2D inversion of electrical resistivity investigation of contaminant plume around a dumpsite near Onitsha expressway in southeastern Nigeria

The study tries to utilize vertical electrical sounding (VES) and 2D resistivity tomography to evaluate the region of influence of the leachate plume on the groundwater around a dumpsite at Onitsha expressway, southeastern Nigeria. The borehole log data were acquired and their respective geoposition logged with Garmin GPS device. In addition, four 1D (VES) soundings and 2D electrical profile data were acquired in the field utilizing the Schlumberger and Wenner profiles respectively. Petrozenith PZ-03 Resistivity meter was used to acquire the electrical data, while RES2DINV and WinResist software were used to interpret the 2D and 1D data respectively. The resulting geoelectic layers were correlated with the borehole logs and were interpreted according to their resistivity distribution. Results of the 2D inversion at profiles 1 and 3 showed low resistivity zones indicating influence from the leachate plume. Profiles 2 and 4 gave low resistivity zone within 14.6 and 44.3 Ωm from surface to between 0.375 and 3.60 m depths indicating influence from leachate plume. Likewise, profiles 1 and 3, which penetrated groundwater, also showed very low resistivity with resistivity ranging from 3.12 to 8.7 Ωm, from surface to few meters depths. This indicates that it has been polluted by the leachate. In contrast, Profiles 2 and 4, from the 2D inversion, has no leachate influence on the groundwater. The VES result showed that the depth to the water table at location 1, 2, 3 and 4 are 21.7 m, 17.9 m, 15.9 m and 12.2 m respectively, with the leachate plume flowing in the southeast direction in line with the groundwater flow direction.