Contaminants of Emerging Concern Under the
November 29, 2021
Clean Water Act
Laura Gatz
Recent decades have seen increased national attention to the presence of emerging contaminants
Analyst in Environmental
or contaminants of emerging concern (CECs) in surface water and groundwater. Although there
Policy
is no federal statutory or regulatory definition of CECs, the term generally refers to unregulated

substances detected in the environment that may present a risk to human health, aquatic life, or
the environment, and for which scientific understanding of potential risks is evolving. CECs

include many different types of manufactured chemicals and substances (e.g., pharmaceuticals,
industrial chemicals, agricultural products, and microplastics) as well as naturally occurring substances (e.g., algal toxins).
Data on CECs that would help determine their risk to humans, aquatic life, or the environment are often limited. Increased
monitoring and detections of one particular group of chemicals, per- and polyfluoroalkyl substances (PFAS), has recently
heightened public and congressional interest in CECs and prompted a broader discussion about how CECs are identified,
detected, and regulated and whether additional actions should be taken to protect human health and the environment. While
several statutes provide authorities to the U.S. Environmental Protection Agency (EPA) and states to address CECs, this
report examines authorities available under the Clean Water Act (CWA)—which Congress established to restore and protect
the quality of the nation’s surface waters.
EPA has several CWA authorities it may use to address CECs, although it faces some challenges in doing so. Under the
CWA, a primary mechanism to control contaminants in surface waters is through permits. The statute prohibits the discharge
of pollutants from any point source (i.e., a discrete conveyance) to waters of the United States without a permit. The CWA
authorizes EPA and states to limit or prohibit discharges of pollutants in the National Pollutant Discharge Elimination System
(NPDES) permits they issue. These permits incorporate technology-based and water-quality-based requirements.
The CWA authorizes EPA and states to address CECs through technology-based effluent limitations using national Effluent
Limitation Guidelines and Standards (ELGs) or by setting technology-based effluent limits in NPDES permits on a case-by-
case basis. The CWA requires EPA to publish ELGs, which are the required minimum standards for industrial wastewater
discharges. The CWA also requires EPA to annually review existing ELGs and publish a biennial plan that includes a
schedule for review and revision of existing ELGs, identifies categories of sources discharging toxic or nonconventional
pollutants that do not have ELGs, and establishes a schedule for promulgating ELGs for any newly identified categories. The
CWA also authorizes EPA and states to use certain NPDES permit authorities to manage CECs, such as imposing
technology-based effluent limits on a case-by-case basis. Although EPA and states have these authorities available to address
CECs, there are some challenges to doing so, including a lack of data available to support new or revised ELGs.
The CWA also authorizes EPA and states to address CECs through water-quality-based requirements. The CWA requires
EPA to publish, and “from time to time thereafter revise” water quality criteria that reflect the latest scientific knowledge.
These criteria are recommendations to states and tribal governments for use in developing their own water quality standards,
which they use to protect and restore waters and to inform water-quality-based effluent limits in permits. Although EPA and
states have authority to address CECs through water-quality-based requirements, they often lack data needed to support
development of criteria or water-quality-based effluent limitations.
The CWA also authorizes EPA to designate contaminants as toxic pollutants or as hazardous substances, which may trigger
other actions under the CWA and the Comprehensive Environmental Response, Compensation, and Liability Act.
Recent congressional interest in CECs has largely focused on addressing one particular group of CECs—PFAS—and on
addressing them through several statutes. In the 117th Congress, the House Subcommittee on Water Resources and
Environment held a hearing focused on CECs and the CWA’s framework for addressing them in surface waters. Some
Members have also introduced bills that propose to address PFAS or other CECs using CWA authorities. In addition,
Congress passed the Infrastructure Investment and Jobs Act (P.L. 117-58), which provides $1 billion over five fiscal years
through the Clean Water State Revolving Fund to address emerging contaminants in wastewater treatment plants.

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Contaminants of Emerging Concern Under the Clean Water Act

Introduction
Over the past couple of decades, national attention to “emerging contaminants” or “contaminants
of emerging concern” (CECs) in surface water and groundwater has been increasing. Although
there is no federal statutory or regulatory definition of CECs, generally, the term refers to
unregulated substances detected in the environment that may present a risk to human health,
aquatic life, or the environment. CECs can include many different types of manmade chemicals
and substances—such as those in personal care products, pharmaceuticals, industrial chemicals,
lawn care and agricultural products, and microplastics—as well as naturally occurring substances
such as algal toxins or manganese.
CECs often enter the environment, including ground and surface waters, via municipal and
industrial wastewater discharges and urban and agricultural storm runoff. Although municipal and
industrial wastewater are both treated prior to discharge into waterways, treatment facilities are
often not designed to remove CECs. The availability of data on CECs—such as concentration and
pervasiveness in the environment or exposure or toxicity data that would help determine their risk
to humans and aquatic life—may be limited.
In some cases, detections of CECs in the environment have triggered a call for action from
federal, state, and local government, as well as Congress. Increased monitoring and detections of
one particular group of chemicals, per- and polyfluoroalkyl substances (PFAS), has heightened
public and congressional interest in these CECs and has also prompted a broader discussion about
how CECs are identified, detected, and regulated and whether additional actions should be taken
to protect human health and the environment.1
Several statutes—including the Safe Drinking Water Act;2 the Toxic Substances Control Act
(TSCA);3 the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA);4 and the Clean Water Act (CWA)5—provide authorities to the U.S. Environmental
Protection Agency (EPA) and states to address particular CECs. In the 117th Congress, Members
have introduced more than 50 bills to address PFAS through various means. Multiple bills would
direct EPA to take regulatory and other actions to address PFAS under several environmental
statutes. Several bills, such as the PFAS Action Act of 2021 (H.R. 2467) and the Clean Water
Standards for PFAS Act of 2021 (H.R. 3622 and S. 1907), would direct EPA to address PFAS
using authorities provided to the agency under the CWA, which Congress established to restore
and protect the quality of the nation’s surface waters.
Global concern about another group of CECs—microplastics—and their potential impacts has
also been mounting.6 Studies have found that treated effluents from wastewater treatment plants

1 See CRS Report R45793, PFAS and Drinking Water: Selected EPA and Congressional Actions, by Elena H.
Humphreys, for an overview of EPA’s ongoing and proposed actions to address PFAS under Safe Drinking Water Act
authorities. See also CRS Report R45986, Federal Role in Responding to Potential Risks of Per- and Polyfluoroalkyl
Substances (PFAS), coordinated by David M. Bearden.
2 42 U.S.C. §300f-300j.
3 15 U.S.C. §2601 et seq.
4 42 U.S.C. §9601 et seq.
5 33 U.S.C. §1251 et seq.
6 While researchers and the government have been working to address plastic pollution for decades, more recently, the
accumulation and potential impacts of plastic pollution have become an emerging issue. Recent studies have shown
that microplastics (i.e., plastic particles less than 5 millimeters in size in any one dimension) are widespread in marine
and freshwater ecosystems and may also have negative ecological impacts. See EPA, State of the Science White Paper:
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can be key sources of microplastics, as can runoff from agricultural sites where sewage sludge
from the wastewater treatment process has been applied as fertilizer.7 As with many other CECs,
wastewater treatment facilities are generally not designed to screen for microplastic debris, such
as microbeads, plastic fragments, or plastic fibers from clothing. Congress has shown interest in
addressing the impacts of plastic pollution. In 2015, Congress passed legislation to ban plastic
microbeads from rinse-off personal care products (Microbead-Free Waters Act of 2015; P.L. 114-
114). In the 117th Congress, some Members have introduced legislation to address plastic waste,
including both broad efforts to address plastic and microplastic through several statutes as well as
legislation focused specifically on efforts to address microplastics through authorities provided
under the CWA.
In addition, the Infrastructure Investment and Jobs Act (IIJA; P.L. 117-58) provides $1 billion
over five fiscal years for the primary financial assistance program that supports wastewater
infrastructure—the Clean Water State Revolving Fund program, authorized by the CWA—for a
range of projects to address emerging contaminants.8
Some stakeholders have asserted that EPA could be more effective in using its existing CWA
authorities to address CECs, while others have suggested a need to identify and address potential
gaps in CWA authorities through amendments to the statute.9 This report examines authorities
available to address CECs under the CWA.
Addressing CECs Through the Clean Water Act
EPA has several CWA authorities it may use to address CECs, although it faces some challenges
in doing so. The CWA’s stated objective is “to restore and maintain the chemical, physical, and
biological integrity of the Nation’s waters.”10 To help achieve this objective, the CWA prohibits
the discharge of pollutants from any point source (e.g., a discrete conveyance, such as a pipe,
ditch, etc.) to waters of the United States without a permit.11 Under the CWA, one of the primary
mechanisms to protect or improve surface water quality is to limit or prohibit discharges of
contaminants, including CECs, in National Pollutant Discharge Elimination System (NPDES)
permits.12 The CWA authorizes EPA and delegated states to set limits or prohibit discharges of

