Data & Methodology — Delaware County

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

Contaminant Data — All Analytes

93 well testing events on record, covering 19 analytes. Data spans 1925 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. PA Avg
PFOA municipal 54 2024–2025 74%
228% of limit ↑ 144% above
Radon 5 2020 100%
233% of limit ↑ 80% above
Manganese 35 1956–1983 66%
100% of limit ↓ 80% below
Iron 42 1925–1983 81%
55% of limit ↓ 91% below
PFOS municipal 54 2024–2025 41%
66% of limit ↓ 48% below
Chloride 50 1925–1983 100%
8% of limit ↓ 29% below
Nitrate 49 1925–2020 92%
27% of limit ↑ 52% above
Arsenic 33 1980–2020 48%
10% of limit ↓ 66% below
Fluoride 35 1956–1983 51%
2% of limit ↓ 44% below
HFPO-DA (GenX) municipal 54 2024–2025 0%
— —
Lead 26 1980–1983 4%
0% of limit ↓ 100% below
Nitrite 33 1980–2020 27%
2% of limit ↑ 33% above
PFHxS municipal 20 2024–2025 0%
— —
PFNA municipal 20 2024–2025 25%
78% of limit ~ typical
Sulfate 42 1925–1983 100%
12% of limit ↓ 29% below
Sodium 40 1925–1983 100%
— ↓ 48% below
pH 54 1956–2020 100%
— ~ typical
PFBS municipal 54 2024–2025 72%
— ~ typical
Hardness 42 1925–1983 100%
— ↓ 44% 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 PA.

Compare your result with Delaware County

Of the 33 arsenic tests on record for Delaware County (1980–2020), 52% found none.

Of the 50 chloride tests on record for Delaware County (1925–1983), 0% found none, and half were below 19 mg/L.

Of the 35 fluoride tests on record for Delaware County (1956–1983), 49% found none.

Of the 42 iron tests on record for Delaware County (1925–1983), 19% found none, and half were below 105 µg/L.

Of the 26 lead tests on record for Delaware County (1980–1983), 96% found none.

Of the 35 manganese tests on record for Delaware County (1956–1983), 34% found none.

Of the 49 nitrate tests on record for Delaware County (1925–2020), 8% found none, and half were below 2.5 mg/L.

Of the 34 pfoa tests on record for Delaware County (2025), 6% found none, and half were below 8.84 ng/L.

Of the 34 pfos tests on record for Delaware County (2025), 35% found none, and half were below 2.02 ng/L.

Of the 42 sulfate tests on record for Delaware County (1925–1983), 0% found none, and half were below 30.5 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • PFOA 54 samples
  • Manganese 35 samples
  • Iron 42 samples
  • PFOS 54 samples
  • Chloride 50 samples
  • Nitrate 49 samples
  • Arsenic 33 samples
  • Fluoride 35 samples
  • HFPO-DA (GenX) 54 samples
  • Lead 26 samples
  • Nitrite 33 samples
  • Sulfate 42 samples
  • Sodium 40 samples
  • pH 54 samples
  • PFBS 54 samples
  • Hardness 42 samples

Limited data (<15 samples) — interpret with caution

  • Radon 5 samples

Public vs. Private Water in Delaware County

23 Active public water systems
151,505 Residents on public water
18% Households on private wells

Public water systems in Delaware 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 Delaware 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 Delaware County Prevalence PA Average Source Year
Nitrate Cancer prevalence 6.9% 7.0% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Delaware 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

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