- PWSID
- CA4010001
- State
- California
- System type
- community water system (CWS)
- Population served
- 17,963
- City
- Arroyo Grande
- Counties
- San Luis Obispo County
- Primary source water
- surface water (purchased)
- UCMR 5 sampling
- 2023-12-19 to 2024-09-10 · 3 entry point(s) · water types: GW;MX
- Service-area boundary
- authoritative
PFOS 1–3 × its limit highest single result
PFOS 1–3 × its limit worst entry-point average
Open on the California map · All California systems · All results
These are monitoring results collected under EPA's Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) at entry points, where treated water enters the distribution system; they are not tap-water samples. They are not compliance determinations: compliance with EPA's 2024 PFAS limits is judged on running annual averages of compliance monitoring, required from 2029, so a single UCMR 5 result at or above a limit is not a violation. “< MRL” means the compound was not quantified at EPA's minimum reporting level; it does not mean zero.
Water purchased from
- Pismo Beach Water Department (CA4010008)
Seller's highest results: PFOA <MRL · PFOS <MRL · HI 0 - City Of Grover Beach Public Works Dept (CA4010004)
Seller's highest results: PFOA <MRL · PFOS <MRL · HI 0 - Oceano Comm Services Dist. (CA4010005)
Seller's highest results: PFOA <MRL · PFOS <MRL · HI 0 - Lopez Project (CA4010022)
Seller not monitored under UCMR 5.
Seller results are the seller's own entry-point samples, not measurements of this system's water. This system's own samples (below) may reflect purchased water, its own sources, or both.
Compared with EPA's 2024 values
| Highest single result | Worst entry-point average* | Limit | |
|---|---|---|---|
| PFOA (ppt) | 5.8 | 3.62 | 4 |
| PFOS (ppt) | 6.8 | 4.17 | 4 |
| Hazard Index | 0.555 | 0.427 | 1.0† |
“<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
| Highest single result | Worst entry-point average* | California | |
|---|---|---|---|
| PFHxS (ppt) | 5.5 | 4.22 | 3 (guidance) |
| PFOA (ppt) | 5.8 | 3.62 | 4 (guidance) |
| PFOS (ppt) | 6.8 | 4.17 | 4 (guidance) |
| PFBS (ppt) | 11 | 10.07 | 500 (guidance) |
| PFHxA (ppt) | 3.5 | 2.55 | 1,000 (guidance) |
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 2023-12-19 to 2024-09-10 · 3 entry point(s) · water types: GW;MX · 8 sampling visits. PFAS in ppt (ng/L).
| Date | Entry point | Event | PFOA | PFOS | HI | Other detections |
|---|---|---|---|---|---|---|
| 2023-12-19 | Well 10 (GW) | SE1 | <4 | <4 | 0 | lithium 21.8 µg/L |
| 2023-12-19 | Well 9 (GW) | SE1 | <4 | <4 | 0 | lithium 42.1 µg/L |
| 2023-12-19 | Wells 1, 3, 4, 5, 7 & 8 & Lopez (MX) | SE1 | 4.1 | 4.3 | 0.415 | PFHxA 3.4, PFPeA 4.5, lithium 10.6 µg/L |
| 2024-03-12 | Wells 1, 3, 4, 5, 7 & 8 & Lopez (MX) | SE2 | <4 | <4 | 0.304 | PFPeA 3.9, lithium 11.6 µg/L |
| 2024-06-19 | Well 10 (GW) | SE2 | <4 | <4 | 0 | lithium 27.4 µg/L |
| 2024-06-19 | Well 9 (GW) | SE2 | <4 | <4 | 0 | lithium 60 µg/L |
| 2024-06-19 | Wells 1, 3, 4, 5, 7 & 8 & Lopez (MX) | SE3 | 5.8 | 6.8 | 0.555 | PFHxA 3.5, PFPeA 4.1, lithium 13.6 µg/L |
| 2024-09-10 | Wells 1, 3, 4, 5, 7 & 8 & Lopez (MX) | SE4 | 4.6 | 5.6 | 0.435 | PFHxA 3.3, PFPeA 3.3, lithium 14 µg/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
240 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.
