Mapping petroleum hydrocarbon contamination around tankers park facility at Orile-Iganmu, Apapa, Lagos Metropolitan City

Abstract

In this study, an assessment of subsoil conditions at a site purportedly contaminated by petroleum hydrocarbon spillage was carried out with a view to map and delineate the extent of migration of contaminant plumes and characterization of the aliphatic hydrocarbons in the soils. To achieve these objectives, geophysical electrical resistivity techniques and geochemical analysis of soil samples were carried out. For the geo-electrical measurements, 2-D Electrical Resistivity Imaging and Vertical Electrical Soundings (VES) were conducted while a hand held auger was used to collect soil samples at different depths from four different locations. The soil samples were analyzed for their extractible Total Petroleum Hydrocarbon (eTPH) content using the gas chromatography technique. Results from the geo-electrical measurements are presented as inverted resistivity models and geo-electric sections from which the layers were delineated on the basis of their resistivity distributions. The resistivity sections showed three distinct zones with resistivity values ranging from 0.13–10, 12–60, and 65–120 Ωm were delineated for the area. The contaminated zones were identified as resistivity anomalies with relatively high resistivity. The contaminated zones deduced from the resistivity sections suggests that the hydrocarbon plumes have accumulated as lens in the unsaturated zone and have not only spread throughout the surface but also migrated vertically to different depths as revealed in the resistivity sections. The chromatograms result showed the presence of hydrocarbons in terms of extractible total petroleum hydrocarbon (eTPH) concentrations. The different components of hydrocarbons detected were identified with their characteristics peaks. The values of the eTPH range from 1.2 to 3.75 mg/kg for contaminated area were correlated with high resistivity anomalies and between 0.14 and 0.79 mg/kg for the uncontaminated area that serves as control. The hydrocarbon contaminant plumes detected from the impacted area might not have reached the groundwater table from the measurement of static water levels made from the boreholes and hand hug wells.