Feasibility Study and Technical Report - Pretivm

On low-head applications, a submersible pump will be used. For a decline developmentheading, a submersible pump will be used at the drilling face to pump water to a sump.In sumps that require higher flows and heads, a submersible pump will feed a train ofhorizontal pumps. Each pump station has 100% redundancy such that the loss of anysingle pump will not disable the system.Intermediary levels will drain via borehole to the main pumping levels. Each sump willstage water to the next higher sump in the mine. All of the underground dewateringsumps will report to the VOK Zone 1,330 Level sump through a network of boreholes andpressure piping, before leaving the mine and reporting at the surface 1,400 Level watertreatment plant.Every pump station will be equipped with dirty water and clean water sections, the waterdecanting into the clean water section before pumping. This will allow the majority of theslimes to settle prior to pumping. This is important as high levels of fines in the pumpwater can reduce impellor life on the pumps.Discharge piping and pumps were sized to accommodate the water flows expected fromeach pumping station. Though lower stations will have higher inflows, they will bepumping water from fewer levels and will therefore have lower volumes of water to movethan higher stations. It is assumed that the pumps will not be running full time, but willcycle as required. For this reason, pump capacity was designed to be larger than theinflow, such that the maximum required operation, relative to time, is limited to 80% orless for any pump. The pipe capacity was sized in a similar manner.To minimize upfront capital, the pump procurement will be staged such that pumps onlyarrive as their assigned sumps are excavated. Table 16.16 shows the pump installationschedule. Figure 16.18 is a line diagram of the dewatering system.Pretium Resources Inc. 16-51 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC