PFAS Observer
On August 18, 2026, a unanimous panel of the U.S. Court of Appeals for the D.C. Circuit upheld EPA’s designation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund). In Chamber of Commerce of the United States v. EPA, the court rejected challenges to EPA’s interpretation of CERCLA Section 102(a), the adequacy of its notice and comment process, its analysis of costs and benefits, and its decision to proceed despite uncertainty about future response actions and costs.
This decision is already being invoked in a separate D.C. Circuit challenge to EPA’s 2024 PFAS drinking water rule promulgated under the Safe Drinking Water Act (SDWA). Six days after the CERCLA decision, respondent intervenors cited it as supplemental authority in American Water Works Association v. EPA, No. 24-1188, ahead of oral argument scheduled for September 18, 2026. The Chamber of Commerce decision may assist the respondent intervenors on certain notice and comment and economic analysis arguments, but its significance should not be overstated. The principal challenges to the standards for the four PFAS subject to EPA’s Hazard Index-based maximum contaminant level (MCL) turn on requirements specific to the SDWA, and EPA itself now agrees that those provisions were promulgated through an unlawful process.
The SDWA Rule and the Pending Challenge
EPA’s 2024 PFAS National Primary Drinking Water Regulation established maximum contaminant level goals (MCLGs, non-enforceable public health target) of zero and MCLs (legally enforceable drinking water standard) of 4 parts per trillion for PFOA and PFOS. The rule also established individual MCLs of 10 parts per trillion for perfluorohexanesulfonic acid (PFHxS), perfluorononanoic acid (PFNA) and hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX). For mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and perfluorobutanesulfonic acid (PFBS), the rule established a Hazard Index MCL of 1. PFBS has no individual MCL and is regulated only through the mixture standard. The rule refers to those four substances collectively as the “Hazard Index PFAS.” The Hazard Index is calculated by dividing the measured concentration of each detected Hazard Index PFAS by its health-based water concentration and summing the results; the total may not exceed 1.
Petitioners raise four principal challenges to the rule. First, they assert that EPA failed to follow the proper process for making regulatory determinations and promulgating associated standards for the Hazard Index PFAS. Second, they argue the occurrence data—information from state monitoring programs showing whether and at what concentrations the substances occur in public water systems—was insufficient to support regulatory determinations for PFNA, HFPO-DA and mixtures of Hazard Index PFAS. Third, petitioners contend that the Hazard Index does not qualify as an enforceable MCL under SDWA. Finally, they challenge EPA’s evaluation of costs, benefits and feasibility.
EPA now takes divergent positions on the two groups of standards. For PFOA and PFOS, EPA followed the SDWA’s procedural sequence: notice and comment on a preliminary regulatory determination, followed by a final determination that precedes or accompanies proposed drinking water standards, and then a separate comment period on those standards. EPA continues to defend those provisions. For the Hazard Index PFAS, however, EPA proposed the preliminary regulatory determinations and the standards concurrently in 2023 and finalized both in 2024. EPA now agrees with petitioners that this concurrent approach violated SDWA’s requirement that the agency provide notice and comment on preliminary regulatory determinations before or concurrent with the proposal of drinking water standards. The respondent intervenors disagree and contend that SDWA permitted the concurrent approach.
Based on this concession, EPA moved for partial vacatur of the Hazard Index PFAS provisions and has separately proposed to rescind them through rulemaking. The D.C. Circuit denied EPA’s request for summary vacatur and subsequently declined to sever and hold the Hazard Index PFAS issues in abeyance pending the rescission. As a result, the court will address all challenged provisions at oral argument, even though EPA has withdrawn its defense of the Hazard Index PFAS standards and the respondent intervenors alone continue to defend those provisions.
The Respondent Intervenors Cite Chamber of Commerce on Notice and Costs
The respondent intervenors’ August 24 supplemental authority letter identifies two aspects of Chamber of Commerce that they contend support EPA’s drinking water rule: (1) the court’s treatment of notice and comment, and (2) its review of EPA’s economic analysis. Neither aspect directly resolves the SDWA-specific issues at the heart of this case.