A Summary of Literature on the Chemical Toxicity of Plastics Pollution to Aquatic Life and Aquatic-Dependent
Wildlife, December 2016, https://www.epa.gov/trash-free-waters/epa-reports#wp. Also see EPA Office of Wetlands,
Oceans and Watersheds, Microplastics Expert Workshop Report, December 2017, https://www.epa.gov/sites/
production/files/2018-03/documents/microplastics_expert_workshop_report_final_12-4-17.pdf.
7 EPA, State of the Science White Paper. See also Paul Kay et al., “Wastewater Treatment Plants as a Source of
Microplastics in River Catchments,” Environmental Science and Pollution Research, vol. 25, no. 20 (July 2018), pp.
20264-20267.
8 For additional discussion, see CRS Report R46892, Infrastructure Investment and Jobs Act: Drinking Water and
Wastewater Infrastructure, by Elena H. Humphreys and Jonathan L. Ramseur.
9 Association of Clean Water Administrators (ACWA) and Association of State Drinking Water Administrators
(ASDWA), Recommendations Report—Contaminants of Emerging Concern Workgroup, May 2019,
https://www.asdwa.org/wp-content/uploads/2019/05/ASDWA-ACWA-Report-on-Contaminants-of-Emerging-
Concern-2019.pdf, p. 9.
10 CWA §101(a); 33 U.S.C. §1251(a).
11 CWA §301; 33 U.S.C. §1311. Point source is defined at CWA §502(14); 33 U.S.C. §1362(14).
12 33 U.S.C. §1342. Under CWA Section 402, states and EPA issue NPDES permits to municipal and nonmunicipal
point sources to authorize their discharges. Note that 47 states are authorized to administer their own NPDES permits.
EPA administers NPDES permits in Massachusetts, New Hampshire, New Mexico, the District of Columbia, and
certain territories and Indian lands. Per CWA Section 502(3) (33 U.S.C. §1362(3)), state is defined to include a state,
the District of Columbia, or any of the U.S. territories. Per CWA Section 518 (33 U.S.C. §1377), EPA is authorized to
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pollutants in permits through technology-based effluent (i.e., discharge) limitations and standards
and through water-quality-based effluent limitations, which are established through water quality
standards and criteria. Technology-based effluent limitations are specific numerical limits (i.e.,
maximum allowable levels of specific pollutants) that represent the minimum level of control that
must be established in a permit.13 In cases where technology-based effluent limitations are not
adequate to meet applicable water quality standards, the permits also incorporate water-quality-
based effluent limitations.14 Water-quality-based effluent limitations are specific limits established
in a permit that, if not exceeded in the discharge, allow for attainment of water quality standards
in the receiving water.15 Water quality standards—established by states, territories, tribes, and
EPA—define the desired condition or level of protection of a water body and what is needed to
achieve or protect that condition.16 In addition, the CWA authorizes EPA to designate
contaminants as toxic pollutants (CWA §307) or as hazardous substances (CWA §311), which
may trigger other actions under the CWA and CERCLA.17 This section first identifies the
authorities available under the CWA, their applicability to CECs, and potential challenges with
EPA use of these authorities.
Technology-Based Requirements
The CWA requires EPA to establish technology-based effluent limitations for various categories
of point sources/dischargers.18 Technology-based requirements consider the performance of
specific technologies as well as economic achievability. These limits do not specify what
technologies must be employed; rather, they establish the levels of specific pollutants that are
allowable in the discharge based on the performance of technologies identified as representing
specified levels of control (e.g., best available technology economically achievable, best
conventional pollutant control technology). CWA Section 301 prescribes the levels of control
required. EPA broadly classifies NPDES permittees as either (1) publicly owned treatment works
(POTWs)19 or (2) non-POTWs, which include all other point sources and are also often called
nonmunicipal facilities or industrial facilities.20

treat an Indian tribe as a state for certain sections of the CWA, including the sections pertaining to CWA permitting.
13 CWA §301(b); 33 U.S.C. §1311(b); 40 C.F.R. §125.3.
14 40 C.F.R. §122.44(d).
15 40 C.F.R. §122.44(d). Water-quality-based effluent limitations apply at the point of discharge, such as the end of the
outfall pipe discharging into a water body.
16 40 C.F.R. §131.3(i)-(j). Water quality standards apply throughout the water body and reflect the maximum levels of
specific pollutants that can be present in a water body and still allow that water body to meet its designated use.
17 33 U.S.C. §1317; 33 U.S.C. §1321. Such designations also trigger hazardous substance designations (and liability)
under CERCLA.
18 CWA §301(b); 33 U.S.C. §1311(b); CWA §304(b); 33 U.S.C. §1314(b); CWA §306; 33 U.S.C. §1316; CWA §307;
33 U.S.C. §1317.
19 Per 40 C.F.R. §403.3(q), a POTW is a treatment works as defined by CWA Section 212, which is owned by a state or
municipality (as defined by CWA Section 502(4)). The definition includes any devices and systems used in the storage,
treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes
sewers, pipes, and other conveyances only if they convey wastewater to a POTW. The term also means the
municipality that has jurisdiction over the indirect discharges to and the discharges from the treatment works.
20 Non-POTWs include other point sources, such as industrial and commercial facilities, industrial stormwater,
concentrated animal feeding operations, and vessel discharges. Federal facilities fall under the non-POTW source
category. EPA, NPDES Permit Writers’ Manual, 2010, https://www.epa.gov/sites/production/files/2015-09/documents/
pwm_2010.pdf.
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The CWA requires POTWs to meet secondary treatment standards as determined by EPA.21
Secondary standards are based on performance data for POTWs that use physical and biological
treatment to remove or control conventional pollutants.22
As shown in Figure 1, the CWA requires non-POTW dischargers to achieve specified levels of
control based on (1) whether a discharger directly or indirectly discharges into a water of the
United States (an indirect discharger discharges to a POTW for treatment prior to discharge into a
water of the United States), (2) whether the discharger is a new or existing source, and (3) the
category of pollutant (conventional, toxic,23 or nonconventional24).25

21 CWA §301(b)(1)(B); 33 U.S.C. §1311(b)(1)(B). As directed by CWA Section 304(d)(1), EPA promulgated
secondary treatment standards for biochemical oxygen demand, total suspended solids, and pH. See 40 C.F.R. §133 for
secondary treatment standards. The CWA and federal regulations allow adjustments to secondary treatment
requirements for biochemical oxygen demand and total suspended solids for equivalent to secondary facilities, per 40
C.F.R. §133.105.
22 Conventional pollutants include biochemical oxygen demand, total suspended solids, fecal coliform, pH, and oil and
grease. CWA Section 304(a)(4) designates biological oxygen demand, suspended solids, fecal coliform, and pH as
conventional pollutants. It also authorizes EPA to revise the list of conventional pollutants from time to time. EPA
designated oil and grease as an additional conventional pollutant in 1979 (EPA, “Identification of Conventional
Pollutants,” 44 Federal Register 44501, 1979). The list of conventional pollutants is codified at 40 C.F.R. §401.16.
23 Toxic pollutant includes the 65 pollutants and classes of pollutants on EPA’s Toxic Pollutant List. Section 307(a)(1)
(33 U.S.C. §1317(a)(1)) directed EPA to adopt an initial list of toxic pollutants presented in Committee Print 95-30 of
the House Committee on Public Works and Transportation (U.S. Congress, House Committee on Public Works and
Transportation, Data Relating to H.R. 3199 (Clean Water Act of 1977), committee print, 95th Cong., November 1977,
H.Prt. 95-30 [Washington: GPO, 1977], pp. 3-4). This list included both individual chemicals and categories of
chemical compounds. As presented in the legislative history, this initial list was negotiated between EPA and the
Natural Resources Defense Council in Natural Resources Defense Council v Train (U.S. Congress, House Committee
on Public Works and Transportation, Subcommittee on Investigations and Review, Water Contamination by Toxic
Pollutants: An Assessment of Regulation, committee print, 95th Cong., September 1977, 95-26, p. 6). The Toxic
Pollutant List is codified at 40 C.F.R. §401.15. In 1977, EPA developed the Priority Pollutant List to make Toxic
Pollutant List implementation more practical for water testing and regulatory purposes. The Priority Pollutant List
includes individual chemicals, rather than groups of pollutants, for which EPA has published analytical test methods.
Originally, the list included 129 pollutants. In 1981, when three pollutants were removed from the Toxic Pollutant List,
they were also removed from the Priority Pollutant List. Accordingly, the Priority Pollutant List, codified at 40 C.F.R.
§423, Appendix A, currently contains 126 pollutants.
24 Nonconventional pollutant includes any pollutants other than those identified as conventional or toxic pollutants.
25 CWA §301(b); 33 U.S.C. §1311(b); CWA §304(b); 33 U.S.C. §1314(b); CWA §306; 33 U.S.C. §1316; CWA §307;
33 U.S.C. §1317.
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Figure 1. Clean Water Act Technology Levels of Control Required for Non-POTW
Dischargers by Pollutant Category

