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BbB Excavating, Inc. -Montgomery Gravel Prt Stormwater Management Plan Page 5 The CKP Ditch is an irrigation ditch with a capacity of approximately 12 cfs. Although seepage from the CKP Ditch historically irrigated grassland on the property, B&B ' Excavating recently piped the ditch through the property. The CKP Ditch is not expected to influence site drainage or require special provisions in this SWMP. 1 Starmwater. Runoff As shown on Drawing 1, the site is segmented into two basins via Skillman Gulch. Basin A is comprised of 15.0 acres, including 9.6 acres to be disturbed by excavation or ' operation (CN for hard packed gravel = 85; CN for grass slopes = 72; Composite CN = 80). Basin B has 25.4 acres, including 10.5 acres to be disturbed (Composite CN = 77). According to the Eagle County Soil Surveys, site geomorphology is characterized by "Type B" hydrologic soils with a predominance of Dahlquist-Southace Complex and ' Tridell-Brownsto series. Based on the Soil Conservation Service's rainfall-runoff equations, the 100-year runoff volumes for a 24-hour duration (2.4 inches of precipitation) is 1.05 acre-feet and 1.5 acre-feet for Basins A and B, respectively. As a requirement for the Special Use Permit, a berm 3 feet in height has been constructed at the 6,460-foot contour line. This berm is significant because it hydraulically disconnects the site from the Eagle River and Skillman Gulch. For most yeazs, no stormwater dischazge from the site should be anticipated. 1 Process Water::.. ' Presently, process water is not used on site. However, this will change in the future when at least two operational ponds are constructed. These ponds will be located above ' the bermed area and filled with water from the Fagle River. The water augmentation plan states that the ponds will be no greater than 0.57 acres in surface azea and have a capacity of no more than 5.7 acre-feet. Surface drainage will be diverted azound the ' process water ponds to prevent commingling.