Collaborative Research: Colloid Mobilization and Transport in the Vadose Zone

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9909508SaiersColloids, mobilized within the vadose zone during rainfall events, scavenge and carry contaminants to underlying groundwater. Despite the importance of colloids as agents of vadose-zone contaminant transport, the factors influencing colloid movement through partially saturated porous media have not been rigorously explored nor formalized into a quantitative model. In particular, the role of flow transients on colloid interactions at solid-water interfaces, at air-water interfaces, and within thin films of water has not been adequately investigated to date. This research, carried out jointly by investigators at Yale and at UVA, will integrate laboratory-scale and field-scale experiments with mathematical modeling. We will measure colloid transport in laboratory experiments conducted with ideal media and with intact cores, and we will use these data to guide the development of a numerical model for the coupled advective-dispersive transport and mass transfer of colloids in unsaturated soils. The structure of the numerical model identified from analysis of the laboratory-scale experiments will form the foundation for a stochastic streamtube model, a model capable of accounting for the effects of spatial variability in soil properties on colloid fate and transport. The streamtube model will be tested against data from a field experiment in which colloid mobilization and transport is measured in response to transient flow events induced by controlled sprinkling over an instrumented field plot. Our work represents the first systematic approach to identifying the controls on colloid movement in water-unsaturated media under transient-flow conditions and provides a means to evaluate the contribution of the colloid track to contaminant fluxes within vadose-zone environments.