INVESTIGATION OF OIL/DIESEL CONTAMINATION AND WASTE WATER SEEPAGE USING 2-D ELECTRICAL RESISTIVITY AND GROUND PENETRATION RADAR

Abstract

Geophysical surveys were carried out at two separate locations within the Mountain Top University Main campus located inside MFM Prayer City, Ibafo, Ogun State, Nigeria in order to investigate an oil/diesel and waste water contamination sites using 2D Electrical Resistivity Tomography and Ground Penetrating Radar. The objectives of the study are to delineate the extent of the contamination at both sites while also determining the potential effects the contamination could have on its surroundings and other bio life existing within its proximity. xii At the first location, four 2D ERT traverse lines were established using 0.2 m and 0.5 electrode spacing with the aim of providing a high-resolution image of the subsurface. At the second location, eleven 2D ERT lines were established on eight traverses with 0.1m electrode spacing (two 2D ERT lines were overlapped on lines 5 to 7). Similarly, four GPR traverse lines were established using 450 MHz antenna in location 1. At the second location, eight GPR traverses were surveyed with a 450 MHz antenna and the eighth traverse is perpendicular to others in the North to South direction along the slope of the investigated area. In the first location, the results of the electrical resistivity have shown that the waste water seepage is represented by relatively low electrical resistivity range 1 to 20 Ωm and have penetrated a depth range of 2.7 to 3.5 m. The increase water saturation in the seepage polluted region has resulted in increased amplitude in the radargram and has helped in delineating the seepage region. Additional pipe other than the visually observed pipe in the investigated area has been mapped with the GPR method which could be another source of seepage. At the second location, the oil/diesel waste is characterised by relatively high electrical resistivity range of 120 to 13,161 Ωm and have penetrated a depth range of 0.2 to 0.85 m while the oil/diesel waste has resulted in amplitude attenuation on the GPR method. It can be concluded that the waste water contamination to the ground surface is a result of more than one pipe leaking at different positions besides the possibility of the underground tank leakage. There is no evidence from the result to support that the contamination has invaded any potential groundwater source although its effects on the biosphere are not immiscible. In location 2, the trend of flow of the oil/diesel waste effected by the topographical changes of the site and is observed to have spread laterally beyond its point of entry onto the site. The result has provided localized spots of possible oil/diesel waste accumulation that can be used for mitigation measures