Nueces County Water Control and Improvement District 3 received its third arsenic violation on April 22, even though the most recent water sample came in below the federal limit. The violation stems from how the EPA calculates compliance — using a running annual average rather than a single sample.
The most recent arsenic sample, collected April 7, measured 0.0076 milligrams per liter. The federal maximum contaminant level, or MCL, is 0.010 mg/L, meaning that the individual sample is within the legal limit.
NCWCID #3 gets third arsenic violation even as latest sample drops below federal limit
However, compliance is determined by a running annual average, or RAA — the average of the last four quarterly samples. That four-quarter average currently sits at 0.011 mg/L, which is above the federal limit.
Here is what the quarterly timeline looks like:
- Q3 2025 — Aug. 8 sample: 0.0108 mg/L — No violation
- Q4 2025 — Dec. 11 sample: 0.0131 mg/L — First violation issued Jan. 23
- Q1 2026 — Jan. 29 sample: 0.0115 mg/L — Second violation issued Feb. 19
- Q2 2026 — April 7 sample: 0.0076 mg/L — Level dropped, but four-quarter average remains 0.011 mg/L — Third violation issued April 22
The RAA system exists to protect people from long-term arsenic exposure, not just one elevated reading. These rules were established by the EPA to protect consumers against the effects of long-term, chronic exposure…