USEPA Opens Public Comment on Long-Awaited PFAS MCL

On March 14, 2023, the United States Environmental Protection Agency (USEPA) proposed the first national drinking water standard for ‘forever chemicals.’ The agency opened up a public comment process on its proposed regulation to set Federal Maximum Contaminant Levels (MCLs) for six per- and polyfluoroalkyl substances (PFAS): perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, also known as GenX), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS).

The proposed National Primary Drinking Water Regulation (NPDWR) would set enforceable regulatory levels for drinking water sources at 4 parts per trillion (ppt) for PFOA and 4 ppt for PFOS. In addition, USEPA proposes to regulate PFNA, GenX, PFHxS, and PFBS as a mixture using a Hazard Index (HI) approach. USEPA is also proposing health-based, non-enforceable Maximum Contaminant Level Goals (MCLGs) for these six PFAS. An MCLG is defined by USEPA as 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 PFOA and PFOS MCLs are based on the lowest concentration at which USEPA determined that PFOA and PFOS can reliably be measured in finished drinking water. Based on the multi-laboratory data acquired for the Unregulated Contaminant Monitoring Rule (UCMR) 5 rule, USEPA has defined the practical quantitation limit (PQL) for PFOA and PFOS to be equal to the UCMR 5 minimum reporting level (MRL) of 4.0 ppt.

Consistent with the statutory definition of MCLG, USEPA establishes MCLGs of zero for carcinogens classified as Carcinogenic to Humans or Likely to be Carcinogenic to Humans. USEPA has determined that both PFOA and PFOS are Likely to be Carcinogenic to Humans based on sufficient evidence of carcinogenicity in humans and animals; and, therefore, have taken a health-protective approach in establishing the MCLG.

Since PFHxS, HFPO-DA, PFNA, and PFBS have been found to co-occur in mixtures in drinking water, including with other PFAS, USEPA is proposing the HI approach rather than establishing individual MCLs or MCLGs. The HI approach is used to account for additive non-cancer effects. A HI is the sum of hazard quotients (HQs) from multiple substances where HQs are the ratio of potential exposure to a substance and the level at which no health effects are expected. USEPA is proposing the MCL for mixtures of PFHxS, HFPO-DA, PFNA, and PFBS as equal to the MCLG: as proposed, the HI must be equal to or less than 1.0.

To determine the HQ for these four PFAS, the amount of each PFAS detected in drinking water would be compared to its associated Health-Based Water Concentration (HBWC) proposed in the rule, which is defined by USEPA as the level at which no health effects are expected for that PFAS. The HBWCs that USEPA uses to calculate the HI are proposed to be 9.0 ppt for PFHxS; 10.0 ppt for HFPO-DA; 10.0 ppt for PFNA; and 2000.0 ppt for PFBS. The HQs would then be summed to calculate the HI using the following formula:

USEPA has preliminarily determined that regulating these six PFAS is anticipated to reduce the overall public health risk from all other PFAS that co-occur and are co-removed. Their regulation is anticipated to provide public health protection at the majority of known sites with PFAS- impacted drinking water.

Upcoming Webinars and Public Hearing

USEPA will be holding two informational webinars about the proposed PFAS NDPWR on March 16, 2023, and March 29, 2023. In addition, USEPA will hold a public hearing on May 4th, 2023, to receive public comment and will present the proposed requirements of the draft NPDWR. More information about submitting comments and registering to participate in the webinar or hearing can be found here. The public comment period will open following the proposed rule publishing in the Federal Register and will run for 60 days.


USEPA anticipates finalizing the rule by the end of 2023. Several states have drafted, proposed, or finalized health-based regulatory and/or guidance values for PFAS in various environmental media. The promulgation of these MCLs, along with their basis, will certainly impact rulemaking at the state level.

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EHS Support has a reputation for developing innovative approaches for client advocacy and offers a wide range of services to support PFAS challenges in the changing regulatory landscape. Reach out to Dana McCue or Ceil Mancini today and explore how the EHS Support Team can help you stay in compliance with rapidly changing PFAS regulations.

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