- Notice and Comment. On notice, the respondent intervenors rely on the court’s holding that the Administrative Procedure Act (APA) did not require another opportunity to comment on data and calculations that “simply expand[ed] on and confirm[ed]” information provided with the proposed rule. In the CERCLA rulemaking, EPA’s proposed Economic Assessment quantified direct notification costs, discussed indirect costs qualitatively, and requested comment on whether and how to evaluate additional costs and benefits. In response to comments requesting a more detailed analysis, EPA’s final Regulatory Impact Analysis increased the upper end of its estimate of the annual administrative costs of reporting PFOA and PFOS releases under CERCLA from $370,000 to $1.63 million and quantified certain downstream costs that the proposed analysis had discussed only qualitatively. The court held that the final analysis was a logical outgrowth of the proposal because it addressed issues EPA had presented for comment and did not use a new methodology to reach a materially new or different conclusion.
The respondent intervenors argue that this holding undercuts the petitioners’ claim of prejudice because the occurrence data added to the final drinking water rule confirmed EPA’s proposed conclusions. Petitioners, however, contend that the SDWA itself—not just the APA—required a second comment period, whether or not the added data independently triggered further notice under the APA. Petitioners also cite the expanded final dataset, including data from nine states that had not been available at proposal, to argue that they lost an opportunity to address the data and its implications for EPA’s occurrence and cost estimates. EPA separately argues that its process prevented comment on the proposed standards with the benefit of the final determinations, including its decision to regulate PFBS only as part of mixtures.
- Economic Analysis. The respondent intervenors also cite the CERCLA court’s rejection of challenges to EPA’s cost and benefit analysis. The court stated that EPA may estimate costs within a “broad zone of reasonable estimation” and held that the CERCLA petitioners had not met their “high” burden because EPA explained its approach and considered and rejected their preferred analysis. The respondent intervenors argue that the SDWA petitioners similarly have not met their burden. The petitioners contend that EPA underestimated compliance costs, relied on benefits it did not quantify and that lack adequate record support, and improperly analyzed several standards together. EPA continues to defend the economic analysis for PFOA and PFOS, while the respondent intervenors defend the analysis for the entire rule. They argue that EPA used inputs specific to each contaminant and reasonably considered some standards together because PFAS may occur together and treatment technologies may remove several PFAS at once, making separate analyses prone to double counting or omitting costs and benefits.
That analogy has limits. In Chamber of Commerce, the court assumed without deciding that CERCLA required EPA to consider costs and benefits. The SDWA, by contrast, expressly requires EPA to publish a health risk reduction and cost analysis when proposing an MCL, to set each MCL as close to its MCLG as feasible, and, if the benefits of an MCL set at the feasible level would not justify the costs, to adjust the MCL to a level at which the benefits do justify the costs. The respondent intervenors therefore cite Chamber of Commerce only for the proposition that courts should defer to EPA’s economic judgments, not as resolving whether EPA satisfied these distinct SDWA requirements. Their letter also does not contend that the decision resolves the petitioners’ challenges to the occurrence determinations or the Hazard Index, which turn on the SDWA’s text and the drinking water rulemaking record.
Practical Implications
While these questions remain before the court, all provisions of the 2024 drinking water rule remain in effect. EPA’s proposed rescission of the Hazard Index PFAS provisions is not final, nor is its proposal to allow qualifying public water systems to request an extension of the PFOA and PFOS compliance deadline to 2031. Public water systems should therefore continue planning under the existing rule, which requires them to complete initial monitoring by April 26, 2027, and comply with the MCLs by April 26, 2029.
The rule is also relevant to parties involved in real estate transactions, project development and industrial operations. Finalized MCLs may affect remediation targets, treatment system design and the timeline for site closure. Parties conducting due diligence on acquisitions, financings or development projects should evaluate potential PFAS liabilities—including future compliance costs and the risk that pending litigation could alter the regulatory baseline—as part of their environmental risk allocation.
An MCL does not automatically become the cleanup level in every CERCLA matter. Because EPA set the PFOA and PFOS maximum contaminant level goals at zero, however, their MCLs may serve as applicable or relevant and appropriate requirements (ARARs) that CERCLA remedies must attain where the groundwater or surface water is a current or potential drinking-water source. Whether this standard applies will depend on site-specific circumstances. Due diligence, project planning and contractual allocation of PFAS risk should therefore account for the current rule, the pending litigation and EPA’s related rulemakings.
Pillsbury’s Environmental and Natural Resources practice advises clients on PFAS regulation, drinking water requirements, permitting, site investigation and remediation, CERCLA liability, litigation, and the identification and allocation of environmental risks in commercial agreements and transactions. We will continue to monitor the litigation and EPA’s related rulemakings.