Data & Methodology — Shasta County

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

Contaminant Data — All Analytes

284 well testing events on record, covering 27 analytes. Data spans 1951 to 2022.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Radon 27 2007–2010 100%
79% of limit ~ typical
Manganese 166 1979–2024 36%
20% of limit ↓ 94% below
Iron 160 1979–2024 39%
7% of limit ↓ 95% below
PFOS municipal 72 2023–2025 3%
276% of limit ↑ 33% above
PFOA municipal 72 2023–2025 3%
352% of limit ↑ 112% above
Arsenic 142 1979–2024 83%
10% of limit ↓ 74% below
Lead 56 1979–2022 43%
1% of limit ↓ 92% below
PFHxS municipal 72 2023–2025 3%
72% of limit ↑ 29% above
Nitrate 20 2007–2019 95%
10% of limit ↓ 56% below
Uranium 85 2007–2024 81%
0% of limit ↓ 98% below
Sulfate 232 1960–2024 94%
2% of limit ↓ 92% below
Nitrite 85 2007–2024 22%
0% of limit ↓ 84% below
HFPO-DA (GenX) municipal 69 2023–2025 0%
— —
Fluoride 225 1959–2024 85%
2% of limit ↓ 64% below
Boron 23 2007–2024 87%
2% of limit ↓ 88% below
Chromium (total) 23 2007–2024 57%
2% of limit ↓ 26% below
1,2,3-Trichloropropane 23 2007–2024 0%
— —
Chloride 242 1959–2024 100%
1% of limit ↓ 96% below
PFNA municipal 72 2023–2025 0%
— —
Perchlorate 23 2007–2024 30%
2% of limit ↓ 66% below
Tds 23 2007–2024 100%
— ↓ 55% below
PFBS municipal 72 2023–2025 6%
— ↑ 36% above
Sodium 242 1959–2024 100%
— ↓ 83% below
Hardness 241 1959–2022 100%
— ↓ 67% below
E. coli 18 2010–2019 0%
— —
pH 255 1959–2024 100%
— ~ typical
Total Coliform 18 2010–2019 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 Shasta County

Of the 142 arsenic tests on record for Shasta County (1979–2024), 17% found none, and half were below 0.885 µg/L.

Of the 242 chloride tests on record for Shasta County (1959–2024), 0% found none, and half were below 3.15 mg/L.

Of the 23 chromium (total) tests on record for Shasta County (2007–2024), 43% found none, and half were below 0.7 µg/L.

Of the 225 fluoride tests on record for Shasta County (1959–2024), 15% found none, and half were below 100 µg/L.

Of the 160 iron tests on record for Shasta County (1979–2024), 61% found none.

Of the 56 lead tests on record for Shasta County (1979–2022), 57% found none.

Of the 166 manganese tests on record for Shasta County (1979–2024), 64% found none.

Of the 20 nitrate tests on record for Shasta County (2007–2019), 5% found none, and half were below 942 µg/L.

Of the 232 sulfate tests on record for Shasta County (1960–2024), 6% found none, and half were below 3.6 mg/L.

Of the 23 tds tests on record for Shasta County (2007–2024), 0% found none, and half were below 179 mg/L.

Of the 85 uranium tests on record for Shasta County (2007–2024), 19% found none, and half were below 28 ng/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)

  • Radon 27 samples
  • Manganese 166 samples
  • Iron 160 samples
  • PFOS 72 samples
  • PFOA 72 samples
  • Arsenic 142 samples
  • Lead 56 samples
  • PFHxS 72 samples
  • Nitrate 20 samples
  • Uranium 85 samples
  • Sulfate 232 samples
  • Nitrite 85 samples
  • Fluoride 225 samples
  • Boron 23 samples
  • Chromium (total) 23 samples
  • 1,2,3-Trichloropropane 23 samples
  • Chloride 242 samples
  • PFNA 72 samples
  • Perchlorate 23 samples
  • Tds 23 samples
  • PFBS 72 samples
  • Sodium 242 samples
  • Hardness 241 samples
  • E. coli 18 samples
  • pH 255 samples
  • Total Coliform 18 samples

Public vs. Private Water in Shasta County

177 Active public water systems
210,786 Residents on public water
7% Households on private wells

Public water systems in Shasta 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 Shasta 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 Shasta County Prevalence CA Average Source Year
Arsenic Cancer prevalence 7.9% 6.2% 2020
Arsenic Kidney disease rate 2.8% 3.0% 2020

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