By Edward (Ned) Witte and Heather Davis, Earth & Water Law

The U.S. Environmental Protection Agency (EPA) has again shifted its regulatory stance on PFAS, steering the storm in a new and uncertain direction. On September 11, 2025, EPA asked the U.S. Court of Appeals for the D.C. Circuit, where the American Water Works Association et al. v. EPA matter has been in a prolonged abeyance, to vacate four of the six national drinking water limits (maximum contaminant levels, or MCLs) the Biden EPA adopted just last year under the Safe Drinking Water Act (SDWA).

If granted, the motion would “undo” the federal SDWA standards for:

• HFPO-DA (GenX)
• PFNA
• PFHxS
• The Hazard Index approach for PFAS mixtures (including PFBS)

 
Two standards – for PFOA and PFOS – remain on course. For these two PFAS compounds, EPA is not backing down on SDWA regulation but has signaled it will try to extend compliance deadlines by two years into 2031.

Why the Shift in Course?

The Trump EPA has asserted that the Biden EPA short-circuited the SDWA process. EPA’s rulemaking standards require a distinct “regulatory determination” (with its own notice and comment) before proposing and finalizing national primary drinking water regulations. For PFOA and PFOS, EPA’s motion states that the proper sequence was followed. For the other four PFAS, however, EPA now asserts the agency improperly combined the steps, effectively denying the public a fair chance to weigh in.

Rather than continuing to defend the rule as the “harmless error” defense might allow, in its most recent motion, EPA told the court it must restart the process from scratch. Industry and water system parties to the AWWA case agree, but environmental groups, including NRDC, strongly oppose the proposed “undo,” calling it an “end-run” around the SDWA’s anti-backsliding protections.

What Is Vacatur and Why Now?

Vacatur is the name for the legal process by which a court eliminates a promulgated rule’s binding effect. To pursue this resolution, EPA’s motion leans on the D.C. Circuit’s 1993 Allied-Signal v. Nuclear Regulatory Commission test, which considers:

1. Seriousness of the alleged error. EPA says the error is fundamental, requiring an entirely new regulatory sequence – a restart for rulemaking for the four PFAS standards.
2. Potentially disruptive consequences. Because the first monitoring deadlines aren’t until 2027, EPA contends vacatur now avoids unnecessary compliance costs for limits that may soon change.

 
This is not the first time EPA rulemaking has been subject to vacatur. In North Carolina v. EPA (2008), the D.C. Circuit vacated the Clean Air Interstate Rule (CAIR) after finding EPA failed to follow statutory commands. EPA itself conceded that it had to go back and properly re-promulgate the program, which it later did through the Cross-State Air Pollution Rule (CSAPR). The current PFAS motion seeks a court determination to follow a similar arc of agency self-correction.

According to Earth & Water Law Partner Susan Bodine, who is familiar with the AWWA case, if the court vacates a rule, the legal effect is as if it never existed. While the SDWA prohibits revisions to MCLs unless they maintain or provide for greater protection of the health of persons (anti-backsliding), if the MCL never existed, there can be no backsliding. 

Status of the Litigation

The PFAS MCLs have been challenged by both drinking water utilities and by industry. Litigation has resumed, and after additional briefs are filed, the court will hear arguments challenging EPA’s PFOA and PFOS limits as infeasible and based on feasibility and an improper cost–benefit analysis.  The environmental groups will defend the current MCLs for all six PFAS regulated by the Biden EPA. Under the schedule agreed to by the parties (but not yet adopted by the court), the briefing in the case will not be completed until December 2025. As a result, the uncertainty is likely to continue until late spring 2026. 

The Eye of the Hurricane for SDWA Regulation

For regulated parties, especially public water systems, this development is not calm seas but the “eye of the hurricane”—a pause that invites careful planning, not complacency, before regulatory turbulence returns.

• Here to stay (for now): federal SDWA PFOA and PFOS MCLs remain in effect, with a compliance deadline of 2029, although EPA is evaluating ways to extend that deadline to 2031.
• In effect for now but potentially going away (pending the court’s decision): MCLs for GenX, PFNA, PFHxS, and the Hazard Index standard.
• States keep moving: Independent state PFAS standards remain untouched and can be stricter than federal rules.

 
What to Do Now?

1. Stay the course on PFOA/PFOS. Until the court acts and until EPA takes final action on the compliance deadlines, affected parties should keep building monitoring, treatment, and funding plans—calibrated to state standards and the current 2029 compliance horizon.a
2. Plan for the PFAS MCLs. Be ready for two outcomes: (a) vacatur and a re-do rulemaking; or (b) the court denies EPA’s motion and current standards stand.
3. Map state footprints. State PFAS rules may drive compliance regardless of what happens at the federal level. 
4. Design flexibility into projects. Capital projects should include alternatives to address either outcome.
5. Communicate clearly. All PFAS MCL obligations remain in effect for now. If and when that changes, act and communicate accordingly.

 
Conclusion

EPA’s latest move confirms that PFAS regulation remains a fickle storm system—shifting course, unpredictable, and disruptive – continued uncertainty. Federal action may pause, but state action presses ahead. Stakeholders navigating this environment should treat the present moment as an opportunity to reassess, realign, and prepare for the next phase of PFAS regulation.