Data & Methodology — Butte County

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

Contaminant Data — All Analytes

469 well testing events on record, covering 27 analytes. Data spans 1951 to 2021.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Radon 21 1996–2010 100%
35% of limit ↓ 62% below
PFOS municipal 138 2020–2025 17%
142% of limit ↓ 32% below
Manganese 160 1959–2021 38%
21% of limit ↓ 93% below
Nitrate 300 1952–2021 96%
13% of limit ↓ 45% below
PFHxS municipal 138 2020–2025 20%
55% of limit ~ typical
Sulfate 284 1952–2021 100%
3% of limit ↓ 84% below
Arsenic 165 1959–2021 92%
10% of limit ↓ 74% below
Iron 160 1960–2021 30%
14% of limit ↓ 89% below
PFOA municipal 138 2020–2025 6%
89% of limit ↓ 47% below
1,2,3-Trichloropropane 36 2002–2021 3%
180% of limit ↓ 87% below
Chloride 316 1952–2021 100%
2% of limit ↓ 92% below
Fluoride 183 1952–2021 90%
2% of limit ↓ 64% below
HFPO-DA (GenX) municipal 138 2020–2025 0%
— —
Nitrite 98 1996–2021 12%
1% of limit ↓ 39% below
Uranium 92 1997–2021 93%
0% of limit ↓ 93% below
PFNA municipal 138 2020–2025 1%
98% of limit ↑ 84% above
Boron 35 2006–2021 77%
2% of limit ↓ 87% below
Chromium (total) 37 2002–2021 65%
2% of limit ↓ 37% below
Lead 86 1959–2021 52%
2% of limit ↓ 84% below
Perchlorate 35 2006–2021 46%
3% of limit ↓ 63% below
Tds 37 2002–2021 100%
— ↓ 49% below
Sodium 291 1952–2021 100%
— ↓ 83% below
E. coli 26 2006–2021 0%
— —
pH 411 1952–2021 100%
— ~ typical
Hardness 313 1952–2021 100%
— ↓ 42% below
PFBS municipal 138 2020–2025 7%
— ↓ 23% below
Total Coliform 26 2002–2021 4%
— ~ 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 Butte County

Of the 165 arsenic tests on record for Butte County (1959–2021), 8% found none, and half were below 1 µg/L.

Of the 316 chloride tests on record for Butte County (1952–2021), 0% found none, and half were below 5.71 mg/L.

Of the 37 chromium (total) tests on record for Butte County (2002–2021), 35% found none, and half were below 0.8 µg/L.

Of the 183 fluoride tests on record for Butte County (1952–2021), 10% found none, and half were below 100 µg/L.

Of the 160 iron tests on record for Butte County (1960–2021), 70% found none.

Of the 86 lead tests on record for Butte County (1959–2021), 48% found none.

Of the 160 manganese tests on record for Butte County (1959–2021), 62% found none.

Of the 300 nitrate tests on record for Butte County (1952–2021), 4% found none, and half were below 1.15 mg/L.

Of the 28 pfoa tests on record for Butte County (2020–2021), 79% found none.

Of the 28 pfos tests on record for Butte County (2020–2021), 82% found none.

Of the 284 sulfate tests on record for Butte County (1952–2021), 0% found none, and half were below 8 mg/L.

Of the 37 tds tests on record for Butte County (2002–2021), 0% found none, and half were below 202 mg/L.

Of the 92 uranium tests on record for Butte County (1997–2021), 7% found none, and half were below 0.118 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Radon 21 samples
  • PFOS 138 samples
  • Manganese 160 samples
  • Nitrate 300 samples
  • PFHxS 138 samples
  • Sulfate 284 samples
  • Arsenic 165 samples
  • Iron 160 samples
  • PFOA 138 samples
  • 1,2,3-Trichloropropane 36 samples
  • Chloride 316 samples
  • Fluoride 183 samples
  • HFPO-DA (GenX) 138 samples
  • Nitrite 98 samples
  • Uranium 92 samples
  • PFNA 138 samples
  • Boron 35 samples
  • Chromium (total) 37 samples
  • Lead 86 samples
  • Perchlorate 35 samples
  • Tds 37 samples
  • Sodium 291 samples
  • E. coli 26 samples
  • pH 411 samples
  • Hardness 313 samples
  • PFBS 138 samples
  • Total Coliform 26 samples

Public vs. Private Water in Butte County

88 Active public water systems
232,141 Residents on public water
17% Households on private wells

Public water systems in Butte 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 Butte 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 Butte County Prevalence CA Average Source Year
Arsenic Kidney disease rate 3.2% 3.0% 2020
Arsenic Cancer prevalence 6.8% 6.2% 2020

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