Full contaminant data, sample history, and sourcing for San Patricio County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
259 well testing events on record, covering
18 analytes.
Data spans 1938 to 1998.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. TX Avg
Chloride
61
1938–1965
100%
192% of limit
↑ 437% above
Uranium
18
1990–2021
61%
74% of limit
↑ 377% above
Arsenic
51
1990–2021
45%
91% of limit
↑ 138% above
Iron
68
1945–2021
49%
33% of limit
↓ 78% below
Manganese
53
1955–2021
60%
25% of limit
↓ 62% below
Sulfate
60
1938–1965
100%
17% of limit
↓ 40% below
Fluoride
212
1938–2021
100%
25% of limit
~ typical
HFPO-DA (GenX)
municipal
34
2023–2025
0%
—
—
Lead
50
1990–2021
10%
15% of limit
~ typical
Nitrate
65
1950–1997
95%
1% of limit
↓ 95% below
PFHxS
municipal
34
2023–2025
0%
—
—
PFNA
municipal
34
2023–2025
0%
—
—
PFOA
municipal
34
2023–2025
0%
—
—
PFOS
municipal
34
2023–2025
0%
—
—
Hardness
61
1938–1965
100%
—
~ typical
PFBS
municipal
34
2023–2025
3%
—
↓ 27% below
pH
56
1950–2016
100%
—
~ typical
Sodium
11
1938–1965
100%
—
↑ 348% above
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 TX.
Compare your result with San Patricio County
Of the 51 arsenic tests on record for San Patricio County (1990–2021),
55% found none.
Of the 61 chloride tests on record for San Patricio County (1938–1965),
0% found none, and half were below 480 mg/L.
Of the 212 fluoride tests on record for San Patricio County (1938–2021),
0% found none, and half were below 995 µg/L.
Of the 68 iron tests on record for San Patricio County (1945–2021),
51% found none.
Of the 50 lead tests on record for San Patricio County (1990–2021),
90% found none.
Of the 53 manganese tests on record for San Patricio County (1955–2021),
40% found none, and half were below 5.67 µg/L.
Of the 65 nitrate tests on record for San Patricio County (1950–1997),
5% found none, and half were below 110 µg/L.
Of the 60 sulfate tests on record for San Patricio County (1938–1965),
0% found none, and half were below 43 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Chloride 61 samples
Uranium 18 samples
Arsenic 51 samples
Iron 68 samples
Manganese 53 samples
Sulfate 60 samples
Fluoride 212 samples
Lead 50 samples
Nitrate 65 samples
Hardness 61 samples
pH 56 samples
Limited data (<15 samples) — interpret with caution
Sodium 11 samples
No private-well PFAS data for San Patricio County
We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in San Patricio 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 San Patricio County
20Active public water systems
69,407Residents on public water
6%Households on private wells
Public water systems in San Patricio 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 Patricio 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.
This report aggregates data from the following public databases:
Water Quality Portal (WQP) — groundwater sample results for San Patricio County from EPA, USGS, and state agencies. Browse WQP data →
EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for San Patricio County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying San Patricio County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near San Patricio County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near San Patricio County, used in contamination risk scoring. Superfund site search →
CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →
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 TX with at least one sample for that analyte.