Source: CRS, based on CWA §§301, 304, 306, and 307.
Notes: EPA regulations define new source as “any building, structure, facility, or installation from which there is
or may be a ‘discharge of pol utants,’ the construction of which commenced: (a) after promulgation of standards
of performance under CWA Section 306 which are applicable to such source, or (b) after proposal of standards
of performance in accordance with Section 306 of CWA which are applicable to such source, but only if the
standards are promulgated in accordance with section 306 within 120 days of their proposal” (40 C.F.R. §122.2).
An existing source is any source that is not a new source or a new discharger (40 C.F.R. §122.29 (a)(3)).
Effluent Limitation Guidelines and Standards (ELGs)
The CWA requires EPA to publish national regulations for non-POTW dischargers—called
Effluent Limitation Guidelines and Standards (ELGs)—which set minimum standards for specific
pollutants in industrial wastewater discharges based on the specified levels of control.26 Since
1972, EPA has developed ELGs for 59 industrial categories.27 For direct dischargers, states or
EPA incorporate the limits established in ELGs into the NPDES permits they issue. For indirect
dischargers, pretreatment standards established in ELGs to prevent pass through and interference
at the POTW apply.28

26 CWA §304(b); 33 U.S.C. §1314(b); CWA §306(b); 33 U.S.C. §1316(b); CWA §307(b)-(c); 33 U.S.C. §1317(b)-(c).
27 40 C.F.R. Chapter 1, Subchapter N, “Effluent Guidelines and Standards.” See also EPA, “Industrial Effluent
Guidelines,” https://www.epa.gov/eg/industrial-effluent-guidelines.
28 The national pretreatment program is a component of the NPDES program, which involves federal, state, and local
regulatory agencies. Local municipalities are mostly responsible for implementing and enforcing pretreatment
requirements. EPA and states authorized to act as the approval authority for POTWs in their states may approve a
POTW’s pretreatment program. If approved, the POTW is the control authority responsible for ensuring compliance
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The CWA requires EPA to annually review all existing ELGs to determine whether revisions are
appropriate.29 In addition, CWA Section 304(m) requires EPA to publish a plan every two years
that includes a schedule for review and revision of promulgated ELGs, identifies categories of
sources discharging toxic or nonconventional pollutants that do not have ELGs, and establishes a
schedule for promulgating ELGs for any newly identified categories.30
In its 2002 draft Strategy for National Clean Water Industrial Regulations, EPA described a
process for identifying existing ELGs that the agency should consider revising as well as
industrial categories that may warrant development of new ELGs.31 As outlined in the strategy,
EPA considers four main factors when prioritizing existing ELGs for possible revision: (1) the
amount and type of pollutants in an industrial category’s discharge and the relative hazard to
human health or the environment, (2) the availability of an applicable and demonstrated
wastewater treatment technology, process change, or pollution prevention measure that can
reduce pollutants in the discharge and the associated risk to human health or the environment; (3)
the cost, performance, and affordability or economic achievability of the wastewater treatment
technology, process change, or pollution prevention measure; and (4) the opportunity to eliminate
inefficiencies or impediments to pollution prevention or technological innovation or promote
innovative approaches.32 EPA considers nearly identical factors in deciding whether to develop
new ELGs.33
EPA uses a variety of screening-level analyses to address these factors. These analyses evaluate
discharge monitoring reports and EPA’s Toxic Release Inventory to rank industrial categories
according to the total toxicity of their wastewater.34 In 2012, the Government Accountability
Office recommended that the annual review include additional industrial hazard data sources to
augment its screening-level reviews.35 In response, EPA has begun to use additional data sources
that provide information about CECs or new pollutant discharges, industrial process changes, and
new and more sensitive analytical methods, among other things. For example, EPA has reviewed
data from the agency’s Office of Pollution Prevention and Toxics to identify potential CECs.36
If EPA identifies an industrial discharge category warranting further review, it conducts a more
detailed review, which may lead to a new or revised guideline.37

with pretreatment standards. If a POTW does not have an approved pretreatment program, the control authority is the
approved state authorized to act as the approval authority or, in unapproved states, the EPA. See 40 C.F.R. §403,
“General Pretreatment Regulations for Existing and New Sources of Pollution.”
29 CWA §304(b); 33 U.S.C. §1314(b); CWA §304(g); 33 U.S.C. §1314(g); CWA §304(m)(1)(A); 33 U.S.C.
§1314(m)(1)(A). Also, per CWA Section 301(d) (33 U.S.C. §1311(d)), EPA is required to review effluent limitations
required by CWA Section 301(b)(2) at least every five years. EPA issues regulations that simultaneously address both
of these.
30 33 U.S.C. §1314(m).
31 EPA, A Strategy for National Clean Water Industrial Regulations (Draft), November 2002.
32 EPA, Final 2016 Effluent Guidelines Program Plan, EPA-821-R-18-001, April 2018, https://www.epa.gov/eg/2016-
effluent-guidelines-plan-documents. See also EPA, A Strategy for National Clean Water Industrial Regulations, pp. 20-
25.
33 EPA, A Strategy for National Clean Water Industrial Regulations, p. 23.
34 EPA, Final 2016 Effluent Guidelines Program Plan, pp. 2-3–2-11.
35 U.S. Government Accountability Office, Water Pollution: EPA Has Improved Its Review of Effluent Guidelines but
Could Benefit from More Information on Treatment Technologies, GAO-12-845, September 2012,
https://www.gao.gov/products/GAO-12-845.
36 EPA, Final 2016 Effluent Guidelines Program Plan, p. 2-4.
37 EPA, Final 2016 Effluent Guidelines Program Plan, p. 2-5.
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EPA’s Recent Biennial Plans
EPA’s two most recent biennial plans—the final Effluent Guidelines Program Plan 14 (published
in January 2021) and the Preliminary Effluent Guidelines Program Plan 15 (published in
September 2021)—have, as required, included details on the agency’s ongoing efforts to
determine whether it should update ELGs for several different industrial categories.38 Both of
these biennial plans include a focus on the agency’s efforts to determine whether ELGs for
several industrial categories should be updated to address PFAS. EPA noted that while there has
been significant study in recent years of the presence of PFAS in the environment and in drinking
water, there has been relatively little study of the discharges of PFAS to surface water and
wastewater treatment facilities.39 Hence, EPA’s recent biennial plans and related actions have
included efforts to identify and collect information about PFAS discharges.
EPA’s Preliminary Effluent Guidelines Program Plan 14 and EPA’s PFAS Action Plan, both
published in October 2019, announced that the agency was beginning a detailed multi-industry
study of PFAS use, treatment, and discharge to evaluate if certain industrial sources warranted
regulation through ELGs.40 EPA’s final Effluent Guidelines Program Plan 14 provided an update
on the PFAS multi-industry study. It also discussed several ongoing regulatory actions, including
an advanced notice of proposed rulemaking for the Organic Chemicals, Plastics, and Synthetic
Fibers (OCPSF) point source category to solicit information and data about PFAS manufacturers
and formulators, which it published in March 2021.41
In September 2021, EPA published its Preliminary Effluent Guidelines Program Plan 15 for
public review and comment.42 In this preliminary plan, EPA announced several actions pertaining
to PFAS, including a rulemaking to revise the OCPSF category ELGs to address PFAS discharges
from PFAS manufacturers; plans to conduct a rulemaking to revise the Metal Finishing ELGs to
address PFAS discharges from chromium electroplating facilities; and plans to conduct detailed
studies on PFAS in discharges from landfills as well as textile and carpet manufacturers.43
In October 2021, EPA issued its PFAS Strategic Roadmap, which broadened its goals to address
PFAS discharges through ELGs, and targeted the end of 2024 as the deadline for “significant
progress in its ELG regulatory work.”44 Specifically, EPA established timelines for action on
various industrial categories, including nine industrial categories also identified in the proposed
“PFAS Action Act of 2021” legislation as well as other industrial categories such as landfills.45
These categories include OCPSF; Pulp, Paper, and Paperboard; Textile Mills; Electroplating;