Well 10 facility 91803 · sample point 4010001803 · groundwater
| Compound | MRL | 2023-12-19 SE1 | 2024-06-19 SE2 |
|---|---|---|---|
| 11Cl-PF3OUdS | 5 ppt | < 5 | < 5 |
| 4:2 FTS | 3 ppt | < 3 | < 3 |
| 6:2 FTS | 5 ppt | < 5 | < 5 |
| 8:2 FTS | 5 ppt | < 5 | < 5 |
| 9Cl-PF3ONS | 2 ppt | < 2 | < 2 |
| ADONA | 3 ppt | < 3 | < 3 |
| HFPO-DA | 5 ppt | < 5 | < 5 |
| NEtFOSAA | 5 ppt | < 5 | < 5 |
| NFDHA | 20 ppt | < 20 | < 20 |
| NMeFOSAA | 6 ppt | < 6 | < 6 |
| PFBA | 5 ppt | < 5 | < 5 |
| PFBS | 3 ppt | < 3 | < 3 |
| PFDA | 3 ppt | < 3 | < 3 |
| PFDoA | 3 ppt | < 3 | < 3 |
| PFEESA | 3 ppt | < 3 | < 3 |
| PFHpA | 3 ppt | < 3 | < 3 |
| PFHpS | 3 ppt | < 3 | < 3 |
| PFHxA | 3 ppt | < 3 | < 3 |
| PFHxS | 3 ppt | < 3 | < 3 |
| PFMBA | 3 ppt | < 3 | < 3 |
| PFMPA | 4 ppt | < 4 | < 4 |
| PFNA | 4 ppt | < 4 | < 4 |
| PFOA | 4 ppt | < 4 | < 4 |
| PFOS | 4 ppt | < 4 | < 4 |
| PFPeA | 3 ppt | < 3 | < 3 |
| PFPeS | 4 ppt | < 4 | < 4 |
| PFTA | 8 ppt | < 8 | < 8 |
| PFTrDA | 7 ppt | < 7 | < 7 |
| PFUnA | 2 ppt | < 2 | < 2 |
| lithium | 9 µg/L | 21.8 | 27.4 |
Well 9 facility 91802 · sample point 4010001802 · groundwater
| Compound | MRL | 2023-12-19 SE1 | 2024-06-19 SE2 |
|---|---|---|---|
| 11Cl-PF3OUdS | 5 ppt | < 5 | < 5 |
| 4:2 FTS | 3 ppt | < 3 | < 3 |
| 6:2 FTS | 5 ppt | < 5 | < 5 |
| 8:2 FTS | 5 ppt | < 5 | < 5 |
| 9Cl-PF3ONS | 2 ppt | < 2 | < 2 |
| ADONA | 3 ppt | < 3 | < 3 |
| HFPO-DA | 5 ppt | < 5 | < 5 |
| NEtFOSAA | 5 ppt | < 5 | < 5 |
| NFDHA | 20 ppt | < 20 | < 20 |
| NMeFOSAA | 6 ppt | < 6 | < 6 |
| PFBA | 5 ppt | < 5 | < 5 |
| PFBS | 3 ppt | < 3 | < 3 |
| PFDA | 3 ppt | < 3 | < 3 |
| PFDoA | 3 ppt | < 3 | < 3 |
| PFEESA | 3 ppt | < 3 | < 3 |
| PFHpA | 3 ppt | < 3 | < 3 |
| PFHpS | 3 ppt | < 3 | < 3 |
| PFHxA | 3 ppt | < 3 | < 3 |
| PFHxS | 3 ppt | < 3 | < 3 |
| PFMBA | 3 ppt | < 3 | < 3 |
| PFMPA | 4 ppt | < 4 | < 4 |
| PFNA | 4 ppt | < 4 | < 4 |
| PFOA | 4 ppt | < 4 | < 4 |
| PFOS | 4 ppt | < 4 | < 4 |
| PFPeA | 3 ppt | < 3 | < 3 |
| PFPeS | 4 ppt | < 4 | < 4 |
| PFTA | 8 ppt | < 8 | < 8 |
| PFTrDA | 7 ppt | < 7 | < 7 |
| PFUnA | 2 ppt | < 2 | < 2 |
| lithium | 9 µg/L | 42.1 | 60 |
Wells 1, 3, 4, 5, 7 & 8 & Lopez facility 91801 · sample point 4010001801 · MX
| Compound | MRL | 2023-12-19 SE1 | 2024-03-12 SE2 | 2024-06-19 SE3 | 2024-09-10 SE4 |
|---|---|---|---|---|---|
| PFBS | 3 ppt | 11 | 7.3 | 11 | 11 |
| PFHxA | 3 ppt | 3.4 | < 3 | 3.5 | 3.3 |
