Leaching of Contaminants to Groundwater

Abstract

In this chapter the water flow and contaminant transport processes in the unsaturated or vadose zone are described. These processes include water retention and hydraulic conductivity, evapotranspiration, preferential flow, root water uptake (water flow) and diffusion, dispersion, advection and volatilization (contaminant transport). The equation governing transport of dissolved contaminants in the vadose zone is obtained by combining the contaminant mass balance with equations defining the total concentration of the contaminant and the contaminant flux density. Further attention is this chapter is given to nonequilibrium transport, stochastic models, multicomponent reactive solute transport, multiphase flow and transport. Mathematical models should be critical components of any effort to understand and predict site-specific subsurface water flow and contaminant transport processes. Generally, models range from relatively simple analytical approaches for analyzing contaminant transport problems during one-dimensional steady-state flow, to sophisticated numerical models for addressing multi-dimensional variably-saturated flow and contaminant transport problems at the field scale. An overview is given of several existing analytical and numerical models. Moreover, several applications to unsaturated flow and geochemical transport modeling are presented in this chapter.