2021-09-27_REVISION - M1990057 - Laserfiche WebLink

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Mr. Dustin Czapla 3 CDRMS September 24,2021 7. Rule 6.4.5 Exhibit E — Reclamation Plan On page 5-5 of Exhibit E the application states that the TSF will be capped with 18" of suitable material. The paragraph preceding this statement describes 16" of cover material. Please clarify this discrepancy. Response This statement will be corrected to read "The TSF will be capped with 8 inches of till and 4 inches of topsoil/SPGM prior to initiating revegetation activities." The cover system has been designed based on guidance from the Mine Environment Neutral Drainage (MEND) program and will use construction materials. Emphasis has been placed on optimizing the number of capping materials necessary to complete the closure objectives of the TSF. Figure 6-1 shows a conceptual plan view of the TSF, and Figure 6-2 is a simplified cross section of the proposed cover system. (See permit for references) TSF Closure -Cover Reclamation: A dry cover over the TSF tailings surface will be created by recontouring the earth fill cover to minimize ingress of surface water and to pass runoff into an engineered channel towards the South of the TSF to an ephemeral tributary to California Gulch. This dry closure option will prevent water ponding on the reclaimed TSF surface to promote a dry cover in perpetuity. (See Rule 6.4.5 Exhibit E - Reclamation Plan and Rule 6.4.6 Exhibit F - Reclamation Plan Map Figure 6-1 and Figure 6-2 in permit). Closure Cover Development: General aspects of the TSF closure design include: • The tailings management plan will be designed and operated to keep the supernatant pond away from the embankments and towards the northwest corner of the facility. • At the end of production, the supernatant pond will be pumped or evaporated prior to TSF reclamation and closure activities. The tailings will be allowed to desiccate to increase their density and bearing capacity prior to placement of capping materials. • Stockpiled till and topsoil/SPGM will be spread over the tailings surface using a LGP dozer, excavator or other suitable equipment to establish a trafficable surface. Preliminary review shows the results confirm the current estimate for the range of subsidence expected to form at the base of the till material. • A low permeability glacial till will be placed above the tailings to minimize water infiltration into the tailings deposit. • A growth medium of topsoil or SPGM will be placed above the till to promote vegetation growth to return the area to the natural pre-mining conditions of the surrounding ecosystem. • An engineered channel will drain surface water flows (upon meeting the water quality requirements) at the South end of the TSF into the unnamed drainage. Advantages of TSF closure include: • Confidence (based on experience) in achieving the required tailings deposition. • Hazards associated with a pond of standing water or uncapped tailings area are mitigated.