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EPA UCMR 5 results for public water system CA4010007 serving San Luis Obispo County (California). 7 of 29 PFAS detected.
UCMR 5 is a one-time EPA monitoring program, not a compliance determination. The values shown are the highest single sample result at any of the system's sampling points; one result above 4.0 ppt does not mean the system violates the PFAS rule, which is judged on running annual averages under separate compliance monitoring. Results describe the public water system, not an individual home.
| PFAS | Highest result (ppt) | Samples with detection | EPA limit (2024 rule) |
|---|---|---|---|
| PFPeA (perfluoropentanoic acid) | 22 | 2 of 26 | — |
| PFHxA (perfluorohexanoic acid) | 20 | 2 of 26 | — |
| PFBS (perfluorobutane sulfonic acid) | 8.1 | 5 of 26 | Hazard Index component (2024 rule; proposed for rescission) |
| PFHpA (perfluoroheptanoic acid) | 6.3 | 2 of 26 | — |
| PFOA (perfluorooctanoic acid) | 6.3 | 2 of 26 | 4.0 ppt (MCL, 2024 rule) |
| PFBA (perfluorobutanoic acid) | 6.1 | 1 of 26 | — |
| PFHxS (perfluorohexane sulfonic acid) | 5.2 | 5 of 26 | 10 ppt (2024 rule; proposed for rescission) |
ppt = parts per trillion (ng/L). EPA reports UCMR 5 results in µg/L; we multiply by 1,000. “Samples with detection” counts results at or above the UCMR 5 minimum reporting level.
In April 2024 EPA set enforceable limits (MCLs) of 4.0 ppt each for PFOA and PFOS, plus 10 ppt for PFHxS, PFNA and HFPO-DA (GenX) and a Hazard Index for mixtures, with compliance based on a running annual average at each sampling point and due in 2029 (EPA ↗). In May 2026 EPA proposed letting systems request two more years for PFOA/PFOS (to April 2031) and rescinding the PFHxS, PFNA, GenX and Hazard Index limits (EPA: extension proposal ↗ · EPA: rescission proposal ↗). These are proposals, not final rules, as of the date this page was built.