Historic mining across the Bendigo goldfield reached an average mining depth of 750 m over an area of about 16 km by 4 km, with two shafts exceeding 1400 m._x000D_
Mining ceased in the mid 1900s due in part to increased dewatering and ventilation demands. Water extraction technology of the day, combined with multiple mine ownership, did not allow uninterrupted and thus economic mining activity to prosper._x000D_
Today Bendigo Mining Limited (BML) is targeting gold-bearing reefs beneath the water-filled historic mine workings. To ensure mining activity can proceed without the risk of water inrush, historic workings are being dewatered by submersible pumps in historic shafts and through a series of underground drain holes intersecting old workings. Due to the high heads involved, individual drain hole development requires rigorous safety control implementation and assessment prior to drilling._x000D_
Water extracted via drain holes is pumped to the surface through a series of pipe lines and rising mains in conjunction with two staged pumping stations._x000D_
Both stations are equipped with high-speed centrifugal pumps, each capable of pumping 40 L/s at a static head of approximately 300 m._x000D_
BML, which operates beneath and within a large city, is confronted with unusual environmental and social challenges compared to many within the mining industry. The raw mine water, which contains elevated salt levels, is piped through residential areas and must comply with strict controls to prevent impacts on the surrounding environment. The final delivery point is BML's water treatment plant at the north end of the city._x000D_
The water treatment plant utilises chemical pretreatment and reverse osmosis._x000D_
It is able to process 7 ML of mine water per day at full production. The product is approximately 5 ML of reusable irrigation quality water, which is made available to the Bendigo community for public gardens, sporting facilities and rural irrigation. The 2 ML of brine is directed to a purpose-built evaporation pond facility located 7 km north of the water treatment facility._x000D_
FORMAL CITATION:Morrison, W, 2008. Mine dewatering - Bendigo Goldfield, in Proceedings Tenth Underground Operators' Conference 2008, pp 63-70 (The Australasian Institute of Mining and Metallurgy: Melbourne).