Elevated fluoride and selenium in west Texas groundwater.

Fluoride and selenium concentrations, along with total dissolved solids and depth of intake, were compiled, mapped, and analyzed for 634 water wells in the High Plains Aquifer, northwest Texas. Approximately 19% of fluoride observations exceeded the maximum contaminant level (MCL) for drinking water. Additionally, 4% of selenium observations exceeded the MCL for drinking water, and 19% exceeded the recommended limit for irrigation water. Concentrations were considerably higher in the southern part of the study area, especially in relatively deep public supply and irrigation wells. Though human activity may influence fluoride and selenium levels, natural sources largely account for patterns observed in this study.