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structures ponds about 6 acre -feet in capacity. This would be obtained by a combination of below -grade <br />excavation and, if practicable, small above grade embankments. Each structure would capable of <br />completely containing the 10 year, 24 hour storm runoff from a watershed that includes 100 acres at one - <br />year revegetation growth, and 100 acres of recently re- seeded lands, plus a sediment storage volume of at <br />least one year. A spillway system would be included to discharge the 25 year flow. The attached <br />SEDCAD file presents the typical design. Because the location of these small sediment ponds can be <br />optimized based on final post- mining topography and reclamation progression, it is not practical to <br />prepare detailed designs for these at the present time. Rather, the "near source" sediment ponds would be <br />designed and submitted to CDRMS as the mine progresses toward the south. <br />The watershed SEDCAD model is complex and is in some cases difficult to correlate to the attached <br />Exhibit 7 -23 Figure Al. To aid in mapping the model to the watershed hydrologic conditions presented <br />on this figure, a sketch of the various components in the model has been developed and is attached. It <br />includes the assigned SEDCAD structure identification numbers and shows their relationship to one <br />another. <br />• <br />r <br />Exh. 7 -23A -2 Revision Date 3/25/11 <br />Revision No.: PR -03 <br />