Techniques and Methods 6-A35 The computer program PHAST (PHREEQC
And HST3D) simulates multicomponent, reactive solute transport
in three-dimensional saturated groundwater flow systems. PHAST
is a versatile groundwater flow and solute-transport simulator
with capabilities to model a wide range of equilibrium and
kinetic geochemical reactions. The flow and transport
calculations are based on a modified version of HST3D that is
restricted to constant fluid density and constant temperature.
The geochemical reactions are simulated with the geochemical
model PHREEQC, which is embedded in PHAST. Major enhancements in
PHAST Version 2 allow spatial data to be defined in a
combination of map and grid coordinate systems, independent of a
specific model grid (without node-by-node input). At run time,
aquifer properties are interpolated from the spatial data to the
model grid; regridding requires only redefinition of the grid
without modification of the spatial data. PHAST is applicable to
the study of natural and contami