Geophysical Investigation of the Old Gaborone Dumpsite, Botswana

A surface geophysical investigation consisting of electromagnetic (EM) and resistivity survey techniques was carried out on the Gaborone old dumpsite that was commissioned in 1982 and decommissioned in 1992. The aim of the study was to map the physical boundaries of the decommissioned dumpsite, map the distribution of waste and identify zones of leachate concentrations within the dumpsite The results of conductivity measurements using the EM technique show a wide distribution of conductive materials, which represents zone of active leaching. This zone is mostly concentrated in the centre of the old dumpsite. Inhase measurements also identified zones occupied by metallic waste that are less distributed over the dumpsite. Results of the resistivity survey indicate a three layer structure in the area. The top layer is a more resistive cover material (68 - 127 Ωm.) and varies in thickness from place to place. The second layer is a low resistivity zone (3-40 Ωm) and indicates a zone of high leachate activities. At the bottom is a more resistive layer (greater than 500 Ωm) which is likely to be basement rocks that underlie the old dumpsite. The resistivity survey results provide better information about the subsurface conditions in the old dumpsite.