, and 
PFBS) and the regulatory thresholds under consideration, EPA did not 
model national costs associated with potential HI exceedances as a 
direct result of these compounds. To assess the potential impact of 
these compounds, EPA conducted an analysis of the additional, or 
incremental, system level impact that occurrence of these compounds 
would have on treatment costs. To do so, EPA used a model system 
approach. For further detail on the assumptions and findings of EPA's 
analysis of incremental costs, please see Chapter 5 in USEPA (2023j) 
and Appendix N in USEPA (2023i).
e. PWS Implementation Administration Costs
    EPA estimated PWS costs associated with one-time actions to begin 
implementation of the rule including reading and understanding the rule 
and attending training provided by primacy agencies. EPA assumes that 
systems will conduct these activities during years one through three of 
the period of analysis. Table 32 lists the data elements and 
corresponding values associated with calculating the costs of these 
one-time implementation administration actions.

          Table 32--Implementation Administration Startup Costs
                                 [2021$]
------------------------------------------------------------------------
          Data element description                Data element value
------------------------------------------------------------------------
The labor rate per hour for systems........  $35.48 (systems <=3,300).
                                             $37.84 (systems 3,301-
                                              10,000).
                                             $39.94 (systems 10,001-
                                              50,000).
                                             $41.70 (systems 50,001-
                                              100,000).
                                             $48.74 (systems >100,000).
The average hours per system to read and     4 hours per system.
 adopt the rule.
The average hours per system to attend one-  16 hours per system
 time training provided by primacy agencies.  (systems <=3,300).
                                             32 hours per system
                                              (systems >3,300).
------------------------------------------------------------------------

    Estimated national annualized PWS implementation and administration 
startup costs for the proposed option are $1.71 million (3% discount 
rate) and $3.52 million (7% discount rate). National annualized PWS 
cost estimates are further summarized in Table 37.
f. PWS Monitoring Costs
    EPA assumes that the proposed rule will require initial and long-
term monitoring. As Table 33 shows, surface and ground water systems 
serving 10,000 or more people will collect one sample each quarter, at 
each entry point, during the initial 12-month monitoring period. 
Surface water systems serving 10,000 or fewer people are also required 
to collect a quarterly sample at each entry point during the initial 
12-month period. Ground water systems that serve 10,000 or fewer people 
will be required to sample once at each entry point on a semi-annual 
basis for the first 12-month monitoring period.
    Long-term monitoring requirements differ based on two factors: (1) 
system size, and (2) whether a system can demonstrate during the 
initial monitoring period that they are ``reliably and consistently'' 
below the proposed MCLs for PFAS. EPA has set the PWS size threshold at 
systems serving 3,300 or fewer people. The threshold for systems to 
demonstrate that they are ``reliably and consistently'' below the 
proposed MCLs is set at a trigger level of one-third the MCLs for PFOA 
or PFOS (1.3 ppt) or the HI (0.33). For systems below the trigger level 
values during the initial 12-month monitoring period and in future 
long-term monitoring periods may conduct triennial monitoring. Systems 
serving 3,300 or fewer people will collect one triennial sample per 
entry point. Systems providing water for more than 3,300 people will 
take one sample in two consecutive quarters at each entry point, 
totaling two samples in each triennial period. For systems with 
concentration values at or above the trigger level regardless of system 
size, a quarterly sample must be taken at each entry point.
    For any samples that have a detection, the system will analyze the 
field reagent blank samples collected at the same time as the 
monitoring sample. Systems that have an MCL exceedance will collect one 
additional sample from the relevant entry point to confirm the results.

                   Table 33--Initial and Long-Term Sampling Frequencies per System Entry Point
----------------------------------------------------------------------------------------------------------------
                                                                Long-Term
                                              Long-term      monitoring: \a\     Long-term monitoring: \1\ PFAS
 Initial  monitoring    Initial 12-month     monitoring      PFAS detection      detection >=1.3 ppt  (PFOA or
system size  category  monitoring  period    system size    <1.3 ppt (PFOA or          PFOS) or HI >=0.33
                                              category      PFOS) or HI <0.33
----------------------------------------------------------------------------------------------------------------
<=10,000.............  Surface Water: 1           <=3,300  1 triennial sample  1 sample every quarter.
                        sample every
                        quarter.
                       Ground Water: 1
                        sample every 6-
                        month period.

[[Page 18698]]

 
>10,000..............  Surface Water and           >3,300  2 triennial         1 sample every quarter.
                        Ground Water: 1                     samples (1 sample
                        sample every                        in two
                        quarter.                            consecutive
                                                            quarters).
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ EPA used the following thresholds to distinguish whether PFAS concentrations are reliably and consistently
  below the MCL: PFOA and PFOS--one-third the MCL for each option; PFHxS--one-third the health benchmark of 9
  ppt or 3 ppt.

    For the national cost analysis, EPA assumes that systems with 
either UCMR 5 data or monitoring data in the State PFAS Database (see 
Section 3.1.4 in USEPA, 2023j) will not need to conduct the initial 
year of monitoring. As a simplifying assumption for the cost analysis, 
EPA assumes all systems serving a population of greater than 3,300 have 
UCMR 5 data and those with 3,300 or less do not. For the State PFAS 
Database, EPA relied on the PWSIDs stored in the database and exempted 
those systems from the first year of monitoring in the cost analysis. 
Note these simplifying assumptions may result in a small underestimate 
of initial monitoring costs. Under UCMR 5, individual water systems 
would be able to request the full release of data from the labs for use 
in determining their compliance monitoring frequency. PWSs may be able 
to use these lab analyses to demonstrate a ``below trigger level'' 
concentration using the UCMR 5 analyses by following up with the lab 
for a more detailed results report. EPA requests comment on these 
underlying assumptions.
    EPA used system-level distributions, as described in Cadwallader et 
al. (2022), to simulate entry point concentrations and estimate PFAS 
occurrence relative to the proposed option MCLs and trigger levels. 
Based on these occurrence distributions, EPA estimates that the large 
majority of water systems subject to the proposed rule (approx. 52,000) 
will have EPs with concentrations below the proposed trigger level and 
would conduct reduced monitoring on a triennial basis. EPA estimates 
that the remainder of water systems subject to the proposed rule 
(approx. 14,000) will have at least one or more EPs exceed the proposed 
trigger level and therefore would be required to conduct quarterly 
monitoring. EPA requests comment on these estimates and the underlying 
assumptions.
    EPA assumes that systems with an MCL exceedance will implement 
actions to comply with the MCL by the compliance date. EPA assumes a 
treatment target, for systems required to treat for PFAS, that includes 
a margin of safety so finished water PFAS levels at these systems are 
80 percent of the MCL or HI. This target is insufficient to meet the 
triennial monitoring threshold. Therefore, systems implementing 
treatment will continue with quarterly monitoring. All other systems 
that do not have PFAS concentrations at or below the trigger level 
threshold will also continue quarterly monitoring.
    For all systems, the activities associated with the sample 
collection in the initial 12-month monitoring period are the labor 
burden and cost for the sample collection and analysis, as well as a 
review of the sample results. Table 34 presents the data elements and 
corresponding values associated with calculating sampling costs during 
the implementation monitoring period.

                        Table 34--Sampling Costs
                                 [2021$]
------------------------------------------------------------------------
          Data element description                Data element value
------------------------------------------------------------------------
The labor rate per hour for systems........  $35.48 (systems <=3,300).
                                             $37.84 (systems 3,301-
                                              10,000).
                                             $39.94 (systems 10,001-
                                              50,000).
                                             $41.70 (systems 50,001-
                                              100,000).
                                             $48.74 (systems >100,000).
The number of samples per entry point per    2 samples (Ground Water
 monitoring round for the initial             systems <=10,000).
 monitoring in Year 1.                       4 samples (all systems)
                                              \1\.
The number of samples per entry point per    4 samples (all other
 long-term monitoring year for entry points   systems).
 that exceed the triennial monitoring
 threshold.
The number of samples per entry point per    1 sample (systems <=3,300).
 long-term monitoring round for entry        2 samples (systems >3,300).
 points that meet the triennial threshold.
The hours per sample to travel to sampling   1 hour.
 locations, collect samples, record any
 additional information, submit samples to
 a laboratory, and review results.
The laboratory analysis cost per sample for  $376.
 EPA Method 533.
The laboratory analysis cost per sample for  $302.
 EPA Method 537.1.
The laboratory analysis cost per sample for  $327.\2\
 field reagent blank under EPA Method 533.
The laboratory analysis cost per sample for  $266.\ 2\
 the field reagent blank under EPA Method
 537.1.
------------------------------------------------------------------------
Notes:
\1\ Systems greater than 3,300 will rely on UCMR 5 data and a subset of
  other systems will rely on data in the State PFAS Monitoring Database
  discussed in USEPA, 2023j.
\2\ This incremental sample cost applies to all samples that exceed
  MDLs. EPA used the Method 537.1 detection limits to apply this cost
  because Method 533 does not include detection limits.

    Estimated national annualized PWS sampling costs for the proposed 
option are $90.32 million (3 discount rate) and $92.97 million (7% 
discount rate). National annualized PWS cost estimates are further 
summarized in Table 37.

[[Page 18699]]

g. Treatment Administration Costs
    Any system with an MCL exceedance adopts either a treatment or non-
treatment alternative to comply with the proposed rule. The majority of 
systems are anticipated to install treatment technologies while a 
subset of systems will choose alternative methods. EPA assumes that 
systems will bear administrative costs associated with these treatment 
or non-treatment compliance actions (i.e., permitting costs). EPA 
assumes that systems will install treatment in the fourth year of the 
period of analysis. Table 35 presents the data elements and 
corresponding values associated with calculating treatment 
administration costs.

                Table 35--Treatment Administration Costs
                                 [2021$]
------------------------------------------------------------------------
          Data element description                Data element value
------------------------------------------------------------------------
The labor rate per hour for systems........  $35.48 (systems <=3,300).
                                             $37.84 (systems 3,301-
                                              10,000).
                                             $39.94 (systems 10,001-
                                              50,000).
                                             $41.70 (systems 50,001-
                                              100,000).
                                             $48.74 (systems >100,000).
The hours per entry point for a system to    3 hours (systems <=100)
 notify, consult, and submit a permit        5 hours (systems 101-500).
 request for treatment installation \a\.
                                             7 hours (systems 501-
                                              1,000).
                                             12 hours (systems 1,001-
                                              3,300).
                                             22 hours (systems 3,301-
                                              50,000).
                                             42 hours (systems >50,000).
The hours per entry point for a system to    6 hours.
 notify, consult, and submit a permit
 request for source water change or
 alternative method \1\.
------------------------------------------------------------------------
Notes:
\1\ EPA applied the cost per entry point for this economic analysis
  because the notification, consultation, and permitting process occurs
  for individual entry points.

h. Public Notification (PN) Costs
    EPA's cost analysis assumes full compliance with the rule 
throughout the period of analysis and, as a result, EPA does not 
estimate costs for the PN requirements in the proposed rule for systems 
with certain violations. The proposed rule designates MCL violations 
for PFAS as Tier 2, which requires systems to provide PN as soon as 
practical, but no later than 30 days after the system learns of the 
violation. The system must repeat notice every three months if the 
violation or situation persists unless the primacy agency determines 
otherwise. At a minimum, systems must give repeat notice at least once 
per year. The proposed rule also designates monitoring and testing 
procedure violations as Tier 3, which requires systems to provide 
public notice not later than one year after the system learns of the 
violation. The system must repeat the notice annually for as long as 
the violation persists. For approximate estimates of the potential 
burden associated with Tier 2 and 3 PNs, please see USEPA (2023j).
i. Primacy Agency Costs
    EPA assumes that primacy agencies will have upfront implementation 
costs as well as costs associated with system actions related to 
sampling and treatment. The activities that primacy agencies are 
expected to carry out under the proposed rule include:
     Reading and understanding the rule and adopting regulatory 
requirements,
     Providing primacy agency officials training for the rule 
implementation,
     Providing systems with training and technical assistance 
during the rule implementation,
     Reporting to EPA on an ongoing basis any PFAS-specific 
information under 40 CFR 142.15 regarding violations as well as 
enforcement actions and general operations of PWS programs,
     Reviewing the sample results during the implementation 
monitoring period and the SMF period, and
     Reviewing and consulting with systems on the installation 
of treatment technology or alternative methods, including source water 
change.
    With the exception of the first four activities listed above, the 
primary agency burdens are incurred in response to action taken by 
PWSs; for instance, the cost to primacy agencies of reviewing sample 
results depends on the number of samples taken at each entry point by 
each system under an Agency's jurisdiction. Table 36 presents the data 
elements and corresponding values associated with calculating primacy 
agency costs.

                     Table 36--Primacy Agency Costs
                                 [2021$]
------------------------------------------------------------------------
          Data element description                Data element value
------------------------------------------------------------------------
The labor rate per hour for primacy          $58.14.
 agencies \1\.
The average hours per primacy Agency to      416 hours per primacy
 read and understand the rule, as well as     Agency.
 adopt regulatory requirements.
The average hours per primacy Agency to      250 hours per primacy
 provide initial training to internal staff.  Agency.
The average hours per primacy Agency to      2,080 hours per primacy
 provide initial training and technical       Agency.
 assistance to systems.
The average hours per primacy Agency to      0.
 report annually to EPA information under
 40 CFR 142.15 regarding violations,
 variances and exemptions, enforcement
 actions and general operations of State
 PWS programs.
The hours per sample for a primacy Agency    1 hour.
 to review sample results.

[[Page 18700]]

 
The hours per entry point for a primacy      3 hours (systems <=100).
 agency to review and consult on             5 hours (systems 101-500).
 installation of a TT \2\.                   7 hours (systems 501-
                                              1,000).
                                             12 hours (systems 1,001-
                                              3,300).
                                             22 hours (systems 3,301-
                                              50,000).
                                             42 hours (systems >50,000).
The hours per entry point for a primacy      4 hours.
 agency to review and consult on a source
 water change \2\.
------------------------------------------------------------------------
Notes:
\1\ In USBLS (2022), State employee wage rate of $33.91 from National
  Occupational Employment and Wage Estimates, United States, BLS SOC
  Code 19-2041, ``State Government, excluding schools and hospitals--
  Environmental Scientists and Specialists, Including Health,'' hourly
  mean wage rate. May 2020 data (published in March 2021): https://www.bls.gov/oes/current/oes192041.htm. Wages are loaded using a factor
  of 62.2 from the Bureau of Labor Statistics (BLS) Employer Costs for
  Employee Compensation report, Table 3, March 2020. Percent of total
  compensation--Wages and Salaries--All Workers--State and Local
  Government Workers (https://www.bls.gov/news.release/archives/ecec_06182020.pdf). See worksheet BLS Table 3. The final loaded wage
  is adjusted for inflation.
\2\ EPA assumes that the proposed PFAS rule will have no discernable
  incremental burden for quarterly or annual reports to SDWIS/Fed.

    Estimated national annualized primacy agency costs for the proposed 
option are $7.96 million (3% discount rate) and $8.76 million (7% 
discount rate). National annualized cost estimates are further 
summarized in Table 37.
    In addition to the costs described above, a primacy agency may also 
have to review the certification of any Tier 2 or 3 PNs sent out by 
systems. EPA assumes full compliance with the proposed rule and 
therefore does not include this cost in national estimated cost totals 
but provides a brief discussion of the possible primacy agency burden 
associated with this component in USEPA (2023j).
    In Table 37, EPA summarizes the total annualized quantified cost of 
the proposed option at both a 3 percent and 7 percent discount rate 
expressed in millions of 2021 dollars. The first three rows show the 
annualized PWS sampling costs, the annualized PWS implementation and 
administrative costs, and the annualized PWS treatment costs. The 
fourth row shows the sum of the annualized PWS costs. At a 3 percent 
discount rate, the expected annualized PWS costs are $769 million. The 
uncertainty range for annualized PWS costs are $699 million to $862 
million. Finally, annualized primacy agency implementation and 
administrative costs are added to the annualized PWS costs to calculate 
the total annualized cost of the proposed option. At a 3 percent 
discount rate, the expected total annualized cost of the proposed rule 
is $777 million. The uncertainty range for the total annualized costs 
of the proposed rule is $706 million to $872 million. At a 7 percent 
discount rate, the expected total annualized cost of the proposed 
option is $1.211 billion, while the uncertainty range for the total 
annualized costs of the proposed option is $1.103 billion to $1.353 
billion. Note as described in section j. Data Limitations and 
Uncertainties in the Cost Analysis below, given the available 
occurrence data for the other compounds in the proposed rule (PFNA, 
HFPO-DA, and PFBS) and the regulatory thresholds under consideration, 
EPA did not model national costs associated with potential HI 
exceedances as a direct result of these compounds; therefore, the 
additional treatment cost, from co-occurrence of PFNA, HFPO-DA, PFBS or 
other PFAS, at systems already required to treat because of PFOA, PFOS, 
or PFHxS MCL and HI exceedances are not quantitatively assessed in the 
national cost estimates. Nor are treatment costs for systems that 
exceed the HI based on the combined occurrence of PFNA, HFPO-DA, PFBS, 
and PFHxS (where PFHxS itself does not exceed 9 ppt) included in the 
national monetized cost estimates. These potential additional costs are 
described in Section 5.3.1.4 of USEPA (2023j) and Appendix N of USEPA 
(2023i).
    In these sections of the Economic Analysis, EPA uses a model system 
approach to explore the potential costs of treatment at a system that: 
(1) has no detections of PFOA, PFOS, or PFHxS (modeled in the national 
analysis), but has occurrence of all the other PFAS included in the HI 
(HFPO-DA, PFBS, and PFNA), and (2) has occurrence of PFOA, PFOS, and 
PFHxS identical to the national model but also has occurrence of all 
the other PFAS included in the HI (HFPO-DA, PFBS, and PFNA). The first 
type of system represents additional systems that are not currently 
captured in the national costs but would incur treatment costs under 
the HI. The second type of system illustrates a range of potential 
incremental treatment costs for systems that are already treating to 
remove PFOA, PFOS, and/or PFHxS in the national cost analysis. EPA 
analyzed system costs for GAC, IX, and OR for two scenarios: high 
occurrence of the three PFAS not included in the national analysis and 
medium occurrence of those PFAS. The model system analysis found for IX 
and RO/NF that costs were slightly less or the same as modeled system 
treatment costs under a national cost scenario across both types of 
systems defined above, the medium and high PFAS scenarios, and across 
model system size categories. The assessment of GAC produced more 
variability in results. For systems that are not currently captured in 
the national costs but would incur treatment costs under the HI, EPA 
found under the medium PFAS concentrations cost would be the same or 
slightly less than a model system treating for the PFAS included in the 
national analysis. The systems representing the potential incremental 
treatment costs for systems that are already treating to remove PFOA, 
PFOS, and/or PFHxS in the national cost analysis, the model system 
analysis under the medium scenario found that costs of treatment would 
increase by 1-9 percent, depending on system size and other cost 
assumptions associated with bed life changes as a result of TOC 
assumptions. Under the high PFAS scenario across both types of systems 
GAC treatment costs were found to range from 0 to 77% higher than 
treatment of national PFAS values depending on system size and other 
costing assumptions like bed life. This high-end cost increase of 77 
percent is unlikely to occur at a large number of systems given the 
assumed high levels of PFAS and the assumed high levels of

[[Page 18701]]

TOC at 2 mg/L. It is also likely that systems facing these GAC 
treatment cost will select IX or RO/NF as lower cost alternative 
treatments and therefore national cost estimates are unlikely to be 
substantially underestimated. EPA requests comment on these estimated 
impacts and the assumption that HI exceedances resulting from these 
additional compounds will not significantly impact overall compliance 
costs.
    The national annualized costs below do not reflect costs of 
hazardous waste disposal for GAC and IX media. As a general matter, EPA 
notes that such wastes are not currently regulated under Federal law as 
a hazardous waste. To address stakeholder concerns, including those 
raised during the SBREFA process, EPA conducted a sensitivity analysis 
with an assumption of hazardous waste disposal for illustrative 
purposes only. As part of this analysis, EPA generated a second full 
set of unit cost curves that are identical to the curves used for the 
national cost analysis with the exception that spent GAC and spent IX 
resin are considered hazardous. EPA acknowledges that if Federal 
authorities later determine that PFAS-contaminated wastes require 
handling as hazardous wastes, the residuals management costs are 
expected to be higher. See Appendix N.2 of USEPA (2023j) for a 
sensitivity analysis describing the potential increase in costs 
associated with hazardous waste disposal (USEPA, 2023i).

                                                  Table 37--National Annualized Costs, Proposed Option
                                              [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0; million $2021]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               3% Discount rate                            7% Discount rate
                                                                 ---------------------------------------------------------------------------------------
                                                                  5th Percentile   Expected        95th       5th Percentile   Expected        95th
                                                                        \1\          value    Percentile \1\        \1\          value    Percentile \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Annualized PWS Sampling Costs...................................          $76.12      $90.32         $106.95          $78.54      $92.97         $109.19
Annualized PWS Implementation and Administration Costs..........            1.71        1.71            1.71            3.52        3.52            3.52
Annualized PWS Treatment Costs..................................          617.05      676.56          762.05        1,008.88    1,105.66        1,232.92
Total Annualized PWS Costs \2\ \3\ \4\..........................          698.90      768.57          861.78        1,096.29    1,202.09        1,341.19
Primacy Agency Rule Implementation and Administration Cost......            6.86        7.96            9.18            7.67        8.76           10.04
Total Annualized Rule Costs \2\ \3\ \4\.........................          705.85      776.54          871.50        1,102.71    1,210.91        1,352.71
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding. Percentiles cannot be summed because cost components are not perfectly correlated.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section XIII.I of this preamble and Table 71. This
  range does not include the uncertainty described in Table 41.
\2\ Total quantified national cost values do not include the incremental treatment costs associated with the co-occurrence of HFPO-DA, PFBS, and PFNA at
  systems required to treat for PFOA, PFOS, and PFHxS. The total quantified national cost values do not include treatment costs for systems that would
  be required to treat based on HI exceedances apart from systems required to treat because of PFHxS occurrence alone. See Appendix N, Section 3 of the
  Economic Analysis (USEPA, 2023i) for additional detail on co-occurrence incremental treatment costs and additional treatment costs at systems with HI
  exceedances.
\3\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported in this table do not include costs
  associated with hazardous waste disposal of spent filtration materials. To address stakeholder concerns about potential costs for disposing PFAS-
  contaminated wastes as hazardous should they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA, 2023i) for additional detail.
\4\ See Table 70 for a list of the nonquantifiable costs, and the potential direction of impact these costs would have on the estimated monetized total
  annualized costs in this table.

    In Table 38, Table 39, and Table 40, EPA summarizes the total 
annualized quantified cost of options 1a, 1b, and 1c, respectively.

                                                     Table 38--National Annualized Costs, Option 1a
                                                     [PFOA and PFOS MCLs of 4.0 ppt; million $2021]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               3% Discount rate                            7% Discount rate
                                                                 ---------------------------------------------------------------------------------------
                                                                  5th Percentile   Expected        95th             5th        Expected        95th
                                                                        \1\          value    Percentile \1\   Percentile\1\     value    Percentile \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Annualized PWS Sampling Costs...................................          $75.54      $89.45         $105.44          $77.76      $92.10         $108.29
Annualized PWS Implementation and Administration Costs..........            1.71        1.71            1.71            3.52        3.52            3.52
Annualized PWS Treatment Costs..................................          601.03      661.40          745.31          984.54    1,079.05        1,205.22
Total Annualized PWS Costs \2\ \3\..............................          680.76      752.56          848.52        1,066.70    1,174.69        1,314.49
Primacy Agency Rule Implementation and Administration Cost......            6.83        7.89            9.12            7.59        8.69            9.96
Total Annualized Rule Costs \2\ \3\.............................          687.54      760.45          857.04        1,078.01    1,183.41        1,324.41
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding. Percentiles cannot be summed because cost components are not perfectly correlated.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section XIII.I of this preamble and Table 71. This
  range does not include the uncertainty described in Table 41.

[[Page 18702]]

 
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported in this table do not include costs
  associated with hazardous waste disposal of spent filtration materials. To address stakeholder concerns about potential costs for disposing PFAS-
  contaminated wastes as hazardous should they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA, 2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable costs, and the potential direction of impact these costs would have on the estimated monetized total
  annualized costs in this table.

                                                     Table 39--National Annualized Costs, Option 1b
                                                     [PFOA and PFOS MCLs of 5.0 ppt; million $2021]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               3% Discount rate                            7% Discount rate
                                                                 ---------------------------------------------------------------------------------------
                                                                  5th Percentile   Expected        95th             5th        Expected        95th
                                                                        \1\          value    Percentile \1\   Percentile\1\     value    Percentile \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Annualized PWS Sampling Costs...................................          $66.40      $78.38          $93.04          $68.77      $80.92          $95.70
Annualized PWS Implementation and Administration Costs..........            1.71        1.71            1.71            3.52        3.52            3.52
Annualized PWS Treatment Costs..................................          479.50      527.00          597.91          778.40      853.94          960.05
Total Annualized PWS Costs \2\ \3\..............................          549.52      607.08          686.67          854.64      938.38        1,052.52
Primacy Agency Rule Implementation and Administration Cost......            6.03        6.94            8.03            6.74        7.69            8.84
Total Annualized Rule Costs \2\ \3\.............................          555.94      614.03          694.18          860.01      946.07        1,064.56
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding. Percentiles cannot be summed because cost components are not perfectly correlated.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section XIII.I of this preamble and Table 71. This
  range does not include the uncertainty described in Table 41.
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported in this table do not include costs
  associated with hazardous waste disposal of spent filtration materials. To address stakeholder concerns about potential costs for disposing PFAS-
  contaminated wastes as hazardous should they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA, 2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable costs, and the potential direction of impact these costs would have on the estimated monetized total
  annualized costs in this table.

                                 Table 40--National Annualized Costs, Option 1c
                                 [PFOA and PFOS MCLs of 10.0 ppt; Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
                                            5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   percentile
                                            \1\        value        \1\          \1\        value        \1\
----------------------------------------------------------------------------------------------------------------
Annualized PWS Sampling Costs.........       $46.19     $52.84       $64.34       $48.33     $55.14       $66.82
Annualized PWS Implementation and              1.71       1.71         1.71         3.52       3.52         3.52
 Administration Costs.................
Annualized PWS Treatment Costs........       214.02     233.87       257.12       336.54     367.40       404.42
Total Annualized PWS Costs \2\ \3\....       264.49     288.43       317.66       390.39     426.06       468.83
Primacy Agency Rule Implementation and         4.28       4.76         5.65         4.91       5.40         6.28
 Administration Cost..................
Total Annualized Rule Costs \2\ \3\...       269.11     293.19       323.45       395.35     431.46       474.75
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding. Percentiles cannot be summed because cost
  components are not perfectly correlated.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 71. This range does not include the uncertainty described in Table 41.
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported
  in this table do not include costs associated with hazardous waste disposal of spent filtration materials. To
  address stakeholder concerns about potential costs for disposing PFAS-contaminated wastes as hazardous should
  they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA,
  2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable costs, and the potential direction of impact these costs
  would have on the estimated monetized total annualized costs in this table.

j. Data Limitations and Uncertainties in the Cost Analysis
    Table 41 lists data limitations and characterizes the impact on the 
quantitative cost analysis. EPA notes that in most cases it is not 
possible to judge the extent to which a particular limitation or 
uncertainty could affect the cost analysis. EPA provides the potential 
direction of the impact on the cost estimates when possible but does 
not prioritize the entries with respect to the impact magnitude.

[[Page 18703]]

                Table 41--Limitations That Apply to the Cost Analysis for the Proposed PFAS Rule
----------------------------------------------------------------------------------------------------------------
        Uncertainty/assumption          Effect on quantitative analysis                   Notes
----------------------------------------------------------------------------------------------------------------
WBS engineering cost model assumptions  Uncertain......................  The WBS engineering cost models require
 and component costs.                                                     many design and operating assumptions
                                                                          to estimate treatment process
                                                                          equipment and operating needs. Chapter
                                                                          5 of the Economic Analysis (USEPA,
                                                                          2023j) addressed the bed life
                                                                          assumption. The Technologies and Costs
                                                                          document (USEPA, 2023h) and individual
                                                                          WBS models in the rule docket provide
                                                                          additional information. The component-
                                                                          level costs approximate national
                                                                          average costs, which can over- or
                                                                          under-estimate costs at systems
                                                                          affected by the proposed rule.
Compliance forecast...................  Uncertain......................  The forecast probabilities are based on
                                                                          historical full-scale compliance
                                                                          actions. Site-specific water quality
                                                                          conditions, changes in technology, and
                                                                          changes in market conditions can
                                                                          result in future technology selections
                                                                          that differ from the compliance
                                                                          forecast.
TOC concentration.....................  Uncertain......................  The randomly assigned values from the
                                                                          two national distributions are based
                                                                          on a limited dataset. Actual TOC
                                                                          concentrations at systems affected by
                                                                          the proposed rule can be higher or
                                                                          lower than the assigned values.
Insufficient UCMR 3 data for PFBS and   Underestimate..................  The HI in the proposed option would
 PFNA and no UCMR 3 data for HFPO-DA                                      regulate PFBS, PFNA, and HFPO-DA in
 were available to incorporate into                                       addition to the modeled PFAS. In
 the Bayesian hierarchical occurrence                                     instances when concentrations of PFBS,
 model.                                                                   PFNA, and/or HFPO-DA are high enough
                                                                          to cause a HI exceedance, the modeled
                                                                          costs may be underestimated. If these
                                                                          PFAS occur in isolation at levels that
                                                                          affect treatment decisions, or if they
                                                                          occur in sufficient concentration to
                                                                          result in an exceedance when the
                                                                          concentration of PFHxS alone would be
                                                                          below the HI, then costs would be
                                                                          underestimated. Note that EPA has
                                                                          conducted an analysis of the potential
                                                                          changes in system level treatment cost
                                                                          associated with the occurrence of
                                                                          PFBS, PFNA, and HFPO-DA using a model
                                                                          system approach which is discussed in
                                                                          detail in Chapter 5 and Appendix N of
                                                                          the Economic Analysis (USEPA, 2023j;
                                                                          USEPA, 2023i).
POU not included in compliance          Overestimate...................  If POU devices can be certified to meet
 forecast.                                                                concentrations that satisfy the
                                                                          proposed rule, then small systems may
                                                                          be able to reduce costs by using a POU
                                                                          compliance option instead of
                                                                          centralized treatment or source water
                                                                          changes.
Process wastes not classified as        Underestimate..................  The national cost analysis reflects the
 hazardous.                                                               assumption that PFAS-contaminated
                                                                          wastes are not considered hazardous
                                                                          wastes. As a general matter, EPA notes
                                                                          that such wastes are not currently
                                                                          regulated under Federal law as a
                                                                          hazardous waste. To address
                                                                          stakeholder concerns, including those
                                                                          raised during the SBREFA process, EPA
                                                                          conducted a sensitivity analysis with
                                                                          an assumption of hazardous waste
                                                                          disposal for illustrative purposes
                                                                          only. As part of this analysis, EPA
                                                                          generated a second full set of unit
                                                                          cost curves that are identical to the
                                                                          curves used for the national cost
                                                                          analysis with the exception that spent
                                                                          GAC and spent IX resin are considered
                                                                          hazardous. EPA acknowledges that if
                                                                          Federal authorities later determine
                                                                          that PFAS-contaminated wastes require
                                                                          handling as hazardous wastes, the
                                                                          residuals management costs in the WBS
                                                                          treatment cost models are expected to
                                                                          be higher. See Appendix N of the
                                                                          Economic Analysis (USEPA, 2023j;
                                                                          USEPA, 2023i) for a sensitivity
                                                                          analysis describing the potential
                                                                          increase in costs associated with
                                                                          hazardous waste disposal at 100% of
                                                                          systems treating for PFAS. The costs
                                                                          estimated in Appendix N are consistent
                                                                          with EPA OLEM's ``Interim Guidance on
                                                                          the Destruction and Disposal of
                                                                          Perfluoroalkyl and Polyfluoroalkyl
                                                                          Substances and Materials Containing
                                                                          Perfluoroalkyl and Polyfluoroalkyl
                                                                          Substances.'' \1\
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ EPA Office of Land and Emergency Management's Interim Guidance on the Destruction and Disposal of
  Perfluoroalkyl and Polyfluoroalkyl Substances and Materials Containing Perfluoroalkyl and Polyfluoroalkyl
  Substances can be found at https://www.epa.gov/system/files/documents/2021-11/epa-hq-olem-2020-0527-0002_content.pdf.

