Conductive zones characterization using VLF-EM technique around a landfill on basement complex formation of Southwestern Nigeria

Abstract

The conductive zones in the vicinities of the Saje dumpsite in Abeokuta metropolis, Ogun State, Southwestern Nigeria, were characterized  employing the Very Low Frequency-Electromagnetic (VLF-EM) geophysical technique. The subsurface spatial distributions  were mapped, and the migration and accumulation of leachate plumes in the fault lines or fractures were indicated. The survey traverses  ranging from 140-200 m were laid from the dumpsite to the residential area with station intervals between 5 and 15 m using the ABEM  WADI VLF meter. Nine traverses were created in the North of the dumpsite in the W-E direction, while five traverses were laid in the  western region of the dumpsite in the N-S direction. The VLF meter's in-built filtering program and Fraser and Karous-Hjelt program  filtered the real signatures obtained. The results were shown as 2D KarousHjelt pseudo-sections and Fraser anomaly curves, which  depicted features with varying degrees of conductive and resistive regions in different directions. The anomaly curves showed prominent  conductive signatures, which indicated massive accumulations of contaminants from the dumpsite. Also, the orientations of the conductive dwarf peaks of the signatures suggested appreciable massive contaminant regions. Furthermore, several cavities of both  conductive and resistive responses were observed across the 2D Karous-Hjelt models to a depth of about 30 m. The results generally  revealed conductive zones to distances of 35 and 75 m on the western and northern regions of the dumpsite, respectively. The regular  patterns of conductive responses indicated fault lines as significant leachate plume trackways in the dumpsite subsurface.