Quantification of the impacts of a domestic waste site on a Karoo aquifer
Mndaweni, Sakhile Sibusiso Edwin
MetadataShow full item record
Waste generation is a widespread phenomenon around the world, of which the majority is disposed by landfilling. In landfills, waste constitutes an integral part of the hydrological system, and thus poses a threat to down-gradient groundwater and surface water receptors. This research was undertaken with the purpose of determining the interactions between landfill and the underlying Karoo aquifer, investigating the impacts of a domestic waste landfill on the aquifer and further predicting the magnitude of future contamination. A domestic waste landfill site at Sasol Synfuels (Secunda), located on the Karoo aquifer, was investigated in order to achieve these objectives. This site (Charlie I Landfill) has been used by the refinery to dispose of all non-hazardous/general waste produced for the past twenty years. It is not lined. There is no information available on the type and volume of waste disposed, and the impact on groundwater was not quantified. The landfill is classified as GMB+ (i.e. producing significant amounts of leachate), with the bord-and-pillar mining method taking place underneath the site at the depths of 90- 120m. This implies a lower probability of subsidence at this position. Field investigations indicate that there is a contaminant plume emanating from the landfill, which is mostly concentrated in the upper part of the soil horizon. This horizon is mainly composed of clayey loams and clay, averaging 3m in depth with a laboratory estimated maximum hydraulic conductivity of 0.0128 m/day. It is underlain by the Karoo sediments (sandstones and shales). Regional groundwater levels have been disturbed by the presence of the landfill site, with the higher water table closer to the site and the deeper water table moving away from the site. According to the blow yields obtained, slug tests for boreholes and piezometers, as well as the pumping tests, an average K- value of 10-2 was obtained for the aquifer, except in regions where a dolerite sill or fractures exists. Soil and water quality analyses indicate little contamination to groundwater; while contamination is mainly concentrated in the upper soil zone (i.e. originates from the surface leachate springs at the edge of the landfill). Modelling of the contaminant plume also indicates a slow migration of the plume to the adjacent areas. The physical properties of soils indicate that retardation (by biochemical reactions, sorption, cation-exchange etc.) of contaminants will occur with only very small quantities reaching groundwater. The presence of leachate springs and low levels of contaminant concentrations in groundwater indicates a limited vertical movement of contaminants. Therefore, leachate produced by the landfill site does not infiltrate into the groundwater system.