D. Method for Estimating Benefits

    EPA's quantification of health benefits resulting from reduced PFAS 
exposure in drinking water was driven by PFAS occurrence estimates, 
pharmacokinetic (PK) model availability, information on exposure-
response relationships, and available information to monetize avoided 
cases of illness. In the Economic Analysis, EPA either quantitatively 
assesses or qualitatively discusses health endpoints associated with 
exposure to PFAS. EPA assesses potential benefits quantitatively if 
evidence of exposure and health effects is likely, it is possible to 
link the outcome to risk of a health effect, and there is no overlap in 
effect with another quantified endpoint in the same outcome group. 
Particularly, the most consistent epidemiological associations with 
PFOA and PFOS include decreased immune system response, decreased 
birthweight, increased serum lipids, and increased liver enzymes 
(particularly ALT). The available evidence indicates effects across 
immune, developmental, cardiovascular, and hepatic organ systems at the 
same or approximately the same level of exposure.
    Table 42 presents an overview of the categories of health benefits 
expected to result from the implementation of treatment that reduces 
PFAS levels in drinking water. Of the PFAS compounds included in the 
proposed rule, EPA quantifies some of the adverse health effects 
associated with PFOA and PFOS. EPA also quantifies one adverse health 
effect of PFNA in a sensitivity analysis only. These compounds have 
likely evidence linking exposure to a particular health endpoint and 
have reliable PK models connecting the compound to PFAS blood serum. PK 
models describe the distribution of chemicals in the body and 
pharmacodynamic relation between blood concentration and clinical 
effects. Benefits from avoided adverse health effects of HFPO-DA, PFHxS 
and PFBS are discussed qualitatively in this section.
    As Table 42 demonstrates, only a subset of the avoided morbidity 
and mortality stemming from reduced PFAS levels in drinking water can 
be quantified and monetized. The monetized benefits evaluated in the 
Economic Analysis for the proposed rule include changes in human health 
risks associated with CVD and infant

[[Page 18704]]

birth weight from reduced exposure to PFOA and PFOS in drinking water 
and RCC from reduced exposure to PFOA. EPA also quantified benefits 
from reducing bladder cancer risk due to the co-removal of non-PFAS 
pollutants via the installation of drinking water treatment, discussed 
in greater detail in USEPA (2023j).
    EPA was not able to quantify or monetize other benefits, including 
those related to other reported health effects including immune, liver, 
endocrine, metabolic, reproductive, musculoskeletal, other cancers. EPA 
discusses these benefits qualitatively in more detail below, as well as 
in Section 6.2 of USEPA (2023j).

                                      Table 42--Overview of Health Benefits Categories Considered in the Analysis of Changes in PFAS Drinking Water Levels
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                           Health outcome                                                          PFAS Compound \1\ \2\ \3\                                       Benefits analysis \4\
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                                               Discussed           Discussed
                Category                           Endpoint               PFOA          PFOS          PFNA          PFHxS         PFBS         HFPO-DA      quantitatively       qualitatively
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Lipids..................................  Total cholesterol.........            X             X         \e\ X                                                             X
                                          High-density lipoprotein          \5\ X         \5\ X                                                                           X
                                           cholesterol (HDLC).
                                          Low-density lipoprotein               X             X         \5\ X                                                                                 X
                                           cholesterol (LDLC).
CVD.....................................  Blood pressure............                          X                                                                           X
Developmental...........................  Birth weight..............            X             X             X         \5\ X         \5\                   X
                                          Small for gestational age             X                       \5\ X             X                                                           X
                                           (SGA), non-birth weight
                                           developmental.
Endocrine...............................  Thyroid hormone disruption                                                                                          X
Hepatic.................................  ALT.......................            X             X         \5\ X             X                                                           X
Immune..................................  Antibody response                     X             X         \5\ X             X                                                           X
                                           (tetanus, diphtheria).
Metabolic...............................  Leptin....................            X                                                                                                             X
Renal...................................  Organ weight..............                                                                                                          X
Musculoskeletal.........................  Osteoarthritis, bone                  X                       \5\ X                                                                                 X
                                           mineral density.
Hematologic.............................  Vitamin D levels,                                                                                                                           X
                                           hemoglobin levels,
                                           albumin levels.
Cancer..................................  RCC.......................            X                                                                                         X
                                          Testicular................            X                                                                                                             X
                                          Other.....................                                                                        \5\ 
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
\1\ Fields marked with ``X'' indicate the PFAS compound for which there is evidence of an association with a given health outcome in epidemiological studies.
\2\ Fields marked with ``'' indicate the PFAS compound for which there is evidence of an association with a given health outcome only in toxicological studies.
\3\ Note that only PFOA and PFOS effects were modeled in the assessment of benefits under the proposed rule. PFNA was modeled only in sensitivity analyses of birth weight benefits (See
  Economic Analysis Appendix K in USEPA (2023i)).
\4\ Outcomes with likely evidence of an association between a PFAS compound and a health outcome are assessed quantitatively unless (1) there is an overlap within the same outcome group (e.g.,
  LDLC overlaps with total cholesterol, and SGA overlaps with low birth weight), or (2) it is not possible to link the outcome to the risk of the health effect (e.g., evidence is inconclusive
  regarding the relationship between PFOS exposure and leptin levels and associated health outcomes). Such health outcomes are discussed qualitatively.
\5\ Evidence of the relationship between the PFAS compound and the health outcome is not conclusive. Note that EPA sought comments from the EPA SAB on the CVD exposure-response approach
  (USEPA, 2023j). The SAB recommended that EPA evaluate how the inclusion of HDLC effects would influence results. EPA evaluated the inclusion of HDLC effects in a sensitivity analysis,
  described in Appendix K.

    EPA developed PK models to evaluate blood serum PFAS levels in 
adults resulting from exposure to PFAS via drinking water. To date, EPA 
has developed PK models for PFOA and PFOS. EPA used baseline and 
regulatory alternative PFOA/PFOS drinking water concentrations as 
inputs to its PK model to estimate blood serum PFOA/PFOS concentrations 
for adult males and females. For further detail on the PK model and its 
application in EPA's benefits analysis, please see EPA's Proposed MCLG 
documents (USEPA, 2023b; USEPA, 2023c) and Section 6.3 of USEPA 
(2023j).
1. Quantified Developmental Effects
    Research indicates that exposure to PFOA and PFOS is associated 
with developmental effects, including infant birth weight (Verner et 
al., 2015; USEPA, 2016e; USEPA, 2016f; USEPA, 2023b; USEPA, 2023c; 
Negri et al., 2017; ATSDR, 2021; Waterfield et al., 2020). The route 
through which the embryo and fetus are exposed prenatally to PFOA and 
PFOS is maternal blood serum via the placenta. Most studies of the 
association between maternal serum PFOA/PFOS and birth weight report 
negative relationships (Verner et al., 2015; Negri et al., 2017; 
Dzierlenga et al., 2020). EPA's PK model assumes that mothers were 
exposed to PFOA/PFOS from birth to the year in which pregnancy 
occurred.
    EPA quantified and valued changes in birth weight-related risks 
associated

[[Page 18705]]

with reductions in exposure to PFOA and PFOS in drinking water. Entry 
point-specific time series of the differences between serum PFOA/PFOS 
concentrations under baseline and regulatory alternatives are inputs 
into this analysis. For each entry point, evaluation of the changes in 
birth weight impacts involves the following key steps:
    1. Estimating the changes in birth weight based on modeled changes 
in serum PFOA/PFOS levels and exposure-response functions for the 
effect of serum PFOA/PFOS on birth weight;
    2. Estimating the difference in infant mortality probability 
between the baseline and regulatory alternatives based on changes in 
birth weight under the regulatory alternatives and the association 
between birth weight and mortality;
    3. Identifying the infant population affected by reduced exposure 
to PFOA/PFOS in drinking water under the regulatory alternatives;
    4. Estimating the changes in the expected number of infant deaths 
under the regulatory alternatives based on the difference in infant 
mortality rates and the population of surviving infants affected by 
increases in birth weight due to reduced PFOA/PFOS exposure; and
    5. Estimating the economic value of reducing infant mortality based 
on the Value of a Statistical Life and infant morbidity based on 
reductions in medical costs associated with changes in birth weight for 
the surviving infants based on the cost of illness.
    EPA also considered the potential benefits from reduced exposure to 
PFNA that may be realized as a direct result of the proposed rule. The 
Agency explored the birth weight impacts of PFNA in a sensitivity 
analysis, using a unit PFNA reduction scenario (i.e., 1.0 ppt change) 
and Lu and Bartell (2020) to estimate PFNA blood serum levels resulting 
from PFNA exposures in drinking water. To estimate blood serum PFNA 
based on its drinking water concentration, EPA used a first-order 
single-compartment model whose behavior was previously demonstrated to 
be consistent with PFOA PKs in humans (Bartell et al., 2010). In 
addition to the PFOA-birth weight and PFOS-birth weight effects 
analyzed in the Economic Analysis, EPA examined the effect of inclusion 
of PFNA-birth weight effects using estimates from two studies (Lenters 
et al., 2016; Valvi et al., 2017). EPA found that inclusion of a 1.0 
ppt PFNA reduction could increase annualized birth weight benefits 5.4-
7.7-fold, relative to the scenario that quantifies a 1.0 ppt reduction 
in PFOA and a 1.0 ppt reduction in PFOS only. The range of estimated 
PFNA-related increases in benefits is driven by the exposure-response, 
with smaller estimates produced using the slope factors from Lenters et 
al. (2016), followed by Valvi et al. (2017). EPA notes that the PFNA 
slope factor estimates are orders of magnitude larger than the slope 
factor estimates used to evaluate the impacts of PFOA/PFOS reductions. 
EPA also notes that the PFNA slope factor estimates are not precise, 
with 95% CIs covering wide ranges that include zero (i.e., serum PFNA 
slope factor estimates are not statistically significant at 5% level). 
Caution should be exercised in making judgements about the potential 
magnitude of change in the national benefits estimates based on the 
results of these sensitivity analyses, although conclusions about the 
directionality of these effects can be inferred. EPA did not include 
PFNA effects in the national benefits estimates for the proposed 
rulemaking because of limitations associated with the UCMR 3 PFNA 
occurrence data and the slope factor estimates are less precise. For 
more information, see Appendix K of USEPA (2023j).
    To estimate changes in birth weight resulting from reduced exposure 
to PFOA and PFOS under the regulatory alternatives, EPA relied on the 
estimated time series of changes in serum PFOA/PFOS concentrations 
specific to women of childbearing age and serum-birth weight exposure-
response functions provided in recently published meta-analyses. For 
more detail on the evaluation of the studies used in these meta-
analyses, please see EPA's Proposed Maximum Contaminant Level Goal for 
PFOA and PFOS in Drinking Water (USEPA, 2023b; USEPA, 2023c) and 
Section 6.4 of USEPA (2023j).
    Changes in serum PFOA and PFOS concentrations are calculated for 
each PWS entry point during each year in the analysis period. EPA 
assumes that, given long half-lives of PFOS and PFOA, any one-time 
measurement during or near pregnancy is reflective of a critical window 
and not subject to considerable error. The mean change in birth weight 
per increment in long-term PFOA and PFOS exposure is calculated by 
multiplying each annual change in PFOA and PFOS serum concentration 
(ng/mL serum) by the PFOA and PFOS serum-birth weight exposure-response 
slope factors (g birth weight per ng/mL serum) provided in Table 43, 
respectively. The mean annual change in birth weight attributable to 
changes in both PFOA and PFOS exposure is the sum of the annual PFOA- 
and PFOS-birth weight change estimates. Additional detail on the 
derivation of the exposure-response functions can be found in Appendix 
D in USEPA (2023i). Appendix K in USEPA (2023i) presents an analysis of 
birth weight risk reduction considering slope factors specific to the 
first trimester.

        Table 43--Serum Exposure-Birth Weight Response Estimates
------------------------------------------------------------------------
                    Compound                     g/ng/mL serum  (95% CI)
------------------------------------------------------------------------
PFOA \1\.......................................      -10.5 (-16.7, -4.4)
PFOS \2\.......................................        -3.0 (-4.9, -1.1)
------------------------------------------------------------------------
Notes:
\1\ The serum-birth weight slope factor for PFOA is based on the main
  random effects estimate from Negri et al. (2017); Steenland et al.
  (2018).
\2b\ The serum-birth weight slope factor for PFOS is based on an EPA
  reanalysis of Dzierlenga et al. (2020).

    EPA places a cap on estimated birth weight changes in excess of 200 
g, assuming that such changes in birth weight are unreasonable even as 
a result of large changes in PFOA/PFOS serum concentrations. This cap 
is based on existing studies that found that changes to environmental 
exposures result in relatively modest birth weight changes (Windham and 
Fenster, 2008; Klein and Lynch, 2018; Kamai et al., 2019).
    Low birth weight is linked to a number of health effects that may 
be a source of economic burden to society in the form of medical costs, 
infant mortality, parental and caregiver costs, labor market 
productivity loss, and education costs (Chaikind and Corman, 1991; 
Behrman and Butler, 2007; Behrman and Rosenzweig, 2004; Joyce et al., 
2012; Kowlessar et al., 2013; Colaizy et al., 2016; Nicoletti et al., 
2018; Klein and Lynch, 2018). Recent literature also linked low birth 
weight to educational attainment and required remediation to improve 
students' outcomes, childhood disability, and future earnings 
(Jelenkovic et al., 2018; Temple et al., 2010; Elder et al., 2020; 
Hines et al., 2020 Chatterji et al., 2014; Dobson et al., 2018).
    EPA's analysis focuses on two categories of birth weight impacts 
that are amenable to monetization associated with incremental changes 
in birth weight: (1) medical costs associated with changes in infant 
birth weight and (2) the value of avoiding infant mortality at various 
birth weights. The birth weight literature related to other sources of 
economic burden to society (e.g., parental and caregiver costs and 
productivity losses) is limited in geographic coverage, population 
size, and range of birth weights evaluated

[[Page 18706]]

and therefore cannot be used in the economic analysis of birth weight 
effects from exposure to PFOA/PFOS in drinking water (ICF, 2021).
    Two studies showed statistically significant relationships between 
incremental changes in birth weight and infant mortality: Almond et al. 
(2005) and Ma and Finch (2010). Ma and Finch (2010) used 2001 National 
Center for Health Statistics (NCHS) linked birth/infant death data for 
singleton and multiple birth infants among subpopulations defined by 
sex and race/ethnicity to estimate a regression model assessing the 
associations between 14 key birth outcome measures, including birth 
weight, and infant mortality. They found notable variation in the 
relationship between birth weight and mortality across race/ethnicity 
subpopulations, with odds ratios for best-fit birth weight-mortality 
models ranging from 0.8-1 (per 100 g birth weight change). Almond et 
al. (2005) used 1989-1991 NCHS linked birth/infant death data for 
multiple birth infants to analyze relationships between birth weight 
and infant mortality within birth weight increment ranges. For their 
preferred model, they reported coefficients in deaths per 1,000 births 
per 1 g increase in birth weight that range from -0.420 to -0.002. 
However, the data used in these studies (Almond et al., 2005 and Ma, 
2010) are outdated (1989-1991 and 2001, respectively). Given the 
significant decline in infant mortality over the last 30 years (ICF, 
2020) and other maternal and birth characteristics that are likely to 
influence infant mortality (e.g., average maternal age and rates of 
maternal smoking), the birth weight-mortality relationship estimates 
from Almond et al. (2005) and Ma and Fitch (2010) are likely to 
overestimate the benefits of birth weight changes.
    Considering the discernible changes in infant mortality over the 
last 30 years, EPA developed a regression analysis to estimate the 
relationship between birth weight and infant mortality using the most 
recently available Period/Cohort Linked Birth-Infant Death Data Files 
published by NCHS from the 2017 period/2016 cohort and the 2018 period/
2017 cohort (CDC, 2017, 2018). EPA selected variables of interest for 
the regression analysis, including maternal demographic and 
socioeconomic characteristics, maternal risk and risk mitigation 
factors (e.g., number of prenatal care visits, smoker status), and 
infant birth characteristics. EPA included several variables used in Ma 
and Fitch (2010) (maternal age, maternal education, marital status, and 
others) as well as additional variables to augment the set of 
covariates included in the analyses. In addition, EPA developed 
separate models for different race/ethnicity categories (non-Hispanic 
Black, non-Hispanic White, and Hispanic) and interacted birth weight 
with categories of gestational age, similar to Ma and Finch (2010). 
Appendix E to USEPA (2023i) provides details on model development and 
regression results.
    Table 44 presents the resulting odds ratios and marginal effects 
(in terms of deaths per 1,000 births for every 1 g increase in birth 
weight) estimated for changes in birth weight among different 
gestational age categories in the mortality regression models for non-
Hispanic Black, non-Hispanic White, and Hispanic race/ethnicity 
subpopulations. Marginal effects for birth weight among gestational age 
categories vary across different race/ethnicity subpopulations. The 
marginal effects for birth weight among different gestational age 
categories are higher in the non-Hispanic Black model than in the non-
Hispanic White and Hispanic models, particularly for extremely and very 
preterm infants, indicating that low birth weight increases the 
probability of mortality within the first year more so among non-
Hispanic Black infants than among non-Hispanic White and Hispanic 
infants.
    EPA relies on odds ratios estimated using the birth weight-
mortality regression model to assess mortality outcomes of reduced 
exposures to PFOA/PFOS in drinking water under the regulatory 
alternatives. To obtain odds ratios specific to each race/ethnicity and 
100 g birth weight increment considered in the birth weight benefits 
model,\6\ EPA averaged the estimated odds ratios for 1 g increase in 
birth weight over the gestational age categories using the number of 
infants (both singleton and multiple birth) that fall into each 
gestational age category as weights. Separate gestational age category 
weights were computed for each 100 g birth weight increment and race/
ethnicity subpopulation within the 2017 period/2016 cohort and 2018 
period/2017 cohort Linked Birth-Infant Death Data Files. The weighted 
birth weight odds ratios are then used in conjunction with the 
estimated change in birth weight and baseline infant mortality rates to 
determine the probability of infant death under the regulatory 
alternatives, as described further in Section 6.4 of USEPA (2023j).
---------------------------------------------------------------------------

    \6\ The birth weight risk reduction model evaluates changes in 
birth weight in response to PFOA/PFOS drinking water level 
reductions for infants who fall into 100 g birth weight increments 
(e.g., birth weight 0-99 g, 100-199 g, 200-299 g. . . 8,000-8,099 g, 
8,100-8,165 g).

  Table 44--Race/Ethnicity and Gestational Age-Specific Birth Weight Marginal Effects and Odds Ratios From the
                                         Mortality Regression Models \1\
----------------------------------------------------------------------------------------------------------------
                                           Gestational age        Marginal effect per
                 Race                        category \2\        1,000 births (95% CI)     Odds ratio (95% CI)
----------------------------------------------------------------------------------------------------------------
Non-Hispanic Black...................  Extremely Preterm......  -0.20400 (-0.21910, -    0.99817 (0.99802,
                                                                 0.18890).                0.99832)
                                       Very Preterm...........  -0.04580 (-0.04820, -    0.99816 (0.99804,
                                                                 0.04340).                0.99827)
                                       Moderately Preterm.....  -0.01030 (-0.01080, -    0.99852 (0.99846,
                                                                 0.009850).               0.99857)
                                       Term...................  -0.00453 (-0.00472, -    0.99856 (0.99851,
                                                                 0.00434).                0.9986)
Non-Hispanic White...................  Extremely Preterm......  -0.12160 (-0.13080, -    0.99866 (0.99855,
                                                                 0.11240).                0.99878)
                                       Very Preterm...........  -0.03290 (-0.03430, -    0.9985 (0.99842,
                                                                 0.03140).                0.99858)
                                       Moderately Preterm.....  -0.00677 (-0.00702, -    0.99867 (0.99863,
                                                                 0.00652).                0.99872)
                                       Term...................  -0.00228 (-0.00236, -    0.99865 (0.99861,
                                                                 0.00221).                0.99868)

[[Page 18707]]

 
Hispanic.............................  Extremely Preterm......  -0.15260 (-0.16770, -    0.99835 (0.99817,
                                                                 0.13750).                0.99853)
                                       Very Preterm...........  -0.03290 (-0.03510, -    0.99846 (0.99835,
                                                                 0.03070).                0.99858)
                                       Moderately Preterm.....  -0.00626 (-0.00659, -    0.99856 (0.99849,
                                                                 0.00592).                0.99862)
                                       Term...................  -0.00219 (-0.00229, -    0.99849 (0.99844,
                                                                 0.00208).                0.99855)
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Data based on the 2016/17 and 2017/18 CDC Period Cohort Linked Birth-Infant Death Data Files obtained from
  NCHS/National Vital Statistics System (NVSS). Marginal effects and odds ratios are estimated using a
  regression model that also includes covariates representative of infant birth characteristics in addition to
  birth weight, maternal demographic characteristics, and maternal risk factors. All effects were statistically
  significant at the 5% level. Additional details are included in Appendix E to the Economic Analysis.
\2\ Gestational age categories defined as extremely preterm (<=28 weeks), very preterm (>28 weeks and <=32
  weeks), moderately preterm (>32 weeks and <=37 weeks), and term (>37 weeks).

    EPA weighted the race/ethnicity-specific odds ratios in Table 44 by 
the proportions of the infant populations who fell into each 
gestational age within a 100 g birth weight increment, based on the 
2016/17 and 2017/18 period cohort data, to obtain a weighted odds ratio 
estimate for each modeled race/ethnicity subpopulation and 100 g birth 
weight increment.
    Based on reduced serum PFOA/PFOS exposures under the regulatory 
alternatives and the estimated relationship between birth weight and 
infant mortality, EPA estimates the subsequent change in birth weight 
for those infants affected by decreases in PFOA/PFOS and changes in the 
number of infant deaths. EPA evaluated these changes at each PWS entry 
point affected by the regulatory alternatives and the calculations are 
performed for each race/ethnicity group, 100 g birth weight category, 
and year of the analysis. Additional detail on the calculations EPA 
used to estimate changes in birth weight, the affected population size, 
and infant deaths avoided, and the number of surviving infants is 
provided in Chapter 6 of USEPA (2023j).
    EPA used the Value of a Statistical Life to estimate the benefits 
of reducing infant mortality and the cost of illness to estimate the 
economic value of increasing birth weight in the population of 
surviving infants born to mothers exposed to PFOA and PFOS in drinking 
water. EPA's approach to monetizing benefits associated with 
incremental increases in birth weight resulting from reductions in 
drinking water PFOA/PFOS levels relies on avoided medical costs 
associated with various ranges of birth weight. Although the economic 
burden of treating infants at various birth weights also includes non-
medical costs, very few studies to date have quantified such costs 
(Klein and Lynch, 2018; ICF, 2021). EPA selected the medical cost 
function from Klein and Lynch (2018) to monetize benefits associated 
with the estimated changes in infant birth weight resulting from 
reduced maternal exposure to PFOA/PFOS.\7\
---------------------------------------------------------------------------

    \7\ The Klein and Lynch (2018) report was externally peer 
reviewed by three experts with qualifications in economics and 
public health sciences. EPA's charge questions to the peer reviewers 
sought input on the methodology for developing medical cost 
estimates associated with changes in birth weight. The Agency's 
charge questions and peer reviewer responses are available in the 
docket.
---------------------------------------------------------------------------

    Using the incremental cost changes from Klein and Lynch (2018), EPA 
calculates the change in medical costs resulting from changes in birth 
weight among infants in the affected population who survived the first 
year following birth, provided in Table 45.

                           Table 45--Simulated Cost Changes for Birth Weight Increases
                                                     [$2021]
----------------------------------------------------------------------------------------------------------------
                                                                      Simulated cost changes for birth weight
                                                                      increases, dollars per gram ($2021) \3\
                      Birth weight \1\ \2\                       -----------------------------------------------
                                                                   +0.04 lb (+18   +0.11 lb (+50  +0.22 lb (+100
                                                                        g)              g)              g)
----------------------------------------------------------------------------------------------------------------
2 lb (907 g)....................................................        -$126.53        -$112.87        -$109.39
2.5 lb (1,134 g)................................................         -$94.88         -$84.64         -$82.03
3 lb (1,361 g)..................................................         -$71.15         -$63.47         -$61.51
3.3 lb (1,497 g)................................................         -$59.86         -$53.40         -$51.75
4 lb (1,814 g)..................................................         -$40.00         -$35.69         -$34.59
4.5 lb (2,041 g)................................................         -$30.00         -$26.76         -$25.93
5 lb (2,268 g)..................................................         -$22.49         -$20.07         -$19.45
5.5 lb (2,495 g)................................................          -$0.93          -$0.84          -$0.84
6 lb (2,722 g)..................................................          -$0.91          -$0.83          -$0.83
7 lb (3,175 g)..................................................          -$0.88          -$0.80          -$0.80
8 lb (3,629 g)..................................................          -$0.85          -$0.77          -$0.77
9 lb (4,082 g)..................................................           $3.15           $2.87           $2.89
10 lb (4,536 g).................................................           $3.54           $3.23           $3.26
----------------------------------------------------------------------------------------------------------------
Notes:

[[Page 18708]]

 
\1\ Values for birth weight have been converted from lb to g.
\2\ Note that simulated medical costs increase, rather than decrease, in response to increased birth weight
  changes among high birth weight infants (those greater than 8 lb). Among high birth weight infants, there is a
  higher risk of birth trauma, metabolic issues, and other health problems (Klein and Lynch, 2018).
\3\ Values scaled from $2010 to $2021 using the medical care CPI (Bureau of Labor Statistics, 2021).

    Tables 46 to 49 provide the health effects avoided and valuation 
associated with birth weight impacts. EPA estimated that, over the 
evaluation period, the proposed rule will result in an average annual 
benefit from avoided reductions in birth weight from $139 million 
($2021, 7% discount rate) to $178 million ($2021, 3% discount rate).

                            Table 46--National Birth Weight Benefits, Proposed Option
                                  [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Increase in Birth Weight (millions of         114.2      209.3        329.7        114.2      209.3        329.7
 grams)...............................
Number of Birth Weight-Related Deaths         676.8    1,232.7      1,941.0        676.8    1,232.7      1,941.0
 Avoided..............................
Total Annualized Birth Weight Benefits       $97.36    $177.66      $279.49       $74.62    $139.01      $219.43
 (Million $2021) \2\..................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                               Table 47--National Birth Weight Benefits, Option 1a
                                         [PFOA and PFOS MCLs of 4.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Increase in Birth Weight (millions of         111.7      206.3        326.9        111.7      206.3        326.9
 grams)...............................
Number of Birth Weight-Related Deaths         665.4    1,214.7      1,915.4        665.4    1,214.7      1,915.4
 Avoided..............................
Total Annualized Birth Weight Benefits       $95.73    $175.05      $276.44       $74.66    $136.97      $217.02
 (Million $2021) \2\..................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                               Table 48--National Birth Weight Benefits, Option 1b
                                         [PFOA and PFOS MCLs of 5.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Increase in Birth Weight (millions of          97.6      181.9        292.1         97.6      181.9        292.1
 grams)...............................
Number of Birth Weight-Related Deaths         578.9    1,069.5      1,707.3        578.9    1,069.5      1,707.3
 Avoided..............................
Total Annualized Birth Weight Benefits       $83.27    $154.13      $246.43       $64.94    $120.59      $193.47
 (Million $2021) \2\..................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

[[Page 18709]]

                               Table 49--National Birth Weight Benefits, Option 1c
                                        [PFOA and PFOS MCLs of 10.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Increase in Birth Weight (millions of          51.0      109.2        195.3         51.0      109.2        195.3
 grams)...............................
Number of Birth Weight-Related Deaths         299.5      643.3      1,140.5        299.5      643.3      1,140.5
 Avoided..............................
Total Annualized Birth Weight Benefits       $43.22     $92.70      $164.19       $34.18     $72.51      $125.80
 (Million $2021) \2\..................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

2. Quantified Cardiovascular Effects
    CVD is one of the leading causes of premature mortality in the 
United States (D'Agostino et al., 2008; Goff et al., 2014; Lloyd-Jones 
et al., 2017). As discussed in EPA's Proposed Maximum Contaminant Level 
Goals for PFOA and PFOS in Drinking Water, exposure to PFOA and PFOS 
through drinking water contributes to increased serum PFOA and PFOS 
concentrations and potentially elevated levels of total cholesterol and 
elevated levels of systolic blood pressure (USEPA, 2023b; USEPA, 
2023c). Changes in total cholesterol and blood pressure are associated 
with changes in incidence of CVD events such as myocardial infarction 
(i.e., heart attack), ischemic stroke, and cardiovascular mortality 
occurring in populations without prior CVD event experience (D'Agostino 
et al., 2008; Goff et al., 2014; Lloyd-Jones et al., 2017).
    EPA recognizes that the epidemiologic literature that provides 
strong support for an effect of PFOA and PFOS on cholesterol and blood 
pressure does not provide direct support for an effect of PFOA and PFOS 
on the risk of CVD. Therefore, EPA uses the approach outlined below to 
link changes in CVD risk biomarkers (i.e., cholesterol and blood 
pressure) to changes in CVD risk.
    For each entry point, evaluation of the changes in CVD risk 
involves the following key steps:
    1. Estimation of annual changes in total cholesterol and blood 
pressure levels using exposure-response functions for the potential 
effects of serum PFOA/PFOS on these biomarkers;
    2. Estimation of the annual incidence of fatal and non-fatal first 
hard CVD events, defined as fatal and non-fatal myocardial infarction, 
fatal and non-fatal ischemic stroke or other coronary heart disease 
death occurring in populations without prior CVD event experience 
(D'Agostino et al., 2008; Goff et al., 2014; Lloyd-Jones et al., 2017), 
and post-acute CVD mortality corresponding to baseline and regulatory 
alternative total cholesterol and blood pressure levels in all 
populations alive during or born after the start of the evaluation 
period; and
    3. Estimation of the economic value of reducing CVD mortality and 
morbidity from baseline to regulatory alternative levels, using the 
Value of a Statistical Life and cost of illness measures, respectively.
    Given the breadth of evidence linking PFOA and PFOS exposure to 
effects on total cholesterol and blood pressure in general adult 
populations, EPA quantified public health impacts of changes in these 
well-established CVD risk biomarkers (D'Agostino et al., 2008; Goff et 
al., 2014; Lloyd-Jones et al., 2017) by estimating changes in incidence 
of several CVD events. Specifically, EPA assumed that PFOA/PFOS-related 
changes in total cholesterol and blood pressure had the same effect on 
the CVD risk as the changes unrelated to chemical exposure and used the 
Pooled Cohort Atherosclerotic Cardiovascular Disease (ASCVD) model 
(Goff et al., 2014) to evaluate their impacts on the incidence of 
myocardial infarction, ischemic stroke, and cardiovascular mortality 
occurring in populations without prior CVD event experience.
    The ASCVD model includes total cholesterol as a predictor of first 
hard CVD events. EPA did not identify any readily available 
relationships for PFOA or PFOS and total cholesterol that were 
specifically relevant to the age group of interest (40-89 years, the 
years for which the ASCVD model estimates the probability of a first 
hard CVD event). Therefore, the Agency developed a meta-analysis of 
studies reporting associations between serum PFOA or PFOS and total 
cholesterol in general populations (e.g., populations that are not a 
subset of workers or pregnant women). Statistical analyses that combine 
the results of multiple studies, such as meta-analyses, are widely 
applied to investigate the associations between contaminant levels and 
associated health effects. Such analyses are suitable for economic 
assessments because they can improve precision and statistical power 
(Engels et al., 2000; Deeks, 2002; R[uuml]cker et al., 2009).
    EPA identified 14 studies from which to derive slope estimates for 
PFOA and PFOS associations with serum total cholesterol levels. 
Appendix A to USEPA (2023i) provides further detail on the studies 
selection criteria, meta-data development, meta-analysis results, and 
discussion of the uncertainty and limitations inherent in EPA's 
exposure-response analysis.
    EPA developed exposure-response relationships between serum PFOA/
PFOS and total cholesterol for use in the CVD analysis using the meta-
analyses restricted to studies of adults in the general population 
reporting similar models. When using studies reporting linear 
associations between total cholesterol and serum PFOA or PFOS, EPA 
estimated a positive increase in total cholesterol of 1.57 (95% CI: 
0.02, 3.13) mg/dL per ng/mL serum PFOA (p-value=0.048), and of 0.08 
(95% CI: -0.01, 0.16) mg/dL per ng/mL serum PFOS (p-value=0.064). Based 
on the systematic review conducted by EPA to develop EPA's Proposed 
Maximum Contaminant Level Goals for PFOA and PFOS in Drinking Water, 
the available evidence supports a positive association between PFOS and 
total cholesterol in the general population. For more information on 
the systematic review and results, see USEPA, 2023b and USEPA, 2023c.
    PFOS exposure has been linked to other cardiovascular outcomes, 
such as systolic blood pressure and hypertension (Liao et al., 2020; 
USEPA,

[[Page 18710]]

2023c). Because systolic blood pressure is another predictor used by 
the ASCVD model, EPA included the estimated changes in blood pressure 
from reduced exposure to PFOS in the CVD analysis. EPA selected the 
slope from the Liao et al. (2020) study--a high confidence study 
conducted based on U.S. general population data from NHANES cycles 
2003-2012. The evidence on the associations between PFOA and blood 
pressure is not as consistent as for PFOS. Therefore, EPA is not 
including effect estimates for the serum PFOA-blood pressure 
associations in the CVD analysis.
    EPA relies on the life table-based approach to estimate CVD risk 
reductions because (1) changes in serum PFOA/PFOS in response to 
changes in drinking water PFOA/PFOS occur over multiple years, (2) CVD 
risk, relying on the ASCVD model, can be modeled only for those older 
than 40 years without prior CVD history, and (3) individuals who have 
experienced non-fatal CVD events have elevated mortality implications 
immediately and within at least five years of the first occurrence. 
Recurrent life table calculations are used to estimate a PWS entry 
point-specific annual time series of CVD event incidence for a 
population cohort characterized by sex, race/ethnicity, birth year, age 
at the start of the PFOA/PFOS evaluation period (i.e., 2023), and age- 
and sex-specific time series of changes in total cholesterol and blood 
pressure levels obtained by combining serum PFOA/PFOS concentration 
time series with exposure-response information. Baseline and regulatory 
alternatives are evaluated separately, with regulatory alternative 
total cholesterol and blood pressure levels estimated using baseline 
information on these biomarkers from external statistical data sources 
and modeled changes in total cholesterol and blood pressure due to 
conditions under the regulatory alternatives.
    EPA estimated the incidence of first hard CVD events based on total 
cholesterol serum and blood pressure levels using the ASCVD model (Goff 
et al., 2014), which predicts the 10-year probability of a hard CVD 
event to be experienced by a person without a prior CVD history. EPA 
adjusted the modeled population cohort to exclude individuals with pre-
existing conditions, as the ASCVD risk model does not apply to these 
individuals. For blood pressure effects estimation, EPA further 
restricts the modeled population to those not using antihypertensive 
medications for consistency with the exposure-response relationship. 
Modeled first hard CVD events include fatal and non-fatal myocardial 
infarction, fatal and non-fatal ischemic stroke, and other coronary 
heart disease mortality. EPA also has estimated the incidence of post-
acute CVD mortality among survivors of the first myocardial infarction 
or ischemic stroke within 6 years of the initial event.
    The estimated CVD risk reduction resulting from reducing serum PFOA 
and serum PFOS concentrations is the difference in annual incidence of 
CVD events (i.e., mortality and morbidity associated with first-time 
CVD events and post-acute CVD mortality) under the baseline and 
regulatory alternatives. Appendix G to USEPA (2023i) provides detailed 
information on all CVD model components, computations, and sources of 
data used in modeling.
    EPA uses the Value of a Statistical Life to estimate the benefits 
of reducing mortality associated with hard CVD events in the population 
exposed to PFOA and PFOS in drinking water. EPA relies on cost of 
illness-based valuation that represents the medical costs of treating 
or mitigating non-fatal first hard CVD events (myocardial infarction, 
ischemic stroke) during the three years following an event among those 
without prior CVD history, adjusted for post-acute mortality.
    The annual medical expenditure estimates for myocardial infarction 
and ischemic stroke are based on O'Sullivan et al. (2011). The 
estimated expenditures do not include long-term institutional and home 
health care. For non-fatal myocardial infarction, O'Sullivan et al. 
(2011) estimated medical expenditures are $51,173 ($2021) for the 
initial event and then $31,871, $14,065, $12,569 annually within 1, 2, 
and 3 years after the initial event, respectively. For non-fatal 
ischemic stroke, O'Sullivan et al. (2011) estimated medical 
expenditures are $15,861 ($2021) for the initial event and then 
$11,521, $748, $1,796 annually within 1, 2, and 3 years after the 
initial event, respectively. Annual estimates within 1, 2, and 3 years 
after the initial event include the incidence of secondary CVD events 
among survivors of first myocardial infarction and ischemic stroke 
events.
    To estimate the present discounted value of medical expenditures 
within 3 years of the initial non-fatal myocardial infarction, EPA 
combined O'Sullivan et al. (2011) myocardial infarction-specific 
estimates with post-acute survival probabilities based on Thom et al. 
(2001) (for myocardial infarction survivors aged 40-64) and Li et al. 
(2019) (for myocardial infarction survivors aged 65+). To estimate the 
present discounted value of medical expenditures within 3 years of the 
initial non-fatal ischemic stroke, EPA combined O'Sullivan et al. 
(2011) ischemic stroke-specific estimates with post-acute survival 
probabilities based on Thom et al. (2001) (for ischemic stroke 
survivors aged 40-64, assuming post-acute myocardial infarction 
survival probabilities reasonably approximate post-acute ischemic 
stroke survival probabilities) and Li et al. (2019) (for ischemic 
stroke survivors aged 65+). EPA did not identify post-acute ischemic 
stroke mortality information in this age group, but instead applied 
post-acute myocardial infarction mortality estimates for ischemic 
stroke valuation. Table 50 presents the resulting myocardial infarction 
and ischemic stroke unit values.

