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Cross Mine(M1977-410) Technical Revision No.5 <br /> Mix Design Information(per cubic yard): <br /> Cement: 622 lbs <br /> Water 323 lbs <br /> Cellular Foam: 18.7 cf <br /> Air Content: 69% <br /> Unit Weight: 35.0 pcf <br /> w/cm ratio: 0.52 <br /> Permeability(ASTM D2434): 8.7 x 10-2 cm/sec <br /> Compressive Strength <br /> 7-Day: 100 psi <br /> 28-day: 214 psi <br /> The completed cellular concrete backfill will be significantly stronger than the soil which originally <br /> comprised the slope while imposing only a fraction of the weight. This will serve to increase stability of <br /> the slope below the county road. The flowable nature of the backfill will allow it to completely <br /> encapsulate the tunnel lining system in a solid mass to create robust permanent support for the mine <br /> entrance. The previous nature of the backfill will allow groundwater to freely drain from the slope in <br /> order to ensure long-term stability. <br /> Placing the cellular concrete backfill was originally scheduled for April 1, 2020 but was postponed due to <br /> the Corona virus and social distancing concerns. At this time,it is not known when the work will resume. <br /> Following placement, the cellular concrete backfill will harden rapidly and allow rehabilitation of the <br /> tunnel to resume within several days. <br /> The slopes immediately above and adjacent to the portal will require additional work to provide long- <br /> term stability. Once repair of the collapse void feature has been approved,GIR's engineer will verify the <br /> geotechnical stability of the overall slopes above and adjacent to the portal, or develop appropriate <br /> measures to enhance stability of the slope,and provide this information to DRMS. <br /> 6.3. Mine Water <br /> Water is discharged from the Idaho Tunnel by means of an 8-in diameter Schedule 40 PVC routed to a <br /> series of three settling ponds (Ponds 3a, b and c). Figure 1 depicts the proposed Cross-Caribou water <br /> system after completion of the proposed action. Included on this figure is the maximum gravity-flow <br /> capacity for each of the pipeline segments in the system. These data are summarized in Table 1 along <br /> with other pertinent information on each pipeline segment. As indicated on Figure 1 and Table 1, the <br /> system has far more capacity than required to accommodate the amount of mine water that can be <br /> anticipated based on historic flow rates, more than 20x in the case of the flow from the Idaho Tunnel. <br /> The mine currently manages discharges directly into Coon Track Creek below Pond 2 under Colorado <br /> Department of Public Health and Environment(CDPHE)Water Quality Control Division (WQCD) National <br /> Pollutant Discharge Elimination System NPDES)Permit CO-0032751,as shown on Figure 1 and Map 2. <br /> 16 <br />