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** Area includes the 20.32 acres contributed by the North Refuse <br />• Collection ditch, the 19.81 acres contributed by the South Refuse <br />Collection Ditch, and 2.72 acres from a small area surrounding and <br />including the pond. <br />Time of Concentration, Tc <br />Time of concentration is calculated by using the SCS upland method. all <br />hydraulic lengths, drainage heights and slopes are measured directly from <br />a 1"=200' scale map. The values calculated for each structure are shown <br />on a subwatershed basis in the SEDCAD+ printouts contained in their <br />respective design calculations section in the following text of this <br />exhibit. <br />Curve Number, CN <br />Curve numbers were obtained from the surface water control system plan <br />submitted by Rocky Mountain Geotechnical (RMG) and contained in the <br />• original Southfield Permit. RMG utilized procedures set forth in <br />Procedures for Determining Peak Flows in Colorado, Technical Release No. <br />55, USDA-Soil Conservation Service, 1980. Curve numbers for the Magpie <br />Creek Diversion were determined using the SCS method also. Based on soil <br />type and vegetation cover, curve numbers were determined for disturbed and <br />undisturbed conditions as follows: <br />Drainage Structure <br />Permanent Diversion No. 1 <br />West Refuse Collection Ditch <br />North Refuse Collection Ditch <br />*South Refuse Collection Ditch <br />Sedimentation Pond No. 1 <br />**Sedimentation Pond No. 4 <br />• Sedimentation Pond No. 5 <br />Land Conditions <br />Undisturbed <br />Disturbed <br />Disturbed <br />Disturbed <br />Undisturbed <br />Disturbed <br />Undisturbed <br />Undisturbed <br />Water Surface <br />Disturbed <br />Undisturbed <br />Curve Number <br />69 <br />80 <br />80 <br />80 <br />69 <br />82 <br />75 <br />69 <br />100 <br />82 <br />75 <br />8 R Revised - December, 1991 <br />