Data & Methodology — McMullen County

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

Contaminant Data — All Analytes

270 well testing events on record, covering 14 analytes. Data spans 1942 to 2015.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. TX Avg
Chloride 111 1942–2016 100%
45% of limit ↑ 25% above
Sulfate 110 1942–2016 100%
38% of limit ↑ 32% above
Iron 116 1942–2018 78%
54% of limit ↓ 65% below
Uranium 10 2009–2018 30%
124% of limit ↑ 697% above
Arsenic 52 1992–2018 27%
138% of limit ↑ 263% above
Manganese 66 1963–2018 62%
30% of limit ↓ 53% below
Nitrate 114 1942–2016 94%
4% of limit ↓ 82% below
Fluoride 219 1942–2018 100%
22% of limit ~ typical
Lead 52 1992–2018 12%
18% of limit ~ typical
Nitrite 2 2015–2016 0%
— —
Radon 1 2015 100%
37% of limit ~ typical
Sodium 111 1942–2016 100%
— ↑ 244% above
pH 110 1942–2016 100%
— ~ typical
Hardness 111 1942–2016 100%
— ↓ 93% 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 McMullen County

Of the 52 arsenic tests on record for McMullen County (1992–2018), 73% found none.

Of the 111 chloride tests on record for McMullen County (1942–2016), 0% found none, and half were below 112 mg/L.

Of the 219 fluoride tests on record for McMullen County (1942–2018), 0% found none, and half were below 900 µg/L.

Of the 116 iron tests on record for McMullen County (1942–2018), 22% found none, and half were below 100 µg/L.

Of the 52 lead tests on record for McMullen County (1992–2018), 88% found none.

Of the 66 manganese tests on record for McMullen County (1963–2018), 38% found none, and half were below 5.95 µg/L.

Of the 114 nitrate tests on record for McMullen County (1942–2016), 6% found none, and half were below 400 µg/L.

Of the 110 sulfate tests on record for McMullen County (1942–2016), 0% found none, and half were below 94.5 mg/L.

Have a number from your lab? Enter it to see where it falls. Nothing is sent anywhere.

Want the full picture for your well? Check all your results.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Chloride 111 samples
  • Sulfate 110 samples
  • Iron 116 samples
  • Arsenic 52 samples
  • Manganese 66 samples
  • Nitrate 114 samples
  • Fluoride 219 samples
  • Lead 52 samples
  • Sodium 111 samples
  • pH 110 samples
  • Hardness 111 samples

Limited data (<15 samples) — interpret with caution

  • Uranium 10 samples
  • Nitrite 2 samples
  • Radon 1 sample

No private-well PFAS data for McMullen County

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

3 Active public water systems
1,051 Residents on public water
35% Households on private wells

Public water systems in McMullen 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 McMullen 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 McMullen County Prevalence TX Average Source Year
Arsenic Cancer prevalence 8.1% 6.1% 2020
Arsenic Kidney disease rate 4.4% 3.3% 2020

Source: CDC PLACES county-level estimates. Raw data: Download McMullen 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 TX with at least one sample for that analyte.

Last updated: 2026-08-04

Full methodology →