Characterization and Monitoring of Leachate Plume migration in Active Dumpsite within Basement Complex of Southwest Nigeria using Integrated Geophysical Methods

Infiltration of leachate plume from dumpsite into nearby shallow aquifer units poses a considerable threat to groundwater quality and human health. This study employed integrated geophysical methods (Very low frequency-electromagnetic (VLF-EM) and 2D electrical resistivity tomography (ERT) techniques) to map the conductive lineament structures, extent of leachate plume accretion and migration for likely pollution of nearby shallow groundwater sources. The VLF-EM and 2D ERT surveys were carried out with the aid of ABEM WADI VLF-EM meter and Campus Tigre model terrameter, respectively. Nine VLF-EM traverses of lengths varying between 120 and 250 m and nine 2D ERT traverses (with lengths ranging between 80 and 120 m) utilizing Wenner array arrangement and electrode separation distance varying from 5 to 25 m were mapped in the dumpsite. Control traverses of VLF-EM and 2D ERT surveys were also carried out at roughly 400 m away from the dumpsite. VLF-EM and 2D ERT data were processed and interpreted utilizing Fraser and Karous Hjelt filters as well as RES2DINV code, respectively. The integrated results of Fraser graphs and Karous Hjelt pseudo sections of VLF-EM data revealed west - leaning leachate plumes/conductive lineaments of several depths that cut transversely the dumpsite. However, 2D inverse resistivity sections showed leachate plume of < 10 Ωm that has migrated up to a depth of about 6.5 m at the west side of the dumpsite. The study recognized more of regions of accumulated leachate plume to depths that could have permeate the shallow aquifer units on the western part of the dumpsite.