Abstract: The Island Copper Mine pit near Port Hardy, Vancouver Island, B.C., Canada, was flooded in 1996 with seawater and capped with fresh water to form a meromictic (permanently stratified) pit lake of maximum depth 350 m and surface area 1.72 km². The pit lake is being developed as a treatment system for acid rock drainage. The physical structure and water quality has developed into three distinct layers: a brackish and well-mixed upper layer; a plume stirred intermediate layer; and a thermally convecting lower layer. Concentrations of dissolved metals have been maintained well below permit limits by fertilization of the surface waters. The initial mine closure plan proposed removal of heavy metals by metal-sulfide precipitation via anaerobic sulfate-reducing bacteria, once anoxic conditions were established in the intermediate and lower layers. Anoxia has been achieved in the lower layer, but oxygen consumption rates have been less than initially predicted, and anoxia has yet to be achieved in the intermediate layer. If anoxia can be permanently established in the intermediate layer then biogeochemical removal rates may be high enough that fertilization may no longer be necessary. < copyright > 2006 ASCE.

Abstract: Acid mine drainage (AMD) is one of the most significant environmental challenges facing the mining industry worldwide. It occurs as a result of natural oxidation of sulphide minerals contained in mining wastes at operating and closed/decommissioned mine sites. AMD may adversely impact the surface water and groundwater quality and land use due to its typical low pH, high acidity and elevated concentrations of metals and sulphate content. Once it develops at a mine, its control can be difficult and expensive. If generation of AMD cannot be prevented, it must be collected and treated. Treatment of AMD usually costs more than control of AMD and may be required for many years after mining activities have ceased. Therefore, application of appropriate control methods to the site at the early stage of the mining would be beneficial. Although prevention of AMD is the most desirable option, a cost-effective prevention method is not yet available. The most effective method of control is to minimize penetration of air and water through the waste pile using a cover, either wet (water) or dry (soil), which is placed over the waste pile. Despite their high cost, these covers cannot always completely stop the oxidation process and generation of AMD. Application of more than one option might be required. Early diagnosis of the problem, identification of appropriate prevention/control measures and implementation of these methods to the site would reduce the potential risk of AMD generation. AMD prevention/control measures broadly include use of covers, control of the source, migration of AMD, and treatment. This paper provides an overview of AMD prevention and control options applicable for developing, operating and decommissioned mines.

Abstract: In the late 1890s, silver, lead and zinc deposits were discovered along the headwaters of the Blackfoot River, northeast of Missoula, Mont. Settlers began mining the metals in earnest, and eventually the mines became known as the Upper Blackfoot Mining Complex (UBMC). Many of the mines were operated long enough to supply metals for World War II weaponry, but after the war the mines were abandoned, and by the 1960s, their orange-tainted runoff began to concern both passersby and state officials. In 1991, the state contacted the current owners of several of those mines-including the Mike Horse and the Anaconda-to negotiate a voluntary cleanup. The American Smelting and Refining Co. (ASARCO) and the Atlantic Richfield Co. (ARCO) agreed to remediate the sites' metal-enriched, moderately to severely acidic drainage, which was discharging into the upper Blackfoot River. As part of effort to reclaim the Mike Horse and Anaconda mines, engineers with McCulley, Frick and Gilman Inc. (MFG), Boulder, Colo., developed an integrated, passive wetland treatment system that will take several years to reach full treatment capacity in the high-elevation environment, but will last for decades. (Constructed and restored wetlands have also been part of the remediation of other UBMC mines, such as the Carbonate and Paymaster mines.) The Mike Horse and Anaconda system, designed to meet National Pollutant Discharge Elimination Systems (NPDES) restrictions, concentrates primarily on zinc and iron and, to a lesser extent, on copper, lead and other metals.