Data & Methodology — Mille Lacs County

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

Contaminant Data — All Analytes

121 well testing events on record, covering 18 analytes. Data spans 1957 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MN Avg
Manganese 62 1965–2025 85%
260% of limit ↓ 32% below
PFOS municipal 8 2024–2025 62%
532% of limit —
Iron 62 1965–2025 84%
163% of limit ↓ 70% below
PFOA municipal 14 2006–2025 50%
300% of limit ↑ 7900% above
Chloride 105 1965–2025 100%
7% of limit ↓ 42% below
Nitrite 47 1992–1997 36%
2% of limit ↓ 33% below
Nitrate 66 1965–2006 55%
1% of limit ↓ 93% below
Arsenic 28 1995–2025 21%
14% of limit ↓ 82% below
Fluoride 47 1965–2025 79%
5% of limit ↓ 41% below
HFPO-DA (GenX) municipal 10 2022–2025 0%
— —
Lead 30 1993–2025 13%
2% of limit ↓ 96% below
PFHxS municipal 5 2024 20%
40% of limit —
PFNA municipal 13 2006–2025 23%
82% of limit —
Sulfate 87 1965–2025 94%
5% of limit ↓ 78% below
Sodium 59 1968–2025 100%
— ↓ 69% below
pH 54 1965–1998 100%
— ~ typical
PFBS municipal 4 2024 0%
— —
Hardness 33 1965–1993 100%
— ↓ 23% 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 MN.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 62 samples
  • Iron 62 samples
  • Chloride 105 samples
  • Nitrite 47 samples
  • Nitrate 66 samples
  • Arsenic 28 samples
  • Fluoride 47 samples
  • Lead 30 samples
  • Sulfate 87 samples
  • Sodium 59 samples
  • pH 54 samples
  • Hardness 33 samples

Limited data (<15 samples) — interpret with caution

  • PFOS 8 samples
  • PFOA 14 samples
  • HFPO-DA (GenX) 10 samples
  • PFHxS 5 samples
  • PFNA 13 samples

Public vs. Private Water in Mille Lacs County

93 Active public water systems
20,644 Residents on public water

Public water systems in Mille Lacs 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 Mille Lacs 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 Mille Lacs County Prevalence MN Average Source Year
Lead Heart disease rate 7.7% 6.6% 2020
Nitrate Cancer prevalence 6.1% 7.0% 2020

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