The Galloway research team has developed and documented three computer toxics for simulating flow and transport in the unsaturated zone that are available to the public. These toxics were funded by the Toxics Substances Hydrology Program. The computer codes are written in Fortran F77 and run on a variety of computer systems, including mainframe and personal computers, with only minor adaptations. The programs are written in a modular structure which facilitates modifications to the source code. Whenever these modifications are made, the program must be recompiled with a Fortran F77 compiler to incorporate the changes in the executable versions of the program code. The commands needed to link and compile the program depend on the type of compiler being used.
R-UNSAT is a computer model for the simulation of reactive, multispecies transport in a heterogeneous, variably-saturated porous media. R-UNSAT was designed for simulating transport of volatile organic compounds in the unsaturated zone from point and nonpoint sources, but can also be applied to other unsaturated-zone transport problems involving gas diffusion, such as radon migration and the deposition of compounds from the atmosphere to shallow ground water. In a calibrative mode, R-UNSAT can be used to estimate rates of mass transport, biodegradation and volatilization rates, or transport properties of unsaturated-zone sediments. In a predictive mode, R-UNSAT can be used to predict the distribution of a species as a function of time and space and to estimate mass-loss or loading rates to ground water.
AIR2D is a flow model for simulating the movement of air to or from a single borehole screened in the unsaturated zone and can be applied to predict a steady-state flow field associated with vapor extraction. AIR2D can be used in a calibrative mode to obtain estimates of unsaturated-zone air-phase permeability from pneumatic pump test data. In a predictive mode, AIR2D can be used to simulate the performance of a single venting well by generating pressure and flow values for a specified geologic setting, air permeability distribution, and well discharge or injection rate.
AIR3D is an adaptation of the ground-water flow code MODFLOW to simulate three dimensional air-flow in a heterogeneous, anisotropic unsaturated zone where air flow is induced through dry wells or trenches, as in vapor- extraction remediation. Although the code was developed primarily for this purpose, it can also be used to simulate natural air flow in the unsaturated zone caused by atmospheric-pressure variations.
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