- PWSID
- NY5903150
- State
- New York
- System type
- community water system (CWS)
- Population served
- 300
- City
- Mt. Kisco
- Counties
- Westchester County
- Primary source water
- groundwater under the influence of surface water
- UCMR 5 sampling
- 2023-01-17 to 2023-10-24 · 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
PFOS ≥ 3 × its limit highest single result
PFOS ≥ 3 × its limit worst entry-point average
Open on the New York map · All New York 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) | 27.8 | 24.95 | 4 |
| PFOS (ppt) | 106 | 94.45 | 4 |
| Hazard Index | 5.663 | 5.063 | 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 New York standards
| Highest single result | Worst entry-point average* | New York | |
|---|---|---|---|
| PFOA (ppt) | 27.8 | 24.95 | 10 |
| PFOS (ppt) | 106 | 94.45 | 10 |
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 2023-01-17 to 2023-10-24 · 1 entry point(s) · water types: GU · 4 sampling visits. PFAS in ppt (ng/L).
| Date | Entry point | Event | PFOA | PFOS | HI | Other detections |
|---|---|---|---|---|---|---|
| 2023-01-17 | Control Room (GU) | SE1 | 24.8 | 95 | 5.533 | PFBA 28.8, PFHpA 43.1, PFHxA 65, PFPeA 102.5, PFPeS 7 |
| 2023-07-18 | Control Room (GU) | SE2 | 21.7 | 85.8 | 4.133 | PFBA 23.6, PFHpA 35.6, PFHxA 63.1, PFPeA 83.3, PFPeS 5.9 |
| 2023-08-30 | Control Room (GU) | SE3 | 25.5 | 91 | 4.923 | PFBA 27.4, PFHpA 41.2, PFHxA 67.9, PFPeA 94.6, PFPeS 6.1 |
| 2023-10-24 | Control Room (GU) | SE4 | 27.8 | 106 | 5.663 | PFBA 30.5, PFHpA 45.5, PFHxA 69, PFPeA 106, PFPeS 6.7 |
“<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.
Control Room facility 20001 · sample point EP001 · groundwater under the influence of surface water
| Compound | MRL | 2023-01-17 SE1 | 2023-07-18 SE2 | 2023-08-30 SE3 | 2023-10-24 SE4 |
|---|---|---|---|---|---|
| PFBA | 5 ppt | 28.8 | 23.6 | 27.4 | 30.5 |
| PFBS | 3 ppt | 6.1 | 4.9 | 5.5 | 5.6 |
| PFHpA | 3 ppt | 43.1 | 35.6 | 41.2 | 45.5 |
| PFHxA | 3 ppt | 65 | 63.1 | 67.9 | 69 |
| PFHxS | 3 ppt | 51 | 41.3 | 44.8 | 51.6 |
| PFNA | 4 ppt | 4.3 | < 4 | 4.4 | 5 |
| PFOA | 4 ppt | 24.8 | 21.7 | 25.5 | 27.8 |
| PFOS | 4 ppt | 95 | 85.8 | 91 | 106 |
| PFPeA | 3 ppt | 102.5 | 83.3 | 94.6 | 106 |
| PFPeS | 4 ppt | 7 | 5.9 | 6.1 | 6.7 |
| 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 |
| PFMBA | 3 ppt | < 3 | < 3 | < 3 | < 3 |
| PFMPA | 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 |
|---|---|---|---|---|---|---|---|---|
| PFBA | 4 | 100% | 30.5 2023-10-24 | 27.57–27.57 | 27.4 | 28.8 | 30.5 | 30.5 |
| PFBS | 4 | 100% | 6.1 2023-01-17 | 5.53–5.53 | 5.5 | 5.6 | 6.1 | 6.1 |
| PFHpA | 4 | 100% | 45.5 2023-10-24 | 41.35–41.35 | 41.2 | 43.1 | 45.5 | 45.5 |
| PFHxA | 4 | 100% | 69 2023-10-24 | 66.25–66.25 | 65 | 67.9 | 69 | 69 |
| PFHxS | 4 | 100% | 51.6 2023-10-24 | 47.17–47.17 | 44.8 | 51 | 51.6 | 51.6 |
| PFOA | 4 | 100% | 27.8 2023-10-24 | 24.95–24.95 | 24.8 | 25.5 | 27.8 | 27.8 |
| PFOS | 4 | 100% | 106 2023-10-24 | 94.45–94.45 | 91 | 95 | 106 | 106 |
| PFPeA | 4 | 100% | 106 2023-10-24 | 96.6–96.6 | 94.6 | 102.5 | 106 | 106 |
| PFPeS | 4 | 100% | 7 2023-01-17 | 6.42–6.42 | 6.1 | 6.7 | 7 | 7 |
| PFNA | 4 | 75% | 5 2023-10-24 | 3.42–4.42 | 4.3 | 4.4 | 5 | 5 |
Never detected (20): 11Cl-PF3OUdS, 4:2 FTS, 6:2 FTS, 8:2 FTS, 9Cl-PF3ONS, ADONA, HFPO-DA, NEtFOSAA, NFDHA, NMeFOSAA, PFDA, PFDoA, PFEESA, PFHpS, PFMBA, PFMPA, 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 2023-01-03 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 171ad949e257 · 2026-10-18T04:10Z · UCMR 5 release Jul2026 · SDWIS 2026Q3. Data and methods.