38 EPA, Effluent Guidelines Program Plan 14, EPA-821-R-21-001, January 2021, https://www.epa.gov/eg/2014-
effluent-guidelines-plan-documents. EPA, Preliminary Effluent Guidelines Program Plan 15, EPA-821-R-21-003,
September 2021, https://www.epa.gov/eg/preliminary-effluent-guidelines-program-plan.
39 EPA, Effluent Guidelines Program Plan 14, p. 6-3. EPA, Preliminary Effluent Guidelines Program Plan 15, p. 6-3.
40 EPA, EPA’s Per- and Polyfluoroalkyl Substances (PFAS) Action Plan, EPA 823R18004, February 14, 2019, pp. 6,
29-30, https://www.epa.gov/pfas/previous-actions-address-pfas. EPA, Preliminary Effluent Guidelines Program Plan
14, EPA-821-R-19-005, October 2019, https://www.epa.gov/sites/default/files/2019-10/documents/prelim-eg-plan-
14_oct-2019.pdf.
41 Effluent Guidelines Program Plan 14. See also EPA, “Clean Water Act Effluent Limitations Guidelines and
Standards for the Organic Chemicals, Plastics and Synthetic Fibers Point Source Category,” 86 Federal Register
14560, March 17, 2021.
42 EPA, “Preliminary Effluent Guidelines Program Plan 15,” 86 Federal Register 5115, September 14, 2021.
43 EPA, Effluent Guidelines Program Plan 15.
44 EPA, PFAS Strategic Roadmap: EPA’s Commitments to Action 2021-2024, October 2021, pp. 13-14,
https://www.epa.gov/pfas/pfas-strategic-roadmap-epas-commitments-action-2021-2024.
45 Ibid; H.R. 2467, §17.
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Metal Finishing; Leather Tanning and Finishing; Paint Formulating; Electrical and Electronic
Components; and Plastics Molding and Forming.46 EPA’s planned actions include47
 undertaking rulemakings to restrict PFAS discharges from the industrial
categories where EPA has sufficient data to do so (OCPSF, Metal Finishing, and
Electroplating categories);48
 conducting detailed studies for industrial categories for which EPA has
preliminary data, but not enough to determine whether rulemaking is warranted
(Electrical and Electronic Components, Textile Mills, and Landfills);49
 initiating data reviews for industrial categories for which stakeholders have
expressed concern about potential PFAS discharges, but for which there is little
known information on such discharges (Leather Tanning and Finishing, Plastics
Molding and Forming; and Paint Formulating);50 and
 monitoring two industrial categories where the phase out of PFAS is projected by
2024 (Pulp, Paper, and Paperboard and Airports).51
Options to Address CECs Through Technology-Based Requirements
Both EPA and states have authority under the CWA to address CECs through technology-based
effluent limitations using ELGs or by setting technology-based effluent limits in NPDES permits
on a case-by-case basis. In addition, the CWA authorizes EPA to add contaminants to the Toxic
Pollutant List.
ELGs
When EPA develops an ELG for a new industrial category or revises an existing ELG, it is for the
industrial category—not a specific pollutant. However, as evidenced in the agency’s recent
effluent guidelines program plans, EPA may initiate a cross-industry review of particular
pollutants (such as the agency has done with PFAS and nutrients). EPA uses such reviews to
prioritize further study of the industrial categories that may be candidates for ELG development
or revision to control the discharges of those particular pollutants.52 If EPA were to determine that
new or revised ELGs are warranted to control discharges of those pollutants, and the agency had
the necessary data to support the development or revision, the agency could initiate a rulemaking
process to do so.

46 H.R. 2467, §17. EPA, PFAS Strategic Roadmap, p. 14.
47 EPA, PFAS Strategic Roadmap, p. 14.
48 EPA anticipates issuing a proposed rule for OCPSF by summer 2023 and for Metal Finishing and Electroplating by
summer 2024. The existing ELGs for Electroplating are codified at 40 C.F.R. §413.
49 EPA anticipates these studies to be completed by fall 2022 to inform its decision about a potential rulemaking by the
end of 2022. The existing ELGs for Electrical and Electronic Components are codified at 40 C.F.R. §469.
50 EPA aims to complete these studies by winter 2023 to inform its decision about whether sufficient data are available
to initiate a potential rulemaking. The existing ELGs for Leather Tanning and Finishing are codified at 40 C.F.R. §425;
for Plastics Molding and Forming at 40 C.F.R. §463; and for Paint Formulating at 40 C.F.R. §446.
51 EPA plans to discuss the results of the monitoring and any potential regulatory action in the Final Effluent Limitation
Guideline Program Plan 15 in fall 2022.
52 EPA, Final 2016 Effluent Guidelines Program Plan, p. 7-1.
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Establishing Technology-Based Effluent Limits in NPDES Permits on a Case-by-
Case Basis and Other NPDES Authorities
The CWA also authorizes EPA and states to impose technology-based effluent limits in NPDES
permits on a case-by-case basis when “EPA-promulgated effluent limitations are inapplicable.”53
This includes when EPA has not developed ELGs for the industry or type of facility being
permitted or pollutants or processes are present that were not considered when the ELG was
developed.54 This provides a means for the permitting authority to restrict pollutants in a facility’s
discharge even when an ELG is not available. CWA regulations require best professional
judgment to set case-by-case technology-based effluent limits, applying criteria that are similar to
the analysis EPA uses to develop ELGs but are performed by the permit writer for a single
facility.55
The CWA also authorizes permitting authorities (EPA or states) to require facilities with NPDES
permits to monitor for certain pollutants or conduct special studies as a means to collect data for
future limitation development.56 In addition, the permitting authority may include best
management practices in permits to control or abate the discharge of pollutants on a case-by-case
basis when “the practices are reasonably necessary ... to carry out the purposes and intent of the
CWA.”57 However, the use of some of these authorities may be limited when analytical methods
to detect specific pollutants are unavailable. For further discussion, see “Challenges to Addressing
CECs Through Technology-Based Requirements.”
Toxic Pollutant List
The CWA also authorizes EPA to designate contaminants as toxic pollutants, which can trigger
other actions under the CWA and CERCLA. (For a discussion of the effect of designating a
contaminant as a toxic pollutant on the treatment of that contaminant under CERCLA, see
“Designating CECs as Toxic Pollutants or Hazardous Substances.”) CWA Section 307 authorizes
EPA to designate toxic pollutants and promulgate ELGs that establish requirements for those
toxic pollutants.58 Section 307(a)(1) directed EPA to publish a specified list of individual toxic
pollutants or combination of pollutants and, from time to time, add or remove any pollutant that

53 CWA §402(a)(1)(B); 33 U.S.C. §1342(a)(1)(B); 40 C.F.R. §125.3(c).
54 EPA, NPDES Permit Writers’ Manual, September 2010, pp. 5-45–5-46, https://www.epa.gov/npdes/npdes-permit-
writers-manual.
55 40 C.F.R. §125.3(d).
56 CWA §402(a)(2); 33 U.S.C. §1342(a)(2). EPA, NPDES Permit Writers’ Manual, September 2010, pp. 9-2-9-3,
https://www.epa.gov/npdes/npdes-permit-writers-manual.
57 CWA §402(a)(1)-(2). 40 C.F.R. § 122.44(k).
58 33 U.S.C. §1317.
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possesses certain properties.59 EPA adopted the initial list of 65 toxic pollutants in 1978, as
directed by Congress.60 Since that time, the list of 65 toxic pollutants has generally not changed.61
Section 307(a)(1) directs EPA to “take into account the toxicity of the pollutant, its persistence,
degradability, the usual or potential presence of the affected organisms in any waters, the
importance of the affected organisms, and the nature and extent of the effect of the toxic pollutant
on such organisms” when revising the Toxic Pollutant List.62 Section 307(a)(2) authorizes EPA to
develop effluent limitations for any pollutant on the Toxic Pollutant List based on best available
technology.63 Notably, however, EPA has the authority to develop effluent limitations for any
pollutant regardless of whether it is on the Toxic Pollutant List.
Adding a pollutant to the Toxic Pollutant List would trigger an additional requirement for states.
Section 303(c)(2)(B) of the CWA64 requires states, whenever reviewing, revising, or adopting
water quality standards, to adopt numeric criteria for all toxic pollutants listed pursuant to Section
307, for which EPA has published water quality criteria under Section 304(a).65 EPA and states
use both the ELGs for industrial categories and state water quality standards in establishing
pollutant limits in permits under Section 402.66 (See Figure 1.)
Challenges to Addressing CECs Through Technology-Based Requirements
EPA and states face a number of challenges in addressing CECs through technology-based
effluent limitations. In particular, EPA officials stated that in developing a new ELG or updating
an existing ELG, the agency needs to gather extensive supporting information.67 This effort
includes identifying the pollutants of concern; evaluating the levels, prevalence, and sources of
those pollutants of concern; determining whether the pollutants are in treatable quantities and

