Determination of leachate curtailment capacity of selected dumpsites in Ogun State southwestern Nigeria using integrated geophysical methods

Abstract

Indiscriminate disposal of wastes generated by increasing human population and industries pollute surface and groundwater, consequently creating health hazards. Leachate contamination by waste disposal sites and its extent of pollution have been studied in Ogun State with little or no consideration for the subsurface lithology underlying the disposal sites. The study aimed at using integrated geophysical exploration methods to map the structure of the subsurface layers to adjudge leachate curtailment capacities of Oke saje (Abeokuta) and Ijagun (Ijebu ode). Very Low Frequency Electromagnetic (VLF-EM) method and Electrical Resistivity (ER) method were carried out along established traverses at both sites. The results of the combined methods revealed that Oke Saje dumpsite is characterized by topsoil, weathered layer, fresh and fractured basement, which are the geoelectric layers. The weathered segment contains clayey layer of thickness ranging from 0.5–23 m which provides a reliable seal that protects the underlying aquifer from leachate pollution. Three to four Geoelectric layers: topsoil, contaminated sand (of thickness 0.5-22 m) and laterite were detected for Ijagun dumpsite. This lithology is an indication that leachate curtailment capacity of the dumpsite is very poor. Keywords: Dumpsite, VLF-EM, VES, Leachate, Protective capacity