The U.S. Environmental Protection Agency (EPA) has finalized its proposed rule establishing National Primary Drinking Water Regulation (NPDWR) for certain PFAS compounds. The final rule sets Maximum Contaminant Levels (MCL) in drinking water for five PFAS compounds and a Hazard Index MCL for a mixture of four PFAS:

• Perfluorooctanoic acid (PFOA)
• Perfluorooctane sulfonic acid (PFOS)
• Perfluorohexane sulfonic acid (PFHxS)
• Perfluorononanoic acid (PFNA)
• Hexafluoroprophylene oxide dimer acid and its ammonium salt (HFPO-DA, or GenX)
• Mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and perfluorobutane sulfonic acid (PFBS)

The final rule also establishes health-based and non-enforceable Maximum Contaminant Level Goals (MCLG) for the regulated PFAS compounds.

The chart below shows the MCLGs and MCLs for each regulated PFAS under the final rule:

*The Hazard Index is made up of a sum of fractions. Each fraction compares the level of each PFAS measured in the water to the health-based water concentration.

The final rule departs from EPA’s 2023 proposed NPDWR in several ways. Perhaps the most significant departure is that the final rule establishes individual MCLs for PFHxS, HFPO-DA, and PFNA. In the proposed rule, those PFAS were included in a novel Hazard Index MCL, along with PFBS, but EPA did not at that time propose individual MCLs. Instead, EPA identified Health Based Water Concentrations (HBWCs) for the four Hazard Index PFAS for the first time. In addition, the final rule sets the MCL for PFHxS at 10 ppt rather than the 9 ppt EPA identified as the HBWC in the proposed rule. 

Public water systems must complete initial monitoring for these PFAS by 2027, followed by ongoing compliance monitoring. If monitoring shows that drinking water levels exceed the MCLs, public water systems have until 2029 to implement solutions that reduce the levels of PFAS to comply with the regulatory requirements.

The final rule applies to public water systems classified as Community Water Systems, such as public water authorities and private water companies, and Non-Transient Non-Community Water Systems, such as schools, universities, and factories. Transient Non-Community Water Systems, such as gas stations or shopping malls, are not subject to the final rule.

The final rule will become effective 60 days after publication in the Federal Register.