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Spring 2023

The EPA’s proposed maximum contaminant levels for PFAS could affect public drinking water systems and industrial facilities alike.

EPA proposes maximum contaminant levels for six PFAS

April 18, 2023

This spring, the U.S. EPA proposed new federal limits for PFAS in drinking water. If finalized, these limits would become the first nationwide enforceable levels for PFAS in drinking water and could lead to investigations of potential upstream sources.

The proposed National Primary Drinking Water Regulation (NPDWR) addresses six PFAS and includes maximum contaminant levels (MCLs) that are lower than any state threshold—4 parts per trillion for PFOA and PFOS. The EPA also proposes that four other PFAS (GenX, PFBS, PFNA, and PFHxS) be treated as a mixture, with the MCL set using an additive approach known as a unitless Hazard Index (HI) of 1.0 (see graphic) rather than a concentration. This is commonly used for Superfund cleanups but is novel in application to MCLs.

An HI is not the sum concentrations, but rather the sum of the ratios for each PFAS to its Health-Based Water Concentration (HBWC): 10 ppt for GenX; 2,000 ppt for PFBS; 10 ppt for PFNA; and 9 ppt for PFHxS. With this approach, each PFAS can be detected below their HBWC and result in an HI of greater than 1 (see above for an example of HI=1.4).

The MCLs would supersede state-specific drinking water limits and require monitoring of public drinking water systems, which bear ultimate responsibility for meeting applicable MCLs. If public drinking water systems have detections above the MCLs, investigations of potential upstream source contributors may follow.

Industrial facilities and other dischargers may start seeing PFAS limits in their NPDES permits, and the MCLs could be used as default groundwater remediation standards, driving cleanups or further investigation.

For facilities that have not yet taken action to evaluate their PFAS exposure, it’s an important time to determine your risk profile. To learn more about this EPA announcement and how these new limits could affect your facility, contact us or follow the conversation on our Insights blog.

About the author

Casy Fath, PFAS technical lead and geologist at Barr, has a decade of experience with contaminated site investigation and cleanup for a variety of soil and groundwater remediation projects. His experience includes leading investigations at sites with historical releases of per- and polyfluoroalkyl substances (PFAS), chlorinated solvents, metals, and other contaminants of concern.