Advective-Diffusive Contaminant Migration in Unsaturated Sand and Gravel

Abstract

A method is presented for estimating the diffusion coefficients for chloride and sodium in unsaturated coarse sand and fine gravel based on parameters obtained from saturated diffusion tests conducted for similar material. The method is tested by comparing the observed and predicted diffusion profiles through unsaturated soil. The method is shown to work well for predicting the advective-diffusive migration of chloride and sodium through a two-layer soil system consisting of a compacted clayey silt underlain by an unsaturated fine gravel. Over the range of conditions examined, it is concluded that existing solute transport theory along with the proposed procedure for estimating the unsaturated diffusion coefficients can adequately predict chloride and sodium diffusion through both unsaturated coarse sand and fine gravel as well as predict advective-diffusive transport through a compacted clayey layer and underlying unsaturated fine gravel.