- PWSID
- SD4680046
- State
- South Dakota
- System type
- non-transient non-community water system (NTNCWS)
- Population served
- 4,100
- City
- Keystone
- Counties
- Pennington County
- Primary source water
- groundwater
- UCMR 5 sampling
- 2023-05-03 to 2024-03-18 · 1 entry point(s) · water types: GW
- Service-area boundary
- parcel-based (EPA non-community layer)
PFOS 1–3 × its limit highest single result
PFOS 1–3 × its limit worst entry-point average
Open on the South Dakota map · All South Dakota 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.
Compared with EPA's 2024 values
| Highest single result | Worst entry-point average* | Limit | |
|---|---|---|---|
| PFOA (ppt) | <MRL | 0 | 4 |
| PFOS (ppt) | 10.6 | 10.2 | 4 |
| Hazard Index | 2.082 | 1.044 | 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).
No South Dakota PFAS drinking-water standard in effect or proposed as of 2026-10-17: No state PFAS drinking-water standard; follows federal NPDWR (BCLP state survey, Jan 2026).
Sampling history
Sampled 2023-05-03 to 2024-03-18 · 1 entry point(s) · water types: GW · 4 sampling visits. PFAS in ppt (ng/L).
| Date | Entry point | Event | PFOA | PFOS | HI | Other detections |
|---|---|---|---|---|---|---|
| 2023-05-03 | Treatment Plant (GW) | SE1 | n/a | n/a | n/a | lithium 33.7 µg/L |
| 2023-06-14 | Treatment Plant (GW) | SE1 | <4 | 9.8 | 2.082 | none |
| 2023-11-07 | Treatment Plant (GW) | SE2 | <4 | n/a | 0 | lithium 29.5 µg/L |
| 2024-03-18 | Treatment Plant (GW) | SE2 | n/a | 10.6 | 1.05 | none |
“<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
60 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.
Treatment Plant facility 10001 · sample point EP1NEW · groundwater
| Compound | MRL | 2023-05-03 SE1 | 2023-06-14 SE1 | 2023-11-07 SE2 | 2024-03-18 SE2 |
|---|---|---|---|---|---|
| PFBS | 3 ppt | – | 3.2 | < 3 | – |
| PFHxS | 3 ppt | – | 20.8 | – | 10.5 |
| PFOS | 4 ppt | – | 9.8 | – | 10.6 |
| 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 | – |
| 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 | – |
| PFMBA | 3 ppt | – | < 3 | < 3 | – |
| PFMPA | 4 ppt | – | < 4 | < 4 | – |
| PFNA | 4 ppt | – | < 4 | < 4 | – |
| PFOA | 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 | 33.7 | – | 29.5 | – |
Statistics by compound
| Compound | Results | Detected | Highest (date) | Mean bounds | KM median | P75 | P90 | P95 |
|---|---|---|---|---|---|---|---|---|
| PFHxS | 2 | 100% | 20.8 2023-06-14 | 15.65–15.65 | fewer than 4 results: raw values only | |||
| PFOS | 2 | 100% | 10.6 2024-03-18 | 10.2–10.2 | fewer than 4 results: raw values only | |||
| lithium | 2 | 100% | 33.7 2023-05-03 | 31.6–31.6 | fewer than 4 results: raw values only | |||
| PFBS | 2 | 50% | 3.2 2023-06-14 | 1.6–3.1 | fewer than 4 results: raw values only | |||
Never detected (26): 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, PFHxA, PFMBA, PFMPA, PFNA, PFOA, PFPeA, 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 2023-01-11 to 2025-12-16; 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 ba837c0e69f6 · 2026-10-18T04:04Z · UCMR 5 release Jul2026 · SDWIS 2026Q3. Data and methods.