One-Dimensional Transport with Equilibrium Chemistry (OTEQ) — A Reactive Transport Model for Streams and Rivers Techniques and Methods Book 6, Chapter B6 U.S. Department of the Interior U.S. Geological Survey Cover. Upper workings of the Pennsylvania Mine in the headwaters of Peru Creek, Colorado. Photograph by Robert L. Runkel, U.S. Geological Survey, September 2009. One-Dimensional Transport with Equilibrium Chemistry (OTEQ): A Reactive Transport Model for Streams and Rivers By Robert L. Runkel Toxic Substances Hydrology Program Techniques and Methods Book 6, Chapter B6 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2010 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1–888–ASK–USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1–888–ASK–USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. 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. iii Contents Abstract . 1 1 Introduction . 2 1.1 Overview . 2 1.2 Applicability . 2 1.3 Related Reading . 2 1.4 Report Organization. 2 1.5 Acknowledgments . 3 2 Theory . 4 2.1 Overview . 4 2.2 Conceptual Model, Governing Equations, and the Sequential Iteration Method . 5 2.2.1 Model Assumptions . 5 2.2.2 Derivation of Governing Equations . 6 2.2.3 A General Solution Scheme based on Sequential Iteration. 8 2.3 Process Formulation . 11 2.3.1 pH . 11 2.3.2 Precipitation/Dissolution. 11 2.3.3 Sorption . 13 2.3.4 Oxidation/Reduction. 20 2.3.5 Transient Storage . 22 2.3.6 Settling of Solid Phases. 24 2.4 Numerical Solution . 24 2.4.1 The Conceptual System — Segmentation. 24 2.4.2 Boundary Conditions . 25 2.4.3 Initial Conditions. 26 3 User’s Guide . 27 3.1 Conceptual System, Revisited . 27 3.2 Input/Output Structure . 28 3.3 Input Format . 29 3.3.1 Units . 30 3.3.2 Internal Comments. 30 3.3.3 The Control File. 30 3.3.4 The Parameter File . 31 3.3.5 The Flow File . 40 3.3.6 The MINTEQ Input File. 43 3.3.7 The MINTEQ Database Files. 45 3.4 Input File Preparation and Model Execution. 45 3.4.1 Preparation of the Control File . 45 3.4.2 Preparation of the Parameter and Flow Files — Use of MINTEQ . 45 3.4.3 Preparation of the MINTEQ input file — Use of PROTEQ . 46 3.4.4 Execution of OTEQ . 47 iv 3.5 Output Analysis . 48 3.5.1 The Solute and Solid Output Files . 48 3.5.2 Concentration-Distance Output Files . 49 3.5.3 The Post-Processor, POSTEQ . 49 3.5.4 Plotting Alternatives . 49 4 Model Applications . .50 4.1 Application 1: Time-Variable Simulation of a Solute Pulse with Precipitation . 50 4.1.1 The Control File — Application 1. 51 4.1.2 The Parameter File — Application 1. 51 4.1.3 The Steady Flow File — Application 1 . 54 4.1.4 The MINTEQ Input File — Application 1 . 54 4.1.5 Simulation Results — Application 1 . 55 4.1.6 Numerical Issues — Application 1 . 56 4.2 Application 2: Time-Variable Simulation of pH and pH-Dependent Precipitation . 57 4.2.1 The Parameter and Flow Files — Application 2 . 58 4.2.2 The MINTEQ Input File — Application 2 . 59 4.2.3 Simulation Results — Application 2 . 59 4.3 Application 3: Time-Variable Simulation of Copper Sorption to the Streambed . 61 4.3.1 The Parameter File — Application 3. 61 4.3.2 The Unsteady Flow File — Application 3 . 64 4.3.3 The MINTEQ Input File — Application 3 . 64 4.3.4 Simulation Results — Application 3 . 66 4.3.5 Numerical Issues — Application 3 . 66 4.4 Application 4: Steady-State Simulation of Existing Conditions and Remedial Action 68 4.4.1 Quasi-Steady-State Simulations . 68 4.4.2 Modeling Existing Conditions and Remediation . 69 4.4.3 Simulation Results — Application 4 . 70 4.5 Application 5: Steady-State Simulation of Sorption onto Water-Borne Precipitates 70 4.5.1 The Parameter, Flow, and MINTEQ Input Files — Application 5 . 72 4.5.2 Specification of H and CO3: The Case of Waterborne Solid Phases. 73 4.5.3 Simulation Results — Application 5 . ..