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• Runoff Curve numbers assigned to the undisturbed and reclaimed lands in various stages <br />of reclamation have been selected in accordance with Table 1 in "Methodologies and <br />Assumptions for Sedimentation Pond Design Evaluations" in Exhibit 7 of TR -73. It <br />should be noted that for the reclaimed lands, these runoff curve numbers are higher than <br />those previously used on the Colowyo Mine site, generating proportionately greater <br />runoff volumes and flow rates than those used in the original design of East Taylor <br />Sedimentation Pond. Soil erodibility factors and other parameters used in estimating <br />sediment concentration in runoff are also drawn from that exhibit. <br />• <br />r� <br />Results of the SEDCAD modeling are summarized in Exh. 7, Table 6 in Vol. 21), and <br />briefly described here. The 10 year, 24 hour storm generates 5.03 acre feet of runoff at <br />the sediment pond location. The peak pool elevation while routing the 10year /24 hour <br />storm does not engage the emergency spillway, and the settleable solids concentration in <br />the primary spillway effluent is also well below the 0.5 ml /1 standard. The 25 year, 24 <br />hour storm does engage the emergency spillway, and would route through the structure at <br />a depth of 0.27 feet in the emergency spillway, leaving 1.23 feet of freeboard. <br />Exh. 7- Sec16 -3 Revision Date: 12/31/10 <br />Revision No.: TR -81 <br />