GGSD Program Details for PHREEQC

PHREEQC

Category	Geochemistry
Publisher	US Geological Survey
Platform	DOS, Mac, UNIX, Linux, Sun
Status	Public domain
Description	PHREEQC is a program designed to perform a wide variety of low temperature aqueous geochemical calculations. It is based on an ion association aqueous model and has capabilities for speciation and saturation index calculations; batch reaction and 1D transport calculations involving reversible reactions, which include aqueous, mineral, gas, solid solution, surface complexation, and ion exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits. For speciation and batch reaction calculations, it solves sets of nonlinear mole balance and mass action equations that define an ion association model. A Newton-Raphson formulation is used to iteratively arrive at a solution to the equations. A numerical method is provided by using an optimizing solver that allows both equality and inequality equations. The solver is used to obtain the intermediate estimates of changes in the unknowns at each iteration. For inverse modeling, a set of linear mole balance equations are solved. The equations contain additional unknowns that account for uncertainty in the analytical data. The optimizing solver is used to solve the linear equations while maintaining the uncertainty terms within specified limits. For transport modeling, the partial differential equations of transport are solved by an operator splitting scheme that sequentially solves for advective and dispersive transport, followed by chemical equilibration that is equivalent to batch reaction calculations for each cell. Time steps are selected to maintain numerical accuracy. If kinetic reactions are modeled, another splitting of operators is implemented and a 5th order Runge-Kutta method is used to integrate the ordinary differential equations of the kinetic reactions.
Cost	Free on WWW
Data formats supported	None stated
Supplier in France	OECD Nuclear Energy Agency
Supplier in United States of America	International Ground Water Modeling Center
Supplier in United States of America	US Geological Survey