- PWSID
- CT0340011
- State
- Connecticut
- System type
- community water system (CWS)
- Population served
- 62,055
- City
- Danbury
- Counties
- Fairfield County
- Primary source water
- surface water
- UCMR 5 sampling
- 2024-12-10 to 2025-09-17 · 2 entry point(s) · water types: SW
- Service-area boundary
- authoritative
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.
Water purchased from
- Aquarion-Berkshire (CT0090292)
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) | 5.4 | 4.53 | 4 |
| PFOS (ppt) | <MRL | 0 | 4 |
| Hazard Index | 0.002 | 0.002 | 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 Connecticut guidance levels
| Highest single result | Worst entry-point average* | Connecticut | |
|---|---|---|---|
| PFOS (ppt) | 0 | 0 | 10 (guidance) |
| PFNA (ppt) | 0 | 0 | 12 (guidance) |
| PFOA (ppt) | 5.4 | 4.53 | 16 (guidance) |
| HFPO-DA (GenX) (ppt) | 0 | 0 | 19 (guidance) |
| PFHxS (ppt) | 0 | 0 | 49 (guidance) |
| PFHxA (ppt) | 3.6 | 1.73 | 240 (guidance) |
| PFBS (ppt) | 4.3 | 4.03 | 760 (guidance) |
| PFBA (ppt) | 0 | 0 | 1,800 (guidance) |
| 6:2 Cl-PFESA (ppt) | 0 | 0 | 2 (guidance) |
| 8:2 Cl-PFESA (ppt) | 0 | 0 | 5 (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 2024-12-10 to 2025-09-17 · 2 entry point(s) · water types: SW · 8 sampling visits. PFAS in ppt (ng/L).
| Date | Entry point | Event | PFOA | PFOS | HI | Other detections |
|---|---|---|---|---|---|---|
| 2024-12-10 | Margerie TP (SW) | SE1 | 4.9 | <4 | 0 | PFHxA 3.3, PFPeA 3.3 |
| 2024-12-10 | West Lake TP (SW) | SE1 | 5.4 | <4 | 0.002 | PFPeA 3.2 |
| 2025-03-18 | Margerie TP (SW) | SE2 | <4 | <4 | 0 | none |
| 2025-03-18 | West Lake TP (SW) | SE2 | 4.1 | <4 | 0.002 | none |
| 2025-06-11 | Margerie TP (SW) | SE3 | 4.4 | <4 | 0 | none |
| 2025-06-11 | West Lake TP (SW) | SE3 | 4.2 | <4 | 0.002 | none |
| 2025-09-17 | Margerie TP (SW) | SE4 | 5 | <4 | 0 | PFHxA 3.6, PFPeA 3.4 |
| 2025-09-17 | West Lake TP (SW) | SE4 | 4.4 | <4 | 0.002 | 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
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.
Margerie TP facility 38771 · sample point 3 · surface water
| Compound | MRL | 2024-12-10 SE1 | 2025-03-18 SE2 | 2025-06-11 SE3 | 2025-09-17 SE4 |
|---|---|---|---|---|---|
| PFHxA | 3 ppt | 3.3 | < 3 | < 3 | 3.6 |
| PFOA | 4 ppt | 4.9 | < 4 | 4.4 | 5 |
| PFPeA | 3 ppt | 3.3 | < 3 | < 3 | 3.4 |
| 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 |
| PFBS | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| 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 |
| 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 |
West Lake TP facility 46152 · sample point 3 · surface water
| Compound | MRL | 2024-12-10 SE1 | 2025-03-18 SE2 | 2025-06-11 SE3 | 2025-09-17 SE4 |
|---|---|---|---|---|---|
| PFBS | 3 ppt | 3.5 | 4.3 | 4 | 4.3 |
| PFOA | 4 ppt | 5.4 | 4.1 | 4.2 | 4.4 |
| PFPeA | 3 ppt | 3.2 | < 3 | < 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 |
| PFHxA | 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 |
|---|---|---|---|---|---|---|---|---|
| PFOA | 8 | 88% | 5.4 2024-12-10 | 4.05–4.55 | 4.4 | 4.9 | 5.4 | 5.4 |
| PFBS | 8 | 50% | 4.3 2025-03-18 | 2.01–3.51 | <MRL | 4 | 4.3 | 4.3 |
| PFPeA | 8 | 38% | 3.4 2025-09-17 | 1.24–3.11 | <MRL | 3.2 | 3.4 | 3.4 |
| PFHxA | 8 | 25% | 3.6 2025-09-17 | 0.86–3.11 | <MRL | <MRL | 3.6 | 3.6 |
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, 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.