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

Two-dimensional diffusive and advective-diffusive chloride transport through clay and
silt, respectively, was investigated using laboratory models. The observed chloride concentration
plumes in the soil samples as well as the chloride concentration-versus-time profiles in the source
reservoirs were predicted using the computer code MIGRATEv9. Equivalent horizontal and
vertical chloride diffusion coefficients reasonably predicted the observed concentration plumes
and concentration-versus-time indicating that soils were homogeneous and isotropic. The predicted
diffusion coefficients were in the range of the reported values for similar soils. The effect of
downward Darcy flux in the advection-diffusion tests on the chloride concentration plumes was
assessed by comparing the shapes of the plumes with those in the pure diffusion tests. The
downward Darcy flux caused the concentration plumes in the advection-diffusion tests to migrate
further in the vertical direction compared to that in the horizontal direction. All plumes spread
symmetrically with respect to the vertical axis of symmetry of the silt samples, and the applied
horizontal base flow had no significant effect on the symmetrical shape of the plumes in the
advection-diffusion tests. Overall, the existing two-dimensional advective-diffusive-dispersive
contaminant transport theory as implemented in the computer code MIGRATEv9 reasonably
predicted the chloride migration through silt and clay.