EPA is proposing to rescind its regulatory determinations to regulate 4 PFAS--perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid and its ammonium salt (HFPO-DA, commonly known as GenX chemicals), and mixtures of these three PFAS plus perfluorobutane sulfonic acid (PFBS)--under the SDWA. The EPA is also proposing to rescind all associated regulatory provisions currently codified in the EPA's 2024 PFAS NPDWR exclusive to these PFAS that were promulgated pursuant to the regulatory determinations that the EPA is now proposing to rescind, including the final MCLs that would have required monitoring, and where necessary, treatment by PWSs. This proposed action is necessary to correct the unlawful procedure under which these regulations were promulgated. Under the EPA's prior interpretation, the EPA proposed and finalized regulatory determinations and regulations for these PFAS simultaneously and in tandem. Under the best reading of the statute, the EPA is not authorized to take such actions simultaneously and therefore, the Agency proposes to rescind those regulatory determinations, MCLGs and associated portions of the 2024 PFAS NPDWR. The EPA is seeking public comment on this proposal. Comments must be received on or before July 20, 2026. POC is Nicole Shao, tele: 202-564-6779; email: PFASNPDWR@epa.gov. (Federal Register 20 May 2026 [Proposed Rule] Pages 29413-29425)