59 33 U.S.C. §1317(a)(1). Section 307(a)(1) directed EPA to adopt an initial list of 65 toxic pollutants presented in
Committee Print 95-30 of the House Committee on Public Works and Transportation. (U.S. Congress, House
Committee on Public Works and Transportation, Data Relating to H.R. 3199 (Clean Water Act of 1977), committee
print, 95th Cong., November 1977, H.Prt. 95-30 [Washington: GPO, 1977], pp. 3-4.) These pollutants included both
individual chemicals and categories of chemical compounds. As presented in the legislative history, this initial list was
negotiated among parties to a 1976 settlement agreement between EPA and the Natural Resources Defense Council in
the case of Natural Resources Defense Council v Train (U.S. Congress, House Committee on Public Works and
Transportation, Subcommittee on Investigations and Review, Water Contamination by Toxic Pollutants: An Assessment
of Regulation, committee print, 95th Cong., September 1977, 95-26, p. 6).
60 EPA, “Publication of Toxic Pollutant List,” 43 Federal Register 4108, January 31, 1978.
61 EPA removed three pollutants from the list in 1981 after determining that the chemical properties of the pollutants
are such that they do not pose a risk to human health or the environment by exposure through water. However, delisting
these three pollutants did not change the 65 entries on the Toxic Pollutant List because they were specific compounds
listed within two broader categories of listed compounds—halomethanes and haloethers. (See EPA, “Removal of
Dichlorodifluoromethane and Trichlorofluoromethane from the Toxic Pollutant List Under Section 307(a)(1) of the
Clean Water Act,” 46 Federal Register 2266, January 8, 1981; EPA, “Removal of Bis-(Chloromethyl) Ether (BCME)
from the Toxic Pollutant List Under Section 307(a)(1) of the Clean Water Act,” 46 Federal Register 10723, February
4, 1981.) The Toxic Pollutant List is codified in federal regulation at 40 C.F.R. §401.15.
62 33 U.S.C. §1317(a)(1).
63 33 U.S.C. §1317(a)(2).
64 33 U.S.C. §1313(c)(2)(B).
65 33 U.S.C. §1314(a).
66 33 U.S.C. §1342.
67 Personal communication between CRS and EPA staff, August 6, 2019.
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whether effective treatment technologies are available; and developing economic data to project
the cost of treatment, among other things.68
Also, EPA and state officials have asserted that it is difficult for the agency and its CWA programs
to keep pace with the growth of new chemicals in commerce.69 Accordingly, the agency is
generally reactive rather than proactive in addressing CECs. EPA officials stated that identifying
demonstrated treatment technologies and documenting their efficiency is especially challenging.70
The officials further stated that the most difficult task is showing that any technology selected as
the basis for an ELG is economically achievable for the industry.71
In addition, EPA and states often lack analytical methods to measure an emerging contaminant.72
Even where analytical methods are available, there is still often a lack of data on the levels of the
contaminant in dischargers’ effluent and/or in the receiving surface waters. The two sources of
data most readily available to EPA—discharge monitoring report data and toxic release inventory
data—are limited to specific contaminants on which industry is required to report.73 EPA stated
that the agency’s capacity to collect data—including obtaining clearance to request and collect
the data and undertaking the extensive effort to do so—is limited in light of their staffing levels
and resources.74
Should EPA have enough data to determine that a new or revised ELG is warranted and announce
its intent to do so in an effluent guidelines program plan, the time it takes to issue the regulation
varies, according to EPA officials. CWA Section 304(m) establishes a three-year time limit for
new ELGs.75 For revised ELGs, the EPA officials stated that the time can vary depending upon

68 Personal communication between CRS and EPA staff, August 6, 2019. See also CWA §304(b); 33 U.S.C. §1314(b);
and EPA, Final 2016 Effluent Guidelines Program Plan, p. 2-2.
69 Personal communication between CRS and EPA staff, August 6, 2019. See also ACWA, ASDWA,
Recommendations Report.
70 Personal communication between CRS and EPA staff, August 6, 2019.
71 Personal communication between CRS and EPA staff, August 6, 2019.
72 For example, in EPA’s PFAS Action Plan, the agency commits in the short term to developing analytical methods to
“detect, identify, and quantify” known PFAS of concern in media, including wastewater and groundwater. EPA also
commits to developing analytical methods for new, unknown PFAS in the long term. See EPA, Per- and
Polyfluoroalkyl Substances (PFAS) Action Plan, February 2019, https://www.epa.gov/sites/production/files/2019-02/
documents/pfas_action_plan_021319_508compliant_1.pdf, p. 34. As another example, in 2017, EPA convened a
Microplastics Expert Workshop to identify and prioritize the scientific information needed to understand the risks
posed by microplastics. In its report summarizing experts’ recommendations, EPA concluded that “development of
reliable, reproducible, and high-quality methods for microplastics is fundamental and of utmost importance for
understanding microplastics risks.” See EPA, Microplastics Expert Workshop Report. Also, in its Final 2016 Effluent
Guidelines Program Plan, EPA describes its ongoing investigation looking at engineered nanomaterials and states that
it will continue to look for opportunities to inform current data gaps, including development of analytical methods to
detect and quantify engineered nanomaterials.
73 Personal communication between CRS and EPA staff, August 6, 2019. See also EPA, Final 2016 Effluent Guidelines
Program Plan, pp. 2-4 and 3-5.
74 Personal communication between CRS and EPA staff, August 6, 2019. See also “As Democrats Push Steep PFAS
Deadlines, Regan Seeks More Resources,” InsideEPA, October 6, 2021. Note that under the Paperwork Reduction Act
(44 U.S.C. §3501 et seq.), EPA can contact—with a survey or questionnaire—up to nine entities without first obtaining
approval from the Office of Management and Budget. If EPA decides to contact 10 or more entities, the act requires the
agency to prepare an Information Collection Request. In November 2018, EPA’s Assistant Administrator for the Office
of Water issued a memorandum clarifying its processes for collecting information from nine or fewer individuals or
entities under CWA Section 308. The memorandum is available at https://www.epa.gov/sites/production/files/2018-11/
documents/policy-use-of-cwa-308-letters.pdf. See also “As Democrats Push Steep PFAS Deadlines, Regan Seeks More
Resources,” InsideEPA, October 6, 2021.
75 33 U.S.C. §1314(m).
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the availability of data and the level of complexity—some may be very technical and involve
many wastestreams.76 Two of the more recently issued ELGs—revisions of the oil and gas
extraction and steam electric power generating categories—took five and six years, respectively.77
Water-Quality-Based Requirements
Under the CWA, water quality standards translate the goals of the act (e.g., fishable and
swimmable waters, no toxic pollutants in toxic amounts) into measurable objectives to protect or
improve water quality.78 States, territories, and authorized tribes (hereinafter referred to
collectively as states) are required to adopt water quality standards for waters of the United
States, subject to EPA approval.79 They may also adopt standards for additional surface waters if
their own state laws allow them to do so.80
Water quality standards consist of three key required components:81
1. Designated uses for each water body—for example, recreation (swimming or
boating), aquatic life support, fish consumption, public water supply, agriculture;
2. Criteria, which describe the conditions in a water body necessary to support the
designated uses—expressed as concentrations of pollutants or other quantitative
measures or narrative statements; and
3. An antidegradation policy for maintaining existing water quality.
States have the primary authority to adopt, review, and revise their water quality standards and
implementation procedures. The CWA requires states to review their water quality standards at
least once every three years.82 EPA is required to review the states’ water quality standards.83

76 Personal communication between CRS and EPA staff, August 6, 2019.
77 Note that these time frames include notice-and-comment requirements under the Administrative Procedure Act. EPA
announced its intent to revise the Oil and Gas Extraction ELG to develop pretreatment standards for discharges from
unconventional oil and gas facilities to POTWs in 2011 (76 Federal Register 66286) and published its final rule for the
Oil and Gas Extraction ELG in 2016 (81 Federal Register 41845). EPA announced its intent to revise the Steam
Electric Power Generating ELG in 2009 (74 Federal Register 68603) and issued its final rule in 2015 (80 Federal
Register 67838). Note that in November 2019, EPA announced a proposed rule to revise the Steam Electric Power
Generating ELG applicable to two of the six wastestreams covered in the 2015 rule and finalized the rule in 2020 (85
Federal Register 64650). On August 3, 2021, EPA announced its decision to initiate a proposed rulemaking to revise
the Steam Electric Power Generating ELG “to determine whether more stringent limitations and standards are
appropriate and consistent with the technology-forcing statutory scheme and the goals of the CWA.” EPA intends to
sign the notice of proposed rulemaking for public comment in the fall of 2022 (86 Federal Register 41801). For more
information on the Steam Electric Power Generating ELG, see CRS In Focus IF10778, Overview of the Steam Electric
Power Generator Effluent Limitation Guidelines and Standards, by Laura Gatz.
78 Section 101(a) of the CWA (33 U.S.C. §1251(a)) includes the objective and goals of the act. One of the goals—
“water quality which provides for the protection and propagation of fish, shellfish, and wildlife and provides for
recreation in and on the water”—is often referred to in shorthand as “fishable and swimmable waters.”
79 CWA §303(c); 33 U.S.C. §1313(c). Per Section 502(3) of the CWA (33 U.S.C. §1362(3)), state is defined to include
a state, the District of Columbia, or any of the U.S. territories. Per Section 518 of the CWA (33 U.S.C. §1377), EPA is
authorized to treat an Indian tribe as a state for certain sections of the CWA, including the sections pertaining to water
quality standards. EPA regulations at 40 C.F.R. §131.8 lay out the requirements and process by which a tribe may
request and be approved to administer its own water quality standards program.
80 CWA §510; 33 U.S.C. §1370.
81 See CWA Section 303(c)(2)(A) for designated uses and criteria and CWA Sections 101(a) and 303(d)(4)(B) for
antidegradation. Also see EPA’s implementing regulations at 40 C.F.R. §131.
82 CWA §303(c); 33 U.S.C. §1313(c).
83 If EPA approves the water quality standards, they become effective. If EPA disapproves the water quality standards,
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Water Quality Criteria
Water quality criteria prescribe limits on specific contaminants or conditions in a water body that
protect particular designated uses of the water body. Both the EPA and states have roles in
establishing water quality criteria under CWA Section 304(a) and 303(c)(2), respectively.
EPA Role
CWA Section 304(a) requires EPA to develop and publish and “from time to time thereafter
revise” criteria for water quality that accurately reflect the latest scientific knowledge.84 These
criteria are recommendations to states for use in developing their own water quality standards.
EPA has developed several different types of criteria, including human health criteria, aquatic life
criteria, and recreational criteria.85 EPA has also published guidelines for deriving water quality
criteria, which the agency uses to develop new criteria under Section 304(a). These guidelines
also serve as guidance to states as they adjust water quality criteria developed under Section
304(a) to reflect local conditions or develop their own scientifically defensible water quality
criteria.86
EPA most recently updated its human health criteria in 2015, revising 94 of the 122 existing
human health criteria.87 EPA last updated its methodology for deriving human health criteria in
2000,88 incorporating “significant scientific advances in key areas such as cancer and non-cancer
risk assessments, exposure assessments, and bioaccumulation in fish.”89
EPA’s national recommended aquatic life criteria table currently includes 59 criteria.90 Many of
these criteria were published prior to 1990. In the past 10 years, EPA has published two new
criteria.91 EPA has not updated its guidelines for deriving aquatic life criteria since 1985.92
According to EPA, however, the guidelines allow for best professional judgment, which they have
used in more recent criteria development and updates.93 The agency recognizes that since 1985,

