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• <br />assumed impervious area was 100% and the area with no depressions was 100 %. NOAA <br />Atlas 2 Volume III - Colorado was used to determine the 10 year 24 hour total precipitation <br />(3 inches). A SCS Type II storm was used to model the 10 year 24 hour storm. <br />The model predicts the peak runoff to be 5.73 inches with 3 inches of runoff (zero <br />infiltration). The required ditch size to convey that flow is a trapezoidal channel with a <br />bottom width of 0.5 ft, a height of 1 ft, side slopes of 1:1, and a minimum slope of 3.25 %. If a <br />slope drain is used a minimum pipe diameter of 18 inches is recommended. It is likely the <br />exposed slope will be bedrock, in which case a slope drain would not be necessary. It is also <br />recommended that at the bottom of the slope where water is discharged be protected from <br />erosion using D50 =12 inch rip -rap over filter fabric. <br />Attached please find the output from the model. Please note the catchment in question is <br />Sub -b1, the trapezoid channel is Link -05, and the pipe is Link -04. <br />If you have questions, concerns, or would like to discuss this further please dori t hesitate to <br />call. n . <br />Thanks, <br />Marc Kenney <br />CO PE #41215 <br />CPSWQ #0623 <br />CPESC #5695 <br />mjk/ <br />attachments <br />a_ <br />SAPROJECTS11134 Agapito - New Elk Mine\DesignlSto mNET\Substation re -grade Calc Summary.doc <br />TR 54 Page E 19(15) -438 <br />Page 2 <br />Revised 11/2/10 <br />