As previously reported, in the context of litigation by utilities challenging Maximum Contaminant Levels (“MCLs”) for PFAS in drinking water, the United States Environmental Protection Agency (“EPA”) filed a Motion to Vacate the MCLs for PFHxS, PFNA, HFPO‑DA, and the hazard‑index mixture (“Index PFAS”) that were promulgated under the Biden Administration.   The EPA Motion was filed in September.  Following an abeyance, briefing has resumed. 

On December 3, the EPA filed a combined submission that included: (1) a reply supporting EPA’s September 11 motion for partial vacatur, and (2) an opposition to the Respondent-Intervenors’ request to file a revised, enlarged merits brief. The Respondent-Intervenors are the Buxmont Coalition for Safe Water, et al., and the Natural Resources Defense Council (collectively, “Intervenors”), both environmental organizations that seek to defend the MCLs in the face of EPA’s decision to abandon them.

In its Reply, EPA asks the Court of Appeal’s motions panel to decide first a threshold statutory question under the Safe Drinking Water Act (“SDWA”): whether the SDWA requires a two-step process consisting of a separate, sequential notice-and-comment on the regulatory determination (that is, the agency’s decision to promulgate a regulation) followed by a notice-and-comment on the proposed rule (that is, the proposed regulation itself).

Under EPA’s reading of 42 U.S.C. § 300g-1(b)(1)(E), the agency must finalize a “determination to regulate” through a notice and comment process before proposing the rule, and the statute gives EPA a 24‑month window to propose the rule that begins on the date of that final determination.  EPA argues that the phrase “may publish [the] proposed regulation concurrent with the determination to regulate” means the earliest lawful proposal date is the same day the final determination is published, assuming that notice and comment has been completed on the determination to regulate; it is permissive because EPA is not required to propose the rule that day, but also limiting because EPA may not issue a proposed regulation until the notice and comment process is completed on its determination to regulate. In other words, “concurrent” sets the earliest permissible date as the date the determination is final.  It does not create an option to propose a rule during the preliminary determination process. 

Brief reader clarification: EPA also reads each statutory reference to a “determination to regulate” to mean the final determination, not an interim step.  EPA argues that the consistent usage is what makes “concurrent” operate as the earliest lawful proposal date and preserves the separate notice-and-comment rounds Congress required.

EPA also states it is waiving any harmless-error defense and argues the error was not harmless because the second, statutorily mandated notice-and-comment opportunity never occurred. EPA maintains that setting aside this portion of the Rule is warranted given the seriousness of the procedural defect and the lack of disruptive consequences, noting that initial monitoring deadlines begin in 2027 and that EPA continues to defend the PFOA/PFOS portions of the rule.

EPA further urges denial of Intervenors’ request to “double” their word allotment, arguing that Intervenors may refile a revised brief of the same length if the Court refers the vacatur motion to the merits panel.

On December 3, Petitioners-the American Water Works Association and the Association of Metropolitan Water Agencies (collectively, “Petitioners”), representing drinking water utilities, professionals, and public water drinking systems, filed a separate opposition to Intervenors’ motion to file a revised and enlarged merits brief.

Petitioners’ Position

Petitioners concur with EPA in contending that the motions panel can and should decide EPA’s partial vacatur request without referring it to the merits panel.  The petitioners emphasize the Court’s equitable authority to grant voluntary vacatur in analogous circumstances and note EPA’s May 14, 2025 public announcement and Unified Agenda entry signaling reconsideration of Index PFAS.

According to Petitioners, deciding EPA’s motion now would streamline merits briefing and avoid unnecessary duplication. They likewise oppose Intervenors’ expansion request, noting EPA’s existing merits brief remains on the docket and asserting that additional pages are unnecessary because Intervenors have already defended the Index PFAS provisions in motion practice and the merits materials are already before the Court.

Intervenors’ Reply

On December 17, 2025, Intervenors filed their reply supporting leave to file a revised and expanded brief. They argue that EPA’s mid-litigation change in position warrants a revised brief with an expanded word limit to avoid prejudice and ensure complete and coherent merits presentation. Intervenors contend they should be permitted to address Petitioners’ record-based challenges to the Index PFAS provisions in EPA’s place and to replace cross-references that may become inoperative if EPA omits those arguments from its final brief.

Intervenors further argue that EPA’s plan to reconsider the Index PFAS provisions neither moots the disputes nor justifies denying expanded briefing because the provisions remain in effect. They note that an agency’s abandonment of a defense does not eliminate a live controversy. Finally, Intervenors urge the Court to refer EPA’s vacatur motion to the merits panel, asserting that a motions-panel decision would not meaningfully narrow the merits and could risk bifurcating complex issues across two panels.

We will continue monitoring this case and provide updates.  The case is American Water Works Association, et al v. EPA, D.C. Cir., No. 24-1188 (consolidated with Nos. 24-1191, 24-1192).