Contaminant delineation of a dumpsite using geophysical and hydrochemical data: a case study of Agbado-Oja, Ogun, Nigeria

Open dumping is a common solid waste disposal method in major cities in Nigeria. The habit of open dumping has a detrimental effect on the surrounding environment, as it discharges leachate from the dumpsites into the aquifers, leading to several waterborne diseases. This study was designed to examine the extent of leachate contamination at open dumpsites in the Agbado-Oja (Oju Irin) metropolis of Ogun, Nigeria. The geophysical properties were determined by electrical resistivity tomography (ERT). The 2D resistivity imaging data were processed using DIPROFWIN software. The results show that part of the dumpsite with low resistivity (3 Ωm) at a depth of 27.4 m was characterized as substrate materials, indicating decomposed organic materials known as leachate that penetrated up to a depth of 27.4 m. The leachate was also observed to have infiltrated the subsurface to a depth of roughly 30 m in some parts of the profile. The hydrochemical data were analyzed by geochemical analysis, and the results were observed to decline in the order of EC > TS > TDS > COD > Cl > TSS > BOD > pH > Fe >Zn > Cu > Cr > Cd. The investigated geochemical parameters were below the WHO permissible limits, except for pH, EC, BOD, and Fe. Elevated BOD levels in the samples revealed a high organic influence of the dumpsite, exceeding the drinking water standard.