Yes. EPA's final UCMR 5 results show Thermalito Water & Sewer Dist averaged 4.1 ppt of PFOS at its worst sampling point, 1.0 times the EPA limit of 4 ppt.
Thermalito Water & Sewer Dist is a public water system drawing on surface water, based in Oroville, California, serving about 12,136 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 8 times across 5 sampling points between Jan 2023 and Jan 2024.
| PFAS | Detected | Highest | Worst point avg | EPA limit |
|---|---|---|---|---|
| PFOS Perfluorooctanesulfonic acid |
2 of 8 | 4.6 ppt | 4.1 ppt | 4 ppt |
Not detected: PFNA, PFUnA, PFHxA, PFTA, PFTrDA, NEtFOSAA, NMeFOSAA, PFDoA, PFDA, PFBS, 11Cl-PF3OUdS, PFHxS, PFHpA, PFEESA, PFOA, PFPeS, PFPeA, PFHpS, 9Cl-PF3ONS, NFDHA, PFMBA, PFMPA, 4:2 FTS, 6:2 FTS, PFBA, HFPO-DA, ADONA, 8:2 FTS.
Lithium, tested in the same program: highest 76 ppb, detected in 2 of 8 samples. EPA's health-based screening level is 10 ppb.
In April 2024 EPA set enforceable limits of 4 ppt for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and GenX, and a hazard index of 1 for mixtures. Utilities were given until 2029 to comply. In May 2026 EPA proposed keeping only the PFOA and PFOS limits and moving that deadline to 2031. Until that proposal is final, the 2024 limits stand.
Compliance is judged on a running annual average at each entry point, so we show the average at this system's worst sampling point next to its single highest result. UCMR 5 results do not by themselves put a utility in or out of compliance.
Two routes work for PFAS. For drinking and cooking water only, a reverse osmosis system certified to NSF/ANSI 58 with a PFOA/PFOS reduction claim is the cheapest proven option. To treat every tap and shower, a whole-house carbon system with enough contact time works, but check that the maker has PFAS test data, not just a marketing claim. See the best filters for PFAS and how PFAS removal works.
All 707 tested systems in California
95965
As reported by the utility to EPA. Neighbouring ZIPs are often split between systems; your water bill names yours.
Well & Tap. "PFAS in Thermalito Water & Sewer Dist water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CA0410008. https://wellandtap.com/pfas/california/thermalito-water-and-sewer-dist/
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CA0410008). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
