PREDICTION AND EXPERIMENTAL VALIDATION OF LIQUID-PHASE DIFFUSION RESISTANCE IN UNSATURATED SOILS

Determination of liquid-phase diffusion through unsaturated soils is i mportant for estimating contaminant transport in soils and design of r emediation processes for contaminated soils and groundwater. Liquid-ph ase diffusion through unsaturated soils is governed by both the pore s ize distribution and water distribution of the soil matrix. Diffusion tube experiments were carried out using several soils packed to field densities to determine the effective diffusivity of chloride ion as a function of soil moisture content. Chloride was selected to serve as a non-volatile, non-sorbing tracer species. A transport model was devel oped to predict liquid-phase tortuosity as a function of readily obtai ned soil parameters, including density, moisture content, particle siz e distribution and pore size distribution. The basis of the model was parallel diffusion resistances in the inter- and intra-particle pore r egimes. The new model was found to provide an accurate prediction of o bserved experimental results. Previously reported models did not agree with experimental results over significant portions of the experiment al domain investigated.