Announcement of Preliminary Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List

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The Safe Drinking Water Act (SDWA), as amended in 1996, requires that the U.S. Environmental Protection Agency (EPA) determine whether to regulate at least five unregulated contaminants every five years. The decision to regulate or not to regulate a contaminant is known as a regulatory determination. In most cases, the contaminants chosen for regulatory determination are selected from the most recent Contaminant Candidate List (CCL), which the SDWA requires the EPA to publish every five years. This document presents the preliminary regulatory determinations and supporting rationale for contaminants listed on the EPA's fifth CCL (CCL 5). Since the fourth round of regulatory determinations was published in March 2021, the EPA has made determinations to regulate per- and polyfluoroalkyl substances (PFAS), including individual determinations for three PFAS: perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), hexafluoropropylene oxide dimer acid and its ammonium salt (HFPO-DA, also known as GenX or GenX chemicals); and mixtures including two or more of these three PFAS and perfluorobutanesulfonic acid (PFBS). In April 2024, the agency issued a final National Primary Dri