EPA proposes national primary drinking water regulation for six PFAS


Mar. 14, 2023

The EPA has proposed a National Primary Drinking Water Regulation (NPDWR) establishing new enforceable maximum contaminant limits (MCLs) for certain per- and polyfluoroalkyl substances (PFAS) known to occur in drinking water along with health-based, non-enforceable maximum contaminant level goals (MCLGs). The proposed MCLs for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are 4 parts per trillion individually, a limit stricter than any state has enacted. The EPA has proposed a novel approach for regulating the remaining four PFAS substances, perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS), by establishing a combined enforceable MCL at a “hazard index” of 1.0. This is a pre-publication of the proposed rule which should be published in the Federal Register soon.

Regulatory background

  • Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic fluorinated organic compounds used in industrial and consumer products for their resistance to water, heat, and stains. They are used as surface treatments on clothing and carpeting, cookware, and in food packaging, cosmetics, and fire-fighting foam (AFFF). Fluoropolymers also have dielectric and fire-resistant properties that have a wide range of electrical and electronic applications, including architecture, automotive uses, cabling materials, electronics, pharmaceutical and biotech manufacturing, and semiconductor manufacturing (Gardiner, 2014).
  • Known as “forever chemicals,” PFAS last a long time and certain components of them break down slowly due to their resilience and ability to accumulate in environmental systems and the human body. According to the EPA, depending on the individual PFAS, health effects can include negative impacts on fetal growth after exposure during pregnancy, other aspects of development, reproduction, liver, thyroid, immune function, and/or the nervous system, and increased risk of cardiovascular and other health impacts. 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.
  • PFOA and PFOS are two of the most widely studied and longest used PFAS. According to the EPA, 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.
  • In October 2021, the EPA developed the PFAS Strategic Roadmap which is focused on three objectives: (1) Research to increase understanding of PFAS exposures and toxicities, human health and ecological effects, and effective interventions that incorporate the best available science; (2) Restrict to prevent PFAS from entering air, land, and water that can damage human health and the environment; and (3) Remediate to broaden and accelerate the cleanup of PFAS contamination to protect human health and ecological systems.
  • Section 1412(b)(1)(A) of the Safe Drinking Water Act (SWDA) requires EPA to establish National Public Drinking Water Regulations (NPDWR) 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 judgment of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by PWSs. The SWDA requires the EPA to establish a Contaminant Candidate List (CCL) comprised of a list of drinking water contaminants to be considered for future regulation. Starting with the first CCL in 1998, regulatory determinations on a minimum of five contaminants are made by the EPA every five years. Nationwide data on chemical contaminants is required in order to establish the CCLs.
  • In March 2021, EPA issued a final regulatory determination to regulate PFOS and PFOA as part of the Fourth Contaminant Candidate List, which identified 109 contaminants that are currently not subject to any proposed or promulgated national drinking water regulations. EPA collects the data under the Unregulated Contaminant Monitoring Regulations (UCMR) where monitoring is conducted at drinking water utilities for contaminants of interest.
  • In December 2021, EPA finalized the Unregulated Contaminant Monitoring Rules cycle 5 (UCMR 5) to require the collection of new data on 29 PFAS in drinking water by public water systems (PWSs). The objective of this data collection was to improve EPA’s understanding of the frequency that these 29 PFAS are found in the nation’s drinking water systems and at what levels.
  • Under the SDWA, the EPA also issued health advisories (HAs) for drinking water contaminants. Health advisories are non-regulatory and reflect EPA’s assessment of the best available peer-reviewed science. The interim updated health advisories for PFOA and PFOS supersede EPA’s 2016 health advisories for PFOA and PFOS.
  • Provisional HAs were issued in 2009 for PFOA and PFOS, which were superseded in 2016 and again in 2022 by interim lifetime drinking water health advisories of 0.004 parts per trillion (ppt) for PFOA and 0.02 ppt for PFOS. Additional final HAs were issued for hexafluoropropylene oxide (HFPO) dimer acid and its ammonium salt (GenX chemicals) at 10 ppt and perfluorobutane sulfonic acid and its potassium salt (PFBS) at 2,000 ppt. The EPA conducted webinars and outreach based on these HAs to inform the public of the new advisories and options that water utilities and systems could take if PFAS are detected at levels above the HAs.
  • The Bipartisan Infrastructure Law provides $11.7 billion to 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. 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.

