Investigation of subsurface contaminants leachate within Ansaru-Islam Secondary School, Ilorin, Nigeria

Abstract

This study adopts the use of Vertical Electrical Sounding (VES) and 2-D resistivity imaging (employing Schlumberger and Wenner array configurations) to investigate and map the extent of leachate’s migration and its possible impacts on groundwater within Abata Asunkere dumpsite, Ilorin, Kwara State. This study was inspired by the unrestrained manner of garbage dumping in the area over time, which poses great threat to the availability of clean water for the increasing populace. To delineate the subsurface, 2-D resistivity imaging data were acquired along two traverses, while the VES data were randomly acquired along the established traverses. The 2-D resistivity imaging and VES data were processed using Res2D and IPI2Win software respectively. The results of the 2-D and VES revealed five (5) geoelectric sections, which correspond to the topsoil, clayey sand, weathered basement, fractured basement and fresh basement rocks with H, QH and KH sounding signature curve types. The topsoil has layer thickness of 0.5 - 1.7 m and resistivity values ranging from 11.9 - 165 Ωm. The clayey sand has layer thicknesses between 0.7 - 2.8 m and resistivity values ranging from 20.1 - 56 Ωm. The weathered basement has thickness of 0.9 - 16.3 m and resistivity values ranging from 2.09 - 5.25 Ωm. The fractured to fresh basement has resistivity values ranging from 26.8 - 3000 Ωm with thickness ranging from 5.3 m to infinity. The third layer with low resistivity values of 2.09 - 3.52 Ωm at depth range 0.9 - 10 m is suggestive of leachate contamination. The outcome of this study indicates that some regions around the dumpsite are susceptible to leachate’s contamination, which has tendencies to permeate the unconfined aquifers in the study area if not properly monitored and controlled.