Geoelectrical Imaging at an Abandoned Waste Dump Site in Ibadan, Southwestern Nigeria

Abstract

Leachate-effluent from refuse dump site is an important source of groundwater pollution. Consequently, assessing the impact of leachate is an active area of groundwater research. Geoelectrical imaging was carried out at an abandoned waste dump site in Ibadan, southwestern Nigeria, with the aim of determining how accurately electrical measurements could delineate the influx of leachate into groundwater and surface water. Eight electricalresistivity profiles were measured. Four of the traverses were conducted on the dump site whereas two traverses were measured towards the lower side to assess possible ingress of the leachate. The other two lines were measured about 300 m from the site to serve as control. Elevation data were collected using Global Positioning System. The resistivity data were inverted using the least-square technique. The inversion delineated regions of low resistivity ( 20 Ωm). The highest resistivity regions (>100 Ωm) were interpreted as regolith derived from chemical weathering of the crystalline bedrock. Resistivity-derived thickness of the leachate zone was consistent with the thickness derived from the elevation data. It could be inferred that there was high concentration of leachate towards the lower elevation hence the adjoining stream is prone to pollution. This study showed that 2D imaging can be effective in imaging pollution plumes around refuse dump sites. The method can be useful to assess opportunity for remediation measures in situations where the leachate has reached the groundwater system.