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Techniques and Methods 6-B6

One-Dimensional Transport with Equilibrium Chemistry (OTEQ) — A Reactive Transport Model for Streams and Rivers

By Robert L. Runkel

Abstract

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OTEQ is a mathematical simulation model used to characterize the fate and transport of waterborne solutes in streams and rivers. The model is formed by coupling a solute transport model with a chemical equilibrium submodel. The solute transport model is based on OTIS, a model that considers the physical processes of advection, dispersion, lateral inflow, and transient storage. The equilibrium submodel is based on MINTEQ, a model that considers the speciation and complexation of aqueous species, acid-base reactions, precipitation/dissolution, and sorption.

Within OTEQ, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (waterborne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach. The model’s ability to simulate pH, precipitation/dissolution, and pH-dependent sorption provides a means of evaluating the complex interactions between instream chemistry and hydrologic transport at the field scale.

This report details the development and application of OTEQ. Sections of the report describe model theory, input/output specifications, model applications, and installation instructions. OTEQ may be obtained over the Internet at http://water.usgs.gov/software/OTEQ.

First posted February 11, 2010

For additional information contact:

Director, USGS Colorado Water Science Center
Box 25046, Mail Stop 415
Denver, CO 80225

http://co.water.usgs.gov

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Runkel, R.L., 2010, One-dimensional transport with equilibrium chemistry (OTEQ) — A reactive transport model for streams and rivers: U.S. Geological Survey Techniques and Methods Book 6, Chapter B6, 101 p.



Contents

Abstract

Introduction

Theory

User's Guide

Model Applications

Software Guide

References Cited

Glossary

Appendix 1. Modifications to the MINTEQ Database


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