Monitoring the contamination dynamics and flow pathway of oil spill using 3D-4D ERT in a pollution site

For effective in situ remediation planning to reduce environmental concerns, detailed monitoring of pollution dynamics and the preferred flow path of the contaminated plume are critical indicators. Time-lapse electrical resistivity tomography (TL-ERT) has emerged as a popular monitoring tool for identifying target decontamination areas during remediation planning and analyzing contamination dynamics at polluted sites. In this study, twelve (12) survey lines were executed in a 200 by 100 m² grid at four time scales at a pollution site in Kegbara Dere, Ogoniland, Southern Nigeria. The grid lines were collated into a 3-D dataset using a 3-D collation code. The independent inversion of the 3-D datasets displayed acute variations in the electrical resistivity (ER) of the contaminants in response to precipitation. 3-D depth slices revealed six layers at depths ranging from 2.50 to 21.9 m. Time-based evaluations from the 3-D ERT models show a reduction in the ER of the contaminant plume during the rainy season. This tendency is due to the diluting impact of rainfall, which raises the water content of the soil during the rainy season. The TL 3-D datasets were used to perform 4-D ERT inversion with an in-house code, and the results were examined to show the real-time position of the contaminated plume and the migration flow pathway moving southwest of the spill site. A maximum depth of 48.0 m was investigated. The 4-D inversion was capable of eliminating time-related inversion artifacts in order to identify the preferred flow route of contaminant plumes at the spill site. 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 (50 and 600 µg/L). 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 concentrations also displayed elevated amounts in the specimens. The direction of groundwater flow is towards BH₄, located southwest of the spill site, indicating the most potential receptor area at risk of contamination. Based on this, future TL-ERT monitoring programs should be integrated with geochemical data systems, providing local validation of variation in ER of pollution sites using 4-D ERT inversion capable of minimizing the effects of rainfall on the TL dataset.