Data & Methodology — Suffolk County

Full contaminant data, sample history, and sourcing for Suffolk County. For readers who want to go beyond the summary.

Contaminant Data — All Analytes

17518 well testing events on record, covering 23 analytes. Data spans 1919 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. NY Avg
Manganese 13999 1919–2023 56%
80% of limit ↓ 24% below
Iron 14619 1919–2023 68%
60% of limit ↓ 62% below
Nitrate 12337 1919–2023 78%
17% of limit ↑ 109% above
PFOA municipal 584 2023–2025 4%
128% of limit —
PFOS municipal 584 2023–2025 3%
120% of limit —
Arsenic 1399 1919–2022 23%
10% of limit ↓ 75% below
Chloride 13921 1919–2023 100%
4% of limit ↓ 93% below
Sulfate 11115 1919–2023 97%
3% of limit ↓ 80% below
PFHxS municipal 584 2023–2025 4%
39% of limit —
Lead 2181 1971–2022 4%
0% of limit ↓ 99% below
Nitrite 10864 1919–2023 33%
0% of limit ↓ 68% below
Fluoride 4325 1934–2023 30%
2% of limit ↓ 50% below
HFPO-DA (GenX) municipal 584 2023–2025 0%
— —
PFNA municipal 584 2023–2025 1%
57% of limit —
Radon 26 2012–2016 100%
35% of limit ↓ 73% below
Uranium 71 2006–2022 32%
0% of limit ↓ 98% below
E. coli 13 2007–2022 6%
— —
Fecal Coliform 14 1980–2019 17%
— —
Hardness 11437 1919–2023 100%
— ↓ 78% below
PFBS municipal 584 2023–2025 1%
— —
pH 16044 1919–2023 100%
— ~ typical
Sodium 11334 1919–2023 100%
— ↓ 84% below
Total Coliform 16 1980–2022 3%
— —

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.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 13999 samples
  • Iron 14619 samples
  • Nitrate 12337 samples
  • Arsenic 1399 samples
  • Chloride 13921 samples
  • Sulfate 11115 samples
  • Lead 2181 samples
  • Nitrite 10864 samples
  • Fluoride 4325 samples
  • Radon 26 samples
  • Uranium 71 samples
  • Hardness 11437 samples
  • pH 16044 samples
  • Sodium 11334 samples
  • Total Coliform 16 samples

Limited data (<15 samples) — interpret with caution

  • E. coli 13 samples
  • Fecal Coliform 14 samples

No private-well PFAS data for Suffolk County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Suffolk 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 Suffolk 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.

Contaminant Associated Condition Suffolk County Prevalence NY Average Source Year
Arsenic Cancer prevalence 7.0% 6.7% 2020
Arsenic Kidney disease rate 2.8% 2.9% 2020
Lead Heart disease rate 4.7% 6.4% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Suffolk County CDC PLACES data →

Data Sources

This report aggregates data from the following public databases:

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.

Last updated: 2026-07-15

Full methodology →