Uranium is a persistent and costly subsurface contaminant across the U.S. and at nuclear sites around the world. It is frequently present in shallow aquifer or capillary fringe sediments, where it is subjected to seasonal variations in soil moisture, temperature, redox conditions, and relative permeability. Because uranium mobility is redox dependent and uranium complexes strongly to environmental ligands such as carbonate and organic matter, local biogeochemical variability profoundly influences uranium behavior. Transitions in local biogeochemical conditions such as onset of reducing or oxidizing conditions are often driven by hydrological transitions, such as spring inundation of the unsaturated zone or draining of shallow sediments under summer drought. This temporal coupling creates conditions under which hydrological transitions can trigger profound changes in uranium bioavailability and transport modes.<br/> <br/>Our program group has been studying geochemical and hydrological controls over uranium mobilization in the shallow contaminated floodplain at the Riverton, WY legacy ore processing site.  This work shows that that rapid changes in uranium speciation and redox status are triggered by changes in sediment saturation state, facilitating robust coupling to seasonal downward and upward water transport. This geochemical-hydrological coupling facilitates exchange between the aquifer, traps uranium in shallow sediments, and creates conditions that prolong uranium plume longevity. In aggregate, our findings emphasize the importance of ‘hot moment’ activity to uranium behavior and the importance of seasonal hydrological context to uranium redox transitions and mobilization.<br/>

Hydrological-geochemical controls over uranium mobility in unsaturated zone sediments

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.