Heavy Metal Contamination of Soil Beneath a Waste Disposal Site at Dengkil, Selangor, Malaysia

Abstract

Heavy metals leaching from solid waste facilities pose concerns because of the metal ions being distributed to surroundings through surface, subsurface, lateral and/or vertical movement of water. In view of this concern, heavy metals, namely Fe, Mn, Cu, Cr, Ni, Zn, Pb, and Co, in soil horizons beneath the Ampar Tenang waste disposal site at Dengkil, Selangor, were extensively studied through chemical analyses of 21 representative soil samples collected in triplicate. The soil samples were collected from nine augered boreholes. Three of the boreholes are located within the disposal site and three each up-slope and down-slope of the disposal site. Soils sampled from the soil-waste interface (ATI) within the dumping site show relatively high concentrations of most of the heavy metals analyzed as compared with samples collected from upslope area (ATU) of the dumping site. Soil samples from a downslope area (ATD) show a slightly elevated concentration of heavy metals. The results of chemical analyses also show that Cr, Zn and Pb have higher levels of concentration among all studied heavy metals. It was found that, in most cases, the heavy metal concentrations were generally high within the near surface soil layer and decreased in concentration with increasing depth. Site observations indicate that, in addition to the vertical infiltration of leachate from the solid waste, shallow groundwater level strongly influences contaminant dispersion in soils below the waste site. Properties of the soil indicate that the Ampar Tenang soil (ATS) is more permeable than the minimum limit of formation permeability required underlying a waste disposal site. The acidic-pH soil environment and groundwater fluctuations also influence the mobility of heavy metals spatially and vertically in the vicinity of the waste disposal site at Ampar Tenang.