Abstract
A Two-dimensional (2D) geoelectrical survey has been conducted on a suspected hydrocarbon contaminated (oil spills) site at Okpare-Olomu community, Ughelli South Local Government Area of Delta State, with the aim of assessing the intensity and extent of hydrocarbon contaminationat an oil spill site. Five (5) traverses were surveyed employing dipole-dipole array with maximum length of 200 m. The survey was conducted during the wet season to ensure that the electrodes made good contact with the earth. Four (4) traverses (1–4) were surveyed at the contaminated site while one traverse (5) was surveyed at a distance from the contaminated area which serves as control traverse. Analysis of the results revealed that topsoil (sand), clayey sand, and clay make up the background subsoil within the site. This subsoil resistivity varies between 43ohm-m and 554 ohm-m. The resistivity of the sand layer ranges from 292 ohm-m to 554 ohm-m, and its thickness ranges from 0 to 10 m. The clayey sand has a resistivity range of 81 ohm-m to a little over 154 ohm-m, and the depth of the clayey sand is between 10 – 20 m. The clay layer has a resistivity of 43 ohm-m and extends from 15 to 50 m. The results from traverses 1–4 show that the topsoil (0–10 m) is characterized by resistivity values that are generally > 4000 ohm-m (4045–10512 ohm-m) across all four traverses, the second layer (clayey sand) extends from depths of 10–25 m across all four traverses and the resistivity value falls at 611 – 3408 ohm-m, while the third layer (clay) is characterized by resistivity values of between 326 – 1940 ohm-m.These characteristic resistivity values along traverses 1 – 4 show an elevated values compared to the resistivity values of corresponding layers from the control traverse. These results indicate that the hydrocarbon has polluted these layers. These findings also suggest that, as indicated by the geometry of the contaminant plume, the contaminant is already migrating through the underlying strata (clayey sand and clay). Furthermore, the sections demonstrate that the contamination intensity is strongest along traverse 1 and particularly at horizontal distances of 40–60 m, whereas the least impacted zone is along traverse four (4), indicating the contaminant’s lateral flow direction.The result of this investigation has once again underscored the effectiveness of electrical resistivity method and particularly 2D resistivity technique employing dipole-dipole array in environmental investigations.It is recommended that Bioremediation should be embarked upon by the Government to protect the agricultural and regional groundwater system of the study area.
Keywords