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

139 well testing events on record, covering 19 analytes. Data spans 1946 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MN Avg
Manganese 92 1964–2007 95%
414% of limit ~ typical
Iron 95 1964–2007 94%
447% of limit ~ typical
PFOA municipal 17 2005–2025 82%
156% of limit ↑ 4047% above
Arsenic 45 1985–2006 100%
47% of limit ↓ 42% below
PFOS municipal 10 2024–2025 90%
30% of limit —
Sulfate 103 1964–2007 97%
10% of limit ↓ 59% below
Lead 44 1994–2006 89%
1% of limit ↓ 98% below
Nitrate 66 1964–2007 80%
0% of limit ↓ 100% below
Chloride 107 1964–2007 100%
2% of limit ↓ 87% below
Fluoride 74 1964–2007 95%
5% of limit ↓ 44% below
HFPO-DA (GenX) municipal 2 2024–2025 0%
— —
Nitrite 46 1973–2007 87%
0% of limit ↓ 98% below
PFHxS municipal 2 2024–2025 100%
80% of limit —
PFNA municipal 6 2024–2025 67%
6% of limit —
Uranium 35 2006 100%
5% of limit ↑ 24% above
Sodium 76 1964–2007 100%
— ↓ 80% below
pH 79 1964–1997 100%
— ~ typical
PFBS municipal 2 2024–2025 50%
— —
Hardness 24 1964–1985 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 MN.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 92 samples
  • Iron 95 samples
  • PFOA 17 samples
  • Arsenic 45 samples
  • Sulfate 103 samples
  • Lead 44 samples
  • Nitrate 66 samples
  • Chloride 107 samples
  • Fluoride 74 samples
  • Nitrite 46 samples
  • Uranium 35 samples
  • Sodium 76 samples
  • pH 79 samples
  • Hardness 24 samples

Limited data (<15 samples) — interpret with caution

  • PFOS 10 samples
  • PFNA 6 samples

Public vs. Private Water in Douglas County

153 Active public water systems
30,896 Residents on public water

Public water systems in Douglas 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 Douglas 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 Douglas County Prevalence MN Average Source Year
Arsenic Cancer prevalence 8.7% 7.0% 2020
Arsenic Kidney disease rate 2.4% 2.9% 2020
Lead Heart disease rate 5.2% 6.6% 2020

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

Last updated: 2026-07-15

Full methodology →