Simulation of Contaminant Migration Through a Soil Layer Due to an Instantaneous Source ERDAL COKCA, H. TOLGA BILGE, BERNA UNUTMAZ Department of Civil Engineering, Middle East Technical University, 06531 Ankara, Turkey Received 13 August 2008; accepted 9 December 2008 ABSTRACT: Analytical and numerical simulation models help civil and environmental engineering students to understand the physical and chemical processes that influence contaminant transport through a saturated soil layer, including advective and dispersive transport as well as sorption. The basic principles for simulation of contaminant migration through a saturated soil were introduced. Using the spreadsheet program MS Excel, based on existing analytical solution for two-dimensional transport of contaminants in a saturated soil layer, concentrations at several coordinates at several times were calculated. A MATLAB code was developed using finite difference approach for numerical solution. The programming steps followed for analytical and numerical solutions were explained. The analytical and numerical solution was compared. An example of the simulation models for the contaminant transport through a saturated soil layer is given. The study shows that the analytical solution and the numerical solution, for the given problem, match in an acceptable range. ß 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 19: 385398, 2011; View this article online at wileyonlinelibrary.com; DOI 10.1002/cae.20320 Keywords: advection; contaminant migration; dispersion; soil; sorption INTRODUCTION As stated by Accreditation Board for Engineering and Technol- ogy (ABET, www.abet.org), an engineering student, immediately after his/her graduation, should be able to: (a) appropriately model the physical world with mathematics through differential equations, science, and engineering, (b) use systematic, modern step-by-step problem-solving approach while identifying, for- mulating, and solving engineering problems, (c) use the techniques, skills, and modern engineering tools (computer programs) necessary for engineering practice. By considering the above criteria, in this paper, analytical and numerical simulation models and modeling steps are explained for the contaminant transport through a saturated soil layer. Many hazardous materials have entered the ground uninten- tionally through leakage in tanks, releasing large quantities of contaminants (e.g., instantaneous source), in Figure 1 plan view of plume developed from an instantaneous point source at three different times is given [1] (i.e., a real-world, physical problem). The transport mechanisms and governing transport equa- tions and the solutions of governing partial differential equations are given for instantaneous sources [18]. The use of these relatively simple analytical equations has a number of applica- tions [7]; such as a simple check to more complicate models that require numerical solutions. More importantly, calculations using simple analytical equations provide a powerful conceptual knowledge of the effects of sorption, transformation, advection, and dispersion on the rate of subsurface transport. The migration and fate of contaminants dissolved in ground water are studied by using the spreadsheet program MS Excel for analytical solution; the approach considers the advective and dispersive transport of solutes dissolved in ground water, which may undergo linear sorption (i.e., retardation). In this study, a MATLAB code is developed using finite difference approach for numerical solution. Engineers should never rely on a single solution, because errors can be disastrous and expensive, and the results should be checked in as many ways as possible (analytical methods and numerical methods). The analytical and numerical solutions of a two-dimensional (2D) contaminant migration through a soil layer due to an instantaneous (pulse) source were compared in this study. MODELING OF CONTAMINANT MIGRATION THROUGH A SOIL LAYER DUE TO AN INSTANTANEOUS SOURCE In this study, modeling of contaminant migration through a soil layer due to an instantaneous source [i.e., a real-world (physical) problem] was made by following the steps as shown in Figure 2. Correspondence to E. Cokca (ecokca@metu.edu.tr). ß 2009 Wiley Periodicals Inc. 385