2011-09-16_REVISION - M1990057 (9)

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• Layout 25ft wide geotextile liner down impoundment slope, for access ramp. • Liner sandbagged as appropriate. Overliner Material Placement, Slope Ballast Installation • Performed by Owner, monitored by Mill Superintendent and/or Owner's Engineer. • Grade top of overliner layer on ramp and bottom of impoundment ( +/- 1 ") on 50' grid. • Low ground pressure, smaller equipment will operate on minimum lft depth overliner material. Ramp will have minimum 1.5ft of material. Tailings Slurry Piping, Decant Water Pumps • Performed by Owner, monitored by Mill Superintendent and/or Owner's Engineer. CDRMS question 6. Please provide the Division with the anticipated total maximum load on the TSF. UMC Response The Phase 1 facility at capacity, prior to Phase 2, will have a load on the polypropylene liner and clay liner of 28 feet of tailings. The density of the tailings material is approximately 21cf /st wet. The maximum Phase 1 load is 5881bs /sf on the polypropylene liner and clay liner. As designed, the polypropylene liner is in direct contact with the clay liner. CDRMS question 7. The TSF design # lan calls or installin_ a leak detection s stem. The Division re uires additional design details in order to evaluate the effectiveness of the proposed leak detection system. Will the leak detection system utilize a mat or trenches to collect leachate? What is the volume of the collection system? Will the collected leachate be returned to the mill? Please specify how the Operator will determine if there is a leak in the Polypropylene Geomembrane. In addition, locate the collection system on Exhibit TSF -02. UMC Response Exhibit TSF -05 shows additional details on the leak collection system and sump. The leak detection system is installed level with the top lift of the 2 -6in lifts of 1 x 10 -6 cm/s clay, prior to the installation of the 45mi1 polypropylene geomembrane liner. The leak detection system is a wick drain system capable of intercepting liquid within the leak detection zone and conveying the liquid to a collection sump for storage. The wick drain is 12 "wide, 1 inch thick, trenched in the 12in clay liner on approximate 50ft centers and is laid out as shown on Exhibit TSF -05. The volume of the collection system is limited to the sump and is approximately 90 gallons. The sump is accessed through a 4in PVC pipe to the top of the impoundment. Collected leachate will be returned to the TSF and then recycled to the mill through the impoundment decant pump(s). The leak detection system requires a manual inspection of the sump through the 4in PVC pipe. If leachate is detected (indicating a leak in the 45mi1 polypropylene), the level will be monitored, a small pump will be installed in the PVC pipe and the Division notified of fluids from the leak detection system. If groundwater is detected (indicating a leak in the 12in clay liner), the level will be monitored, a small pump will be installed in the PVC pipe, the groundwater pumped to the impoundment and the Division notified of fluids from the leak detection system. M1990 -057 September 16, 2011