GEOELECTRIC DELINEATION OF SUBSURFACE LEACHATE CONTAMINANT CONTROLLED CONDUCTIVE GROUNDWATER IN LAGOS STATE

The volume of Leachate produced is a function of the amount of water percolating through the refuse dumpsite in Igando area of Lagos state and this had threatened the groundwater obtained at different location in the area. Ineffective waste disposal system has resulted in health hazards such as periodic epidemic and communicable diseases due to the percolation of contaminant leachate, produced from the landfill, into the groundwater aquifer. 2D electrical resistivity imaging and vertical electrical sounding (VES) can be helpful in mapping areas of contaminated soil and groundwater quality. The results of the sounding interpretation and the 2D resistivity structures revealed three subsurface layers: the topsoil, sand clay (brackish water), sandstone (good quality fresh water). The results also showed the shallow occurrence as well as the thin porous overburden units overlying the layers, the sandstone zones and the resistivity structures constitute the major aquifer units of the study area. It was also observed that the mapped area that contained sand layers was found to be water bearing formation which has been polluted thereby making the groundwater around the landfill to be conductive. The results further revealed that Leachate from the landfill has a minimal impact on groundwater and this can be attributed to the existing sub-soil at the dumpsite consisting of clay which is deduced to have a significant influence on the natural water percolation of Leachate into the groundwater.