Mapping Contaminant Plumes from Illegal Dumpsite Using Electrical Resistivity in Aba, South East Nigeria

The proliferation of unregulated waste dumpsites in Aba, Abia State, poses severe risks to shallow groundwater quality, as leachate generated from decomposing organic and industrial waste migrates through the unsaturated zone into productive aquifer horizons. This study maps the lateral and vertical extent of contaminant plumes emanating from two illegal dumpsites in Aba using two-dimensional electrical resistivity tomography. The Wenner-Schlumberger array was deployed along 8 profiles with electrode spacings of 5 metres to achieve adequate lateral resolution of the near-surface contamination zone. Inverted resistivity models were interpreted in conjunction with water quality data from 15 hand-dug wells within 300 metres of each dumpsite. Low-resistivity zones in the range of 1 to 10 ohm-metres, extending to depths of 8 to 18 metres at downslope positions from the dumpsites, are interpreted as leachate-saturated zones. Groundwater sample analyses confirm elevated concentrations of total dissolved solids, nitrate, and heavy metals at wells within these low-resistivity zones. The mapped plume geometry is used to construct a conceptual contaminant migration model for each site. The study concludes with recommendations for dumpsite closure, capping, and monitoring well installation to protect community water sources. Keywords: leachate plume, electrical resistivity, illegal dumpsite, Aba, groundwater contamination