Challenge. Evaluate impacts on water resources from various alternatives for closing a large open pit at a mine site surrounded by a World Heritage national park and upstream of RAMSAR Convention wetlands.
Solution. INTERA’s modeling expertise was used to support the development and optimization of mine closure strategies. A major part of this work included developing and applying a groundwater flow and solute transport model to facilitate closure planning for one of the mine’s large open pits. The model was used to evaluate various pit closure scenarios based on predictions of potential solute loadings from the pit backfill to nearby surface water resources. Backfill in the pit consisted of tailings, waste rock, and a high-density brine used to improve stability. Tailings-related sources were legislatively required to be assessed over a 10,000-year period whereas leaching from waste rock and other sources were evaluated for as low as reasonably practicable (ALARP). We also applied a systems assessment methodology to evaluate the effectiveness of a selected closure scenario in preventing tailings, which are being used to backfill the pit, from adversely impacting surface water and groundwater resources over the next 10,000 years. These tools played a key role in establishing support and obtaining approval from regulators and other stakeholders for the recommended closure strategy.
