MBS will be attending the 2014 Goldfields Environmental Management Group Workshop in Kalgoorlie, from 21 to 23 May! Not only will Dave Allen be presenting a paper on Pit Lakes: Liability or Legacy? (abstract below) and Kristy giving a presentation on the Sirius Nova Project but we will also have a booth where you can come by for some freebies and a chat. Look out for the following staff members!
R. GarnhamA, D. AllenB, K. GanzaB & S. Pelliccia
AGroundwater Resource Management
WA currently has 2,000 mine voids of which more than half have potential to form pit lakes following cessation of mining. Miners are reluctant to backfill with waste rock or tailings because of very high costs and the risk of sterilising remaining resources.
In 2003, the former Water and Rivers Commission (now Department of Water), published Mine Void Water Resource Issues In Western Australia, to provide guidance on understanding environmental issues associated with mining below the water table and managing potential impacts as part of mine closure planning. The importance of managing pit lakes as part of mine closure planning has been reinforced through inclusion in the Guidelines for Preparing Mine Closure Plans (DMP & EPA 2012) and the Mining Rehabilitation Fund Act 2012 (and associated Regulations) which recognise pits as liability requiring payment of a levy until appropriately rehabilitated.
Predicting final water levels in pit lakes requires a good understanding of hydrogeological and climatic conditions. The time required to attain a stable water level may vary from several years to hundreds of years. Changes in water quality and chemistry are much more difficult to predict and may take thousands of years to equilibrate with pit and aquifer geology.
This paper will outline the tools available to hydrologists and geochemists for predicting final pit lake levels and water quality parameters including salinity, acidity, alkalinity and concentrations of toxicants. A recent study of an existing pit at the Nifty Copper Operation in the Eastern Pilbara region of Western Australia will be used as a case study. Hydrological and geochemical modelling was used in concert to predict pit lake water quality at 300 years subsequent to mine closure. Final water quality will be controlled by the relative contributions of two diverse water sources; well buffered alkaline water from the Nifty Carbonate Member aquifer and acidic and metalliferous drainage from a pyritic black shale hanging wall exposed in the pit.