EPA has announced its first ever National Primary Drinking Water Regulation (NPDWR) proposal for six PFAS substances in drinking water. Importantly, EPA is proposing legally enforceable national standards, called Maximum Contaminant Levels (MCLs), for two of the most commonly found PFAS substances – perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) – at the lowest level labs can reliably measure, 4.0 parts per trillion (ppt).

This is a marked, though expected, departure from the interim Health Advisory Levels for PFOA (0.004 ppt) and PFOS (0.02 ppt) that EPA announced early last summer, both of which were below the level of detection (determining whether a substance is present) and quantitation (the ability to determine reliably how much of a substance is present).

The 4.0 ppt MCLs for PFOA and PFOS, if finalized, would be lower than any mandatory state level, including in Maine, which has an interim standard of 20 ppt for the six most commonly found PFAS (alone or in combination). And despite proposing MCLs for PFOA and PFOS at detectable levels, EPA also is proposing health-based, non-enforceable Maximum Contaminant Level Goals (MCLGs) for these two substances at zero.

As part of its rulemaking, EPA also is proposing enforceable water concentration limits using a Hazard Index formula for mixtures of four additional PFAS: perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). Under the proposed rule, water utilities would be required to monitor PFAS, notify customers if the levels are above the proposed limits, and reduce levels exceeding those proposed limits.

The pre-publication version of the rule is available here. EPA will accept public comment on the proposed rule until 60 days after the date of publication of the proposed rule in the Federal Register. EPA will also hold a public hearing on May 4, 2023 to receive verbal comments on the rule proposal. The rule is expected to be final by the end of 2023 or in early 2024.