9 Hydrological Considerations in Mine Closure

In most jurisdictions, mining companies are required to provide a conceptual closure plan for a proposed mine as part of the environmental assessment submitted for initial project approval. Good practice involves regular updates to the closure plan and costs of closure during the life of the mine, with the greatest granularity added to the closure plan toward the end of the life of the mine as ore reserves approach depletion. Closure objectives that accommodate the character of the hydrogeologic regime are an important part of the planning process. From a hydrogeologic perspective, the main objectives of the closure plan are to: (i) address the risk that at some future point in time changes in the hydrogeologic regime could influence stability of geotechnical structures, and (ii) minimize the risk of water quality impacts to receiving waters in nearby watersheds. In addition, in some circumstances mining-induced subsidence of the land surface can alter surface water drainage patterns and groundwater – surface water interactions. Such a possibility needs to be considered in establishing the closure plan.