- PWSID
- 010106001
- State
- Connecticut
- System type
- community water system (CWS)
- Population served
- 22,171
- City
- Mashantucket
- Counties
- New London County
- Primary source water
- groundwater under the influence of surface water
- UCMR 5 sampling
- 2023-08-09 to 2024-05-13 · 1 entry point(s) · water types: GU
- Service-area boundary
- EPA-modeled (Random Forest) — approximate: estimated by EPA with a statistical model, not a surveyed service area
Tribal public water system, regulated by EPA Region 1 rather than by Connecticut. Connecticut drinking-water standards do not apply; the EPA values below do.
PFOA 1–3 × its limit highest single result
PFOA 1–3 × its limit worst entry-point average
Open on the Connecticut map · All Connecticut 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) | 7.4 | 5.28 | 4 |
| PFOS (ppt) | <MRL | 0 | 4 |
| Hazard Index | 0.002 | 0.001 | 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).
Sampling history
Sampled 2023-08-09 to 2024-05-13 · 1 entry point(s) · water types: GU · 7 sampling visits. PFAS in ppt (ng/L).
| Date | Entry point | Event | PFOA | PFOS | HI | Other detections |
|---|---|---|---|---|---|---|
| 2023-08-09 | MPTN WTP (GU) | SE1 | n/a | n/a | n/a | none |
| 2023-09-27 | MPTN WTP (GU) | SE1 | 7.4 | <4 | 0.002 | PFBA 6.3, PFHpA 3.5, PFHxA 9.2, PFPeA 18.2 |
| 2023-10-10 | MPTN WTP (GU) | SE2 | <4 | <4 | 0 | PFPeA 3.6 |
| 2024-01-10 | MPTN WTP (GU) | SE3 | n/a | n/a | n/a | none |
| 2024-02-07 | MPTN WTP (GU) | SE3 | 7.1 | <4 | 0.002 | PFBA 6.2, PFHpA 3.6, PFHxA 9.9, PFPeA 18.5 |
| 2024-04-03 | MPTN WTP (GU) | SE4 | n/a | n/a | n/a | none |
| 2024-05-13 | MPTN WTP (GU) | SE4 | 6.6 | <4 | 0.002 | PFBA 6.5, PFHpA 3.3, PFHxA 9.7, PFPeA 19.1 |
“<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
120 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.
MPTN WTP facility 00006 · sample point TP1 · groundwater under the influence of surface water
| Compound | MRL | 2023-08-09 SE1 | 2023-09-27 SE1 | 2023-10-10 SE2 | 2024-01-10 SE3 | 2024-02-07 SE3 | 2024-04-03 SE4 | 2024-05-13 SE4 |
|---|---|---|---|---|---|---|---|---|
| PFBA | 5 ppt | – | 6.3 | < 5 | – | 6.2 | – | 6.5 |
| PFBS | 3 ppt | – | 3.6 | < 3 | – | 3.6 | – | 3.4 |
| PFHpA | 3 ppt | – | 3.5 | < 3 | – | 3.6 | – | 3.3 |
| PFHxA | 3 ppt | – | 9.2 | < 3 | – | 9.9 | – | 9.7 |
| PFOA | 4 ppt | – | 7.4 | < 4 | – | 7.1 | – | 6.6 |
| PFPeA | 3 ppt | – | 18.2 | 3.6 | – | 18.5 | – | 19.1 |
| 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 | – |
| PFDA | 3 ppt | – | < 3 | < 3 | – | < 3 | – | < 3 |
| PFDoA | 3 ppt | – | < 3 | < 3 | – | < 3 | – | < 3 |
| PFEESA | 3 ppt | – | < 3 | < 3 | – | < 3 | – | < 3 |
| PFHpS | 3 ppt | – | < 3 | < 3 | – | < 3 | – | < 3 |
| PFHxS | 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 |
| PFOS | 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 | < 9 | – | < 9 | < 9 | – | < 9 | – |
Statistics by compound
| Compound | Results | Detected | Highest (date) | Mean bounds | KM median | P75 | P90 | P95 |
|---|---|---|---|---|---|---|---|---|
| PFPeA | 4 | 100% | 19.1 2024-05-13 | 14.85–14.85 | 18.2 | 18.5 | 19.1 | 19.1 |
| PFBA | 4 | 75% | 6.5 2024-05-13 | 4.75–6 | 6.2 | 6.3 | 6.5 | 6.5 |
| PFBS | 4 | 75% | 3.6 2023-09-27 | 2.65–3.4 | 3.4 | 3.6 | 3.6 | 3.6 |
| PFHpA | 4 | 75% | 3.6 2024-02-07 | 2.6–3.35 | 3.3 | 3.5 | 3.6 | 3.6 |
| PFHxA | 4 | 75% | 9.9 2024-02-07 | 7.2–7.95 | 9.2 | 9.7 | 9.9 | 9.9 |
| PFOA | 4 | 75% | 7.4 2023-09-27 | 5.28–6.28 | 6.6 | 7.1 | 7.4 | 7.4 |
Never detected (24): 11Cl-PF3OUdS, 4:2 FTS, 6:2 FTS, 8:2 FTS, 9Cl-PF3ONS, ADONA, HFPO-DA, NEtFOSAA, NFDHA, NMeFOSAA, PFDA, PFDoA, PFEESA, PFHpS, PFHxS, PFMBA, PFMPA, PFNA, PFOS, PFPeS, 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 2023-01-10 to 2026-04-06; 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, 2020 (Census replaced Connecticut's 8 counties with 9 planning regions in 2022+ files; SDWIS county-served records still use the 8 historic counties, so the 2020 county boundaries (the last vintage with them) are used for Connecticut.)
- EPA/USGS NHDPlus V2 (medium resolution) flowlines, Strahler order 2+
Data build d689ff4ca87e · 2026-10-18T04:04Z · UCMR 5 release Jul2026 · SDWIS 2026Q3. Data and methods.