EPA PFAS drinking‑water rule triggers Idaho adoption; DEQ sampling finds PFAS detections, some sources near proposed MCLs

The Department of Environmental Quality told the House Environment, Energy and Technology Committee that EPA’s finalized PFAS drinking‑water rule requires Idaho to adopt federal monitoring, reporting and maximum contaminant level (MCL) requirements and that the department’s sampling has identified PFAS detections in multiple public water system sources.

"PFOS is a compound that breaks down very slowly," said Tyler Forcionati, drinking water bureau chief, describing why the group of per‑ and polyfluoroalkyl substances (PFAS) has drawn regulatory attention. He summarized EPA’s April 2024 final rule, which establishes enforceable maximum contaminant levels for specified PFAS analytes and adds monitoring, reporting and public‑notification requirements for community and nontransient noncommunity public water systems.

Under the federal schedule DEQ described, public water systems must complete initial monitoring by April 2027 and transition to routine monitoring thereafter; systems must include PFAS results in consumer confidence reports beginning April 2027, must provide public notification if an MCL is exceeded starting April 2029, and must achieve compliance with an MCL by April 2029.

DEQ outlined three sampling efforts: Department of Defense monitoring near installations (Mountain Home Air Force Base detections led a system to install treatment in 2018 at about $1.36 million and O&M estimated at $100,000; that source was taken offline in 2020); EPA’s Unregulated Contaminant Monitoring Rule (UCMR5), which selected a random sample of 61 Idaho public water systems in 2023–25 for expanded PFAS testing; and DEQ’s voluntary PFAS sampling project, funded through EPA grants, which has sampled raw source water at 381 of 3,219 active sources (about 12%) and found detections at 66 sources. At the system level, DEQ sampled 203 of the state’s 2,016 regulated public water systems (about 10%) and found detections at 58 systems (about 28% of those sampled).

DEQ said 14 systems in its voluntary sampling had one or more sources with measurements that could exceed the finalized federal MCL; that represented 25 impacted sources and 11 of those 25 sources had two or more regulated analytes above the finalized MCL thresholds in the results DEQ reported. The range of detections DEQ reported spanned low‑ppt levels up to 42 parts per trillion for certain analytes; PFOS was the most common detection. DEQ said it offers confirmation sampling to systems and that, where detected, it can sample neighboring systems on a voluntary basis.

DEQ described existing mitigation funding: standard Drinking Water State Revolving Fund loans, bipartisan infrastructure law funds (about $7.5 million per year for drinking water and about $1 million for wastewater for state fiscal years 2023–2027), and other emergent contaminant funding streams. To be eligible for the emerging contaminants funds, DEQ said systems must submit a letter of interest and document a PFAS issue; the next LOI cycle runs Oct. through Jan. for SFY27 funding.

The department also presented docket 580-108-2401, which incorporates the federal 40 CFR Part 141 Subpart Z PFAS requirements into Idaho rules and updates the CFR reference date to July 1, 2024; DEQ said adopting the federal rule is necessary to maintain state primacy under the Safe Drinking Water Act. DEQ presented the proposed rule as non‑discretionary and said the Drinking Water Advisory Committee and state utilities supported adoption.

Committee members asked whether PFAS is proven carcinogenic; Forcionati said scientific evidence is evolving and recent studies are leaning toward carcinogenicity for some PFAS compounds. Members also asked about treatment technologies; Forcionati said common treatment options include granular activated carbon, ion exchange and reverse osmosis and that costs can be substantial for small systems.

DEQ asked the committee to support adoption of the federal PFAS requirements into state rule to preserve primacy and provide a regulatory framework for monitoring and compliance. The committee did not vote at the hearing.