2011-09-16_REVISION - M1990057 (9)

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CDRMS question 8. The Applicant has stated that following the construction of Phase 1 TSF, the historic tailings will be placed back into the Phase 1 TSF. Please describe how the tailings will be placed back into Phase 1 TSF and describe what measures will be taken to ensure the embankment and liner are not compromised during replacement of the historic tailings. UMC Response UMC is permanently installing a tailings thickener on the southeast corner of the mill building for use in the mill tailings circuit. The historic tailings will be loaded by skid steer, placed in the tailings thickener, water added to approximately a 70% solids slurry and the resulting slurry pumped (using the designed mill tailings disposal system) into the newly constructed TSF. The clay liner pad under the historic tailings will be placed in the TSF in the same manner. CDRMS question 9. The Applicant has stated that the impoundment liner will be held in place with material from the ore stockpiles. What is the source of the ore material? The Division is concerned the 45mi1 liner may be compromised by placing material with sharp edges on top of it. The Division suggests placing a soil or sand cover over the liner before placing material from the ore stockpile. Will the material remain in the TSF once it is place there? Please describe what measures will be taken to protect the liner from damage resulting from placement of ore material. UMC Response UMC has committed to the Division to initiate removal of the existing onsite ore stockpiles within 60days following startup. The overliner material is currently stockpiled on the west side of the mill entrance road, at the "Y" for the lower access (south) road. This material is angular and of varying size, but predominately -lin with a large fine proportion. UMC is placing a 12oz non -woven geotextile liner over the polypropylene liner on the bottom of the impoundment to protect the liner from puncture. The impoundment bottom is approximately 16,000sf. A service ramp (at 2:1 slope) will be built from the top of the embankment to the bottom of the impoundment and the geotextile liner will also be placed under this ramp. The bottom of the impoundment will have a lft deep overliner placed on the geotextile liner. The ramp will have a 1.5ft deep layer of overliner material. Only low ground pressure equipment will be allowed on the access ramp. This material will remain in the pond following startup of the facility. Approximately 875st of material will be used in the overliner. This overliner is to prevent "lift" of the liner material in high winds and provide a service layer to access the pond without puncturing the liner during the start up phase of the mill. The slopes of the impoundment will not receive direct placement of overliner material. Ballast tubes from the top of the embankment to the bottom of the impoundment, typically constructed from 6in PVC tubes or geotextile socks and filled with the same overliner material, will hold the liner down following installation until the tailings cover the exposed liner. These ballast tubes will be held in place from the top by keying into the anchor trench and extend lft onto the overliner on the impoundment bottom. The ballast tubes will not prevent lift, but will minimize lift CDRMS question 10. Please specify what the anticipated maximum hydrostatic head over the geomembrane will be. In addition, specify how the Operator will monitor the hydrostatic head within the TSF. The Division requires that the hydrostatic head not exceed two feet, please commit to maintaining a hydrostatic head of less than two feet. M1990 -057 September 16, 2011