Ohio PFAS Standards - Drinking Water & Groundwater Action Levels

Overview

PFAS regulation in Ohio is a moving target. As of June 2026, there are two overlapping sets of numbers that consultants, water systems, and property owners need to understand: Ohio’s current PFAS Action Plan levels and the federal Maximum Contaminant Levels finalized in April 2024. Under its PFAS Action Plan 2.0, Ohio revised its drinking water Action Levels to match the 2024 federal MCLs - 4 ppt for PFOA and PFOS, and 10 ppt each for PFHxS, PFNA, and GenX. The federal MCLs are the enforceable standard for public water systems; Ohio’s Action Plan values are guidance only.

Ohio does not currently have state-specific enforceable PFAS cleanup standards for groundwater outside the drinking water context. There is no PFAS-specific rule under the Ohio Voluntary Action Program (OAC 3745-300), and BUSTR’s corrective action tables do not include PFAS compounds. Ohio EPA has begun rulemaking to adopt enforceable PFAS drinking water MCLs, anticipated to be final and enforced by spring 2027. For contaminated site work, consultants are generally screening against the federal MCLs for drinking water scenarios and EPA RSLs for non-drinking water scenarios.

Bottom line for consultants: If you’re doing site assessment or due diligence work in Ohio and PFAS is a potential concern, screen groundwater results against the federal MCLs (4 ppt for PFOA and PFOS). Ohio’s Action Plan 2.0 guidance now matches the federal MCLs. If you encounter a reference to Ohio’s older “70 ppt” levels in legacy documents, those reflect the 2019/2020 Action Plan (1.0) and should not be used for current screening.

Federal PFAS MCLs (The Enforceable Standard)

In April 2024, EPA finalized the first-ever National Primary Drinking Water Regulation for PFAS. These are legally enforceable limits for public water systems.

PFAS Compound	MCL	MCLG	Status (as of June 2026)
PFOA	4 ppt	0	In effect - EPA has proposed to keep this standard
PFOS	4 ppt	0	In effect - EPA has proposed to keep this standard
PFHxS	10 ppt	10 ppt	In effect, proposed for rescission (May 2026)
PFNA	10 ppt	10 ppt	In effect, proposed for rescission (May 2026)
HFPO-DA (GenX)	10 ppt	10 ppt	In effect, proposed for rescission (May 2026)
Hazard Index (PFHxS + PFNA + HFPO-DA + PFBS mixture)	HI = 1	HI = 1	In effect, proposed for rescission (May 2026)

Key Compliance Dates

Public water systems must complete initial PFAS monitoring by 2027 and were originally required to comply with MCLs by 2029. On May 18, 2026, EPA proposed a rule that would let systems request a two-year extension of the PFOA/PFOS compliance deadline to 2031. That proposal does not change the 4 ppt MCLs themselves; it only extends the time to comply for systems that request and are granted an exemption. Comments on the proposal close July 20, 2026.

What’s Proposed for Rescission and What’s Not

In May 2025, EPA announced its intent to keep the PFOA and PFOS MCLs at 4 ppt while rescinding the MCLs for PFHxS, PFNA, HFPO-DA (GenX), and the Hazard Index mixture. EPA acted on that intent on May 18, 2026, when it announced a proposed rule to rescind the regulatory determinations for those four compounds; the proposal was published in the Federal Register on May 20, 2026 (Docket EPA-HQ-OW-2025-0654). EPA’s stated reasoning is that the determinations for those four compounds were not promulgated in accordance with the Safe Drinking Water Act and must be corrected. The comment period closes July 20, 2026, and EPA intends to take final action in 2026.

Until EPA finalizes that rescission, the 2024 MCLs for all six compounds remain technically in force. A January 2026 federal court ruling declined to vacate the limits, so the values stay on the books pending the rulemaking. The practical takeaway: PFOA and PFOS at 4 ppt are settled, and the status of the other four is in active flux but not yet rescinded.

Ohio PFAS Action Plan Levels (Current)

Ohio’s PFAS Action Plan, originally released in December 2019 under Governor DeWine’s executive order, established action levels for PFAS in drinking water. These are guidance values - not enforceable regulatory standards - used to trigger response protocols when detected in public water systems. Under Action Plan 2.0, Ohio updated its Action Levels to match the 2024 federal MCLs for all six compounds.

PFAS Compound	Ohio 2024 Action Level	Basis
PFOA	4 ppt	Matches federal MCL (revised from 70 ppt single or combined)
PFOS	4 ppt	Matches federal MCL (revised from 70 ppt single or combined)
PFHxS	10 ppt	Matches federal MCL (revised from 140 ppt)
PFNA	10 ppt	Matches federal MCL (revised from 21 ppt)
GenX (HFPO-DA)	10 ppt	Matches federal MCL (revised from 700 ppt)
PFBS	2,000 ppt	Health Based Water Reference Concentration, U.S. EPA 2023 (revised from 140,000 ppt)

Context on the Original 2019/2020 Levels

The original Action Plan (1.0) used 70 ppt combined for PFOA and PFOS, based on the U.S. EPA 2016 Health Advisory Level, plus 700 ppt GenX, 140,000 ppt PFBS, 140 ppt PFHxS, and 21 ppt PFNA. If you encounter a reference to a “70 ppt” PFAS standard in Ohio legacy documents, it refers to those original action levels and is no longer current.

