Geophysical Characterization of the Abandoned Gaborone Landfill, Botswana: Implications for Abandoned Landfills in Arid Environments

A geophysical investigation using electromagnetics (EM), electrical resistivity and ground penetrating radar was carried out on the abandoned Gaborone landfill that was decommissioned in 1992 after being active for ten years. The aim of the study was to map the physical boundaries of the decommissioned landfill, map the distribution of waste and identify zones of leachate within and below the landfill. The results of EM conductivity measurements show a wide distribution of conductive materials, which represents a zone of active leaching which is mostly concentrated in the centre of the landfill. In-phase EM measurements also identified zones occupied by metallic waste that are less distributed over the landfill. Results of the resistivity survey indicated a three layer resistivity structure within and surrounding the landfill. The top layer is a more resistive cover material (68 - 127 ohm-m) and varies in thickness from over the landfill. The second layer is a low resistivity zone (3-40 ohm-m) and indicates a zone of high leachate activities. At the bottom is a more resistive layer (greater than 500 ohm-m) which is likely bedrock that underlies the abandoned landfill. The ground penetrating radar images also indicated a three layer structure over the landfill which is similar to the resistivity results. All the methods implied that the leachate has not penetrated the bedrock but the large amount of leachate suggests that it may leak into the unlined landfill in the future despite being in an arid environment. Of the three methods, the resistivity survey provided the most complete information on the subsurface conditions of and beneath the landfill.
electromagnetics; electrical resistivity; ground penetrating radar; landfill; Botswana
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