Earth Science Malaysia (ESMY)

The contamination of groundwater by hydrocarbons presents a significant challenge for the residents of the Kegbara Dere community in Ogoniland, Rivers State, Southern Nigeria. The area has been plagued by oil spillage, and the damage done to Ogoniland as a result of oil spillage is so massive that the United Nation (UN) did a report on the extent of pollution in the area. This study aimed to identify and characterize the extent of the groundwater system contamination in the study area. The electrical resistivity imaging and geochemical methods were adopted. 2D electrical resistivity imaging (ERI) along four (4) traverses was processed and analyzed to obtain resistivity-depth sections of the subsurface. Three unique geoelectric zones were delineated, with the intermediate zone identified as the contaminated aquiferous unit. This unit’s resistivity values ranged from 10,804 to 100,000 Ωm along line Lx3, 324 to 23,497 Ωm along line Lx5, 1019 to 10,000 Ωm along line Ly6, and from 1000 to 10,000 Ωm along line Ly5 extending from the surface (0.0 m) to depths between 10 m and 20 m and to a profound depth of approximately 40 m. These high resistivity anomalies are characteristic of hydrocarbon contamination since hydrocarbons have a higher electrical resistivity compared to water. This coincides with the depth of the aquifer that serves as the major origin of edible water exploited by the local population and shows that the aquifer system below the study area, usually exploited for groundwater, has been invaded by hydrocarbon contamination plumes. The groundwater specimens from five boreholes were established to have a common total petroleum hydrocarbon (TPH) amount of 739.51 μg/L, above the DPR target and intervention thresholds of 50 and 600 μg/L, respectively. Groundwater specimens with summed polycyclic aromatic hydrocarbons (ΣPAHs) consist of amounts ranging from 0.36 to 1.89 μg/L in BH-1 to 5, that outweigh the DPR target threshold of 0.15 μg/L. Additionally, BTEX concentration was observed in greater levels in the water specimens above the DPR allowance. These findings explain that the area’s groundwater is heavily contaminated by dissolved-phase contaminants due to hydrocarbon pollution. The groundwater migration flow route at the spill site shows that the dominant flow direction is towards BH4, located northwest (N-W) of the spill site. A broad characterization of the subsurface as obtained from 2D ERI and geochemical results calls for effective remediation planning at the spill site aided by information about the very possible receptor locations at high possibility of contamination, which was defined in the groundwater flow pattern at the spill site.