Data & Methodology — Dauphin County

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

Contaminant Data — All Analytes

428 well testing events on record, covering 22 analytes. Data spans 1931 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. PA Avg
Manganese 266 1956–2023 88%
1520% of limit ↑ 201% above
Iron 282 1931–2023 86%
1588% of limit ↑ 173% above
PFOS municipal 245 2023–2025 42%
160% of limit ↑ 26% above
PFOA municipal 245 2023–2025 35%
108% of limit ~ typical
Radon 47 1993–2023 100%
16% of limit ↓ 88% below
Arsenic 77 1972–2023 87%
20% of limit ↓ 32% below
Nitrate 118 1931–2023 98%
21% of limit ~ typical
Chloride 162 1931–2023 74%
2% of limit ↓ 77% below
Fluoride 114 1953–2023 82%
2% of limit ↓ 44% below
HFPO-DA (GenX) municipal 204 2023–2025 0%
— —
Lead 51 1972–2023 12%
2% of limit ↓ 63% below
Nitrite 66 1976–2023 18%
2% of limit ↑ 30% above
PFHxS municipal 40 2023–2025 30%
38% of limit ~ typical
PFNA municipal 40 2023–2025 0%
— —
Sulfate 253 1931–2023 96%
21% of limit ↑ 21% above
Uranium 15 1993–2023 47%
3% of limit ↑ 45% above
Total Coliform 4 1993–2023 84%
— ~ typical
Sodium 233 1953–2023 96%
— ↓ 69% below
pH 296 1953–2023 100%
— ~ typical
PFBS municipal 208 2023–2025 36%
— ~ typical
Hardness 118 1931–2023 98%
— ~ typical
E. coli 4 1995–2023 22%
— ~ 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 Dauphin County

Of the 77 arsenic tests on record for Dauphin County (1972–2023), 13% found none, and half were below 1.1 µg/L.

Of the 162 chloride tests on record for Dauphin County (1931–2023), 26% found none, and half were below 4 mg/L.

Of the 114 fluoride tests on record for Dauphin County (1953–2023), 18% found none, and half were below 100 µg/L.

Of the 282 iron tests on record for Dauphin County (1931–2023), 14% found none, and half were below 1.6 mg/L.

Of the 51 lead tests on record for Dauphin County (1972–2023), 88% found none.

Of the 266 manganese tests on record for Dauphin County (1956–2023), 12% found none, and half were below 510 µg/L.

Of the 118 nitrate tests on record for Dauphin County (1931–2023), 2% found none, and half were below 2.05 mg/L.

Of the 205 pfoa tests on record for Dauphin County (2025), 63% found none.

Of the 205 pfos tests on record for Dauphin County (2025), 57% found none.

Of the 253 sulfate tests on record for Dauphin County (1931–2023), 4% found none, and half were below 50 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 266 samples
  • Iron 282 samples
  • PFOS 245 samples
  • PFOA 245 samples
  • Radon 47 samples
  • Arsenic 77 samples
  • Nitrate 118 samples
  • Chloride 162 samples
  • Fluoride 114 samples
  • HFPO-DA (GenX) 204 samples
  • Lead 51 samples
  • Nitrite 66 samples
  • Sulfate 253 samples
  • Uranium 15 samples
  • Sodium 233 samples
  • pH 296 samples
  • PFBS 208 samples
  • Hardness 118 samples

Limited data (<15 samples) — interpret with caution

  • Total Coliform 4 samples
  • E. coli 4 samples

Public vs. Private Water in Dauphin County

146 Active public water systems
294,267 Residents on public water
27% Households on private wells

Public water systems in Dauphin 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 Dauphin 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 Dauphin County Prevalence PA Average Source Year
Lead Heart disease rate 5.7% 7.2% 2020
Arsenic Cancer prevalence 6.9% 7.0% 2020
Arsenic Kidney disease rate 2.6% 3.0% 2020

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