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Section 5 <br />Carnation Mine <br />5.1 Existing Drainage Conditions <br />Carnation Mine has a drainage area of approximately 12.0 acres. Surface drainage <br />flows north and northwest over a series of earthen berms. A portion of south half of <br />the site drains into a sediment pond that is located in the middle of the site. The <br />drainage from the berms and the sediment ponds discharges to the north into an <br />unnamed tributary of Big Gypsum Creek, located approximately 1/2 mile north of the <br />mine area. <br />5.2 Drainage Plan <br />CDM delineated five basins based on the existing mine surface as illustrated in <br />Exhibit D-1; <br />1. Basin 1 - Surface water run-on from offsite south of the surface mine facilities. <br />2. Basin 2 - Surface facilities area. <br />3. Basin 3 - WRA and sediment pond. <br />4. Basin 4 - Mild slope area containing water bars and vegetation. <br />5.3 Peak Discharge Estimate <br />CDM estimated the 100-year peak discharge using the following USGS regionalized <br />flood-frequency equations for Colorado (USGS 2000): <br />118.4(A)o.'15 <br />Qioo - - <br />where: <br />Q100 =100-year peak flow in cfs <br />A = drainage area in square miles <br />As discussed previously, CDM increased the calculated discharge from the flood- <br />frequency equation by the standard error or 78 percent. Table 5-1 presents CDM's <br />estimated 100-year peak discharges for each basin of the Carnation Mine. CDM used <br />the 100-year peak discharges to design the surface water drainage structures. <br />Table 5-1 100- ear Peak Discharges for the Carnation Mine Basins <br /> 100-year peak discharge <br /> Area Calculated Increased b SE <br />Basin ac s -mi cfs cfs <br />1 6.02 0.00941 4.21 7.50 <br />2 0.83 0.00130 1.02 1.82 <br />3 1.80 0.00281 1.77 3.16 <br />4 3.34 0.00521 2.76 4.92 <br /> <br />5-1 <br />OAS4986 - Denison\Task Order 1 - Sunday Mines Drainage Studfflepor*inal ReportVinal Sunday Mines Drainage Report_052208.dw