Integrated Geophysical and Geochemical Characterization of Hydrocarbon Contamination at the Ajeokpori Artisanal Refinery Site, Ogale, Niger Delta, Nigeria

Hydrocarbon contamination remains a major environmental and public health challenge in Ogoniland, Niger Delta, Nigeria, where legacy pollution and ongoing artisanal refining have complicated remediation planning. This study integrated geophysical, geochemical, and hydrogeological methods to delineate the extent of contamination at the Ajeokpori artisanal refinery site in Ogale, Eleme Local Government Area. Vertical Electrical Sounding using the Schlumberger array, 2D resistivity profiling using the Wenner array, 3D resistivity modeling, borehole logging, and laboratory analyses of soil and groundwater were combined to characterize subsurface conditions and contaminant migration. Eight VES points and fifteen boreholes were investigated, with a control site located 200 m upstream for comparison. Four geoelectric layers were identified to a maximum depth of 20.2 m, comprising silty sand topsoil, sandy silt, coarse sand, and medium sand. Contaminated-site resistivity ranged from 102 to 5860 Ω·m, while the control site ranged from 885 to 5100 Ω·m. Hydrocarbon-impacted zones were associated with low resistivity anomalies ≤700 Ω·m, which corresponded to elevated Total Petroleum Hydrocarbon concentrations ranging from 25 to 9,100 mg/kg. Groundwater TPH reached 8,050 µg/L, and plume migration followed southwestward groundwater flow in a high-permeability setting. A strong inverse relationship between soil resistivity and TPH concentration further supported the reliability of the integrated interpretation. The findings demonstrate that combined resistivity imaging and geochemical verification provide a robust basis for contamination delineation and remediation planning in hydrocarbon-impacted coastal plain aquifers.