FINITE-ELEMENT METHOD FOR CONTAMINANT TRANSPORT IN UNSATURATED SOILS

A numerical model to simulate miscible contaminant transport through unsaturated soils is presented. To account for the influence of multiple nonequilibrium sources on the contaminant transport, six governing phenomena of the miscible contaminant transport (i.e., convection, mechanical dispersion, molecular diffusion, adsorption, degradation, and immobile water effect) are integrated into the present model. The pollutant volumetric concentration in mobile water is taken as primary unknown, whereas the pollutant concentration in immobile water and the solid particles of soils are treated as state variables at the element integration points. Based on a splitting of the generalized convective operator from the diffusive operator, a modified version of the characteristic Galerkin method is developed to discretize the equations governing the contaminant transport phenomena. A fully explicit algorithm is then derived for the numerical solution of the finite-element equations in time domain. The numerical examples illustrate the performance and the capability of the presented model and algorithms.