2012-08-13_REVISION - M1982090 (2)

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CBCI intends to maintain the sedimentation pond as a permanent feature on its private property. However, certain slopes at certain depths are required to meet DRMS reclamation standards. A description of those reclamation standards and estimated costs to ensure that they are met are included in Section 6.0 of this submittal. Section 3.0 Discharge Conveyance The water discharging from the 14L portal is currently channelized to flow through a partial flume, surrounded by a concrete dam, and equipped with 24 inch and 12 inch corrugated metal pipe (CMP) intakes (Photos 3 and 4). Historically the 24 inch pipe conveyed flows to the mill, and the 12 inch pipe conveyed flows directly to the sedimentation pond. Currently both pipes terminate approximately 95 feet from the partial flume and are suspended approximately 10 feet above the right bank of Imogene Creek (Photo 5). All of the discharge from the 14L portal is conveyed through these pipes directly into Imogene Creek. In order to convey the discharge from the 14L portal to the re- constructed sedimentation pond, a new piping system will have to be installed from the point of intake near the portal to approximately 775 feet northwest to the pond (Figure 2). Since the existing partial flume is rusted out and two separate CMPs is no longer necessary, a new flume, concrete dam, and single point of intake will be installed within the footprint of the existing structure (Photos 3 and 4). There is no evidence that the discharge flows have ever exceeded the capacity of the existing pipes, therefore a single 27 inch CMP could provide the equivalent volume capacity of the existing 24 inch and 12 inch CMPs combined. However, to accommodate for partial plugging or blockage, a 30 inch CMP will be installed and equipped with a hinged steel grate at the intake to prevent large debris from entering the pipe. The planned course of the 30 inch CMP will be similar to the historic pipes; from the flume the pipe will be oriented westerly for approximately 315 feet, then northerly 460 feet to the pond (Figure 2). The only structural challenge anticipated is at the Imogene Creek crossing, which occurs approximately 75 feet west from the point of intake (Photo 5). A manual valve and "T" will be installed at the edge of the Imogene Creek crossing in the event that the pond or down - gradient discharge pipe requires maintenance. The span of Imogene Creek where the 30 inch CMP will be placed was measured in the field to be 52 feet across. Suspending the 30 inch CMP over the 52 foot creek crossing will require pouring concrete footers at the top of the slopes on both sides of the creek. The pipe will be fastened parallel over a steel beam (or beams) that is fastened to the concrete footers. The appropriate beam(s) will be selected to safely and structurally accommodate the maximum load that could be carried in the pipe at any one time (see Attachment D for an example). The maximum load is based on 52 feet of 30 inch wide, 0.079 inch gauge CMP weighing 36 pounds per foot (0.9 tons) that is 100% filled with water (maximum volume of 255 cubic feet; 7.48 gallons per cubic foot; 8.34 pounds per gallon; 8.0 tons). The total maximum load that could be suspended is approximately 8.9 tons (excluding the load of the steel support) distributed over 52 feet. During and after construction of the crossing, no fill materials will be placed in Imogene Creek or along the banks of the creek. All of the construction materials that span the crossing can be placed and secured using hand tools and a trackhoe. Equipment and supplies to be relied upon for the construction of the discharge conveyance is included in Attachment F. Technical Revision, Camp Bird Mine 112 Permit (Permit No. M -1982 -090) Page 6