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 NewtonRaphson 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 RungeKutta 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 
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