On April 10, 2024, the Environmental Protection Agency (EPA) finalized a National Primary Drinking Water Regulation under the Safe Drinking Water Act to establish Maximum Contaminant Levels (MCLs) for five per- and polyfluoroalkyl substances (PFAS):

• Perfluorooctanoic acid (PFOA)
• Perfluorooctane sulfonic acid (PFOS)
• Perfluorononanoic acid (PFNA)
• Hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX)
• Perfluorohexane sulfonic acid (PFHxS)

Additionally, EPA required the use of the Hazard Index to establish site-specific limitations for PFAS mixtures of two or more of PFHxS, GenX, PFNA, and perfluorobutane sulfonate (PFBS).

Although the scientific understanding of PFAS is still evolving, EPA touted the final rule as a measure that “will reduce PFAS exposure for approximately 100 million people, prevent thousands of deaths, and reduce tens of thousands of serious illnesses.”

The statement reflects EPA’s current position regarding the risks prevented by PFAS and its continued push for broader PFAS regulation. Since EPA issued its PFAS Strategic Roadmap in late 2021, the agency has sought to establish a comprehensive, whole-of-agency approach to regulating PFAS, using the agency’s existing regulatory authorities created by the Safe Drinking Water Act, the Clean Water Act, the Clean Air Act, the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or Superfund), and the Toxic Substances Control Act (TSCA), among others. More discussion of the Biden Administration’s PFAS Strategic Roadmap, and how the current approach differs from the approach in the prior Trump administration can be found here.

Final Rule Tweak’s EPA’s Initial Proposal
EPA’s final rule modifies the agency’s initial proposal, which Pillsbury covered here. Most notably, the final rule fixes the MCLs for PFHxS, GENX and PFNA at 10 parts per trillion (ppt). The proposed rule recommended using the EPA’s Hazard Index, which EPA typically uses to evaluate health risks resulting from exposure to mixtures of related chemicals, for these three PFAS compounds.

By contrast, the final rule held firm to the initial proposal of an MCLs of 4 ppt for PFOA and PFOS. These MCLs are an order of magnitude lower than EPA’s existing advisory levels of 70 ppt, which various industry groups have criticized as unduly conservative and based on flawed science. The new standards reflect the agency’s concerns regarding these two PFAS. Specifically, the preamble to the final rule provides that PFOA and PFOS have no level below which is safe for drinking. A zero MCL is not achievable, so EPA set the MCLs at 4 and the MCL goal at zero.

Implications
The final rule stands to raise the stakes for potentially responsible parties at PFAS remediation sites, given how MCLs serve as de facto cleanup levels for regulators and courts alike. Taken in tandem with EPA’s anticipated designation of PFOA and PFOS as hazardous substances under CERCLA, the final rule’s regulatory impact stands to significantly increase the duration and costs of cleanups and may stretch the capabilities of remediation and monitoring technologies employed at active cleanup sites.

The MCLs also raise questions of how regulators will manage active remediation sites in states that have issued groundwater remediation standards or drinking water standards less stringent than 4 ppt for PFOA and PFOS or 10 ppt for PFNA, GenX and PFHxS. Specifically, remediating parties that have delineated groundwater contamination to these less stringent standards may be compelled to recharacterize the extents of PFAS plumes in light of the new MCLs.

Path Forward
In finalizing the rule on April 10, 2024, EPA has met a critical deadline. The agency must finalize rules by mid-May or else risk the possibility of the 2024 election causing a change in administration and control of Congress, leading to repeal of rules under the Congressional Review Act (CRA). However, given the length of the preamble and the fact that EPA received more than 1,600 public comments to the proposed rule, rulemaking challenges are exceedingly likely.

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