Geophysical and Geotechnical Assessment of the Effects of Barikin-Sale Dumpsite on Groundwater Quality, Minna, North-Central Nigeria

Abstract

Abstract Discharge of leachate from refuse dumpsites is a source ofgroundwater pollution within its immediate environment of location. Geophysical investigation of an uncontrolled open solid waste dumpsite located at Barikin -SaIe area o Minna was carried out for possible contamination of groundwater. The investigation is aimed at delineating groundwater contamination due to leachate percolation thereby assessing the quality of groundwater from hand dug wells and boreholes within the dumpsite and the surrounding environment. A total of ten ( 10) Vertical Electrical sounding (VES) points with maximum current electrode spacing of 20m and two (2) 2D Subsurface Electricalimaging were investigated within and outside the dumpsite to possible movement of to the area. Schlumberger configuration was used for the VES while the Wenner configuration was used for the subsurface imaging. The VES data were analysed and a maximum of three (3) geoelectricsections identified; the top soil. weathered basement and the fractured/fresh basement. The obtained apparent resistivity for those layers were between 19.40m and 122.60m for the first layer, 18.20m and 33.40m for the secondlayer and 93.50m and 166.40m for the third layer respectively. The range of thickness for the first layer is 0.9m and I .8m and for the second layer are 4.0m and 5.3m respectively. The 2D resistivity data were processed and inverted using the RES2DlNV software. The inverse resistivity models of the subsurface from the 2D electrical imaging revealed low resistivity value <20Qm which is taken to be leachate derived from decomposed waste while these wastes that cannot decompose are occurring as isolated parts with slightly higher resistivity value of>20Qm. The areas With the highest resistivity value of were further interpreted 10 be chemical weathering product of crystalline bedrock considered to be regolith. From the estimated hydraulic conductivity (K) from the sieve analysis, the values range between I .97 x 10-4 and 2.52 x 10-5m/s. These values are high and they correspond to leachate movement through the Interconnected pore spaces of the soil underlying the waste dumpsite. This further clarifies the geophysical investigation results. From the results, it could be concluded that leachates are concentrated within the lower part of the dumpsite; therefore the surrounding environment groundwater sources are vulnerable go leachate contamination from the dumpsite.