PHREEQM-2D is a multi-component mass transport model consisting of two coupled simulation programs: HST2D and PHREEQE. PHREEQE is a geochemical reaction model developed by the U.S. Geological Survey. PHREEQM-2D includes dissolution/precipitation and ion exchange, and supports kinetic computations for one mineral.

HST2D-PC is a finite difference simulation program for density-dependent ground-water flow and associated heat and solute transport in two-dimensional saturated flow configurations. HST2D-PC is based on the HST2D model developed by the U.S. Geological Survey from the three-dimensional HST3D model. The governing equations include terms for advection, conduction, dispersion, first-order decay, and retardation. The three governing equations in HST2D are coupled through the interstitial pore velocity, the dependence of the fluid density on pressure, temperature, and solute-mass fraction, and the dependence of the fluid viscosity on temperature and solute-mass fraction. HST2D handles a variety of time-varying source and sinks terms and boundary conditions, including given pressure, temperature and concentration, given water, solute and heat flux, and leakage boundary conditions.

HST2D is used to calculate the pressure distribution (coupled to heat and/or dissolved solids transport, if necessary), and to derive velocities. The velocities are used by PHREEQM-2D to compute the chemical transport. Then, PHREEQE is used to calculate the chemical reactions, followed by the calculation of numerical dispersion. PHREEQM-2D compensates for the latter and calculates physical dispersion and diffusion using the corrected dispersion coefficient. Finally, PHREEQE is used again to obtain an improved calculation of the chemical reactions.

Both HST2D and PHREEQM-2D have menu-driven program modules to prepare and edit the extensive input files required to run the (DOS_based) programs. Output is in the form of text files with echo of input and results, simulation log files, files which can be processed in spreadsheet programs, and graphic output (contours) to screen and file.

SYSTEM REQUIREMENTS

Intel 80386/80486 based computer with math coprocessor, at least 3 Mb of free RAM, DOS 5.0 or higher, VGA graphics board and monitor, hard drive with about 4 Mb free disk space.

Authors: A. Willemsen IF Technology, Arnhem, The Netherlands (PHREEQM-2D); Hagoort & Associates, Delft, The Netherlands (HST2D-PC).