Proposed PFAS National Primary Drinking Water Regulation

  • The EPA is proposing a national primary drinking water regulation to establish enforceable maximum contaminant limits (MCLs) for individually for PFOA and PFOS in drinking water at 4.0 ppt. The EPA is also proposing health-based unenforceable maximum contaminant level goals (MCLG) for PFOA and PFOS in public drinking water at zero (0). An MCLG is the maximum level of a contaminant in drinking water where there is no known or anticipated negative effect on an individual’s health, allowing for a margin of safety. The SDWA generally requires EPA to set an MCL “as close as feasible to” the MCLG.
  • Upon examination of health effects information, EPA found that exposure through drinking water to a mixture of PFAS which individually would not likely result in adverse health effects will likely result in adverse health effects when combined (dose additivity). 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 (GenX Chemicals), PFNA, and PFBS because of their “ known and additive toxic effects and occurrence and likely co-occurrence in drinking water.”
  • The EPA is proposing an HI of 1.0 for these four PFAS substances – PFNA, PFHxS, PFBS, and GenX Chemicals – as both the MCLG and enforceable MCL in drinking water individually and in mixtures (POFA and PFOS are not included). The EPA’s Science Advisory Board (SAB) has stated that utilizing an HI is reasonable where health endpoints of the chosen compounds are similar for estimating the potential aggregate health hazards associated with the occurrence of chemical mixtures in environmental media” (EPA-SAB-22-008). The HI provides an indication of overall potential risk of a mixture as well as of the individual. HIs have been used at contaminated Superfund sites (under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Superfund Amendments and Reauthorization Act (SARA)). A Hazard Index considers how toxic each of the four PFAS are and allows a site-specific determination based on the specific drinking water concentrations.
  • The technical definition of a hazard index is the sum of component hazard quotients (HQs), which are calculated by dividing the measured regulated PFAS component contaminant concentration in water (ppt) by the associated Health-Based Water Concentration (HBWC in ppt). The HBWC s are: 9.0 ppt for PFHxS, 10.0 ppt for HFPO-DA; 10.0 ppt for PFNA; and 2000 ppt for PFBS (USEPA, 2023a). The HQs are the ration of potential exposure to a substance and the level at which no health effects are expected. HBWC are levels protective of health effects over a lifetime of exposure, including sensitive populations and life stages.
PFOA (CAS RN CAS 45285-51-6) Zero 4.0 parts per trillion (ng/L)
PFOS (CAS RN 45298-90-6) Zero 4.0 ppt
PFNA (CAS RN 72007-68-2) 1.0 (unitless)
Hazard Index
1.0 (unitless)
Hazard Index
PFHxS (CAS RN 108427-53-8)
PFBS (CAS RN 45187-15-3)
HFPO-DA (GenX Chemicals)
(CAS RN 122499-17-6)


