U.S. Geological Survey phreeqc(1) NAME phreeqc - A program for speciation, batch-reaction, one- dimensional transport, and inverse geochemical calculations SYNOPSIS phreeqc [infile [outfile [database [screen_output]]] OPTIONS infile the name of the PHREEQC input file outfile the name of the file to which PHREEQC output will be written database the name of the PHREEQC database screen_output the name of the file to which screen output will be directed If no arguments are specified, the program prompts for the input, output, and database file names. If only infile is specified, then outfile defaults to infile.out. If no database file is specified, the phreeqc.dat database distributed with PHREEQC will be used. ABSTRACT PHREEQC is a computer program written in the C programming language that is designed to perform a wide variety of low- temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and one-dimensional (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 (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits. METHOD For speciation and batch-reaction calculations, PHREEQC 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 robust 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, yet 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. HISTORY--See RELEASE.TXT DATA REQUIREMENTS Proper use of the program requires adequate knowledge of geochemistry and a proper formulation of the problem. Input is arranged in keyword data blocks, which can appear in any order. Data fields for a keyword are read in a free format, thus they are not column dependent. For speciation modeling, analytical data for a solution composition (SOLUTION keyword) are needed. For batch-reaction modeling, the initial solution composition is required (SOLUTION or MIX data block). Other equilibrium reactants may be defined with EQUILIBRIUM_PHASES, EXCHANGE, SURFACE, GAS_PHASE, and SOLID_SOLUTION data blocks. Nonequilibrium reactions may be defined with KINETICS and RATES, REACTION, and REACTION_TEMPERATURE data blocks. For 1D transport modeling, the data for batch-reaction modeling are needed for each cell in the modeled system. In addition, physical information is needed about column dimensions, time steps, boundary conditions, and dispersivity. For inverse modeling, the solution composition of the final solution and one or more initial solutions are needed (SOLUTION data block). Uncertainty limits must be defined explicitly or by default for each element and element redox state in the solutions. In addition, the identity and composition of a set of plausible reactants and products are needed. Three default databases are included that contain the definition of aqueous species, exchange species, surface species, and mineral and phases for a set of elements. The database phreeqc.dat contains information for Al, B, Ba, Br, C, Ca, Cd, Cl, Cu, F, Fe, H, K, Li, Mg, Mn, N, Na, O, P, S, Si, Sr, Zn. The database wateq4f.dat contains the additional constituents Ag, As, Cs, Fulvate, Humate, I, Ni, Rb, Se, and U. The database minteq.dat is derived from the thermodynamic data of the program MINTEQA2. If additional elements, species, or phases are needed, then chemical reactions, log K, and data for the temperature dependence of log K are needed for each additional species and phase. SYSTEM REQUIREMENTS PHREEQC is written in ANSI C. Generally, the program is easily installed on most computer systems. The code has been used on UNIX-based computers and on IBM-compatible computers with processors running at 100 megahertz or faster. DOCUMENTATION Parkhurst, D.L., and Appelo, C.A.J., 1999, User's guide to PHREEQC (Version 2)--a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Water- Resources Investigations Report 99-4259, 312 p. Thorstenson, D.C., and Parkhurst, D.L., 2002, Calculation of individual isotope equilibrium constants for implementation in geochemical models: U.S. Geological Survey Water-Resources Investigations Report 02-4172, 129 p. RELATED DOCUMENTATION Charlton, S.R., Macklin, C.L. and Parkhurst, D.L., 1997, PHREEQCI--a graphical user interface for the geochemical computer program PHREEQC: U.S. Geological Survey Water- Resources Investigations Report 97-4222, 9 p. Charlton, S.R., and Parkhurst, D.L., 2002, PhreeqcI--A graphical user interface to the geochemical model PHREEQC: U.S. Geological Survey Fact Sheet FS-031-02, 2 p. Parkhurst, D.L., Thorstenson, D.C., and Plummer, L.N., 1980, PHREEQE--a computer program for geochemical calculations: U.S. Geological Survey Water-Resources Investigations Report 80-96, 195 p. (Revised and reprinted, 1990.) Plummer, L.N., Parkhurst, D.L., Fleming, G.W., and Dunkle, S.A., 1988, A computer program incorporating Pitzer's equations for calculation of geochemical reactions in brines: U.S. Geological Survey Water-Resources Investigations Report 88-4153, 310 p. Plummer, L.N., Prestemon, E.C., and Parkhurst, D.L., 1991, An interactive code (NETPATH) for modeling NET geochemical reactions along a flow PATH: U.S. Geological Survey Water-Resources Investigations Report 91-4078, 227 p. Plummer, L.N., Prestemon, E.C., and Parkhurst, D.L., 1994, An interactive code (NETPATH) for modeling NET geochemical reactions along a flow PATH--version 2.0: U.S. Geological Survey Water-Resources Investigations Report 94-4169, 130 p. REFERENCES Appelo, C.A.J., and Postma, D., 1993, Geochemistry, groundwater and pollution: Rotterdam, Netherlands, and Brookfield, Vermont, A.A. Balkema. Appelo, C.A.J., and Willemsen, A., 1987, Geochemical calculations and observations on salt water intrusions. I: A combined geochemical/mixing cell model: Journal of Hydrology, v. 94, p. 313-330. Parkhurst, D.L., and Plummer, L.N., 1993, Geochemical models, in Alley, W.M., ed., Regional ground-water quality: New York, Van Nostrand Reinhold, chap. 9, p. 199-225. Plummer, L.N., 1984, Geochemical modeling: A comparison of forward and inverse methods, in Hitchon, B., and Wallick, E.I., eds., Proceedings First Canadian/American Conference on Hydrogeology--Practical Applications of Ground Water Geochemistry, Banff, Alberta, Canada: Worthington, Ohio, National Water Well Association, p. 149-177. TRAINING PHREEQC is taught as part of the courses Geochemistry for Ground-Water Systems (GW3021TC) at the USGS National Training Center. CONTACTS Operation: U.S. Geological Survey David Parkhurst Denver Federal Center, MS 413 Lakewood, CO 80225 dlpark@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications. SEE ALSO netpath(1) - Interactive program for calculating NET geochemical reactions and radiocarbon dating along a flow PATH phreeqci(1) - Graphical user interface for PHREEQC phrqpitz(1) - A program for geochemical calculations in brines wateq4f(1) - A program for calculating speciation of major, trace, and redox elements in natural waters