Data & Methodology — Alameda County

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

Contaminant Data — All Analytes

4736 well testing events on record, covering 25 analytes. Data spans 1952 to 2015.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. CA Avg
Boron 1 2008 100%
188% of limit ↑ 1034% above
Manganese 841 1961–2022 66%
140% of limit ↓ 55% below
Nitrate 3967 1954–2022 96%
34% of limit ↑ 43% above
PFOS municipal 87 2023–2025 16%
256% of limit ↑ 23% above
Chloride 4304 1952–2022 100%
44% of limit ↑ 47% above
Sulfate 1318 1954–2022 100%
27% of limit ↑ 34% above
Iron 1101 1959–2022 71%
13% of limit ↓ 89% below
PFOA municipal 87 2023–2025 8%
108% of limit ↓ 35% below
Arsenic 127 1974–2022 75%
12% of limit ↓ 69% below
Uranium 67 1981–2022 99%
5% of limit ~ typical
Lead 104 1974–2022 21%
4% of limit ↓ 57% below
PFHxS municipal 87 2023–2025 18%
66% of limit ~ typical
Radon 14 2007 100%
7% of limit ↓ 92% below
PFNA municipal 87 2023–2025 0%
— —
Chromium (total) 1 2008 100%
5% of limit ↑ 85% above
1,2,3-Trichloropropane 1 2008 0%
— —
Fluoride 1810 1954–2022 99%
5% of limit ↓ 28% below
HFPO-DA (GenX) municipal 87 2023–2025 0%
— —
Nitrite 2972 1974–2022 64%
1% of limit ~ typical
Perchlorate 1 2008 100%
16% of limit ↑ 139% above
Tds 1 2008 100%
— ↑ 140% above
pH 1 2008 100%
— ~ typical
Hardness 2275 1954–2022 100%
— ↑ 34% above
PFBS municipal 87 2023–2025 14%
— ~ typical
Sodium 1258 1954–2022 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 Alameda County

Of the 127 arsenic tests on record for Alameda County (1974–2022), 25% found none, and half were below 1 µg/L.

Of the 4304 chloride tests on record for Alameda County (1952–2022), 0% found none, and half were below 110 mg/L.

Of the 1810 fluoride tests on record for Alameda County (1954–2022), 1% found none, and half were below 200 µg/L.

Of the 1101 iron tests on record for Alameda County (1959–2022), 29% found none, and half were below 20 µg/L.

Of the 104 lead tests on record for Alameda County (1974–2022), 79% found none.

Of the 841 manganese tests on record for Alameda County (1961–2022), 34% found none, and half were below 20 µg/L.

Of the 3967 nitrate tests on record for Alameda County (1954–2022), 4% found none, and half were below 3.1 mg/L.

Of the 1318 sulfate tests on record for Alameda County (1954–2022), 0% found none, and half were below 68 mg/L.

Of the 67 uranium tests on record for Alameda County (1981–2022), 1% found none, and half were below 1.53 µg/L.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Manganese 841 samples
  • Nitrate 3967 samples
  • Chloride 4304 samples
  • Sulfate 1318 samples
  • Iron 1101 samples
  • Arsenic 127 samples
  • Uranium 67 samples
  • Lead 104 samples
  • Fluoride 1810 samples
  • Nitrite 2972 samples
  • Hardness 2275 samples
  • Sodium 1258 samples

Limited data (<15 samples) — interpret with caution

  • Boron 1 sample
  • Radon 14 samples
  • Chromium (total) 1 sample
  • 1,2,3-Trichloropropane 1 sample
  • Perchlorate 1 sample
  • Tds 1 sample
  • pH 1 sample

No private-well PFAS data for Alameda County

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

27 Active public water systems
2,249,634 Residents on public water
1% Households on private wells

Public water systems in Alameda 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 Alameda 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 Alameda County Prevalence CA Average Source Year
Arsenic Cancer prevalence 5.0% 6.2% 2020
Arsenic Kidney disease rate 2.4% 3.0% 2020
Lead Heart disease rate 4.5% 6.3% 2020

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