Geophysical and geochemical study of the contaminant impact of Oke-Tage solid waste dumpsite, Southwestern Nigeria

The physicochemical properties of groundwater, geochemical characteristics and subsurface formation of the Oke-Tage waste dumpsite soil material were assessed to determine the impact of the leachate generated from the waste dumpsite on the quality of the groundwater within the study area. Water samples collected from hand-dug wells were analyzed to determine groundwater quality, while soil samples were examined for their geochemical characteristics. Ten Vertical Electrical Sounding (VES) surveys were carried out with an electrode spacing (AB/2) increasing from 1 to 200 m. Also, four 2D electrical resistivity profilings were done using the dipole-dipole configuration. The hydro-chemical analysis showed an elevated Cadmium (Cd) and Lead (Pb) concentration above the maximum permissible limits. The physicochemical results indicated that the Electrical Conductivity (EC) ranged from 1900 to 3670 µS/m, while Total Dissolved Solid (TDS) ranged from 585 to 620 mg/L. The health risk assessment showed no significant health risks associated with exposure to the metals due to HI values less than 1. Based on the VES result, four geoelectric layers comprising topsoil, weathered layer, fractured basement, and fresh basement were identified. The 2D resistivity structures revealed that the topsoil and weathered layers practically merged and are characterized by relatively low resistivity (< 30 Ωm) beneath the dump site. The study concluded that the groundwater and soil in the vicinity of the investigated Oke-Tage waste dumpsite had been negatively impacted to levels that called for caution especially using the water for regular potability purposes.