Data & Methodology — Chester County

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

Contaminant Data — All Analytes

2130 well testing events on record, covering 22 analytes. Data spans 1908 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. PA Avg
PFOA municipal 518 2023–2025 67%
136% of limit ↑ 46% above
PFOS municipal 516 2023–2025 51%
112% of limit ~ typical
Radon 759 1986–2021 100%
18% of limit ↓ 86% below
Manganese 1252 1957–2023 70%
40% of limit ↓ 92% below
Nitrate 1596 1925–2023 91%
31% of limit ↑ 74% above
Iron 1278 1925–2023 68%
13% of limit ↓ 98% below
Lead 707 1973–2023 26%
7% of limit ↑ 44% above
Nitrite 1496 1973–2023 17%
1% of limit ↓ 27% below
Chloride 1450 1925–2023 100%
5% of limit ↓ 55% below
Sulfate 1311 1925–2023 98%
9% of limit ↓ 50% below
Arsenic 602 1974–2023 39%
10% of limit ↓ 66% below
Fluoride 1000 1949–2023 40%
2% of limit ↓ 44% below
HFPO-DA (GenX) municipal 480 2023–2025 0%
82% of limit ↑ 261% above
PFHxS municipal 95 2023–2025 7%
35% of limit ↓ 24% below
PFNA municipal 95 2023–2025 2%
52% of limit ↓ 23% below
Uranium 260 1986–2021 47%
1% of limit ↓ 71% below
Total Coliform 1 1994–2021 42%
— ~ typical
Sodium 1070 1925–2023 100%
— ↓ 56% below
pH 1904 1949–2023 100%
— ~ typical
PFBS municipal 480 2023–2025 57%
— ~ typical
Hardness 1099 1925–2023 100%
— ↓ 49% below
E. coli 1 1994–2021 44%
— ~ 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 PA.

Compare your result with Chester County

Of the 602 arsenic tests on record for Chester County (1974–2023), 61% found none.

Of the 1450 chloride tests on record for Chester County (1925–2023), 0% found none, and half were below 12 mg/L.

Of the 1000 fluoride tests on record for Chester County (1949–2023), 60% found none.

Of the 1278 iron tests on record for Chester County (1925–2023), 32% found none, and half were below 11.3 µg/L.

Of the 707 lead tests on record for Chester County (1973–2023), 74% found none.

Of the 1252 manganese tests on record for Chester County (1957–2023), 30% found none, and half were below 6 µg/L.

Of the 1596 nitrate tests on record for Chester County (1925–2023), 9% found none, and half were below 2.7 mg/L.

Of the 423 pfoa tests on record for Chester County (2025), 28% found none, and half were below 3.9 ng/L.

Of the 421 pfos tests on record for Chester County (2025), 43% found none, and half were below 2.24 ng/L.

Of the 1311 sulfate tests on record for Chester County (1925–2023), 2% found none, and half were below 21.1 mg/L.

Of the 260 uranium tests on record for Chester County (1986–2021), 53% found none.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • PFOA 518 samples
  • PFOS 516 samples
  • Radon 759 samples
  • Manganese 1252 samples
  • Nitrate 1596 samples
  • Iron 1278 samples
  • Lead 707 samples
  • Nitrite 1496 samples
  • Chloride 1450 samples
  • Sulfate 1311 samples
  • Arsenic 602 samples
  • Fluoride 1000 samples
  • HFPO-DA (GenX) 480 samples
  • Uranium 260 samples
  • Sodium 1070 samples
  • pH 1904 samples
  • PFBS 480 samples
  • Hardness 1099 samples

Limited data (<15 samples) — interpret with caution

  • Total Coliform 1 sample
  • E. coli 1 sample

Public vs. Private Water in Chester County

271 Active public water systems
301,923 Residents on public water
41% Households on private wells

Public water systems in Chester 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 Chester 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 Chester County Prevalence PA Average Source Year
Arsenic Cancer incidence rate 422.8% 448.6% 2022
Arsenic Cancer prevalence 7.1% 7.0% 2020
Arsenic Kidney disease rate 2.6% 3.0% 2020
Lead Heart disease rate 4.9% 7.2% 2020

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

Last updated: 2026-08-04

Full methodology →