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EPA proposes maximum contaminant levels for six PFAS in drinking water

EPA proposes maximum contaminant levels for six PFAS in drinking water

The U.S. Environmental Protection Agency (EPA) announced on March 14, 2023, the much-anticipated proposed National Primary Drinking Water Regulation (NPDWR) for six per- and polyfluoroalkyl substances (PFAS). The proposal, like NPDWR for other chemicals, includes non-enforceable Maximum Contaminant Level Goals (MCLGs) and enforceable Maximum Contaminant Levels (MCLs), as shown below.

Non-enforceable MCLGs always accompany MCLs as part of MCL establishment and development. The EPA has proposed MCLGs of zero for PFOA and PFOS. This is a result of the EPA’s determination that PFOA and PFOS are “likely to be carcinogenic in humans.” The established MCLGs for many contaminants are zero. In these instances, as is proposed for PFOA and PFOS, the MCLs are often set at the practical quantitation limit (PQL; i.e., analytical capabilities), which is proposed at 4 parts per trillion (ppt) for each. Note that these proposed MCLs are lower than any values currently enforced at any state level.

The proposal for the four additional PFAS compounds (GenX, PFBS, PFNA, and PFHxS) was something of a surprise, given that they are not included in the EPA’s PFAS Strategic Roadmap, which was first published in October 2021 and updated in November 2022. The EPA is proposing the MCL for these four PFAS to be set as a mixture using an additive approach known as Hazard Index (HI; see graphic below). The HI approach is commonly used for Superfund cleanups but has never been applied to MCLs. Some current MCLs consider the total summed concentrations of multiple contaminants (e.g., polychlorinated biphenyls or PCBs); however, none use the “sum of ratios” additive approach of an HI.

An HI is not the sum concentrations, but rather the sum of the ratios for each PFAS to its Health-Based Water Concentration (HBWC): 10 ppt for GenX; 2,000 ppt for PFBS; 10 ppt for PFNA; and 9 ppt for PFHxS. With this approach, each PFAS can be detected below their HBWC and result in an HI of greater than 1 (see above for an example of HI=1.4).

Once finalized and promulgated, MCLs—which would be enforceable and would supersede state-specific drinking water limits—would require monitoring of public water systems, regardless of the actions or regulations in an individual state. Note that public water systems serving 3,300 people or more will be required to test their water as part of the fifth Unregulated Contaminant Monitoring Rule (UCMR 5) from 2023 to 2025. Eight hundred randomly selected small systems serving up to 3,000 people will also be part of this monitoring rule. This means that most public drinking water systems in the United States will be testing for PFAS, and specifically the six in this proposed rule, over the next two years. Once UCMR 5 testing is complete, and if the proposed MCLs are finalized, water systems that exceed the MCLs will likely be required to address the exceedance (i.e., install treatment systems or otherwise reduce contamination).

For industrial facilities, the proposed MCL has the following potential impacts:

  1. Drinking water standards under the NPDWR can be used as default groundwater remediation standards; these MCLs may drive cleanups at sites being investigated under various state and federal programs.

  2. As outlined in the EPA’s PFAS Strategic Roadmap, if public drinking water systems have detections over the MCLs, the EPA plans to address sources and thus will investigate potential contributors upstream of the public water facility.

The addition of four PFAS compounds signals that the EPA believes they are common in production or the environment. Many of these compounds are “replacement” chemicals for PFOA or PFOS and can be found in aqueous film-forming foam (AFFF) and other chemical products, impacting many industries, including mining, oil and gas, power, landfills, and manufacturing.

The proposed MCLs and the work associated with UCMR 5 can reasonably be expected to increase the number of sources tested for these six PFAS compounds. This proposed rule continues to signal the federal government’s actions to address PFAS. With the ubiquitous nature of PFAS in the environment and these proposed thresholds, facilities that have not yet taken action to evaluate their PFAS exposure are encouraged to determine their risk profile.  

Barr has been assisting public and industrial facilities with PFAS in their permits, conducting sampling and analysis with the goal of source reduction, and assisting in water treatment design for PFAS for over two decades. Contact us to learn more about our PFAS work and what Barr can do for you.


  • GenX: hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals)

  • PFAS: per- and polyfluoroalkyl substances

  • PFBS: perfluorobutane sulfonic acid

  • PFHxS: perfluorohexane sulfonic acid

  • PFNA: perfluorononanoic acid

  • PFOA: perfluorooctanoic acid

  • PFOS: perfluorooctane sulfonic acid

About the author

Casy Fath, former PFAS technical lead and geologist at Barr, has a decade of experience with contaminated site investigation and cleanup for a variety of soil and groundwater remediation projects. His experience includes leading investigations at sites with historical releases of per- and polyfluoroalkyl substances (PFAS), chlorinated solvents, metals, and other contaminants of concern. He has expertise with all phases of investigation and cleanup under Resource Conservation and Recovery Act (RCRA) Corrective Action, Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and similar programs in several states.

Related projects

Assessment of PFAS use

A manufacturing client hired Barr to provide a desktop assessment of PFAS use in its operations and the potential impacts. A class of emerging contaminants, PFAS has seen increased regulation throughout the U.S. The purpose of the assessment was to provide a snapshot of the facility’s current operations to inform the client on potential risks associated with PFAS.

Per- and polyfluoroalkyl substances (PFAS)

Multi-site PFAS remedial investigation and remediation

PFAS have been detected in public water supplies and private wells at or near active and former manufacturing facilities owned by Saint-Gobain. At these sites in the eastern United States, a group of potentially responsible parties is working with local, state, and federal regulatory authorities. Barr is part of a collaborative consulting team conducting remedial investigations and feasibility studies.

Well drilling observation for contaminated site investigation.

PFAS-impacted drinking water response and treatment plant design

Aqueous-film-forming foam (AFFF), containing PFAS, has long been used for fire-suppression and firefighter training at the Bemidji airport, as it has at many airports across the country. The PFAS have migrated into groundwater and are being captured by the city’s drinking-water-supply wells. In 2017, the Minnesota Department of Health updated the health-based advisory values (HBVs) for two types of PFAS. The city asked Barr to identify immediate and short- and long-term response actions to keep their water supply in compliance with the new HBVs.

Water treatment vessels being installed for City of Bemidji


Casy Fath
PFAS Technical Lead and Geologist
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