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WATER RESOURCES RESEARCH, VOL. 42, W04404, doi:10.1029/2005WR003979, 2006

Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions

Gary P. Curtis

U.S. Geological Survey, Menlo Park, California, USA


James A. Davis

U.S. Geological Survey, Menlo Park, California, USA


David L. Naftz

U.S. Geological Survey, West Valley City, Utah, USA


Abstract

The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KD values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling KD values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated KD values varied temporally and spatially because of the differential transport of U(VI) and alkalinity and the nonlinearity of U(VI) adsorption. The model also simulated the observed U(VI) tailing, which would not be expected from a constant KD model. The simulated U(VI) concentrations were sensitive to the recharge flux because of the increased flux of U(VI) to the aquifer. The geochemical behavior of U(VI) was most sensitive to the alkalinity and was relatively insensitive to pH.

Received 21 January 2005; accepted 3 January 2006; published 7 April 2006.

Keywords: adsorption; reactive transport; solute transport; uranium.

Index Terms: 1009 Geochemistry: Geochemical modeling (3610, 8410); 1803 Hydrology: Anthropogenic effects (4802, 4902); 1831 Hydrology: Groundwater quality; 1832 Hydrology: Groundwater transport.

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Citation: Curtis, G. P., J. A. Davis, and D. L. Naftz (2006), Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions, Water Resour. Res., 42, W04404, doi:10.1029/2005WR003979.