EPA Proposes National Drinking Water Standards for 6 PFAS

May 2, 2023

By: Martha Maier

On March 29th, EPA proposed the much anticipated national drinking water standards setting maximum contamination levels (MCLs) for six PFAS, building on its initial proposal to regulate PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanoic sulfonate). EPA expects to finalize the rule by the end of 2023.

These are the proposed MCLs


Compound Proposed MCL (enforceable levels)
PFOA 4.0 ppt (also expressed as ng/L)
PFOS 4.0 ppt
PFNA 1 (unitless) 

Hazard Index Approach 

HFPO-DA (aka “GenX Chemicals”)

The MCLs for PFOA and PFOS are “set at the lowest feasible quantitation level”. In an effort to capture the additive effects of PFNA, PFHxS, PFBS, and the GenX chemicals, the MCLs incorporate a Hazard Index approach. This tool is currently used in Superfund cases but not previously for MCLs. The concentration of each of the four PFAS (in ppt) is inserted into the equation below; the limit is 1. The EPA provided a fact sheet explaining the process.

Initial monitoring frequency would depend on the size of the facility (quarterly for groundwater systems serving greater than 10,000 as well as all surface water systems; twice within a 12-month period, at least 90 days apart, for smaller systems). If initial concentrations are below “trigger levels” (1/3 of the MCL levels), the facility would be eligible for reduced monitoring requirements.

The 60-day public comment period ends on May 30, 2023. EPA will be holding a public hearing on May 4.

According to the agency’s news release, “If finalized, the proposed regulation will require public water systems to monitor for these chemicals. It will also require systems to notify the public and reduce PFAS contamination if levels exceed the proposed regulatory standards. EPA anticipates that if fully implemented, the rule will, over time, prevent thousands of deaths and reduce tens of thousands of serious PFAS-attributable illnesses. This action establishes nationwide protection from PFAS pollution for all people, including environmental justice communities.”

The announcement comes after the White House Office of Management and Budget completed its review of EPA’s proposed PFAS drinking water standards for PFOS and PFOA on March 3, which was the statutory deadline for EPA to issue the proposed regulations. (EPA missed its self-imposed deadline of December 2022 to release the proposal.)

Updated Toxicity Assessment

EPA also released an updated toxicity assessment for PFOS alongside the proposed rulemaking. The assessment now identifies PFOS as a likely carcinogen – a change from the previous draft finding that there was “suggestive evidence of carcinogenic potential” and responds to recommendations that the Science Advisory Board made as part of the rulemaking process. (EPA previously characterized PFOA as a likely carcinogen.) Other documentation supporting the proposed regulation can be found here.

Martha Maier
PFAS Program Leader
Martha Maier is the PFAS Program Leader and PFAS subject matter expert for Montrose Environmental Group, Inc. She is the former president and owner of Vista Analytical Laboratory in El Dorado Hills, CA, and has over 35 years of experience in environmental testing, primarily involving high-resolution mass spectrometry for the analysis of chemicals such as dioxins, PCBs, and chlorinated pesticides. Martha led the PFAS program at Vista from the development of their in-house LC-MS/MS method for serum in 2007 to becoming one of the most respected analytical PFAS service providers in North America. She earned her BS in chemistry and philosophy at the University of Wisconsin-Madison. She is a co-chair of the ITRC PFAS Sampling and Analysis Subcommittee.

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