               Table 50--Cost of Illness-Based Value of Non-Fatal First CVD Event Used in Modeling
----------------------------------------------------------------------------------------------------------------
                                                                                  Present discounted value of 3-
                                                                                     year medical expenditures
                                                                                   ($2021) \1\ \2\, adjusted for
    Type of first non-fatal hard CVD event                  Age group                post-acute mortality \3\
                                                                                 -------------------------------
                                                                                    3% discount     7% discount
                                                                                       rate            rate
----------------------------------------------------------------------------------------------------------------
Myocardial Infarction (MI)....................  40-65 years.....................        $105,419        $104,155
                                                66+ years.......................          92,658          91,881
Ischemic Stroke (IS)..........................  40-65 years.....................          29,154          29,017
                                                66+ years.......................          26,844          26,762
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Estimates of annual medical expenditures are from O'Sullivan et al. (2011);

[[Page 18711]]

 
\2\ Original values from O'Sullivan et al. (2011) were inflated to $2021 using the medical care CPI (Bureau of
  Labor Statistics, 2021);
\3\ Post-acute myocardial infarction mortality data for those aged 40-64 years is from Thom et al. (2001);
  probabilities to survive 1 year, 2 years, and 3 years after the initial event are 0.93, 0.92, and 0.90,
  respectively. EPA applies these mortality values to derive the ischemic stroke value in this age group. Post-
  acute myocardial infarction mortality data and post-acute IS mortality data for persons aged 65 and older are
  from Li et al. (2019). For myocardial infarction, probabilities to survive 1 year, 2 years, and 3 years after
  the initial event are 0.68, 0.57, and 0.49, respectively. For ischemic stroke, probabilities to survive 1
  year, 2 years, and 3 years after the initial event are 0.67, 0.57, and 0.48, respectively.

    Table 51 to Table 54 provide the health effects avoided and 
valuation associated with CVD. EPA estimated that, over the evaluation 
period, the proposed option will result in an average annual benefit 
from avoided CVD cases and deaths from $421 million ($2021, 7% discount 
rate) to $533 million ($2021, 3% discount rate).

                                Table 51--National CVD Benefits, Proposed Option
                                  [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal MI Cases Avoided..      1,251.5    6,081.0     11,738.7      1,251.5    6,081.0     11,738.7
Number of Non-Fatal IS Cases Avoided..      1,814.0    8,870.8     17,388.5      1,814.0    8,870.8     17,388.5
Number of CVD Deaths Avoided..........        753.6    3,584.6      7,030.9        753.6    3,584.6      7,030.9
Total Annualized CVD Benefits (Million      $111.78    $533.48    $1,051.00       $85.94    $421.10      $822.88
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                                   Table 52--National CVD Benefits, Option 1a
                                         [PFOA and PFOS MCLs of 4.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal MI Cases Avoided..      1,248.7    5,983.8     11,614.9      1,248.7    5,983.8     11,614.9
Number of Non-Fatal IS Cases Avoided..      1,786.4    8,729.6     17,149.5      1,786.4    8,729.6     17,149.5
Number of CVD Deaths Avoided..........        744.6    3,527.8      6,951.5        744.6    3,527.8      6,951.5
Total Annualized CVD Benefits (Million      $110.45    $525.05    $1,035.36       $86.32    $414.45      $817.79
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                                   Table 53--National CVD Benefits, Option 1b
                                         [PFOA and PFOS MCLs of 5.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal MI Cases Avoided..      1,105.9    5,220.7     10,215.4      1,105.9    5,220.7     10,215.4
Number of Non-Fatal IS Cases Avoided..      1,609.3    7,624.2     15,029.5      1,609.3    7,624.2     15,029.5
Number of CVD Deaths Avoided..........        645.9    3,084.6      6,102.2        645.9    3,084.6      6,102.2
Total Annualized CVD Benefits (Million       $99.73    $459.09      $908.82       $72.72    $362.42      $717.85
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

[[Page 18712]]

                                   Table 54--National CVD Benefits, Option 1c
                                        [PFOA and PFOS MCLs of 10.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal MI Cases Avoided..        619.0    3,032.5      6,320.7        619.0    3,032.5      6,320.7
Number of Non-Fatal IS Cases Avoided..        878.1    4,445.9      9,439.4        878.1    4,445.9      9,439.4
Number of CVD Deaths Avoided..........        343.8    1,806.7      3,835.8        343.8    1,806.7      3,835.8
Total Annualized CVD Benefits (Million       $51.00    $268.78      $571.32       $41.85    $212.18      $450.51
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

3. Quantified Kidney Cancer Effects
    Data on the association between PFOA exposure and kidney cancer 
(i.e., RCC) are limited but suggest a positive association between 
exposure and increased risk of RCC. Epidemiology studies indicated that 
exposure to PFOA was associated with an increased risk of RCC 
(California Environmental Protection Agency, 2021; USEPA, 2016e; ATSDR, 
2021; USEPA, 2023b). In the PFOA HESD (USEPA, 2016e), EPA characterized 
the evidence for PFOA effects on RCC as ``probable'' based on two 
occupational population studies (Raleigh et al., 2014; Steenland and 
Woskie, 2012) and two high-exposure community studies (Vieira et al., 
2013; Barry et al., 2013). A recent study of the relationship between 
PFOA and RCC in U.S. general populations found strong evidence that 
exposure to PFOA causes RCC in humans (Shearer et al., 2021). As such, 
EPA selected RCC as a key outcome when assessing the health impacts of 
reduced PFOA exposures.
    EPA quantified and valued the changes in RCC risk associated with 
reductions in serum PFOA levels that are in turn associated with 
reductions in drinking water PFOA concentrations under the regulatory 
alternatives. PWS entry point-specific time series of the differences 
between serum PFOA concentrations under baseline and regulatory 
alternatives are inputs into this analysis. For each PWS entry point, 
evaluation of the changes in RCC impacts involves the following key 
steps:
    1. Estimating the changes in RCC risk based on modeled changes in 
serum PFOA levels and the exposure-response function for the effect of 
serum PFOA on RCC;
    2. Estimating the annual incidence of RCC cases and excess 
mortality among those with RCC in all populations corresponding to 
baseline and regulatory alternative RCC risk levels, as well as 
estimating the regulatory alternative-specific reduction in cases 
relative to the baseline, and
    3. Estimating the economic value of reducing RCC mortality from 
baseline to regulatory alternative levels, using the Value of a 
Statistical Life and cost of illness measures, respectively.
    To identify an exposure-response function, EPA reviewed three 
studies highlighted in the HESD for PFOA (USEPA, 2016e) and a recent 
study discussed in both the California Environmental Protection 
Agency's Office of Environmental Health Hazard Assessment (OEHHA) PFOA 
Public Health Goals report (California Environmental Protection Agency, 
2021) and EPA's Proposed Maximum Contaminant Level Goal (MCLG) for PFOA 
(USEPA, 2023b). Steenland et al. (2015) observed an increase in kidney 
cancer deaths among workers with high exposures to PFOA. Vieira et al. 
(2013) found that kidney cancer was positively associated with high and 
very high PFOA exposures. Barry et al. (2013) found a slight trend in 
cumulative PFOA serum exposures and kidney cancer among the C8 Health 
Project population. In a large case-control general population study of 
the relationship between PFOA and kidney cancer in 10 locations across 
the U.S., Shearer et al. (2021) found strong evidence that exposure to 
PFOA causes RCC, the most common form of kidney cancer, in humans.
    To evaluate changes between baseline and regulatory alternative RCC 
risk resulting from reduced exposure to PFOA, EPA relied on the 
estimated time series of changes in serum PFOA concentrations (Section 
6.3) and the serum-RCC exposure-response function provided by Shearer 
et al. (2021): 0.00178 (ng/mL)-1. The analysis from Shearer et al. 
(2021) was designed as a case-control study with population controls 
based on 10 sites within the U.S. population. Shearer et al. (2021) 
included controls for age, sex, race, ethnicity, study center, year of 
blood draw, smoking, and hypertension. Results showed a strong and 
statistically significant association between PFOA and RCC. EPA 
selected the exposure-response relationship from Shearer et al. (2021) 
because it included exposure levels typical in the general population 
and was found to have a low risk of bias based on EPA's Proposed 
Maximum Contaminant Level Goal for PFOA (USEPA, 2023b).
    The linear slope factor based on Shearer et al. (2021) enables 
estimation of the changes in lifetime RCC risk associated with reduced 
lifetime serum PFOA levels. Because baseline RCC incidence statistics 
are not readily available from the NCI public use data, EPA used kidney 
cancer statistics in conjunction with an assumption that RCC comprises 
90% of all kidney cancer cases to estimate baseline lifetime 
probability of RCC (USEPA, 2023b). EPA estimated the baseline lifetime 
RCC incidence for males at 1.89% and the baseline lifetime RCC 
incidence for females at 1.05%. Details of these calculations are 
provided in Appendix H to USEPA (2023i).
    Similar to its approach for estimating of CVD risk reductions, EPA 
relies on the life table approach to estimate RCC risk reductions. The 
outputs of the life table calculations are the PWS entry point-specific 
estimates of the annual change in the number of RCC cases and the 
annual change in excess RCC population mortality. For more detail on 
EPA's application of the life table to cancer benefits analyses, please 
see Appendix H to USEPA (2023j).
    Although the change in PFOA exposure likely affects the risk of 
developing RCC beyond the end of the

[[Page 18713]]

analysis period (the majority of RCC cases manifest during the latter 
half of the average individual lifespan; see Appendix H to USEPA 
(2023j), EPA does not capture effects after the end of the period of 
analysis, 2104. Individuals alive after the end of the period of 
analysis likely benefit from lower lifetime exposure to PFOA. Lifetime 
health risk model data sources include EPA SDWIS, age-, sex-, and race/
ethnicity-specific population estimates from the U.S. Census Bureau 
(2020), the Surveillance, Epidemiology, and End Results (SEER) program 
database (Surveillance Research Program--National Cancer Institute, 
202a; 2020b), and the Centers for Disease Control and Prevention (CDC) 
NCHS. Appendix H to USEPA (2023i) provides additional detail on the 
data sources and information used in this analysis as well as baseline 
kidney cancer statistics. Appendix B to USEPA (2023i) describes 
estimation of the affected population.
    EPA uses the Value of a Statistical Life to estimate the benefits 
of reducing mortality associated with RCC in the population exposed to 
PFOA in drinking water. EPA uses the cost of illness-based valuation to 
estimate the benefits of reducing morbidity associated with RCC.
    EPA used the medical cost information from a recent RCC cost-
effectiveness study by Ambavane et al. (2020) to develop cost of 
illness estimates for RCC morbidity. Ambavane et al. (2020) used a 
discrete event simulation model to estimate the lifetime treatment 
costs of several RCC treatment sequences, which included first and 
second line treatment medication costs, medication administration 
costs, adverse effect management costs, and disease management costs 
on- and off-treatment. To this end, the authors combined RCC cohort 
data from CheckMate 214 clinical trial and recent US-based healthcare 
cost information assembled from multiple sources (see supplementary 
information from Ambavane et al. (2020)). Ambavane et al. (2020) found 
that RCC treatment sequences using a combination of two immunotherapy 
drugs as the first line medications were the most cost-effective.
    Table 55 summarizes RCC morbidity cost of illness estimates derived 
by EPA using Ambavane et al. (2020)-reported disease management costs 
on- and off-treatment along with medication, administration, and 
adverse effect management costs for the first line treatment that 
initiated the most cost-effective treatment sequences as identified by 
Ambavane et al. (2020), i.e., the nivolumab/ipilimumab drug 
combination. This is a forward-looking valuation approach in that it 
assumes that the clinical practice would follow the treatment 
recommendations in Ambavane et al. (2020) and other recent studies 
cited therein. EPA notes that the second line treatment costs are not 
reflected in EPA's cost of illness estimates, because Ambavane et al. 
(2020) did not report information on the expected durations of the 
treatment-free interval (between the first line treatment 
discontinuation and the second line treatment initiation) and the 
second line treatment phase, conditional on survival beyond 
discontinuation of the second line treatment. As such, EPA valued RCC 
morbidity at $251,007 ($2021) during year 1 of the diagnosis, $190,969 
($2021) during year 2 of the diagnosis, and $1,596 ($2021) starting 
from year 3 of the diagnosis. Additionally, EPA assumed that for 
individuals with RCC who die during the specific year, the entire year-
specific cancer treatment regimen is applied prior to the death event. 
This may overestimate benefits if a person does not survive the entire 
year.

                                                            Table 55--RCC Morbidity Valuation
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                            First line
                                                            First line      First line    adverse effect      Disease
                      Time interval                         medication    administration    management      management     Total ($2018)   Total ($2021)
                                                            ($2018) \1\     ($2018) \1\     ($2018) \1\     ($2018) \1\                         \4\
                                                                                                \3\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Monthly cost, month 1-3 from diagnosis \1\ \5\..........          32,485             516              78              73          33,152          35,927
Monthly cost, month 4-24 from diagnosis \2\ \6\.........          13,887             647              78              73          14,685          15,914
Monthly cost, month 25+ from diagnosis \7\..............  ..............  ..............  ..............             123             123             133
Annual cost, year 1 from diagnosis......................         222,438           7,371             934             878         231,621         251,007
Annual cost, year 2 from diagnosis......................         166,644           7,764             934             878         176,220         190,969
Annual cost, year 3+ from diagnosis.....................  ..............  ..............  ..............           1,473           1,473           1,596
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
\1\ Ambavane et al. (2020) Table 1.
\2\ Ambavane et al. (2020) p. 41, a maximum treatment duration assumption of 2 years.
\3\ The adverse effect management costs of $1,868 in Ambavane et al. (2020) Table 1 were reported for the treatment duration. EPA used the treatment
  duration of 24 months (i.e., 2 years) to derive monthly costs of $77.83.
\4\ To adjust for inflation, EPA used U.S. BLS CPI for All Urban Consumers: Medical Care Services in U.S. (City Average).
\5\ First line treatment induction.
\6\ First line treatment maintenance.
\7\ Treatment-free interval.

    Tables 56 to 59 provide the health effects avoided and valuation 
associated with RCC. EPA estimated that, over the evaluation period, 
the proposed rule will result in an average annual benefit from avoided 
RCC cases and deaths from $217 million ($2021, 7% discount rate) to 
$301 million ($2021, 3% discount rate).

[[Page 18714]]

                                Table 56--National RCC Benefits, Proposed Option
                                  [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal RCC Cases Avoided.      1,313.6    6,872.0     17,387.8      1,313.6    6,872.0     17,387.8
Number of RCC-Related Deaths Avoided..        308.7    1,927.8      5,049.3        308.7    1,927.8      5,049.3
Total Annualized RCC Benefits (Million       $54.23    $300.56      $758.03       $45.36    $217.37      $515.89
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                                   Table 57--National RCC Benefits, Option 1a
                                         [PFOA and PFOS MCLs of 4.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal RCC Cases Avoided.      1,289.6    6,753.3     17,147.8      1,289.6    6,753.3     17,147.8
Number of RCC-Related Deaths Avoided..        300.5    1,895.2      4,960.4        300.5    1,895.2      4,960.4
Total Annualized RCC Benefits (Million       $52.92    $295.53      $744.64       $45.09    $213.78      $508.56
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                                   Table 58--National RCC Benefits, Option 1b
                                         [PFOA and PFOS MCLs of 5.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal RCC Cases Avoided.      1,017.6    5,681.7     14,962.1      1,017.6    5,681.7     14,962.1
Number of RCC-Related Deaths Avoided..        235.9    1,602.1      4,317.6        235.9    1,602.1      4,317.6
Total Annualized RCC Benefits (Million       $42.28    $250.60      $643.71       $36.32    $182.24      $446.80
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

                                   Table 59--National RCC Benefits, Option 1c
                                        [PFOA and PFOS MCLs of 10.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal RCC Cases Avoided.        433.5    2,903.0      8,205.4        433.5    2,903.0      8,205.4
Number of RCC-Related Deaths Avoided..        101.1      831.8      2,406.2        101.1      831.8      2,406.2
Total Annualized RCC Benefits (Million       $18.58    $131.44      $367.38       $17.34     $97.30      $260.54
 $2021) \2\...........................
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.

[[Page 18715]]

 
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized total annualized benefits in this table.

4. Key Limitations and Uncertainties in the Benefits Analysis
    The section below discusses the uncertainty information 
incorporated in the quantitative benefits analysis. There are 
additional sources of uncertainty and limitations that could not be 
modeled quantitatively as part of the national benefits analysis. These 
sources of uncertainty are characterized in detail in Section 6.8 of 
USEPA (2023j). This summary includes uncertainties that are specific to 
application of PK models for blood serum PFAS concentration estimation, 
developmental effects (i.e., infant birth weight) modeling, CVD impacts 
modeling, RCC impacts modeling, and modeling of bladder cancer impacts 
from GAC treatment-related reductions in the sum of four 
trihalomethanes (THM4). Table 60 below presents the key limitations and 
uncertainties that apply to the benefits analysis for the proposed 
rule. EPA notes that in most cases it is not possible to judge the 
extent to which a particular limitation or uncertainty could affect the 
magnitude of the estimated benefits. Therefore, in each table below, 
EPA notes the potential direction of the impact on the quantified 
benefits (e.g., a source of uncertainty that tends to underestimate 
quantified benefits indicates expectation for larger quantified 
benefits) but does not prioritize the entries with respect to the 
impact magnitude.

  Table 60--Key Limitations and Uncertainties That Apply to Benefits Analyses Considered for the Proposed PFAS
                                                      Rule
----------------------------------------------------------------------------------------------------------------
                                              Effect on  benefits
         Uncertainty/assumption                     estimate                             Notes
----------------------------------------------------------------------------------------------------------------
EPA quantified benefits for three health  Underestimate..............  For various reasons, EPA has not
 endpoints for PFOA and PFOS.                                           quantified the benefit of removing PFOA
                                                                        and PFOS from drinking water for most of
                                                                        the health endpoints PFOA and PFOS are
                                                                        expected to impact. See discussion in
                                                                        section C for more information about
                                                                        these nonquantifiable benefits.
EPA has only quantified benefits for one  Underestimate..............  Treatment technologies installed to
 co-removed contaminant group (THM4).                                   remove PFAS can also removes numerous
                                                                        other contaminants, including other
                                                                        unregulated PFAS, additional regulated
                                                                        and unregulated DBPs, heavy metals,
                                                                        organic contaminants, pesticides, among
                                                                        others. These co-removal benefits may be
                                                                        significant, depending on co-occurrence,
                                                                        how many facilities install treatment
                                                                        and which treatment option they select.
EPA has not quantified benefits for any   Underestimate..............  PFHxS, PFNA, PFBS, and HFPO-DA each have
 health endpoint for PFHxS, PFNA, PFBS,                                 substantial health impacts on multiple
 and HFPO-DA.                                                           health endpoints. See discussion in
                                                                        section D for more information about
                                                                        these nonquantifiable benefits.
The analysis considers PFOA/PFOS          Overestimate...............  Some SDWIS population served estimates
 concentrations from NTNCWSs.                                           for NTNCWSs represent the both the
                                                                        population that has regular exposure to
                                                                        the NTNCWS' drinking water (e.g., the
                                                                        employees at a location) and the peak
                                                                        day transient population (e.g.,
                                                                        customers) who have infrequent exposure
                                                                        to the NTNCWS' drinking water.
                                                                        Estimating the demographic distribution
                                                                        and the share of daily drinking water
                                                                        consumption for these two types of
                                                                        NTNCWS populations would be difficult
                                                                        across many of the industries which
                                                                        operate NTNCWSs. The inclusion of NTNCWS
                                                                        results is an overestimate of benefits
                                                                        because daily drinking water consumption
                                                                        for these populations is also modeled at
                                                                        their residential CWS.
EPA assumes that the effects of PFOA and  Uncertain..................  The exposure-response functions used in
 PFOS exposures are independent.                                        benefits analyses assume that the
                                                                        effects of serum PFOA/PFOS on the health
                                                                        outcomes considered are independent and
                                                                        therefore additive. Due to limited
                                                                        evidence, EPA does not consider
                                                                        synergies or antagonisms in PFOA/PFOS
                                                                        exposure-response.
The derivation of PFOA/PFOS exposure-     Overestimate...............  The new data and EPA's proposed MCLGs
 response functions for the relationship                                indicate that the levels at which
 between PFOA/PFOS serum and associated                                 adverse health effects could occur are
 health outcomes assumes that there are                                 much lower than previously understood
 no threshold serum concentrations below                                when EPA issued the 2016 health
 which effects do not occur.                                            advisories for PFOA and PFOS (70 parts
                                                                        per trillion or ppt)--including near
                                                                        zero for certain health effects.
                                                                        Therefore, the exposure-response
                                                                        functions used in benefits analyses
                                                                        assume that there are no threshold serum
                                                                        concentrations below which effects do
                                                                        not occur. This could result in a slight
                                                                        overestimate of benefits for certain
                                                                        health endpoints.
The exposure-response functions used to   Overestimate...............  Analyses evaluating the evidence on the
 estimate risk assume causality.                                        associations between PFAS exposure and
                                                                        health outcomes are ongoing and EPA has
                                                                        not conclusively determined causality.
                                                                        As described in Section 6.2, EPA modeled
                                                                        health risks from PFOA/PFOS exposure for
                                                                        endpoints for which the evidence of
                                                                        association was found to be likely.
                                                                        These endpoints include birth weight,
                                                                        total cholesterol, and RCC. While the
                                                                        evidence supporting causality between
                                                                        DBP exposure and bladder cancer has
                                                                        increased since EPA's Stage 2 DBP Rule
                                                                        (NTP, 2021; Weisman et al., 2022),
                                                                        causality has not yet been conclusively
                                                                        determined (Regli et al., 2015).

[[Page 18716]]

 
The analysis assumes that quantified      Uncertain..................  EPA did not model birth weight, CVD, RCC,
 benefits categories are additive.                                      and bladder cancer benefits jointly, in
                                                                        a competing risk framework. Therefore,
                                                                        reductions in health risk in a specific
                                                                        benefits category do not influence
                                                                        health risk reductions in another
                                                                        benefits category. For example, lower
                                                                        risk of CVD and associated mortality
                                                                        implies a larger population that could
                                                                        benefit from cancer risk reductions,
                                                                        because cancer incidence grows
                                                                        considerably later in life.
The analysis does not take into account   Underestimate..............  The benefits analysis does not reflect
 population growth and other changes in                                 the effects of growing population that
 long-term trends.                                                      may benefit from reduction in PFOA/PFOS
                                                                        exposure. Furthermore, EPA uses present-
                                                                        day information on life expectancy,
                                                                        disease, environmental exposure, and
                                                                        other factors, which are likely to
                                                                        change in the future.
For PWSs with multiple entry points, the  Uncertain..................  Data on the populations served by each
 analysis assumes a uniform population                                  entry point are not available and EPA
 distribution across the entry points.                                  therefore uniformly distributes system
                                                                        population across entry points. Effects
                                                                        of the regulatory alternative may be
                                                                        greater or smaller than estimated,
                                                                        depending on actual populations served
                                                                        by affected entry points. For one large
                                                                        system serving more than one million
                                                                        customers EPA has sufficient data on
                                                                        entry point flow to proportionally
                                                                        assign effected populations.
EPA does not characterize uncertainty     Uncertain..................  EPA did not quantitatively characterize
 associated with the Value of                                           the uncertainty for the VSL reference
 Statistical Life (VSL) reference value                                 value and income elasticity. Because the
 or VSL elasticity.                                                     economic value of avoided premature
                                                                        mortality comprises the majority of the
                                                                        overall benefits estimate, not
                                                                        considering uncertainty surrounding the
                                                                        VSL is a limitation.
----------------------------------------------------------------------------------------------------------------

E. Nonquantifiable Benefits of PFOA and PFOS Exposure Reduction

    In this section EPA qualitatively discusses the potential health 
benefits resulting from reduced exposure to PFOA and PFOS in drinking 
water. These nonquantifiable benefits are expected to be realized as 
avoided adverse health effects as a result of the proposed NPDWR, in 
addition to the benefits that EPA has quantified. EPA anticipates 
additional benefits associated with developmental, cardiovascular, 
liver, immune, endocrine, metabolic, reproductive, musculoskeletal, and 
carcinogenic effects beyond those benefits associated with decreased 
PFOA and PFOS that EPA has quantified. The evidence for these adverse 
health effects is briefly summarized below.
    EPA identified a wide range of potential health effects associated 
with exposure to PFOA and PFOS using five comprehensive Federal 
government documents that summarize the recent literature on PFAS 
(mainly PFOA and PFOS) exposure and its health impacts: EPA's Health 
Effects Support Documents for PFOA and PFOS, hereafter referred to as 
EPA HESDs (USEPA, 2016e; USEPA, 2016f); EPA's Proposed Maximum 
Contaminant Level Goals for PFOA and PFOS in Drinking Water (USEPA, 
2023b; USEPA, 2023c); and the U.S. Department of Health and Human 
Services Agency for Toxic Substances and Disease Registry's (ATSDR) 
Toxicological Profile for Perfluoroalkyls (ATSDR, 2021). Each source 
presents comprehensive literature reviews on adverse health effects 
associated with PFOA and PFOS. EPA notes that the National Academies of 
Science, Engineering, and Medicine also published a report which 
includes a review of the adverse health effects for numerous PFAS 
(NASEM 2022). That document is included in the docket for this proposed 
rulemaking.
    The most recent literature reviews on PFAS exposures and health 
impacts, which are included in EPA's Proposed Maximum Contaminant Level 
Goal for PFOA and PFOS in Drinking Water (USEPA, 2023b; USEPA, 2023c), 
discuss the weight of evidence supporting associations between PFOA or 
PFOS exposure with health outcomes as indicative (likely), inadequate, 
or suggestive. For the purposes of the reviews conducted to develop the 
proposed MCLGs, an association is deemed indicative when findings are 
consistent and supported by substantial evidence. The association is 
inadequate if there is a lack of information or an inability to 
interpret the available evidence (e.g., findings across studies). The 
association is suggestive if findings are consistent but supported by a 
limited number of studies or analyses, or only observed in certain 
populations or species. Note that these determinations are based on 
information available as of February 2022.
    Developmental effects: Exposure to PFOA and PFOS during 
developmental life stages is linked to developmental effects including 
but not limited to the infant birth weight effects that EPA quantified. 
Other developmental effects include SGA, birth length, head 
circumference at birth, and other effects (Verner et al., 2015; USEPA, 
2016e; USEPA, 2016f; Negri et al., 2017; ATSDR, 2021; Waterfield et 
al., 2020; USEPA, 2023b; USEPA, 2023c). SGA is a developmental health 
outcome of interest when studying potential effects of PFOA/PFOS 
exposure because SGA infants have increased health risks during 
pregnancy and delivery as well as post-delivery (Osuchukwu and Reed, 
2022). Epidemiology evidence related to PFOA/PFOS exposure was mixed; 
some studies reported increased risk of SGA with PFOA/PFOS exposure, 
while other studies observed null results (USEPA, 2023b; USEPA, 2023c). 
For instance, some studies suggested a potentially positive association 
between PFOA exposure and SGA (Govarts et al., 2018; Lauritzen et al., 
2017; Y. Wang et al., 2016; USEPA, 2023b). For PFOS, few patterns were 
discernible, and overall confidence of an association between the two 
factors was low (USEPA, 2023c). Similarly, ATSDR found no strong 
associations between PFOA or PFOS exposure and increases in risk of SGA 
infants (ATSDR, 2021). Toxicology studies on PFOS exposures in rodents 
reported effects on multiple developmental toxicity endpoints 
(including increased mortality, decreased BW and BW change, skeletal 
and soft tissue effects, and delayed eye-opening) (USEPA, 2023c). For 
additional details on developmental studies and their individual 
outcomes, see Chapter 3.4.1 (Developmental) in USEPA (2023b) and USEPA 
(2023c).

