Data & Methodology — Delta County

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

Contaminant Data — All Analytes

197 well testing events on record, covering 20 analytes. Data spans 1915 to 2015.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. MI Avg
Iron 128 1930–2015 99%
67% of limit ↓ 81% below
PFOS municipal 8 2024–2025 38%
250% of limit ↑ 114% above
Manganese 98 1915–2015 97%
40% of limit ↓ 55% below
Sulfate 143 1915–2015 100%
13% of limit ↓ 37% below
Chloride 173 1915–2015 100%
5% of limit ↓ 75% below
Lead 22 1976–2015 32%
33% of limit ↑ 64% above
Arsenic 22 1976–2015 18%
10% of limit ↓ 67% below
Fluoride 65 1941–2015 100%
8% of limit ~ typical
HFPO-DA (GenX) municipal 8 2024–2025 0%
— —
Nitrate 48 1948–2015 58%
0% of limit ↓ 86% below
Nitrite 25 1976–2015 12%
1% of limit ~ typical
PFHxS municipal 8 2024–2025 0%
— —
PFNA municipal 10 2010–2025 0%
— —
PFOA municipal 12 2010–2025 0%
— —
Radon 9 1990–2002 100%
7% of limit ~ typical
Uranium 19 1981–2015 84%
0% of limit ↓ 70% below
Sodium 134 1922–2015 100%
— ↓ 49% below
pH 63 1952–2015 100%
— ~ typical
PFBS municipal 8 2024–2025 0%
— —
Hardness 179 1922–2015 100%
— ~ typical

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.

Compare your result with Delta County

Of the 22 arsenic tests on record for Delta County (1976–2015), 82% found none.

Of the 173 chloride tests on record for Delta County (1915–2015), 0% found none, and half were below 12 mg/L.

Of the 65 fluoride tests on record for Delta County (1941–2015), 0% found none, and half were below 330 µg/L.

Of the 128 iron tests on record for Delta County (1930–2015), 1% found none, and half were below 200 µg/L.

Of the 22 lead tests on record for Delta County (1976–2015), 68% found none.

Of the 98 manganese tests on record for Delta County (1915–2015), 3% found none, and half were below 20 µg/L.

Of the 48 nitrate tests on record for Delta County (1948–2015), 42% found none.

Of the 143 sulfate tests on record for Delta County (1915–2015), 0% found none, and half were below 33 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 128 samples
  • Manganese 98 samples
  • Sulfate 143 samples
  • Chloride 173 samples
  • Lead 22 samples
  • Arsenic 22 samples
  • Fluoride 65 samples
  • Nitrate 48 samples
  • Nitrite 25 samples
  • Uranium 19 samples
  • Sodium 134 samples
  • pH 63 samples
  • Hardness 179 samples

Limited data (<15 samples) — interpret with caution

  • PFNA 10 samples
  • PFOA 12 samples
  • Radon 9 samples

Public vs. Private Water in Delta County

70 Active public water systems
26,794 Residents on public water
47% Households on private wells

Public water systems in Delta 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 Delta 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 Delta County Prevalence MI Average Source Year
PFOS Cancer prevalence 6.2% 7.2% 2020
Lead Heart disease rate 6.3% 7.4% 2020

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

Full methodology →