Data & Methodology — Rock County

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

Contaminant Data — All Analytes

201 well testing events on record, covering 18 analytes. Data spans 1953 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MN Avg
Manganese 100 1958–2021 81%
520% of limit ~ typical
Iron 110 1958–2022 71%
432% of limit ↓ 40% below
PFOA municipal 3 2025 67%
286% of limit ↓ 33% below
Sulfate 155 1958–2023 100%
31% of limit ↑ 65% above
Nitrate 73 1958–1997 95%
6% of limit ↓ 74% below
Arsenic 54 1993–2021 89%
10% of limit ↓ 88% below
Lead 54 1993–2021 26%
1% of limit ↓ 98% below
Chloride 170 1958–2025 100%
5% of limit ↓ 30% below
Fluoride 117 1958–2023 99%
8% of limit ↑ 23% above
HFPO-DA (GenX) municipal 1 2025 0%
— —
Nitrite 60 1996–1997 42%
2% of limit ↑ 66% above
PFHxS municipal 1 2025 0%
— —
PFNA municipal 1 2025 0%
— —
PFOS municipal 4 2025 75%
16% of limit ↓ 92% below
Hardness 37 1958–1996 100%
— ~ typical
PFBS municipal 1 2025 0%
— —
pH 89 1958–1997 100%
— ~ typical
Sodium 120 1958–2023 100%
— ↓ 41% 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 Rock County

Of the 54 arsenic tests on record for Rock County (1993–2021), 11% found none, and half were below 0.869 µg/L.

Of the 170 chloride tests on record for Rock County (1958–2025), 0% found none, and half were below 13.4 mg/L.

Of the 117 fluoride tests on record for Rock County (1958–2023), 1% found none, and half were below 340 µg/L.

Of the 110 iron tests on record for Rock County (1958–2022), 29% found none, and half were below 504 µg/L.

Of the 54 lead tests on record for Rock County (1993–2021), 74% found none.

Of the 100 manganese tests on record for Rock County (1958–2021), 19% found none, and half were below 165 µg/L.

Of the 73 nitrate tests on record for Rock County (1958–1997), 5% found none, and half were below 500 µg/L.

Of the 155 sulfate tests on record for Rock County (1958–2023), 0% found none, and half were below 78 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 100 samples
  • Iron 110 samples
  • Sulfate 155 samples
  • Nitrate 73 samples
  • Arsenic 54 samples
  • Lead 54 samples
  • Chloride 170 samples
  • Fluoride 117 samples
  • Nitrite 60 samples
  • Hardness 37 samples
  • pH 89 samples
  • Sodium 120 samples

Limited data (<15 samples) — interpret with caution

  • PFOA 3 samples
  • PFOS 4 samples

Public vs. Private Water in Rock County

8 Active public water systems
9,495 Residents on public water
8% Households on private wells

Public water systems in Rock 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 Rock 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 Rock County Prevalence MN Average Source Year
Arsenic Cancer prevalence 8.3% 7.0% 2020
Arsenic Kidney disease rate 3.2% 2.9% 2020
Lead Heart disease rate 5.5% 6.6% 2020

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