Data & Methodology — Monroe County

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

Contaminant Data — All Analytes

98 well testing events on record, covering 19 analytes. Data spans 1961 to 2017.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MI Avg
Sulfate 69 1961–1992 99%
88% of limit ↑ 447% above
Iron 58 1961–1992 97%
31% of limit ↓ 84% below
PFOA municipal 28 2010–2025 18%
152% of limit —
Manganese 58 1961–1992 95%
16% of limit ↓ 88% below
Chloride 69 1961–1992 100%
5% of limit ↓ 61% below
Arsenic 50 1971–1992 12%
35% of limit ~ typical
Fluoride 56 1961–1992 100%
25% of limit ↑ 215% above
HFPO-DA (GenX) municipal 24 2023–2025 0%
— —
Lead 50 1971–1992 8%
0% of limit ↓ 100% below
Nitrate 70 1961–1992 39%
0% of limit ↓ 100% below
Nitrite 47 1979–1992 0%
— —
PFHxS municipal 25 2023–2025 4%
6% of limit —
PFNA municipal 25 2023–2025 0%
— —
PFOS municipal 25 2023–2025 4%
90% of limit —
Uranium 6 1979–1986 50%
0% of limit ↓ 63% below
Hardness 70 1961–1992 100%
— ↑ 356% above
PFBS municipal 25 2023–2025 4%
— —
pH 70 1961–1992 100%
— ~ typical
Sodium 58 1961–1992 100%
— ↑ 27% above

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)

  • Sulfate 69 samples
  • Iron 58 samples
  • PFOA 28 samples
  • Manganese 58 samples
  • Chloride 69 samples
  • Arsenic 50 samples
  • Fluoride 56 samples
  • Lead 50 samples
  • Nitrate 70 samples
  • Nitrite 47 samples
  • PFHxS 25 samples
  • PFNA 25 samples
  • PFOS 25 samples
  • Hardness 70 samples
  • PFBS 25 samples
  • pH 70 samples
  • Sodium 58 samples

Limited data (<15 samples) — interpret with caution

  • Uranium 6 samples

Public vs. Private Water in Monroe County

82 Active public water systems
136,030 Residents on public water
12% Households on private wells

Public water systems in Monroe 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 Monroe 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 Monroe County Prevalence MI Average Source Year
Arsenic Cancer prevalence 9.9% 7.2% 2023
PFOA Cancer prevalence 6.3% 7.2% 2020
Arsenic Kidney disease rate 3.2% 3.2% 2020

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