Data & Methodology — Nevada County

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

Contaminant Data — All Analytes

158 well testing events on record, covering 27 analytes. Data spans 1960 to 2022.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Manganese 87 1980–2022 57%
23% of limit ↓ 93% below
Iron 87 1980–2022 57%
6% of limit ↓ 95% below
Arsenic 85 2002–2022 82%
5% of limit ↓ 86% below
Radon 16 2007–2008 100%
9% of limit ↓ 90% below
PFOA municipal 47 2020–2025 2%
115% of limit ↓ 31% below
PFOS municipal 47 2020–2025 2%
122% of limit ↓ 41% below
Uranium 82 2007–2022 68%
0% of limit ↓ 94% below
Boron 55 2015–2021 58%
1% of limit ↓ 92% below
Chromium (total) 58 2002–2021 12%
1% of limit ↓ 52% below
1,2,3-Trichloropropane 58 2002–2021 0%
— —
Lead 50 2002–2022 40%
7% of limit ↓ 26% below
Nitrate 89 1961–2022 67%
3% of limit ↓ 89% below
PFHxS municipal 47 2020–2025 0%
— —
PFNA municipal 47 2020–2025 0%
— —
Chloride 103 1961–2022 100%
2% of limit ↓ 94% below
Fluoride 89 1962–2022 85%
2% of limit ↓ 71% below
HFPO-DA (GenX) municipal 47 2020–2025 0%
— —
Nitrite 82 2007–2022 11%
0% of limit ↓ 92% below
Perchlorate 55 2015–2021 31%
2% of limit ↓ 69% below
Sulfate 92 1961–2022 98%
1% of limit ↓ 93% below
Tds 58 2002–2021 97%
— ↓ 57% below
Hardness 104 1961–2022 99%
— ↓ 68% below
Sodium 103 1961–2022 99%
— ↓ 91% below
pH 133 1961–2022 100%
— ~ typical
PFBS municipal 47 2020–2025 2%
— ↓ 48% below
Total Coliform 25 2002–2016 6%
— ~ typical
E. coli 25 2015–2016 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 Nevada County

Of the 85 arsenic tests on record for Nevada County (2002–2022), 18% found none, and half were below 0.4 µg/L.

Of the 103 chloride tests on record for Nevada County (1961–2022), 0% found none, and half were below 4.62 mg/L.

Of the 58 chromium (total) tests on record for Nevada County (2002–2021), 88% found none.

Of the 89 fluoride tests on record for Nevada County (1962–2022), 15% found none, and half were below 70 µg/L.

Of the 87 iron tests on record for Nevada County (1980–2022), 43% found none, and half were below 6.1 µg/L.

Of the 50 lead tests on record for Nevada County (2002–2022), 60% found none.

Of the 87 manganese tests on record for Nevada County (1980–2022), 43% found none, and half were below 1.09 µg/L.

Of the 89 nitrate tests on record for Nevada County (1961–2022), 33% found none, and half were below 142 µg/L.

Of the 92 sulfate tests on record for Nevada County (1961–2022), 2% found none, and half were below 3.21 mg/L.

Of the 58 tds tests on record for Nevada County (2002–2021), 3% found none, and half were below 165 mg/L.

Of the 82 uranium tests on record for Nevada County (2007–2022), 32% found none, and half were below 29.8 ng/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 87 samples
  • Iron 87 samples
  • Arsenic 85 samples
  • Radon 16 samples
  • PFOA 47 samples
  • PFOS 47 samples
  • Uranium 82 samples
  • Boron 55 samples
  • Chromium (total) 58 samples
  • 1,2,3-Trichloropropane 58 samples
  • Lead 50 samples
  • Nitrate 89 samples
  • PFHxS 47 samples
  • PFNA 47 samples
  • Chloride 103 samples
  • Fluoride 89 samples
  • HFPO-DA (GenX) 47 samples
  • Nitrite 82 samples
  • Perchlorate 55 samples
  • Sulfate 92 samples
  • Tds 58 samples
  • Hardness 104 samples
  • Sodium 103 samples
  • pH 133 samples
  • PFBS 47 samples
  • Total Coliform 25 samples
  • E. coli 25 samples

Public vs. Private Water in Nevada County

84 Active public water systems
103,685 Residents on public water
30% Households on private wells

Public water systems in Nevada 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 Nevada 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 Nevada County Prevalence CA Average Source Year
Arsenic Cancer prevalence 9.3% 6.2% 2020
Arsenic Kidney disease rate 3.5% 3.0% 2020

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