pfasmcldrinking-watercerclaregulatory-update

PFAS Drinking Water Standards - Where Things Stand in 2026

The Short Version

If you need to know which PFAS numbers to use right now, here’s the current status as of March 2026:

PFOA and PFOS - The federal MCLs of 4 parts per trillion (ppt) each are staying. EPA confirmed it will keep these standards. The compliance deadline for public water systems has been extended from 2029 to 2031. PFOA and PFOS are also designated hazardous substances under CERCLA (Superfund), effective July 2024. The Trump administration has confirmed it will retain and defend that designation.

PFHxS, PFNA, HFPO-DA (GenX), and PFBS - EPA intends to rescind the individual MCLs (10 ppt for PFHxS, PFNA, and GenX) and the Hazard Index mixture standard that were finalized in April 2024. As of February 2026, EPA stated it will “commence the rulemaking process imminently” to rescind these. The D.C. Circuit denied EPA’s request to sever these challenges from the ongoing litigation in March 2026. These standards are technically still in effect but their future is uncertain.

What Happened

In April 2024, the Biden administration finalized the first-ever National Primary Drinking Water Regulation (NPDWR) for PFAS (Per- and Polyfluoroalkyl Substances). The rule set MCLs for six PFAS compounds and gave public water systems until 2027 to complete initial monitoring and until 2029 to comply with the MCLs.

The rule was immediately challenged in court by water utilities and industry groups who argued EPA underestimated compliance costs and used an untested Hazard Index approach for regulating PFAS mixtures.

In May 2025, the Trump EPA announced it would keep the PFOA and PFOS MCLs but pull back on the other four PFAS. Specifically:

Kept: PFOA MCL at 4 ppt, PFOS MCL at 4 ppt. Compliance deadline extended to 2031.

Being rescinded: Individual MCLs for PFHxS (10 ppt), PFNA (10 ppt), and HFPO-DA/GenX (10 ppt). The Hazard Index MCL for mixtures of PFHxS, PFNA, GenX, and PFBS is also being rescinded.

EPA’s stated reasoning is that the regulatory determinations for these four compounds need to be reconsidered to ensure they follow the Safe Drinking Water Act (SDWA) process properly.

CERCLA Hazardous Substance Status

Separately from the drinking water standards, EPA designated PFOA and PFOS as hazardous substances under CERCLA in April 2024 (effective July 2024). This designation triggers Superfund cleanup authority, release reporting requirements (reportable quantity of one pound in 24 hours), and cost recovery provisions.

In September 2025, the Trump administration confirmed it will retain and defend the CERCLA designation for PFOA and PFOS. The U.S. Chamber of Commerce’s legal challenge to the designation is being litigated in the D.C. Circuit. Oral argument was held January 20, 2026, with a decision possible later this year.

EPA is also planning a framework rule to guide future CERCLA hazardous substance designations, which could eventually cover additional PFAS compounds.

On the RCRA (Resource Conservation and Recovery Act) side, EPA plans to finalize a rule by April 2026 that would add nine PFAS compounds to the list of hazardous constituents, requiring corrective action for releases at permitted hazardous waste facilities.

What This Means for Consultants

For drinking water compliance: PFOA and PFOS at 4 ppt are the numbers. Public water systems need to be monitoring and planning for compliance by 2031. The status of the other four PFAS MCLs is in limbo - if you’re advising a water system, monitor the rulemaking closely.

For site assessment and cleanup: PFOA and PFOS are CERCLA hazardous substances. This means PFAS should be evaluated at sites where PFOA/PFOS may have been used, released, or disposed of. Phase I ESAs should consider PFAS as a potential concern even though they remain “non-scope” under ASTM E1527-21 (because the CERCLA designation postdates the standard). The practical advice: include PFAS in your scope of work at sites with industrial history, firefighting foam use, or wastewater/biosolids handling.

For state programs: Many states have their own PFAS standards or guidance values that may differ from the federal MCLs. Ohio’s action plan levels (70 ppt combined PFOA/PFOS) are less restrictive than the federal MCLs (4 ppt each). When both federal and state standards exist, the more restrictive typically applies for public water systems. For voluntary cleanup programs, check which standards your state program uses. See our Ohio PFAS Groundwater and Drinking Water Standards page for Ohio-specific details.

For property transactions: The CERCLA hazardous substance designation for PFOA and PFOS increases the importance of evaluating PFAS risk during due diligence. Properties with potential PFAS contamination carry Superfund liability implications that didn’t exist before July 2024.

What to Watch

Several developments expected in 2026 could change the landscape:

The D.C. Circuit’s decision on the CERCLA hazardous substance designation challenge could uphold, modify, or vacate the rule. A decision is expected sometime this year.

EPA’s proposed rule to rescind the PFHxS/PFNA/GenX/PFBS MCLs and extend the PFOA/PFOS compliance deadline is expected to be finalized in spring 2026.

EPA’s RCRA rulemaking to add nine PFAS to the hazardous constituents list is targeted for finalization by April 2026.

Congressional action on “passive receiver” liability protections for water utilities and other entities that did not manufacture or intentionally use PFAS remains possible but uncertain.

We will update this post and our PFAS standards pages as these developments occur.