City Of Atwater

Compared with EPA's 2024 values

“<MRL” = every result for the compound was below its reporting limit. * Mean of all samples at each entry point with non-detects = 0 (EPA compliance convention; the Hazard Index also uses non-detects = 0); a screening comparison, not a formal running annual average. † Rescission proposed May 2026. PFOA/PFOS MCL 4 ppt (2024 NPDWR, in effect). PFHxS, PFNA, HFPO-DA (10 ppt each) and the Hazard Index (1.0) are 2024 NPDWR values; EPA proposed rescinding them on 18 May 2026 (comment period closed 20 Jul 2026).

Compared with California guidance levels

Sum standards add the listed compounds within each sample (non-detects = 0). State compliance is normally judged on averages over time; these are screening comparisons.

Sampling history

Sampled 2023-10-31 to 2024-05-07 · 8 entry point(s) · water types: GW · 16 sampling visits. PFAS in ppt (ng/L).

“<4” = not detected at the reporting limit shown; “n/a” = not analyzed in that sample. Highlighted = at or above the 4 ppt MCL. HI computed per sample with non-detects as 0. Other detections lists every other quantified compound (lithium in µg/L).

All results by entry point

480 results. Each column is one sampling visit (date and UCMR 5 sample event). A number is a measured concentration; “< 4” = below the minimum reporting level shown; “–” = not analyzed in that visit. PFAS in ppt (ng/L); lithium in µg/L.

Statistics by compound

Never detected (20): 11Cl-PF3OUdS, 4:2 FTS, 8:2 FTS, 9Cl-PF3ONS, ADONA, HFPO-DA, NEtFOSAA, NFDHA, NMeFOSAA, PFDA, PFDoA, PFEESA, PFHpS, PFMBA, PFMPA, PFNA, PFTA, PFTrDA, PFUnA, lithium.

Left-censored Kaplan–Meier statistics (Helsel 2005; Helsel & Lee 2006, NADA for R). Units: ppt; lithium µg/L. Each compound has one reporting limit, so the Kaplan–Meier mean equals the upper mean bound (non-detects at the MRL); the lower bound sets non-detects to 0. “<MRL” = the percentile falls below the reporting limit and cannot be estimated. These describe this system's UCMR 5 samples, not population estimates.

Sources

• EPA UCMR 5 occurrence data text files (UCMR5_All.txt; samples 2023-01-09 to 2026-06-17; data summary dated Jul 2026)
• EPA SDWIS via ECHO SDWA downloads, quarter 2026Q3
• EPA Public Water System Service Areas v3 (Mar 2026)
• US Census Bureau cartographic boundary counties 1:500k, 2024
• EPA/USGS NHDPlus V2 (medium resolution) flowlines, Strahler order 2+

Data build 90f0922cd84f · 2026-10-18T04:12Z · UCMR 5 release Jul2026 · SDWIS 2026Q3. Data and methods.