Data & Methodology — Madera County

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

Contaminant Data — All Analytes

402 well testing events on record, covering 25 analytes. Data spans 1950 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Radon 53 1992–2014 100%
43% of limit ↓ 53% below
1,2,3-Trichloropropane 45 2006–2024 20%
660% of limit ↓ 54% below
Manganese 213 1979–2024 62%
7% of limit ↓ 98% below
Arsenic 204 1984–2024 99%
20% of limit ↓ 48% below
Uranium 171 1993–2024 95%
6% of limit ~ typical
PFOS municipal 84 2023–2025 5%
140% of limit ↓ 33% below
Nitrate 316 1955–2023 89%
25% of limit ~ typical
Chloride 372 1950–2024 100%
10% of limit ↓ 68% below
Iron 249 1958–2024 57%
3% of limit ↓ 97% below
PFOA municipal 84 2023–2025 4%
132% of limit ~ typical
Fluoride 312 1957–2024 95%
4% of limit ↓ 42% below
PFHxS municipal 84 2023–2025 2%
102% of limit ↑ 83% above
Lead 159 1985–2024 38%
6% of limit ↓ 40% below
Sulfate 355 1955–2024 100%
4% of limit ↓ 80% below
Boron 45 2006–2024 100%
2% of limit ↓ 87% below
Chromium (total) 45 2006–2024 87%
2% of limit ~ typical
HFPO-DA (GenX) municipal 79 2023–2025 0%
— —
Nitrite 179 1987–2024 8%
0% of limit ↓ 72% below
Perchlorate 42 2006–2024 71%
7% of limit ~ typical
PFNA municipal 84 2023–2025 0%
— —
Tds 45 2006–2024 100%
— ↓ 33% below
PFBS municipal 84 2023–2025 11%
— ↑ 116% above
Hardness 365 1953–2023 100%
— ↓ 51% below
Sodium 368 1950–2024 100%
— ↓ 60% below
pH 373 1955–2024 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 CA.

Compare your result with Madera County

Of the 204 arsenic tests on record for Madera County (1984–2024), 1% found none, and half were below 2 µg/L.

Of the 372 chloride tests on record for Madera County (1950–2024), 0% found none, and half were below 24 mg/L.

Of the 45 chromium (total) tests on record for Madera County (2006–2024), 13% found none, and half were below 2.2 µg/L.

Of the 312 fluoride tests on record for Madera County (1957–2024), 5% found none, and half were below 150 µg/L.

Of the 249 iron tests on record for Madera County (1958–2024), 43% found none.

Of the 159 lead tests on record for Madera County (1985–2024), 62% found none.

Of the 213 manganese tests on record for Madera County (1979–2024), 38% found none, and half were below 0.69 µg/L.

Of the 316 nitrate tests on record for Madera County (1955–2023), 11% found none, and half were below 2 mg/L.

Of the 355 sulfate tests on record for Madera County (1955–2024), 0% found none, and half were below 10 mg/L.

Of the 45 tds tests on record for Madera County (2006–2024), 0% found none, and half were below 267 mg/L.

Of the 171 uranium tests on record for Madera County (1993–2024), 5% found none, and half were below 1.63 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Radon 53 samples
  • 1,2,3-Trichloropropane 45 samples
  • Manganese 213 samples
  • Arsenic 204 samples
  • Uranium 171 samples
  • PFOS 84 samples
  • Nitrate 316 samples
  • Chloride 372 samples
  • Iron 249 samples
  • PFOA 84 samples
  • Fluoride 312 samples
  • PFHxS 84 samples
  • Lead 159 samples
  • Sulfate 355 samples
  • Boron 45 samples
  • Chromium (total) 45 samples
  • Nitrite 179 samples
  • Perchlorate 42 samples
  • PFNA 84 samples
  • Tds 45 samples
  • PFBS 84 samples
  • Hardness 365 samples
  • Sodium 368 samples
  • pH 373 samples

Public vs. Private Water in Madera County

204 Active public water systems
184,893 Residents on public water
24% Households on private wells

Public water systems in Madera 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 Madera 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 Madera County Prevalence CA Average Source Year
Arsenic Cancer prevalence 5.9% 6.2% 2020
Arsenic Kidney disease rate 3.5% 3.0% 2020
Lead Heart disease rate 7.2% 6.3% 2020

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

Last updated: 2026-09-10

Full methodology →