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An overview of the work by Corwin and coworkers (Corwin 1991, 1992; Corwin and Waggoner 1991a, 1991b; Corwin et al. 1991, 1992) is presented for the contaminant transport software package TETrans. The overview discusses past published work as well as unpublished data. Included in the overview is a discussion of the reasons for TETrans' development, verification of its predictive capability, sensitiviity analysis, its ability to model preferential flow, its strengths and limitations, and potential future modifications.
TETrans (acronym for Trace Element Transport), is a one-dimensional, functional model of solute transport through the vadose zone under transient-state conditions introduced by Corwin and Waggoner (1991a, 1991b). The complete TETrans software package consists of an interactive tutorial, user's guide and applications software. Both IBM-compatible and Apple Macintosh versions are available. TETrans is specifically designed around the philosophy of user-friendliness both in its operation and in the readily-available input parameters required for its operation. These features are meant to enhance TETrans' utility as a real-world application software tool for simulating the movement of nonvolatile organic and inorganic pollutants through soil and into the groundwater.
TETrans utilizes a mass-balance approach to determine solute concentration distributions in the soil over time and solute-loading to the groundwater. Several modeling options are available for simulating such transport-influencing factors as plant water uptake, hydraulic bypass and adsorption. In the Macintosh version, TETrans makes full use of the Macintosh interface to enhance the user-friendliness of the model. All functions are available from menu bars, pull-down menus, and dialog boxes; and simulation results are displayed in text and graphics (both two- and three-dimensional) windows.
TETrans differs from other transport models in the straightforward manner in which it handles the exacerbating problem of preferential flow or bypass. TETrans accounts for hydraulic bypass through a single hydraulic parameter, termed the mobility coefficient (Corwin and Waggoner 1991a, 1991b; Corwin et al. 1991). The mobility coefficient, γ, is the fraction of soil water within a soil layer which is subject to piston displacement. The mobility coefficient reflects the deviation of water flow from strict piston displacement. The mobility coefficient is determined from simple chemical analysis of chloride in the soil solution through the soil profile following the application of a plug of chloride in the irrigation water.
A comparison of predicted soil solution boron concentrations using both TETrans and the Hanks' et al. (1980) solute transport model to measured concentrations shows an improved ability of TETrans to simulate the movement of boron, particularly near the soil surface where preferential flow through cracks created from wetting and drying is a factor (Corwin 1992). The simulated results for both transport models were similar below 0.30 m.
miscible displacement, piston flow, transient-state flow, vadose zone, unsaturated flow, contaminant transport
Soil Scientist, U. S. Salinity Laboratory, USDA-ARS, Riverside, CA