NORTHERN CALIFORNIA RECORD

U.S. Environmental Protection Agency (USEPA) announced a proposed rulemaking that would establish legally enforceable federal primary Maximum Contaminant Levels (“MCLs”) for six per- and polyfluoroalkyl substances (PFAS) in drinking water. In addition to creating enforceable drinking water standards, these MCLs, if adopted, could be used as a benchmark for establishing groundwater remediation goals or be used in other regulatory or litigation contexts. USEPA expects to finalize the rulemaking by the end of this calendar year.

The rulemaking, also referred to as USEPA’s National Primary Drinking Water Regulation (NPDWR), proposes to establish primary MCLs for the following six different PFAS compounds:

• Perfluorooctanoic acid (PFOA)
• Perfluorooctane sulfonic acid (PFOS)
• Perfluorononanoic acid (PFNA)
• Hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals)
• Perfluorohexane sulfonic acid (PFHxS)
• Perfluorobutane sulfonic acid (PFBS).

Under the proposed rule, PFOA and PFOS would be treated as individual contaminants, both with primary MCLs set at 4.0 parts per trillion (ppt or ng/L). For PFHxS, PFNA, PFBS, and HFPO-DA (commonly referred to as GenX Chemicals), USEPA proposes the use of a “Hazard Index” MCL where the maximum limit is based on any mixture containing one or more of the four compounds. Compliance with the Hazard Index MCL is calculated as the sum of the ratios of the measured concentration compared to the allowable concentration. To determine the Hazard Index, water systems will need to monitor and compare the amount of each PFAS compound in drinking water to its associated Health-Based Water Concentration (HBWC), which is the level at which no health effects are expected for that compound. Water systems will need to then add the comparison values for each compound contained within the mixture. A value greater than 1.0 (the index is unit less) would be considered an exceedance of the proposed Hazard Index MCL. USEPA intends to provide water systems with a web-based form that will automatically calculate the Hazard Index to assist with determining compliance.

USEPA’s proposed rule will require public water systems to monitor for the six PFAS compounds, notify the public of the concentrations detected, and reduce concentrations in drinking water if they exceed the proposed primary MCLs. While there are existing methods available to monitor for the constituents (e.g., method 1633 for PFOA and PFOS), treatment technologies to remove the constituents (e.g., granular activated carbon (GAC), anion exchange resins (AIX), reverse osmosis (RO), and nanofiltration) remain expensive, a significant concern to regulated entities.

Importantly, if a state does not have PFAS-related drinking water standards in-line with USEPA’s final rule, the state will, at a minimum, be required to establish new regulations to conform to USEPA’s standards. As we previously reported, California’s Office of Environmental Health Hazard Assessment (OEHHA) is currently working on public health goals (PHGs) for PFAS chemicals in drinking water. The State Water Resources Control Board plans to utilize the PHGs in the process of establishing MCLs, which now must consider the federal baseline, if established.

Original source can be found here.