This paper describes a fascinating case history: Management of Aquifer Depressurization System in Hazelwood Mine, Latrobe Valley, Australia by J. Fernando of International Power and D. Nag of Monash University.

Here is why they undertake aquifer depressurization at this open pit mine:

To prevent catastrophic floor heave, it is necessary to maintain the water pressure levels in the aquifers below the Target Aquifer Pressure levels. The Target Aquifer Pressure level is established by calculating the weight of the overlying materials against aquifer pressure including a factor of safety. The equilibrium pressure is that pressure which just balances the weight of the overlying sediments and aquifer pressures. Consequently, as the depth of the open cut is increased, the weight of overlying sediments is reduced, and the required amount of aquifer depressurisation is increased to achieve balance. It is assumed that the weight of the overlying sediments of clay and coal provide the reactive force required for stability. The shear strength of the material separating the aquifer and open cut base cannot be relied upon for assistance because of the large floor area and the presence of near vertical joints that penetrate the full thickness of coal seams.

The paper proceeds to describe the details of how they achieve this. Here are their conclusions---enough to whet your interest to read the paper.

  • Effective and efficient management of aquifer depressurisation system could help reduce environmental impacts due to groundwater extraction for coal winning process.
  • Further effective depressurisation maintains Mine stability for safe mining operation.
  • Aquifer level depletion cannot be avoided; however effective management of aquifer depressurisation could slow down the aquifer level depletion. The current rate of depletion a kilometre away from the Mine is 2.6 metres per year for M1 aquifer and 50 mm per year for M2 aquifer.
  • Land subsidence can be maintained at a lower rate and total subsidence predicted closer to north of the Mine where Morwell township is located will be 0.2 metres by the end of 2030. Rate of subsidence from 2000 to 2030 is 6.7 mm/year.

This paper and a number of others have just been added to the InfoMine library courtesy of Raj Singal who gave us permission to choose and post our favorites from the CD of the proceedings of the conference he organized called Mine Planning and Equipment Selection and Environmental Issues and Waste Management in Energy and Mineral Production for the 2007 conference held in Bangkok, Thailand. The full CD is available through the InfoMine eStore.