Data & Methodology — Cook County

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

Contaminant Data — All Analytes

52 well testing events on record, covering 25 analytes. Data spans 1941 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. GA Avg
Manganese 20 1967–2015 80%
80% of limit ↑ 34% above
Sulfate 42 1943–2015 100%
8% of limit ↑ 286% above
Iron 20 1967–2015 70%
5% of limit ↓ 88% below
Nitrate 41 1943–2015 90%
0% of limit ↓ 96% below
Fluoride 42 1943–2015 88%
8% of limit ↑ 50% above
PFOA municipal 10 2023 0%
— —
Chloride 48 1943–2015 100%
3% of limit ↑ 37% above
Arsenic 12 1967–2015 67%
1% of limit ↓ 85% below
PFNA municipal 10 2023 0%
— —
HFPO-DA (GenX) municipal 10 2023 0%
— —
Nitrite 18 1976–2015 6%
1% of limit ~ typical
HFPO-DA (GenX) municipal 10 2023 0%
— —
Chloride 48 1943–2015 100%
3% of limit ↑ 37% above
Arsenic 12 1967–2015 67%
1% of limit ↓ 85% below
Fluoride 42 1943–2015 88%
8% of limit ↑ 50% above
Lead 14 1967–2015 64%
1% of limit ↓ 60% below
Nitrite 18 1976–2015 6%
1% of limit ~ typical
PFHxS municipal 10 2023 0%
— —
PFNA municipal 10 2023 0%
— —
Radon 2 1993–2005 100%
15% of limit ~ typical
Uranium 10 1993–2015 90%
0% of limit ↓ 76% below
Hardness 42 1943–2015 100%
— ↑ 78% above
PFBS municipal 10 2023 0%
— —
pH 43 1943–2015 100%
— ~ typical
Sodium 42 1943–2015 100%
— ↓ 34% 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 GA.

Compare your result with Cook County

Of the 48 chloride tests on record for Cook County (1943–2015), 0% found none, and half were below 6.4 mg/L.

Of the 42 fluoride tests on record for Cook County (1943–2015), 12% found none, and half were below 300 µg/L.

Of the 20 iron tests on record for Cook County (1967–2015), 30% found none, and half were below 4.35 µg/L.

Of the 20 manganese tests on record for Cook County (1967–2015), 20% found none, and half were below 32.4 µg/L.

Of the 41 nitrate tests on record for Cook County (1943–2015), 10% found none, and half were below 23 µg/L.

Of the 42 sulfate tests on record for Cook County (1943–2015), 0% found none, and half were below 19.7 mg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 20 samples
  • Sulfate 42 samples
  • Iron 20 samples
  • Nitrate 41 samples
  • Fluoride 42 samples
  • Chloride 48 samples
  • Nitrite 18 samples
  • Chloride 48 samples
  • Fluoride 42 samples
  • Nitrite 18 samples
  • Hardness 42 samples
  • pH 43 samples
  • Sodium 42 samples

Limited data (<15 samples) — interpret with caution

  • Arsenic 12 samples
  • Arsenic 12 samples
  • Lead 14 samples
  • Radon 2 samples
  • Uranium 10 samples

No private-well PFAS data for Cook County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Cook County. PFAS testing for private wells requires a dedicated lab panel (~$300–$500). If you are near a military base, airport, or industrial site, consider testing proactively. Learn more about PFAS →

Public vs. Private Water in Cook County

11 Active public water systems
10,057 Residents on public water
48% Households on private wells

Public water systems in Cook 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 Cook 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 Cook County Prevalence GA Average Source Year
Nitrate Cancer prevalence 6.8% 6.3% 2020

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

Last updated: 2026-08-04

Full methodology →