  • Three years after promulgation, EPA is proposing requirements would take effect for all community water systems (CWS) and non-transient, non-community water systems (NTNCWS), such as schools and factories, to monitor for PFOA, PFOS, PFHxS, HFPO-DA and its ammonium salt, PFNA, and PFBS. Many have questioned if these levels are detectable. The lowest concentration of a contaminant that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions is the practical quantitation level or PQL. EPA has identified PQLs at 3.0 for PFBS, 4.0 individually for PFOS, PFOA, PFHxS, and PFNA; and 5.0 for GenX chemicals in determining the proposed MCLs.
  • PWSs must sample entry points to the distribution system using a monitoring regime based on EPA’s Standardized Monitoring Framework (SMF) for Synthetic Organic Compounds (SOCs) where the monitoring frequency for any PWS depends on previous monitoring results. Groundwater systems serving greater than 10,000 people and all surface water systems will be required to monitor quarterly for regulated PFAS. In order to reduce costs for systems, systems would be allowed to use previously collected monitoring data to satisfy the initial monitoring requirements, if the sampling was conducted using EPA Methods 533 or 537.1 as part of UCMR 5 or other state-level or other appropriate monitoring campaigns. Additional monitoring timelines are outlined in the proposal.
  • 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). In keeping with the SMF, EPA is also proposing that based upon the initial monitoring results, 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. The proposed reduced-monitoring trigger level is set at a level that is useful in determining whether the contaminant is present in a sample rather than to determine its specific concentration. This will help to determine the presence of PFAS and monitoring frequency. EPA is seeking comments on adjusting trigger levels to 2.0 ppt for PFOA and PFOS and 0.5 for HI PFAS.
  • Compliance will be determined based on analytical results at each sampling point. For systems monitoring quarterly, compliance will be determined by running annual averages at the sampling point. If a system takes more than one compliance sample during each quarter at a particular location, the system must average all samples taken at that location during that quarter. A system would not be considered in violation of an MCL unless or until it has completed one year of quarterly sampling (except where a sample would be high enough to cause the annual average to exceed an MCL).


  • Stakeholders have also expressed concern about the ability to treat PFAS. Water systems with PFAS levels that exceed the proposed MCLs would need to take action to provide safe and reliable drinking water. Section 1412(b)(4)(E) of the SDWA requires the EPA to list technology, treatment techniques, among other means to meet the MCLs which are referred to as Best Available Technologies or BAT.
  • The EPA is proposing the following technologies as BAT for PFAS removal from drinking water: granular activated carbon (GAC), anion exchange (AIX), and high-pressure membrane technologies (RO and NF). These treatments 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. Additional detail on treatment processes are available here.

Community Right-to-Know

  • The proposed regulation requires public water systems to notify the public if monitoring detects these PFAS at levels that exceed the proposed regulatory standards. A CWS must prepare and deliver to its customers an annual Consumer Confidence Report (CCR) also known as an Annual Water Quality Report, which provides information about their local drinking water quality, as well as information regarding the water system compliance with drinking water regulations. If this rule is finalized as proposed, CWSs would be required to report measured levels of PFOA, PFOS, PFHxS, GenX Chemicals, PFNA, and PFBS, and the Hazard Index for the mixtures of PFHxS, GenX Chemicals, PFNA, and PFBS to the community.

Economic Analysis

  • The PFAS NPDWR is a significant regulatory action which required the EPA to perform an economic analysis of the effect of the rule. If a regulation has an annual effect of more than $100 million or adversely effects an industry sector, it is considered significant. Consequently, the EPA also released the economic analysis as required by the SDWA. AgencyIQ has provided a review of the analysis which may be reviewed here.

Next Steps

  • The proposed National Primary Drinking Water Regulation (NPDWR), if finalized, will provide a nationwide, health-protective maximum contaminant levels and goals for PFOA and PFOS and MCGLs and HIs in drinking water for PFHxS, GenX Chemicals, PFNA, and PFBS. Once finalized, this action would affect public water systems which serve at least 25 individuals and would include any collection, treatment, storage, distribution facilities under the control of a state and tribal agencies responsible for drinking water regulatory development and enforcement.
  • The EPA has posed numerous issues for comment throughout the proposal. Comments will be accepted with reference to Docket No. EPA-HQ-OW-2022-0114, for 60 days from publication. It is expected that the comments will range widely and represent both industry and environmental interest groups in addition to individuals.
  • The EPA plans to release the final version of the PFAS NPDWR most likely in January 2024. However due to the delays in the proposed version, it could be even later.
  • The EPA will be holding two informational webinars about the proposed PFAS NDPWR. The first on March 16, 2023 will be a general overview, and the second on March 29, 2023 will be a technical overview. Both webinars will be held from 2:00 to 3:00 PM ET. The EPA will also be holding a public hearing on May 4, 2023.

To contact the author of this analysis, please email Patricia Iscaro.
To contact the editor of this analysis, please email Scott Stephens.

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