Electrical Resistivity Imaging and Lithological Modelling of Hydrocarbon Contaminated Soil in Ogoni, Rivers State, Nigeria

Site characterization is critical for effective environmental remediation because it provides the essential data to identify contamination, assess risks, and guide the selection of the most appropriate, cost-effective remediation strategies. A non-intrusive Electrical Resistivity Imaging (ERI) technique was used in combination with intrusive methods to determine the subsoil and groundwater contamination status. The ERI was carried out along a criss-crossing network of VES lines and analyzed using RES2DIV, RES3DIV and Earth-Imager softwares to generate geo-electric tomographs that serve as ground models which are then compared with results of physical assessment of samples from boreholes. Resistivity signature for mature oil contamination was determined and used as cutoff to discriminate between hydrocarbon contamination and other geo-electric horizons. Based on this, contaminated sections of the sub-soil were delineated to define the precise structure and spatial distribution of the contamination zone, as well as determine the volume of soil for remediation. Similarly, lithologic logs derived from borings at the project area were concatenated to produce a 3-dimensional Fence diagram as well as ground model where the contaminated zone could be compared with that generated from the ERI. These ground models are then embedded and overlain on Google Imagery after georectification to relate with ground features and for ease of physical identification on the site. These results suggest that ERI with its minimum footprint and negligible cost can offer substantial benefits in the assessment and delineation of hydrocarbon contaminated zones for effective remediation. Furthermore, the results suggest that the approach can the risk failure of remediation efforts or promote inefficiency, ultimately improving environmental and public health protection.