the state has 90 days to revise them. If the state does not do so, EPA is required to promulgate standards that meet
CWA requirements. CWA §303(c)(3); 33 U.S.C. §1313(c)(3).
84 CWA §304(a)(1); 33 U.S.C. §1314(a)(1).
85 EPA, “Basic Information on Water Quality Criteria,” https://www.epa.gov/wqc/basic-information-water-quality-
criteria.
86 EPA, Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health, October 2000,
p. iii, https://www.epa.gov/sites/production/files/2018-10/documents/methodology-wqc-protection-hh-2000.pdf; EPA,
Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their
Uses, 1985, pp. 2-3, https://www.epa.gov/sites/production/files/2016-02/documents/guidelines-water-quality-
criteria.pdf.
87 EPA, “Final Updated Ambient Water Quality Criteria for the Protection of Human Health,” 80 Federal Register
36986, June 29, 2015; EPA, “National Recommended Water Quality Criteria—Human Health Criteria Table,”
https://www.epa.gov/wqc/national-recommended-water-quality-criteria-human-health-criteria-table.
88 EPA, Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health.
89 EPA, Fact Sheet: Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health—
Revised Methodology, 2000, https://www.epa.gov/wqc/fact-sheet-methodology-deriving-ambient-water-quality-
criteria-protection-human-health-revised#copy.
90 EPA, “National Recommended Water Quality Criteria—Aquatic Life Criteria Table,” https://www.epa.gov/wqc/
national-recommended-water-quality-criteria-aquatic-life-criteria-table.
91 According to personal communication between CRS and EPA staff on May 29, 2019, in the past 10 years, EPA
developed new criteria for two substances: carbaryl and acrolein.
92 EPA, Guidelines for Deriving Numerical National Water Quality Criteria.
93 Personal communication between CRS and EPA staff, May 29, 2019. Also see EPA, Guidelines for Deriving
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there has been substantial scientific advancement that warrants updating these guidelines.94 EPA
formally initiated the guidelines revision process in 2015. However, according to EPA officials,
the agency shifted its focus from updating the guidelines to determining whether available data
and research support development of human health criteria for PFAS.95 In doing so, EPA officials
indicated they planned to use information gathered for the guidelines revision and also noted that
they are not tied to the 1985 guidelines due to the best professional judgment clause included
therein.96
EPA’s recreational water quality criteria are national recommendations for all inland and coastal
waters that have a primary contact recreation (i.e., swimming) designated use. EPA establishes
recreational water quality criteria to help protect against illness caused by organisms—such as
viruses, bacteria, and their associated toxins—in water bodies.97 In 2012, EPA updated its
recreational water quality criteria, which it had last issued in 1986.98 Additionally, in June 2019,
EPA published final recreational water quality criteria for two algal toxins, which are commonly
present in harmful algal blooms, to supplement the 2012 recreational water quality criteria.99 In
addition, EPA is currently developing recreational water quality criteria for coliphage, a viral
indicator of fecal contamination.100
State Role
States use EPA’s criteria as guidance in developing their own water quality standards. CWA
Section 303(c)(2) requires states to adopt criteria to protect the designated uses of their water
bodies and to also adopt criteria for all toxic pollutants listed pursuant to Section 307(a)(1), for
which EPA has published criteria under Section 304(a). States’ water quality criteria must be
based on sound scientific rationale, contain sufficient parameters or constituents to protect the
designated uses, and support the most sensitive use for water bodies with multiple designated
uses.101 EPA regulations further require that states should establish numeric criteria based on
CWA Section 304(a) guidance, CWA Section 304(a) guidance modified to reflect site-specific
conditions, or other scientifically defensible methods.102 Where numeric criteria cannot be
established, states are required to establish narrative criteria or criteria based on biomonitoring

Numerical National Water Quality Criteria, p. 9.
94 EPA, “Aquatic Life Criteria and Methods for Toxics,” https://www.epa.gov/wqc/aquatic-life-criteria-and-methods-
toxics#sab.
95 As discussed further under “Challenges to Addressing CECs Through Water-Quality-Based Requirements,” EPA
announced in its 2021 PFAS Strategic Roadmap that it will develop national recommended ambient water quality
criteria for PFAS to protect aquatic life and human health.
96 Personal communication between CRS and EPA staff, May 29, 2019.
97 EPA, “Recreational Water Quality Criteria and Methods,” https://www.epa.gov/wqc/recreational-water-quality-
criteria-and-methods#rec.
98 EPA, 2012 Recreational Water Quality Criteria, December 2012, https://www.epa.gov/sites/production/files/2015-
10/documents/rec-factsheet-2012.pdf.
99 EPA, “Recommended Human Health Recreational Ambient Water Quality Criteria or Swimming Advisories for
Microcystins and Cylindrospermopsin,” 84 Federal Register 26413, June 6, 2019.
100 EPA, “Recreational Water Quality Criteria and Methods,” https://www.epa.gov/wqc/recreational-water-quality-
criteria-and-methods#rec. See “Development of Recreational Water Quality Criteria for Coliphage” section.
101 40 C.F.R. §131.11.
102 40 C.F.R. §131.11(b).
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methods.103 States may adopt more stringent criteria than what EPA recommends, including for
pollutants or parameters for which EPA has not promulgated Section 304(a) criteria.104
Options to Address CECs Through Water-Quality-Based Requirements
EPA and states may establish water quality criteria for CECs. If EPA were to establish criteria
under CWA Section 304(a) for a CEC, that action alone would not necessarily require states to
adopt criteria for that contaminant. As explained above, the CWA requires that states adopt
criteria to protect their designated uses into their water quality standards. EPA’s regulations
provide that if a state does not adopt new or revised criteria for parameters for which EPA has
published new or updated recommendations, then the state shall provide an explanation.105 States
are explicitly required, as explained above, to adopt criteria for a contaminant if EPA designates it
as a toxic pollutant under CWA Section 307 and publishes criteria for that contaminant under
Section 304(a).106
Once a state has adopted water quality criteria for a contaminant as part of its state water quality
standards and those standards have been approved, several CWA tools are available for achieving
those standards. The primary tool is to limit or prohibit discharges of the contaminant in NPDES
permits. In some cases, the technology-based effluent limits may already enable attainment of
state water quality standards. In instances where they do not, the permit writer is required to
establish water-quality-based effluent limitations.107 If a water body is not attaining its designated
use (i.e., is “impaired” for that use), the Total Maximum Daily Load (TMDL) may also be
used.108 A TMDL, essentially a “pollution diet” for a water body, is the maximum amount of a
pollutant that a water body can receive and still meet water quality standards and an allocation of
that amount to the pollutant’s sources (including a margin of safety).109 TMDLs consider point
sources, which can be addressed through permits, as well as nonpoint (diffuse) sources, which are
more often addressed through best management practices and related efforts under CWA Section
319 nonpoint source management programs.110
Challenges to Addressing CECs Through Water-Quality-Based Requirements
A key challenge is often a lack of data about the occurrence, concentration, and persistence of
CECs in the environment, as well as the effects on human health and aquatic life. Detection of a
contaminant does not necessarily trigger regulatory measures. Information on the potential for the
contaminant to adversely affect human health and aquatic life, potential exposure pathways, and
other data would also be needed to inform such decisions.
Developing new water quality criteria or updating existing criteria can often be time intensive,
particularly in cases where data are limited. The general process for developing criteria involves a

