Occurrence and Contaminant Background Support Document for the Final PFAS National Primary Drinking Water Regulation
U.S. Environmental Protection Agency
EPA 815-R-24-013
April, 2024
Executive Summary
On March 3, 2021 (86 FR 12272; USEPA, 2021a), the United States Environmental Protection Agency (EPA) announced its decision to regulate perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) under the Safe Drinking Water Act (SDWA).
Subsequently, on March 14, 2023, the EPA announced its preliminary decision to regulate four additional per- and polyfluoroalkyl substance (PFAS) compounds including Hexafluoropropylene Oxide Dimer Acid (HFPO-DA) and its ammonium salt (also known as “GenX Chemicals”), perfluorobutane sulfonic acid (PFBS), perfluorohexane sulfonic acid (PFHxS), and perfluorononanoic acid (PFNA), and also proposed Maximum Contaminant Level Goals (MCLGs) and National Primary Drinking Water Regulations (NPDWRs) for PFOA and PFOS and an MCLG and NPDWR through a Hazard Index (HI) approach for the four additional PFAS (USEPA, 2023a). The EPA is finalizing determinations to individually regulate PFHxS, PFNA, and HFPO-DA, as well as finalizing a determination to regulate any combination of these three PFAS and PFBS in mixtures. Concurrently, the agency is finalizing MCLGs and NPDWRs for PFOA, PFOS, PFNA, PFHxS, and HFPO-DA and an HI MCLG and NPDWR for mixtures containing two or more of PFNA, PFHxS, HFPO-DA, and PFBS. The final determination to individually regulate PFNA, PFHxS, and HFPO-DA is based on the finding that these three contaminants meet the SDWA criteria for regulating a contaminant: 1) the contaminant may have an adverse effect on the health of persons, 2) the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems (PWSs) with a frequency and at levels of public health concern, and 3) in the sole judgment of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by PWSs. The final determination to regulate mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS under an HI approach is similarly based on these three SDWA criteria when considering these four contaminants in mixtures, particularly their dose additive adverse health effects, substantial likelihood of co-occurrence, and meaningful opportunity to reduce health effects of these mixtures. Regarding the individual regulation of PFBS, the EPA is deferring the final individual regulatory determination for PFBS to further evaluate the three regulatory determination criteria previously described under SDWA and consequently is not promulgating an individual NPDWR or MCLG for PFBS in this action.
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