Data & Methodology — Mercer County

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

Contaminant Data — All Analytes

538 well testing events on record, covering 22 analytes. Data spans 1923 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. NJ Avg
PFOA municipal 40 2021–2025 42%
202% of limit ~ typical
PFOS municipal 40 2021–2025 40%
196% of limit ~ typical
Manganese 239 1950–2022 79%
80% of limit ↓ 83% below
Iron 248 1925–2022 80%
17% of limit ↓ 96% below
Radon 91 1985–2012 99%
12% of limit ↓ 71% below
Nitrate 227 1925–2022 90%
25% of limit ~ typical
Arsenic 151 1983–2022 68%
11% of limit ↓ 34% below
PFHxS municipal 39 2021–2025 23%
32% of limit ↓ 27% below
Lead 184 1972–2022 31%
2% of limit ↓ 93% below
Chloride 252 1925–2022 100%
7% of limit ↓ 77% below
Uranium 71 1985–2022 83%
5% of limit ~ typical
Fluoride 196 1949–2022 74%
2% of limit ↓ 52% below
HFPO-DA (GenX) municipal 40 2021–2025 0%
— —
Nitrite 186 1983–2022 18%
1% of limit ↓ 35% below
PFNA municipal 39 2021–2025 5%
43% of limit ~ typical
Sulfate 248 1925–2022 99%
10% of limit ↓ 42% below
Total Coliform 1 2006–2022 0%
— —
Sodium 251 1949–2022 100%
— ↓ 73% below
pH 456 1949–2022 100%
— ~ typical
PFBS municipal 36 2021–2025 11%
— ~ typical
Hardness 250 1925–2022 100%
— ~ typical
E. coli 1 2006–2022 0%
— —

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.

Compare your result with Mercer County

Of the 151 arsenic tests on record for Mercer County (1983–2022), 32% found none, and half were below 0.36 µg/L.

Of the 252 chloride tests on record for Mercer County (1925–2022), 0% found none, and half were below 17 mg/L.

Of the 196 fluoride tests on record for Mercer County (1949–2022), 26% found none, and half were below 100 µg/L.

Of the 248 iron tests on record for Mercer County (1925–2022), 20% found none, and half were below 21.1 µg/L.

Of the 184 lead tests on record for Mercer County (1972–2022), 69% found none.

Of the 239 manganese tests on record for Mercer County (1950–2022), 21% found none, and half were below 21 µg/L.

Of the 227 nitrate tests on record for Mercer County (1925–2022), 10% found none, and half were below 1.8 mg/L.

Of the 248 sulfate tests on record for Mercer County (1925–2022), 1% found none, and half were below 24 mg/L.

Of the 71 uranium tests on record for Mercer County (1985–2022), 17% found none, and half were below 1.2 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • PFOA 40 samples
  • PFOS 40 samples
  • Manganese 239 samples
  • Iron 248 samples
  • Radon 91 samples
  • Nitrate 227 samples
  • Arsenic 151 samples
  • PFHxS 39 samples
  • Lead 184 samples
  • Chloride 252 samples
  • Uranium 71 samples
  • Fluoride 196 samples
  • HFPO-DA (GenX) 40 samples
  • Nitrite 186 samples
  • PFNA 39 samples
  • Sulfate 248 samples
  • Sodium 251 samples
  • pH 456 samples
  • PFBS 36 samples
  • Hardness 250 samples

Limited data (<15 samples) — interpret with caution

  • Total Coliform 1 sample
  • E. coli 1 sample

Public vs. Private Water in Mercer County

97 Active public water systems
323,956 Residents on public water
11% Households on private wells

Public water systems in Mercer 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 Mercer 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 Mercer County Prevalence NJ Average Source Year
Lead Heart disease rate 5.1% 5.8% 2020
Arsenic Cancer prevalence 6.1% 6.2% 2020
Arsenic Kidney disease rate 2.5% 2.7% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Mercer 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: 2026-08-04

Full methodology →