Mapping and Monitoring of Leachate Plume Migration at an Open Waste Disposal Site Using Non-Invasive Methods

A geophysical survey was carried out in a potentially polluted open waste disposal site in a densely populated part of Zaria, Kaduna State, Nigeria with the aim of imaging the subsurface to delineate leachate plumes and their pathways into the groundwater at shallow depths and to monitor the extent of the vertical and lateral migration over a period of ten months. The survey applied the Induced Polarization and Electrical Resistivity tomography using 2D approach. The horizontal and vertical extent of leachate plumes were delineated by the geo-electrical imaging as a response to the varying electrical resistivity in the contaminated area. The migration rates of 2.05 m/month, in the lateral direction as well as 0.53 m/month in the vertical direction, were obtained. The rate of migration in the horizontal direction was higher than that in the vertical direction by a very significant margin of 1.42 m/month. The vertical motion was impeded by the presence of clay as revealed by the inverted resistivity models with resistivity values in the range of 82.0 to 100. The Induced Polarization survey result indicates that the waste in the dumpsite was buried to as much depth as over 10.0 m. The rate of migration was found to depend on the compaction of the soil texture, the presence of loose soil, fractures, depressions, undulations and dipping topography.