URANIUM IN GROUNDWATER AND ITS POTENTIALS AS A NATURAL CONTAMINANT IN THE CHEROKEE BASIN, SOUTHEASTERN KANSAS, USA

Safe and easily accessible clean portable water is critical for public health. The ingestion of radioactive nuclides such as uranium has been associated with renal and cancer-related issues in humans. Many previous studies have focused on anthropogenic uranium contamination. Here, we examine the potential for natural uranium contamination resulting from water-rock interaction in black shales. After uranium ores, black shales are the second most important uranium host. Immobile uranium can be mobilized and absorbed into groundwater under ideal geochemical circumstances such as redox status, carbonate speciation, and alkalinity. The sedimentary succession in the Cherokee Basin in southeastern Kansas includes several black shales interbedded with limestones. Gamma-ray logs from oil and gas wells revealed a very high level of radioactivity in the black shales, reaching 740 API in some areas, suggesting the presence of radioactive uranium in these rocks.

To examine whether these units are sources of groundwater uranium contamination, we collected and chemically analyzed groundwater samples from domestic wells screened in the Ozark carbonate aquifer. The samples had pH in the order of 6.27 to 7.96 and alkalinity ranging from 0.6 to 18 mM. Some of the samples had high sulfate, ammonium, and nitrate concentrations, up to 373 mg/L, 45 mg/L, and 15 mg/L, respectively.

The goal of this study was to investigate the connection between black shales and uranium concentrations in groundwater. Uranium levels were generally low; however, we found numerous other redox-sensitive solutes, specifically mercury, manganese, nickel, and iron, present in concentrations in the order of 0.02 mg/L, 3.3 mg/L, 0.2mg/L, and 11 mg/L, respectively. These are well above the primary or secondary US EPA standards for drinking water. Our results have implications for the best practices for household water well owners and target depths for potential water well owners to ensure drinking water quality, consequently reducing the prevalence of cancer associated with the consumption of trace metal-contaminated groundwater.