Facilitating Open Pit Mine Closure with Managed Aquifer Recharge

Area of Science:

• Hydrogeology
• Environmental Engineering
• Groundwater Management

Background:

• Open pit mining dewatering significantly lowers regional water tables.
• Post-closure, natural water table recovery is slow, potentially taking centuries.
• Backfilling mine pits can aid recovery, but injection offers accelerated restoration.

Purpose of the Study:

• To investigate the efficacy of subsurface water re-injection for accelerating groundwater table recovery post-mining.
• To determine the optimal distance for water re-injection to minimize operational pumping and maximize recovery rates.
• To quantify the impact of re-injection on groundwater drawdown reduction over time.

Main Methods:

• Numerical modeling of groundwater flow and water table dynamics.
• Analysis of hydrogeological parameters like aquifer hydraulic diffusivity.
• Parametric studies varying injection distance, mine life, and pit backfill status.

Main Results:

• An optimal re-injection distance exists, typically 2-9 times the mine pit radius.
• Optimal distance correlates positively with aquifer hydraulic diffusivity and mine operational duration.
• Significant drawdown reduction (10-90%) achieved post-mining via optimal injection, especially with backfilled pits.

Conclusions:

• Subsurface water re-injection is a viable strategy to accelerate groundwater table recovery after mine closure.
• Strategic placement of injection wells is crucial for optimizing both operational efficiency and post-closure recovery.
• Managed aquifer recharge, particularly in backfilled pits, offers substantial benefits for hydrological restoration.