Abstract

Author:
Stanley Uchechukwu Ezea*, Difference Odeyovwi Ogagarueb, Hasan K. AktarakÇic

Doi: 10.26480/gsrj.02.2024.55.70

This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Time-lapse electrical resistivity tomography (TL-ERT) surveys and geochemical analysis of groundwater samples were employed to monitor hydrocarbon pollution dynamics of contaminant plume at the Kegbara Dere oil spill site of Ogoniland in southern Nigeria. The study was designed to evaluate the contamination condition of the spill site and assess the concentration of dissolved phase contaminants to proffer the best remediation strategies. Twelve (12) 2-D lines were executed in a grid at four distinct time points. The independent inversion of the 3-D data sets displayed acute variations in the apparent resistivity of the contaminants and a maximum depth of 41.8 m was investigated. Time-dependent evaluations of the 3-D ERT models show a reduction in the apparent resistivity of the contaminant plume in the rainy season when correlated with the dry season. This tendency is attributed to the dilution effect of rainfall, which increases the water content of the soil during the wet season. The percentage change in conductivity and resistivity at the end of time-lapse two and three monitoring periods showed a change in conductivity from -15 to -25% with a corresponding change in the resistivity from 40 to 80%. The implication is that the electrical resistivity/conductivity of hydrocarbon contamination at the spill site is changing at a constant rate percent, driven by the geological characteristics of the subsoil and seasonal variations in water content. Investigation of water specimens collected from five boreholes at the spill site displayed the average amount of total petroleum hydrocarbon (TPH) for the specimens as 739.51 µg/L which surpassed the directorate of petroleum resources (DPR) margins. The summed poly aromatic hydrocarbons (ƩPAHs) amount in the specimens is valued up to 0.70 µg/L in BH1, 0.79 µg/L in BH2, 0.36 µg/L in BH3, 1.00 µg/L in BH4 and 1.89 µg/L in BH5, which are beyond the DPR target margin of 0.15 µg/L. BTEX compositions also displayed elevated amounts in the specimens. The direction of groundwater flow is towards borehole-4, located southwest of the spill site indicating the most receptor area at risk of contamination. The study’s results were used to set up a well-planned monitoring program at the spill site to continually gather real-time information about the movement, and interactions of the contaminant plumes with the subsurface environment for effective clean-up execution of the area.