Numerical modelling of contaminant transport in unsaturated soils

This paper presents the development and validation of a numerical model for simulation of the flow of air and water and contaminant transport through unsaturated soils. The governing differential equations include two mass balance equations for the water phase and air phase together with a balance equation for contaminant transport through the two phases. In the model the nonlinear system of the governing differential equations is solved using a finite element method in the space domain and a finite difference scheme in the time domain. The governing equations of the miscible contaminant transport including advection, dispersion, and diffusion effects are presented. The mathematical framework and the numerical implementation of the model are described in detail. The model is validated by application to standard experiments on contaminant transport in unsaturated soils. Finally, the merits and limitations of the model are highlighted.