| PFHxS | 3 ppt | 4.1 | 3 | 5.5 | 4.3 |
| PFOA | 4 ppt | 4.1 | < 4 | 5.8 | 4.6 |
| PFOS | 4 ppt | 4.3 | < 4 | 6.8 | 5.6 |
| PFPeA | 3 ppt | 4.5 | 3.9 | 4.1 | 3.3 |
| 11Cl-PF3OUdS | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| 4:2 FTS | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| 6:2 FTS | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| 8:2 FTS | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| 9Cl-PF3ONS | 2 ppt | < 2 | < 2 | < 2 | < 2 |
| ADONA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| HFPO-DA | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| NEtFOSAA | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| NFDHA | 20 ppt | < 20 | < 20 | < 20 | < 20 |
| NMeFOSAA | 6 ppt | < 6 | < 6 | < 6 | < 6 |
| PFBA | 5 ppt | < 5 | < 5 | < 5 | < 5 |
| PFDA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFDoA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFEESA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFHpA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFHpS | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFMBA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFMPA | 4 ppt | < 4 | < 4 | < 4 | < 4 |
| PFNA | 4 ppt | < 4 | < 4 | < 4 | < 4 |
| PFPeS | 4 ppt | < 4 | < 4 | < 4 | < 4 |
| PFTA | 8 ppt | < 8 | < 8 | < 8 | < 8 |
| PFTrDA | 7 ppt | < 7 | < 7 | < 7 | < 7 |
| PFUnA | 2 ppt | < 2 | < 2 | < 2 | < 2 |
| lithium | 9 µg/L | 10.6 | 11.6 | 13.6 | 14 |
Statistics by compound
| Compound | Results | Detected | Highest (date) | Mean bounds | KM median | P75 | P90 | P95 |
|---|---|---|---|---|---|---|---|---|
| lithium | 8 | 100% | 60 2024-06-19 | 25.14–25.14 | 14 | 27.4 | 60 | 60 |
| PFBS | 8 | 50% | 11 2023-12-19 | 5.04–6.54 | <MRL | 11 | 11 | 11 |
| PFHxS | 8 | 50% | 5.5 2024-06-19 | 2.11–3.61 | <MRL | 4.1 | 5.5 | 5.5 |
| PFPeA | 8 | 50% | 4.5 2023-12-19 | 1.98–3.48 | <MRL | 3.9 | 4.5 | 4.5 |
| PFHxA | 8 | 38% | 3.5 2024-06-19 | 1.27–3.15 | <MRL | 3.3 | 3.5 | 3.5 |
| PFOA | 8 | 38% | 5.8 2024-06-19 | 1.81–4.31 | <MRL | 4.1 | 5.8 | 5.8 |
| PFOS | 8 | 38% | 6.8 2024-06-19 | 2.09–4.59 | <MRL | 4.3 | 6.8 | 6.8 |
Never detected (23): 11Cl-PF3OUdS, 4:2 FTS, 6:2 FTS, 8:2 FTS, 9Cl-PF3ONS, ADONA, HFPO-DA, NEtFOSAA, NFDHA, NMeFOSAA, PFBA, PFDA, PFDoA, PFEESA, PFHpA, PFHpS, PFMBA, PFMPA, PFNA, PFPeS, PFTA, PFTrDA, PFUnA.
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.