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