Data & Methodology — San Benito County

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

Contaminant Data — All Analytes

105 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
Radon 2 2011–2013 100%
108% of limit ~ typical
Manganese 93 2006–2022 94%
30% of limit ↓ 90% below
Iron 92 2006–2022 67%
14% of limit ↓ 88% below
Sulfate 93 2006–2022 99%
16% of limit ~ typical
Arsenic 39 2006–2022 97%
16% of limit ↓ 60% below
Nitrate 93 2006–2022 66%
9% of limit ↓ 60% below
Chloride 93 2006–2022 100%
15% of limit ↓ 49% below
Uranium 93 2006–2022 90%
9% of limit ↑ 73% above
PFOA municipal 54 2022–2025 7%
89% of limit ↓ 47% below
PFHxS municipal 54 2022–2025 4%
86% of limit ↑ 54% above
PFOS municipal 54 2022–2025 2%
875% of limit ↑ 320% above
Perchlorate 1 2008 0%
— —
Fluoride 39 2006–2022 92%
7% of limit ~ typical
HFPO-DA (GenX) municipal 54 2022–2025 0%
— —
Nitrite 93 2006–2022 39%
0% of limit ↓ 68% below
PFNA municipal 54 2022–2025 2%
26% of limit ↓ 51% below
Lead 39 2006–2022 28%
1% of limit ↓ 90% below
Chromium (total) 1 2008 100%
2% of limit ~ typical
1,2,3-Trichloropropane 1 2008 0%
— —
Boron 1 2008 100%
87% of limit ↑ 424% above
Tds 1 2008 100%
— ↑ 67% above
E. coli 18 2022 0%
— —
PFBS municipal 54 2022–2025 4%
— ↑ 87% above
Total Coliform 18 2022 0%
— —
pH 93 2006–2022 100%
— ~ typical
Hardness 92 2006–2022 100%
— ↓ 53% below
Sodium 92 2006–2022 100%
— ↓ 30% below

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 San Benito County

Of the 39 arsenic tests on record for San Benito County (2006–2022), 3% found none, and half were below 1.5 µg/L.

Of the 93 chloride tests on record for San Benito County (2006–2022), 0% found none, and half were below 38.6 mg/L.

Of the 39 fluoride tests on record for San Benito County (2006–2022), 8% found none, and half were below 260 µg/L.

Of the 92 iron tests on record for San Benito County (2006–2022), 33% found none, and half were below 14.3 µg/L.

Of the 39 lead tests on record for San Benito County (2006–2022), 72% found none.

Of the 93 manganese tests on record for San Benito County (2006–2022), 6% found none, and half were below 12.3 µg/L.

Of the 93 nitrate tests on record for San Benito County (2006–2022), 34% found none, and half were below 222 µg/L.

Of the 93 sulfate tests on record for San Benito County (2006–2022), 1% found none, and half were below 39.5 mg/L.

Of the 93 uranium tests on record for San Benito County (2006–2022), 10% found none, and half were below 1.75 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 93 samples
  • Iron 92 samples
  • Sulfate 93 samples
  • Arsenic 39 samples
  • Nitrate 93 samples
  • Chloride 93 samples
  • Uranium 93 samples
  • PFOA 54 samples
  • PFHxS 54 samples
  • PFOS 54 samples
  • Fluoride 39 samples
  • HFPO-DA (GenX) 54 samples
  • Nitrite 93 samples
  • PFNA 54 samples
  • Lead 39 samples
  • E. coli 18 samples
  • PFBS 54 samples
  • Total Coliform 18 samples
  • pH 93 samples
  • Hardness 92 samples
  • Sodium 92 samples

Limited data (<15 samples) — interpret with caution

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

Public vs. Private Water in San Benito County

63 Active public water systems
82,670 Residents on public water
16% Households on private wells

Public water systems in San Benito 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 San Benito 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 San Benito County Prevalence CA Average Source Year
Arsenic Cancer prevalence 5.5% 6.2% 2020
Arsenic Kidney disease rate 2.8% 3.0% 2020

Source: CDC PLACES county-level estimates. Raw data: Download San Benito 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

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