Coupled Solute Migration Through Clay Barrier Materials

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9616854 The traditional advection-dispersion theory for miscible contaminant (solute) migration through soil in reality represents a limiting case of the more general coupled-flow theory in which the coupling terms (e.g. water flow due to chemico-osmosis) are assumed to be zero. While this assumption is generally acceptable in the case of miscible contaminant migration through relatively high permeability materials, the accuracy of this assumption in terms of the relatively low-permeability, fine-grained materials typical of pollutant barriers has not been formally evaluated. The goal of this study is to evaluate the significance of chemico-osmosis and electro-osmosis on the migration of miscible contaminants through engineered clay barriers used for waste containment and in situ remediation. The following objectives will be addressed: * coupled flow parameters (e.g. hydraulic, chemico- osmotic, and electro-osmotic conductivity; electrical conductance; and osmotic efficiency coefficient) for clay soils will be measured under several different test conditions (stress, compaction, solute concentration and type); * parameters expected to dominate solute transport under low-flow conditions will be measured independently for the same soils, solutes, and test conditions; * measured migration rates of the solutes through laboratory soil columns will be compared with predicted rates using analytical models based on both the coupled flow and the advective-diffusive modeling approaches; and * a finite difference model will be developed and used to evaluate the potential effect of volume change on solute mass flux for both coupled flow and the advective-diffusive modeling approaches. ***