Data & Methodology — Walworth County

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

Contaminant Data — All Analytes

213 well testing events on record, covering 20 analytes. Data spans 1945 to 2021.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. WI Avg
Iron 170 1945–2021 99%
329% of limit ↑ 39% above
Manganese 163 1945–2021 99%
60% of limit ↓ 56% below
Arsenic 23 1976–2021 83%
14% of limit ~ typical
PFOA municipal 44 2022–2025 16%
108% of limit ↑ 610% above
PFOS municipal 44 2022–2025 7%
103% of limit ↑ 74% above
Chloride 156 1945–2021 100%
1% of limit ↓ 73% below
Nitrate 138 1954–2021 86%
2% of limit ↓ 89% below
Fluoride 129 1945–2021 100%
5% of limit ~ typical
HFPO-DA (GenX) municipal 44 2022–2025 0%
— —
Lead 23 1976–2021 26%
0% of limit ↓ 52% below
Nitrite 62 1954–2021 74%
0% of limit ↓ 69% below
PFHxS municipal 44 2022–2025 16%
36% of limit ↑ 161% above
PFNA municipal 44 2022–2025 5%
6% of limit ↑ 94% above
Radon 7 2000–2001 100%
7% of limit ↓ 58% below
Sulfate 166 1945–2021 98%
7% of limit ~ typical
Uranium 19 1983–2021 74%
9% of limit ↑ 274% above
Hardness 172 1945–2021 100%
— ↑ 37% above
PFBS municipal 44 2022–2025 30%
— ↑ 198% above
pH 186 1945–2021 100%
— ~ typical
Sodium 102 1945–2021 100%
— ~ 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 WI.

Compare your result with Walworth County

Of the 23 arsenic tests on record for Walworth County (1976–2021), 17% found none, and half were below 1.2 µg/L.

Of the 156 chloride tests on record for Walworth County (1945–2021), 0% found none, and half were below 3 mg/L.

Of the 129 fluoride tests on record for Walworth County (1945–2021), 0% found none, and half were below 200 µg/L.

Of the 170 iron tests on record for Walworth County (1945–2021), 1% found none, and half were below 978 µg/L.

Of the 23 lead tests on record for Walworth County (1976–2021), 74% found none.

Of the 163 manganese tests on record for Walworth County (1945–2021), 1% found none, and half were below 30 µg/L.

Of the 138 nitrate tests on record for Walworth County (1954–2021), 14% found none, and half were below 90 µg/L.

Of the 166 sulfate tests on record for Walworth County (1945–2021), 2% found none, and half were below 16.2 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 170 samples
  • Manganese 163 samples
  • Arsenic 23 samples
  • PFOA 44 samples
  • PFOS 44 samples
  • Chloride 156 samples
  • Nitrate 138 samples
  • Fluoride 129 samples
  • HFPO-DA (GenX) 44 samples
  • Lead 23 samples
  • Nitrite 62 samples
  • PFHxS 44 samples
  • PFNA 44 samples
  • Sulfate 166 samples
  • Uranium 19 samples
  • Hardness 172 samples
  • PFBS 44 samples
  • pH 186 samples
  • Sodium 102 samples

Limited data (<15 samples) — interpret with caution

  • Radon 7 samples

CDC Health Outcome Correlations

Where contaminants detected in Walworth 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 Walworth County Prevalence WI Average Source Year
Arsenic Cancer prevalence 6.0% 7.0% 2020
Arsenic Kidney disease rate 2.5% 2.9% 2020

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

Last updated: 2026-07-15

Full methodology →