PHREEQCI—A Graphical User Interface to the

 Geochemical Model PHREEQC

U.S. Department of the Interior USGS Fact Sheet FS-031-02

U.S. Geological Survey April 2002

Figure 1. Main screen of PHREEQCI, with the SOLUTION keyword dialog box open.

PHREEQCI Version 2 is a complete

Windows-based graphical user interface to

the geochemical computer program

PHREEQC (Version 2). PHREEQCI can be

used interactively to perform all the

modeling capabilities of PHREEQC—

speciation, batch-reaction, onedimensional (1D) reactive-transport, and

inverse modeling.

Applications:

• Mine drainage

• Radioactive-waste isolation

• Contaminant migration

• Natural and engineered aquifer

remediation

• Aquifer storage and recovery

• Water treatment

• Natural systems

• Laboratory experiments

Features of the interface:

• Compatible with Windows 95 and 98,

Windows NT 4.0, Windows ME, Windows

2000, and Windows XP

• Automated installation using

InstallShield

• Interactive access to all of the

capabilities of PHREEQC—create and

modify input data files, run simulations,

and display results

Modeling capabilities:

• Aqueous, mineral, gas, surface, ionexchange, and solid-solution equilibria

• Kinetic reactions

• 1D diffusion or advection and

dispersion with dual-porosity medium

• A powerful inverse modeling capability

allows identification of reactions that

account for the chemical evolution in

observed water compositions

• Extensive geochemical databases

Any use of trade, product, or firm names in this

publication is for descriptive purposes only and

does not imply endorsement by the U.S.

Government.

PHREEQCI Version 2

PHREEQCI Version 2 is a computer

program for simulating chemical

reactions and transport processes in

natural or contaminated water. PHREEQCI

provides all of the capabilities of the

geochemical model PHREEQC

(Parkhurst and Appelo, 1999), including

speciation, batch-reaction, 1D reactivetransport, and inverse modeling.

Data for PHREEQC are entered

through a series of keyword data blocks,

each of which provides a specific type of

information. For example, the

SOLUTION keyword data block defines

the chemical composition of a solution.

PHREEQCI provides tabbed dialog boxes

for each PHREEQC keyword. Figure 1

shows the main screen of PHREEQCI and

the SOLUTION keyword dialog box.

Speciation Modeling

Applications—Speciation modeling

is useful in situations where the

possibility of mineral dissolution or

precipitation needs to be known, as in

water treatment, aquifer storage and

recovery, artificial recharge, and well

injection.

Description—Speciation modeling

uses a chemical analysis of a water to

calculate the distribution of aqueous

species by using an ion-association

aqueous model. The most important

results of speciation calculations are

saturation indices for minerals, which

indicate whether a mineral should dissolve

or precipitate.

Keyword data blocks used in

speciation modeling include:

SOLUTION—define the

chemical composition of a

solution.

SOLUTION_SPREAD—define

the chemical composition of

multiple solutions in a

spreadsheet format.

Batch-Reaction Modeling

Applications—Batch-reaction

modeling can be applied to problems in

laboratory, natural, or contaminated

systems. The reaction capabilities of

PHREEQC have been used frequently in

the study of mine drainage, radioactive-
waste disposal, degradation of organic

matter, and microbially mediated

reactions.

Description—Batch reactions can be

divided into equilibrium and

nonequilibrium reactions. Equilibrium

reactions include equilibration of a

solution with an assemblage of minerals

and specified-pressure gases, ionexchange sites, surface-complexation

sites, a finite gas phase, and (or) solid

solutions. Nonequilibrium reactions

include kinetic reactions, addition or

removal of elements from solution,

mixing, and changing temperature.

Keyword data blocks used in batchreaction modeling include:

EQUILIBRIUM_PHASES—an

assemblage of minerals and gases

that react to equilibrium (or until

exhausted).

EXCHANGE—one or more sets

of reaction sites for exchangeable

ions, an important reaction for

major cations.

SURFACE—one or more sets of

sites that react by surface

complexation, a major reaction for

phosphorus, arsenic, and other

trace elements.

GAS_PHASE—a finite reservoir

of gas that reacts with a solution.

SOLID_SOLUTIONS—solids

that precipitate as mixtures of

minerals, an important reaction

for radionuclides and other trace

metals.

KINETICS—any nonequilibrium

reaction, for which a rate

expression can be formulated.

RATES—BASIC language

statements define rate expressions

for kinetic reactions.

REACTION—addition and

removal of specified elements

from solution.

MIX—mixing together specified

fractions of solutions.

REACTION_TEMPERATURE—

changing the temperature of the

reaction system.

USE—use the composition of

previously defined or saved

(SAVE keyword) SOLUTION,

EQUILIBRIUM_PHASES,

EXCHANGE, SURFACE,

GAS_PHASE,

SOLID_SOLUTION, or a

previously defined KINETICS,

REACTION, MIX, or

REACTION_TEMPERATURE

data block.

SAVE—save the composition

following the batch reaction of the

SOLUTION,

EQUILIBRIUM_PHASES,

EXCHANGE, SURFACE,

GAS_PHASE, or

SOLID_SOLUTION for use in

subsequent reactions.

Transport Modeling

Applications—The reactive transport

capabilities can be used to study

contaminant migration of nutrients,

metals, radionuclides, and organic

compounds; natural and engineered

aquifer remediation; diffusion in sediment

pore water; the chemical evolution of

natural systems; and laboratory column

experiments.

Description—Reactive-transport

modeling simulates advection, dispersion,

and chemical reactions as water moves

through a 1D column. The column is

divided into a number of cells, and

reactant compositions and nonequilibrium

reactions can be defined for each cell. All

of the reactants and reactions described

for batch reactions can be applied to the

cells for transport modeling. The

TRANSPORT keyword data block is used

to simulate advection and dispersion, or

pure diffusion, in the column. The

TRANSPORT data block also can be used

to simulate a dual-porosity medium,

where water flows through the column but

simultaneously allows for diffusion into

stagnant side pores. The ADVECTION

keyword data block is used to simulate

purely advective transport.

 Keyword data blocks for transport

calculations:

TRANSPORT—1D advection,

dispersion, and reaction modeling.

ADVECTION—1D advection and

reaction modeling.

Inverse Modeling

Applications—Inverse modeling can

be used to deduce geochemical reactions

and mixing in local and regional aquifer

systems, and in aquifer storage and

recovery studies.

Description—Inverse modeling

calculates geochemical reactions that

account for the change in chemical

composition of water along a flow path.

For inverse modeling, at least two

chemical analyses of water are needed at

different points along the flow path, as

well as a set of minerals and gases that are

potentially reactive. Mole transfers of

phases are calculated that account for the

change in water composition along the

flow path. The numerical method accounts

for uncertainties in analytical data.

Keyword data block for inverse

modeling:

INVERSE_MODELING—deduce

mixing, mineral, and gas reactions

that account for the chemical

evolution of waters.

How to Obtain PHREEQCI, PHREEQC,

and Additional Information

Versions of PHREEQCI and PHREEQC

may be obtained at no cost from the

USGS at World Wide Web address

http://water.usgs.gov/software. Many

other hydrologic computer models are

also available from this site.

Reports documenting USGS model

programs can be purchased from the

following address:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225-0286

S.R. Charlton and D.L. Parkhurst

References

Parkhurst, D.L. and Appelo, C.A.J., 1999,

User’s guide to PHREEQC (Version

2)—A computer program for

speciation, batch-reaction, onedimensional transport, and inverse

geochemical calculations: U.S.

Geological Survey Water-Resources

Investigations Report 99-4259, 310 p.