Data & Methodology — Polk County

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

Contaminant Data — All Analytes

543 well testing events on record, covering 18 analytes. Data spans 1955 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MN Avg
Iron 118 1964–2023 79%
350% of limit ↓ 51% below
Manganese 117 1964–2023 96%
124% of limit ↓ 75% below
Arsenic 29 1991–2023 86%
109% of limit ↑ 27% above
Nitrate 474 1964–2015 74%
27% of limit ~ typical
Lead 60 1991–2023 12%
67% of limit ↑ 49% above
Chloride 131 1964–2025 100%
2% of limit ↓ 74% below
Sulfate 121 1964–2023 99%
13% of limit ↓ 32% below
Fluoride 62 1964–2023 98%
8% of limit ~ typical
HFPO-DA (GenX) municipal 6 2023–2025 0%
— —
Nitrite 447 1991–2015 57%
2% of limit ↑ 49% above
PFHxS municipal 5 2023–2025 0%
— —
PFNA municipal 6 2023–2025 0%
— —
PFOA municipal 8 2023–2025 25%
45% of limit ↓ 89% below
PFOS municipal 8 2023–2025 25%
13% of limit ↓ 93% below
Hardness 88 1964–2004 100%
— ~ typical
PFBS municipal 5 2023–2025 0%
— —
pH 486 1964–2015 100%
— ~ typical
Sodium 117 1964–2023 100%
— ↓ 29% 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.

Compare your result with Polk County

Of the 29 arsenic tests on record for Polk County (1991–2023), 14% found none, and half were below 9.68 µg/L.

Of the 131 chloride tests on record for Polk County (1964–2025), 0% found none, and half were below 4.95 mg/L.

Of the 62 fluoride tests on record for Polk County (1964–2023), 2% found none, and half were below 300 µg/L.

Of the 118 iron tests on record for Polk County (1964–2023), 21% found none, and half were below 742 µg/L.

Of the 60 lead tests on record for Polk County (1991–2023), 88% found none.

Of the 117 manganese tests on record for Polk County (1964–2023), 4% found none, and half were below 60.2 µg/L.

Of the 474 nitrate tests on record for Polk County (1964–2015), 26% found none, and half were below 1.17 mg/L.

Of the 121 sulfate tests on record for Polk County (1964–2023), 1% found none, and half were below 32 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 118 samples
  • Manganese 117 samples
  • Arsenic 29 samples
  • Nitrate 474 samples
  • Lead 60 samples
  • Chloride 131 samples
  • Sulfate 121 samples
  • Fluoride 62 samples
  • Nitrite 447 samples
  • Hardness 88 samples
  • pH 486 samples
  • Sodium 117 samples

Limited data (<15 samples) — interpret with caution

  • HFPO-DA (GenX) 6 samples
  • PFNA 6 samples
  • PFOA 8 samples
  • PFOS 8 samples

Public vs. Private Water in Polk County

65 Active public water systems
24,567 Residents on public water
30% Households on private wells

Public water systems in Polk 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 Polk 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 Polk County Prevalence MN Average Source Year
Arsenic Cancer prevalence 7.7% 7.0% 2020
Arsenic Kidney disease rate 3.2% 2.9% 2020
Lead Heart disease rate 5.7% 6.6% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Polk 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: 2026-08-04

Full methodology →