Geoelectrical Investigation of Subsurface Contaminants in Uwelu Automobile Market, Benin City, Using 2D and 3D Electrical Resistivity Tomography (ERT)

The high rate of random release of petroleum hydrocarbons, heavy metals and industrial wastes into the environment has led to automobile markets and workshops in Nigeria being perceived as areas of severe environmental concern. This paper will provide a geoelectrical study of the ground water contamination in the Uwelu Automobile market area in Benin City, Edo State with two- and three-dimensional Electrical Resistivity Tomography (2D and 3D ERT). Although the past studies in the field have concentrated mainly on the geochemical and physicochemical study, the available techniques perform inadequately to evaluate the contamination depth and lateral contact. This was done using a PASI Earth Resistivity Meter (Model 16GL-N) and 2D Wenner array method of gaining resistivity data on various traverses across the market. Data processing included powerful inversion programs to produce 2 dimensional sections of resistivity and 3 dimensional volumetric images. The ERT data display a series of low resistivity (35.9 88.7 0m) between a depth of 1.25 m and 6.38 m that can be considered as contaminated areas caused by leachate percolation as well as oil spill and infiltration of metal-bearing wastes. These anomalies were persistent in all the seven traverses meaning that there is extensive near-surface contamination. On the other hand, there were resistivity values greater than 231 (Ωm), observed in deeper zones (>= 10-12m) that might reflect relatively clean lateritic or weathered bed the rock. Three-dimensional resistivity imaging was used to also help delineating the plumes of contamination in space in higher resolution. This paper shows how combined 2D and 3D ERT are an efficient environmental diagnostic tool in use in complex industrial areas, providing an imaging, spatially large alternative to point-sample measurements. This is because the results confirm that environmental decontamination and regulatory action must be taken on highly urbanized markets such as the one in...