Geophysical and geochemical characterization of Odogbo Dumpsite, Ijebu Ijesa, Southwestern Nigeria.

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Due to incessant contamination of the groundwater system near the dumpsite in southwestern Nigeria Basement Complex, this study seeks to evaluate the impact of the Odogbo dumpsite on the local groundwater system by integrating geophysical and geochemical methodologies. Aeromagnetic data covering the study area was acquired, processed, and enhanced to delineate basement features that could potentially be passing plumes to the groundwater system. Concurrently, geoelectric methods using 2-D dipole-dipole imaging and vertical electrical sounding (VES) were utilized to characterize the vulnerability indices of the lithologies underlying the dumpsite. The resistivity data was collected with the UltraminiRES resistivity meter. Vulnerability assessment of the regolith was conducted through longitudinal conductance rating. Water samples from the vicinity of the dumpsite were analyzed using a spectra AA220 atomic absorption spectrophotometer (AAS). The results of magnetic derivatives and analytical signals filters revealed that the Odogbo dumpsite is directly situated atop lineaments trending mainly in an NE-SW direction. The 2-D resistivity model depicted the extent of the leachate plume percolation, characterized by resistivity values below 20 Ωm. The curve types identified from VES results were A, H, HK, and KQ while the geoelectric layers were identified as topsoil, weathered layer, lateritic layer, and fresh/fracture basement. The protective capacity varied across the area, from 0.02 to 0.473 mhos, signifying weak to moderate protective capacity of the overlying layer. Most elemental parameters tested fell below the World Health Organization (WHO) permissible values and some were within WHO standards except iron. All the water sampled were rated poor to unsuitable as their water quality index (WQI) ranged between 232.81357 and 1520.88776 due to high elemental iron content which could be from other sources. The study area is safe from contamination for now but there is a high tendency that the area may be contaminated in future; hence, the need to monitor the region periodically is highly recommended.