ABSTRACT
There are over one thousand open pit mines in Western Australia where mining has extended below the water table. Because evaporation exceeds rainfall the salinity of water that fills these pits is expected to gradually increase. In areas of the state where high groundwater quality and open pit mining coincide there is the potential for degradation of groundwater quality. In late 1999 Mt Magnet Gold NL (MMG) initiated stormwater harvesting in mined-out open pits to provide significant cost savings in the production of water for processing. This initial success has now led to a further application and the granting of approval for harvesting of stormwater in MMG’s Milky Way pit. The local groundwater quality is good and one of MMG’s fresh water production bores is located immediately adjacent to the pit. Stormwater harvesting at this site is expected to offset the rainfall-evaporation deficit, that would otherwise result in a gradual deterioration of the quality of pit water the adjacent water supply.
The paper outlines a simple pit water balance model which has evolved from monitoring of water levels in and around these as well as other mined out open pits and illustrates how, when correctly planned and implemented, surface water harvesting represents a valuable water management strategy for mines in WA’s arid interior. The potential to locally increase high quality water resources, raises numerous additional opportunities, which could lead to new land uses after final mine closure.
