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: The Gilt Edge gold mine is an acid drainage site that has been put on an accelerated closure schedule. The mine ceased activities in 1999 when Dakota Mining Corporation declared bankruptcy forcing the State of South Dakota to immediatly assume water treatment operations. Evaluation of conceptual closure plan options and cost estimates led the State of South Dakota to a decision to seek Federal assistance. The site has quickly moved into reclamation mode for the principal contamination source, the Ruby waste-rock dump. Designs and specifications for capping the Ruby waste-rock dump were prepared while Superfund listing was pursued. In October of 2000, mobilization of the first reclamation contractor began and by December the site was added to the National Priorities List. Capping the waste-rock dump will address a major acid drainage source. Water treatment requirements are expected to decline as conventional methods such as diverting clean water, backfilling, grading, capping, limestone neutralization, and revegetation are implemented. Acid seepage from underground workings, steep highwalls, and some pit backfills will remain. Major field trials of emerging technologies are nearing completion and some are showing promising results. Carbon reduction in a pit lake, and pyrite microencapsulation on simulated waste dumps, are showing initial success. Their application may minimize or eliminate the need for long-term active water treatment which has been a long sought goal for major acid rock drainage sites.