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8120 Gage Street • Frederick, CO 80516 <br />Bus.: (303) 666-6657 • Fax: (303) 666-6743 <br />Memo <br />To: Brad Janes <br />CC: Garrett Varra <br />From: Brad Jones, P.E. <br />Date: August 12, 2009 <br />RE: Heintzelman Seep Ditch <br />In response to comments received from the Division of Reclamation, Mining and Safety, <br />and per my phone conversation with Allen Sorenson on August 11, 2009, I am further <br />clarifying/expanding upon my original memo from June 18, 2009. As previously listed <br />in the June memo, the measurements and observations made to the ditch are the <br />following: <br />• Approximate bottom width of five feet <br />• Greatest approximate depth of four feet <br />• Varying side slopes with a mean of 1.5: <br />• Heavily grassed/vegetated side slopes <br />Using these measurements, I performed some basic calculations using the Hydraflow <br />Express Extension for AutoCAD Civil 3D and determined that the maximum carrying <br />capacity of the ditch is approximately 87 cfs at four feet of depth. The best estimated <br />mean slope of the ditch used in these calculations was 0.15%. Also, an N-Value of 0.050 <br />(taken from the Urban Drainage and Flood Control District Drainage Criteria Manual) <br />was also used in these calculations. <br />The dewatering rate for the mining pit is expected to be approximately 0.72 million <br />gallons per day, which works out to be about 1.11 cfs. This flowrate would represent <br />about 1.28% of the total capacity of the ditch flowing at four feet of depth. <br />The ditch is typically observed to be flowing at less than a foot deep, and rarely deeper <br />than two feet. These depths would represent the ditch flowing at under 7% and about <br />25% of capacity respectively. From this analysis, it is clear that there should be more