URANIUM CONTAMINATION IN DRINKING WATER IN PINE RIDGE RESERVATION, SOUTHWESTERN SOUTH DAKOTA

Residents of the Pine Ridge Reservation in southwestern South Dakota rely on the High Plains Aquifer, the Chamberlain Pass Formation aquifer, and shallow alluvial aquifers for drinking water. Volcanic ash within the aquifers is the primary source of elevated uranium levels in the region’s groundwater. The Chamberlain Pass Formation contains such high concentrations of uranium that it is commercially mined in nearby Crawford, NE. Previous work in this region showed elevated amounts of dissolved uranium (sometimes exceeding 20 ppb) in water used for drinking. The maximum contamination level (MCL) for uranium in drinking water is 30 ppb as determined by the Environmental Protection Agency (EPA), at which level uranium can be harmful to health. Our project has focused on the mechanisms of natural groundwater contamination by different uranium isotopes in and around the Pine Ridge Reservation. In order to address this problem we collected surface and ground water samples near the White Clay Fault near Pine Ridge SD. Sample locations were plotted on a Geographic Information Systems (GIS) map along with data collected during previous studies in this region. Collected samples were analyzed for barium, arsenic, and uranium at the UW-Whitewater Chemistry Department using the Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES). Selected samples were analyzed for U²³⁸ at the UW-Milwaukee Chemistry Department using the Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results from chemical analyses were added to the GIS map.

Preliminary results show significant (up to 60ppb) levels of U²³⁸ in collected surface water samples. Some ground water samples show elevated U²³⁸ (up to 40 ppb) as well. The exact reason(s) behind such high uranium levels in some but not all samples is not yet known. Possible sources of the high U²³⁸ levels might include: the depth of the wells, proximity to the White Clay Fault, surface and ground water interaction, and varying aquifer thickness. Future work on this project will focus on analyzing more water samples collected from the study area and adding those data to our maps. This information might be used to show whether there is a spatial correlation of uranium concentrations within the study area.