Data & Methodology — El Dorado County

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

Contaminant Data — All Analytes

1202 well testing events on record, covering 27 analytes. Data spans 1960 to 2025.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Manganese 711 1986–2022 52%
340% of limit ~ typical
Iron 727 1986–2022 51%
930% of limit ↑ 658% above
PFOA municipal 62 2021–2025 10%
125% of limit ↓ 25% below
Radon 68 1989–2008 100%
14% of limit ↓ 84% below
Arsenic 593 1990–2022 37%
26% of limit ↓ 35% below
PFOS municipal 62 2021–2025 5%
118% of limit ↓ 44% below
Nitrate 544 1986–2022 65%
13% of limit ↓ 46% below
Uranium 210 1986–2022 91%
7% of limit ~ typical
Lead 564 1989–2022 7%
6% of limit ↓ 35% below
Sulfate 711 1986–2022 90%
3% of limit ↓ 86% below
Chloride 721 1986–2022 100%
4% of limit ↓ 88% below
PFNA municipal 62 2021–2025 0%
— —
PFHxS municipal 62 2021–2025 5%
56% of limit ~ typical
Nitrite 151 1986–2022 14%
0% of limit ↓ 84% below
HFPO-DA (GenX) municipal 60 2021–2025 0%
— —
Fluoride 713 1986–2022 45%
3% of limit ↓ 53% below
Perchlorate 40 2016–2021 48%
3% of limit ↓ 59% below
Boron 41 2016–2021 59%
1% of limit ↓ 95% below
Chromium (total) 441 2002–2021 2%
1% of limit ↓ 71% below
1,2,3-Trichloropropane 251 2002–2021 0%
— —
Tds 441 2002–2021 100%
— ↓ 47% below
pH 1163 1986–2022 100%
— ~ typical
Total Coliform 34 2002–2017 92%
— ~ typical
PFBS municipal 62 2021–2025 5%
— ↓ 30% below
Sodium 712 1986–2022 100%
— ↓ 85% below
Hardness 711 1986–2022 100%
— ↓ 62% below
E. coli 34 2016–2017 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 CA.

Compare your result with El Dorado County

Of the 593 arsenic tests on record for El Dorado County (1990–2022), 63% found none.

Of the 721 chloride tests on record for El Dorado County (1986–2022), 0% found none, and half were below 9 mg/L.

Of the 441 chromium (total) tests on record for El Dorado County (2002–2021), 98% found none.

Of the 713 fluoride tests on record for El Dorado County (1986–2022), 55% found none.

Of the 727 iron tests on record for El Dorado County (1986–2022), 49% found none, and half were below 7 µg/L.

Of the 564 lead tests on record for El Dorado County (1989–2022), 93% found none.

Of the 711 manganese tests on record for El Dorado County (1986–2022), 48% found none, and half were below 0.96 µg/L.

Of the 544 nitrate tests on record for El Dorado County (1986–2022), 35% found none, and half were below 465 µg/L.

Of the 711 sulfate tests on record for El Dorado County (1986–2022), 10% found none, and half were below 5.9 mg/L.

Of the 441 tds tests on record for El Dorado County (2002–2021), 0% found none, and half were below 210 mg/L.

Of the 210 uranium tests on record for El Dorado County (1986–2022), 9% found none, and half were below 1.51 µg/L.

Have a number from your lab? Enter it to see where it falls. Nothing is sent anywhere.

Want the full picture for your well? Check all your results.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 711 samples
  • Iron 727 samples
  • PFOA 62 samples
  • Radon 68 samples
  • Arsenic 593 samples
  • PFOS 62 samples
  • Nitrate 544 samples
  • Uranium 210 samples
  • Lead 564 samples
  • Sulfate 711 samples
  • Chloride 721 samples
  • PFNA 62 samples
  • PFHxS 62 samples
  • Nitrite 151 samples
  • HFPO-DA (GenX) 60 samples
  • Fluoride 713 samples
  • Perchlorate 40 samples
  • Boron 41 samples
  • Chromium (total) 441 samples
  • 1,2,3-Trichloropropane 251 samples
  • Tds 441 samples
  • pH 1163 samples
  • Total Coliform 34 samples
  • PFBS 62 samples
  • Sodium 712 samples
  • Hardness 711 samples
  • E. coli 34 samples

Public vs. Private Water in El Dorado County

129 Active public water systems
294,818 Residents on public water
15% Households on private wells

Public water systems in El Dorado 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 El Dorado 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 El Dorado County Prevalence CA Average Source Year
Arsenic Cancer prevalence 8.2% 6.2% 2020
Arsenic Kidney disease rate 2.4% 3.0% 2020
Lead Heart disease rate 5.2% 6.3% 2020

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