INFLUENCE OF MINERALOGICAL AND HYDROLOGICAL HETEROGENEITIES UPON CONTAMINANT MIGRATION

The subsurface at the US Department of Energy Hanford Reservation has been contaminated with historical leakage from nuclear processing storage tanks. Current contaminant distributions in the vadose zone are dependent upon the hydrological and geochemical heterogeneities of the sedimentary deposit, particularly grain size, water content, and mineralogy. The goal of this study is to determine the influence of these sedimentary heterogeneities upon the fate and transport of the contaminants uranium(VI) and CoEDTA. Geochemical reactivity was measured in batch kinetic, isotherm, and miscible displacement experiments. Coupled hydrological and geochemical processes were quantified by the displacement of nonreactive tracers and contaminants through large samples of unsaturated and intact sediments. Mechanisms of U(VI) reaction were found to be influenced by sediment type (siliciclastic or carbonate), surface area, and iron oxide content, while CoEDTA mobility was primarily influenced by Mn-oxide content. Sediment texture and the presence of interbedded fine-grained layers were found to significantly influence the hydrology. This study will highlight findings from the geochemical and hydrological investigations in order to provide an integrated approach to understanding subsurface metal transport at Hanford and elsewhere.