Geophysical mapping of contaminant leachate around a reclaimed open dumpsite

Very low frequency electromagnetic (VLF-EM), 2D Electrical Resistivity Profiling (2D ERP) and Vertical Electrical Sounding (VES) methods of geophysics were deployed to map the extent of leachate contamination in near-surface rocks around a popular reclaimed dumpsite in north central Nigeria. Two years after abandon and waste excavation; the dumpsite was converted to a residential area with over 80 houses under construction. Prior to waste dumping operation, clay-seal was installed at 2 m depth around the dumpsite to prevent leachate from the waste material flowing to the adjoining area. Results from VLF, 2D ERP, and VES show presence of leachate contamination in rocks and soil of the reclaimed dumpsite. Leachate has spread laterally up to a distance of about 1 km on the northern and southern parts of the dumpsite centre, and up to a depth of about 20 m. Compared to the results of similar survey in an area outside the dumpsite, leachate infiltration raised the conductivity signature of the rocks around the dumpsite by about 200%: from 7% to 22%. Both VLF-EM and 2D ERP show the presence of approximate north - south oriented structures/fracture characterised by high conductivity. VES results show the presence of four - five geo-electric layers. Important conclusions from the study are that (i) leachate is still present in the rocks and soil of the reclaimed dumpsite two years after the abandonment and excavation of the waste materials, and (ii) the clay seal installed around the dumpsite could not prevent leachate migration to the adjoining areas.