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• 1) Soil Description -Proposed pond liner <br />The proposed liner will be constructed using similar soil to that is shown <br />on Fig. 1. The liner will be placed with scrapers and compacted to 90$ <br />procter. <br />Ref: Soil and Foundation Investigation <br />For the Proposed Five Earthfilled Embankment <br />Hayden Gulch Coal Mine <br />Routt County, Colorado <br />July 1978 <br />By Chen & Associates <br />Denver, Colorado <br />2) Calculation Details <br />a) Runoff into the active pit <br />Fig. 2 is a typical pit cross-section. For design purposes the <br />pit is assumed to be 2,000 feet long. Using a bench width of <br />200 feet, the pit is: 200 x 5 = 1,000 feet wide (Excluding <br />slopes ) <br />Total Pit Area <br />1,000 x 2,000 = 46 Acres <br />43,560 <br />Total drainage area = 313 acres <br />313 - 46 = 267 acres drain directly to HG-8 <br />• Runoff into the pit area: <br />Assume CN = 89 <br />Then for rainfall = 1.8", .runoff = 0.86" <br />46 x 0.86 = 3.30 Acre - ft of runoff <br />12 <br />Pit Capacity: <br />Can store up to toe of coal without stopping work. <br />Use 10$ slope <br />200 x 0.10 = 20 ft Deep max at toe of backfill <br />20 x 200 - 2,000 sq. ft./lin ft of pit <br />2 <br />2,000 x 2,000 - 92 acre-ft of storage in pit <br />43,560 <br />Runoff will be held in pit until storage is available in HG-8. <br />b) Pond Detention Time <br />An error has been found on DWG. # 0405-06-07 submitted as <br />part of this revision. On that part of the drawing showing <br />details of the primary spillway, the four - 4" diam holes should <br />be 6" in diazneter. All other details remain as shown. <br />Inflow and outflow hydrographs were developed using the TR 20 hydrology <br />program developed by the SCS. These hydrographs are shown as Fig. 3. <br />