Environmental Fate and Transport Analysis with Compartment Modeling

Introduction
GEM Highlights
Getting Started: Two Examples
Organization and Suggested Reading Strategy

GEM User’s Guide
Two Alternative Formulations of PRAM-Like Model
GEM Input Files
GEM Output Files

Compartment Approach, Transport Mechanisms, and Boundary Conditions
Compartment Approach
Mass Balance Equation for Compartment i
System of Transport Mass Balance Equations for Single Chemical
System of Transport Mass Balance Equations for Multiple Chemicals
Extension to Porous Media
Boundary Conditions and Types of Compartments

Source and Sink Terms
Linear Source and Sink Terms
System of Fate and Transport, Mass Balance Equations for Multiple Chemicals
Source and Sink Terms for Nonlinear Systems

Solution Techniques for Steady-State Problems
Linear Systems
Nonlinear Systems
Accuracy of Solutions

Solution Techniques for Dynamic Problems
Introduction
Explicit Forward Time (Euler) Method
Explicit Centered Time (MacCormack) Method
Implicit Back Time Method
Implicit Centered Time (Crank–Nicolson) Method
Cross-Method Comparisons and Summary of Error Characteristics for Linear Problems

Biography

Keith W. Little, Ph.D., P.E., is a consulting engineer specializing in the development and application of mathematical modeling and systems analysis methods to environmental engineering and water resources problems. Dr. Little earned a Ph.D. from the University of North Carolina at Chapel Hill where, in 1985, he was awarded the Bernard Greenberg Award for Excellence in Doctoral Research. This research was the genesis of the GEM software used to illustrate the concepts in this book. Since then, the GEM software has evolved in functionality and application and has been used to support risk assessment-based decision making at the U.S. Environmental Protection Agency (EPA). Dr. Little has enjoyed a 30-year career in environmental engineering and research, including 15 years as a research environmental engineer at RTI International, where he led the environmental modeling group. He has authored numerous technical reports and articles for peer-reviewed journals. He has also been active in various professional organizations and was president of the Colorado section of the American Water Resources Association in 1995. He is currently an independent consultant in Raleigh, North Carolina.

Keith Little’s book provides an excellent introduction to compartmental modeling that is well written and accessible to a wide range of environmental professionals. The text includes sufficient rigor to ensure effective and accurate model application, while keeping the material focused on real-world, practical applications. The accompanying GEM software is the only readily available compartmental model with complete flexibility and extendibility in the model setup. This powerful tool can be used literally to simulate an infinite range of potential modeling scenarios without changes to the underlying source code. Dr. Little’s book and GEM software are welcome contributions to the environmental modeling field.
—Michael Lowry, RTI International, North Carolina, USA

This is an excellent integration of numerical methods with environmental modeling. The compartment technique discussed is broadly applicable to a wide range of environmental problems and media. Well written. The mathematics and derivations are nicely detailed and straightforward to follow. Clearly the best discussion of stability and numerical dispersion available for environmental modelers. Dr. Little’s book covers critical topics that too often receive only a passing mention in more traditional environmental modeling texts.
—Daniel Gallagher, Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, USA

This book is clearly written. It strives to give the uninformed reader an introduction to the topic of environmental modeling and it succeeds. Not only does it motivate and explain the basic concepts of compartmental modeling but it also discusses some of the natural extensions such as incorporating sink and source terms. Also, it gives insight into some of the issues that may arise when using various numerical methods. ... With this book as a resource, the modeler should be well informed on how to approach a problem and issues they should be aware of when analyzing or solving the model.
—Ellen Peterson, Carnegie Mellon University, Pennsylvania, USA