Allan Crowe and Andrew Piggott
This document allows you to operate a simple computer model of groundwater contaminant transport. The model used in this example predicts the downward migration of leachate from a landfill to an underlying aquifer. While the example is hypothetical, it illustrates a number of the real world concerns that are associated with the operation of municipal and industrial landfills. Numerical modelling is an indispensible tool in groundwater studies.
Description of the Setting The example is illustrated in the following figure. A landfill has been constructed above an aquifer that supplies drinking water to a rural population. Leachate that collects at the bottom of the landfill is moving downward toward the aquifer at a rate defined by the hydrogeology of the site. The soil between the landfill and aquifer is a glacial till with a hydraulic conductivity of 1.0e-9 m/s, a porosity of 0.4, and a dispersivity of 1 m; the thickness of the till is 10 m and there is a 1 m difference in the groundwater levels at the base of the landfill and in the aquifer.
Schematic illustration of the example
Definition of the Problem The amount of leachate that reaches the aquifer defines the potential for groundwater contamination, and thus damage to the drinking water supply of the rural residents. Experts have indicated that there is a relatively small risk of contamination from the leachate. You are concerned that the hydraulic conductivity, porosity, and dispersivity values that the experts used in their calculations are overly optimistic, so you intend to determine the sensitivity of the experts' predictions to these properties. To accomplish your task, you must revise the estimates used by the experts and compare the experts' prediction of leachate concentration to your own. The input fields are under "Data".
Authors of the abstract: Allan Crowe and Andrew Piggot
You can learn more about predicting contaminant transport in groundwater by numerical modelling from books such as Groundwater by Allan Freeze and John Cherry (Prentice-Hall Inc., 1979). If you like, you can also look at the computer model that you used to perform the previous exercises; it is based on a simple analytical solution (see Freeze and Cherry, page 391) and is written in the FORTRAN programming language. If you have a FORTRAN compiler, you may be able to download the program and run it on your own computer.