Landfill sites commonly use the space available in disused quarries or special purpose-built structures but not all past landfill operations were adequately controlled or documented such that the site boundaries, and the type and volume of fill are unknown in some old covered landfill sites. Even in controlled sites, the final form and depth extent of the landfill may not conform to those indicated in the original plan submitted to the regulatory authorities during the application for a site license. Thus, a significant amount of work is required in order to accurately define the relevant parameters of a covered landfill site. Our hydrogeophysical interest in landfill sites lies in assessing the pollution threat they pose since they may contain hazardous substances. In conventional geophysical investigation of landfill sites, the usual goals are to determine the geometrical characteristics (size and shape) of the repository and the physiochemical properties of the infill. Of the several non-invasive geophysical methods used in landfill studies, the electrical and electromagnetic (EM) methods are the most popular owing to their inherent ability to detect changes related to variations in fluid content, chemical composition and temperature in the subsurface, and the minimum capital and labor outlay required to use them in small-scale surveys (Whiteley and Jewell, 1992; Meju 2000). Since the presence of saline fluids in the ground enhances its ability to conduct electrical current, it is possible to locate a leachate plume by measuring the resistivity distribution in the subsurface. The main ground resistivity measurement techniques employed in landfill studies are the direct current (dc) resistivity and/or induced polarization (IP) methods (e.g.