[[Page 18717]]

    Cardiovascular effects: In addition to the CVD effects that EPA 
quantified associated with changes in total cholesterol and blood 
pressure from exposure to PFOA or PFOS (see Section 6.2 of USEPA 
(2023j)), available evidence suggests an association between exposure 
to PFOA or PFOS and increased LDLC (ATSDR, 2021; USEPA, 2023b; USEPA, 
2023c). High levels of LDLC lead to the buildup of cholesterol in the 
arteries, which can raise the risk of heart disease and stroke. 
Epidemiology studies showed a positive association between PFOA or PFOS 
exposure and LDLC levels in children (USEPA, 2023b; USEPA, 2023c). In 
particular, the evidence suggested positive associations between serum 
PFOA and PFOS levels and LDLC levels in adolescents ages 12-18, while 
positive associations between serum levels and LDLC levels in younger 
children were observed only for PFOA (ATSDR, 2021). Studies conducted 
on PFOS showed evidence of an association between exposure and LDLC 
levels in adults. For instance, all five epidemiology studies evaluated 
in EPA's Proposed MCLGs for PFOA and PFOS in Drinking Water reported 
positive associations, although the association was only statistically 
significant in obese women. Available evidence regarding the impact of 
PFOA and PFOS exposure on pregnant women was too limited for EPA to 
determine an association (ATSDR, 2021; USEPA, 2023b; USEPA, 2023c). For 
additional details on LDLC studies and their individual outcomes, see 
Chapter 3.4.4 (Cardiovascular) in USEPA (2023b) and USEPA (2023c).
    Liver effects: Several biomarkers can be used clinically to 
diagnose liver diseases, including the ALT. High levels of serum ALT 
may indicate liver damage. Epidemiology data provides consistent 
evidence of a positive association between PFOS/PFOA exposure and ALT 
levels in adults (ATSDR, 2021; USEPA, 2023b; USEPA, 2023c). Studies of 
adults showed consistent evidence of a positive association between 
PFOA exposure and elevated ALT levels at both high exposure levels and 
exposure levels typical of the general population (USEPA, 2023b). There 
is also consistent epidemiology evidence of associations between PFOS 
and elevated ALT levels, although the associations observed were not 
large in magnitude. Study results showed inconsistent evidence on 
whether the observed changes led to changes in specific liver disease 
(USEPA, 2023c).
    Associations between PFOS/PFOA exposure and ALT levels in children 
were less consistent than in adults (USEPA, 2023b; USEPA, 2023c), and 
PFOA toxicology studies showed increases in ALT and other liver enzymes 
across multiple species, sexes, and exposure paradigms (USEPA, 2023b). 
Toxicology studies on the impact of PFOS exposure on ALT in rodents 
also reported increases in ALT and other liver enzyme levels in 
rodents, though these increases were modest (USEPA, 2023c). For 
additional details on the ALT studies and their individual outcomes, 
see Section 3.4.2 (Hepatic) in USEPA (2023b) and USEPA (2023c).
    Immune effects: Proper antibody response helps maintain the immune 
system by recognizing and responding to antigens. Some evidence 
suggests a relationship between PFOA exposure and immunosuppression; 
epidemiology studies showed suppression of at least one measure of the 
antibody response for tetanus and diphtheria among people with higher 
prenatal, childhood, and adult serum concentrations of PFOA (USEPA, 
2023b). It is less clear whether PFOA exposure impacts antibody 
response to vaccinations other than tetanus and diphtheria (ATSDR, 
2021; USEPA, 2023b). Epidemiology evidence suggests that children with 
preexisting immunological conditions are particularly susceptible to 
immunosuppression associated with PFOA exposure (USEPA, 2023b). 
Available studies supported an association between PFOS exposure and 
immunosuppression in children, where increased PFOS serum levels were 
associated with decreased antibody production (USEPA, 2023c). However, 
the association between PFOS exposure and immunosuppression was not 
apparent in adults (USEPA, 2023c).\8\ Other potential associations with 
PFOS exposure with a high degree of uncertainty included asthma and 
infectious diseases (e.g., the common cold, lower respiratory tract 
infections, pneumonia, bronchitis, ear infections) (USEPA, 2023c). 
Animal toxicology study evidence suggested that PFOA or PFOS exposure 
results in effects similarly indicating immune suppression, such as 
reduced response of immune cells (e.g., natural killer cell activity 
and immunoglobulin production) (USEPA, 2023b; USEPA, 2023c). For 
additional details on antibody studies and their individual outcomes, 
see Section 3.4.3 (Immune) in USEPA (2023b) and USEPA (2023c).
---------------------------------------------------------------------------

    \8\ This may be due to the lack of high-quality data at present.
---------------------------------------------------------------------------

    Endocrine effects: Elevated thyroid hormone levels can accelerate 
metabolism and cause irregular heartbeat; low levels of thyroid hormone 
can cause neurodevelopmental effects, tiredness, weight gain, and 
increased susceptibility to the common cold. There is suggestive 
evidence of a positive association between PFOA/PFOS exposure and 
thyroid hormone disruption (ATSDR, 2021; USEPA, 2023b; USEPA, 2023c). 
Epidemiology studies reported inconsistent evidence regarding 
associations between PFOA or PFOS exposure and general endocrine 
outcomes, such as thyroid disease, hypothyroidism, and hypothyroxinemia 
(USEPA, 2023b; USEPA, 2023c). However, studies reported suggestive 
evidence of positive associations for thyroid stimulating hormone (TSH) 
in adults, and the thyroid hormone thyroxine (T4) in children (USEPA, 
2023b; USEPA, 2023c). Toxicology studies indicated that PFOA and PFOS 
exposure leads to decreases in thyroid hormone levels \9\ and adverse 
effects to the endocrine system (ATSDR, 2021; USEPA, 2023b; USEPA, 
2023c). Despite uncertainty around the applicability of animal studies 
in this area, changes in thyroid hormone levels in animals did indicate 
adverse effects after PFOS and PFOA exposure that is relevant to humans 
(USEPA, 2023b; USEPA, 2023c). For additional details on endocrine 
effects studies and their individual outcomes, see Chapter C.2 
(Endocrine) in USEPA (2023k) and USEPA (2023l).
---------------------------------------------------------------------------

    \9\ Decreased thyroid hormone levels are associated with effects 
such as changes in thyroid and adrenal gland weight, hormone 
fluctuations, and organ histopathology (ATSDR, 2021; USEPA, 2023b; 
USEPA, 2023c).
---------------------------------------------------------------------------

    Metabolic effects: Leptin is a hormone that controls hunger, and 
high leptin levels are associated with obesity, overeating, and 
inflammation (e.g., of adipose tissue, the hypothalamus, blood vessels, 
and other areas). Evidence suggests a direct association between PFOA 
exposure and leptin levels in the general adult population (ATSDR, 
2021; USEPA, 2023b). Based on a review of 69 human epidemiology 
studies, evidence of associations between PFOS and metabolic outcomes 
appears inconsistent, but in some studies, suggestive evidence was 
observed between PFOS exposure and leptin levels (USEPA, 2023c). 
Studies examining newborn leptin levels did not find associations with 
maternal PFOA levels (ATSDR, 2021). Maternal PFOS levels were also not 
associated with alterations in leptin levels (ATSDR, 2021). For 
additional details on metabolic effect studies and their individual 
outcomes, see Chapter C.3

[[Page 18718]]

(Metabolic/Systemic) in USEPA (2023k) and USEPA (2023l).
    Reproductive effects: Studies of the reproductive effects from 
PFOA/PFOS exposure have focused on associations between exposure to 
these pollutants and increased risk of gestational hypertension and 
preeclampsia in pregnant women (ATSDR, 2021; USEPA, 2023b; USEPA, 
2023c). Gestational hypertension (high blood pressure during pregnancy) 
can lead to fetal health outcomes such as poor growth and stillbirth. 
Preeclampsia--instances of gestational hypertension where the mother 
also has increased levels of protein in her urine--can similarly lead 
to fetal problems and maternal complications. The epidemiology evidence 
yields mixed (positive and non-significant) associations, with some 
suggestive evidence supporting positive associations between PFOA/PFOS 
exposure and both preeclampsia and gestational hypertension (ATSDR, 
2021; USEPA, 2023b; USEPA, 2023c). For additional details on 
reproductive effects studies and their individual outcomes, see Chapter 
C.1 (Reproductive) in USEPA (2023k) and USEPA (2023l).
    Musculoskeletal effects: Adverse musculoskeletal effects such as 
osteoarthritis and decreased bone mineral density impact bone integrity 
and cause bones to become brittle and more prone to fracture. There is 
limited evidence from studies pointing to effects of PFOS on skeletal 
size (height), lean body mass, and osteoarthritis (USEPA, 2023c). 
Epidemiology evidence suggested that PFOA exposure may be linked to 
decreased bone mineral density, bone mineral density relative to bone 
area, height in adolescence, osteoporosis, and osteoarthritis (ATSDR, 
2021; USEPA, 2023b). Evidence from four PFOS studies suggests that PFOS 
exposure has a harmful effect on bone health, particularly measures of 
bone mineral density, with greater statistically significance of 
effects occurring among females (USEPA, 2023c). Some studies found that 
PFOA/PFOS exposure was linked to osteoarthritis, in particular among 
women under 50 years of age (ATSDR, 2021). However, other reviews 
reported mixed findings on the effects of PFOS exposure including 
decreased risk of osteoarthritis, increased risk for some demographic 
subgroups, or no association (ATSDR, 2021). For additional details on 
musculoskeletal effects studies and their individual outcomes, see 
Chapter C.8 (Musculoskeletal) in USEPA (2023k) and USEPA (2023l).
    Cancer Effects: In EPA's Proposed Maximum Contaminant Level Goal 
for PFOA in Drinking Water, the Agency evaluates the evidence for 
carcinogenicity of PFOA that has been documented in both 
epidemiological and animal toxicity studies (USEPA, 2023b). The 
evidence in epidemiological studies is primarily based on the incidence 
of kidney and testicular cancer, as well as some evidence of breast 
cancer, which is most consistent in genetically susceptible 
subpopulations. Other cancer types have been observed in humans, 
although the evidence for these is generally limited to low confidence 
studies. The evidence of carcinogenicity in animal models is provided 
in three chronic oral animal bioassays in Sprague-Dawley rats which 
identified neoplastic lesions of the liver, pancreas, and testes 
(USEPA, 2023b). EPA determined that PFOA is Likely to Be Carcinogenic 
to Humans, as ``the evidence is adequate to demonstrate carcinogenic 
potential to humans but does not reach the weight of evidence for the 
descriptor Carcinogenic to Humans.'' This determination is based on the 
evidence of kidney and testicular cancer in humans and LCTs, PACTs, and 
hepatocellular adenomas in rats (USEPA, 2023b). EPA's benefits analysis 
for avoided RCC cases from reduced PFOA exposure is discussed in 
Section XII.D of this preamble and in Section 6.6 of USEPA (2023j).
    In EPA's Proposed Maximum Contaminant Level Goal for PFOS in 
Drinking Water, the Agency evaluates the evidence for carcinogenicity 
of PFOS and concluded that several epidemiological studies and a single 
chronic cancer bioassay comprise the evidence database for the 
carcinogenicity of PFOS (USEPA, 2023c). The available epidemiology 
studies report elevated risk of bladder, prostate, kidney, and breast 
cancers after chronic PFOS exposure. However, in developing this 
proposal, EPA did not identify information to quantify the benefits 
that reducing PFOS would have on reducing various cancers in humans. 
The sole animal chronic cancer bioassay study provide support for 
multi-site tumorigenesis in male and female rats. EPA reviewed the 
weight of the evidence and determined that PFOS is Likely to Be 
Carcinogenic to Humans, as ``the evidence is adequate to demonstrate 
carcinogenic potential to humans but does not reach the weight of 
evidence for the descriptor Carcinogenic to Humans.''
    EPA anticipates there are additional nonquantifiable benefits 
related to potential testicular, bladder, prostate, kidney, and breast 
carcinogenic effects summarized above. For additional details on cancer 
studies and their individual outcomes, see Chapter 3.5 (Cancer) in 
USEPA (2023b) and USEPA (2023c).
    After assessing the available health and economic information, EPA 
was unable to quantify the benefits of avoided health effects discussed 
above. The Agency prioritized health endpoints with the strongest 
weight of evidence conclusions for this assessment and readily 
available data for monetization, namely cardiovascular effects, 
developmental effects, and carcinogenic effects. Several other health 
endpoints that had indicative evidence of associations with exposure to 
PFOA or PFOS have not been selected for the Economic Analysis for the 
reasons below.
     While immune effects had indicative evidence of 
associations with exposure to PFOA or PFOS, EPA did not identify the 
necessary information to connect the measured biomarker responses 
(i.e., decrease in antibodies) to a clinical effect that could be 
valued in the Economic Analysis;
     Evidence indicates associations between PFOA and PFOS 
exposure and hepatic effects, such as increases in ALT. However, EPA is 
not able to model this health endpoint because ALT is a non-specific 
biomarker. Similar challenges with non-specificity of the biomarkers 
representing metabolic effects (i.e., leptin) and musculoskeletal 
effects (i.e., bone density) prevented economic analysis of these 
endpoints;
     There is indicative evidence of association with exposure 
to PFOA for testicular cancer; however, the available slope factor 
implied small changes in the risk of this endpoint. Furthermore, 
testicular cancer is rarely fatal which implies low expected economic 
value of reducing this risk because Value of Statistical Life is the 
driver of economic benefits evaluated in the Economic Analysis;
     Finally, other health endpoints, such as SGA and LDLC 
effects, were not modeled in the Economic Analysis because they overlap 
with effects that EPA did model. For example, infants that are 
considered SGA are often born at low birth weight or receive similar 
care to infants born at low birth weight. LDLC is a component of total 
cholesterol and could not be modeled separately as EPA used total 
cholesterol as an input to the ASCVD model to estimate CVD outcomes.

[[Page 18719]]

F. Nonquantifiable Benefits of Removal of PFAS Included in the Proposed 
Regulation and Co-Removed PFAS

    EPA also qualitatively summarized the potential health benefits 
resulting from reduced exposure to PFAS other than PFOA and PFOS in 
drinking water. The proposed option and all regulatory alternatives are 
expected to result in benefits that have not been quantified. Treatment 
responses implemented to reduce PFOA and PFOS exposure under the 
proposed option and Options 1a-c are likely to remove some amount of 
additional PFAS contaminants where they co-occur. Co-occurrence among 
PFAS compounds has been observed frequently as discussed in Section VII 
of this preamble and USEPA (2023e). The proposed option will require 
reduced exposure to PFHxS, HFPO-DA, PFNA, and PFBS to below their 
respective HBWCs. EPA also expects that compliance actions taken under 
the proposed rule will remove additional unregulated co-occurring PFAS 
contaminants where present because the BATs have been demonstrated to 
co-remove additional PFAS (see Section XI of this preamble for more 
information). EPA identified a wide range of potential health effects 
associated with exposure to PFAS compounds other than PFOA and PFOS 
using documents that summarize the recent literature on exposure and 
associated health impacts: ATSDR's Toxicology Profile for 
Perfluoroalkyls (ATSDR, 2021); EPA's summary of HFPO-DA toxicity 
(USEPA, 2021b); publicly available draft IRIS assessments for PFBA, and 
PFHxA (USEPA, 2021k; USEPA, 2022h); a human health assessment for PFBS 
(USEPA, 2021a); and the recent National Academies of Sciences, 
Engineering, and Medicine Guidance on PFAS Exposure, Testing, and 
Clinical Follow-up (NASEM, 2022). Note that the determinations of 
associations between PFAS compounds and associated health effects are 
based on information available as of May 2022, and that the 
finalization of the IRIS assessments may result in slight changes to 
the discussion of evidence. Additional discussion of the evidence from 
epidemiology and toxicology studies for associations between different 
categories of health effects and exposure to additional PFAS can be 
found in Section 6.2 of USEPA (2023j).
    Developmental effects: Toxicology and/or epidemiology studies 
observed evidence of associations with decreased birth weight and/or 
other developmental effects and exposure to PFBA, perfluorodecanoic 
acid (PFDA), PFHxS, HFPO-DA, PFNA, and PFBS. Specifically, data from 
animal toxicological studies support this association for PFBS, PFBA, 
and HFPO-DA while both animal toxicological and epidemiological studies 
support this association for PFDA and PFNA (ATSDR 2021) although some 
mixed results have been found for birth outcomes, particularly birth 
weight. In general, epidemiological studies did not find associations 
between perfluoroalkyl exposure and adverse pregnancy outcomes 
(miscarriage, preterm birth, or gestational age) for PFHxS, PFNA, PFDA, 
or perfluoroundecanoic acid (PFUnA) (ATSDR, 2021; NASEM, 2022).
    Cardiovascular effects: Epidemiology and toxicology studies 
observed evidence of associations between PFNA or PFDA exposures and 
total cholesterol, LDLC, and HDLC. Evidence for associations between 
PFNA exposure and serum lipids levels in epidemiology studies was 
mixed; associations have been observed between serum PFNA levels and 
total cholesterol in general populations of adults but not in pregnant 
women, and evidence in children is inconsistent (ATSDR, 2021). Most 
epidemiology studies did not observe associations between PFNA and LDLC 
or HDLC (ATSDR, 2021).
    Similarly inconsistent evidence was observed for PFDA (ATSDR, 
2021). Other PFAS for which lipid outcomes were examined in toxicology 
or epidemiology studies observed limited to no evidence of 
associations. Studies have examined possible associations between 
various PFAS and blood pressure in humans or heart histopathology in 
animals. However, studies did not find suggestive or likely evidence 
for any PFAS in this summary except for PFOS.
    Hepatic effects: Toxicology studies reported associations between 
exposure to PFAS compounds (PFBA, PFDA, PFHxA, PFHxS, HFPO-DA, and 
PFBS) and hepatotoxicity following inhalation, oral, and dermal 
exposure in animals. The results of these studies provide strong 
evidence that the liver is a sensitive target of PFHxS, PFNA, PFDA, 
PFUnA, PFBS, PFBA, perfluorododecanoic acid (PFDoDA), and PFHxA 
toxicity. Observed effects in rodents include increases in liver 
weight, hepatocellular hypertrophy, hyperplasia, and necrosis (ATSDR, 
2021; USEPA, 2021b; USEPA, 2022h). Increases in serum enzymes (such as 
ALT) and decreases in serum bilirubin were observed in one 
epidemiologic study of PFHxS, and mixed effects were observed for 
epidemiologic studies for PFNA (ATSDR, 2021).
    Immune effects: Epidemiology studies have reported evidence of 
associations between PFDA and PFHxS exposure and antibody response to 
tetanus or diphtheria. There is also some limited evidence for 
decreased antibody response for PFNA, PFUnA, and PFDoDA, although many 
of the studies did not find associations for these compounds. There is 
limited evidence for associations between PFHxS, PFNA, PFDA, PFBS, and 
PFDoDA and increased risk of asthma due to the small number of studies 
evaluating the outcome and/or conflicting study results. The small 
number of studies investigating immunotoxicity in humans following 
exposure to PFHpA and PFHxA did not find associations (ATSDR, 2021). 
Toxicology studies have reported evidence of associations between HFPO-
DA and immune-related endpoints in animals (USEPA, 2021b). No 
laboratory animal studies were identified for PFUnA, PFHpA, PFDoDA, or 
perfluorooctane sulfonamide (FOSA). A small number of toxicology 
studies evaluated the immunotoxicity of other perfluoroalkyls and most 
did not evaluate immune function. No alterations in spleen or thymus 
organ weights or morphology were observed in studies on PFHxS, PFBA, 
and PFDA. A study on PFNA found decreases in spleen and thymus weights 
and alterations in splenic lymphocyte phenotypes (ATSDR, 2021).
    Endocrine effects: Epidemiology studies have observed associations 
between serum PFHxS, PFNA, PFDA, and PFUnA and TSH, triiodothyronine 
(T3), or thyroxine (T4) levels or thyroid disease, however the results 
are not consistent across studies and a large number of studies have 
not found associations (ATSDR, 2021; NASEM, 2022). Toxicology studies 
have reported associations with thyroid hormone disruption in animals 
for PFBA, PFHxA, and PFBS (USEPA, 2021a; 2021k; USEPA, 2022h).
    Metabolic effects: Epidemiology and toxicology studies have 
examined possible associations between various PFAS and metabolic 
effects, including leptin, BW, or body fat in humans or animals (ATSDR, 
2021). However, evidence of associations was not suggestive or likely 
for any PFAS in this summary except for PFOA. Evidence did not include 
changes such as BW gain, pup BW, or other developmentally focused 
weight outcomes (ATSDR, 2021; NASEM, 2022).
    Renal effects: A small number of epidemiology studies with 
inconsistent results evaluated possible associations between PFHxS, 
PFNA, PFDA, PFBS, PFDoDA, or PFHxA and renal functions

[[Page 18720]]

(including estimated glomerular filtration rate and increases in uric 
acid levels) (ATSDR, 2021; NASEM 2022). Toxicology studies have not 
observed impaired renal function or morphological damage following 
exposure to PFHxS, PFDA, PFUnA, PFBS, PFBA, PFDoDA, or PFHxA. 
Associations with kidney weight in animals were observed for HFPO-DA 
and PFBS (ATSDR, 2021; USEPA, 2021b; USEPA, 2021a).
    Reproductive effects: A small number of epidemiology studies with 
inconsistent results evaluated possible associations between PFHxS, 
PFNA, PFUnA, PFDoDA, or PFHxA exposure and reproductive hormone levels 
(ATSDR, 2021). Some associations between PFAS (PFHxS, PFNA, or PFDA) 
exposures and sperm parameters have been observed. While there is 
suggestive evidence of an association between PFHxS or PFNA exposure 
and an increased risk of early menopause, this may be due to reverse 
causation since an earlier onset of menopause would result in a 
decrease in the removal of PFAS via menstrual blood. Epidemiological 
studies provide mixed evidence of impaired fertility (increased risks 
of longer time to pregnancy and infertility), with some evidence for 
PFHxS, PFNA, PFHpA, and PFBS but the results are inconsistent across 
studies or were only based on one study (ATSDR, 2021). Toxicology 
studies have evaluated the potential histological alterations in 
reproductive tissues, alterations in reproductive hormones, and 
impaired reproductive functions. No effect on fertility was observed 
for PFBS, PFHxS or PFDoDA, and no histological alterations were 
observed for PFBS, PFHxS and PFBA. One study found alterations in sperm 
parameters and decreases in fertility in mice exposed to PFNA, and one 
study for PFDoDA observed ultrastructural alterations in the testes 
(ATSDR, 2021).
    Musculoskeletal effects: Epidemiology studies observed evidence of 
associations between PFNA or PFHxS and musculoskeletal effects 
including osteoarthritis and bone mineral density, but data are limited 
to two studies (ATSDR, 2021). Epidemiology studies reported limited to 
no evidence of associations between exposure to PFDA and 
musculoskeletal effects. Toxicology studies reported no morphological 
alterations in bone or skeletal muscle in animals exposed to PFBA, 
PFHxA, PFHxS, or PFBS (ATSDR, 2021).
    Hematological effects: A single epidemiologic study reported on 
blood counts in pregnant Chinese women exposed to PFHxA and observed no 
correlations with any of the hematological parameters evaluated (total 
white blood cell counts, red blood cell (RBC) counts, and hemoglobin) 
(USEPA, 2022h). Epidemiological data were not identified for the other 
PFAS (ATSDR, 2021). A limited number of toxicology studies observed 
alterations in hematological indices following exposure to higher doses 
of PFHxS, PFDA, PFUnA, PFBS, PFBA, PFDoDA, or PFHxA (ATSDR, 2021). 
Toxicology studies observed evidence of association between HFPO-DA 
exposure and hematological effects including decreases in RBC number, 
hemoglobin, and percentage of RBCs in the blood (USEPA, 2021b).
    Other non-cancer effects: A limited number of epidemiology and 
toxicology studies have examined possible associations between other 
PFAS and dermal, ocular, and other non-cancer effects. However, 
evidence of associations was not considered to be suggestive or likely 
for any PFAS compound in this summary except for PFOA and PFOS (ATSDR, 
2021; USEPA, 2021a; USEPA, 2021k; USEPA, 2022h).
    Cancer effects: A small number of epidemiology studies reported 
limited associations between exposure to multiple PFAS (i.e., PFHxS, 
PFDA, PFUnA, and FOSA) and cancer effects. No consistent associations 
were observed for breast cancer risk for PFHxS, PFNA, PFHpA, or PFDoDA; 
increased breast cancer risks were observed for PFDA and FOSA, but this 
was based on a single study (Bonefeld-J[oslash]rgensen et al., 2014). 
No associations between exposure to PFHxS, PFNA, PFDA, or PFUnA, 
individually and prostate cancer risk were observed. However, among men 
with a first-degree relative with prostate cancer, associations were 
observed for PFHxS, PFDA, and PFUnA, but not for PFNA (ATSDR, 2021). 
Epidemiological studies examining potential cancer effects were not 
identified for PFBS, PFBA, or PFHxA (ATSDR, 2021). Aside from a study 
that suggested an increased incidence of liver tumors in rats exposed 
to high doses of HFPO-DA, toxicology studies reported no evidence of 
associations between exposure to PFDA or PFHxA and risk of cancer 
(ATSDR, 2021; USEPA, 2021b).
    Coronavirus Disease 2019 (COVID-19): A cross-sectional study in 
Denmark (Grandjean et al., 2020) showed that PFBA exposure was 
associated with increasing severity of COVID-19, with an OR of 1.77 
[95% Confidence Interval (CI): 1.09, 2.87] after adjustment for age, 
sex, sampling site, and interval between blood sampling and diagnosis. 
However, the study design does not allow for causal determinations.
    A case-control study showed increased risk for COVID-19 infection 
with high urinary PFAS (including PFOA, PFOS, PFHxA, PFHpA, PFHxS, 
PFNA, PFBS, PFDA, PFUnA, PFDoDA, perfluorotridecanoic acid [PFTrDA], 
and perfluorotetradecanoic acid [PFTeDA]) levels (Ji et al., 2021). 
Adjusted odds ratios were 1.94 (95% CI: 1.39, 2.96) for PFOS, 2.73 (95% 
CI: 1.71, 4.55) for PFOA, and 2.82 (95% CI: 1.97, 3.51) for sum PFAS, 
while other PFAS were not significantly associated with COVID-19 
susceptibility after adjusting for confounders.
    In a spatial ecological analysis, Catelan et al. (2021) showed 
higher mortality risk for COVID-19 in a population heavily exposed to 
PFAS (including PFOA, PFOS, PFHxS, PFBS, PFBA, perfluoropentanoic acid 
[PFPeA], PFHxA, and PFHpA) via drinking water in Veneto, Italy. 
Overall, results may indicate a general immunosuppressive effect of 
PFAS and/or increased COVID-19 respiratory toxicity due to a 
concentration of PFBA in the lungs, however the study design precludes 
causal determinations.
    Although these studies provide a suggestion of possible 
associations, the body of evidence does not permit any conclusions 
about the relationship between COVID-19 infection, severity, or 
mortality, and exposures to PFAS.

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

    As part of its health risk reduction and cost analysis, EPA is 
directed by SDWA to evaluate quantifiable and nonquantifiable health 
risk reduction benefits for which there is a factual basis in the 
rulemaking record to conclude that such benefits are likely to occur 
from reductions in co-occurring contaminants that may be attributed 
solely to compliance with the MCL (SDWA 1412(b)(3)(C)(II)). These co-
occurring contaminants are expected to include additional PFAS 
contaminants not directly regulated by the proposed PFAS NPDWR, co-
occurring chemical contaminants such as SOCs, VOCs, and DBP precursors. 
In this section, EPA presents a quantified estimate of the reductions 
in DBP formation potential that are likely to occur as a result of 
compliance with the proposed PFAS NPDWR. The methodology detailed below 
and in Section 6.7.1 of USEPA (2023j) to estimate DBP reductions was 
externally peer reviewed by three experts in GAC treatment for PFAS 
removal and DBP formation potential (USEPA, 2023m). The external peer 
reviewers supported EPA's approach

[[Page 18721]]

and edits based on their recommendations for clarity and completeness 
are reflected in the following analysis and discussion. Some peer 
reviewer comments suggested EPA provide additional baseline data 
summaries for TOC and THM4 occurrence information. EPA intends to 
evaluate and potentially include these additional summaries in the EA 
for the final rule.
    DBPs are formed when disinfectants react with naturally occurring 
materials in water. There is a substantial body of literature on DBP 
precursor occurrence and THM4 formation mechanisms in drinking water 
treatment. EPA regulates 11 individual DBPs from three subgroups: THM4, 
five haloacetic acids (HAA5), and two inorganic compounds (bromate and 
chlorite) under the Stage 2 Disinfectants and Disinfection Byproducts 
Rule (USEPA, 2006a). The formation of THM4 in a particular drinking 
water treatment plant is a function of several factors including 
disinfectant type, disinfectant dose, bromide concentration, organic 
material type and concentration, temperature, pH, and system residence 
times. Epidemiology studies have shown that THM4 exposure, a surrogate 
for chlorinated drinking water, is associated with an increased risk of 
bladder cancer, among other diseases (Cantor et al., 1998; Cantor et 
al., 2010; Costet et al., 2011; Beane Freeman et al., 2017; King and 
Marrett, 1996; Regli et al., 2015; USEPA, 2019d; Villanueva et al., 
2004; Villanueva et al., 2006; Villanueva et al., 2007). These studies 
considered THM4 as surrogate measures for DBPs formed from the use of 
chlorination that may co-occur. The relationships between exposure to 
DBPs, specifically THM4 and other halogenated compounds resulting from 
water chlorination, and bladder cancer are further discussed in Section 
6.7 of USEPA (2023j). Reductions in exposure to THM4 is expected to 
yield public health benefits, including a decrease in bladder cancer 
incidence (Regli et al., 2015). Among other things, Weisman et al. 
(2022) found that there is even a stronger weight of evidence linking 
DBPs and bladder cancer since the promulgation of the 2006 Stage 2 DBP 
regulations and publication of Regli et al. (2015). While not the 
regulated contaminant for this rulemaking, the expected reduction of 
DBP precursors and subsequent DBPs that result from this rulemaking are 
anticipated to reduce cancer risk in the U.S. population.
    GAC adsorption has been used to remove SOCs, taste and odor 
compounds, and NOM during drinking water treatment (Chowdhury et al., 
2013). Recently, many water utilities have installed or are considering 
installing GAC and/or other advanced technologies as a protective or 
mitigation measure to remove various contaminants of emerging concern, 
such as PFAS (Dickenson and Higgins, 2016). Because NOM often exists in 
a much higher concentration (in mg/L) than trace organics (in [mu]g/L 
or ppt) in water, NOM, often measured as TOC, can interfere with the 
adsorption of trace organics by outcompeting the contaminants for 
adsorption sites and by general fouling (blockage of adsorption pores) 
of the GAC.
    NOM and inorganic matter are precursors for the formation of 
trihalomethanes (THMs) and other DBPs when water is disinfected using 
chlorine and other disinfectants to control microbial contaminants in 
finished drinking water. Removal of DBP precursors through adsorption 
onto GAC has been included as a treatment technology for compliance 
with the existing DBP Rules and is a BAT for the Stage 2 DBP Rule. DOM 
can be removed by GAC through adsorption and biodegradation (Crittenden 
et al., 1993; Kim et al., 1997; Yapsakli et al., 2010). GAC is well-
established for removal of THM and haloacetic acid precursors (Cheng et 
al., 2005; Dastgheib et al., 2004; Iriarte-Velasco et al., 2008; 
Summers et al., 2013; Cuthbertson et al., 2019; L. Wang et al., 2019). 
In addition to removal of organic DBPs, GAC also exhibits some capacity 
for removal of inorganic DBPs such as bromate and chlorite (Kirisits et 
al., 2000; Sorlini et al., 2005) and removal of preformed organic DBPs 
via adsorption and biodegradation (Jiang, et al., 2017; Terry and 
Summers, 2018). Further, GAC may offer limited removal of dissolved 
organic nitrogen (Chili et al., 2012).
    Based on an extensive review of published literature in sampling 
studies where both contaminant groups (PFAS and DBPs) were sampled, 
there is limited information about PFAS removal and co-occurring 
reductions in DBPs, specifically THMs. To help inform its Economic 
Analysis, EPA relied on the DBP Information Collection Rule Treatment 
Study Database and DBP formation studies to estimate reductions in THM4 
([Delta]THM4) that may occur when GAC is used to remove PFAS. 
Subsequently, these results were compared to THM4 data from PWSs that 
have detected PFAS and have indicated use of GAC.
    The objective of EPA's co-removal benefits analysis was to 
determine the reduction in bladder cancer cases associated with the 
decrease of regulated THM4 in treatment plants due to the installation 
of GAC for PFAS removal. Evaluation of the expected reductions in 
bladder cancer risk resulting from treatment of PFAS in drinking water 
involves five steps:
    1. Estimating the number of systems expected to install GAC 
treatment in compliance with the proposed PFAS NPDWR and affected 
population size;
    2. Estimating changes in THM4 levels that may occur when GAC is 
installed for PFAS removal based on influent TOC levels;
    3. Estimating changes in the cumulative risk of bladder cancer 
using an exposure-response function linking lifetime risk of bladder 
cancer to THM4 concentrations in residential water supply (Regli et 
al., 2015);
    4. Estimating annual changes in the number of bladder cancer cases 
and excess mortality in the bladder cancer population corresponding to 
changes in THM4 levels under the regulatory alternative in all 
populations alive during or born after the start of the evaluation 
period; and
    5. Estimating the economic value of reducing bladder cancer 
mortality from baseline to regulatory alternative levels, using the 
Value of a Statistical Life and cost of illness measures, respectively.
    EPA expects PWSs that exceed the PFAS MCLs to consider both 
treatment and non-treatment options to achieve compliance with the 
drinking water standard. EPA assumes that the populations served by 
systems with entry points expected to install GAC based on the 
compliance forecast detailed in Section 5.3 of USEPA (2023j) will 
receive the DBP exposure reduction benefits. EPA notes that other 
compliance actions included in the compliance forecast could result in 
DBP exposure reductions, including installation of RO. However, these 
compliance actions are not included in the DBP benefits analysis 
because this DBP exposure reduction function is specific to GAC. 
Switching water sources may or may not result in DBP exposure 
reductions, therefore EPA assumed no additional DBP benefits for an 
estimated percentage of systems that elect this compliance option. 
Lastly, EPA assumed no change in DBP exposure at water systems that 
install IX, as that treatment technology is not expected to remove a 
substantial amount of DBP precursors. EPA also assumes that the PWSs in 
this analysis use chlorine only for disinfection and have conventional 
treatment in place prior to installation of GAC technology.
    EPA used the relationship between median raw water TOC levels and 
changes in THM4 levels estimated in the 1998 DBP Information Collection

[[Page 18722]]

Rule to estimate changes in THM4 concentrations in the finished water 
of PWSs fitted with GAC treatment. For more detail on the approach EPA 
used to apply changes in THM4 levels to PWSs treating for PFAS under 
the proposed rule, please see Section 6.7 of USEPA (2023j).
    EPA models a scenario where reduced exposures to THM4 begin in 
2026. Therefore, EPA assumed that the population affected by reduced 
THM4 levels resulting from implementation of GAC treatment is exposed 
to baseline THM4 levels prior to actions to comply with the rule (i.e., 
prior to 2026) and to reduced THM4 levels from 2026 through 2104. 
Rather than modeling individual locations, EPA evaluates changes in 
bladder cancer cases among the aggregate population per treatment 
scenario and source water type that is expected to install GAC 
treatment to reduce PFAS levels. Because of this aggregate modeling 
approach, EPA used national-level population estimates to distribute 
the SDWIS populations based on single-year age and sex and to grow the 
age- and sex-specific populations to future years. Appendix B to USEPA 
(2023j) provides additional details on estimation of the affected 
population.
    Regli et al. (2015) analyzed the potential lifetime bladder cancer 
risks associated with increased bromide levels in surface source water 
resulting in increased THM4 levels in finished water. To account for 
variable levels of uncertainty across the range of THM4 exposures from 
the pooled analysis of Villanueva et al. (2004), they derived a 
weighted mean slope factor from the odds ratios reported in Villanueva 
et al. (2004). They showed that, while the original analysis deviated 
from linearity, particularly at low concentrations, the overall pooled 
exposure-response relationship for THM4 could be well-approximated by a 
linear slope factor that predicted an incremental lifetime cancer risk 
of 1 in ten thousand exposed individuals (10-4) per 1 [micro]g/L 
increase in THM4. The linear slope factor developed by Regli et al. 
(2015) enables estimation of the changes in the lifetime bladder cancer 
risk associated with lifetime exposures to reduced THM4 levels. Weisman 
et al. (2022) applied the dose-response information from Regli et al. 
(2015) and developed a robust, national-level risk assessment of DBP 
impacts, where the authors estimated that approximately 8,000 of 79,000 
annual U.S. bladder cancer cases are attributable to chlorination DBPs, 
specifically associated with THM4 concentrations.
    EPA estimated changes in annual bladder cancer cases and annual 
excess mortality in the bladder cancer population due to estimated 
reductions in lifetime THM4 exposure using a life table-based approach. 
This approach was used because (1) annual risk of new bladder cancer 
should be quantified only among those not already experiencing this 
chronic condition, and (2) bladder cancer has elevated mortality 
implications.
    EPA used recurrent life table calculations to estimate a water 
source type-specific time series of bladder cancer incidence for a 
population cohort characterized by sex, birth year, and age at the 
beginning of the PFOA/PFOS evaluation period under the baseline 
scenario and the GAC regulatory alternative. The estimated risk 
reduction from lower exposure to DBPs in drinking water is calculated 
based on changes in THM4 levels used as inputs to the Regli et al. 
(2015)-based health impact function, described in more detail in 
Section 6.7 of USEPA (2023j). The life table analysis accounts for the 
gradual changes in lifetime exposures to THM4 following implementation 
of GAC treatment under the regulatory alternative compared to the 
baseline. The outputs of the life table calculations are the water 
source type-specific estimates of the annual change in the number of 
bladder cancer cases and the annual change in excess bladder cancer 
population mortality.
    EPA uses the Value of a Statistical Life to estimate the benefits 
of reducing mortality associated with bladder cancer in the affected 
population. EPA uses the cost of illness-based valuation to estimate 
the benefits of reducing morbidity associated with bladder cancer. 
Specifically, EPA used bladder cancer treatment-related medical care 
and opportunity cost estimates from Greco et al. (2019). Table 61 shows 
the original cost of illness estimates from Greco et al. (2019), along 
with the values updated to $2021 used in this analysis.

