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Section 6 <br />Sunday Mine <br />6.1 Existing Drainage Conditions <br />Sunday Mine has a drainage area of approximately 46.0 acres. Surface drainage flows <br />northwest to a series of temporary sediment basins on the north side of the site, and <br />discharges into an unnamed tributary of Big Gypsum Creek, located approximately <br />1/2 mile north of the mine workings area. <br />6.2 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 - WRA. <br />3. Basin 3 - Surface facilities area. <br />4. Basin 4 - WRA. <br />5. Basin 5 - WRA. <br />6. Basin6 - Surface facilities area and WRA slope. <br />7. Basin 7 - Surface facilities area and WRA slope. <br />6.3 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(Ay"" <br />Q,oo = <br />where: <br />Qioo =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 6-1 presents CDM's <br />estimated 100-year peak discharges for each basin of the Sunday Mine. CDM used the <br />100-year peak discharges to design the surface water drainage structures. <br />COM <br />6-1 <br />OA64986 - DenisonUask Order 1- Sunday Mines Drainage Study%eporfflnel ReporBFlnel Sunday Minas Drainage Ropok O52200.doc