As expected, and as described in our March 15 client alert, EPA today published in the Federal Register its first-ever National Primary Drinking Water Regulation (NPDWR) for six PFAS substances in drinking water.

In this rule, EPA is proposing to set the health-based Maximum Contaminant Level Goals (MCLG) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) at zero, and is proposing enforceable individual Maximum Contaminant Levels (MCLs) of 4.0 parts per trillion (ppt) for each of those two substances.

As noted in our previous alert, the 4.0 ppt MCLs for PFOA and PFOS, if finalized, would be lower than any mandatory state level. For example, Maine has an interim standard of 20 ppt for the six most commonly found PFAS compounds (alone or in combination), which include PFOA and PFOS, and Massachusetts has an enforceable MCL of 20 ppt for the sum of the so-called PFAS‑6 in drinking water.

Like it did in March 2021 for PFOA and PFOS, EPA also is issuing in this rule a preliminary regulatory determination to regulate perfluorohexane sulfonic acid (PFHxS), hexafluoropropylene oxide dimer acid (HFPO-DA) and its ammonium salt (also known as a GenX chemicals), perfluorononanoic acid (PFNA), and perfluorobutane sulfonic acid (PFBS) as contaminants under the Safe Drinking Water Act. EPA is proposing to use a Hazard Index (HI) of 1.0 as the MCLGs for these four PFAS compounds and any mixture containing one or more of them.

EPA will hold a public hearing on the proposed regulation on May 4, 2023, and the deadline for written comments is May 30, 2023.