                                  Table 61--Bladder Cancer Morbidity Valuation
----------------------------------------------------------------------------------------------------------------
                                                                      Cost in                         Cost in
                                                   Cost in first    subsequent     Cost in first    subsequent
  Bladder cancer subtype \1\      Type of cost     year ($2010)    years ($2010)   year ($2021)    years ($2021)
                                                        \2\             \2\             \c\             \3\
----------------------------------------------------------------------------------------------------------------
Non-invasive..................  Medical care....           9,133             916          12,350           1,239
                                Opportunity cost           4,572              24           5,921              31
                                                 ---------------------------------------------------------------
                                   Total cost...          13,705             941          18,272           1,270
----------------------------------------------------------------------------------------------------------------
Invasive......................  Medical care....          26,951           2,455          36,445           3,320
                                Opportunity cost          10,513              77          13,616             100
                                                 ---------------------------------------------------------------
                                   Total cost...          37,463           2,532          50,061           3,420
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ The estimates for non-invasive bladder cancer subtype were used to value local, regional, and unstaged
  bladder cancer morbidity reductions, while the estimates for the invasive bladder cancer subtype were used to
  value distant bladder cancer morbidity reductions.
\2\ The estimates come from Greco et al. (2019).
\3\ To adjust for inflation, EPA used U.S. BLS CPI for All Urban Consumers: Medical Care Services in U.S. (City
  Average).

    Table 62 to 65 presents the estimated changes in bladder cancer 
cases and excess bladder cancer mortality from exposure to THM4 due to 
implementation of GAC treatment by option. EPA estimated that, over the 
evaluation period, the proposed rule will result in an average annual 
benefit from avoided bladder cancer cases and deaths from $131 million 
($2021, 7% discount rate) to $221 million ($2021, 3% discount rate).

[[Page 18723]]

                           Table 62--National Bladder Cancer Benefits, Proposed Option
                                  [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal Bladder Cancer          4,079.1    5,238.6      6,475.3      4,079.1    5,238.6      6,475.3
 Cases Avoided........................
Number of Bladder Cancer-Related            1,436.0    1,844.4      2,280.0      1,436.0    1,844.4      2,280.0
 Deaths Avoided.......................
Total Annualized Bladder Cancer             $173.09    $221.30      $273.62      $102.08    $130.63      $161.56
 Benefits (Million $2021) \2\.........
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized annualized benefits in this table.

                              Table 63--National Bladder Cancer Benefits, Option 1a
                                         [PFOA and PFOS MCLs of 4.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal Bladder Cancer          4,066.1    5,219.4      6,488.8      4,066.1    5,219.4      6,488.8
 Cases Avoided........................
Number of Bladder Cancer-Related            1,431.5    1,837.6      2,284.9      1,431.5    1,837.6      2,284.9
 Deaths Avoided.......................
Total Annualized Bladder Cancer             $171.72    $220.48      $274.24      $101.34    $130.15      $161.56
 Benefits (Million $2021) \2\.........
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized annualized benefits in this table.

                              Table 64--National Bladder Cancer Benefits, Option 1b
                                         [PFOA and PFOS MCLs of 5.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal Bladder Cancer          3,342.7    4,334.3      5,382.5      3,342.7    4,334.3      5,482.5
 Cases Avoided........................
Number of Bladder Cancer-Related            1,176.8    1,526.0      1,895.3      1,176.8    1,526.0      1,895.3
 Deaths Avoided.......................
Total Annualized Bladder Cancer             $141.17    $183.10      $227.85       $83.31    $108.08      $135.37
 Benefits (Million $2021) \2\.........
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized annualized benefits in this table.

                              Table 65--National Bladder Cancer Benefits, Option 1c
                                        [PFOA and PFOS MCLs of 10.0 ppt]
                                                 [Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
           Benefits category                5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\       benefits      \1\          \1\       benefits      \1\
----------------------------------------------------------------------------------------------------------------
Number of Non-Fatal Bladder Cancer          1,615.9    2,175.5      2,807.4      1,615.9    2,175.5      2,807.4
 Cases Avoided........................
Number of Bladder Cancer-Related              568.9      766.0        988.6        568.9      766.0        988.6
 Deaths Avoided.......................
Total Annualized Bladder Cancer              $68.26     $91.90      $118.64       $40.29     $54.25       $70.10
 Benefits (Million $2021) \2\.........
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 72. This range does not include the uncertainty described in Table 60.
\2\ See Table 70 for a list of the nonquantifiable benefits, and the potential direction of impact these
  benefits would have on the estimated monetized annualized benefits in this table.

[[Page 18724]]

H. Comparison of Costs and Benefits

    This section provides a comparison of the costs and benefits of the 
proposed rule, as described in Chapter 7 of the Economic Analysis. 
Included here are estimates of total quantified annualized costs and 
benefits for the proposed option and regulatory alternatives 
considered, as well as considerations for the nonquantifiable costs and 
benefits. EPA notes that it cannot make determinations as to whether 
the costs are justified by the benefits based on quantified costs and 
benefits alone, as SDWA 1412(b)(3)(C)(I) and (II) mandates that the 
Agency must consider nonquantifiable benefits.
    The incremental cost is the difference between quantified costs 
that will be incurred if the proposed rule is enacted over and above 
current baseline conditions. Incremental benefits reflect the avoided 
future adverse health outcomes attributable to PFAS reductions and co-
removal of additional contaminants due to actions undertaken to comply 
with the proposed rule.
    Table 66 provides the incremental quantified costs and benefits of 
the proposed option at both a 3 percent and a 7 percent discount rate 
in 2021 dollars. The top row shows total monetized annualized costs 
including total PWS costs and primacy agency costs. The second row 
shows total monetized annualized benefits including all endpoints that 
could be quantified and valued. For both, the estimates are the 
expected (mean) values and the 5th percentile and 95th percentile 
estimates from the uncertainty distribution. These percentile estimates 
come from the distributions of annualized costs and annualized benefits 
generated by the 4,000 iterations of SafeWater MCBC. Therefore, these 
distributions reflect the joint effect of the multiple sources of 
variability and uncertainty for costs, benefits, and PFAS occurrence, 
as detailed in Sections 5.1.2, 6.1.2, and Chapter 4 of the Economic 
Analysis, respectively (USEPA, 2023j). For further discussion of the 
quantified uncertainties in the Economic Analysis, see Section G of 
this preamble below.
    The third row shows net benefits (benefits minus costs). At a 3 
percent discount rate, the net annual incremental benefits are $461 
million. The uncertainty range for net benefits is a negative $45 
million to $1,141 million. At a 7 percent discount rate, the net annual 
incremental quantified benefits are a negative $297 million. The 
uncertainty range for net benefits is a negative $628 million to $141 
million.

                  Table 66--Annualized Quantified National Costs and Benefits, Proposed Option
                          [PFOA and PFOS MCLs of 4.0 ppt and HI of 1.0; Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
                                            5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\        value        \1\          \1\        value        \1\
----------------------------------------------------------------------------------------------------------------
Total Annualized Rule Costs \2\ \3\         $704.53    $771.77      $850.40    $1,106.01  $1,204.61    $1,321.01
 \4\..................................
Total Annualized Rule Benefits \4\....       659.91   1,232.98     1,991.51       477.69     908.11     1,462.43
                                       -------------------------------------------------------------------------
    Total Net Benefits................       -44.62     461.21     1,141.11      -628.31    -296.50       141.42
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 71 and Table 72. This range does not include the uncertainty described in
  Table 41 for costs and Table 60 for benefits.
\2\ Total quantified national cost values do not include the incremental treatment costs associated with the
  cooccurrence of HFPO-DA, PFBS, and PFNA at systems required to treat for PFOA, PFOS, and PFHxS. The total
  quantified national cost values do not include treatment costs for systems that would be required to treat
  based on HI exceedances apart from systems required to treat because of PFHxS occurrence alone. See Appendix
  N, Section 3 of the Economic Analysis (USEPA, 2023i) for additional detail on co-occurrence incremental
  treatment costs and additional treatment costs at systems with HI exceedances.
\3\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported
  in this table do not include costs associated with hazardous waste disposal of spent filtration materials. To
  address stakeholder concerns about potential costs for disposing PFAS-contaminated wastes as hazardous should
  they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA,
  2023i) for additional detail.
\4\ See Table 70 for a list of the nonquantifiable benefits and costs, and the potential direction of impact
  these benefits and costs would have on the estimated monetized total annualized benefits and costs in this
  table.

    Tables 67 to 69 summarize the total annual costs and benefits for 
Options 1a, 1b, and 1c, respectively.

                     Table 67--Annualized Quantified National Costs and Benefits, Option 1a
                                 [PFOA and PFOS MCLs of 4.0 ppt; Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
                                            5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\        value        \1\          \1\        value        \1\
----------------------------------------------------------------------------------------------------------------
Total Annualized Rule Costs \2\ \3\...      $688.09    $755.82      $833.48    $1,078.51  $1,177.31    $1,292.01
Total Annualized Rule Benefits \3\....       651.19   1,216.08     1,971.01       471.53     895.36     1,456.23
                                       -------------------------------------------------------------------------
    Total Net Benefits................       -36.90     460.26     1,137.53      -606.97    -281.95       164.22
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 71 and Table 72. This range does not include the uncertainty described in
  Table 41 for costs and Table 60 for benefits.

[[Page 18725]]

 
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported
  in this table do not include costs associated with hazardous waste disposal of spent filtration materials. To
  address stakeholder concerns about potential costs for disposing PFAS-contaminated wastes as hazardous should
  they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA,
  2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable benefits and costs, and the potential direction of impact
  these benefits and costs would have on the estimated monetized total annualized benefits and costs in this
  table.

                     Table 68--Annualized Quantified National Costs and Benefits, Option 1b
                                 [PFOA and PFOS MCLs of 5.0 ppt; Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
                                            5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\        value        \1\          \1\        value        \1\
----------------------------------------------------------------------------------------------------------------
Total Annualized Rule Costs \2\ \3\...      $558.71    $611.01      $674.32      $864.74    $942.28    $1,035.56
Total Annualized Rule Benefits \3\....       553.37   1,046.91     1,706.81       398.21     773.33     1,292.96
                                       -------------------------------------------------------------------------
    Total Net Benefits................        -5.34     435.90     1,032.49      -466.53    -168.95       257.40
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 71 and Table 72. This range does not include the uncertainty described in
  Table 41 for costs and Table 60 for benefits.
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported
  in this table do not include costs associated with hazardous waste disposal of spent filtration materials. To
  address stakeholder concerns about potential costs for disposing PFAS-contaminated wastes as hazardous should
  they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA,
  2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable benefits and costs, and the potential direction of impact
  these benefits and costs would have on the estimated monetized total annualized benefits and costs in this
  table.

                     Table 69--Annualized Quantified National Costs and Benefits, Option 1c
                                 [PFOA and PFOS MCLs of 10.0 ppt; Million $2021]
----------------------------------------------------------------------------------------------------------------
                                                  3% Discount rate                     7% Discount rate
                                       -------------------------------------------------------------------------
                                            5th                     95th         5th                     95th
                                         Percentile   Expected   Percentile   Percentile   Expected   Percentile
                                            \1\        value        \1\          \1\        value        \1\
----------------------------------------------------------------------------------------------------------------
Total Annualized Rule Costs \2\ \3\...      $269.36    $292.57      $320.76      $396.22    $430.87      $472.20
Total Annualized Rule Benefits \3\....       280.42     584.80     1,030.56       208.71     436.24       784.59
                                       -------------------------------------------------------------------------
    Total Net Benefits................        11.06     292.23       709.80      -187.51       5.36       312.39
----------------------------------------------------------------------------------------------------------------
Notes:
Detail may not add exactly to total due to independent rounding.
\1\ The 5th and 95th percentile range is based on modeled variability and uncertainty described in section
  XIII.I of this preamble and Table 71 and Table 72. This range does not include the uncertainty described in
  Table 41 for costs and Table 60 for benefits.
\2\ PFAS-contaminated wastes are not considered hazardous wastes at this time and therefore total costs reported
  in this table do not include costs associated with hazardous waste disposal of spent filtration materials. To
  address stakeholder concerns about potential costs for disposing PFAS-contaminated wastes as hazardous should
  they be regulated as such in the future, EPA conducted a sensitivity analysis with an assumption of hazardous
  waste disposal for illustrative purposes only. See Appendix N, Section 2 of the Economic Analysis (USEPA,
  2023i) for additional detail.
\3\ See Table 70 for a list of the nonquantifiable benefits and costs, and the potential direction of impact
  these benefits and costs would have on the estimated monetized total annualized benefits and costs in this
  table.

    The benefit-cost analysis reported dollar figures presented above 
reflect benefits and costs that could be quantified for each regulatory 
alternative given the best available scientific data. EPA notes that 
the quantified benefit-cost results above are not representative of all 
benefits and costs anticipated under the proposed NPDWR. Due to 
occurrence, health, and economic data limitations, there are several 
adverse health effects associated with PFAS exposure and costs 
associated with treatment that EPA could not estimate in a quantitative 
manner.
    PFAS exposure is associated with a wide range of adverse health 
effects including reproductive effects such as decreased fertility; 
increased high blood pressure in pregnant women; developmental effects 
or delays in children, including low birth weight, accelerated puberty, 
bone variations, or behavioral changes; increased risk of some cancers, 
including prostate, kidney, and testicular cancers; reduced ability of 
the body's immune system to fight infections, including reduced vaccine 
response; interference with the body's natural hormones; and increased 
cholesterol levels and/or risk of obesity. Based on the available data, 
EPA is only able to quantify three PFOA- and PFOS-related health 
endpoints in this analysis. All regulatory alternatives are expected to 
produce substantial benefits that have not been quantified. Treatment 
responses implemented to remove PFOA and PFOS under Options 1a-c are 
likely to remove some amount of additional PFAS contaminants where they 
co-occur. Co-occurrence among PFAS compounds has been observed 
frequently as discussed in the PFAS Occurrence Technical Support 
Document (USEPA, 2023e). The proposed option is expected to produce the 
greatest reduction in exposure to PFAS compounds because it includes 
PFHxS, HFPO-DA, PFNA, and PFBS in the regulation. Inclusion of the HI 
will trigger more systems into treatment (as shown in Section 4.4.4 of 
the Economic

[[Page 18726]]

Analysis) and provides enhanced public health protection by ensuring 
reductions of these additional compounds when present above the HI of 
1.0. EPA conducted a sensitivity analysis to evaluate the additional 
benefits anticipated due to regulating PFAS compounds beyond PFOA and 
PFOS. Specifically, EPA's sensitivity analysis demonstrates the 
potential significant quantified benefits associated with infant birth 
weight expected to result from reductions in PFNA under the proposed 
rule. For further discussion of the quantitative and qualitative 
benefits associated with the proposed rule, see Section 6.2 of the 
Economic Analysis.
    EPA also expects that the proposed option will result in additional 
nonquantifiable costs in comparison to Options 1a-c. As noted above, 
the HI is expected to trigger more systems into more frequent 
monitoring and treatment. Due to occurrence data limitations, EPA has 
quantified the national treatment and monitoring costs associated with 
the HI for PFHxS only and has not quantified the cost impacts 
associated with HI exceedances resulting from HFPO-DA, PFNA, and PFBS. 
In instances when concentrations of HFPO-DA, PFNA, and PFBS are high 
enough to cause or contribute to an HI exceedance when the 
concentrations of PFOA, PFOS, and PFHxS would not have already 
otherwise triggered treatment, the modeled costs may be underestimated. 
If these PFAS occur in isolation at levels that affect treatment 
decisions, or if these PFAS occur in combination with PFHxS when PFHxS 
concentrations were otherwise below the HI in isolation (i.e., <9.0 
ppt) then the quantified costs underestimate the impacts of the 
proposed rule. As such, EPA conducted a semi-quantitative analysis of 
the anticipated incremental costs associated with regulating HFPO-DA, 
PFNA, and PFBS (for additional detail, please see USEPA (2023i)).
    Table 70 provides a summary of the likely impact of nonquantifiable 
benefit-cost categories. In each case, EPA notes the potential 
direction of the impact on costs and/or benefits. For example, benefits 
are underestimated if the PFOA and PFOS reductions result in avoided 
adverse health outcomes that cannot be quantified and valued. Sections 
5.7 and 6.8 of the Economic Analysis identify the key methodological 
limitations and the potential effect on the cost or benefit estimates, 
respectively. Additionally, Table 71 summarizes benefits and costs that 
are quantified and nonquantifiable under the proposed rule.

                    Table 70--Potential Impact of Nonquantifiable Benefits (B) and Costs (C)
----------------------------------------------------------------------------------------------------------------
             Source                (Proposed option)       Option 1a           Option 1b           Option 1c
----------------------------------------------------------------------------------------------------------------
Nonquantifiable PFOA and PFOS     B: underestimate..  B: underestimate..  B: underestimate..  B: underestimate.
 health endpoints.
Limitations with available        C: underestimate..  n/a...............  n/a...............  n/a.
 occurrence data for HFPO-DA,
 PFNA, and PFBS.
Nonquantifiable HI (HFPO-DA,      B: underestimate..  n/a...............  n/a...............  n/a.
 PFNA, PFHxS and PFBS) health
 endpoints.
Limitations with available        B+C: underestimate  B+C: underestimate  B+C: underestimate  B+C:
 occurrence data for additional                                                                underestimate.
 PFAS compounds.
Removal of co-occurring non-PFAS  B+C: underestimate  B+C: underestimate  B+C: underestimate  B+C:
 contaminants.                                                                                 underestimate.
POU not in compliance forecast..  C: overestimate...  C: overestimate...  C: overestimate...  C: overestimate.
Unknown future hazardous waste    C: underestimate..  C: underestimate..  C: underestimate..  C: underestimate.
 management requirements for
 PFAS (including HI).
----------------------------------------------------------------------------------------------------------------

                      Table 71--Summary of Quantified and Nonquantified Benefits and Costs
----------------------------------------------------------------------------------------------------------------
                                                                               Methods (economic analysis report
              Category                    Quantified        Non-quantified         section where analysis is
                                                                                           detailed)
----------------------------------------------------------------------------------------------------------------
Costs:
    PWS treatment costs \1\.........                  X                       Section 5.3.1.
    PWS sampling costs..............                  X                       Section 5.3.2.2.
    PWS implementation and                            X                       Section 5.3.2.1.
     administration costs.
    Primacy agency rule                               X                       Section 5.3.2.
     implementation and
     administration costs.
    Hazardous waste disposal for                                          X   Section 5.6.
     treatment media.
    POU not in compliance forecast..                                      X   Section 5.6.
Benefits:
    PFOA and PFOS birth weight                        X                       Section 6.4.
     effects.
    PFOA and PFOS cardiovascular                      X                       Section 6.5.
     effects.
    PFOA and PFOS RCC...............                  X                       Section 6.6.
    Health effects associated with                    X                       Section 6.7.
     disinfection byproducts.
    Other PFOA and PFOS health                                            X   Section 6.2.2.2.
     effects.
    Health effects associated with                                        X   Section 6.2.
     HI compounds (HFPO-DA, PFNA,
     PFBS, PFHxS).
    Health effects associated with                                        X   Section 6.2.
     other PFAS.
----------------------------------------------------------------------------------------------------------------
Notes:
\1\ Due to occurrence data limitations, EPA quantified the national treatment and monitoring costs associated
  with the HI for PFHxS only and has not quantified the national cost impacts associated with HI exceedances
  resulting from PFNA, PFBS, and HFPO-DA.

[[Page 18727]]

I. Quantified Uncertainties in the Economic Analysis

    EPA characterized sources of uncertainty in its estimates of costs 
expected to result from the proposed PFAS NPDWR. EPA conducted Monte-
Carlo based uncertainty analysis as part of SafeWater MCBC. With 
respect to the cost analysis, EPA modeled the sources of uncertainty in 
Table 72.

      Table 72--Quantified Sources of Uncertainty in Cost Estimates
------------------------------------------------------------------------
              Source                     Description of uncertainty
------------------------------------------------------------------------
TOC concentration.................  The TOC value assigned to each
                                     system is from a distribution
                                     derived from the SYR4 ICR database
                                     (see Section 5.3.1.1 in Economic
                                     Analysis).
Compliance technology unit cost     Cost curve selection varies with
 curve selection.                    baseline PFAS concentrations and
                                     also includes a random selection
                                     from a distribution across feasible
                                     technologies (see Section 5.3.1.2
                                     in Economic Analysis), and random
                                     selection from a triangular
                                     distribution of low-, mid-, and
                                     high-cost equipment (25%, 50%, and
                                     25%, respectively).
------------------------------------------------------------------------

    For each iteration, SafeWater MCBC assigned new values to the four 
sources of modeled uncertainty as described in Table 72, and then 
calculated costs for each of the model PWSs. This was repeated 4,000 
times to reach an effective sample size for each parameter. At the end 
of the 4,000 iterations, SafeWater MCBC outputs the expected value as 
well as the 90% confidence interval for each cost metric (i.e., bounded 
by the 5th and 95th percentile estimates for each cost component). 
Detailed information on the data used to model uncertainty is provided 
in Appendix L to USEPA (2023i).
    Additionally, EPA characterized sources of uncertainty in its 
analysis of potential benefits resulting from changes in PFAS levels in 
drinking water. The analysis reports uncertainty bounds for benefits 
estimated in each health endpoint category modeled for the proposed 
rule. Each lower (upper) bound value is the 5th (95th) percentile of 
the category-specific benefits estimate distribution represented by 
4,000 Monte Carlo draws.
    Table 73 provides an overview of the specific sources of 
uncertainty that EPA quantified in the benefits analysis. In addition 
to these sources of uncertainty, reported uncertainty bounds also 
reflect the following upstream sources of uncertainty: baseline PFAS 
occurrence, affected population size and demographic composition, and 
the magnitude of PFAS concentration reductions. These analysis-specific 
sources of uncertainty are further described in Appendix L to USEPA 
(2023i).

    Table 73--Quantified Sources of Uncertainty in Benefits Estimates
------------------------------------------------------------------------
              Source                     Description of uncertainty
------------------------------------------------------------------------
Health effect-serum PFAS slope      The slope factors that express the
 factors.                            effects of serum PFOA and serum
                                     PFOS on health outcomes (birth
                                     weight, CVD,\1\ and RCC) are based
                                     either on EPA meta-analyses or high-
                                     quality studies that provide a
                                     central estimate and a confidence
                                     interval for the slope factors. EPA
                                     assumed that the slope factors
                                     would have a normal distribution
                                     within their range.
RCC risk reduction cap............  EPA implemented a cap on the
                                     cumulative RCC risk reductions due
                                     to reductions in serum PFOA based
                                     on the population attributable
                                     fraction (PAF) estimates for a
                                     range of cancers and environmental
                                     contaminants. This parameter is
                                     treated as uncertain; its
                                     uncertainty is characterized by a
                                     log-uniform distribution with a
                                     minimum set at the smallest PAF
                                     estimate identified in the
                                     literature and a maximum set at the
                                     largest PAF estimate identified in
                                     the literature. The central
                                     estimate for the PAF is the mean of
                                     this log-uniform distribution.
------------------------------------------------------------------------
Note:
\1\ The slope factors contributing to the CVD benefits analysis include
  the relationship between total cholesterol and PFOA and PFOS, the
  relationship between HDLC and PFOA and PFOS, and the relationship
  between blood pressure and PFOS.

J. Cost-Benefit Determination

    When proposing an NPDWR, the Administrator shall publish a 
determination as to whether the benefits of the MCL justify, or do not 
justify, the costs based on the analysis conducted under paragraph 
1412(b)(3)(C). With this proposed rule, the Administrator has 
determined that the quantified and nonquantifiable benefits of the 
proposed PFAS NPDWR justify the costs.
    Sections XIII.A to XIII.I of this preamble summarize the results of 
this proposed rule analysis. As indicated in section XIII.H of this 
preamble, EPA discounted the estimated monetized cost and benefit 
values using both 3 and 7 percent discount rates. In Federal regulatory 
analyses, EPA follows OMB Circular A4 (OMB, 2003) guidance which 
recommends using both 3 percent and 7 percent is intended to account 
for the different streams of monetized benefits and costs affected by 
regulation. The 7 percent discount rate represents the estimated rate 
of return on capital in the U.S. economy, to reflect the opportunity 
cost of capital when ``the main effect of a regulation is to displace 
or alter the use of capital in the private sector.'' Regulatory 
effects, however, can fall on both capital and private consumption.\10\ 
In 2003, Circular A-4 estimated the rate appropriate for discounting 
consumption effects at 3 percent. The estimated monetized costs and 
benefits of this rulemaking result in expected annual net benefits 
(total monetized annual benefits minus total monetized annual costs) of 
$461.21 million at a 3 percent discount rate and -$296.50 at a 7 
percent discount rate. There are a variety of considerations with 
respect to the capital displacement in this particular proposal. For 
example, a meaningful number of PWSs may not be managed as profit-
maximizing private sector investments, which could impact the degree to 
which the rate of return on the use of capital in the private sector 
applies to PWS costs. Federal funding is expected to defray many such 
PWS

[[Page 18728]]

costs; \11\ where that occurs, such costs are transferred to the 
government. Additionally, to the extent that the benefits extend over a 
long time period into the future, including to future generations, 
Circular A-4 advises agencies to consider conducting sensitivity 
analyses using lower discount rates. Regardless, the impacts in this 
rulemaking are such that costs are expected to occur in the nearer 
term, and in particular that larger one-time capital investments are 
expected to occur in the near term; and public health benefits are 
expected to occur over the much longer term. Discounting across an 
appropriate range of rates can help explore how sensitive net benefits 
are to assumptions about whether effects fall more to capital or more 
to consumption.
---------------------------------------------------------------------------

    \10\ Private consumption is the consumption of goods and 
services by households for the direct satisfaction of individual 
needs (rather than for investment).
    \11\ As noted above in this preamble, ``Infrastructure 
Investment and Jobs Act, also referred to as the Bipartisan 
Infrastructure Law (BIL), invests over $11.7 billion in the Drinking 
Water State Revolving Fund (SRF); $4 billion to the Drinking Water 
SRF for Emerging Contaminants; and $5 billion to Small, Underserved, 
and Disadvantaged Communities Grants.''
---------------------------------------------------------------------------

    EPA has followed Circular A-4's default recommendations to use 3 
and 7 percent rates to represent the range of potential impacts 
accounting for diversity in stakeholders' time preferences. The Agency 
views the 3 to 7 percent range of costs and benefits as characterizing 
a significant portion of the uncertainty in the discount rate and views 
the quantified endpoint values as demonstrating a range of monetized 
costs and benefits which encompass a significant portion of the 
uncertainty associated with discount rates. Material unquantified 
benefits expected as a result of this proposed rulemaking are discussed 
in greater detail later in this section.
    The quantified analysis is limited in its characterization of 
uncertainty. In Section XIII.H, Table 66 of this preamble, EPA provides 
5th and 95th percentile values associated with the 3 and 7 percent 
discounted expected values for net benefits. These values represent the 
quantified, or modeled, potential range in the expected net benefit 
values associated with the variability in system characteristics and 
the uncertainty resulting from the following variables; the baseline 
PFAS occurrence; the affected population size; the compliance 
technology unit cost curves, which are selected as a function of 
baseline PFAS concentrations and population size, the distribution of 
feasible treatment technologies, and the three alternative levels of 
treatment capital costs; the concentration of TOC in a system's source 
water which impacts GAC O&M costs; the demographic composition of the 
systems population; the magnitude of PFAS concentration reductions; the 
health effect-serum PFOA and PFOS slope factors that quantify the 
relationship between changes in PFAS serum level and health outcomes 
for birth weight, CVD, and RCC; and the cap placed on the cumulative 
RCC risk reductions due to reductions in serum PFOA. These modeled 
sources of uncertainty are discussed in more detail in section XIII.I 
of this preamble. What the quantified 5th and 95th percentile values do 
not include are a number of factors which impact both costs and 
benefits but for which the Agency did not have sufficient data to 
include in the quantification of uncertainty. The factors influencing 
the proposed rule cost estimates that are not quantified in the 
uncertainty analysis are detailed in section XIII.C.j and Table 41 of 
this preamble. These uncertainty sources include: the specific design 
and operating assumptions used in developing treatment unit cost; the 
use of national average costs that may differ from the geographic 
distribution of affected systems; the possible future deviation from 
the compliance technology forecast; and the degree to which actual TOC 
source water values differ from EPA's estimated distribution. EPA has 
no information to indicate a directional influence of the estimated 
costs with regard to these uncertainty sources. To the degree that 
uncertainty exists across the remaining factors it would most likely 
influence the estimated 5th and 95th percentile range and not 
significantly impact the expected value estimate of costs. Section 
XIII.D and Table 60, of this preamble, discuss the sources of 
uncertainty affecting the estimated benefits not captured in the 
estimated 5th and 95th reported values. The modeled values do not 
capture the uncertainty in: the exposure that results from daily 
population changes at NTNCWSs or routine population shifting between 
PWSs, for example spending working hours at a NTNCWS or CWS and home 
hours at a different CWS; the exposure-response functions used in 
benefits analyses assume that the effects of serum PFOA/PFOS on the 
health outcomes considered are independent, additive, and that there 
are no threshold serum concentrations below which effects do not occur; 
the distribution of population by size and demographics across entry 
points within modeled systems and future population size and 
demographic changes; and the Value of Statistical Life reference value 
or income elasticity used to update the VSL. Given information 
available to the Agency four of the listed uncertainty sources would 
not affect the benefits expected value but the dispersion around that 
estimate. They are the unmodeled movements of populations between PWS 
which potentially differing PFAS concentrations; the independence and 
additivity assumptions with regard to the effects of serum PFOA/PFOS on 
the health outcomes; the uncertainty in the population and demographic 
distributions among entry points within individual systems; and the VSL 
value and the income elasticity measures. Two of the areas of 
uncertainty not captured in the analysis would tend to indicate that 
the quantified benefits numbers are overestimates. First, the data 
available to EPA with regard to population size at NTNCWs while likely 
capturing peaks in populations utilizing the systems does not account 
for the variation in use and population and would tend to overestimate 
the exposed population. The second uncertainty, which definitionally 
would indicate overestimates in the quantified benefits values is the 
assumption that there are no threshold serum concentrations below which 
health effects do not occur. One factor not accounted for in the 
quantified analysis associated with the underestimation of benefits is 
the impact of general population growth over the extended period of 
analysis.
    In addition to the quantified cost and benefit expected values, the 
modeled uncertainty associated within the 5th and 95th percentile 
values, and the un-modeled uncertainty associated with a number of 
factors listed above, there are also significant nonquantifiable costs 
and benefits which are important to the overall weighing of costs and 
benefits. Table 70 provides a summary of these nonquantifiable cost and 
benefit categories along with an indication of the directional impact 
each category would have on total costs and benefit. Tables 41 and 60 
also provide additional information on a number of these 
nonquantifiable categories.
    On the nonquantifiable costs side of the equation EPA had 
insufficient nationally representative data to precisely characterize 
occurrence of HFPO-DA, PFNA, and PFBS at the national level and 
therefore could not include complete treatment costs associated with; 
the co-occurrence of these PFAS at systems already required to treat as 
a result of estimated PFOA, PFOS, or PFHxS levels, which would shorten 
the filtration media life and therefore increase operation costs; and 
the occurrence of HFPO-DA, PFNA,

[[Page 18729]]

and/or PFBS at levels high enough to cause systems to exceed the HI and 
have to install PFAS treatment. EPA expects that the quantified 
national costs are marginally underestimated as a result of this lack 
of sufficient nationally representative occurrence data for purposes of 
model integration. In an effort to better understand the costs 
associated with treatment of potentially co-occurring HFPO-DA, PFNA, 
and PFBS at systems already required to treat and the potential costs 
resulting from an HI exceedance associated with the same chemicals EPA 
estimated the potential unit treatment costs for model systems under 
both scenarios for differing assumed HI PFAS concentrations. The 
analysis is discussed in section 5.3.1.4 and Appendix N of the Economic 
Analysis (USEPA, 2023j; USEPA, 2023i). Two additional nonquantifiable 
cost impacts stemming from insufficient co-occurrence data could also 
potentially shorten filtration media life and increase operation costs. 
The co-occurrence of other PFAS and other non-PFAS contaminants not 
regulated in the proposed rule could both increase costs to the extent 
that they reduce media life. EPA did not include POU treatment in the 
compliance technology forecast because current POU units are not 
certified to remove PFAS to the standards required in the proposed 
rule. Once certified this technology may be a low-cost treatment 
alternative for some subset of small systems. Not including POU 
treatment in this analysis has resulted in a likely overestimate of 
cost values. Appendix N of the Economic Analysis (USEPA, 2023j; USEPA, 
2023i) contains a sensitivity analysis that estimates there may be a 
national annual costs of $30 to $61 million, discounted at 3 and 7 
percent, respectively, which would accrue to systems if the waste 
filtration media from GAC and IX were handled as hazardous waste. This 
sensitivity analysis includes only disposal costs and does not consider 
other potential environmental costs associated with the disposal of the 
waste filtration media.
    There are significant nonquantifiable sources of benefits that were 
not captured in the quantified benefits estimated for the proposed 
rule. While EPA was able to monetize some of the PFOA and PFOS benefits 
related to CVD, infant birthweight, and RCC effects, the Agency was 
unable to quantify additional negative health impacts. EPA did not 
quantify PFOA and PFOS benefits related to health endpoints including 
developmental, cardiovascular, hepatic, immune, endocrine, metabolic, 
reproductive, musculoskeletal, and other types of carcinogenic effects. 
See Section XIII.E, of this preamble, for additional information on the 
nonquantifiable impacts of PFOA and PFOS. Further, the Agency did not 
quantify any health endpoint benefits associated with the potential 
reductions in HI PFAS, which include PFHxS, HFPO-DA, PFNA, and PFBS, or 
other co-occurring non-regulated PFAS which would be removed by the 
installation of required filtration technology at those systems with 
PFOA, PFOS, or HI exceedances. The nonquantifiable benefits impact 
categories associated with PFHxS, HFPO-DA, and PFBS include 
developmental, cardiovascular, immune, hepatic, endocrine, metabolic, 
reproductive, musculoskeletal, and carcinogenic effects. In addition, 
EPA did not quantify the potential developmental, cardiovascular, 
immune, hepatic, endocrine, metabolic, reproductive, musculoskeletal, 
and carcinogenic impacts related to the removal of other co-occuring 
non-regulated PFAS. See Section XIII.F, of this preamble, for 
additional information on the nonquantifiable impacts of PFHxS, HFPO-
DA, PFNA, and PFBS and other non-regulated co-occurring PFAS.
    The treatment technologies installed to remove PFAS can also remove 
numerous other non-PFAS drinking water contaminants which have negative 
health impacts including additional regulated and unregulated DBPs (the 
quantified benefits assessment does estimate benefits associated with 
THM4), heavy metals, organic contaminants, and pesticides, among 
others. The removal of these co-occurring non-PFAS contaminants could 
have significant positive health benefits. In total these 
nonquantifiable benefits are anticipated to be significant and are 
discussed qualitatively in Section 6.2 of the Economic Analysis (USEPA, 
2023j).
    To fully weigh the costs and benefits of the action the Agency 
considered the totality of the monetized values, the potential impacts 
of the unquantified uncertainties described above, and the 
nonquantifiable costs and benefits. The Administrator has determined 
that the benefits of this proposed regulation justify the costs.

