Investigation of the Extent of Contamination at an Automobile Market in Benin City, Edo State, Nigeria Using Very Low Frequency Electromagnetic Survey

Abstract

Automobile spare-part markets pose serious sources of underground pollution in fast-growing cities of the developing world since petroleum products and metal bearing wastes are dumped carelessly. Very Low Frequency (VLF) Electromagnetic (EM) method was used to evaluate shallow contamination of the subsurface at Evbareke automobile spare parts market, Benin City, South South Nigeria. Twenty-two VLF-EM traverses were obtained in this active polluted and also in comparatively uninterrupted control areas to outline the conductive anomalies linked to hydrocarbon and heavy-metal contaminations. A 2-dimensional conductivity model showed extensive and spatially dispersed conductive layers that are mainly found in the depths of 5-20 m. The conductivity anomalies are large-scale when they are located directly below the location of visible surface contamination whereas control traverses experienced weak contrasts in conductivity, which is a confirmation that the anomalies are anthropogenic. The findings indicated that the contamination of the site is superficial in nature, laterally discontinuous and highly dependent on surface spill sites and on local hydrogeological circumstances. This investigation demonstrated that the VLF-EM technique is a very effective, non-invasive technique for contamination plumes mapping in urban automobile markets and also offers baseline geophysical data to aid environmental monitoring and remediation planning in this type of environment.