Hydrological and geochemical processes and closure options for below water table open pit mines.

Post-mining landscapes will always be different to pre-mining landscapes. The challenge is to understand the impacts of mining activities, and how these impacts can be altered or ameliorated by management. Optimising pit closure outcomes for water quantity, quality and dependent-ecosystems and environments requires detailed knowledge of groundwater and surface water systems and their connectivity to potential pit lakes.

Dewatering of below – water table mine pits is necessary to create a dry mining environment. Mine dewatering lowers the regional water table surrounding the mine pit, and this zone of reduced water table can extend over tens of kilometres. After the cessation of mine dewatering, the area surrounding the mine that is subject to reduced groundwater levels will continue to increase, before eventually decreasing. Thus, it is possible that ecosystems that are not affected by drawdown during the mine’s operational life might still be affected after mine closure. Accurate prediction of water table drawdown after mine closure requires detailed information on the aquifer system surrounding the mine, including geological structures that might act as barriers to groundwater flow. Such information is required beyond the region that is directly impacted by water table drawdown during mining operations.