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PFAS: EPA proposes enforceable drinking water regulations for 6 PFAS; more stringent than Wisconsin

March 14, 2023
9 minute read

PFAS: EPA proposes enforceable drinking water regulations for 6 PFAS; more stringent than Wisconsin

March 14, 2023
9 minute read

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On March 14, 2023, the United States Environmental Projection Agency (EPA) announced its long-awaited regulation of per- and polyfluoroalkyl substances (PFAS) in drinking water by proposing enforceable maximum contaminant levels (MCLs) for six PFAS compounds. The proposed regulation for PFAS under the umbrella of EPA’s Safe Drinking Water Act National Primary Drinking Water Regulations is expected to be finalized by the end of 2023. In certain states, such as Wisconsin, where drinking water regulations exist for PFAS, the more stringent value applies or, when final, will apply to public drinking water suppliers.


EPA proposes to set the enforceable drinking water standard for the two most widely studied PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), at 4 parts per trillion (ppt).

The federal standard contrasts with current Wisconsin drinking water standards for PFOA and PFOS set at 70 ppt. The less restrictive Wisconsin values were set in February 2022 at the whim of now departed Wisconsin Natural Resources Board members. The now resigned officials forced a modification to a less stringent standard against the recommendation of Wisconsin state officials.


This proposed federal regulation applies to drinking water from public drinking water suppliers, not groundwater from private potable wells. Two thirds of Wisconsinites receive their drinking water from groundwater via private potable wells. The Safe Drinking Water Act does not regulate private wells and this proposed rule does not set any requirements or standards for private well owners.

On December 14, 2022, Wisconsin DNR received approval of a scope statement to renew its effort to regulate PFOA and PFOS in groundwater, adding perfluorobutane sulfonic acid and its potassium salt (PFBS) and hexafluoropropylene oxide (HFPO-DA) dimer acid and its ammonium salt (“GenX” chemicals) to the collection of PFAS compounds to be regulated by the Wisconsin DNR. According to the Wisconsin DNR scope statement proposing to regulate PFAS in groundwater: “Without numerical health-based standards, groundwater regulatory programs will not protect the public health of Wisconsin residents.”

Wisconsin DNR has 30 months, or until June 2025 to complete its administrative rulemaking to set Wis. Admin. Code ch. NR 140 enforceable standards and preventative action limits or the regulation will expire.


EPA proposes to set specific numeric values for PFOA and PFOS, but to regulate four additional PFAS utilizing a Hazard Index formula. The four PFAS to be addressed using the Hazard Index are PFBS, GenX chemicals, PFNA and PFBS. According to the EPA Fact Sheet released with the proposed regulation:

The Hazard Index is a tool used to evaluate health risks of simultaneous exposure to mixtures of related chemicals. To prevent health risks from mixtures of certain PFAS in drinking water, EPA is proposing that water systems use this Hazard Index approach to regulate PFHxS, GenX Chemicals, PFNA, and PFBS. To determine the Hazard Index for these four PFAS, water systems would monitor and compare the amount of each PFAS in drinking water to its associated Health- Based Water Concentration (HBWC), which is the level at which no health effects are expected for that PFAS. Water systems would add the comparison values for each PFAS contained within the mixture. If the value is greater than 1.0, it would be an exceedance of the proposed Hazard Index MCL for these four PFAS. For ease of use, EPA intends to provide water systems with a web-based form that will automatically calculate the Hazard Index.

The Hazard Index appears to be a novel approach to addressing the other PFAS compounds as no current federal MCL utilizes a Hazard Index. It is possible that most industry comments on the proposed rule will be focused on the decision to utilize a Hazard Index and the costs to municipalities to treat its drinking water to essentially “non-detect” quantifications of certain PFAS.


The EPA first proposed setting MCLs for certain PFAS in its October 2021 Strategic Roadmap. This proposal to regulate 6 PFAS under the Safe Drinking Water Act framework is parallel to the effort to regulate PFOA and PFOS as “hazardous substances” under the federal Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), also known as the “Superfund” environmental clean-up law. The September 2022 proposed rule to designate PFOA and PFOS as hazardous substances is expected to be finalized in September 2023. The public comment period for this rule ended on November 7, 2023.

There is open litigation at the Wisconsin Appeals level where industry groups are calling for the Wisconsin DNR to first establish a rule to list its chemicals to be considered “hazardous substances” prior to regulating substances under the Wisconsin Spills Law (Wis. Stat. ch. 292). The Waukesha Circuit Court decision was stayed in summer 2022 pending appeal from the Wisconsin Department of Justice.

The Safe Drinking Water Act proposed regulation states the goal for PFOA and PFOS in drinking water is zero. This recommendation is consistent with federal health advisory levels below detectable limits that no amount of PFOA and PFOS is safe to drink.


  • Additional PFAS. Today’s action represents federal PFAS regulations beyond the well-studied PFOA and PFOS. The next logical PFAS substances for consideration as CERCLA hazardous substances are PFBS, GenX chemicals, PFNA and PFBS.
  • Remedial action sites. What impact these proposed drinking water regulations have on environmental contamination cleanup sites remains to be seen. Delineating any chemical substance in groundwater to a level of 4 ppt is extremely difficult. Proposing a cleanup standard that incorporates the Hazard Index concept is not easy. Further, whether the standards proposed by EPA today become points of reference in setting remedial actions, including as CERCLA Applicable or Relevant and Appropriate Requirements, or ARARs, is also unclear.
  • Necessary actions. Current Wisconsin law specifies for substances that do not have an applicable Wis. Admin. Code ch. NR 140 enforcement standard, the Wisconsin DNR has broad authority to take or direct entities to “conduct any necessary actions, such as developing site-specific environmental standards in cooperation with the department of health services, to protect public health, safety, or welfare or prevent a significant damaging effect on groundwater or surface water quality for present or future consumptive or non-consumptive uses.” Wis. Admin. Code § NR 722.09(2)(b)2.
  • More stringent standards guiding regulatory decisions. For remedial action sites with completed drinking water exposure pathways (people drinking PFAS contaminated groundwater using their potable well), the more stringent federal level will likely apply. The more stringent levels which will drive decisions such as horizontal delineation of groundwater plumes, accepted areas of groundwater monitoring, adequacy of proposed mitigation remedies, and emergency water supply replacement and temporary provision of bottled water.

For more information on this topic, or to learn how Godfrey & Kahn can help, contact a member of our Environmental Strategies Practice Group.

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