Mine Waste Cover System Design ù Linking Predicted Performance to Groundwater and Surface Water Impacts

Current best management practice requires the placement of a cover onto most types of mine waste including tailings, waste rock and/or spent heap leach rock at closure of the mine. The objectives of a cover system may vary from site to site but generally include dust and erosion control; chemical stabilisation of acid-forming mine waste (through control of oxygen ingress) contaminant release control (through control of infiltration); and/or provision of a growth medium for establishment of sustainable vegetation. In our experience, there has been a general tendency by stakeholders to develop performance criteria for cover systems, which are tied directly to these specific design objectives. In many cases, this practice has led to the development of single, often very conservative, numerical values of cover performance criteria such as ænet percolationÆ, ærate of oxygen ingressÆ and/or æplant density/mixtureÆ. In our opinion, there is a need to develop cover performance criteria on a case-by-case basis and with due consideration of the short-term and long-term impacts on the receiving environment at a particular site. This paper puts forward a methodology for developing site-specific performance criteria for a cover system designed to isolate acid-forming mine waste and to control acid rock drainage. The proposed methodology links the predicted performance of a cover system to groundwater and surface water impacts. This way, the appropriate level of control (of oxygen ingress and/or net percolation) required by the cover system can be determined. A case study is presented that illustrates the application of the methodology proposed in this paper.