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Section 4 <br />St. Jude Mine <br />4.1 Existing Drainage Conditions <br />St. Jude Mine has a drainage area of approximately 12.7 acres. Surface drainage flows <br />northeast to an earthen berm, which directs the flow to the northwest into a <br />temporary sediment basin on the northwest side of the site. The basin discharges to <br />the north into an unnamed tributary of Big Gypsum Creek, located approximately 3/4 <br />mile north of the mine workings area. <br />4.2 Drainage Plan <br />CDM delineated five basins based on the existing mine surface as illustrated in <br />Exhibit C-1: <br />1. Basin 1- Surface water run-on from offsite southwest of the surface mine <br />facilities. <br />2. Basin 2 - Surface water run-on from offsite southeast of the surface mine facilities. <br />3. Basin 3 - Surface facilities area. <br />4. Basin 4 - North WRA-slope. <br />5. Basin 5 - East WRA slope. <br />4.3 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 />Q100 =I 18.4(Ay' 715 <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 4-1 presents CDM's <br />estimated 100-year peak discharges for each basin of the St. Jude Mine. CDM used the <br />100-year peak discharges to design the surface water drainage structures. <br />4-1 <br />0184906 - Denison\Task Order 1 - Surday Mime Drehrge Study,R.portfiml ReporfiFinal Sunday Mies Dreinege Report-052208.d=