Long-term simulation of water and vapour phase transport in unsaturated-saturated soil

The simplification of a multi phase mass transport model to simulate the long-term transport of volatile organic contaminants migration is investigated. The resulting simplifications to the governing equations are: the water velocity is steady-state, the soil gas is immobile, and the organic phase compound is immobile. In this study, these assumptions are applied to a two-dimensional two-phase mass transport finite element model.;The assumption of steady-state water flow in the unsaturated zone is justified through a statistical comparison of the transient water flow to the steady-state flow. In the search for the limitations of this assumption, a sensitivity analysis was performed by perturbing the length of time in which the rainfall was averaged, the saturated hydraulic conductivity, the soil porosity, the residual water saturation, and the soil retention parameters. The results indicate that this assumption cannot be applied to a soil with saturated hydraulic conductivity less than 0.1 m/day or a soil with residual water saturations less than 0.01.;In the field simulation, the simplified model is capable of demonstrating the effect of long-term contaminant migration in the unsaturated-saturated zone. It shows that after 7 years, all the residual saturation is dissolve and volatile which will not be demonstrated by short-simulation of contaminant migration.