Data & Methodology — Douglas County

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

Contaminant Data — All Analytes

893 well testing events on record, covering 18 analytes. Data spans 1936 to 2022.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. WI Avg
Iron 548 1949–1986 49%
103% of limit ↓ 56% below
Manganese 549 1954–1986 34%
110% of limit ~ typical
Chloride 567 1936–2005 92%
0% of limit ↓ 96% below
Sulfate 549 1936–1986 91%
3% of limit ↓ 63% below
Lead 300 1976–1986 0%
— —
Fluoride 358 1954–1986 18%
5% of limit ~ typical
Nitrate 544 1949–1986 58%
0% of limit ↓ 97% below
Nitrite 14 1962–1982 79%
1% of limit ~ typical
PFHxS municipal 15 2022–2023 0%
— —
PFNA municipal 15 2022–2023 7%
2% of limit ↓ 49% below
PFOA municipal 15 2022–2023 47%
4% of limit ↓ 77% below
PFOS municipal 15 2022–2023 0%
— —
Arsenic 7 1976 43%
20% of limit ↑ 29% above
HFPO-DA (GenX) municipal 15 2022–2023 0%
— —
Sodium 538 1954–1986 100%
— ↓ 87% below
pH 877 1949–2005 100%
— ~ typical
PFBS municipal 15 2022–2023 0%
— —
Hardness 554 1936–1986 100%
— ↓ 93% 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 WI.

Compare your result with Douglas County

Of the 567 chloride tests on record for Douglas County (1936–2005), 8% found none, and half were below 400 µg/L.

Of the 358 fluoride tests on record for Douglas County (1954–1986), 82% found none.

Of the 548 iron tests on record for Douglas County (1949–1986), 51% found none.

Of the 300 lead tests on record for Douglas County (1976–1986), 100% found none.

Of the 549 manganese tests on record for Douglas County (1954–1986), 66% found none.

Of the 544 nitrate tests on record for Douglas County (1949–1986), 42% found none, and half were below 20 µg/L.

Of the 549 sulfate tests on record for Douglas County (1936–1986), 9% found none, and half were below 6.1 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 548 samples
  • Manganese 549 samples
  • Chloride 567 samples
  • Sulfate 549 samples
  • Lead 300 samples
  • Fluoride 358 samples
  • Nitrate 544 samples
  • PFHxS 15 samples
  • PFNA 15 samples
  • PFOA 15 samples
  • PFOS 15 samples
  • HFPO-DA (GenX) 15 samples
  • Sodium 538 samples
  • pH 877 samples
  • PFBS 15 samples
  • Hardness 554 samples

Limited data (<15 samples) — interpret with caution

  • Nitrite 14 samples
  • Arsenic 7 samples

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

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