Full contaminant data, sample history, and sourcing for Frio County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
572 well testing events on record, covering
20 analytes.
Data spans 1928 to 2018.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. TX Avg
Iron
326
1928–2018
93%
133% of limit
~ typical
Manganese
223
1939–2018
72%
44% of limit
↓ 32% below
Chloride
73
1928–2015
100%
11% of limit
↓ 69% below
Sulfate
71
1928–2015
100%
24% of limit
~ typical
Nitrate
109
1928–2015
91%
4% of limit
↓ 82% below
Fluoride
511
1939–2018
99%
10% of limit
↓ 58% below
Arsenic
170
1990–2018
1%
14% of limit
↓ 62% below
HFPO-DA (GenX)
municipal
12
2023–2025
0%
—
—
Lead
170
1990–2018
4%
28% of limit
↑ 66% above
Nitrite
2
2015
0%
—
—
PFHxS
municipal
12
2023–2025
0%
—
—
PFNA
municipal
12
2023–2025
0%
—
—
PFOA
municipal
12
2023–2025
0%
—
—
PFOS
municipal
12
2023–2025
0%
—
—
Radon
2
2015
100%
28% of limit
↓ 22% below
Uranium
51
2010–2018
12%
7% of limit
↓ 53% below
Hardness
70
1928–2015
100%
—
~ typical
PFBS
municipal
12
2023–2025
0%
—
—
pH
57
1939–2015
100%
—
~ typical
Sodium
70
1928–2015
100%
—
↓ 62% 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 TX.
Compare your result with Frio County
Of the 170 arsenic tests on record for Frio County (1990–2018),
99% found none.
Of the 73 chloride tests on record for Frio County (1928–2015),
0% found none, and half were below 28 mg/L.
Of the 511 fluoride tests on record for Frio County (1939–2018),
1% found none, and half were below 400 µg/L.
Of the 326 iron tests on record for Frio County (1928–2018),
7% found none, and half were below 378 µg/L.
Of the 170 lead tests on record for Frio County (1990–2018),
96% found none.
Of the 223 manganese tests on record for Frio County (1939–2018),
28% found none, and half were below 11.3 µg/L.
Of the 109 nitrate tests on record for Frio County (1928–2015),
9% found none, and half were below 300 µg/L.
Of the 71 sulfate tests on record for Frio County (1928–2015),
0% found none, and half were below 60 mg/L.
Of the 51 uranium tests on record for Frio County (2010–2018),
88% found none.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Iron 326 samples
Manganese 223 samples
Chloride 73 samples
Sulfate 71 samples
Nitrate 109 samples
Fluoride 511 samples
Arsenic 170 samples
Lead 170 samples
Uranium 51 samples
Hardness 70 samples
pH 57 samples
Sodium 70 samples
Limited data (<15 samples) — interpret with caution
Nitrite 2 samples
Radon 2 samples
No private-well PFAS data for Frio County
We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Frio County.
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 Frio County
7Active public water systems
15,824Residents on public water
8%Households on private wells
Public water systems in Frio 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 Frio 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 Frio 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 Frio County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Frio 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 Frio County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Frio 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.