GEOC 20 |
| Concentrations of U(VI) in a groundwater plume beneath the former 300-Area process ponds (Hanford, Washington) are above the regulatory limit. To develop a conceptual model and remedial action plan, information is needed to evaluate the future release of uranium from vadose zone sediments beneath the ponds. Combined with spectroscopic measurements, extraction techniques and isotopic exchange experiments were employed to estimate chemical speciation and U(VI) release kinetics from a vadose zone depth-sequence. Sediments at shallow depths exhibited U(VI) release to groundwater by dissolution and desorption processes. Deeper sediments appear to release only adsorbed U(VI), but also contain co-precipitated U released by strong extractions which dissolve crystalline phases. The rate of U(VI) release was strongly dependent on alkalinity, which varies markedly in the aquifer due to infiltrating Columbia River water. Sediments at the water table serve as both sources and sinks for U(VI) migrating from the upper vadose zone to the river. |
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Frontiers in Geochemistry: Commemorating the 25th Anniversary of the ACS-Geochemistry Division
1:30 PM-4:50 PM, Sunday, 10 September 2006 Moscone Center -- Room 262, Oral
Division of Geochemistry |