English

Abstract

Golden Sunlight mine is located northeast of Whitehall, MT. Two cover systems were installed on the west waste rock complex and tailings area in order to minimize water infiltration and acid drainage. The covers were designed to function as a store-release system and are composed of coarse and fine materials being 0.80 m thick on the waste rock and 1.8 m thick at the tailings area. In order to study the influence of thickness, material properties, vegetation and climate on the performance of the cover systems, a laboratory testing program was carried out to identify the properties of the cover at different depths. In addition, thermal conductivity sensors were installed at three field monitoring stations located on the waste rock dump and tailings area in order to evaluate the variation of suction in the cover profiles. These data were used to calibrate a numerical modeling program that assessed infiltration rates through the covers under different vegetation and climate conditions. The simulation results were used to correlate internal variations in grain size and hydraulic conductivity with cover performance in terms of measured suction profiles and infiltration rates. The results show that vegetation plays a critical role in cover performance and becomes most important during wet and very wet years. The simulations and field measurement also revealed that the internal properties of the cover control infiltration patterns, showing upward and downward fluxes at different zones within the cover. It is shown that while increasing layer thickness reduces the dependence of cover performance on vegetation conditions, the establishment and sustainability of vegetation remains most important with respect to satisfactory long-term performance of store-release cover systems. Additional Keywords: Store-release cover, numerical modeling