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EPA Issues Final National Drinking Water Standard for Six PFAS Compounds

On April 10, 2024, after receiving nearly 122,000 comments on the proposed rule, the United States Environmental Protection Agency (“EPA”) announced its final National Primary Drinking Water Regulation (“NPDWR”) for six perfluoroalkyl and polyfluoroalkyl (“PFAS”) compounds. EPA’s announcement comes in advance of final publication of the rule, which is expected to be posted in the Federal Register in the coming days.

What Does the Final Rule Do?

EPA’s final rule establishes Maximum Contaminant Levels (“MCLs”) for six PFAS compounds: PFOA, PFOS, PFNA, PFHxS, HFPO-DA (GenX chemicals), and PFBS. MCLs are legally enforceable standards and represent the maximum amount of each PFAS compound (either alone or in a mixture) that can be present in drinking water provided by a public water system. The final rule further establishes Maximum Contaminant Level Goals (“MCLGs”), which are health-based goals that represent the level of PFAS that may be present in drinking water where there is no known negative health impact. MCLGs are advisory only and therefore not legally enforceable.

What are the Final MCL and MCLGs for the Six Identified PFAS Compounds?

The final rule establishes MCLs and MCLGs using a combination of individual limits and hazard index levels, which is a risk management tool that uses a ratio to establish the potential negative health impact of a chemical mixture. EPA has established individual limits for five compounds: PFOA, PFOS, PFNA, PFHxS, and HFPO-DA (GenX). The Hazard Index level is used to set the MCL for chemical mixtures containing two or more of the following four PFAS compounds: PFNA, PFHxS, HFPO-DA (GenX), and PFBS.

The final MCLs and MCLGs are as follows:

PFAS Compound Maximum Contaminant Level (MCL) [Enforceable] Maximum Contaminant Level Goal (MCLG) [Not Enforceable]


4 parts per trillion (ppt)

0 ppt


4 ppt

0 ppt


10 ppt

10 ppt


10 ppt

10 ppt

HFPO-DA (GenX Chemicals)

10 ppt

10 ppt

Mixture of two or more of the following: PFNA, PFHxS, HFPO-DA (GenX), PFBS

Hazard Index = 1

Hazard Index = 1

When Do the Final MCLs and MCLGs Take Effect?

In addition to setting the MCLs and MCLGs for these six PFAS compounds, the final rule imposes several affirmative obligations on public drinking water systems. First, within three years of promulgation (by 2027) public drinking water systems must complete initial monitoring for these six PFAS compounds and make the results publicly available as part of their Annual Water Quality reports. Second, if PFAS is detected in quantities exceeding the MCLs, public water systems must notify the public and will have 5 years (until 2029) to implement solutions to address any PFAS MCL exceedances.

What is the Expected Impact of the Final Rule?

EPA estimates that more than 66,000 public drinking water systems nationwide will be required to comply with the new rule and approximately 6-10% of those systems will need to take action to reduce PFAS in their public drinking water to meet the new MCLs. EPA in turn expects that the rule will reduce or eliminate PFAS exposure for approximately 100 million people who obtain their drinking water from a public drinking water system and will cost approximately $1.5 billion per year. EPA has further announced new funding opportunities through the Bipartisan Infrastructure Law and Drinking Water State Revolving Funds.

How Will the Rule Impact States with Existing Drinking Water Standards?

Over the past several years many states have established their own PFAS drinking water standards in the absence of enforceable federal rules or guidance. Many, if not all, of these state standards are now less restrictive than the new federal MCLs. With the promulgation of EPA’s new rule, states must now ensure that their regulations are at least as stringent as the new MCLs. States will have two years to adopt new rules and apply for federal approval to oversee implementation of the new drinking water standards. As a practical matter, public drinking water systems that have implemented treatment technology to meet these now less restrictive state drinking water standards may be required to revisit or replace their existing treatment technology.

Finally, EPA will be holding three webinars for communities, water systems, and drinking water professionals on the final PFAS NPDWR on April 16, 23, and 30, 2024. More information and registration for the webinar can be found here.

If you have questions or would like additional information, please contact Mathew J. Todaro, Maye C. Emlein, or any other member of the Environment & Land Use Group. More information on the proposed rule, published in March 2023, can be found here.