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COLORADO LEGACY LAND <br /> TECHNICAL REVISION#28 <br /> The primary goal of this project is to intercept and divert stormwater from the ephemeral drainage above the <br /> North Waste Rock Pile(NWRP) around the waste rock,and into Ralston Creek. The previous site owner,Cotter <br /> Corporation N.S.L.(Cotter)submitted a design in Technical Revision#23 for a diversion ditch. CLL is submitting <br /> Technical Revision#28,to revise this design and provide a schedule for construction. <br /> Drainage Design: <br /> The hydrology used for the design is the same hydrology used for Technical Revision #23,which used the SCS <br /> Runoff Curve Number procedure. The SCS method predicts a 100-year runoff event will have a peak flow of 67.7 <br /> cubic feet per second(cfs)from the unnamed drainage about the NWRP. An additional,11.4 cfs will flow laterally <br /> into the proposed ditch from the 4.1 acres uphill of the NWRP access road. See Attachment 2 for the additional <br /> hydrology calculations. Table 1 summarizes the range of hydraulic conditions in the proposed ditch,details are <br /> provided in the attached design sheets. <br /> HYDRAULI <br /> Flow Rate Slope Flow Depth Velocity <br /> Stations cfs Condition % in f s <br /> 5+00 to 6+88.43 67.7 Minimum Sloe 5.0 25 10.86 <br /> Maximum Slope 40 15.4 23.76 <br /> 1+00 to 5+00 79.1 Minimum Sloe 7.5 24.4 13.15 <br /> Maximum Sloe 30 17.8 22.17 <br /> Notes: <br /> %=percent <br /> cfs=cubic feet per second <br /> in=inch(s) <br /> fps=feet per second <br /> Drainage Construction: <br /> The NWRP diversion ditch will intercept all runoff originating from the ephemeral drainage above the NWRP up <br /> to the 100-year return interval runoff event. Additionally,two test pits were dug in the drainage above the NWRP <br /> to determine the depth to bedrock. One test pit identified a location was where the bedrock is approximately 4 <br /> feet below grade. At this location a concrete seal (wall) will be poured against the bedrock; forcing all runoff <br /> water into the drainage ditch. The ditch follows the alignment of the existing access road as it descends toward <br /> Ralston Creek. The ditch terminates just before crossing the Lower Road, which parallels Ralston Creek. The <br /> flow will discharge onto a concrete-lined, low-flow crossing of the Lower Road and then into a riprap apron <br /> before discharging into Ralston Creek. <br /> Schedule for Implementation: <br /> The NWRP diversion pipeline project is expected to be completed in 2019. The attached Gantt chart presents <br /> the construction schedule and milestones for the project. This project includes four phases: <br /> 1. January to May 2019—Engineering Design and Preparation <br /> 2. May to August 2019—Regulatory Review,Response and Approval <br /> 3. August to September 2019—Mobilization and Procurement <br /> 4. September to October 2019—Construction <br /> PAGE 9 OF 10 <br />