Abstract

GoPhast is a graphical user interface (GUI) for the USGS model PHAST.  PHAST simulates multi-component, reactive solute transport in three-dimensional saturated ground-water flow systems. PHAST can model both equilibrium and kinetic geochemical reactions. PHAST is derived from HST3D (flow and transport) and PHREEQC (geochemical calculations). The flow and transport calculations are restricted to constant fluid density and constant temperature.  The complexity of the input required by PHAST makes manual construction of its input files tedious and error-prone.  A GUI can streamline the creation of the input file and help reduce errors.  GoPhast allows the user to define the spatial input for the PHAST flow and transport data file by drawing points, lines, or polygons on top, front, and side views of the model grid. These objects can have as many as two associated formulas that define their extent perpendicular to the view plane. These formulas allows the objects to be three-dimensional.  Formulas are also used to specify the values of spatial data (data sets) both globally and for individual objects.  The values of data sets can be specified independently of the spatial and temporal discretization of the model through the use of objects.  Thus, the grid and simulation periods in the model can be changed without requiring spatial data pertaining to the hydrogeologic framework and boundary conditions to be respecified by the user.  This report describes how to use GoPhast with examples.  GoPhast runs on Windows 2000, Windows XP and Linux.