Geoelectrical And Geotechnical Characterization of Oil Spill Areas in Agbura

Soil investigation and characterization within an oil spill location in Agbura was carried out via the conduct of vertical electrical sounding (VES) and geotechnical analysis in order to determine both lateral and vertical spread of the spill. The VES and boreholes were sited at specific positions with respect to the primary spill point and samples were collected at designated depths for physical examination, geotchnical appraisal and determination of the rate of infiltration. From the results, the resistivity values of the soil profile at the impact site shows that the first geolelectric layer had a high resistivity of 1558 Ohm-m and was composed of sandy clay based on laboratory tests. The second layer was clayey with resistivity of 679 Ohm-m. The third and fourth layers were fine - medium grained sands with resistivity values of 925 ohm-m and 1280 Ohm-m respectively. The unsually high resitivity values at the impact site comparative to the control site is attributed to the hydrocarbon content in the sediments. Further analysis of the geoelectric data show that resistivity values of VES sites within 150m downslope of the impact point were similar to resistivity values at the spill impact point, whereas VES sites within the same lateral distance upslope were comparatively lower and relatively similar to values obtained at the control site. From the geotechnical results, permeability values of the first and second layers of the soil based on Hazen and Kozney-Carmen empirical formulae ranges between 2.51×10-6 to 3.94×10-6 m/s and 2.26×10-6 to 4.14×10-6 m/s respectively, with an average of 3.11×10-6 m/s. while permeability based on Kozney-Carman formula ranged between. The permeability values indicate that the spill could infiltrate to an approximate depth of 3m within a period of 1 month. The occurrence of the clayey layers acted as natural barriers to the infiltration process, hence, most of the oil seem to be trapped in the second geoelectric layer (approximately 0.8 - 3.2m ). Proactive measures should therefore be put in place to prevent incessant occurrence of oil spills, while rapid response to cases of spill is strongly advocated to mitigate widespread contamination.