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EPA releases maximum contaminant levels for PFAS in drinking water

EPA releases maximum contaminant levels for PFAS in drinking water

Today, the U.S. Environmental Protection Agency (EPA) announced the much-anticipated National Primary Drinking Water Regulation (NPDWR) for six per- and polyfluoroalkyl substances (PFAS) under the Safe Drinking Water Act (SDWA). The regulation, like NPDWR for other chemicals, includes enforceable maximum contaminant levels (MCLs), as shown below. The new federal MCLs are considered the maximum allowable concentrations in parts per trillion (ppt) of select PFAS in public drinking water systems.

The new federal regulations establish a common national threshold for allowable concentrations of PFAS in drinking water, moving away from a patchwork of state rules and regulations. Individual states are still allowed to establish their own drinking water rules and regulations for PFAS, provided they are lower than the federal MCLs. However, if current state-enforceable levels are higher than the federal MCLs, public water systems within that state must abide by the federal levels.

New federal MCLs for select PFAS in public drinking water systems

Understanding MCLs

Individual MCLs are set for five different PFAS, but an approach known as a Hazard Index (HI) applies to three of these individual PFAS and includes a fourth PFAS called PFBS, which doesn’t have a stand-alone MCL. The HI approach treats these PFAS as a mixture using an additive approach (see graphic below). The HI approach is commonly used for Superfund cleanups, but this is the first time it’s being applied to MCLs. Some current MCLs for other compounds 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 of concentrations, but rather the sum of the ratios for each PFAS relative to its Health-Based Water Concentration (HBWC): 10 ppt for GenX; 2,000 ppt for PFBS; 10 ppt for PFNA; and 10 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).

The final rule requires public water systems to monitor for the PFAS listed above and to complete initial monitoring by 2027, followed by ongoing compliance monitoring. Water systems must also provide the public with information on the levels of these PFAS in their drinking water beginning in 2027.

In the final rule, the EPA also set a five-year timeline (by 2029) to implement solutions that reduce these PFAS if monitored drinking water levels exceed the federal MCLs. Beginning in 2029, public water systems that have PFAS in drinking water that violate one or more of the MCLs must take action to reduce these levels and provide notification to the public of the violation.

Impacts for industrial facilities

For industrial facilities, the new PFAS MCLs have the following impacts:

  • The Clean Water Act (CWA) requires states to use water quality criteria to derive effluent limits for National Pollutant Discharge Elimination System (NPDES) permits that regulate point-source discharges to waterbodies. When developing effluent limits for an NPDES permit, discharge limits must protect the uses of the receiving waterbody. If the receiving waterbody is a drinking water source, MCLs will influence the derivation of human health-based water quality criteria and related permit effluent limits.

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

  • 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 facilities that have potentially contributed to PFAS impacts in the public water system supply. This includes certain manufacturing facilities, mining operations, oil and gas operations, and landfills. Any facility that may have used products containing PFAS in their operations may be targeted as potential sources for investigation and cleanup.

  • Although MCLs are enforceable only for public water systems, they are also often used as maximum allowable concentrations in private water systems (i.e., private drinking water wells). Similar to public water systems, if private drinking water wells have PFAS detections over the MCLs, regulators may investigate nearby potential contributors.

Taking action

The new MCLs and required monitoring will likely increase the number of sources tested for PFAS compounds and may identify additional water systems that do not meet these new standards. We believe that this new regulation will be litigated, which may delay its full implementation. However, in light of these new thresholds and considering the ubiquitous nature of PFAS in the environment, 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 authors

Sara Ramsden, PFAS market lead, vice president, and senior environment engineer, has more than 15 years of experience with contaminated site investigation and cleanup for a variety of soil, groundwater, and vapor remediation projects. Her experience includes managing a high-profile investigation of per- and polyfluoroalkyl substances (PFAS) with multiple stakeholders. Sara also managed a large vapor-intrusion sampling and mitigation project located in a residential urban area and led the project team assisting with one of the largest and most complex brownfield redevelopments in Minnesota. Her other areas of focus include Phase I environmental assessments, site investigation planning, response action plan preparation, remedial design, brownfield grant applications, and multi-party coordination.

Katie Wolohan, PFAS market lead and senior environmental engineer, has more than 12 years of environmental consulting experience and assists clients with industrial and municipal water and wastewater treatment, water reuse, and environmental compliance and permitting. She works with clients to navigate water and wastewater treatment challenges and options from conceptual design and bench and pilot testing through full-scale system start-up. Katie has assisted with the evaluation, design, and implementation of several water treatment systems, including a specialized acid-recovery ion-exchange system, an advanced oxidation process system for the removal of 1,4-dioxane from drinking water, and multiple per- and polyfluoroalkyl substance (PFAS) treatment systems.

Casy Fath, former PFAS technical lead and senior 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.

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The SDWA gives individual states the opportunity to set and enforce their own drinking water criteria, provided the criteria are at least as stringent as the EPA’s national criteria. Under the CWA, states use water quality criteria to derive effluent limits for NPDES permits that regulate point source discharges to waterbodies. When developing effluent limits for an NPDES permit, discharge limits must protect the uses of the receiving waterbody. If the receiving waterbody is a drinking water source, MCLs will influence the derivation of human health-based water quality criteria and related permit effluent limits. Read the article.

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Sara Ramsden, PFAS Market Lead, Vice President, and Senior Environmental Engineer
Sara Ramsden
PFAS Market Lead, Vice President, and Senior Environment Engineer


Katie Wolohan, PFAS Market Lead and Senior Environmental Engineer
Katie Wolohan
PFAS Market Lead, Senior Environmental Engineer


Casy Fath, PFAS Technical Lead and Senior Geologist
Casy Fath
PFAS Technical Lead, Senior Geologist

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