Feasibility Study and Technical Report - Pretivm

Contact WaterThere are three expected sources of contact water during construction and operations:• the upper laydown area where the waste rock transfer and pre-production orewill be stored• the mill building and portal site, which require an extensive cut into bedrock(some of which is currently assumed to be PAG)• groundwater seepage to the underground mine tunnels.Runoff from the former two sources will be managed by storage and treatment. Contactwater ponds will be sized to contain runoff from the 24-hour, 10-year return periodrainfall event (102 mm). The contained runoff will be pumped to the water treatmentplant for treatment prior to release into Brucejack Lake. The water treatment plant hasbeen designed with a maximum capacity of 7,440 m 3 /d.Groundwater seepage into the underground workings is expected to vary fromapproximately 2,140 to 4,080 m 3 /d throughout the LOM. This water will initially be sentto the water treatment plant for treatment before being sent to the process plant, whereits use will be maximized in process. Excess treated groundwater will be used asfluidizing water and discharged to Brucejack Lake at depth. As noted in Section 18.12.,there will be a constant flow through the pipeline at all times to keep the subaqueoustailings deposit at the end of the outfall fluidized. When the thickened tailings are usedin the backfill plant, flow will be maintained with water.It is assumed that outflows from Brucejack Lake will be of suitable water quality fordischarge to Brucejack Creek following water treatment.Diversion ChannelsFresh water diversion channels will be constructed around the plant site. The channelswill discharge directly to Brucejack Lake.Process Water RequirementsThe average water requirement for the Brucejack process plant is 3,134 m 3 /d, based ona mill throughput of 2,700 t/d. This water is required for the tailings slurry to the lake,the underground paste backfill, the concentrate slurry, and minor evaporative losseswithin the plant (approximately 7 m 3 /d). The process water will be sourced from:• treated underground seepage water• ore moisture (approximately 3% by weight)• reclaim from the lake.Reclaim from the lake is required because there are periods when the groundwaterinflows are predicted to be less than the process requirement.Pretium Resources Inc. 20-17 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC