As discussed in a previous post, EPA recently issued a final rule establishing drinking water standards, known as maximum contaminant levels (MCLs), for six per- and polyfluoroalkyl substances (PFAS).  The final rule became effective on June 25, 2024.  The rule, among other things, provides public water systems three years to conduct initial PFAS monitoring and five years to make any necessary capital improvements to comply with the new MCLs. 

While the new MCLs principally apply to public water systems, they also will have a less obvious—and more immediate—effect on groundwater remediation standards.  At the federal level, MCLs will be used as default groundwater remediation standards at Superfund sites for PFAS which have been designated as hazardous substances under CERCLA.  EPA also uses MCLs to inform its Regional Screening Levels (RSLs), which are conservative standards used to screen chemicals at Superfund sites.  Thus, PFAS detections at or above the RSLs will generally need to be evaluated at Superfund sites, and the burden will be on the remediator to show why EPA should accept groundwater remediation standards that are less stringent than the new MCLs.

The federal MCLs for PFAS also will have an effect on some state-level groundwater remediation standards.  For example, Pennsylvania has regulations providing that federal MCLs automatically become default groundwater remediation standards for Act 2 sites.  In New Jersey, existing groundwater remediation standards will remain in effect until the New Jersey Department of Environmental Protection (NJDEP) promulgates new state MCLs which meet or exceed the new federal MCLs, which it has two years to do.  At that point, the new state MCLs will become Ground Water Quality Criteria.   

In many states, however, federal and state MCLs do not automatically become groundwater remediation standards (all states have two years to align their MCLs with federal MCLs).  While some of these states have previously promulgated groundwater remediation standards for PFAS or are in the process of developing such standards, other states do not have PFAS groundwater remediation standards and do not appear likely to develop them soon. 

In short, the new federal MCLs now serve as potential groundwater remediation standards at all federal superfund sites and some state remediation sites.  Other states are expected to have groundwater remediation standards for PFAS soon, while others appear content without such standards.  It therefore remains important to stay apprised of the PFAS regulations which apply to each property, facility, and remediation site in which you are interested.

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