MODELING NONEQUILIBRIUM CONTAMINANT TRANSPORT PROCESSES IN SOILS AND GROUNDWATER

摘要

Accurate simulation of contaminant transport processes in the subsurface remains a major challenge in many science and engineering applications. In this paper we review a broad range of dual-porosity and dual-permeability formulations for modeling nonequilibrium or preferential fluid flow and contaminant transport in macroporous soils or fractured rock. We focus especially on transport processes in the variably-saturated vadose zone between the soil surface and the groundwater table. One effective modeling approach for flow is to use composite functions for the unsaturated hydraulic conductivity to account for the separate effects of macropores and micropores, and to combine this approach with a mobile-immobile water type nonequilibrium formulation for solute transport. Two example problems are given to illustrate the potentially important effects of preferential flow on the simulation results. One application concerns pesticide transport in a tile-drained field for which only limited data were available for model calibration. A second application involves the long-term environmental fate of a radionuclide decay chain released from a mining installation in Amazonia processing ore containing natural occurring radioactive materials.