Geo-electrical modeling of leachate contamination at a major waste disposal site in south-eastern Nigeria

Abstract

The contamination of aquifers due to the leaching of organic and inorganic waste materials deposited in landfills and open dumpsites leads to serious degradation of the environment. To determine the extent of leaching and to assess the migration of the leachate into the surrounding aquifer, vertical electrical sounding (VES) and electrical resistivity tomography (ERT) surveys were carried out along a heavily contaminated waste disposal site in South-eastern Nigeria. The results obtained from the vertical electrical soundings show that the area comprises three subsurface layers, and that the aquifer lies between the second and third layer. Computation of longitudinal conductance values shows that the overall protective capacity of the aquifer is weak; hence, the capacity for leachate contamination within the aquifer is higher. Models obtained from the electrical resistivity tomography surveys indicate the direction of the leachate plumes and also show the extent of leachate percolation into the aquifer. On the electrical resistivity tomography models, the locations of anomalous low resistivity zones indicate the presence of leachate. The results show that the leachate is moving rapidly towards the aquifer and this will create serious environmental degradation to valuable water resources in the area, thereby affecting health of humans and livestock within this heavily populated zone. Further, the results from the resistivity surveys confirm that the resistivity technique is a powerful tool for delineating the presence of leachate plumes and for indicating to what extent the leachate has infiltrated into the surrounding aquifer.