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Archive: Part 02 - GPSS Science & Policy Summit - Presentation of Student Research (1)

156 views · Published 9 July 2014 · 25:23 · Indexed 4 November 2026

Channel: UW Video · 2014 · Education

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Investigating Uranium Nuclide Fractionation in Sediments and Waters Using MC-ICPMS: A Case Study of Contamination from the Juniper Mine, Stanislaus National Forest
Theresa M. Kayzar (1), Megan L. Lobaugh (2), Adam C. Villa (3), Ross W. Williams (4),and Amy M. Gaffney (4)
    This study investigates uranium transport in Red Rock Creek. Red Rock Creek is located in the Stanislaus National Forest in the Sierra Nevada range of California. One branch of the stream originates in the abandoned Juniper Uranium Mine. The Juniper Mine operated from 1956-1966 during which it is estimated to have produced 500 tons of uranium ore (USDA Forest Service Release, June 10, 2003). The mine is considered a point source for the influx of uranium to a natural surface hydrologic environment: a "clean creek". High-precision MC-ICP-MS isotopic analysis of chemically separated uranium from water, sediment leachates, and leached sediment samples allows us to characterize the downstream distribution and isotopic fractionation of uranium in the creek system. Results from this work show measurable isotopic variability due to mine contamination. (234U)/(238U) in waters and sediment leachates from the contaminated zone of Red Rock Creek are lower than those from the clean creek. Leached sediments show the opposite relationship (234U)/(238U) values from the contaminated creek are higher than the clean creek. The influence of the mine on the (234U)/(238U) ratio decreases downstream. Measured uranium concentrations are higher in the contaminated headwater creek leached sediments than the mine tailing sample suggesting that uranium has been transferred from the mine and accumulated in the stream. The distribution of uranium in these systems suggests that adsorption is a key element of uranium transfer along the creek. In clean creek samples, uranium is concentrated in the leached sediment residues. While in the contaminated creek, uranium is concentrated on the sediment surfaces (~70-80% of U in leachate). Contamination levels of uranium only exceed the EPA maximum contaminant level (MCL) for drinking water in the closest proximity sample to the mine. Uranium returns to below MCL 0.04 miles downstream of the mixing point.
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