XIV. Request for Comment on Proposed Rule

    The Agency is requesting comment on this proposed NPDWR for PFAS. 
In the proposal, the Agency highlighted numerous areas where specific 
public comment will be helpful for EPA in developing a final rule. EPA 
specifically requests comment on the following topics within each 
section of this preamble.

Section III--Regulatory Determinations for Additional PFAS

     EPA requests comment on its preliminary regulatory 
determination for PFHxS and its evaluation of the statutory criteria 
that supports the finding. EPA also requests comment on if there are 
additional data or studies EPA should consider that support or do not 
support the Agency's preliminary regulatory determination for PFHxS, 
including additional health information and occurrence data.
     EPA requests comment on its preliminary regulatory 
determination for HFPO-DA and its evaluation of the statutory criteria 
that supports the finding. EPA also requests comment on if there are 
additional data or studies EPA should consider that support or do not 
support the Agency's preliminary regulatory determination for HFPO-DA, 
including additional health information and occurrence data.
     EPA requests comment on its preliminary regulatory 
determination for PFNA and its evaluation of the statutory criteria 
that supports the finding. EPA also requests comment on if there are 
additional data or studies EPA should consider that support or do not 
support the Agency's preliminary regulatory determination for PFNA, 
including additional health information and occurrence data.
     EPA requests comment on its preliminary regulatory 
determination for PFBS and its evaluation of the statutory criteria 
that supports the finding. EPA also requests comment on if there are 
additional data or studies EPA should consider that support or do not 
support the Agency's preliminary regulatory determination for PFBS, 
including additional health information and occurrence data.
     EPA requests comment on whether there are other peer-
reviewed health or toxicity assessments for other PFAS the Agency 
should consider as a part of this action.
     EPA requests comment on its evaluation that regulation of 
PFHxS, HFPO-DA, PFNA, PFBS, and their mixtures, in addition to PFOA and 
PFOS, will provide protection from PFAS that will not be regulated 
under this proposed rule.

Section V--Maximum Contaminant Level Goal

     EPA requests comment on the derivation of the proposed 
MCLG for PFOA and its determination that PFOA

[[Page 18730]]

is Likely to be Carcinogenic to Humans and whether the proposed MCLG is 
set at the level at which there are no adverse effects to the health of 
persons and which provides an adequate margin of safety. EPA is also 
seeking comment on its assessment of the noncancer effects associated 
with exposure to PFOA and the toxicity values described in the support 
document on the proposed MCLG for PFOA.
     EPA requests comment on the derivation of the proposed 
MCLG for PFOS, its determination that PFOS is Likely to be Carcinogenic 
to Humans and whether the proposed MCLG is set at the level at which 
there are no adverse effects to the health of persons and which 
provides an adequate margin of safety. EPA is also seeking comment on 
its assessment of the noncancer effects associated with exposure to 
PFOS and the toxicity values described in the support document on the 
proposed MCLG for PFOS.
     EPA requests comment on the general HI approach for the 
mixture of four PFAS.
     EPA requests comment on the merits and drawbacks of the 
target-specific HI or RPF approach.
     EPA requests comment on significant figure use when 
calculating both the HI MCLG and the MCL. EPA has set the HI MCLG and 
MCL using two significant figures (i.e., 1.0). EPA requests comment on 
the proposed use of two significant figures for the MCLG when 
considering underlying health information and for the MCL when 
considering the precision of the analytical methods.
     EPA requests comment on the derivation of the HBWCs for 
each of the four PFAS considered as part of the HI.
     EPA requests comment on whether the HBWCs should instead 
be proposed as stand-alone MCLGs in addition to or in lieu of the 
mixture MCLGs.

Section VI--Maximum Contaminant Level

     EPA requests comment on its proposed determination to set 
MCLs at 4.0 ppt for PFOA and PFOS and whether 4.0 ppt is the lowest PQL 
that can be achieved by laboratories nationwide.
     EPA seeks comment on its PFOA and PFOS evaluation of 
feasibility for the proposal, including analytical measurement and 
treatment capability, as well as reasonable costs, as defined by SDWA.
     EPA seeks comment on its evaluation of feasibility for the 
proposed HI MCL finding, including analytical measurement and treatment 
capability, as well as reasonable costs, as defined by SDWA.
     EPA requests comment on implementation challenges and 
considerations for setting the MCL at the PQLs for PFOA and PFOS, 
including on the costs and benefits related to this approach.
     EPA requests comment on the underlying assumptions that 
sufficient laboratory capacity will be available with the proposed 
MCLs; that demand will be sufficiently distributed during rule 
implementation to allow for laboratory capacity; and on the cost 
estimates related to these assumptions.
     EPA requests comment on its proposal of using an HI 
approach for PFHxS, HFPO-DA, PFNA, and PFBS, including whether it can 
be clearly implemented and achieves the goal of protecting against dose 
additive noncancer health effects.
     EPA requests comment on its proposed decision to establish 
stand-alone MCLs for PFOA and PFOS in lieu of including them in the HI 
approach.
     EPA requests comment on whether establishing a traditional 
MCLG and MCL for PFHxS, HFPO-DA, PFNA, and PFBS instead of, or in 
addition to, the HI approach would change public health protection, 
improve clarity of the rule, or change costs.

Section VII--Occurrence

     EPA requests comment on the number of systems estimated to 
solely exceed the HI (but not the PFOA or PFOS MCLs) according to the 
approach outlined in USEPA (2023e).

Section IX--Monitoring and Compliance Requirements

     EPA requests comment on the proposed monitoring 
flexibility for groundwater systems serving 10,000 or fewer to only 
collect two samples at each EPTDS to satisfy initial monitoring 
requirements.
     EPA requests comment on monitoring-related flexibilities 
that should be considered to further reduce burden while also 
maintaining public health protection including a rule trigger level at 
different values than the currently proposed values of 1.3 ppt for PFOA 
and PFOS and 0.33 for the HI PFAS (PFHxS, HFPO-DA, PFNA, and PFBS), 
specifically alternative values of 2.0 ppt for PFOA and PFOS and 0.50 
for the HI PFAS. EPA also requests comment other monitoring 
flexibilities identified by commenters.
     EPA requests comment on the proposed allowance of a water 
system to potentially have each EPTDS on a different compliance 
monitoring schedule based on specific entry point sampling results 
(i.e., some EPTDS being sampled quarterly and other EPTDS sampled only 
once or twice during each three-year compliance period), or if 
compliance monitoring frequency should be consistent across all of the 
system's sampling points.
     EPA requests comments on whether water systems should be 
permitted to apply to the primacy agency for monitoring waivers. 
Specifically, EPA is requesting comment on the allowance of monitoring 
waivers of up to nine years if after at least one year of sampling 
results are below the proposed rule trigger level. Similarly, EPA also 
requests comment on whether allowance of monitoring waivers of up to 
nine years should be permitted based on previously acquired monitoring 
data results that are below the proposed rule trigger level. 
Additionally, EPA is also requesting comment on the identification of 
possible alternatives to traditional vulnerability assessments that 
should be considered to identify systems as low risk and potentially 
eligible for monitoring waivers.
     EPA requests comment on if all water systems, regardless 
of system size, be allowed to collect and analyze one sample per three-
year compliance period if the system does not detect regulated PFAS in 
their system at or above the rule trigger level.
     EPA requests comment on its proposal to allow the use of 
previously acquired monitoring data to satisfy initial monitoring 
requirements including the data collection timeframe requirements and 
if other QA requirements should be considered.
     EPA requests comment on whether EPA should consider an 
alternative approach to what is currently proposed when calculating 
compliance with proposed MCLs. Specifically, in the case where a 
regulated PFAS is detected but below its proposed PQL, rather than 
using zero for the measurement value of the specific PFAS in the 
running annual average compliance calculation, that the proposed rule 
trigger levels (1.3 ppt for PFOA and PFOS and 0.33 of each of the HI 
PFAS PQLs (i.e., PFHxS=1.0, HFPO-DA=1.7, PFNA=1.3, and PFBS=1.0)) be 
used as the values in calculating the running annual average for 
compliance purposes.
     EPA requests comment on other monitoring related 
considerations including laboratory capacity and QA/QC of drinking 
water sampling.
     EPA seeks comment on the Agency's proposed initial 
monitoring timeframe, particularly for NTNCWS or all systems serving 
3,300 or fewer.

[[Page 18731]]

Section X--Safe Drinking Water Right to Know

     EPA requests comment on its proposal to designate 
violations of the proposed MCLs as Tier 2.
     EPA requests comment on what may be needed for water 
systems to effectively communicate information about the PFAS NPDWR to 
the public.

Section XI--Treatment Technologies

     EPA requests comment on whether PWSs can feasibly treat to 
4.0 ppt or below.
     EPA requests additional information on PFAS removal 
treatment technologies not identified in the proposed rule that have 
been shown to reduce levels of PFAS to the proposed regulatory 
standard.
     EPA requests comment on the co-removal of the HI chemicals 
(PFHxS, PFBS, PFNA, and HFPO-DA) when GAC, IX, or RO are used in the 
treatment of PFOA and/or PFOS.
     EPA requests comment on whether there are additional 
technologies which are viable for PFAS removal to the proposed MCLs as 
well as any additional costs which may be associated with non-treatment 
options such as water rights procurement.
     EPA estimates GAC treatment will be sufficiently available 
to support cost-effective compliance with this proposed regulation, and 
requests comment on whether additional guidance on applicable 
circumstances for GAC treatment is needed.
     EPA is seeking comment on the benefits from using 
treatment technologies (such as reverse osmosis and GAC) that have been 
demonstrated to co-remove other types of contaminants found in drinking 
water and whether employing these treatment technologies are sound 
strategies to address PFAS and other regulated or unregulated 
contaminants that may co-occur in drinking water.
     EPA requests comment on the estimates for disposing of 
drinking water treatment residuals or regenerating drinking water 
treatment media including assumptions related to the transport distance 
to disposal sites and other costs that arise out of disposal of PFAS 
contaminated drinking water treatment residuals.
     EPA requests comment on the availability of facilities to 
dispose of or regenerate drinking water treatment media that contains 
PFAS. EPA requests comment on whether there will be sufficient capacity 
to address the increased demand for disposal of drinking water 
treatment residuals or to regenerate media for reuse by drinking water 
treatment facilities.
     EPA requests comment on the impacts that the disposal of 
PFAS contaminated treatment residuals may have in communities adjacent 
to the disposal facilities.
     EPA requests comment on the type of assistance that would 
help small public water systems identify laboratories that can perform 
the required monitoring, evaluate treatment technologies and determine 
the most appropriate way to dispose of PFAS contaminated residuals and 
waste the systems may generate when implementing the rule.

Section XII--Rule Implementation and Enforcement

     EPA is seeking comment as to whether there are specific 
conditions that should be mandated for systems to be eligible for 
exemptions under 1416 to ensure that they are only used in rare 
circumstances where there are no other viable alternatives and what 
those conditions would be.

Section XIII--HRRCA

     EPA requests comment on all components of the HRRCA for 
the proposed NPDWR.
     In the Economic Analysis, EPA presented estimated costs 
and benefits of regulatory alternatives for PFOA and PFOS if setting 
MCLs at 5.0 ppt and 10.0 ppt. EPA is requesting comment on its 
evaluation of these alternatives within the Economic Analysis.
     EPA requests comment on the methodology used to estimate 
national costs for the proposed rule and regulatory alternatives. EPA's 
cost analysis can be found in Chapter 5 of the Economic Analysis.
     EPA is requesting comment on the WBS models, including the 
range of component levels assumed in the input to the models, and the 
range of cost estimates for GAC, IX, and centralized RO.
     EPA requests comment on Table 26 which provides the 
initial treatment technology compliance forecast, presented in 
percentages of systems adopting GAC, PFAS-selective IX, centralized RO, 
system interconnection, and use new wells across system design flows 
and TOC levels. This information is used in EPA's cost and benefit 
modeling. Please also comment on the potential for point-of-use 
devices, including those using RO or activated carbon as a compliance 
option.
     EPA requests comment on the cost of treatment when 
additional co-occurring but not targeted PFAS chemicals are found in 
source water.
     EPA requests comment generally on its estimation of 
sampling costs. The Agency is also specifically requesting comment on 
the ability of systems to demonstrate they are reliably and 
consistently below 1.3 ppt for PFOA and PFOS and 0.33 ppt for PFAS 
regulated by the HI in order to qualify for reduced monitoring.
     EPA requests comment on the underlying assumptions that, 
under UCMR 5, individual water systems would be able to request the 
full release of data from the labs for use in determining their 
compliance monitoring frequency and that PWSs may be able to use these 
lab analyses to demonstrate a ``below trigger level'' concentration 
using the UCMR 5 analyses by following up with the lab for a more 
detailed results report.
     EPA requests comment on the costs associated with the 
storage, transportation and underground injection of the brine 
concentrate residuals from the RO/NF process.
     EPA requests comment on the small system affordability 
analysis, including both the national affordability determination using 
EPA's existing 2.5% of MHI methodology and the supplemental analyses 
using use of alternative metrics (i.e., expenditure margins at 1% of 
MHI and 2.5% of lowest quintile income). EPA's national small system 
affordability determination can be found in Section 9.12.1 of the 
Economic Analysis. EPA's supplementary affordability analyses can be 
found in Section 9.12.2 of the Economic Analysis.
     EPA requests comment on the discussion of estimated PN 
costs provided in the proposed rule.
     EPA requests comment on the assumption that exceedances of 
HI PFAS not included in the national cost analyses (HFPO-DA, PFBS, and 
PFNA) will not significantly impact overall compliance costs and 
national costs estimates are, therefore, unlikely to be substantially 
underestimated.
     EPA requests comments on the approaches we used to 
estimate each of the health impacts of exposure to the PFAS chemicals 
covered in this proposed rule, including the transparency of the 
assumptions we made and the impact of these assumptions on the 
magnitude of the risks avoided by the proposed regulatory action.
     EPA requests comment on whether factors such as 
anticipated Federal funding, the structure of PWSs relative to private 
enterprises, or the nature of the public health benefits should be 
further explored in the final rule analysis, including as it relates to 
the estimated range of impacts under the applied discount rates.

[[Page 18732]]

Section XV--Statutory and Executive Order Reviews

     EPA requests comment on all aspects of its EJ analysis, 
particularly its choice of comparison groups to determine potential 
demographic disparities in anticipated PFAS exposure and its use of 
thresholds against which to examine anticipated exposures. For more 
information, please see section XV.J of this preamble.

XV. Statutory and Executive Order Reviews

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

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is an economically significant regulatory action that 
was submitted to the Office of Management and Budget (OMB) for review. 
Any changes made in response to OMB recommendations have been 
documented in the docket. EPA prepared an analysis of the potential 
costs and benefits associated with this action. This analysis, the 
Economic Analysis (USEPA, 2023j), is available in the docket and is 
summarized in section XIII of this preamble.

B. Paperwork Reduction Act (PRA)

    The information collection activities in this proposed rule have 
been submitted for approval to the Office of Management and Budget 
(OMB) under the PRA. The Information Collection Request (ICR) document 
that EPA prepared has been assigned EPA ICR number 2732.01. You can 
find a copy of the ICR in the docket for this rule at https://www.regulations.gov/docket/EPA-HQ-OW-2022-0114, and it is briefly 
summarized here.
    The monitoring information collected as a result of the proposed 
rule should allow primacy agencies and EPA to determine appropriate 
requirements for specific systems and evaluate compliance with the 
proposed rule. For the first three-year period following rule 
promulgation, the major information requirements concern primacy agency 
activities to implement the rule including adopting the NPDWR into 
state regulations, providing training to state and PWS employees, 
updating their monitoring data systems, and reviewing system monitoring 
data and other requests. Compliance actions for drinking water systems 
(including monitoring, administration, and treatment costs) would not 
begin until after three years due to the proposed effective date of 
this rule. More information on these actions is described in Section 
XII of this preamble and in Chapter 9 from the Economic Analysis of the 
Proposed PFAS NPDWR (USEPA, 2023j).
    The respondents/affected entities are PWSs and primacy agencies. 
The collection requirements are mandatory under SDWA (42 U.S.C. 300g-
7). For the first three years after publication of the rule in the FR, 
information requirements apply to an average of 38,089 respondents 
annually, including 38,033 PWSs and 56 primacy agencies. The burden 
associated with the proposed rule over the three years covered by the 
ICR is 3.8 million hours, for an average of 1.3 million hours per year. 
The total costs over the three-year period is $142.6 million, for an 
average of $47.5 million per year (simple average over three years). 
The average burden per response (i.e., the amount of time needed for 
each activity that requires a collection of information) is 6.6 hours 
for PWSs and 1.1 hours for primacy agencies; the average cost per 
response is $234.41 for PWSs and $60.89 for primacy agencies. Details 
on the calculation of the proposed rule information collection burden 
and costs can be found in the ICR for the proposed rule.
    Burden is defined at 5 CFR 1320.3(b) and means the total time, 
effort, and financial resources required to generate, maintain, retain, 
disclose, or provide information to or for a Federal agency. This 
includes the time needed to review instructions; develop, acquire, 
install, and utilize technology and systems for the purposes of 
collecting, validating, and verifying information, processing and 
maintaining information, and disclosing and providing information; 
adjust the existing ways to comply with any previously applicable 
instructions and requirements; train personnel to be able to respond to 
a collection of information; search data sources; complete and review 
the collection of information; and transmit or otherwise disclose the 
information.
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collected for information unless it displays a 
currently valid OMB control number. The OMB control numbers for EPA's 
regulations in 40 CFR are listed in 40 CFR part 9.
    Submit your comments on the Agency's need for this information, the 
accuracy of the provided burden estimates and any suggested methods for 
minimizing respondent burden to EPA using the docket identified at the 
beginning of this proposed rule. EPA will respond to any ICR-related 
comments in the final rule. You may also send your ICR-related comments 
to OMB's Office of Information and Regulatory Affairs using the 
interface at www.reginfo.gov/public/do/PRAMain. Find this particular 
information collected by selected ``Currently under Review--Open for 
Public Comments'' or by using the search function. OMB must receive 
comments no later than May 30, 2023.

C. Regulatory Flexibility Act (RFA)

    Pursuant to section 603 of the Regulatory Flexibility Act (RFA), 
EPA prepared an initial regulatory flexibility analysis (IRFA) that 
examines the impact of the proposed rule on small entities along with 
regulatory alternatives that could minimize the impact. The complete 
IRFA is available in Section 9.3 of the Economic Analysis in the docket 
and is summarized here.
    For purposes of assessing the impacts of this proposed rule on 
small entities, EPA considered small entities to be water systems 
serving 10,000 people or fewer. This is the threshold specified by 
Congress in the 1996 Amendments to SDWA for small water system 
flexibility provisions. As required by the RFA, EPA proposed using this 
alternative definition in the FR (USEPA, 1998c), sought public comment, 
consulted with the Small Business Administration (SBA), and finalized 
the small water system threshold in the Agency's Consumer Confidence 
Report Regulation (USEPA, 1998d). As stated in the document, the 
alternative definition would apply to all future drinking water 
regulations.
    The SDWA is the core statute addressing drinking water at the 
Federal level. Under the SDWA, EPA sets public health goals and 
enforceable standards for drinking water quality. As previously 
described, the proposed PFAS NPDWR requires water systems to minimize 
certain PFAS in drinking water. EPA is proposing to regulate PFAS in 
drinking water to improve public health protection by reducing drinking 
water exposure to PFAS in drinking water.
    The proposed rule contains provisions that would affect 
approximately 62,000 small PWSs. A small PWS serves between 25 and 
10,000 people. These water systems include approximately 45,000 CWSs 
that serve the year-round residents and approximately 17,000 NTNCWSs 
that serve the same persons over six months per year (e.g., a PWS that 
is an office park or school). The proposed PFAS NPDWR includes 
development of legally enforceable regulatory standards

[[Page 18733]]

with requirements for monitoring, PN, and treatment or non-treatment 
options for water systems exceeding the regulatory standard. This 
proposed rule also include reporting, recordkeeping, and other 
administrative requirements. States are required to implement operator 
certification (and recertification) programs per SDWA Section 1419 to 
ensure operators of CWSs and NTNCWSs, including small water system 
operators, have the appropriate level of certification.
    Under the proposed rule requirements, small CWSs and NTNCWs serving 
10,000 or fewer people are required to conduct initial monitoring or 
demonstrate recent, previously collected monitoring data to determine 
the level of certain PFAS in their water system. Based on these initial 
monitoring results, systems will be required to conduct ongoing 
monitoring at least every three years or as often as four times per 
year. Systems that exceed the drinking water standard will be required 
to choose between treatment and non-treatment as the compliance option. 
Under the proposed rule, EPA estimates that approximately 18,000 small 
CWSs (40 percent of small CWSs) could incur annual total PFAS NPDWR 
related costs of more than one percent of revenues, and that 
approximately 10,000 small CWSs (22 percent of small CWSs) could incur 
annual total costs of three percent or greater of revenue. See Section 
9.3 of the proposed PFAS NPDWR Economic Analysis for more information 
on the characterization of the impacts under the proposed rule.
    As required by section 609 (b) of the RFA, EPA also convened a 
Small Business Advocacy Review (SBAR) Panel to obtain advice and 
recommendations from small entity representatives (SERs) that 
potentially would be subject to the rule's requirements. On May 24, 
2022, EPA's Small Business Advocacy Chairperson convened the Panel, 
which consisted of the Chairperson, the Director of the Standards and 
Risk Management Division within EPA's Office of Ground Water and 
Drinking Water, the Administrator of the Office of Information and 
Regulatory Affairs within OMB, and the Chief Counsel for Advocacy of 
the SBA. Prior to convening the Panel, EPA conducted outreach with SERs 
that will potentially be affected by this regulation and solicited 
comments from them. Additionally, after the Panel was convened, the 
Panel provided additional information to the SERs and requested their 
input. In light of the SERs' comments, the Panel considered the 
regulatory flexibility issues and elements of the IRFA specified by 
RFA/Small Business Regulatory Enforcement Fairness Act (SBREFA) and 
developed the findings and discussion summarized in the SBAR report. 
For example, the SBAR Panel recommended several flexibilities in 
monitoring requirements for small systems, including the use of 
existing monitoring data (such as the UCMR 5) for initial monitoring 
purposes; as well as reduced compliance monitoring requirements 
specifically for small groundwater systems. EPA is including these 
flexibilities as a part of the proposed rule requirements. The report 
includes a number of other observations and recommendations to meet the 
statutory obligations for achieving small-system compliance through 
flexible regulatory compliance options. The report was finalized on 
August 1, 2022 and transmitted to the EPA Administrator for 
consideration. A copy of the full SBAR Panel Report is available in the 
rulemaking docket (USEPA, 2022a).

D. Unfunded Mandates Reform Act (UMRA)

    This action contains a Federal mandate under the Unfunded Mandates 
Reform Act (UMRA), 2 U.S.C. 1531-1538 that may result in expenditures 
of $100 million or more for state, local, and tribal governments, in 
the aggregate, or the private sector in any one year. Accordingly, EPA 
has prepared a written statement required under section 202 of UMRA 
that is included in the docket for this action (see Chapter 9 of the 
Economic Analysis for the Proposed PFAS NPDWR) and briefly summarized 
here.
    Consistent with UMRA section 205, EPA identified and analyzed a 
reasonable number of regulatory alternatives to determine the MCL 
requirement in the proposed rule. Sections VI, IX, X, and XII of this 
preamble describe the proposed options. See section XIII of this 
preamble and Chapter 9 of the Economic Analysis for the Proposed PFAS 
NPDWR (USEPA, 2023j) for alternative options that were considered.
    Consistent with the intergovernmental consultation provisions of 
UMRA section 204, EPA consulted with governmental entities affected by 
this rule. EPA describes the government-to-government dialogue and 
comments from state, local, and tribal governments in section XV.E 
Executive Order 13132: Federalism and section XV.F Executive Order 
13175: Consultation and Coordination with Indian Tribal Governments of 
this document.
    Consistent with UMRA section 205, EPA identified and analyzed a 
reasonable number of regulatory alternatives to determine the 
regulatory requirements in the proposed PFAS NPDWR. Section VI of this 
preamble describes the proposed option. See section XIII of this 
preamble and Section 9.4 in the Economic Analysis of the Proposed PFAS 
NPDWR (USEPA, 2023j) for alternative options that were considered.
    This action may significantly or uniquely affect small governments. 
EPA consulted with small governments concerning the regulatory 
requirements that might significantly or uniquely affect them. EPA 
describes this consultation above in the RFA, section XV.C of this 
preamble.

E. Executive Order 13132: Federalism

    EPA has concluded that this action has federalism implications 
because it imposes substantial direct compliance costs on state or 
local governments, and the Federal government will not provide the 
funds necessary to pay those costs. However, EPA notes that the Federal 
government will provide a potential source of funds necessary to offset 
some of those direct compliance costs through the BIL. EPA estimates 
that the net change in primacy agency related cost for state, local, 
and tribal governments in the aggregate is estimated to be $8 million 
(3 percent discount rate) or $9 million (7 percent discount rate).
    EPA provides the following federalism summary impact statement. EPA 
consulted with State and local governments early in the process of 
developing the proposed action to allow them to provide meaningful and 
timely input into its development. EPA held a federalism consultation 
on February 24, 2022. EPA invited the following national organizations 
representing State and local elected officials to a virtual meeting on 
February 24, 2022: The National Governors' Association, the National 
Conference of State Legislatures, the Council of State Governments, the 
National League of Cities, the U.S. Conference of Mayors, the National 
Association of Counties, the International City/County Management 
Association, the National Association of Towns and Townships, the 
County Executives of America, and the Environmental Council of States. 
Additionally, EPA invited the Association of State Drinking Water 
Administrators, the Association of Metropolitan Water Agencies, the 
National Rural Water Association, the American Water Works Association, 
the American Public Works Association, the Western Governors' 
Association, the

[[Page 18734]]

Association of State and Territorial Health Officials, the National 
Association of Country and City Health Officials, and other 
organizations to participate in the meeting. In addition to input 
received during the meeting, EPA provided an opportunity to receive 
written input within 60 days after the initial meeting. A summary 
report of the views expressed during federalism consultations is 
available in the Docket (EPA-HQ-OW-2022-0114).
    In addition to the federalism consultation, regarding state 
engagement more specifically, EPA notes there were multiple meetings 
held by the Association of State Drinking Water Administrators where 
EPA gathered input from state officials related to the considerations 
for the development of the proposed rule. EPA utilized this state input 
to inform this rule proposal.

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

    This action has tribal implications, it imposes direct compliance 
costs on tribal governments, and the Federal government will not 
provide funds necessary to pay those direct compliance costs. However, 
EPA notes that the Federal government will provide a potential source 
of funds necessary to offset some of those direct compliance costs 
through the BIL.
    EPA has identified 998 PWSs serving tribal communities, 84 of which 
are federally owned. EPA estimates that tribal governments will incur 
PWS compliance costs of $5 million per year attributable to monitoring, 
treatment or non-treatment actions to reduce PFAS in drinking water, 
and administrative costs, and that these estimated impacts will not 
fall evenly across all tribal systems. The proposed PFAS NPDWR does 
offer regulatory relief by providing flexibilities for all water 
systems to potentially utilize pre-existing monitoring data in lieu of 
initial monitoring requirements and for groundwater CWSs and NTNCWSs 
serving 10,000 or fewer to reduce initial monitoring from quarterly 
monitoring during a consecutive 12-month period to only monitoring 
twice during a consecutive 12-month period. These flexibilities may 
result in implementation cost savings for many tribal systems since 98 
percent of tribal CWSs and 94 percent of NTNCWs serve 10,000 or fewer 
people.
    Accordingly, EPA provides the following Tribal summary impact 
statement as required by section 5(b) of Executive Order 13175. 
Consistent with EPA Policy on Consultation and Coordination with Indian 
Tribes (May 4, 2011), EPA consulted with Tribal officials and their 
representatives early in the process of developing this proposed 
regulation to permit them to have meaningful and timely input into its 
development. EPA conducted consultation with Indian Tribes beginning on 
February 7, 2022 and ending on April 16, 2022. The consultation 
included two national webinars with interested tribes on February 23, 
2022, and March 8, 2022, where EPA provided proposed rulemaking 
information and requested input. A total of approximately 35 tribal 
representatives participated in the two webinars. Updates on the 
consultation process were provided to the National Tribal Water Council 
and EPA Region 6's Regional Tribal Operations Committee upon request at 
regularly scheduled monthly meetings during the consultation process. 
Additionally, EPA received written comments from the following Tribes 
and Tribal organizations: Little Traverse Bay Bands of Odawa Indians, 
Sault Ste. Marie Tribe of Chippewa Indians, and National Tribal Water 
Council. A summary report of the webinars and views expressed during 
the consultation is available in the Docket (EPA-HQ-OW-2022-0114).

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

    This action is subject to Executive Order 13045 because it is an 
economically significant regulatory action as defined by Executive 
Order 12866, and EPA believes that the environmental health or safety 
risk addressed by this action has a disproportionate effect on 
children. Additionally, the Agency's 2021 Policy on Children's Health 
(https://www.epa.gov/children/epas-policy-evaluating-risk-children) is 
to protect children from environmental exposures by consistently and 
explicitly considering early life exposures (from conception, infancy, 
early childhood and through adolescence) and lifelong health in all 
human health decisions through identifying and integrating data when 
conducting risk assessments of children's health. Accordingly, EPA has 
evaluated the environmental health or safety effects of PFAS found in 
drinking water on children and estimated the risk reduction and health 
endpoint impacts to children associated with adoption of treatment or 
non-treatment options to reduce PFAS in drinking water. The results of 
these evaluations are contained in the Economic Analysis of the 
Proposed PFAS NPDWR (USEPA, 2023j) and described in section XIII of 
this preamble. Copies of the Economic Analysis of the Proposed PFAS 
NPDWR and supporting information are available in the Docket (EPA-HQ-
OW-2022-0114).

