We previously reported that the U.S. Chamber of Commerce and two other trade groups are challenging EPA’s designation of PFOA and PFOS as hazardous substances under the federal Comprehensive Environmental Response, Compensation, and Liability Act (“CERCLA”). The D.C. Circuit heard oral argument on January 20, 2026. As discussed below, the litigants filed a series of Rule 28(j) letters (allowing a party to cite new legal authorities discovered after briefing closes and the others to respond) to sharpen the central dispute: whether EPA’s reliance on its Regulatory Impact Analysis (“RIA”) and its cost figures were “critical information” to the agency decision on the final rule that should have been disclosed at the proposed rule stage for public comment.

Petitioners Point to a Fifth Circuit Vacatur

On February 19, 2026, petitioners flagged Airlines for America v. U.S. Department of Transportation (“Airlines II”), an en banc Fifth Circuit decision. In that case, the court unanimously vacated a Department of Transportation (“DOT”) rule after the DOT conceded it failed to seek comment on a study “critical to the Rule’s issuance.” Petitioners drew a parallel, arguing that EPA similarly introduced a new “totality of the circumstances” balancing test and a 278‑page RIA in the final rule, neither of which appeared in EPA’s proposal. Petitioners highlighted preamble language showing EPA “weighed the quantitative and qualitative costs and benefits evaluated in the RIA” and treated certain cleanup costs as an “advantage” of designation, claiming those undisclosed materials drove EPA’s final decision.

EPA and Intervenors Push Back

Both EPA and the environmental and community respondent‑intervenors filed responses on February 24, 2026. EPA first objected that petitioners improperly used their 28(j) letter to introduce additional record citations rather than simply flagging a new legal authority. On the merits, EPA rejected petitioners’ analogy to Airlines II, stressing that Airlines II turned on DOT’s concession of error and agreement to vacatur (circumstances absent here). The agency maintained that the RIA’s indirect‑cost estimates were expressly labeled “illustrative,” rested on uncertain assumptions, and were not critical to EPA’s designation decision. Instead, EPA argued that the CERCLA designation rests on a largely qualitative evaluation of dangers posed by PFOA and PFOS, together with CERCLA’s remedial purpose.

The respondent‑intervenors echoed EPA’s position, emphasizing that CERCLA’s goal is to promote cleanup and protect public health—not to maximize economic benefits. They also argued that EPA’s proposal already presented both qualitative and direct‑cost analyses sufficient to satisfy any notice obligation.

What to Watch

The case now rests with Judges Millett, Katsas, and Rao. If the panel concludes EPA’s qualitative analysis stands on its own and the RIA’s numbers were immaterial, the final rule will likely survive. If, on the other hand, the Court views EPA’s adoption of a new methodology and cost analysis in the final rule (without prior notice) as “critical information” that should have been disclosed under D.C. Circuit precedent, petitioners’ requested remand with vacatur becomes more likely. In the meantime, the CERCLA designation remains effective. Companies with potential PFAS liabilities should continue to prepare for information requests, evaluate reporting obligations, and monitor the docket.

The case is Chamber of Com. v. EPA, D.C. Cir., No. 24‑1193.