Assessment of groundwater contamination around active dumpsite in Ibadan southwestern Nigeria using integrated electrical resistivity and hydrochemical methods

Investigation of groundwater contamination due to leachate migration in a solid waste disposal site was done using both geophysical and hydrochemical methods. The main goals were to delineate groundwater contamination due to leachate percolation and thus assessment of quality of groundwater from nearby hand-dug wells bordering the dumpsite for drinking purpose. A total of ten resistivity traverses were acquired within and outside the dumpsite using Wenner configuration with constant electrode separation ranging from 5 to 25 m. The 2D resistivity data were processed and inverted using RES2DINV and RES3DINV softwares, respectively. Geochemical assessment of groundwater samples were carried out according to APHA standards while hydrochemical facies of the sampled groundwater was evaluated using Piper Trilinear software. The inverse resistivity models of the subsurface from 2D and 3D imaging revealed low resistivity value less than 10 Ω m suspected to be leachate while 3D inverse sections allowed delineation of leachate, weathered layer, bedrock and seepage path from the dumpsite. The extent of migration was more pronounced in the southern part of the dumpsite, hence possible contamination of shallow groundwater system as dumpsite ages. The results of physico-chemical analyses showed the groundwater samples to be within the limits of WHO/NSDWQ for drinking purpose. However, higher values of concentrations of most analyzed parameters were noticed in well 1 due to its nearness to dumpsite and well 10 due to agricultural activities, respectively. Interpretation of Piper diagram showed CaHCO₃ to be dominant facie in the area while alkaline earth metals (\({\text{Ca}}^{2 + } , \;{\text{Mg}}^{2 + }\)) and weak acids (HCO₃ ⁻, CO₃ ⁻) are dominant cations and anions during both climatic seasons. Groundwater in the study area is of hard, fresh and alkaline in nature.