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A Multi-Rate Mass Transfer Model for Field-Scale Uranium Transport in a Physically and Chemically Heterogeneous Aquifer

Monday, April 12, 2010: 2:10 p.m.
Continental A (Westin Tabor Center, Denver)
Rui Ma, Ph.D. , Department of Geology, University of Alabama, Tuscaloosa, AL
Chunmiao Zheng , Department of Geology, University of Alabama, Tuscaloosa, AL
Chongxuan Liu , Pacific Northwest National Laboratory, Richland, WA
John Zachara , Pacific Northwest National Laboratory, Richland, WA
Henning Prommer, Ph.D. , Land and Water, CSIRO, Wembley, Western Australia 6913, Australia
Janek Greskowiak , Land and Water, CSIRO, Wembley, Western Australia 6913, Australia
The concentration of uranium contaminants has remained high in the 300 Area of the Hanford site in southeast Washington State in spite of cessation of liquid effluent discharge to the source pond and removal of contaminated soils years ago. Kinetic U(VI) release resulted from diffusive mass transfer from intragrain, intra-coating, and intragrain aggregate regions of sediments has been observed in column systems [Qafoku et al., 2005; Liu et al., 2008] and proved by microscopic and spectroscopic characterizations of the sediments [Arai et al., 2007]. In this study, we have developed a three-dimensional multi-rate mass transfer model to plan for an urannium tracer experiment at the 300A site. The field-scale reactive transport model was developed on the basis of laboratory-characterized uranium surface complexation reactions (SCR) and multi-rate mass transfer processes, and field-measured hydrogeochemical conditions. This reactive transport model was used to (1) assess the impact of multi-scale mass transfer processes on uranium release from aquifer materials, (2) identify the differences and similarities between the sensitivities of key flow, transport and geochemical parameters at the laboratory and field scales, and (3) evaluate the optimal experimental and monitoring designs that result in the most robust estimates of mass transfer coefficients.

References:

Liu, C., J. M. Zachara, N. P. Qafoku, and Z. Wang (2008), Scale-dependent desorption of uranium from contaminated subsurface sediments, Water Resour. Res., 44, W08413, doi: 10.1029/2007WR006478.

Arai, Y., M. A. Marcus, N. Tamura, J. A. Davis, and J. M. Zachara (2007), Spectroscopic Evidence for Uranium Bearing Precipitates in Vadose Zone Sediments at the Hanford 300-Area Site, Environ. Sci. Technol. 41, 4633-4639.

Qafoku, N. P., J. M. Zachara, C. Liu, P. L. Gassman, O. S. Qafoku, and S. C. Smith (2005), Kinetic desorption and sorption of U(VI) during reactive transport in a contaminated Hanford sediment, Environ. Sci. Technol., 39(9), 3157-3165.

See more of: Reactive Transport Modeling
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