EPA finalized national primary drinking water regulations for six per- and polyfluoroalkyl substances (PFAS): perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA), and perfluorobutane sulfonic acid (PFBS); the Agency also finalized a Hazard Index of 1 as the maximum contaminant level goal and maximum contaminant level for any mixture containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS.