AN ANALYTICAL SOLUTION OF MACRODISPERSIVITY FOR ADSORBING SOLUTE TRANSPORT IN UNSATURATED SOILS

An analytical solution of macrodispersivity was derived for the adsorb ing solute transport in physically and chemically heterogeneous unsatu rated soils under the condition of gravity-dominated flow. The unsatur ated hydraulic conductivity and water content were treated as spatial random functions. The chemical adsorption was described by a linear eq uilibrium isotherm, and the adsorption coefficient was represented as a spatial random function with specified correlation structures. The c losed-form expression for macrodispersivity was expressed as a functio n of the hydraulic and adsorbing statistical properties of the unsatur ated soil. For a short solute travel distance the macrodispersivity li nearly increased with the increase of the solute plume travel distance . The macrodispersivity approached an asymptotic value when the center of the solute plume moved a long distance, The general solution quant ified the effects of various factors, such as variabilities of the wat er content and unsaturated hydraulic conductivity, mean water content, and the retardation factor, on the macrodispersivity.