The Environmental Protection Agency (EPA) has filed a motion in the lawsuit that challenges its rule that set limits on per- and polyfluoroalkyl substances (PFAS) in drinking water, but the EPA’s motions admits that parts of the PFAS rulemaking process were unlawful, which invalidates parts of that rule.

On Sept. 11, 2025, the EPA filed the motion with the U.S. Court of Appeals for the D.C. Circuit in the case Association of Metropolitan Water Agencies (AMWA) and the American Water Works Association (AWWA) v. EPA and Lee M. Zeldin (formerly Michael S. Regan), which challenged the EPA’s “PFAS National Primary Drinking Water Regulation” the was announced on April 10, 2024, and posted on the Federal Register on April 26, 2024

The rule that was announced on April 10, 2024 set drinking water standards for PFAS substances of from 4.0 parts per trillion to 10 parts per trillion including for perfluorooctanoic acid (PFOA); perfluorooctane sulfonate (PFOS); perfluorononanoic acid (PFNA); perfluorohexane sulfonic acid (PFHxS); and hexafluoropropylene oxide dimer acid (HFPO-DA, also known as “GenX Chemicals”).

In addition, on April 19, 2024, the EPA issued a second PFAS regulation designating perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as the “Superfund.”

The EPA says while it “initially attempted to defend the (April 10, 2024) rule against forceful legal challenges,” but the agency says it has found parts of the PFAS rulemaking process were unlawful, which makes parts of the rule invalid.

In the EPA’s Sept. 11, 2025, court filing the agency says under the Safe Drinking Water Act (SDWA), EPA is required to “publish and seek comment on a preliminary regulatory determination for a contaminant before it may propose a national primary drinking water regulation that set goals and standards for that contaminant.” However, “after reviewing the statute pursuant to a publicly announced reconsideration process, EPA agrees” that “parts of the rulemaking process were unlawful and parts of the rule are thus invalid.”

As a result, EPA requested the court implement “partial vacatur” (setting aside) of the initial PFAS rule that regulates the substances PENA, PFHxS, and HFPO-DA—as well as mixtures of those substances along with a fourth substance, perfluorbutane sulfonic acid (PFBS)—through a “hazard index”.

EPA further requested the “maximum containment level goals” and the “maximum containment levels (standards)” set for those PFAS substances be vacated, because when it came to the hazard index, EPA says it “departed from the statutory scheme by proposing and finalizing a regulatory determination and regulation simultaneously and in tandem.

“Upon review, EPA acknowledges that the prior reading of” the SDWA “as authorizing such simultaneous promulgation and defense of the rule on this basis before the court, were in error.

“EPA further acknowledges that this error denied the public and regulated community the opportunity to adequately comment on and participate in the rulemaking process for the (hazard) index, PFAS goals and standards with the benefit of the finalized regulatory determination,” says the EPA’s motion.

However, while the EPA motion seeks to vacate parts of the PFAS rule, EPA Administrator Lee Zeldin said in a written statement issued Sept. 17, 2025, the agency will defend the rule governing PFOA and PFOS. Furthermore, the agency is taking steps regarding regulatory efforts to address the cleanup of PFOA and PFOS substances while avoiding imposing liability for those contaminates on those who did not produce the substances.

“When it comes to PFOA and PFOS contamination, holding polluters accountable while providing certainty for passive receivers that did not manufacture or generate those chemicals continues to be an ongoing challenge,” Zeldin said.

Furthermore, Zeldin says the EPA’s motion filed on Sept. 17, 2025, is part of ongoing litigation related to the designation of PFOA and PFOS as CERCLA hazardous substances, and that the agency “is currently retaining the (PFOA and PFOS) rule that became effective on July 8, 2024.”

Currently, CERCLA provides EPA with the authority to designate additional hazardous substances beyond those substances listed under other statutes referenced in CERCLA, and in the Clean Water Act; the Clean Air Act; the Resource Conservation and Recovery Act; and the Toxic Substances Control Act.

“CERCLA imposes broad, retroactive, and potentially costly strict liability on those who released hazardous substances to the environment,” but such “liability can attach to entities that did not manufacture or generate the substance but received” those substances “in feedstocks, products, or waste,” said Zeldin, who added “such entities are sometimes referred to as ‘passive receivers’.”

Subsequently, EPA says it intends to develop a CERCLA “framework rule” that is to consider the costs to manufacturers, passive receivers, consumers, and the economy at large, and provide a uniform approach to guide future hazardous substance designations, including how the EPA will consider the costs of proposed designations.