Data & Methodology — Lassen County

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

Contaminant Data — All Analytes

127 well testing events on record, covering 27 analytes. Data spans 1953 to 2023.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Radon 20 2010 100%
138% of limit ↑ 52% above
Manganese 52 1980–2020 58%
40% of limit ↓ 87% below
Nitrate 51 1961–2020 96%
4% of limit ↓ 81% below
Iron 54 1980–2020 52%
8% of limit ↓ 94% below
Arsenic 54 1980–2020 100%
26% of limit ↓ 32% below
Sulfate 85 1961–2020 100%
7% of limit ↓ 64% below
Fluoride 76 1961–2020 97%
6% of limit ~ typical
Chloride 97 1961–2020 100%
4% of limit ↓ 88% below
Perchlorate 5 2010 40%
4% of limit ↓ 42% below
Nitrite 32 2008–2020 25%
0% of limit ↓ 84% below
HFPO-DA (GenX) municipal 14 2024 0%
— —
PFOS municipal 14 2024 0%
— —
Uranium 32 2008–2020 100%
2% of limit ↓ 72% below
PFOA municipal 14 2024 0%
— —
PFNA municipal 14 2024 0%
— —
Boron 5 2010 100%
54% of limit ↑ 223% above
Chromium (total) 5 2010 60%
0% of limit ↓ 84% below
1,2,3-Trichloropropane 5 2010 0%
— —
PFHxS municipal 14 2024 0%
— —
Lead 40 1980–2020 40%
0% of limit ↓ 98% below
Tds 5 2010 100%
— ↑ 79% above
Total Coliform 1 2010–2021 5%
— ~ typical
pH 119 1961–2020 100%
— ~ typical
Sodium 92 1961–2020 100%
— ↓ 48% below
E. coli 1 2010–2021 5%
— ~ typical
Hardness 97 1961–2020 100%
— ↓ 63% below
PFBS municipal 14 2024 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 Lassen County

Of the 54 arsenic tests on record for Lassen County (1980–2020), 0% found none, and half were below 2.65 µg/L.

Of the 97 chloride tests on record for Lassen County (1961–2020), 0% found none, and half were below 9.2 mg/L.

Of the 76 fluoride tests on record for Lassen County (1961–2020), 3% found none, and half were below 225 µg/L.

Of the 54 iron tests on record for Lassen County (1980–2020), 48% found none, and half were below 3.3 µg/L.

Of the 40 lead tests on record for Lassen County (1980–2020), 60% found none.

Of the 52 manganese tests on record for Lassen County (1980–2020), 42% found none, and half were below 0.33 µg/L.

Of the 51 nitrate tests on record for Lassen County (1961–2020), 4% found none, and half were below 429 µg/L.

Of the 85 sulfate tests on record for Lassen County (1961–2020), 0% found none, and half were below 18 mg/L.

Of the 32 uranium tests on record for Lassen County (2008–2020), 0% found none, and half were below 0.456 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Radon 20 samples
  • Manganese 52 samples
  • Nitrate 51 samples
  • Iron 54 samples
  • Arsenic 54 samples
  • Sulfate 85 samples
  • Fluoride 76 samples
  • Chloride 97 samples
  • Nitrite 32 samples
  • Uranium 32 samples
  • Lead 40 samples
  • pH 119 samples
  • Sodium 92 samples
  • Hardness 97 samples

Limited data (<15 samples) — interpret with caution

  • Perchlorate 5 samples
  • Boron 5 samples
  • Chromium (total) 5 samples
  • 1,2,3-Trichloropropane 5 samples
  • Tds 5 samples
  • Total Coliform 1 sample
  • E. coli 1 sample

No private-well PFAS data for Lassen County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Lassen 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 Lassen County

55 Active public water systems
24,759 Residents on public water
36% Households on private wells

Public water systems in Lassen 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 Lassen 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 Lassen County Prevalence CA Average Source Year
Arsenic Cancer prevalence 6.2% 6.2% 2020
Arsenic Kidney disease rate 3.1% 3.0% 2020

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