User's Guide to PHREEQC--a Computer Program for Speciation, Reaction-Path, Advective-Transport, and Inverse Geochemical Calculations

By David L. Parkhurst

U.S. Geological Survey

Water-Resources Investigations Report 95-4227, 1995, 143 p.

This is the user's guide to PHREEQC, a computer program written in the C programming language that performs a wide variety of aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations, (2) reaction-path and advective-transport calculations involving specified irreversible reactions, mixing of solutions, mineral and gas equilibria, surface-complexation reactions, and ion-exchange reactions, and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for composition differences between waters, within specified compositional uncertainties.

TABLE OF CONTENTS

Abstract
INTRODUCTION

Program Capabilities

Program Limitations

How to Obtain the Software and Manual

Installation and Setup of the DOS Version

Installation and Setup of the Unix Version

Purpose and Scope

EQUATIONS FOR SPECIATION AND FORWARD MODELING

Activities and Mass-Action Equations

Equations for the Newton-Raphson Method

NUMERICAL METHOD FOR SPECIATION AND FORWARD MODELING

Application to Aqueous Speciation Calculations

Application to Initial Exchange Calculations

Application to Initial Surface Calculations

Application to Reaction and Transport Calculations

EQUATIONS AND NUMERICAL METHOD FOR INVERSE MODELING
ORGANIZATION OF THE COMPUTER CODE
DESCRIPTION OF DATA INPUT

Conventions for Data Input

Reducing Chemical Equations to a Standard Form

Conventions for Documentation

Overview of Data Files and Keyword Data Blocks

EQUILIBRIUM_PHASES

EXCHANGE_MASTER_SPECIES

EXCHANGE_SPECIES

INVERSE_MODELING

REACTION_TEMPERATURE

SELECTED_OUTPUT

SOLUTION_MASTER_SPECIES

SOLUTION_SPECIES

SURFACE_MASTER_SPECIES

SURFACE_SPECIES

SUMMARY OF DATA INPUT
EXAMPLES

Example 1.-- Speciation Calculation

Example 2.-- Equilibration with Pure Phases

Example 3.-- Mixing

Example 4.-- Evaporation and Homogeneous Redox Reactions

Example 5.-- Irreversible Reactions

Example 6.-- Reaction-Path Calculations

Example 7.-- Gas-Phase Calculations

Example 8.-- Surface Complexation

Example 9.-- Advective Transport and Cation Exchange

Example 10.-- Advective Transport, Cation Exchange, Surface Complexation, and Mineral Equilibria

Example 11.-- Inverse Modeling

Example 12.-- Inverse Modeling with Evaporation

REFERENCES CITED
Attachment A--Listing of Notation
Attachment B--Description of Database Files and Listing