General Solute Transport Model and Its Applications in Contaminant Migration Analysis

摘要

A general solute transport model is developed to simulate solute movement in both homogeneous and nonhomogeneous media. This general model, called Group Transfer Concentration (GTC) model, divides the medium into groups according to the water velocity in each group. Since the water velocity is a function of the hydraulic conductivity of the medium and/or the water content, nonhomogeneity is simulated according to its hydraulic conductivity by dividing the medium into homogeneous subregions. These subregions can be further divided into smaller groups as needed to model dead-end and unsaturated pores. Each group of the GTC model has its own parameters such as dispersion coefficient, retardation factor, and degradation rate. Mass transfer is allowed between every two groups in both the solution and solid phases, and the mass transfer rate is assumed to be proportional to the concentration difference between the two groups. This GTC model can be used for both saturated and unsaturated conditions if the group parameters are appropriately chosen such that the average water content in each group is constant. The GTC model covers the conventional dispersion-advection model, the mobile-immobile pores model, the nonequilibrium adsorption-desorption model, and the jointed porous rock model. A computer program was written to solve the GTC model using the finite-differences method. Experimental breakthrough curves (BTCs) generated by the authors were analyzed using the GTC model. The results showed that the single-group conventional dispersion-advection model can only describe the leading edge of a BTC. The two-group mobile-immobile pores model can be used to predict BTCs under homogeneous saturated conditions. More than two groups are needed to describe BTCs obtained under nonhomogeneous and/or unsaturated conditions. 33 refs., 3 figs., 1 tab. (ERA citation 10:040115)