On March 14, 2023, the United States Environmental Protection Agency (EPA) announced its proposed National Primary Drinking Water Regulation (NPDWR), which would establish legally enforceable levels, called Maximum Contaminant Levels (MCLs), for six PFAS in drinking water. These PFAS chemicals are:
EPA described the proposed MCL of 4 ppt for PFOA and PFOS to be the "lowest feasible level" for which PFOA and PFOS can reliability be measured and removed from drinking water. EPA has also proposed using a "Hazard Index" score as an MCL for a combination of four PFAS compounds - PFHxS, GenX chemicals, PFNA and PFBS. This is the first time that a hazard index approach is being proposed as a federal drinking water MCL standard. In short, a Hazard Index considers how toxic each of the four PFAS are and then uses a site-specific determination based on the specific drinking water concentrations (i.e., the calculation gets complicated).
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