Geoelectrical Investigation of a Proposed Landfill Site in Ogbomoso, Southwestern Nigeria

Abstract

An integrated geophysical investigation was carried out at a proposed landfill site along the new Ibadan-Ilorin Expressway in Ogbomoso, Southwestern Nigeria in order to characterize the subsurface and determine the suitability or otherwise of the site for landfill. The study location is underlain by rocks of the basement complex. 29 Schlumberger Vertical Electrical Soundings were conducted along seven traverses each about 100m long, about 20m apart, with station spacing of about 30m and half current electrode spacing varying between 1 and 100m. The VES data were interpreted quantitatively by partial curve matching and 1-D computer iteration and the layer parameters were used to generate the geoelectric sections. Wenner electrical resistivity profiling was also conducted along the traverses with station spacing of 25m and electrode spacing varied between 5 and 15m, and the data were interpreted using 2D inversion procedures. The VES results revealed three layers defined by the topsoil, clay layer and fractured/fresh bedrock. Depth to the bedrock is generally shallow with a mean of 9.0 3.7m. The mean thickness of the saprolite (mainly comprising clay) is 8.6 4.0m. 2D inversion of the resistivity profiling data revealed intense fracturing of the bedrock. The water table is shallow, ranging from 2 to 6m and may be rather close to the landfill base or fall within the landfill wastes. The study area is underlain by clayey overburden capable of protecting groundwater in the underlying aquifer unit from contamination by the leachate dischargeable from the landfill wastes. However, the presence of shallow water table and bedrock fractures may promote contamination of groundwater in the underlying aquifer unit and pose substantial health risk to the host community. It can therefore be concluded that the study area is not a suitable location for siting landfill.

Keywords: Contamination, Leachate, Clay, Water table, Bedrock fractures

DOI: 10.7176/JEES/11-16-04

Publication date:June 30^th 2021