Data & Methodology — Hillsdale County

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

Contaminant Data — All Analytes

36 well testing events on record, covering 22 analytes. Data spans 1969 to 2022.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MI Avg
Iron 31 1976–2016 87%
623% of limit ↑ 215% above
Manganese 31 1976–2016 97%
76% of limit ↓ 45% below
Arsenic 20 1976–2016 90%
34% of limit ~ typical
Nitrate 27 1976–2016 26%
35% of limit ↑ 785% above
Sulfate 31 1976–2016 100%
14% of limit ~ typical
Chloride 31 1976–2016 100%
6% of limit ↓ 53% below
Fluoride 30 1976–2016 93%
16% of limit ↑ 103% above
HFPO-DA (GenX) municipal 3 2024–2025 0%
— —
Lead 14 1976–2016 7%
0% of limit ↓ 99% below
Nitrite 27 1976–2016 26%
2% of limit ↑ 358% above
PFHxS municipal 2 2024 0%
— —
PFNA municipal 3 2024–2025 0%
— —
PFOA municipal 3 2024–2025 0%
— —
PFOS municipal 2 2024 0%
— —
Radon 6 1998–2002 100%
8% of limit ↓ 77% below
Uranium 14 1976–2016 100%
1% of limit ~ typical
Total Coliform 3 2007–2016 14%
— —
Sodium 31 1976–2016 100%
— ↓ 22% below
pH 33 1976–2016 100%
— ~ typical
PFBS municipal 2 2024 0%
— —
Hardness 31 1976–2016 100%
— ↑ 215% above
E. coli 3 2007–2016 0%
— —

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 MI.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 31 samples
  • Manganese 31 samples
  • Arsenic 20 samples
  • Nitrate 27 samples
  • Sulfate 31 samples
  • Chloride 31 samples
  • Fluoride 30 samples
  • Nitrite 27 samples
  • Sodium 31 samples
  • pH 33 samples
  • Hardness 31 samples

Limited data (<15 samples) — interpret with caution

  • HFPO-DA (GenX) 3 samples
  • Lead 14 samples
  • PFNA 3 samples
  • PFOA 3 samples
  • Radon 6 samples
  • Uranium 14 samples
  • Total Coliform 3 samples
  • E. coli 3 samples

Public vs. Private Water in Hillsdale County

99 Active public water systems
30,157 Residents on public water
34% Households on private wells

Public water systems in Hillsdale 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 Hillsdale 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 Hillsdale County Prevalence MI Average Source Year
Arsenic Cancer prevalence 7.8% 7.2% 2023
Arsenic Cancer prevalence 8.0% 7.2% 2020
Arsenic Kidney disease rate 3.5% 3.2% 2020

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

Last updated: 2026-07-15

Full methodology →