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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 Land Conditions Curve Number <br />Permanent Diversion No. 1 Undisturbed 69 <br />West Refuse Collection Ditch Disturbed 80 <br />North Refuse Collection Ditch Disturbed 80 <br />*South Refuse Collection Ditch Disturbed 80 <br />Undisturbed 69 <br />Sedimentation Pond No. 1 Disturbed 82 <br />Undisturbed 75 <br />**Sedimentation Pond No. 4 Undisturbed 69 <br />. Water Surface 100 <br />Sedimentation Pond No. 5 Disturbed 82 <br />Undisturbed 75 ~~~_ ~~ <br />8 R Revised - January, ]992 <br />