• The US EPA set MCLs for five PFAS between 4 and 10 ppt and an MCL of 1 (unitless) for any mixture of four PFAS, which will lead to new monitoring, reporting, and treatment requirements for public water systems.
• Public water systems have a five-year timeline to comply with the new PFAS MCLs.
• The new PFAS MCLs will affect contaminated site cleanups.
• In a separate proposal, the EPA also has opened the door to further regulation by proposing to require that the largest POTWs sample influent and effluent for PFAS.
• These updates affect public water suppliers, wastewater treatment operators, manufacturers, farmers, among many others.

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The US EPA has not adopted a new maximum contaminant level, or MCL, since 1996. And on April 10, 2024, it adopted MCLs for five PFAS:

PFAS COMPOUND	MCL (in parts per trillion, or ppt)
PFOA	4 ppt
PFOS	4 ppt
PFNA	10 ppt
PFHxS	10 ppt
HFPO-DA (the GenX chemical)	10 ppt

While the final rule did not adopt an MCL for PFBS, it maintained a controversial hazard index approach of 1 (unitless) as the MCL for any mixture containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS.

An MCL is the level below which a public water system may deliver water. The Safe Drinking Water Act requires that public water suppliers sample for and, when present, treat any contaminants exceeding an MCL. The public water system also must publicly disclose the exceedance. The rule, the EPA concludes, also will require public water systems “to make any necessary capital improvements and comply with the PFAS MCLs.”

But MCLs are significant under other laws, too. Regulators, for example, may set cleanup levels at the MCL for contaminated sites. And a new MCL could reopen cleanups for certain contaminated sites. The Department of Defense raised this concern because it has been using a 70 ppt cleanup level for PFAS at military bases—a level significantly higher than the EPA’s PFAS MCLs.

Public water systems will have until 2027 to complete their initial monitoring and, if PFAS is detected, the systems have until 2029 to implement a plan for treatment. Though the rule provides an expanded compliance timeline, many states have expressed concerns over whether there is enough funding available to assure compliance.

The EPA’s rule is one of the many recent changes in an evolving PFAS regulatory landscape. As we previously reported, the EPA has proposed a rule to add nine PFAS to the Resource Conservation and Recovery Act’s list of “hazardous constituents,” which would require considering PFAS during certain hazardous waste investigations and cleanups. The EPA also proposed requiring that certain publicly owned treatment works, or POTWs, take grab samples of industrial user effluent, domestic wastewater influent, POTW influent, and POTW effluent. That information, the EPA proposes, would help identify and prioritize industrial point source categories for PFAS requiring further study and regulation.

California also continues to pursue more stringent PFAS regulation. On April 5, 2024, California’s Office of Environmental Health Hazard Assessment, or OEHHA, adopted public health goals for PFOA and PFOS in drinking water at 0.007 ppt and 1.0 ppt, respectively. While public health goals are not regulatory, the State Water Resources Control Board considers these goals—along with economic and technical feasibility—in setting drinking water standards. For PFAS, those standards must be equal to or lower than the EPA’s MCLs, even though this results in goals set at levels below current reliable detection limits. The goals also reflect the State’s current view of potential health risks and forecast the range of potential future enforceable standards.

These recent PFAS updates further reflect the complex and developing regulatory landscape. These updates affect public water suppliers, wastewater treatment operators, manufacturers, farmers, among many others.