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<br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br />1 <br /> <br /> <br />II <br /> <br />1 <br /> <br /> <br />1 <br />GENERAL LOCATION AND DESCRIPTION <br />Mule Creek Gravel Pit is located about 4 miles south of Divide, Colorado and about 12 miles <br />north of Cripple Creek along the east side of Colorado State Highway No. 67. There currently is <br />a disturbed area from an earlier gravel pit located on the west side. The eastern portion of the site <br />is in the Pike National Forest. The proposed mine boundary is estimated at 21 acres. <br />The terrain of the site is a steep hillside with a poor distribution of pine and aspen trees. The <br />slope is estimated at 3:1. The western portion of the site is currently disturbed from a prior gravel <br />pit and has exposed rock features prevalent. <br />DRAINAGE BASINS AND SUB-BASINS <br />The site is on the western side of an existing hill with no offsite flows influencing the site. The <br />entire site flows to an existing ditch along the eastern side of Colorado State Highway No. 67 <br />flowing south. Due to no offsite flows and one point of discharge, the site was treated as one <br />basin. <br />DRAINAGE DESIGN CRITERIA <br />Rations/ Method Hydrologic Criteria <br />The Rational Method was used to estimate stormwater runoff for the 5-year and 100-year design <br />storm. The Pikes Peak Area Council of Governments' Areawide Urban Runoff Control Manual <br />(PPACG) was used for calculation the 1 hour - 100 year storm and the 1 hour - 5 year storm. <br />Precipitation numbers of Cripple Creek were used, as the site was close in nature to this existing <br />graph. The Rational Method coefficients "C" were selected from the Colorado Springs Drainage <br />Criteria Manual for poor forest and for exposed rock. Please see Appendix 1 : Rational <br />Calculations for runoff calculations. <br />Detention Storage Criteria <br />The Detention Pond was calculated using the Rational Stored Rate Method. Both the 5-year and <br />the 100-year storm will be released at or below historical rates. In addition to this, a Water <br />Quality Capture Volume (WQCV) will be used to release the 2-year storm at a 40-hour time <br />frame. This WQCV will allow small storms to be collected and particles to settle out before being <br />released. This WQCV will be an additional storage to the 5-year/ 100-year storage requirements. <br />The WQCV will be assumed to be full when calculating these 5-year/ 100-year design storms. <br />Please see Appendix 1 : Rational Calculations for the Detention Pond calculations. <br />\\UnvaI6Tb74]3]11Mule Crxk Gavel PitUteports\Dn'vuge Report 037100.doc <br />