A MULTIREGION MODEL DESCRIBING WATER-FLOW AND SOLUTE TRANSPORT IN HETEROGENEOUS SOILS

Many different processes influence chemical breakthrough patterns from soil columns, including chemical kinetics, diffusion, matrix geometry , and flow heterogeneity. TRANSMIT, a multiregion model that reflects many of these features, was used to simulate a suite of solute breakth rough curves from soil columns subjected to both transient and steady- state Bow. When utilized as a two-region model, TRANSMIT matched analy tical solutions for steady-state how through two-region soils. The TRA NSMIT model is easily expanded to describe a wide range of multiregion and two-dimensional geometries and is applicable to transient and ste ady-state Bow typical of both laboratory experiments and field situati ons. Sorption and degradation parameters can be varied, and nonuniform surface boundary conditions, resulting from irrigation method and ban ded chemical placement, can be described.