Study of Leachate Migration at Sungai Sedu, Telok Datuk Waste Disposal Site by Geophysical and Geochemical Methods

Monitoring of contaminated water and soil in waste disposal sites is normally carried out by chemical analysis of surface water, leachate and soils as well as by geophysical measurements. Leachate is defined as any contaminated liquid or wastewater generated from rain water percolating through solid waste materials, accumulating contaminants, and moving into subsurface and surrounding areas. A study was carried out to detect the leachate movement at Sungai Sedu landfill located on ten square acres near Banting town. Geologically, the study area is underlined by Holocene marine clay of Gula and Beruas formations sitting on top of metasedimentary rocks of Kenny Hill Formation. Geophysical surveys using techniques 2D electrical resistivity imaging, vertical resistivity profiling (VRP) as well as geochemical analysis on soil and water samples were used in this study to investigate the level of leachate migration from the dumping spot into the surrounding areas. This was based on characterizing the measured electrical resistivities and analyzing the heavy metal concentrations. The 2D electrical imaging surveys were carried out on 8 profiles while the VRP surveys were conducted in 6 boreholes. Based on resistivity imaging sections, the leachate was detected to migrate at about 3-5 m depth. Basically the electrical resistivity of leachate was less than 1 ohm m. The concentration of heavy metals also showed that the leachate has migrated into the nearby river. The concentration of heavy metals in river bank soil, leachate and surface water samples were high and exceeded the background values especially Ni, Mn, Zn, Cr and As. The electrical conductivity of the river bank soil, leachate, surface water and the surrounding soil samples were approximately 6600 ìS/cm and 20000-50000 ìS/cm, respectively with pH values of 3-5. The high concentrations of heavy metals and soil conductivities indicated the possibility of leachate migration from the dumping site to contaminate the nearby river, soil and groundwater of the study area.