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• <br />EXHIBIT 7, ITEM 20, PART A <br />SECTION 28 SEDIMENTATION POND <br />The location of the Section 28 Sedimentation Pond is presented on Map 41A. The profiles of the <br />associated permanent ditches (Trib A, Trib B, Trib C and Trib D) are presented on Map 3313. <br />Channel designs of these permanent drainage channels are provided in Exhibit 7, Item 20, Part E. <br />Exhibit 7, Item 20, Figure IA-1 shows the breakdown of drainage areas and hydrologic <br />conditions for this sediment pond, and Figure IA-2 provides a diagram of the structures and <br />networking. A design drawing for the impoundment is presented on Figure 1A -3. <br />Section 28 Sedimentation Pond was initially submitted with PR -02 in March 2007. Changes in <br />the limits of mining activity, essentially pulling the southeastern limit of disturbance back to the <br />northwest about one quarter mile, and revisions to the PMT pursuant to TR -81 have resulted in <br />changes to the watershed that warrant a review of the pond hydrology and hydraulics. However, <br />the portion of the tributary watershed to this sedimentation pond that will be disturbed has been <br />reduced pursuant to TR -81. <br />The following pages present the results of two SEDCAD runs for the worst case hydrologic <br />condition, which is taken as the entire tributary watershed reporting but reclamation in various <br />stages of revegetation. The first run provides the results of the 10 year, 24 hour design storm. <br />The 10 year, 24 hour event generates about 47 cfs of peak runoff into the pond and a total runoff <br />volume of about 3.6 acre -feet. Settleable solids discharged from the pond during the 10 year 24 <br />hour storm are well below the allowable standard. The second model run documents the results <br />of the 100 year, 24 hour design event, which has been selected to evaluate the emergency <br />spillway. However, the peak elevation of the pond surface while routing the 100 year, 24 hour <br />storm does not rise high enough to engage the emergency spillway. <br />Table 4 of the introductory text of Exhibit 7, Item 20 provides a summary of the design <br />parameters for this sediment pond. <br />Exh. 7 -20A -1 Revision Date: 12/31/10 <br />Revision No.: TR -81 <br />