The Spatial Distribution of Elevated Uranium in the Treasure Valley Aquifer System, Southwest Idaho
Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Hydrologic Science
Shawn G. Benner, Ph.D.
James McNamara, Ph.D.
Hans Peter Marshall, Ph.D.
The Treasure Valley Aquifer System (TVAS) in southwestern Idaho contains well-documented uranium concentrations over the U.S. Environmental Protection Agency maximum contaminant level of 30 µg/L. With a population in the Treasure Valley projected to reach 1.6 million by 2065, in-depth horizontal and vertical spatial knowledge of the contaminant is needed. This study evaluates the horizontal and vertical spatial nature of uranium in the TVAS and interprets those observations to provide both a conceptual model of uranium behavior, and recommendations for water resource management. A large water quality dataset was compiled, and 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, reduced waters of the TVAS, and ranged from low to very high (0 – 240 µg/L) in the shallow, oxidized 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, likely increase uranium mobility and contribute to elevated concentrations in oxic waters. Domestic well users are at risk for consuming elevated dissolved uranium due to limited monitoring and well depth completion in the shallow portion of the TVAS. To address this risk, measurements of 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 these wells are above drinking water standard), while measurements below these values predict low potential for elevated uranium (100% of wells are below drinking water standard). Additionally, drilling deeper into reducing waters and increased uranium monitoring will protect from elevated uranium concentrations.
Womeldorph, Lloyd A., "The Spatial Distribution of Elevated Uranium in the Treasure Valley Aquifer System, Southwest Idaho" (2019). Boise State University Theses and Dissertations. 1613.