Data & Methodology — Ventura County

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

Contaminant Data — All Analytes

1029 well testing events on record, covering 25 analytes. Data spans 1933 to 2022.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Sulfate 601 1933–2022 100%
164% of limit ↑ 711% above
Manganese 507 1972–2022 89%
172% of limit ↓ 44% below
Chloride 926 1933–2022 100%
27% of limit ~ typical
Iron 520 1966–2022 82%
23% of limit ↓ 82% below
Radon 10 2007–2011 100%
8% of limit ↓ 91% below
Nitrate 476 1952–2022 59%
16% of limit ↓ 33% below
PFOA municipal 140 2023–2025 5%
202% of limit ↑ 22% above
PFOS municipal 140 2023–2025 3%
245% of limit ~ typical
Arsenic 106 1978–2022 83%
7% of limit ↓ 82% below
Fluoride 574 1952–2022 97%
12% of limit ↑ 69% above
HFPO-DA (GenX) municipal 140 2023–2025 0%
— —
Nitrite 393 1990–2022 31%
2% of limit ↑ 62% above
Perchlorate 1 2008 100%
7% of limit ~ typical
Uranium 66 2007–2022 94%
15% of limit ↑ 178% above
Boron 1 2008 100%
4% of limit ↓ 78% below
PFNA municipal 140 2023–2025 0%
— —
Chromium (total) 1 2008 100%
2% of limit ↓ 44% below
1,2,3-Trichloropropane 1 2008 0%
— —
Lead 60 1978–2022 20%
7% of limit ↓ 24% below
PFHxS municipal 140 2023–2025 6%
70% of limit ↑ 26% above
Tds 1 2008 100%
— ↑ 52% above
Sodium 588 1933–2022 100%
— ↑ 48% above
Hardness 593 1933–2022 100%
— ↑ 144% above
PFBS municipal 140 2023–2025 1%
— ↓ 30% below
pH 635 1952–2022 100%
— ~ 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 Ventura County

Of the 106 arsenic tests on record for Ventura County (1978–2022), 17% found none, and half were below 0.6 µg/L.

Of the 926 chloride tests on record for Ventura County (1933–2022), 0% found none, and half were below 68 mg/L.

Of the 574 fluoride tests on record for Ventura County (1952–2022), 3% found none, and half were below 400 µg/L.

Of the 520 iron tests on record for Ventura County (1966–2022), 18% found none, and half were below 40 µg/L.

Of the 60 lead tests on record for Ventura County (1978–2022), 80% found none.

Of the 507 manganese tests on record for Ventura County (1972–2022), 11% found none, and half were below 67 µg/L.

Of the 476 nitrate tests on record for Ventura County (1952–2022), 41% found none, and half were below 105 µg/L.

Of the 601 sulfate tests on record for Ventura County (1933–2022), 0% found none, and half were below 410 mg/L.

Of the 66 uranium tests on record for Ventura County (2007–2022), 6% found none, and half were below 4.23 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Sulfate 601 samples
  • Manganese 507 samples
  • Chloride 926 samples
  • Iron 520 samples
  • Nitrate 476 samples
  • Arsenic 106 samples
  • Fluoride 574 samples
  • Nitrite 393 samples
  • Uranium 66 samples
  • Lead 60 samples
  • Sodium 588 samples
  • Hardness 593 samples
  • pH 635 samples

Limited data (<15 samples) — interpret with caution

  • Radon 10 samples
  • Perchlorate 1 sample
  • Boron 1 sample
  • Chromium (total) 1 sample
  • 1,2,3-Trichloropropane 1 sample
  • Tds 1 sample

No private-well PFAS data for Ventura County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Ventura County. PFAS has been detected in local public water systems (UCMR 5 data) — indicated by the "municipal" badge in the table above — but this does not directly indicate private well contamination. 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 Ventura County

95 Active public water systems
882,799 Residents on public water
2% Households on private wells

Public water systems in Ventura 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 Ventura 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 Ventura County Prevalence CA Average Source Year
Arsenic Cancer prevalence 5.5% 6.2% 2020
Arsenic Kidney disease rate 2.6% 3.0% 2020

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