|
Case histories |
Water Management Consultants Ltd, 2/3 Wyle Cop, Shrewsbury SY1 1UT, UK
Operations began in 1985 at Amax Gold Inc.’s Sleeper Mine in Nevada, and the major open pit has been one of the largest North American gold producers. The orebody in Tertiary volcanic rocks is overlain mainly by the Desert Valley basin fill gravels. Natural groundwater levels at the mine are around 10–15 m below surface, and dewatering has been a major activity since initial overburden stripping. With a final projected mine depth of 215 m, a properly designed and cost-effective dewatering scheme, fully integrated with the mine plan, was required. Field investigation and numerical computer modelling proceeded in parallel, the feedback between the two activities being essential to the optimization of the dewatering scheme.
The basis of effective dewatering has been the interception of groundwater in the overburden before it can reach the pit. This paper describes the groundwater model, based on the USGS MODFLOW code, which was specifically designed to develop a wellfield design for optimum dewatering. The model enabled the determination of the most cost-effective wellfield configuration, pumping rate and distance from the pit. Subsequent field observations showed that real drawdowns were within 50f those predicted.
The interceptor model has also been used to investigate the dewatering rate and cost implications of expanding the pit in the direction of the wellfield; and the implications of power failure at the wellfield for determination of standby generating capacity.