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

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. The public and private water systems 
affected by this action do not, as a rule, generate power. This action 
does not regulate any aspect of energy distribution as the water 
systems that are proposed to be regulated by this rule already have 
electrical service. Finally, EPA has determined that the incremental 
energy used to implement the identified treatment technologies at 
drinking water systems in response to the proposed regulatory 
requirements is minimal. As such, EPA does not anticipate that this 
rule will have a significant adverse effect on the supply, 
distribution, or use of energy.

I. National Technology Transfer and Advancement Act of 1995

    The proposed rule could involve voluntary consensus standards in 
that it would require monitoring for PFAS and analysis of the samples 
obtained from monitoring based on required methods. EPA proposed two 
analytical methods for the identification and quantification of PFAS in 
drinking water. EPA methods 533 and 537.1 incorporate QC criteria which 
allow accurate quantitation of PFAS. Additional information about the 
analytical methods is available in section VIII of this preamble. EPA 
has made, and will continue to make, these documents generally 
available through www.regulations.gov and at the U.S. Environmental 
Protection Agency Drinking Water Docket, William Jefferson Clinton West 
Building, 1301 Constitution Ave. NW, Room 3334, Washington, DC 20460, 
call (202) 566-2426.
    EPA's monitoring and sampling protocols generally include voluntary 
consensus standards developed by agencies such as ASTM International, 
Standard Methods and other such bodies wherever EPA deems these 
methodologies appropriate for compliance monitoring. EPA welcomes 
comments on this aspect of the proposed rulemaking and, specifically, 
invites the public to identify potentially-applicable voluntary 
consensus standards and to explain why

[[Page 18735]]

such standards should be used in this regulation. The Director of the 
FR approved the voluntary consensus standards incorporated by reference 
in Sec.  141.23 of the proposed regulatory text as of April 11, 2007.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    EPA believes that this action does not have disproportionately high 
and adverse human health or environmental effects on minority 
populations or low-income populations, as specified in Executive Order 
12898 (USEPA, 1994). The proposed rule is anticipated to increase the 
level of public health protection for all affected populations without 
having any disproportionately high and adverse human health or 
environmental effects on any population, including any minority 
population. Additionally, EPA has determined that the proposed rule is 
anticipated to mitigate the disproportionate impacts of baseline PFAS 
exposure. The documentation for this decision, including additional 
detail on the methodology, results, and conclusions of EPA's EJ 
analysis, is contained in Chapter 8 of USEPA (2023j) and is available 
in the public docket for this action.
    Consistent with the Agency's Technical Guidance for Assessing 
Environmental Justice in Regulatory Analysis (USEPA, 2016g), EPA 
conducted an EJ analysis to assess the demographic distribution of 
baseline PFAS drinking water exposure and impacts anticipated to result 
from the proposed PFAS NPDWR. EPA conducted two separate analyses: an 
EJ exposure analysis using EJScreen, the Agency's Environmental Justice 
Screening and Mapping Tool (USEPA, 2019e), and an analysis of EPA's 
proposed regulatory option and alternatives using SafeWater MCBC 
(detailed in Section XIII of this preamble). EPA's analyses examine EJ 
impacts on a subset of PWSs across the country, based on availability 
of PFAS occurrence data and information on PWS' service area 
boundaries. In EPA's analysis, results for income, race, and ethnicity 
groups are generally summarized separately due to how underlying 
American Community Survey (ACS) statistics are aggregated at the census 
block group level; for more information, please see: https://www.census.gov/data/developers/data-sets/acs-5year.html (United States 
Census Bureau, 2022). Additional information on both analyses can be 
found in Chapter 8 of USEPA (2023j).
    EPA's EJ exposure analysis using EJScreen utilized hypothetical 
regulatory scenarios, which differ from EPA's proposed option and 
regulatory alternatives (for additional detail, please see Chapter 8 of 
USEPA (2023j). EPA's EJ exposure analysis demonstrated that across 
hypothetical regulatory scenarios evaluated, elevated baseline PFAS 
drinking water exposures, and thus greater anticipated reductions in 
exposure, are estimated to occur in communities of color and/or low-
income populations. For the exposure analysis, EPA examined individuals 
served by PWSs with modeled PFAS exposure above baseline concentration 
thresholds or a specific alternative policy threshold. EPA also 
summarized population-weighted average concentrations in the baseline 
as well as reductions that would accrue to each demographic group from 
hypothetical regulatory scenarios. In this analysis, EPA presents the 
total affected population as a possible metric of comparison, noting 
however that each affected demographic group is reflected also within 
the total affected population. For the purpose of evaluating potential 
EJ concerns, a commonly used demographic category is ``people of 
color,'' which includes those who identify as a race other than White 
and/or as Hispanic. It is possible that EPA understates the magnitude 
of disproportionate baseline exposure to PFAS for people of color 
because the total affected population includes some portion of the 
specific populations of concern. For this reason, EPA included 
information for non-Hispanic White populations in all tables of Section 
8.3 in Chapter 8 of USEPA (2023j). EPA also described differences in 
potential disproportionate impact when comparison is drawn from 
population groups of concern to the non-Hispanic White population 
instead of the total population across all demographic groups. EPA 
requests comment on all aspects of the EJ analysis, including its 
choice of comparison groups to help identify potential demographic 
disparities in anticipated PFAS exposure.
    Additionally, EPA's analysis in SafeWater MCBC evaluated the 
demographic distribution of health benefits and incremental household 
costs anticipated to result from the proposed PFAS NPDWR. EPA's 
proposed option and all regulatory alternatives are anticipated to 
provide benefits across all health endpoint categories for all race/
ethnicity groups. Across all health endpoints, communities of color are 
anticipated to experience the greatest quantified benefits associated 
with EPA's proposed option.
    EPA's analysis in SafeWater MCMC also demonstrated that communities 
of color are anticipated to bear elevated incremental household costs 
associated with the rule. Although the incremental household cost 
differences across race/ethnicity groups are minimal, for communities 
already facing underlying EJ concerns, the impact of these incremental 
cost increases are likely to impose a higher cost burden. In general, 
incremental household costs to all race/ethnicity groups decrease as 
system size increases, an expected result due to economies of scale. 
Due to the overlap in vulnerabilities demonstrated by slightly elevated 
household costs anticipated for particular race/ethnicity groups and 
consistently elevated household costs for households served by small 
systems, communities of color served by small systems are anticipated 
to face compounding burdens. To alleviate potential cost disparities 
identified by EPA's analysis, there may be an opportunity for some 
communities to utilize funding from national legislation, including BIL 
(Public Law 117-58), funds allocated to the Low-Income Household Water 
Assistance Program (LIHWAP) by the American Rescue Plan (Public Law 
117-2), and funding from other sources, to provide financial assistance 
for addressing emerging contaminants. BIL funding has specific 
allocations for both disadvantaged and/or small communities and 
emerging contaminants, including PFAS.
    Additionally, on March 2, 2022, and April 5, 2022, EPA held public 
meetings related to EJ and the development of the proposed NPDWR. The 
meetings provided an opportunity for EPA to share information and for 
communities to offer input on EJ considerations related to the 
development of the proposed rule. During the meeting and in subsequent 
written comments EPA received public comment on topics including 
establishing an MCL for PFAS, affordability of PFAS abatement options, 
limiting industrial discharge of PFAS, and EPA's relationship with 
community groups. For more information on the public meetings, please 
refer to the Environmental Justice Considerations for the Development 
of the Proposed PFAS Drinking Water Regulation Public Meeting Summary 
for each of the meeting dates in the public docket at https://www.regulations.gov/docket/EPA-HQ-OW-2022-0114. Additionally, the 
written public comments are included within the public docket.

[[Page 18736]]

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

    In accordance with sections 1412(d) and 1412(e) of the SDWA, the 
Agency consulted with the NDWAC (or the Council); the Secretary of 
Health and Human Services; and with the EPA SAB.
1. SAB
    The SAB PFAS Review Panel met virtually via a video meeting 
platform on December 16, 2021, and then at three (3) subsequent 
meetings on January 4, 6 and 7, 2022 to deliberate on the Agency's 
charge questions. Another virtual meeting was held on May 3, 2022, to 
discuss their draft report. Oral and written public comments were 
considered throughout the advisory process. EPA sought guidance from 
the EPA SAB on how best to consider and interpret life stage 
information, epidemiological and biomonitoring data, the Agency's 
physiologically-based pharmacokinetic (PBPK) analyses, and the totality 
of PFAS health information to derive a MCLG for PFOA and PFOS, combined 
toxicity framework, and CVD. The documents sent to SAB were EPA's 
Proposed Approaches to the Derivation of a Draft Maximum Contaminant 
Level Goal for Perfluorooctanoic Acid (PFOA) (CASRN 335-67-1) in 
Drinking Water (USEPA, 2021e); EPA's Proposed Approaches to the 
Derivation of a Draft Maximum Contaminant Level Goal for 
Perfluorooctane Sulfonic Acid (PFOS) (CASRN 1763-23-1) in Drinking 
Water (USEPA, 2021f); EPA's Framework for Estimating Noncancer Health 
Risks Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS) (USEPA, 2023d); and EPA's Analysis of Cardiovascular Disease 
Risk Reduction as a Result of Reduced PFOA and PFOS Exposure in 
Drinking Water. On May 3 and July 20, 2022, EPA received input from 
SAB, summarized in the report, Review of EPA's Analyses to Support 
EPA's National Primary Drinking Water Rulemaking for PFAS (USEPA, 
2022a).
    In response to EPA's request that the SAB review EPA's four draft 
documents listed above, the SAB identified subject matter experts to 
augment the SAB Chemical Assessment Advisory Committee (CAAC) and 
assembled the SAB PFAS Review Panel to conduct the review.
    In general, the SAB recognized the time constraints for completing 
the rule-making process and was supportive of EPA's efforts to the 
utilize the latest scientific finding to inform their decisions. The 
SAB applauded the Agency's efforts to develop new approaches for 
assessing the risk of PFAS mixtures and the benefits arising from 
reducing exposure to these chemicals as adopted by EPA in the HI 
approach in this proposed rule. In general, the SAB agreed with many of 
the conclusions presented in the assessments, framework, and analysis. 
The SAB also identified many areas that would benefit from further 
clarification to enhance their transparency and increase their utility. 
The SAB provided numerous recommendations which can be found in the 
SAB's final report (USEPA, 2022a) and some highlights are outlined 
below.
a. Approaches to the Derivation of Draft MCLGs for PFOA and PFOS
    The primary purpose of the Proposed Approaches to the Derivation of 
Draft MCLGs for PFOA and PFOS (USEPA, 2021e; USEPA, 2021f) was to 
develop MCLGs based on the best available health effects information 
for PFOA and PFOS. Each MCLG draft document includes derivation of an 
updated chronic oral RfD, CSF when relevant data were available, and an 
RSC for SAB review. The health effects information used to derive these 
toxicity values and RSC values built upon the information in the 2016 
PFOA and PFOS HESDs (USEPA, 2016e; USEPA, 2016f) and Health Advisories 
(USEPA, 2016a; USEPA, 2016b), respectively. EPA has considered all SAB 
consensus advice in the development of the proposed values derived in 
this health effects assessment and subsequently derived MCLGs for the 
NPDWRs for PFOA and PFOS based on the best available science and EPA 
guidance and precedent. Please see section IV and V of this preamble 
for discussions on the process for derivation of the MCLGs and the 
resulting proposed MCLG values for this proposed action.
    The SAB charge questions for the MCLG draft documents addressed the 
systematic review study identification and inclusion, non-cancer hazard 
identification, cancer hazard identification and slope factor, 
toxicokinetic modeling, RfD derivation, and RSC. The complete list of 
charge questions was included in EPA's documents prepared for the SAB 
(USEPA, 2022a). The SAB provided numerous specific recommendations to 
consider alternative approaches, expand the systematic review steps for 
the health effects assessment, and to develop additional analyses in 
order to improve the rigor and transparency of EPA's documents. The 
complete list of SAB consensus advice is described in their final 
report (USEPA, 2022a).
    In general, the SAB agreed with many of the conclusions presented 
in the assessments, framework, and analyses. The SAB recognized the 
time constraints for completing the rule-making process and supported 
EPA's efforts to use the latest scientific information to inform their 
decisions. The SAB applauded the Agency's efforts to develop new 
approaches for assessing the risk of PFAS mixtures and the benefits 
arising from reducing exposure to PFAS.
    The SAB also identified areas that would benefit from further 
clarification, expansion, and transparency. The SAB provided written 
comments and responses to EPA's charge questions (USEPA, 2022a) and the 
following is a summary of their recommendations and EPA's associated 
revisions.
    Regarding the approaches to deriving MCLG draft documents, the SAB 
stated that the systematic review methods could be more transparent and 
complete. Specifically, study identification and criteria for inclusion 
could be improved. EPA made revisions to the systematic review 
description and process by updating and expanding the scope of the 
literature search; providing greater transparency regarding the study 
inclusion criteria; and adding additional systematic review steps and 
transparently describing each of these steps in the PFOA and PFOS 
systematic review protocols.
    In the charge questions, EPA sought advice on the noncancer health 
assessment, and the SAB recommended that EPA separate hazard and dose-
response assessment systematic review steps. In response, EPA made 
revisions to the noncancer hazard identification by expanding 
systematic review steps beyond study quality evaluation to include 
evidence integration to address the need to separate hazard 
identification and dose-response assessment and to ensure consistent 
hazard decisions; and strengthening rationales for selection of points 
of departure for the noncancer health outcomes. Additionally, the SAB 
advised EPA to focus on the health endpoints with the strongest 
evidence (i.e., liver, immune, serum lipids, development, and cancer).
    EPA consulted with the SAB on the cancer risk assessment. On the 
cancer HI and CSF, the SAB agreed that PFOA was a ``likely'' 
designation but recommended undertaking and describing a more 
structured and transparent discussion of the ``weight of evidence'' for 
both PFOA and PFOS. EPA revised this assessment by following the 
structured approach in the EPA cancer guidelines (USEPA, 2005) to

[[Page 18737]]

develop a weight of evidence narrative for cancer, to consider the data 
for selecting the cancer classification, evaluating and integrating 
mechanistic information, and strengthening the rationales for 
decisions.
    For the toxicokinetics model that EPA sought advice on, SAB 
requested more details on the toxicokinetic modeling including model 
code and parameters and recommended that EPA consider expressing the 
RfD in water concentration equivalents to better account for possible 
life-stage specific differences in exposure rates and toxicokinetics. 
EPA considered the alternate approach suggested by SAB and made 
revisions by evaluating alternative toxicokinetic models and further 
validating the selected model.
    EPA also sought advice on the draft RfD derivation. The SAB advised 
that EPA consider multiple human and animal studies for a variety of 
endpoints and populations. The SAB also stated a need for stronger and 
more transparent justification of benchmark response selections and 
asked EPA to consider adopting a probabilistic framework to calculate 
risk-specific doses. SAB also recommended that EPA clearly state that 
RfDs apply to both short-term and chronic exposure. EPA made revisions 
based on these recommendations by providing additional descriptions and 
rationale for the selected modeling approaches and conducting new dose-
response analyses of additional studies and endpoints.
    On the RSC charge question, SAB supported the selection of a 20% 
RSC, but asked that EPA provide clarity and rationale to support the 
value. To address this recommendation, EPA added clarifying language 
related to the RSC determination from EPA guidance (USEPA, 2000c), 
including the relevance of drinking water exposures and the 
relationship between the RfD and the RSC.
b. Combined Toxicity Framework
    EPA sought advice from an external SAB on the Draft Framework for 
Estimating Noncancer Health Risks Associated with Mixtures of PFAS 
document (USEPA, 2023d). The main purpose of this document was to 
provide a data-driven framework for estimating human health risks 
associated with oral exposures to mixtures of PFAS. The charge 
questions for the SAB pertaining to the framework draft documents 
included whether EPA provided clear support for the assumption of dose 
additivity, and application of the HI, RPF, and mixtures benchmark dose 
(BMD) approaches for the evaluation of mixtures of PFAS. The full list 
of charge questions was included in EPA's documents prepared for the 
SAB (USEPA, 2022a). The SAB agreed in general with the assumption of 
dose additivity at the level of common health effect, and application 
of the HI, RPF and mixture BMD approaches for the evaluation of 
mixtures of PFAS. The SAB identified instances in which the 
communication of the analyses and approaches in EPA's framework 
document could be improved to be clearer.
    On EPA's charge question for dose additivity, the SAB agreed with 
the use of the dose additivity default assumption when evaluating PFAS 
mixtures that have similar effects and concluded that this assumption 
was health protective. SAB recommended a more thoroughly and clearly 
presented list of the uncertainties associated with this approach along 
with information supporting this approach. EPA made revisions that 
added clarity to the text by expanding upon the uncertainties and 
including additional support for using dose additivity.
    The SAB panel agreed with the use of the HI as a screening method 
and decision-making tool. SAB advised that EPA should consider using a 
menu-based framework to support selection of fit-for-purpose 
approaches, rather than a tiered approach as described in the draft 
mixtures document. Based on this feedback, EPA has since reorganized 
the approach to provide a data-driven ``menu of options'' to remove the 
tiered logic flow and is adding text to clarify the flexibility in 
implementation.
    EPA sought SAB's opinion on the RPF approach for estimating health 
risks associated with PFAS mixtures and the SAB panel considered the 
RPF approach to be a reasonable methodology for assessing mixtures. On 
the mixture BMD, the SAB agreed that the mixture BMD approach was a 
reasonable methodology for estimating a mixture-based POD. For both the 
RPF and mixture BMD approach, SAB recommended that EPA's approach would 
be strengthened by the use of PODs from animal studies that are based 
on HEDs rather than administered doses. SAB also requested 
clarification as to the similarities and differences among the RPF and 
mixture BMD approaches. SAB also asked EPA to provide additional 
information on how the proposed mixtures BMD approach would be applied 
in practice. To address these concerns, EPA made revisions to provide 
better context and delineation about the applicability of the data 
across these approaches.
c. CVD Analysis
    EPA consulted with the SAB on the Agency's methodology to determine 
the avoided cases of CVD events (e.g., heart attack, stroke, death from 
coronary heart disease) associated with reductions in exposure to PFOA 
and PFOS in drinking water to support a benefits analysis. 
Specifically, EPA sought SAB comment on the extent to which the 
approach to estimating reductions in CVD risk is scientifically 
supported and clearly described. EPA posed specific charge questions on 
the exposure-response information used in the analysis, the risk model 
and approach used to estimate the avoided cases of CVD events, and 
EPA's discussion of limitations and uncertainties of the analysis. 
Overall, the SAB supported EPA's approach to estimating reductions in 
CVD risk associated with reductions in exposure to PFOA and PFOS in 
drinking water. The SAB provided feedback on several areas of the 
analysis; main points of their feedback and EPA's responses are 
discussed below.
    The SAB noted a discrepancy between the draft CVD document's focus 
on CVD risk, and the draft MCLG documents' conclusions that the 
evidence of CVD was not sufficient to form the basis of a RfD. Based on 
SAB feedback on the draft MCLG document's assessment of CVD related 
risks, EPA has developed an RfD for total cholesterol (For more 
information see USEPA, 2023b; USEPA, 2023c). The derivation of an RfD 
for this endpoint addresses the SAB's concerns about inconsistency 
between the two documents. The SAB also recommended that EPA ensure 
that recommendations for the draft MCLG documents relating to evidence 
identification and synthesis are applied to the CVD endpoint. All 
studies in EPA's CVD benefits analysis were evaluated for risk of bias, 
selective reporting, and sensitivity as applied in EPA's Public Comment 
Draft--Toxicity Assessment and Proposed MCLGs for PFOA and PFOS in 
Drinking Water (USEPA, 2023b; USEPA, 2023c).
    The SAB recommended that EPA provide more discussion as to the 
rationale for selecting CVD for risk reduction analysis and that the 
approach follows the pathway that links cholesterol to cardiovascular 
events rather than looking at the reported effects of PFAS directly on 
CVD. The SAB also recommended that EPA consider risk reduction analyses 
for other endpoints. In Section 6.5 of the Economic Analysis, EPA 
discusses the rationale for quantifying CVD and analytical assumptions. 
Sections 6.4 and

[[Page 18738]]

6.6 discusses the Agency's quantified risk reduction analyses for other 
adverse health effects, including infant birthweight effects and RCC, 
respectively. In Section 6.2.2 EPA assesses the qualitative benefits of 
other adverse health effects of PFAS.
    Although the SAB generally agreed with the meta-analysis, life 
table and risk estimation methods, the SAB recommended that EPA provide 
additional clarity as to the application of these approaches and 
conduct additional sensitivity analyses. In response to these comments, 
EPA expanded documentation and conducted additional sensitivity 
analyses to evaluate the impact of inclusion or exclusion of certain 
studies in the meta-analyses of exposure-response estimates. Further, 
EPA expanded documentation and conducted additional sensitivity 
analyses to assess the effects of using a key single study approach 
versus the meta-analysis approach to inform the exposure-response 
estimates. EPA identified two suitable key studies for use in the 
single study approach. EPA found that the single study approach 
resulted in increased benefits, and this trend was driven by the larger 
estimates of PFAS-total cholesterol slope factors and inverse 
associations in the HDLC effect for one or both contaminants in the key 
single studies. EPA elected to retain the meta-analysis approach in the 
benefits analysis because the Agency identified several studies on 
adults in the general population with large numbers of participants and 
low risk of bias, and in this case the meta-analytical approach offers 
an increased statistical power over the single study approach. While 
the single study approach is common for RfD derivations, the meta-
analysis pooled estimate provides a slope factor that represents the 
average response across a larger number of studies, which is useful in 
evaluating benefits resulting from changes in CVD risk on a national 
scale.
    The SAB also recommended that EPA evaluate how inclusion of HDLC 
effects would influence the results and provide further justification 
for the inclusion or exclusion of HDLC and blood pressure effects. EPA 
found that, as expected, inclusion of HDLC effects decreases annualized 
CVD benefits and inclusion of blood pressure effects slightly increases 
annualized CVD benefits. Because HDLC was shown to have a stronger 
effect than blood pressure on annualized CVD benefits, inclusion of 
blood pressure and HDLC effects together decreases annualized CVD 
benefits. For more information see sensitivity analyses evaluating 
these effects in Appendix K of the EA. Inclusion of HDLC effects into 
the national analysis would reduce national benefits estimates but 
would not change EPA's bottom-line conclusion that the quantifiable and 
nonquantifiable benefits of the rule justify the quantifiable and 
nonquantifiable costs. After further examination of the evidence for 
HDLC and blood pressure effects, EPA elected to include blood pressure 
effects because the findings from a single high confidence study and 
several medium confidence studies conducted among the general 
population provided consistent evidence of an association between PFOS 
exposure and blood pressure. EPA did not include HDLC effects in the 
national benefits analysis because available evidence of associations 
between PFOS exposures and HDLC levels is inconsistent and there is no 
evidence of an association between PFOA exposures and HDLC levels.
    Finally, the SAB noted that while the ASCVD model is a reasonable 
choice for estimating the probability of first time CVD events, it is 
not without limitations. The panel recommended that EPA include more 
discussion of the accuracy of its predictions, particularly for sub-
populations. EPA expanded its evaluation of the ASCVD model's 
limitations, including a comparison of the ASCVD model predictions with 
race/ethnicity and sex-specific CVD incidence from CDC's public health 
surveys (See Section 6.5.3.2 and Appendix G of the Economic Analysis 
for details). Results show that the ASCVD model coefficients for the 
non-Hispanic Black model are more consistent with data on CVD 
prevalence and mortality for Hispanic and non-Hispanic other race 
subpopulations than the ASCVD model coefficients for the non-Hispanic 
White model.
2. NDWAC
    The Agency consulted with NDWAC during the Council's April 19, 
2022, virtual meeting. A summary of the NDWAC recommendations is 
available in the National Drinking Water Advisory Council, Fall 2022 
Meeting Summary Report (NDWAC, 2022 https://www.federalregister.gov/documents/2022/03/29/2022-06576/meeting-of-the-national-drinking-water-advisory-council) and the docket for this proposed rule. EPA carefully 
considered NDWAC recommendations during the development of a proposed 
drinking water rule for PFAS, including PFOA and PFOS.
3. HHS
    On September 28, 2022, EPA consulted with the Department of Health 
and Human Services (HHS). EPA provided information to HHS officials on 
the draft proposed NPDWR and considered HHS input as part of the 
interagency review.

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USEPA. 2021d. Announcement of Final Regulatory Determinations for 
Contaminants on the Fourth Drinking Water Contaminant Candidate 
List. Federal Register. 86 FR 12272, March 3, 2021.
USEPA. 2021e. Proposed Approaches to the Derivation of a Draft 
Maximum Contaminant Level Goal for Perfluorooctanoic Acid 
(PFOA)(CASRN 335-67-1) in Drinking Water. EPA 822-D-21-001. 
Available on the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:16490947993:::RP,18:P18_ID:2601.
USEPA. 2021f. Proposed Approaches to the Derivation of a Draft 
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Available on the internet at: https://sab.epa.gov/ords/sab/f?p=100:18:16490947993:::RP,18:P18_ID:2601.
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Activated Carbon Drinking Water Treatment. Available on the internet 
at: https://www.epa.gov/system/files/documents/2022-03/gac-documentation-.pdf_0.pdf.
USEPA. 2021h. Work Breakdown Structure-Based Cost Model for Ion 
Exchange Treatment of Per- and Polyfluoroalkyl Substances (PFAS) in 
Drinking Water.
USEPA. 2021i. Work Breakdown Structure-Based Cost Model for Reverse 
Osmosis/Nanofiltration Drinking Water Treatment. Available on the 
internet at: https://www.epa.gov/system/files/documents/2022-03/ronf-documentation-.pdf.pdf.
USEPA. 2021j. Work Breakdown Structure-Based Cost Model for 
Nontreatment Options for Drinking Water Compliance. Available on the 
internet at: https://www.epa.gov/sites/default/files/2019-07/documents/wbs-nontreatment-documentation-june-2019.pdf.

[[Page 18746]]

USEPA. 2021k. IRIS Toxicological Review of Perfluorobutanoic Acid 
(PFBA) and Related Salts (Public Comment and External Review Draft, 
2021). EPA/635/R-20/424. Retrieved from https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=350051.
USEPA. 2022a. Transmittal of the Science Advisory Board Report 
titled, ``Review of EPA's Analyses to Support EPA's National Primary 
Drinking Water Rulemaking for PFAS.'' EPA-22-008. Available on the 
internet at: https://sab.epa.gov/ords/sab/f?p=114:12:15255596377846.
USEPA. 2022b. Drinking Water Contaminant Candidate List 5--Final. 
Federal Register. 87 FR 68060, November 14, 2022.
USEPA. 2022c. PFAS Strategic Roadmap: EPA's Commitments to Action 
2021-2024. Available on the internet at: https://www.epa.gov/pfas/pfas-strategic-roadmap-epas-commitments-action-2021-2024.
USEPA. 2022d. Drinking Water Health Advisory: Hexafluoropropylene 
Oxide (HFPO) Dimer Acid (CASRN 13252-13-6) and HFPO Dimer Acid 
Ammonium Salt (CASRN 62037-80-3), Also Known as ``GenX Chemicals.'' 
EPA/822/R-22/005. Available on the internet at: https://www.epa.gov/system/files/documents/2022-06/drinking-water-genx-2022.pdf.
USEPA. 2022e. Drinking Water Health Advisory: Perfluorobutane 
Sulfonic Acid (CASRN 375-73-5) and Related Compound Potassium 
Perfluorobutane Sulfonate (CASRN 29420-49-3). EPA/822/R-22/006. 
Available on the internet at: https://www.epa.gov/system/files/documents/2022-06/drinking-water-pfbs-2022.pdf.
USEPA. 2022f. ORD Staff Handbook for Developing IRIS Assessments. 
EPA 600/R-22/268. Available on the internet at: https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=356370.
USEPA. 2022g. Fifth Unregulated Contaminant Monitoring Rule. 
Available on the internet at: https://www.epa.gov/dwucmr/fifth-unregulated-contaminant-monitoring-rule.
USEPA, 2022h. IRIS Toxicological Review of Perfluorohexanoic Acid 
(PFHxA) and Related Salts (Public Comment and External Review 
Draft). EPA/635/R-21/312a. Retrieved from https://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=352767.
USEPA. 2023a. Maximum Contaminant Level Goal (MCLG) Summary Document 
for a Mixture of Four Per- and Polyfluoroalkyl Substances (PFAS): 
GenX Chemicals, PFBS, PFNA and PFHxS. EPA-822-P-23-004.
USEPA. 2023b. Public Comment Draft--Toxicity Assessment and Proposed 
Maximum Contaminant Level Goal (MCLG) for Perfluorooctanoic Acid 
(PFOA) (CASRN 335-67-1) in Drinking Water. EPA-822-P-23-005.
USEPA. 2023c. Public Comment Draft--Toxicity Assessment and Proposed 
Maximum Contaminant Level Goal (MCLG) for Perfluorooctane Sulfonic 
Acid (PFOS) (CASRN 1763-23-1) in Drinking Water. EPA-822-P-23-007.
USEPA. 2023d. Framework for Estimating Noncancer Health Risks 
Associated with Mixtures of Per- and Polyfluoroalkyl Substances 
(PFAS). EPA-822-P-23-003.
USEPA. 2023e. PFAS Occurrence and Contaminant Background Support 
Document. EPA-822-P-23-010.
USEPA. 2023f. EPA Response to Final Science Advisory Board 
Recommendations (August 2022) on Four Draft Support Documents for 
the EPA's Proposed PFAS National Primary Drinking Water Regulation. 
EPA-822-D-23-001.
USEPA. 2023g. Best Available Technologies and Small System 
Compliance Technologies Per- and Polyfluoroalkyl Substances (PFAS) 
in Drinking Water. EPA-822-P-23-009.
USEPA. 2023h. Technologies and Costs for Removing Per- and 
Polyfluoroalkyl Substances from Drinking Water. EPA-822-P-23-011.
USEPA. 2023i. Appendix: Economic Analysis of the Proposed National 
Primary Drinking Water Regulation for Per- and Polyfluoroalkyl 
Substances. EPA-822-P-23-002.
USEPA. 2023j. Economic Analysis of the Proposed National Primary 
Drinking Water Regulation for Per- and Polyfluoroalkyl Substances. 
EPA-822-P-23-001.
USEPA. 2023k. Public Comment Draft--Appendix: Toxicity Assessment 
and Proposed Maximum Contaminant Level Goal for Perfluorooctane 
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Washington, DC EPA-822-P-23-008.
USEPA. 2023l. Public Comment Draft--Appendix: Toxicity Assessment 
and Proposed Maximum Contaminant Level Goal for Perfluorooctanoic 
Acid (PFOA) (CASRN 335-67-1) in Drinking Water. Washington, DC EPA-
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USEPA. 2023m. EPA Response to Letter of Peer Review for Disinfectant 
Byproduct Reduction as a Result of Granular Activated Carbon 
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Steuerwald, U., and Grandjean, P. 2017. Gestational Diabetes and 
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Longnecker, M.P. 2015. Associations of Perfluoroalkyl Substances 
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and Fletcher, T. 2013. Perfluorooctanoic Acid Exposure and Cancer 
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List of Subjects

40 CFR Part 141

    Environmental protection, Indians--lands, Intergovernmental 
relations, National Primary Drinking Water Regulation, PFAS, Monitoring 
and analytical requirements, Reporting and recordkeeping requirements, 
Water supply, Incorporation by reference.

40 CFR Part 142

    Environmental protection, Administrative practice and procedure, 
Indians--lands, Intergovernmental relations, National Primary Drinking 
Water Regulation, PFAS, Monitoring and analytical requirements, 
Reporting and recordkeeping requirements, Water supply.

Michael S. Regan,
Administrator.

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

PART 141--NATIONAL PRIMARY DRINKING WATER REGULATIONS

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

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

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

Sec.  141.2  Definitions.

* * * * *
    Hazard index (HI) is the sum of component hazard quotients (HQs), 
which are calculated by dividing the measured regulated PFAS component 
contaminant concentration in water (e.g., expressed as ppt or ng/l) by 
the associated Health-Based Water Concentration (e.g., HBWC expressed 
as ppt). For PFAS, a mixture HI greater than 1.0 (unitless) is an 
exceedance of the MCL.
    Hazard quotient (HQ) are the ratio of potential exposure to a 
substance and the level at which no health effects are expected.
    Health-based water concentration (HBWC) are levels protective of 
health effects over a lifetime of exposure, including sensitive 
populations and life stages.
    HFPO-DA or GenX chemicals means Chemical Abstract Service 
registration number 122499-17-6, chemical formula C6F11O3-, 
International Union of Pure and Applied Chemistry preferred name 
2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoate, along with its 
conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
* * * * *
    PFBS means Chemical Abstract Service registration number 45187-15-
3, chemical formula C4F9SO3-, perfluorobutane sulfonate, along with its 
conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
    PFHxS means Chemical Abstract Service registration number 108427-
53-8, chemical formula C6F13SO3-, perfluorohexane sulfonate, along with 
its conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
    PFNA means Chemical Abstract Service registration number 72007-68-
2, chemical formula C9F17O2-, perfluorononanoate, along with its 
conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
    PFOA means Chemical Abstract Service registration number 45285-51-
6, chemical formula C8F15CO2-, perfluorooctanoate, along with its 
conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
    PFOS means Chemical Abstract Service registration number 45298-90-
6, chemical formula C8F17SO3-, perfluorooctanesulfonate, along with its 
conjugate acid and any salts, derivatives, isomers or combinations 
thereof.
* * * * *
0
3. Amend Sec.  141.6 by revising paragraph (a) and adding paragraph (l) 
to read as follows:

Sec.  141.6  Effective dates.

