APPLICATION OF GEOELECTRICAL RESISTIVITY AND GROUND PENETRATING RADAR SIGNATURES IN DELINEATING HYDROCARBON POLLUTED SOIL IN OGONI, NIGER DELTA, NIGERIA

The study investigated the importance and image behavior of integrated geophysical methods in mapping contaminant spread beneath the surface of a pollution site in Ogoniland, Southern Nigeria. Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques constrained by Vertical Electrical Sounding (VES) data were employed to investigate the electrical properties of hydrocarbon contaminated soils that resulted from recent oil spills/leakage into the environment. Five (5) ERT and GPR lines and twenty-nine (29) VES data were acquired at the spill site. Basically, the electrical signatures from the resistivity measurements were able to image the subsurface layers and the associated contamination zone. GPR equally imaged the subsurface stratigraphy to a depth of 10.0 m beneath the surface. The interpretation of the five (5) ERT data showed consistency in the resistivity structure indicative of contaminant plumes with anomalously high electrical resistivity in the range of 1000-10,000 Ωm, a possible indication of hydrocarbon contamination. On the GPR radargram, regions of high electrical resistivities were in agreement with reduced GPR reflection behavior (shadow zones) and were limited to the near surface of the surveyed areas. Vertical electrical sounding delineated layers with high resistivity predominantly within the second and fourth geoelectric layers within pollution depths of 2.4 m and 11.9 m, respectively. As a result, the underground aquifer, relatively between 7.5 and 10.5 m, has been infiltrated by hydrocarbons. It can be seen from the study that geoelectric measurements on the surface can describe the distribution of hydrocarbon resistive zones as well as their conductive behavior that may be linked with the biodegradation of oil spills in the subsurface. Thus, the employment of these integrated methods for contaminant monitoring, hydrogeologic studies and remediation planning reduced the uncertainties, and they are of extensive relevance in mapping the geological behavior of polluted soils in contamination sites.