On April 8,  U.S. Environmental Protection Agency (EPA) Administrator Michael S. Regan signed a final rule regulating six per- and polyfluoroalkyl substances (PFAS) under the Safe Drinking Water Act (SDWA). The final rule, which will become effective 60 days after publication in the Federal Register, sets individual maximum contaminant levels (MCLs) for PFOA and PFOS at 4.0 nanograms per liter (ng/L), and for PFHxS, PFNA, and HFPO-DA at 10 ng/L. In addition to these individual MCLs, the rule establishes a hazard index (HI) of one (unitless) as the MCL for any mixture containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS. Under the rule, regulated public water systems (PWS) must conduct and report their initial monitoring within three years after publication, and make any necessary capital improvements to comply with the MCLs within five years after publication.

The key compliance aspects of the new rule are summarized below:

• EPA establishes Methods 533 and 537.1 version 2.0 as the approved analytical methods for compliance monitoring under the rule. According to EPA, either of these two methods is acceptable for compliance.

• PWS have three years to complete initial monitoring (by 2027), followed by ongoing compliance monitoring. PWS must also report their monitoring results to the public beginning in 2027. For the initial monitoring, PWS may choose to use the results of recent, previously conducted monitoring.

• For purposes of determining compliance with each MCL, a PWS must calculate the running annual average (RAA) of results, which could allow some results to exceed the MCL for single measurements if the overall annual average is below the MCL. When calculating the RAA, zero must be used for results less than the practical quantification level (PQL).

• If a system takes more than one compliance sample during each quarter at a particular monitoring location, the system must average all samples taken in the quarter at that location to determine the quarterly average and this will be used in calculating the RAAs. Conversely, if a system does not collect the required compliance samples for a quarter, the RAA will be based on only those quarters where samples were collected during the past four quarters.

• A system will generally not be considered in violation of an MCL until it has completed one year of quarterly sampling (i.e., a system on an annual or triennial monitoring schedule with an exceedance of the MCL is not in violation until it completes one year of quarterly sampling with the sample exceeding the MCL used as the sample result for the first quarter of the RAA). However, regardless of the result of subsequent monitoring, if a quarterly sample result will cause the RAA to exceed an MCL at any sampling point (e.g., the first quarter sample result is greater than twice the MCL and the second quarter sample result is also greater than twice the MCL) or if an annual or triennial sample result causes the RAA to exceed an MCL at any sampling point (i.e., the analytical result is greater than four times the MCL), then the system is out of compliance with the MCL immediately.

• The final rule does not allow composite samples. The final rule also does not allow monitoring waivers (either from EPA or a primacy state).

• The rule includes “right-to-know” requirements for PWS consumer confidence reports (CCR) and public notifications (PN) that include specific EPA-prescribed health effects language for any PFAS that are detected (or show violations) through monitoring.

• Because the MCL compliance date is deferred for five years, systems will not be required to provide PN of MCL violations until 2029; however, primacy states may choose to prescribe an earlier date.

• Through the final rule, EPA is codifying granular activated carbon (GAC), anion exchange (AIX) resins, reverse osmosis (RO), and nanofiltration (NF) as “best available technologies” for PFAS treatment.

• The final rule does not dictate any specific destruction or disposal practices for spent media containing PFAS, but instead simply notes that management options exist, as documented in EPA’s recently updated “Interim Guidance on the Destruction and Disposal of Perfluoroalkyl and Polyfluoroalkyl Substances and Materials Containing Perfluoroalkyl and Polyfluoroalkyl Substances.”

• Over the next two years, states will have to adopt requirements no less stringent than EPA’s rule and then apply for approval (aka primacy) to oversee implementation.

• More than 66,000 PWS will be subject to the new PFAS MCLs. EPA estimates that between 6-10% of these systems may have to take action to reduce PFAS to meet the new standards.

• Under the SDWA appeal procedures, opponents of the final MCLs must file for judicial review in the D.C. Circuit within 45 days after publication. An appeal would not automatically stay the rule, but challengers could seek a stay from the court.  To obtain one, they would have to show, among other things, that they are likely to prevail on the merits (i.e., that EPA committed some procedural or substantive error in the rulemaking) and that they will suffer irreparable injury if they are forced to comply with the rule pending the appeal. This is a very difficult standard to meet and will be even more difficult in light of the deferred compliance dates.