Data & Methodology — Otter Tail County

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

Contaminant Data — All Analytes

1055 well testing events on record, covering 21 analytes. Data spans 1960 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MN Avg
Manganese 581 1964–2025 83%
262% of limit ↓ 31% below
Iron 717 1964–2025 78%
408% of limit ↓ 26% below
PFOA municipal 33 2007–2025 58%
165% of limit ↑ 4300% above
Nitrate 469 1964–2013 78%
64% of limit ↑ 222% above
Arsenic 285 1993–2025 72%
43% of limit ↓ 47% below
PFOS municipal 28 2023–2025 54%
26% of limit —
PFHxS municipal 19 2023–2025 58%
18% of limit —
Sulfate 623 1964–2025 91%
6% of limit ↓ 76% below
Lead 313 1993–2025 10%
1% of limit ↓ 98% below
Nitrite 368 1973–2013 22%
1% of limit ↓ 67% below
Chloride 929 1964–2025 99%
3% of limit ↓ 78% below
Fluoride 512 1964–2025 84%
4% of limit ↓ 52% below
HFPO-DA (GenX) municipal 13 2023–2025 0%
— —
PFNA municipal 15 2007–2025 7%
6% of limit —
Radon 23 1993–2013 100%
9% of limit ↓ 89% below
Uranium 33 1993–2013 39%
2% of limit ↓ 36% below
Hardness 229 1964–2013 100%
— ~ typical
PFBS municipal 21 2023–2025 62%
— —
E. coli 1 1999–2018 6%
— —
pH 529 1964–2013 100%
— ~ typical
Sodium 586 1964–2025 100%
— ↓ 90% 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 581 samples
  • Iron 717 samples
  • PFOA 33 samples
  • Nitrate 469 samples
  • Arsenic 285 samples
  • PFOS 28 samples
  • PFHxS 19 samples
  • Sulfate 623 samples
  • Lead 313 samples
  • Nitrite 368 samples
  • Chloride 929 samples
  • Fluoride 512 samples
  • PFNA 15 samples
  • Radon 23 samples
  • Uranium 33 samples
  • Hardness 229 samples
  • PFBS 21 samples
  • pH 529 samples
  • Sodium 586 samples

Limited data (<15 samples) — interpret with caution

  • HFPO-DA (GenX) 13 samples
  • E. coli 1 sample

Public vs. Private Water in Otter Tail County

279 Active public water systems
44,606 Residents on public water

Public water systems in Otter Tail 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 Otter Tail 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 Otter Tail County Prevalence MN Average Source Year
Arsenic Cancer prevalence 6.1% 7.0% 2020
Arsenic Kidney disease rate 3.5% 2.9% 2020
Lead Heart disease rate 8.4% 6.6% 2020

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