Data & Methodology — Warren County

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

Contaminant Data — All Analytes

189 well testing events on record, covering 20 analytes. Data spans 1918 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. NJ Avg
PFOA municipal 67 2022–2025 37%
128% of limit ↑ 104% above
PFOS municipal 67 2022–2025 19%
152% of limit ↑ 662% above
Uranium 14 1992–2007 71%
12% of limit ↑ 214% above
Manganese 127 1968–2022 63%
4% of limit ↓ 98% below
Nitrate 138 1968–2022 83%
23% of limit —
Chloride 128 1968–2022 100%
7% of limit ↓ 91% below
Iron 128 1968–2022 60%
4% of limit ↓ 99% below
PFNA municipal 68 2022–2025 3%
146% of limit —
Arsenic 116 1986–2022 35%
1% of limit ↓ 96% below
Fluoride 118 1968–2022 58%
2% of limit ↓ 73% below
HFPO-DA (GenX) municipal 68 2022–2025 0%
— —
Lead 108 1986–2022 31%
1% of limit ↓ 99% below
Nitrite 130 1979–2022 18%
1% of limit ↓ 67% below
PFHxS municipal 67 2022–2025 10%
33% of limit ↑ 1550% above
Radon 8 2000–2007 100%
32% of limit ↓ 93% below
Sulfate 128 1968–2022 100%
8% of limit ↓ 50% below
Hardness 123 1968–2022 100%
— ↑ 167% above
pH 138 1968–2022 100%
— ~ typical
PFBS municipal 66 2022–2025 9%
— ↑ 817% above
Sodium 123 1968–2022 100%
— ↓ 96% below

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 NJ.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • PFOA 67 samples
  • PFOS 67 samples
  • Manganese 127 samples
  • Nitrate 138 samples
  • Chloride 128 samples
  • Iron 128 samples
  • PFNA 68 samples
  • Arsenic 116 samples
  • Fluoride 118 samples
  • HFPO-DA (GenX) 68 samples
  • Lead 108 samples
  • Nitrite 130 samples
  • PFHxS 67 samples
  • Sulfate 128 samples
  • Hardness 123 samples
  • pH 138 samples
  • PFBS 66 samples
  • Sodium 123 samples

Limited data (<15 samples) — interpret with caution

  • Uranium 14 samples
  • Radon 8 samples

Public vs. Private Water in Warren County

221 Active public water systems
109,398 Residents on public water

Public water systems in Warren County are regulated by the EPA and must test and report contaminant levels. Private well owners are responsible for their own testing — there is no routine monitoring of private wells by any government agency.

CDC Health Outcome Correlations

Where contaminants detected in Warren 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 Warren County Prevalence NJ Average Source Year
Nitrate Cancer prevalence 7.5% 6.2% 2020
Uranium Kidney disease rate 2.8% 2.7% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Warren 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 NJ with at least one sample for that analyte.

Last updated: 2026-07-15

Full methodology →