Maximum Contaminant Level (MCL) for PFAS

A Maximum Contaminant Level (MCL) is the highest concentration of a contaminant allowed in public drinking water under the U.S. Safe Drinking Water Act (SDWA). In April 2024, EPA finalized MCLs for six PFAS: 4 ppt for PFOA, 4 ppt for PFOS, 10 ppt for PFHxS, 10 ppt for PFNA, 10 ppt for HFPO-DA (GenX), and a Hazard Index of 1 for mixtures of PFHxS, PFNA, HFPO-DA, and PFBS. Public water systems must comply with these standards by 2029.

EPA National Primary Drinking Water Regulation for PFAS (89 FR 32532, April 10, 2024); SDWA §1412.

MCLs for PFAS directly affect water utilities but create cascading liability upstream. Manufacturers whose products or operations release PFAS into water sources may face cost recovery claims from utilities, CERCLA enforcement, or state environmental actions. The 4 ppt limits for PFOA and PFOS are near the practical quantitation limit of current analytical methods, meaning any detectable PFAS release can cause a violation.

A public water system detects combined PFAS levels exceeding the Hazard Index threshold of 1. The system must install treatment technology and may pursue litigation against upstream industrial sources. The treatment cost for a mid-sized system can exceed $10 million.