PHAST (Parkhurst et al., 2010) is a program for simulating groundwater flow, solute transport, and multicomponent geochemical reactions in three-dimensional saturated groundwater flow systems. It can calculate a wide range of equilibrium and kinetic geochemical reactions. Flow and transport calculations are based on a modified version of HST3D, and geochemical reactions are calculatedwith the geochemical model PHREEQC.

Fig. 1: Example of a transport simulation usind PHAST. The pH value is shown in a range between 6.99 (blue) and 8.28 (red) after 100.000 s model time and assuming an inflow from the left and an outflow on the right.

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The most recent version of PHAST may be obtained from the USGS here.

References:

Parkhurst, D.L., Kipp, K.L., and Charlton, S.R., 2010, PHAST Version 2 - A program for simulating groundwater flow, solute transport, and multicomponent geochemical reactions: U.S. Geological Survey Techniques and Methods 6–A35, 235 p.