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Gus Womeldorph

September 11 @ 3:00 pm - 4:00 pm MDT

Thesis Information

Title: The Spatial Distribution of Elevated Uranium in the Treasure Valley Aquifer System

Program: Master of Science in Hydrological Sciences

Advisor: Dr. Shawn G. Benner, Geosciences

Committee Members: Dr. James McNamara, Geosciences, Dr. Hans-Peter Marshall, Geosciences


The Treasure Valley Aquifer System (TVAS) in southwestern Idaho contains well-documented uranium concentrations over the U.S. Environmental Protection Agency drinking water standard of 30 µg/L. With groundwater the primary drinking water source for a population in the Treasure Valley projected to reach 1.5 million by 2040, constraints on the spatial distribution of U can inform management of contaminant. This study evaluates the horizontal and vertical spatial nature of uranium in the TVAS and interprets those observations, providing both a conceptual model of uranium behavior and recommendations for water resource management. A large water quality dataset was compiled from prior monitoring efforts and was supplemented by data collected during a field sampling campaign targeting increased vertical resolution in the aquifer system. To assess the questions posed by the study, statistical tests, spatial analyses, and chemical modeling were performed on the compiled and collected data. Uranium concentrations were found to be low in deep, anoxic waters of the TVAS and ranged from low to very high (0 – 240 µg/L) in the shallow, oxic portions of the system. The contaminant exhibits high variability and elevated levels across the region but does not follow any significant horizontal spatial trends. Redox conditions were found to control uranium mobility throughout the system. Waters high in calcium and carbonates, which readily complex with uranium in the system, control uranium availability and contribute to elevated concentrations in oxic waters. Domestic well users are at risk for consuming dissolved uranium exceeding the drinking water standard due to limited monitoring and well depth completion in the shallow portion of the TVAS. To address this risk, alkalinity and dissolved oxygen can be used as a low-cost screening method for predicting the risk of elevated uranium. Groundwater with alkalinity greater than 150 mg/L and dissolved oxygen greater than 1 mg/L predicts the potential for elevated uranium (43% of wells above drinking water standard), while measurements below these values predict low potential for elevated uranium (100% of wells below drinking water standard). Additionally, drilling deeper into anoxic waters and increased uranium monitoring will protect from elevated uranium concentrations.