Note that Ohio’s PFBS Action Level (2,000 ppt) is based on EPA’s 2023 Health Based Water Reference Concentration rather than an MCL, because PFBS does not have an individual federal MCL - it is regulated federally only as a component of the Hazard Index mixture. PFBS is considered far less toxic than PFOA or PFOS, which is reflected in its much higher action level.

Practical Guidance for Site Assessment Work

Phase I ESAs

PFAS is increasingly relevant to Phase I Environmental Site Assessments in Ohio. Under ASTM E1527-21, the environmental professional must consider “emerging contaminants” when evaluating recognized environmental conditions. Properties with the following historical uses warrant PFAS attention:

• Fire training facilities and airports (AFFF foam use)
• Military bases (Wright-Patterson AFB in Dayton is a well-known Ohio PFAS site)
• Chrome plating and metal finishing operations
• Landfills, especially those that accepted industrial waste
• Wastewater treatment plants
• Properties near any of the above

Phase II ESAs - Which Numbers to Use for Screening

For Phase II sampling programs in Ohio where PFAS is a contaminant of concern:

Groundwater (drinking water scenario): Screen against the federal MCLs - 4 ppt for PFOA and 4 ppt for PFOS. For other PFAS compounds, use the most current EPA RSLs for tap water, though be aware that the regulatory status of PFHxS, PFNA, and GenX is in flux pending the proposed federal rescission.

Groundwater (non-drinking water scenario): Use EPA RSLs for the appropriate exposure pathway. The vapor intrusion pathway is generally not a concern for PFAS (they’re not volatile), but the groundwater-to-surface-water pathway may need evaluation if a site is near a water body.

Soil: EPA RSLs include PFAS screening levels for residential and commercial/industrial soil. Ohio does not have state-specific PFAS soil standards under the VAP.

Important: PFAS analysis requires specialized sampling procedures. Standard sampling equipment used for VOCs and metals will contaminate PFAS samples. See our PFAS Sampling Best Practices guide for detailed field procedures.

BUSTR Sites

PFAS is not currently a chemical of concern under Ohio BUSTR’s corrective action rules (OAC 1301:7-9-13). The BUSTR COC tables (Tables 2.2 and 3.1 in the TGM) do not include any PFAS compounds. However, if AFFF foam was ever used at a petroleum UST site (fire suppression, training), PFAS may be present as a co-contaminant, and separate assessment under a different regulatory framework may be warranted.

Ohio VAP Sites

The Ohio VAP (OAC 3745-300) does not currently include PFAS-specific generic standards. For VAP-enrolled properties where PFAS is a concern, site-specific standards would need to be developed through the risk assessment process. Consultants working on VAP sites with PFAS should coordinate directly with Ohio EPA’s Division of Environmental Response and Revitalization (DERR).

Ohio PFAS Contamination - Key Sites

Several major PFAS contamination sites in Ohio have driven state and federal attention:

• Wright-Patterson Air Force Base (Dayton): PFAS from AFFF firefighting foam has contaminated groundwater affecting the City of Dayton’s Miami Wellfield. Extensive investigation and monitoring is ongoing, with the city investing in treatment infrastructure.
• American CARCO (Harrison Township, Montgomery County): A former metal plating facility that used large amounts of PFOS, ceased operations in 1989. Extremely high PFOS levels were detected in groundwater beginning in 2019, migrating offsite toward the City of Dayton’s Miami Wellfield. Ohio EPA is coordinating with Dayton on source control and treatment options.
• DuPont Washington Works (Parkersburg, WV / Ohio border): The C-8 litigation - one of the largest PFAS cases in the country - stemmed from PFOA contamination of drinking water in Ohio communities along the Ohio River. Ohio reached a $110 million settlement with DuPont in November 2023.
• Columbus and central Ohio: Multiple public water systems in the Columbus area detected PFAS during the statewide sampling program.

What to Watch

The PFAS regulatory landscape will continue to shift through 2026 and beyond. Key developments to monitor:

• EPA rescission rulemaking: EPA’s proposed rule to rescind the MCLs for PFHxS, PFNA, GenX, and the Hazard Index mixture published May 20, 2026. Comments close July 20, 2026, and EPA intends final action in 2026. Until then, those MCLs remain in force.
• EPA PFOA/PFOS compliance extension: A separate proposed rule would let public water systems request an extension of the PFOA/PFOS compliance deadline to 2031. It does not change the 4 ppt MCLs.
• Ohio PFAS MCL rulemaking: Ohio EPA has begun the process to adopt enforceable state PFAS MCLs, anticipated final and enforced by spring 2027. Until then, Ohio’s Action Levels remain guidance values.
• CERCLA hazardous substance designation: EPA designated PFOA and PFOS as hazardous substances under CERCLA. This significantly expands liability at contaminated sites and will affect cleanup obligations at sites across Ohio.
• EPA RSL updates: EPA’s Regional Screening Levels for PFAS in soil and groundwater are updated periodically and serve as the de facto screening tool for site assessment work in Ohio.