    (a) Except as provided in paragraphs (b) through (1) of this 
section the regulations set forth in this part shall take effect on 
June 24, 1977.
* * * * *
    (l) The regulations contained in the revision to Sec. Sec.  141.50, 
141.60, 141.61, 141.154, 141.151 through 141.155; and 141.201 through 
141.211 are effective for the purposes of compliance on [DATE THREE 
YEARS AFTER DATE OF PUBLICATION OF FINAL RULE IN THE FEDERAL REGISTER]
0
4. Amend Sec.  141.28 by revising paragraph (a) to read as follows:

Sec.  141.28  Certified laboratories.

    (a) For the purpose of determining compliance with Sec.  141.21 
through 141.27, 141.30, 141.40, 141.74, 141.89, 141.402, and 141.900 
through 141.905, samples may be considered only if they have been 
analyzed by a laboratory certified by the State except that 
measurements of alkalinity, disinfectant residual, orthophosphate, pH, 
silica, temperature, and turbidity may be performed by any person 
acceptable to the State.
* * * * *

[[Page 18748]]

0
5. Amend Sec.  141.50 by adding paragraphs (a)(24) and (25) and in the 
table in paragraph (b), revising the heading for the second column and 
adding an entry for ``(34)'' and footnote 1 to read as follows:

Sec.  141.50  Maximum contaminant level goals for organic contaminants.

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

------------------------------------------------------------------------
                                         MCLG in mg/l (unless otherwise
             Contaminant                             noted)
------------------------------------------------------------------------
 
                              * * * * * * *
(34) Hazard Index PFAS (PFNA, HFPO-    1.0 (unitless).\1\
 DA, PFHxS, and PFBS).
------------------------------------------------------------------------
\1\ The PFAS Mixture HI MCLG is the sum of component hazard quotients
  (HQs), which are calculated by dividing the measured component PFAS
  concentration in water (e.g., expressed as ppt or ng/l) by the
  corresponding contaminant's Health-Based Water Concentration (e.g.,
  HBWC expressed as ppt). The HBWC for PFHxS is 9.0 ppt; the HBWC for
  HFPO-DA is 10.0 ppt; the HBWC for PFNA is 10 ppt; the HBWC for PFBS is
  2000.0 ppt. A PFAS Mixture HI MCLG greater than 1.0 (unitless)
  indicates an exceedance of the health protective level and indicates
  potential human health risk from the PFAS mixture in drinking water.
  HI MCLG = ([GenXwater]/[10 ppt]) + ([PFBSwater]/[2000 ppt]) +
  ([PFNAwater]/[10 ppt]]) + ([PFHxSwater]/[9.0 ppt]).

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

Sec.  141.60  Effective dates.

    (a) * * *
    (4) The effective date for paragraphs (c)(34) through (36) is [DATE 
OF PUBLICATION OF FINAL RULE IN THE FEDERAL REGISTER].
* * * * *
0
7. Amend Sec.  141.61:
0
a. In the table in paragraph (b) by adding entries for ``45285-51-6'', 
``45298-90-6'', and ``108427-53-8; 122499-17-6; 72007-68-2; 45187-15-
3'' at the end of the table; and
0
b. In the table in paragraph (c) by revising the heading for the third 
column, adding entries for ``(34)'', ``(35)'', and ``(36)'' at the end 
of the table, and adding footnote 1.
    The additions read as follows:

Sec.  141.61  Maximum contaminant levels for organic contaminants.

    (b) * * *

                            BAT for Organic Contaminants in Sec.   141.61 (a) and (c)
----------------------------------------------------------------------------------------------------------------
            CAS. No.                  Contaminant            GAC                PTA                   OX
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
45285-51-6......................  PFOA...............               X
45298-90-6......................  PFOS...............               X
108427-53-8; 122499-17-6; 72007-  Hazard Index PFAS                 X
 68-2; 45187-15-3.                 (PFNA, HFPO-DA,
                                   PFHxS, and PFBS.
----------------------------------------------------------------------------------------------------------------

    (c) * * *

----------------------------------------------------------------------------------------------------------------
                CAS. No.                            Contaminant             MCL (mg/L) (unless otherwise noted)
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
(34) 45285-51-6.........................  PFOA...........................  0.0000040.
(35) 45298-90-6.........................  PFOS...........................  0.0000040.
(36) 108427-53-8; 122499-17-6; 72007-68-  Hazard Index PFAS (PFNA, HFPO-   1.0 (unitless).\1\
 2; 45187-15-3.                            DA, PFHxS, and PFBS.
----------------------------------------------------------------------------------------------------------------
\1\ The PFAS Mixture HI MCL is the sum of component hazard quotients (HQs), which are calculated by dividing the
  measured component PFAS concentration in water (e.g., expressed as ppt) by the relevant Health-Based Water
  Concentration (e.g., HBWC expressed as ppt. The HBWC for PFHxS is 9.0 ppt; the HBWC for HFPO-DA is 10.0 ppt;
  the HBWC for PFNA is 10.0 ppt the HBWC for PFBS is 2000.0 ppt. A PFAS Mixture HI MCL greater than 1.0 is an
  MCL violation. HI MCL = ([GenXwater]/[10 ppt]) + ([PFBSwater]/[2000 ppt]) + ([PFNAwater]/[10 ppt]) +
  ([PFHxSwater]/[9.0 ppt]).

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

Sec.  141.151  Purpose and applicability of this subpart

* * * * *
    (d) For the purpose of this subpart, detected means: at or above 
the levels prescribed by Sec.  141.23(a)(4) for inorganic contaminants, 
at or above the levels prescribed by Sec.  141.24(f)(7) for the 
contaminants listed in Sec.  141.61(a), at or above the levels 
prescribed by Sec.  141.24(h)(18) for the contaminants listed in Sec.  
141.61(c), at or above the levels prescribed by Sec.  141.131(b)(2)(iv) 
for the contaminants or contaminant groups listed in Sec.  141.64, at 
or above the levels prescribed by Sec.  141.25(c) for radioactive 
contaminants, and at or above the levels prescribed Sec.  141.902(a)(9) 
for PFAS listed in Sec.  141.61(c).
* * * * *

[[Page 18749]]

0
9. Amend Sec.  141.154 by adding paragraph (g) to read as follows:

Sec.  141.154  Required additional health information.

* * * * *
    (g) Community water systems that detect any PFAS above the MCL in 
Sec.  141.61(c), as monitored and calculated under the provisions of 
subpart Z of this part must include health effects language for PFAS 
prescribed by appendix A to subpart O of this part.
0
10. Amend appendix A to subpart O by adding entries for ``PFOA'', 
``PFOS'', and ``Hazard Index PFAS (PFHxS, HFPO-DA, PFNA, and PFBS)'' at 
the end of the table and adding footnote 2 immediately after footnote 1 
to read as follows:

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

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                   Traditional     To convert for                                            Major sources in         Health effects
      Contaminant (units)          MCL in mg/L    CCR, multiply by    MCL in CCR units        MCLG            drinking water             language
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
PFOA...........................       0.0000040  1,000,000.........  4.0 ppt...........               0  Discharge from           Some people who drink
                                                                                                          manufacturing and        water containing PFOA
                                                                                                          industrial chemical      in excess of the MCL
                                                                                                          facilities, and          could develop immune
                                                                                                          certain firefighting     health effects, fetal
                                                                                                          activities.              growth effects after
                                                                                                                                   exposure during
                                                                                                                                   pregnancy, certain
                                                                                                                                   types of cancers, or
                                                                                                                                   an increased risk of
                                                                                                                                   cardiovascular
                                                                                                                                   disease or liver
                                                                                                                                   disease.
PFOS...........................       0.0000040  1,000,000.........  4.0 ppt...........               0  Discharge from           Some people, including
                                                                                                          manufacturing and        children, who drink
                                                                                                          industrial chemical      water containing PFOS
                                                                                                          facilities, and          in excess of the MCL
                                                                                                          certain firefighting     could develop immune
                                                                                                          activities.              health effects, fetal
                                                                                                                                   growth effects after
                                                                                                                                   exposure during
                                                                                                                                   pregnancy, certain
                                                                                                                                   types of cancers, or
                                                                                                                                   an increased risk of
                                                                                                                                   cardiovascular
                                                                                                                                   disease or liver
                                                                                                                                   disease.
Hazard Index PFAS (PFHxS, HFPO-  1.0 (unitless)  No conversion.....  No conversion.....         \2\ 1.0  Discharge from           Some people who drink
 DA, PFNA, and PFBS).                                                                                     manufacturing and        water containing
                                                                                                          industrial chemical      PFHxS, HFPO-DA, PFNA,
                                                                                                          facilities, and          and PFBS in excess of
                                                                                                          certain firefighting     the Hazard Index MCL
                                                                                                          activities.              could develop
                                                                                                                                   thyroid, liver, or
                                                                                                                                   developmental health
                                                                                                                                   effects.
--------------------------------------------------------------------------------------------------------------------------------------------------------
 * * * * * * *
\2\ Subpart A of Sec.   141.2.

* * * * *
0
11. Amend appendix A to subpart Q under the Contaminant heading ``D. 
Synthetic Organic Chemicals (SOCs)'' by adding entries for ``31'', 
``32'', and ``33'' in numerical to read as follows:

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

----------------------------------------------------------------------------------------------------------------
                                                    MCL/MRDL/TT violations \2\    Monitoring & testing procedure
                                                 --------------------------------           violations
                                                                                 -------------------------------
                   Contaminant                    Tier of public                  Tier of public
                                                      notice         Citation         notice         Citation
                                                     required                        required
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
31..............................................               2       141.61(c)               3          141.XX
32..............................................               2       141.61(c)               3          141.XX
33..............................................               2       141.61(c)               3          141.XX
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
 * * * * * * *
\1\ Violations and other situations not listed in this table (e.g., failure to prepare Consumer Confidence
  Reports), do not require notice, unless otherwise determined by the primacy agency. Primacy agencies may, at
  their option, also require a more stringent public notice tier (e.g., Tier 1 instead of Tier 2 or Tier 2
  instead of Tier 3) for specific violations and situations listed in this appendix, as authorized under Sec.
  141.202(a) and Sec.   141.203(a).
\2\ MCL--Maximum contaminant level, MRDL--Maximum residual disinfectant level, TT--Treatment technique.

[[Page 18750]]

* * * * *
0
12. Amend appendix B to subpart Q by adding entries for ``PFOA'', 
``PFOS'', and ``Hazard Index PFAS (PFHxS, HFPO-DA, PFNA, and PFBS)'' at 
the end of the table under new heading ``J. PFAS'' and adding footnote 
24 to read as follows:

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

----------------------------------------------------------------------------------------------------------------
                                                                                       Standard health effects
            Contaminant                   MCLG \1\ mg/L           MCL \2\ mg/L           language for public
                                                                                             notification
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                                     J. PFAS
----------------------------------------------------------------------------------------------------------------
PFOA...............................  0.....................  0.0000040.............  Some people, including
                                                                                      children, who drink water
                                                                                      containing PFOA in excess
                                                                                      of the MCL could develop
                                                                                      immune health effects,
                                                                                      fetal growth effects after
                                                                                      exposure during pregnancy,
                                                                                      certain types of cancers,
                                                                                      or an increased risk of
                                                                                      cardiovascular disease or
                                                                                      liver disease.
PFOS...............................  0.....................  0.0000040.............  Some people, including
                                                                                      children, who drink water
                                                                                      containing PFOS in excess
                                                                                      of the MCL could develop
                                                                                      immune health effects,
                                                                                      fetal growth effects after
                                                                                      exposure during pregnancy,
                                                                                      certain types of cancers,
                                                                                      or an increased risk of
                                                                                      cardiovascular disease or
                                                                                      liver disease.
Hazard Index PFAS (PFHxS, HFPO-DA,   1.0 (unitless)........  1.0 (unitless) \24\...  Some people who drink water
 PFNA, and PFBS).                                                                     containing PFHxS, HFPO-DA,
                                                                                      PFNA, and PFBS in excess
                                                                                      of the Hazard Index MCL
                                                                                      could develop thyroid,
                                                                                      liver, or developmental
                                                                                      health effects.
----------------------------------------------------------------------------------------------------------------
\1\ MCLG--Maximum contaminant level goal.
\2\ MCL--Maximum contaminant level.
 * * * * * * *
\24\ Subpart A of Sec.   141.2.
 * * * * * * *

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

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

* * * * *
HI Hazard Index
* * * * *
PFAS Per- and Polyfluoroalkyl Substances
* * * * *
0
14. Subpart Z is added to read as follows:

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

Sec.
141.900 General requirements.
141.901 Analytical requirements.
141.902 Monitoring requirements.
141.903 Compliance requirements.
141.904 Reporting and recordkeeping requirements.
141.905 Violations.

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

Sec.  141.900  General requirements.

    (a) The requirements of this subpart constitute national primary 
drinking water regulations. These regulations establish criteria under 
which control of certain PFAS is required for community water systems 
(CWS) and non-transient, non-community water systems (NTNCWS). Each CWS 
and NTNCWS must comply with the maximum contaminant levels for certain 
PFAS as outlined in this subpart.
    (b) Compliance dates.
    (c) CWS and NTNCWS, unless otherwise noted, must comply with the 
requirement of this subpart.

Sec.  141.901  Analytical requirements.

    (a) General. (1) Systems must use only the analytical methods 
specified in this section to demonstrate compliance with the 
requirement of this subpart.
    (2) The following documents are incorporated by reference. This 
incorporation by reference was approved by the Director of the Federal 
Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies 
may be inspected at EPA's Drinking Water Docket, 1301 Constitution 
Avenue NW, EPA West, Room 3334, Washington, DC 20460 (Telephone: 202-
566-2426); or at the National Archives and Records Administration 
(NARA). For information on the availability of this material at NARA, 
call 202-741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
    (i) EPA method 533: Determination of Per- and Polyfluoroalkyl 
Substances in Drinking Water by Isotope Dilution Anion Exchange Solid 
Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry, 
(December 2019, 815-B-19-020). https://www.epa.gov/dwanalyticalmethods/method-533-determination-and-polyfluoroalkyl-substances-drinking-water-isotope;
    (ii) Method 537.1: Determination of Selected Per- and 
Polyfluorinated Alkyl Substances in Drinking Water by Solid Phase 
Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/
MS) (November 2018, EPA/600/R-18/352). https://cfpub.epa.gov/si/si_public_record_Report.cfm?dirEntryId=343042&Lab=NERL.
    (b) PFAS--(1) Analytical methods. Systems must measure regulated 
PFAS by the methods listed in the following table:

                       Table 1 to Paragraph (b)(1)
------------------------------------------------------------------------
                       Contaminant                          EPA method
------------------------------------------------------------------------
Perfluorooctanesulfonic acid (PFOS).....................      533, 537.1
Perfluorooctanoic acid (PFOA)...........................      533, 537.1
Hazard Index PFAS (PFNA, HFPO-DA, PFHxS, and PFBS)......      533, 537.1
------------------------------------------------------------------------

    (2) Laboratory certification. Analyses under this section for 
regulated PFAS must be conducted by laboratories that have received 
certification by the State.
    (i) Beginning [DATE OF PUBLICATION OF FINAL RULE IN THE FEDERAL 
REGISTER], report quantitative data for concentrations at least as low 
as the ones listed in the following table for all PFAS samples analyzed 
for compliance with Sec.  141.902 (Monitoring Requirements).
    (ii) [Reserved]

[[Page 18751]]

    (iii) To receive certification to conduct analyses for the 
regulated PFAS contaminants, the laboratory must:
    (A) Analyze Performance Evaluation (PE) samples that are acceptable 
to the State at least once during each consecutive 12-month period by 
each method for which the laboratory desires certification.
    (B) Beginning [DATE OF PUBLICATION OF FINAL RULE IN THE FEDERAL 
REGISTER], the laboratory must achieve quantitative results on the PE 
sample analyses that are within the following acceptance limits:

                   Table 2 to Paragraph (b)(2)(iii)(B)
------------------------------------------------------------------------
                                                            Acceptance
                                                              limits
                       Contaminant                          (percent of
                                                            true value)
------------------------------------------------------------------------
Perfluorooctanesulfonic acid (PFOS).....................          70-130
Perfluorooctanoic acid (PFOA)...........................          70-130
Hazard Index PFAS--PFNA.................................          70-130
Hazard Index PFAS--HFPO-DA..............................          70-130
Hazard Index PFAS--PFHxS................................          70-130
Hazard Index PFAS--PFBS.................................          70-130
------------------------------------------------------------------------

Sec.  141.XX.  Monitoring requirements.

    (a) General requirements. (1) Systems must take all samples during 
normal operating conditions at all entry points to the distribution 
system.
    (2) If the system draws water from more than one source and the 
sources are combined before distribution, the system must sample at an 
entry point to the distribution system during periods of representative 
operating conditions.
    (3) Failure to monitor in accordance with the monitoring 
requirements required under paragraph (b) of this section is a 
monitoring violation.
    (4) If a system fails to collect the required number of samples, 
compliance will be based on the total number of samples collected.
    (5) Systems must only use data collected under the provisions of 
this subpart to qualify for reduced monitoring.
    (6) All new systems that begin operation after, or systems that use 
a new source of water after, [DATE OF PUBLICATION OF FINAL RULE IN THE 
FEDERAL REGISTER] must demonstrate compliance with the MCLs within a 
period of time specified by the State. The system must also comply with 
initial sampling frequencies required by the State to ensure that the 
system can demonstrate compliance with the MCLs. Routine and increased 
monitoring frequencies must be conducted in accordance with the 
requirements in this section.
    (7) For purposes of this section, the trigger level is defined as 
1.3 ppt for PFOA and PFOS and a Hazard Index of 0.33 for PFAS.
    (8) Based on initial monitoring results, for each sampling point at 
which a contaminant listed in Sec.  141.61(c) is detected at a level 
greater than or equal to the trigger level, the system must monitor 
quarterly for all regulated PFAS beginning in the next quarter, in 
accordance with Sec.  141.902(a).
    (9) For purposes of this section, a reportable detection means at 
or above one-third of the levels described in the table outlined in 
Sec.  141.903(f)(1)(i)(3).
    (b) Monitoring requirements for PFAS--(1) Initial compliance 
period. (i) Groundwater CWS and NTNCWS serving greater than 10,000 and 
all surface water CWS and NTNCWS must take four consecutive quarterly 
samples for each contaminant listed in Sec.  141.61(c).
    (ii) All groundwater CWS and NTNCWS serving 10,000 or fewer shall 
take two samples for each contaminant listed in 141.61(c) at least 
ninety days apart within a 12-month period.
    (iii) All groundwater under the direct influence (GWUDI) CWS and 
NTNCWS shall follow the surface water CWS and NTNCWS monitoring 
schedule based on system size, though a State may require more frequent 
monitoring on a system-specific basis.
    (iv) Systems must monitor at a frequency indicated in the following 
table:

                                         Table 1 to Paragraph (b)(1)(iv)
----------------------------------------------------------------------------------------------------------------
             Type of system                 Minimum monitoring frequency               Sample location
----------------------------------------------------------------------------------------------------------------
Groundwater CWS and NTNCWS serving        Four consecutive quarters of      EPTDS.
 greater than 10,000 persons and all       samples per entry point to the
 surface water CWS and NTNCWS.             distribution system (EPTDS).
                                           Samples must be taken at least
                                           ninety days apart.
Groundwater CWS and NTNCWS serving        In a consecutive 12-month         EPTDS.
 10,000 or fewer persons.                  period, two samples per each
                                           EPTDS. Samples must be acquired
                                           at least ninety days apart.
----------------------------------------------------------------------------------------------------------------

    (v) To satisfy initial compliance period monitoring requirements a 
State may accept data that has been previously acquired by a water 
system to count toward the initial monitoring requirements listed in 
table 1 to paragraph (b)(1)(iv) of this section. Such data may only be 
used if it was collected in accordance with Sec.  141.40 and that such 
samples were collected starting on or after January 1, 2023. Data 
collected between January 1, 2019, and December 31, 2022, may also be 
used if it is below the rule trigger level of 1.3 ppt for PFOA and PFOS 
and below an HI of 0.33.
    (vi) If systems have multiple years of data, the most recent data 
must be used. If a system has fewer than the number of samples required 
for initial monitoring as listed in the table, then all surface water 
systems, GWUDI systems, and groundwater systems serving greater than 
10,000 must collect at least one sample in each quarter of a calendar 
year that was not acquired, and groundwater systems serving 10,000 or 
fewer must collect one sample in a different quarter of the calendar 
year than the one in which the previous sample was acquired. This must 
be completed by [DATE THREE YEARS AFTER DATE OF PUBLICATION OF FINAL 
RULE IN THE FEDERAL REGISTER].
    (2) Compliance monitoring. (i) Based on initial monitoring results, 
or on compliance monitoring results after the initial monitoring 
period, systems may reduce monitoring at each sampling point at which 
the rule trigger level was not met or exceeded in accordance with the 
following table, except as otherwise provided by the State.

[[Page 18752]]

                     Table 2 to Paragraph (b)(2)(i)
------------------------------------------------------------------------
                                 You may reduce
     If you are a . . .       monitoring if your .      To this level
                                       . .
------------------------------------------------------------------------
CWS and NTNCWS serving more   Averages from         In a consecutive 12-
 than 3,300 persons.           initial monitoring    month period, two
                               period or             samples per each
                               compliance            EPTDS during each
                               monitoring running    three-year
                               annual averages for   compliance period.
                               PFOA and PFOS are     Samples must be
                               each <1.3 ppt and     acquired at least
                               HI <0.33.             ninety days apart.
CWS and NTNCWS serving 3,300  Averages from         One sample at each
 or fewer persons.             initial monitoring    EPTDS during each
                               period or             three-year
                               compliance            compliance period
                               monitoring running    for a total of one
                               annual averages for   sample per three-
                               PFOA and PFOS are     year compliance
                               each <1.3 ppt and     period.
                               HI <0.33.
------------------------------------------------------------------------

    (ii) If a system is monitoring less frequently than quarterly and 
if a contaminant listed in Sec.  141.61(c) is detected at a level 
exceeding the trigger level of 1.3 ppt for either PFOS or PFOA, or a 
Hazard Index of 0.33 for PFNA, PFHxS, HFPO-DA, and PFBS in any sample, 
then the system must monitor quarterly beginning in the next quarter at 
each sampling point which resulted in a detection in accordance with 
Sec.  141.902(a). The triggering sample must be used as the first 
quarter of monitoring for the running annual average calculation.
    (iii) Systems that are at or exceed the trigger level of 1.3 ppt 
for either PFOS or PFOA, or a Hazard Index of 0.33 for PFNA, PFHxS, 
HFPO-DA, and PFBS must conduct quarterly monitoring for regulated PFAS 
for at least four consecutive quarters. If after four consecutive 
quarters of quarterly monitoring, the running annual average is less 
than the trigger level, then the State may determine that the system is 
reliably and consistently below the MCL for regulated PFAS and allow 
the system to return to reduced monitoring as shown in table 2 to 
paragraph (b)(2)(i) of this section.
    (iv) The State may require a confirmation sample for any sampling 
result. If a confirmation sample is required by the State, the result 
must be averaged with the first sampling result and the average must be 
used for the compliance determination as specified by Sec.  141.903. 
States may delete results of obvious sampling errors from this 
calculation.
    (v) The State may increase the required monitoring frequency, where 
necessary, to detect variations within the system (e.g., fluctuations 
in concentration due to seasonal use, changes in water source).
    (vi) Each public water system shall monitor at the time designated 
by the State within each compliance period.

Sec.  141.903  Compliance requirements.

    (a) Compliance with Sec.  141.61(c) shall be determined based on 
the analytical results obtained at each sampling point. If one sampling 
point is in violation of an MCL, the system is in violation of the MCL.
    (b) For systems monitoring more than once per year, compliance with 
the MCL is determined by a running annual average at each sampling 
point.
    (c) If a system fails to collect the required number of samples, 
compliance will be based on the total number of samples collected.
    (d) Systems monitoring triennially whose sample result equals or 
exceeds the trigger level of 1.3 ppt for either PFOS or PFOA, or a 
Hazard Index of 0.33 for PFNA, PFHxS, HFPO-DA, and PFBS must begin 
quarterly sampling. If the sample result exceeds an MCL, the system 
will not be considered in violation of the MCL until it has completed 
one year of quarterly sampling with the triggering sample used as the 
first quarter of monitoring for the running annual average calculation.
    (e) If any sample result will cause the running annual average to 
exceed the MCL at any sampling point, the system is out of compliance 
with the MCL immediately.
    (f) Systems must calculate compliance using the following method:
    (1) For each PFAS regulated by an individual MCL:
    (i) For systems monitoring quarterly, divide the sum of the 
measured concentrations for each analyte by the number of samples 
collected for that analyte during the consecutive quarters. If more 
than one compliance sample for that analyte is available in the 
quarter, systems must average all the results in a quarter then average 
the quarterly averages. If the value calculated exceeds the MCL, the 
system is not in compliance with the MCL requirements.
    (ii) For systems monitoring less frequently than quarterly, report 
the results of each sampling event:
    (A) For systems taking one sample during each three-year compliance 
period, if more than one compliance sample is available systems must 
average all the results to determine compliance. If the value 
calculated exceeds the MCL, the system is required to initiate 
quarterly monitoring with the sampling result used as the first quarter 
of monitoring for the running annual average calculation.
    (B) For systems taking two samples during each three-year 
compliance period, divide the sum of the measured concentrations for 
each analyte by the number of samples collected during the three-year 
compliance period. If more than one compliance sample is available for 
a quarter, systems must average all of the results of that quarter then 
average the two quarterly averages. If the value calculated exceeds the 
MCL, the system is required to initiate quarterly monitoring, with the 
sample result used as the first quarter of monitoring for the running 
annual average calculation.
    (iii) If a sample result is less than the practical quantitation 
limit for a regulated PFAS, in accordance with the following table, 
zero will be used for that analyte to calculate the annual average.

                    Table 1 to Paragraph (f)(1)(iii)
------------------------------------------------------------------------
                       Contaminant                           PQL (ppt)
------------------------------------------------------------------------
PFOA....................................................             4.0
PFOS....................................................             4.0
HFPO-DA.................................................             5.0
PFHxS...................................................             3.0
PFNA....................................................             4.0
PFBS....................................................             3.0
------------------------------------------------------------------------

    (2) For each PFAS regulated under the Hazard Index:
    (i) For systems monitoring quarterly, divide observed sample 
analytical results by the corresponding HBWC listed in Sec.  141.61(c) 
to obtain a Hazard Quotient for each sampling event at each EPTDS. Sum 
the resulting Hazard Quotients together to determine the Hazard Index. 
If more than one compliance sample is available for an analyte in a 
quarter, systems must average all the results for that analyte in that 
quarter and then determine the Hazard Quotient(s) from those average 
values. If the Hazard Index exceeds the MCL, the system is not in 
compliance with the Hazard Index MCL requirements.

[[Page 18753]]

    (ii) For systems monitoring less frequently, divide the observed 
sample analytical results by the corresponding HBWC listed in Sec.  
141.61(c) to obtain a Hazard Quotient. Sum the resulting Hazard 
Quotients together to determine the Hazard Index.
    (A) For systems taking one sample during each three-year compliance 
period, if more than one compliance sample is available for an analyte, 
systems must average all the results for that analyte to determine the 
Hazard Quotient and the Hazard Index. If the Hazard Index exceeds the 
MCL, the system is required to initiate quarterly monitoring with the 
Hazard Index sampling result used as the first quarter of monitoring 
for the running annual average calculation.
    (B) For systems taking two samples during each three-year 
compliance period, if more than one sample is available for an analyte, 
systems must average all the results for that analyte to determine the 
Hazard Quotient(s) and the Hazard Index for that quarter. Average the 
two Hazard Indices calculated during the compliance period. If the 
average of the Hazard Indices exceeds the MCL, the system is required 
to initiate quarterly monitoring with the Hazard Index average sampling 
result used as the first quarter of monitoring for the running annual 
average calculation.
    (iii) If a sample result is less than the practical quantitation 
limit for a regulated PFAS, in accordance with the table in paragraph 
(f)(1)(i)(C) of this section, zero will be used for that analyte to 
calculate the annual average.

Sec.  141.904  Reporting and recordkeeping requirements.

    Systems required to sample must report to the State according to 
the timeframes and provisions of Sec.  141.31. Systems must report the 
information specified in the following table:

                        Table 1 to Sec.   141.904
------------------------------------------------------------------------
        If you are a . . .                  You must report . . .
------------------------------------------------------------------------
System monitoring for regulated     1. All sample results, including the
 PFAS under the requirements of      location, number of samples taken
 Sec.   141.902 on a quarterly       at each location, date, and result
 basis.                              during the previous quarter.
                                    2. The running annual average at
                                     each sampling point of all samples
                                     taken in the last four quarters.
                                    3. Whether, based on Sec.   141.902,
                                     the MCL was violated.
                                    4. Whether, based on Sec.   141.902,
                                     the trigger level was met or
                                     exceeded.
System monitoring for regulated     1. The location, date, and result of
 PFAS under the requirements of      each sample taken during the last
 Sec.   141.902 less frequently      monitoring period.
 than quarterly.
                                    2. The running annual average at
                                     each sampling point of all samples
                                     taken in the last twelve months.
                                    3. Whether, based on Sec.   141.902,
                                     the trigger level was met or
                                     exceeded.
------------------------------------------------------------------------

Sec.  141.905  Violations.

    (a) PFAS MCL violations, both for PFOA and PFOS MCLs as well as the 
Hazard Index MCL are based on a running annual average under Sec.  
141.XX.d. Failure to monitor in accordance with the requirements under 
Sec.  141.XX.c (monitoring requirements) of this section is a 
monitoring violation.
    (b) Compliance with Sec.  141.61(c) must be determined based on the 
analytical results obtained at each sampling point. If one sampling 
point is in violation of an MCL, the system is in violation of the MCL.
    (1) For systems monitoring quarterly, compliance with the MCL is 
determined by a running annual average at each sampling point.
    (2) Systems monitoring triennially whose sample result is at or 
exceeds the trigger level as defined by Sec.  141.902(a)(7) of this 
section must begin quarterly sampling. The system will not be 
considered in violation of the MCL until it has completed one year of 
quarterly sampling.
    (i) If any sample result will cause the running annual average to 
exceed the MCL at any sampling point, the system is out of compliance 
with the MCL immediately.
    (ii) If a system fails to collect the required number of samples, 
compliance will be based on the total number of samples collected.
    (iii) If a sample result is less than the practical quantitation 
limit for regulated PFAS as shown in Sec.  141.903(f)(1)(i)(C), zero 
will be used to calculate the annual average.

PART 142--NATIONAL PRIMARY DRINKING WATER REGULATIONS 
IMPLEMENTATION

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

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

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

Sec.  142.16  Special primacy requirements.

* * * * *
    (r) Requirements for States to adopt 40 CFR part 141, subpart Z. In 
addition to the general primacy requirements elsewhere in this part, 
including the requirements that State regulations be at least as 
stringent as Federal requirements, an application for approval of a 
State program revision that adopts 40 CFR part 141, subpart Z, must 
contain the following:
    (1) The States procedures for use of pre-existing data to meet the 
initial monitoring requirements specified in Sec.  141.902, including 
the criteria that will be used to determine if the data is acceptable.
    (2) The States procedures for ensuring all systems complete the 
initial monitoring period requirements that will result in a high 
degree of monitoring compliance by the regulatory deadlines.
    (i) The initial monitoring plan must describe how systems will be 
scheduled during the initial monitoring period and demonstrate that the 
analytical workload on certified laboratories has been taken into 
account.
    (ii) The State will update the initial monitoring plan as necessary 
and must demonstrate that the monitoring plan is enforceable under 
State law.
    (3) After the initial monitoring period, States establish the 
initial monitoring requirements for new systems and new sources. States 
must explain their initial monitoring schedules and how these 
monitoring schedules ensure that public water systems and sources 
comply with MCL's and monitoring requirements. States must also specify 
the time frame in which new systems will demonstrate compliance with 
the MCLs.
0
17. Amend Sec.  142.62 by revising paragraph (a) to read as follows:

[[Page 18754]]

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

    (a) The Administrator, pursuant to section 1415(a)(1)(A) of the 
Act, hereby identifies the following as the best available technology, 
treatment techniques, or other means available for achieving compliance 
with the maximum contaminant levels for the PFAS listed in Sec.  
141.61(c) of this chapter, for the purposes of issuing variances and 
exemptions, as shown in tables 1 and 2 to this paragraph (a).

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

                 Table 2 to Paragraph (a)--List of Small System Compliance Technologies for PFAS
----------------------------------------------------------------------------------------------------------------
                                                                  Operator skill level   Raw water quality range
          Unit technologies            Limitations \a\ \b\ \c\          required            and considerations
----------------------------------------------------------------------------------------------------------------
Ion Exchange.........................  a, b...................  Basic to Intermediate..  All ground waters.
GAC..................................  B......................  Basic to Intermediate..  All waters.
----------------------------------------------------------------------------------------------------------------
\a\ Mostly operated as a single use. The regeneration solution contains high concentrations of the organic
  solvents not typically used in the regeneration of resins contaminated with other pollutants. Disposal options
  should be considered before choosing this technology.
\b\ Waste media may contain high concentrations of the contaminant. Disposal options should be considered before
  choosing this technology.
\c\ Point of use is not currently accepted as a small system compliance technology, however POU treatment is
  reasonably anticipated to become a compliance option for small systems in the future if third-party
  certification organizations develop a new certification standard that meets or requires treatment to
  concentrations lower than EPA's proposed MCLs.

* * * * *
[FR Doc. 2023-05471 Filed 3-23-23; 11:15 am]
BILLING CODE 6560-50-P