Geoelectrical Investigation of Landfill Site Suitability in Ilorin, Kwara State

This study carries out a geoelectrical investigation to assess the suitability of a proposed solid waste landfill site in Ilorin, Kwara State, North Central Nigeria. Appropriate siting of landfills requires assessment of subsurface permeability, depth to the water table, and the presence of potential leachate migration pathways that could contaminate groundwater. Many Nigerian urban centres site landfills without adequate hydrogeological investigation, leading to groundwater contamination that threatens public health. This study acquires Schlumberger VES data at 24 stations distributed across a 45-hectare proposed landfill area in Ilorin West local government area, with maximum AB/2 spread of 200 metres. Interpreted layer models are used to map the depth to water table, overburden thickness, and clay layer continuity. An electrical resistivity profiling programme of 8 traverses at 5-metre electrode spacing supplements the VES data to detect existing contamination pathways or buried channels. Findings reveal highly variable overburden conditions, with clay layer thicknesses ranging from 0 to 8.5 metres across the site. Three zones in the northeastern sector show continuous clay horizons exceeding 4 metres with average clay resistivities below 8 ohm-metres, indicating potentially low-permeability natural barriers. The southwestern sector shows thin or absent clay with the water table at only 4.2 metres, making it unsuitable for landfill siting. The study produces a suitability zonation map and recommends the northeastern sector for engineered landfill development with clay liner supplementation, while rejecting the southwestern sector on groundwater protection grounds.

Keywords: geoelectrical survey, landfill siting, groundwater protection, Ilorin, clay layer mapping.