English

Abstract

The Osogbo central solid waste dumpsite in Osun State, Nigeria falls within the Ilesha Schist Belt, southwestern basement complex of Nigeria. Thirty-three (33) Vertical Electric Sounding (VES), and 2-D Electric Resistivity Tomography (ERT) data were acquired across various locations in the study area using ABEM Terrameter SAS 300, respectively. Schlumberger configuration with a maximum spread length of 100 m, for the VES was used, while four traverses of ERT were conducted, using Dipole-Dipole Array with average traverse length of 112.50 m. A smoothness-constrained least-squares inversion was then applied to the ERT data using a 2-D inversion algorithm [that is, DIPRO for Windows, version 4.01. Generally, the results defined the contaminated leachate plumes as electrically conductive, with anomalous resistivity values. Both the VES and the 2-D tomography identified zones of low resistivity values, between 24 and 67 ?m, from 10 to 20 m deep, as leachate contaminant plumes. Some of the weathered and fractured basement rocks indicated that the subsurface soil and groundwater have been contaminated by the leachates, which appears to have migrated outside landfill site. Zones within the sub-surface, with resistivity values relatively high (> 300 Ωm) and depth above 30 m might be pollutant free. Solid wastes management calls for the adoption of the best practicable environmental management approach through the governments’ enforcement of circular economic policies, using extended producer responsibility (EPR) model and construction of engineered landfills to replace unsanitary landfills. The conduct of environmental impact assessment (EIA), prior to commencement of operations and phytoremediation of closed sites is also crucial. Key words: Tomography, leachate, pollution, contaminant plume.