STANMOD: Model Use, Calibration, and Validation

Abstract

This article provides an overview of STANMOD, a Windows-based computer software package for evaluating solute transport in soils and groundwater using analytical solutions of the advection-dispersion equation. The software integrates seven separate codes that have been popularly used over the years for a broad range of one-dimensional and multi-dimensional solute transport applications: the CFITM, CFITIM, CXTFIT, CHAIN, and SCREEN models for one-dimensional transport, and the 3DADE and N3DADE models for multi-dimensional transport. All of the models can be run for direct (forward) problems, and several (CFITM, CFITM, CXTFIT, and 3DADE) can also be run for inverse problems. CXTFIT further includes a stochastic stream tube model assuming local-scale equilibrium or nonequilibrium transport conditions. The 3DADE and N3DADE models apply to two- and three-dimensional transport during steady unidirectional water flow assuming equilibrium and nonequilibrium transport, respectively. Nonequilibrium transport can be simulated using the assumption of either physical nonequilibrium (two-region or mobile-immobile type transport) or chemical nonequilibrium (two-site partial equilibrium, partial kinetic sorption). The STANMOD software comes with a large number of example applications illustrating the utility of the different codes for a variety of laboratory and field-scale solute transport problems.