103 40 C.F.R. §131.11(b).
104 CWA §510; 33 U.S.C. §1370.
105 40 C.F.R. §131.20(a).
106 CWA §303(c)(2)(B); 33 U.S.C. §1313(c)(2)(B).
107 Per 40 C.F.R. §122.44(d)(1)(i), limitations must be established in permits to “control all pollutants or pollutant
parameters (either conventional, nonconventional, or toxic pollutants) which the Director determines are or may be
discharged at a level which will cause, have the reasonable potential to cause, or contribute to an excursion above any
State water quality standard, including State narrative criteria for water quality.”
108 CWA §303(d); 33 U.S.C. §1313(d).
109 40 C.F.R. §130.2.
110 33 U.S.C. §1329.
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number of steps, including problem formulation and developing an analysis plan; gathering data
and analyzing relevant studies; drafting the criteria document; a rigorous review process (e.g.,
branch level, office level, interagency, and independent external peer review); public notice and
comment, and revising and publishing the criteria.111 According to EPA officials, the time it takes
to develop or update criteria is often a function of the data that are available.112 EPA officials
noted that developing criteria can take several years or longer. For example, the 2016 update for
the aquatic life water quality criteria for selenium—an effort characterized by EPA as
complicated, in part because of the contaminant’s bioaccumulative properties—took 10 years to
complete.113 In other cases, such as when a contaminant has an existing EPA Integrated Risk
Information System value, developing or updating the human health water quality criteria for that
contaminant may take less time, according to EPA officials.114
In May 2019, a report from the Contaminants of Emerging Concern Workgroup, convened by the
Association of State Drinking Water Administrators and the Association of Clean Water
Administrators, provided recommendations from state regulators regarding the ways state and
federal agencies could improve the management of CECs.115 The report stated the following:
The use of existing authorities and processes under the CWA and [Safe Drinking Water
Act] to establish new criteria or standards is onerous, can take decades to implement, and
does not meet public expectations for timely identification and prioritization of CECs….
However slow these federal processes are, many state agencies do not have the
infrastructure (i.e., sufficient funds and/or staffing levels), regulatory authority, or
technical expertise to derive their own criteria or set their own standards for drinking water,
surface water, groundwater, and fish tissue.
Among numerous other recommendations provided in the report, the CEC workgroup
recommended that EPA work with states to generate a list of priority CECs. To that end, EPA
officials stated that they are developing a more formalized prioritization process for determining
which contaminants warrant criteria development that will incorporate input from multiple
stakeholders (including states), leverage information collected under the Safe Drinking Water Act,
and incorporate monitoring and other data (e.g., ambient water concentrations).116
In EPA’s 2019 PFAS Action Plan, the agency announced that it was working to determine if
available data and research supported the development of CWA Section 304(a) water quality
criteria for human health for PFAS.117 In EPA’s October 2021 PFAS Strategic Roadmap, EPA
announced that it will develop national recommended ambient water quality criteria for PFAS to

111 Personal communication between CRS and EPA staff, May 29, 2019.
112 Personal communication between CRS and EPA staff, May 29, 2019.
113 Personal communication between CRS and EPA staff, May 29, 2019. See also EPA, Aquatic Life Ambient Water
Quality Criterion for Selenium—Freshwater 2016, June 2016, pp. 1-3, https://www.epa.gov/sites/production/files/
2016-07/documents/aquatic_life_awqc_for_selenium_-_freshwater_2016.pdf.
114 Personal communication between CRS and EPA staff, May 29, 2019. EPA’s Integrated Risk Information System
(IRIS) is a human health assessment program that evaluates information on health effects of exposure to environmental
contaminants. For more information on the IRIS program, see EPA, “Integrated Risk Information System,”
https://www.epa.gov/iris. According to EPA officials, because development of IRIS values requires a rigorous review
process, EPA does not do a separate peer review in developing criteria using an IRIS value (personal communication
between CRS and EPA staff, May 29, 2019).
115 ACWA, ASDWA, Recommendations Report.
116 Personal communication between CRS and EPA staff, May 29, 2019. EPA staff stated that, in the past, the agency
has more informally determined the need for criteria through state and stakeholder input.
117 EPA, EPA’s Per- and Polyfluoroalkyl Substances (PFAS) Action Plan, pp. 6, 29.
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protect aquatic life and human health.118 EPA anticipates by winter 2022 it will publish
recommended aquatic life criteria for two PFAS—perfluorooctanoic acid (PFOA) and
perfluorooctane sulfonic acid (PFOS)—and benchmarks for other PFAS for which EPA does not
have sufficient data to define a recommended aquatic life criteria value. EPA anticipates
publishing human health criteria for PFOA and PFOS by fall 2024.119
Designating CECs as Toxic Pollutants or Hazardous Substances
Two sections of the CWA—Sections 307 and 311—authorize EPA to designate contaminants as
toxic pollutants and hazardous substances, respectively. Designating a contaminant under Section
307 or Section 311 of the CWA has implications for how the contaminant is treated under
CERCLA. CERCLA defines the term hazardous substance to include toxic pollutants designated
under CWA Section 307 and hazardous substances designated under CWA Section 311 (as well as
substances designated under certain other statutes and other chemicals that EPA may designate as
hazardous substances).120
Toxic Pollutants—CWA Section 307
EPA’s authority to designate contaminants under CWA Section 307 as toxic pollutants and the
CWA-related implications of that designation are discussed above under “Toxic Pollutant List.”
Hazardous Substances—CWA Section 311
CWA Section 311(b)(2)(A) authorizes EPA to promulgate a rule designating as a “hazardous
substance” any element or compound that, when discharged as specified under the section, would
present an imminent and substantial danger to public health or welfare, including but not limited
to fish, shellfish, wildlife, shorelines, and beaches.121 EPA is authorized to revise the list of
hazardous substances subject to these criteria as may be appropriate. EPA finalized the initial list
of hazardous substances in 1978 and thereafter revised the list in 1979, 1989, and 2011.122

118 EPA, PFAS Strategic Roadmap, p. 15.
119 Ibid.
120 Section 101(14) of CERCLA (42 U.S.C. §9601(14)) generally defines the term hazardous substance to include
hazardous substances designated under Section 311(b)(2)(A) of the CWA; toxic pollutants listed under Section 307(a)
of the CWA; hazardous waste with characteristics identified or listed under Section 3001 of the Solid Waste Disposal
Act (with the exception of wastes excluded from regulation); hazardous air pollutants listed under Section 112 of the
Clean Air Act; any imminently hazardous chemical substance or mixture for which EPA has taken action under Section
7 of TSCA; and other elements, compounds, mixtures, solutions, and substances designated pursuant to Section 102 of
CERCLA.
121 33 U.S.C. §1321(b)(2)(A). CWA Section 311(b)(3) generally prohibits the discharge of a hazardous substance (or
oil) in “harmful” quantities into or upon the navigable waters of the United States, adjoining shorelines, or the waters of
the contiguous zone or in connection with activities under the Outer Continental Shelf Lands Act or the Deepwater Port
Act of 1974 or that may affect natural resources belonging to, appertaining to, or under the exclusive management
authority of the United States. However, Section 311(a)(2) of the CWA (33 U.S.C. §1321(a)(2)) defines the term
discharge to exclude discharges in compliance with a permit issued under CWA Section 402, making such compliant
discharges not prohibited.
122 The list of hazardous substances designated under CWA Section 311 is codified at 40 C.F.R. §116.4. The original
list published by EPA in 1978 included 271 hazardous substances. While 28 substances were added the following year,
the list has changed slightly since that time and currently includes 296 substances.
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Pursuant to Section 311(b)(4), EPA established “harmful” quantities for these substances that are
subject to the reporting of discharges prohibited under Section 311(b)(3).123 Section 311(b)(5)
requires a person in charge of a vessel or facility to notify the National Response Center,
administered by the U.S. Coast Guard, as soon as that person has knowledge of a discharge.124
Discharges permitted under other provisions of the CWA or otherwise allowable under certain
other federal, state, and local regulations are excluded from reporting under CWA Section 311.125
CWA Section 311(c) authorizes federal actions to remove a prohibited discharge of a hazardous
substance (or oil).126 CWA Section 311(f) establishes liability for the recovery of removal costs,
including restoration of damaged natural resources.127 Section 311(e) authorizes enforcement
orders to require a responsible party to abate an imminent and substantial threat to public health
or welfare from a prohibited discharge, or threat of a harmful discharge, of a hazardous substance
(or oil).128
Implications of CWA Designations on CERCLA
If EPA were to designate a CEC, or any contaminant, as a toxic pollutant or hazardous substance
under the CWA, that contaminant would, by statutory definition, be defined as a hazardous
substance under CERCLA. CERCLA authorizes federal actions to respond to a release, or
substantial threat of a release, of a hazardous substance into the environment in coordination with
the states. CERCLA similarly authorizes response actions for releases of other pollutants or
contaminants that may present an imminent and substantial danger to public health or welfare.
CERCLA also establishes liability for response costs and natural resource damages but only for
hazardous substances and not for other pollutants or contaminants.
CERCLA response authority is available for releases of pollutants or contaminants but without
liability to require a potentially responsible party to perform or pay for response actions.
Designating a CEC as a toxic pollutant or hazardous substance under the CWA would have the
effect of establishing liability for their release as a hazardous substance under CERCLA.
However, releases in compliance with a CWA permit would be exempt from liability under
CERCLA as a “federally permitted release” based on the premise that the permit requirements
would mitigate potential risks.129
CWA Section 311 also establishes liability for releases of hazardous substances, but CERCLA
liability and enforcement mechanisms are broader than the CWA. In practice, CERCLA has been
the principal federal authority used to respond to discharges of hazardous substances into surface
waters and to enforce liability, although the enforcement authorities of CWA Section 311 remain

