August 1, 2015.
More than 129 million liters of groundwater are contaminated with uranium at Old Rifle, Colorado – a former uranium-processing site that operated until 1958. The original Department of Energy (DOE) strategy for remediation, involving natural flushing of U from the groundwater through mixing with surface water, has not proven successful. Thin pockets of silt-, clay-, and organic-rich sediments referred to as naturally reduced zones (NRZs) act both as sinks and sources of U to the aquifer, contribute to plume persistence, and appear to be diffusion limited controlled.
To better understand how the NRZs are diffusion limited controlled, a bromide tracer was used to measure uranium diffusivity at two depths from the JB-02 well at Old Rifle: one depth in the middle of the NRZ and one depth at the bottom edge of the NRZ. A NaBr reservoir was allowed to diffuse into the sediments for several days with reservoir samples collected twice a day and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) for bromide concentrations. This data was then used to calculate net flux, effective diffusivity, and the tortuosity effect within the sediments, which will inform uranium management strategies not only at the Old Rifle site but potentially other DOE legacy sites including Riverton, Wyoming and Shiprock, New Mexico.
Environmental Health and Protection | Geochemistry | Hydrology | Natural Resources Management and Policy | Sedimentology | Soil Science
SLAC National Accelerator Laboratory (SLAC)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).