HR: 1340h
AN: H23E-1484    [Abstracts]
TI: The Effect of Variable Geochemical Conditions on the Reactive Transport of U(VI) in Small Scale Tracer Tests
AU: * Curtis, G P
EM: gpcurtis@usgs.gov
AF: U.S. Geological Survey, Water Resources Division, Menlo Park, CA 94025 United States
AU: Fox, P
EM: pfox@usgs.gov
AF: U.S. Geological Survey, Water Resources Division, Menlo Park, CA 94025 United States
AU: Kohler, M
EM: mkohler@usgs.gov
AF: Colorado School of Mines, Environmental Science and Engineering, Golden, CO 80401 United States
AU: Davis, J A
EM: jadavis@usgs.gov
AF: U.S. Geological Survey, Water Resources Division, Menlo Park, CA 94025 United States
AB: Small-scale tracer tests were conducted to evaluate the effect of variable geochemical conditions on the reactive transport of U(VI). The tracer tests were conducted in a shallow alluvial aquifer downgradient from a former uranium mill and a tailings disposal area near Naturita, CO. The U(VI) concentration in the groundwater at the tracer test site was approximately 5 μM, the alkalinity was 8.5 meq/L and the pH was approximately 7.1. Previous studies at the site demonstrated the U(VI) was most sensitive to the alkalinity and least sensitive to the pH values relative to the range of measured values. Uranium migration tests were conducted on a scale of 1-2.5 m and considered variable U(VI) and alkalinity and included Br as an inert tracer. The tracer tests demonstrated that the sediment readily released U(VI) even after many years of contact with the contaminated groundwater suggesting the U(VI) migration is controlled by adsorption reactions. Reactive transport simulations used a surface complexation model developed independently from laboratory bench scale studies to simulate adsorption. The reactive transport simulations gave good predictions of the observed breakthrough of U(VI) when the advection and dispersion parameters were fitted to Br breakthrough. Field studies also included several single well push-pull tests that were conducted at increased and decreased U(VI) and alkalinity values. Reactive transport simulations of these experiments will be presented and compared with the tracer tests simulations.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005