123 33 U.S.C. §1321(b)(4).
124 33 U.S.C. §1321(b)(5).
125 Quantities of “harmful” discharges of hazardous substances subject to reporting under CWA Section 311 are
codified at 40 C.F.R. §117.
126 33 U.S.C. §1321(c).
127 33 U.S.C. §1321(f).
128 33 U.S.C. §1321(e). Such threats may include threats to fish, shellfish, wildlife, public and private property,
shorelines, beaches, habitat, and other living and nonliving natural resources under the jurisdiction or control of the
United States.
129 Section 107(j) of CERCLA (42 U.S.C. §9607(j)) exempts federally permitted releases from liability under the
statute. Section 101(10) of CERCLA (42 U.S.C. §9601(10)) defines the term federally permitted release to include
discharges permitted under Sections 402 and 404 of the CWA and releases permitted under various other federal
environmental laws.
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available to EPA. For a broader discussion of CERCLA, see CRS Report R41039, Comprehensive
Environmental Response, Compensation, and Liability Act: A Summary of Superfund Cleanup
Authorities and Related Provisions of the Act, by David M. Bearden.
Legislation in the 117th Congress
Recent congressional interest in CECs has largely focused on addressing one particular group of
CECs—PFAS—and addressing them through several statutes, such as the Safe Drinking Water
Act.130 In the 117th Congress, some Members have continued to introduce bills that would direct
EPA to take regulatory and other actions to address PFAS under several environmental statutes.
Some bills introduced in the 117th Congress also propose to address PFAS, microplastics, or other
CECs using CWA authorities. In October 2021, the House Transportation and Infrastructure
Committee, Water Resources and Environment Subcommittee, held a hearing focused on CECs—
with particular attention to PFAS and microplastics—and the CWA’s framework for addressing
such contaminants in surface waters.131 In addition, Congress passed the Infrastructure Investment
and Jobs Act, enacted on November 15, 2021 (IIJA; P.L. 117-58), which provides $1 billion over
five fiscal years for the primary financial assistance program that supports wastewater
infrastructure—the Clean Water State Revolving Fund program, authorized by the CWA—for a
range of projects to address emerging contaminants.
Bills introduced by Members in the 117th Congress to address PFAS, microplastics, or other CECs
using CWA authorities include the following:
 H.R. 1915, the Water Quality Protection and Job Creation Act of 2021, would
amend the CWA to create, reauthorize, and revise several programs. The bill
would create a new grant program for owners of publicly owned treatment works
to be used for the implementation of a pretreatment standard or effluent
limitation developed pursuant to the CWA for any PFAS or pollutants identified
by the EPA Administrator as a CEC.
 H.R. 2467, the PFAS Action Act of 2021, would require EPA to take a number of
actions under several statutes. Among these are CWA-related actions focused on
ELGs, water quality criteria, and notification. Some of these actions are similar
to those proposed in H.R. 3622, S. 1907, and H.R. 4224 (as discussed below).
H.R. 2467 would require EPA to develop ELGs for PFAS for nine specified
industrial categories no later than four years after the date of enactment.132 It
would also require EPA to publish human health water quality criteria for PFAS
not later than three years after the date of enactment. The bill includes an
authorization of appropriations for EPA to carry out these requirements. The bill
would also require the owner or operator of an industrial source of PFAS to
notify the applicable treatment facility of any introduction of PFAS to that
treatment works, and provide them with certain information regarding the
identity, quantity, susceptibility to treatment, and potential interference of the
relevant PFAS.

130 For a discussion of select PFAS legislation in the 116th Congress, see CRS Report R45986, Federal Role in
Responding to Potential Risks of Per- and Polyfluoroalkyl Substances (PFAS), coordinated by David M. Bearden.
131 U.S. Congress, House Committee on Transportation and Infrastructure, Subcommittee on Water Resources and
Environment, Emerging Contaminants, Forever Chemicals, and More: Challenges to Water Quality, Public Health,
and Communities, 117th Cong., 1st sess., October 6, 2021.
132 As discussed in an earlier section (“ELGs”), in October 2021, EPA issued its PFAS Strategic Roadmap, which
established timelines for action on certain industrial categories, including the nine industrial categories identified in the
proposed “PFAS Action Act of 2021” legislation.
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 H.R. 3622 and S. 1907, related bills titled the Clean Water Standards for PFAS
Act of 2021, would similarly require EPA to develop ELGs for PFAS for nine
specified industrial categories not later than four years after the date of
enactment. They would require EPA to publish human health water quality
criteria for PFAS not later than two years after the date of enactment. The bills
would authorize appropriations of $200 million for each of FY2022 through
FY2026 for EPA to carry out these requirements.
 H.R. 3701, the Protecting Infrastructure and Promoting the Economy Act (PIPE
Act), would direct EPA to establish a wastewater discretionary grant program to
provide competitive grants to eligible entities for certain eligible wastewater
infrastructure projects. Eligible projects would include measures to reduce the
discharge of PFAS into the environment through publicly owned treatment
works.
 H.R. 4224, the PFAS Transparency Act, would require the owner or operator of
an industrial source of PFAS to notify the applicable treatment work of any
introduction of PFAS to that treatment works, and provide them with certain
information regarding the identity, quantity, susceptibility to treatment, and
potential interference of the relevant PFAS.
 S. 1507, the Plastic Pellet Free Waters Act, would require EPA to promulgate a
rule to prohibit the discharge of plastic or pre-production plastic materials from
facilities regulated by ELGs under the Organic Chemicals, Plastics, and Synthetic
Fibers133 and Plastics Molding and Forming134 industrial categories. It would also
require that the rule prohibit discharges of plastic pellets or other pre-production
plastic materials from point sources that make, use, package, or transport such
materials, and would require that NPDES permits and standards of performance
for vessels reflect these prohibitions.
 H.R. 2238 and S. 984, companion bills titled the Break Free from Plastic
Pollution Act, would require certain actions to address plastic pollution and
microplastics through several statutes. Among other actions, the bills would
require EPA, in consultation with other agencies, to establish a grant program to
fund microfiber reduction projects that either help reduce the generation of
microfiber pollution or improve filtration for the removal of microfiber pollution
from washing machines or wastewater treatment plants. They would also require
EPA to establish a pilot program to test the efficacy and cost effectiveness of
tools, technologies, and techniques to remove microplastics from the
environment and prevent release into the environment. The bills would require
EPA to promulgate revised ELGs, not later than three years after enactment, for
the Organic Chemicals, Plastics, and Synthetic Fibers industrial category and the
Petroleum Refining category135 to address specified requirements. They would
also incorporate the requirements proposed in S. 1507, the Plastic Pellet Free
Waters Act. In addition, they would require that no later than three years after
enactment, EPA promulgate a rule to ensure that proposed CWA permits for
certain facilities identified in the bill address potential environmental justice
impacts.

133 40 C.F.R. §414.
134 40 C.F.R. §463.
135 40 C.F.R. §419.
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Conclusion
While Congress is currently debating how to best address the concerns related to widespread
detections of PFAS, attention to other emerging contaminants (e.g., microplastics and algal
toxins) has also increased, together with the availability of new detection methods and increased
monitoring. Observers note that in the coming years, other CECs will likely emerge and prompt
similar calls for immediate action to protect public health and the environment. Many observers
argue that federal actions to address CECs currently tend to be reactive rather than proactive.
Many of these observers assert that more focus and attention is needed on assessing the toxicity
of chemical substances before they are introduced into commerce. Congress is currently
considering legislation to improve federal coordination and responses to CECs.
Specific to the CWA, some observers advocate for oversight to identify and address potential
gaps or barriers in CWA authorities and processes that make it difficult for EPA and states to
quickly respond when CECs are detected. Other observers assert that EPA could better use its
existing authorities to address CECs. For example, EPA has not updated its ELGs for certain
industrial categories in decades. Accordingly, some observers assert that various ELGs do not
reflect advancements in science or technology that could lead to new effluent limitations for
CECs. Similarly, some stakeholders assert that EPA could better prioritize which CECs warrant
water quality criteria development. EPA’s ability to address these and other recommendations
depends on the availability of resources, treatment technologies, and scientific and economic
data. Moving forward, Congress may be interested in evaluating EPA appropriations for the CWA
programs that support EPA’s efforts to address discharges of CECs. Congress may also be
interested in overseeing the Administration’s implementation of these programs.

Author Information

Laura Gatz

Analyst in Environmental Policy

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
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under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other
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Congressional Research Service
R45998 · VERSION 3 · UPDATED
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