Facilitating Open Pit Mine Closure with Managed Aquifer Recharge

Peter Cook, Anthony D. Miller, Ilka Wallis, Shawan Dogramaci

Research output: Contribution to journalArticlepeer-review

Abstract

Dewatering of open pit mines can lower the regional water table for distances of several kilometers from the pit. When the mine is closed, dewatering operations usually cease, and the water table near the pit begins to rise. If the pit is backfilled, the water table will eventually recover, but this recovery may take several hundred years. However, if the extracted water is re-injected into the subsurface, then this may accelerate recovery of the water table. We show that there is an optimal distance for re-injection, which is sufficiently far from the mine to minimize the amount of groundwater that flows back to the pit during mine operations (and hence necessitate additional pumping) but is still close enough to speed up the water table recovery post-mine closure. The optimal injection distance increases with the aquifer hydraulic diffusivity and the mine life (duration of dewatering and injection), and typically ranges between about two and nine times the radius of the mine pit. Where the mine pit is not backfilled, the relative reduction in drawdown due to injecting all the pumped water at the optimal distance is between approximately 10% and 50% after a recovery time equal to the mining period, increasing to 30% to 90% after a recovery time five times the mining period. The relative drawdown reduction due to managed aquifer recharge will be even greater for a pit which is backfilled when mining ceases.
Original languageEnglish
Number of pages11
JournalGroundwater
Early online date30 Jan 2022
DOIs
Publication statusE-pub ahead of print - 30 Jan 2022

Keywords

  • open pit mine
  • Dewatering
  • managed aquifer recharge
  • regional water table
  • subsurface dam
  • hydraulic diffusivity
  • Drawdown

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