Many quarries in East Cairo are used as solid waste landfills. These locations are now impossible to find from the ground surface due to the urban development of New Cairo. In this study, a subterranean landfill site near the Ring Road in East Cairo, Egypt, was found and delineated using electrical resistivity tomography (ERT) data and multi-temporal high-resolution satellite imagery. Up to 2005, the research location was a WNW-oriented quarry that had been randomly filled with diverse solid materials, according to an analysis of changes shown on the satellite images. Based on the change detection data, ERT survey planning was done. The ERT measurements identified the infill material-occupied electrically conductive zones on the plan view and separated them from the resistive zones, representing the natural soil areas. Two distinct geoelectrical units could be distinguished by combining the satellite images and the ERT results: Unit-2 (the lower unit) is characterized by high resistivity values that characterize the original soil (bedrock), whereas Unit-1 (the upper unit) is defined by low to moderate resistivity values that are the solid waste materials. The contact between the bedrock and the infill materials was mapped and delineated using the closely spaced grid of ERT profiles and the thorough topographic map. Ground surface elevation, the depth of Unit 1's lower boundary, and this unit's thickness change throughout the researched site are some criteria that might be addressed and used to characterize the unit of interest (Unit 1).
