On March 19, 2026, a three-judge panel of the U.S. Court of Appeals for the D.C. Circuit denied EPA’s request to sever and stay challenges to drinking water standards, known as MCLs, for four PFAS (PFHxS, PFNA, HFPO‑DA, and mixtures of any of these three plus PFBS). These four PFAS are referred to as “Index PFAS” because they were regulated under a Hazard Index MCL.
In American Water Works Association (AWWA), et al. v. EPA, industry groups and water utilities challenged EPA’s rule establishing MCLs for six PFAS, which was promulgated in 2024. As previously reported, the Trump EPA decided to defend the MCLs for PFOA and PFOS, but to abandon support for the Biden EPA’s regulatory determinations and regulations for the Index PFAS, which EPA asserts are invalid due to procedural errors.
EPA asserted to the Court that its request to sever and stay the challenge to the Index PFAS would save judicial resources and time since the agency is actively working to rescind the Index PFAS MCLs from a regulatory perspective. On Feb. 24, EPA sent to the White House Office of Management & Budget (OMB) a proposed rule to rescind the MCLs for the Index PFAS, a critical step in the regulatory process. However, after considering the arguments from the water utilities and environmentalists that opposed the motion, the Court ruled against EPA. The water utilities argued that a stay would mean further delays and since the Index PFAS MCLs would remain in place during the stay, the Water Associations’ members would be prejudiced by the delay. The environmental groups argued that litigation of the Index PFAS MCLs is intertwined and cannot be separated from the issues related to the PFOA and PFOS MCLs which the EPA continues to defend.
The Court’s denial of EPA’s request to vacate is yet another setback for the agency as it seeks to undo the Index PFAS MCLs. It is unclear if EPA’s regulatory action will be completed before the Court decides the MCL challenges on the merits. Once OMB’s review of the proposed rule to rescind the MCLs for the Index PFAS is complete, EPA will still need to propose the rule and open it to public comment.
Stay tuned for further updates.