Uranium concentrations and chemical associations in the Southern Gulf Coast Aquifer, Texas

Abstract

ABSTRACT Dissolved concentrations of uranium and potentially associated parameters, including nitrate, alkalinity, calcium, iron, manganese, vanadium, and fluoride, were compiled for 65 water wells sampled between 2015 and 2017 in a southern part of the Gulf Coast Aquifer, Texas. Sampled wells ranged from 3.0 m to 762.2 m deep, with a median depth of 120.0 m. Uranium concentrations ranged from less than 1 μg/L to 243 μg/L, with a median concentration of 5.94 μg/L. At seven wells, uranium concentrations exceeded the EPA drinking water standard of 30 μg/L. Based upon Spearman rank correlation, at a significance level of 0.01, significant positive associations were observed between uranium and vanadium, nitrate, and calcium concentrations. Significant negative associations were found between uranium concentrations and both iron concentrations and pH. Results suggest that processes adding nitrate and calcium to the aquifer may also mobilise uranium, through oxidative dissolution of reduced uranium-bearing minerals and subsequent formation of soluble uranium-calcium-carbonate complexes.