On March 13, the Environmental Protection Agency (EPA) took the long-anticipated step of proposing maximum contaminant level goals (MCLGs), as well as individual maximum contaminant levels (MCLs), for six PFAS compounds under the Safe Drinking Water Act. PFAS are a large family of synthetic chemicals that have been in use since the 1940s. Many PFAS have unique physical and chemical properties that make them highly stable and resistant to degradation in the environment, which is why they are sometimes referred to as “forever chemicals.”

An MCLG is the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, allowing an adequate margin of safety. An MCL is the maximum level allowed of a contaminant or a group of contaminants (i.e., mixture of contaminants) in water that is delivered to any user of a public water system (PWS). The SDWA generally requires EPA to set an MCL “as close as feasible to” the MCLG.

For PFOA and PFOS, EPA is proposing to set the MCLGs at zero and the MCLs at 4.0 ng/L (which is also the lowest level that these compounds can be quantified using currently available analytical methods). For PFHxS, PFNA, PFBS, and Gen X, EPA is proposing to set both the MCLGs and MCLs at a Hazard Index (HI) of 1.0. According to EPA, an HI is a commonly used risk management approach for mixtures of chemicals in which a ratio called a hazard quotient (HQ) is calculated for each chemical by dividing an exposure metric (here, the measured level of each of the four PFAS in drinking water) by a health reference value for each chemical. The individual ratios (HQs) are then summed across the mixture to yield the HI. If the resulting HI is greater than one (1.0), then the exposure metric is greater than the health metric, and potential risk is indicated.

Water systems with PFAS levels that exceed the proposed MCLs (once finalized) would need to take action to provide safe and reliable drinking water (e.g., installing treatment or switching to an uncontaminated water source). Activated carbon, anion exchange (AIX), and high-pressure membrane technologies have all been demonstrated to remove PFAS from drinking water systems, but often at significant capital cost and ongoing operational expense. Given the anticipated impact of the proposed MCLs on public water systems, EPA is proposing to delay the compliance date for three years, following publication of the final rule.

The proposed MCLGs and MCLs are lower in certain respects and higher in others when compared to EPA’s 2022 health advisories for the same chemicals, signaling the potential for a healthy debate of the underlying science. Further, a number of states have adopted their own state-based MCLs, which now will need to be reconsidered if they are less stringent than EPA’s proposed levels.

A 60-day public comment period will begin after EPA’s proposal is published in the Federal Register. In addition, EPA has scheduled a virtual public hearing on the proposal for May 4. EPA is scheduled to finalize the new MCLGs and MCLs by September 3, 2024.

Separately, EPA has proposed to designate PFOA and PFOS as hazardous substances under CERCLA. The comment period on that proposal closed last fall, and EPA is scheduled to finalize the designations in August 2023.