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July 13, 2011 <br />MENU) <br />NU) <br />JUL 2 2 ZOi <br />X DMs;on of R ec,lamation, <br />Miring and Safety <br />G reg Lewicki And Associates/' <br />Travis Marshal <br />Division of Reclamation Mining and Safety I/ <br />101 South 3rd Suite 301 <br />Grand Junction, CO 81501 <br />(970)- 241 -2042 <br />eN141/4 ( SS S <br />11541 Warrington Court Phone (303) 346 -5196 Fax: (303) - 346 -6934 <br />Parker, CO USA 80138 E-Mail:info@lewicki.biz <br />RECEIVED <br />JUL 2 0 2011 I/ <br />GRAND JUNCTION HELD OFFICE <br />DIVISION OF <br />RECLAMATION MINING & SAFETY <br />RE: Craig Ranch Pit - Stormwater Response, Permit # M- 1986- 002 /CN -01/ <br />Travis, <br />Included in this letter are edits that have been made to the conversion application with regards to <br />stormwater management questions that were asked by Tim Cazier of DRMS. The edits and <br />answers follow the outline of the questions of Tim's June 23, 2011 memo to Travis Marshall. <br />1. The permanent ditches, channels and sediment ponds are designed for a 100 year 24 <br />hour type II storm which in this area is 2.6 inches. The Curve number for the entire site <br />is estimated at 88 which was used in the TR - 55 method of determining peak flows. <br />2. The Sediment ponds have been designed to capture the 100 year 24 hour event for the <br />disturbed area and the areas that drain into the disturbed area. The eastern sediment <br />pond will be constructed with a 3 foot tall gravel berm along the northern boundary. <br />This berm will tie into the bed rock slope to create the containment. The western <br />sediment pond will have a 6 foot gravel berms along the northern boundary also tying <br />into the slope to the south to create the containment. These berms will have 3H:1 V side <br />slopes. The western sediment pond will hold 20.9 acre -feet which is greater than the <br />14.62 acre -feet that will flow into the pond during a 100 year event. There will also be 1 <br />foot of free board above the 20.9 acre -feet to the crest of the berm. The eastern <br />sediment pond will hold 12.03 acre -feet which is greater than the 4.92 acre -feet that will <br />drain into it during a 100 year event. This excess will account for the product stockpiles <br />that will be located within the eastern sediment pond during mining. Both of these <br />ponds will easily contain a 100 year event and therefore do not need spillways. The <br />ponds will be installed as soon as any area that drains into them is disturbed. <br />3. The conceptual cross sections are shown on the attached Island Cross Section Figure. <br />Since the islands have been moved outside of the south to north drainage features, the <br />only erosion control technique to be implemented is revegetation. Since the islands <br />were removed from the drainages, the peak flow hitting the upstream face is not <br />included since the vast majority of the runoff will not encounter the islands. Each island <br />