Full contaminant data, sample history, and sourcing for Nassau County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
18742 well testing events on record, covering
23 analytes.
Data spans 1935 to 2024.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. NY Avg
Iron
15506
1935–2023
87%
60% of limit
↓ 69% below
Manganese
15230
1949–2023
65%
0% of limit
↓ 100% below
PFOA
municipal
374
2023–2025
8%
132% of limit
~ typical
Nitrate
15474
1934–2022
98%
16% of limit
↑ 36% above
PFOS
municipal
374
2023–2025
2%
118% of limit
~ typical
Chloride
17777
1903–2023
100%
4% of limit
↓ 88% below
Lead
3469
1971–2022
5%
0% of limit
↓ 89% below
PFNA
municipal
374
2023–2025
3%
77% of limit
~ typical
Sulfate
11115
1934–2023
83%
7% of limit
↓ 50% below
Arsenic
2308
1971–2022
15%
10% of limit
↓ 46% below
Nitrite
15138
1947–2022
61%
0% of limit
↓ 88% below
Fluoride
6825
1934–2023
44%
2% of limit
↓ 55% below
HFPO-DA (GenX)
municipal
374
2023–2025
0%
—
—
PFHxS
municipal
374
2023–2025
2%
43% of limit
~ typical
Radon
9
2012–2016
100%
30% of limit
↓ 73% below
Uranium
22
2006–2022
32%
0% of limit
↓ 98% below
PFBS
municipal
374
2023–2025
1%
—
↓ 22% below
Hardness
15318
1934–2023
100%
—
↓ 86% below
Fecal Coliform
3
1977–2019
10%
—
~ typical
E. coli
4
2007–2022
0%
—
—
pH
16882
1947–2023
100%
—
↓ 21% below
Sodium
10355
1934–2023
97%
—
↓ 81% below
Total Coliform
4
1950–2022
93%
—
~ typical
Distribution shows the share of samples in each concentration band relative to the EPA Maximum Contaminant Level (MCL): Low = below half the MCL, Moderate = between half and the MCL, High = above the MCL. Analytes without an MCL (e.g. sodium, pH) show — in the limit columns. State average is based on county median values across NY.
Compare your result with Nassau County
Of the 2308 arsenic tests on record for Nassau County (1971–2022),
85% found none.
Of the 17777 chloride tests on record for Nassau County (1903–2023),
0% found none, and half were below 8.8 mg/L.
Of the 6825 fluoride tests on record for Nassau County (1934–2023),
56% found none.
Of the 15506 iron tests on record for Nassau County (1935–2023),
13% found none, and half were below 120 µg/L.
Of the 3469 lead tests on record for Nassau County (1971–2022),
95% found none.
Of the 15230 manganese tests on record for Nassau County (1949–2023),
35% found none.
Of the 15474 nitrate tests on record for Nassau County (1934–2022),
2% found none, and half were below 1.52 mg/L.
Of the 11115 sulfate tests on record for Nassau County (1934–2023),
17% found none, and half were below 10.9 mg/L.
Of the 22 uranium tests on record for Nassau County (2006–2022),
68% found none.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Iron 15506 samples
Manganese 15230 samples
Nitrate 15474 samples
Chloride 17777 samples
Lead 3469 samples
Sulfate 11115 samples
Arsenic 2308 samples
Nitrite 15138 samples
Fluoride 6825 samples
Uranium 22 samples
Hardness 15318 samples
pH 16882 samples
Sodium 10355 samples
Limited data (<15 samples) — interpret with caution
Radon 9 samples
Fecal Coliform 3 samples
E. coli 4 samples
Total Coliform 4 samples
No private-well PFAS data for Nassau County
We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Nassau County.
PFAS testing for private wells requires a dedicated lab panel (~$300–$500). If you are near a military base, airport, or industrial site, consider testing proactively. Learn more about PFAS →
CDC Health Outcome Correlations
Where contaminants detected in Nassau County have established associations with specific health outcomes, we cross-reference CDC PLACES county-level prevalence data. This is a contextual signal, not a causal claim.
This report aggregates data from the following public databases:
Water Quality Portal (WQP) — groundwater sample results for Nassau County from EPA, USGS, and state agencies. Browse WQP data →
EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for Nassau County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Nassau County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near Nassau County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Nassau County, used in contamination risk scoring. Superfund site search →
CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →
Methodology
Raw records are downloaded from the Water Quality Portal and normalized to µg/L (ppb). Records are deduplicated by sample ID and date, and certified outliers are excluded. Analyte names are mapped to EPA canonical forms. Detection rates, distribution bands, and MCL comparisons are computed from the normalized dataset.
Distribution bands use the EPA Maximum Contaminant Level as the threshold: concentrations below 50% of the MCL are classed as Low, between 50% and 100% as Moderate, and above 100% as High. For analytes without an MCL (sodium, hardness, pH), distribution is not computed.
State comparison uses the median of county median values across all counties in NY with at least one sample for that analyte.