LABORATORY MODELING OF TWO-DIMENSIONAL DIFFUSIVE AND ADVECTIVE-DIFFUSIVE CHLORIDE TRANSPORT THROUGH SILT AND CLAY

Abstract

Two-dimensional diffusive and advective-diffusive chloride transport through clay andsilt, respectively, was investigated using laboratory models. The observed chloride concentrationplumes in the soil samples as well as the chloride concentration-versus-time profiles in the sourcereservoirs were predicted using the computer code MIGRATEv9. Equivalent horizontal andvertical chloride diffusion coefficients reasonably predicted the observed concentration plumesand concentration-versus-time indicating that soils were homogeneous and isotropic. The predicteddiffusion coefficients were in the range of the reported values for similar soils. The effect ofdownward Darcy flux in the advection-diffusion tests on the chloride concentration plumes wasassessed by comparing the shapes of the plumes with those in the pure diffusion tests. Thedownward Darcy flux caused the concentration plumes in the advection-diffusion tests to migratefurther in the vertical direction compared to that in the horizontal direction. All plumes spreadsymmetrically with respect to the vertical axis of symmetry of the silt samples, and the appliedhorizontal base flow had no significant effect on the symmetrical shape of the plumes in theadvection-diffusion tests. Overall, the existing two-dimensional advective-diffusive-dispersivecontaminant transport theory as implemented in the computer code MIGRATEv9 reasonablypredicted the chloride migration through silt and clay.