ABSTRACT
Gold mining is a growth industry, producing substantial amounts of waste that can impact the environment. It is important to understand the mechanisms of releasing metal elements from these mines and their wastes in order to predict migration of these contaminants and design a mitigation strategy for pollution control and prevention in the local groundwater system. The study focuses on the impacts of variable water saturation on migration and adsorption/desorption characteristics of multiple heavy metal species derived from mine water leachate entering the groundwater environment. A series of batch and column tests was conducted to evaluate the effects of pH on the sorption/desorption characteristics of metals and to estimate the sorption/desorption isotherms of the multiple heavy metal species. The results from the column experiments were then used as input parameters in HYDRUS-2D model to simulate the migration of heavy metals through variably saturated porous media. The computer simulations revealed that the migration of the mixed contaminated plume was governed mainly by the mechanisms prevailing in the unsaturated zone, rather than the hydraulic head gradient in the saturated zone. In addition, decreasing water content resulted in higher sorption, promoted the late arrival of water fronts, and therefore could extend the contaminants’ lifetime in the system. Drier soil tended to retard transport of metals particularly in the shallow unsaturated zone, leading to a possible pathway for the contaminants to get back into the system via plant root uptake. This study provides a basis for understanding processes governing the transport and migration of heavy metals in groundwater, which could lead to a more robust planning strategy for contaminant controls and prevention in the future.
