Delineating leachate-groundwater interaction at Gyadi-Gyadi dumpsite, Kano, using natural electromagnetic (EM) field detector and Vertical Electrical Sounding (VES)

Abstract

Geophysical investigations are mostly used for hydrogeological studies, mining, geotechnical investigation and environmental surveys. Geophysical investigation of groundwater within the dumpsite is highly critical because the extent of interaction between leachate plume/contaminated zone and aquifer zones could significantly reduce groundwater quality. The textural complexity and clay content of soils could change their electrical properties, thus reflecting inconsistent resistivity values using the resistivity method. This research investigates the extent of leachate infiltration from waste dumpsite into groundwater at Gyadi-Gyadi Kano State, using natural Electromagnetic (EM) field and Vertical Electrical Sounding (VES) methods. Six natural EM profiles were obtained in various locations within the study area using PQWT-TC 150 model. Six VES data points were occupied along the EM profile lines using SAS 1000 ABEM resistivity meter. The two techniques employed revealed some intercalations of low resistivity (conductive) as well as very low electrical potential differences in the study area. The low resistivity media are mixtures of leachates into groundwater units, thereby creating formations from the surface to a depth of about 40 m. The first and second layers have experience leachate-aquifer interaction in the northern, southern and eastern parts of the study area to about 40 m depth, and the leachate-aquifer interaction has extended to the deep aquifer of about 70 m depth at the western part. Shallow aquifer has not been infiltrated by leachate at about >100 m away from the waste dumpsite. Therefore, for potable groundwater exploitation in this area, it is advised that boreholes should be sited >100 m away from the dumpsite, where leachate-aquifer interaction has attenuated. The natural EM field detector is evidently constrained by issues of over-generalization and summation of potential values, probably due to its relatively low resolution. Hence it might not be capable of precisely delineating varying geological units. In contrast, the resistivity method is able to delineate and discretize the subsurface into sub-units of different resistive zones. This implies that VES is better suited for accurately defining the true subsurface geology, while the NEF detector is effective for determining the extent of a leachate plume.