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The SEDCAD modeling shows the runoff volume from the 10 year, 24 hour storm to be <br />5.21 acre feet, and the modeled outflow from Prospect Pond meets the settleable solids <br />requirement. The pool in Prospect Pond does not reach the emergency spillway, and <br />peaks about 1.32 feet below it. <br />An additional SEDCAD model has been run on this watershed to evaluate the runoff <br />from the 25 year, 24 hour storm through Prospect Pond. This storm results in the <br />maximum water level with Prospect Pond of 6752.75 feet, or 0.75 feet through the <br />emergency spillway, leaving 2.25 feet of freeboard. Peak outflow through the spillway is <br />22.0 cfs. <br />Temporary Ditches <br />Several diversion ditches will be used to intercept runoff that would otherwise be <br />tributary to the pond and route it back to the pit. Figure Exh. 7 -14R -7 presents the <br />current locations of the ditches that will be used to divert disturbed area runoff back to <br />the East Pit. These are short term in nature and will be removed as backfill and grading <br />progresses. The ditches will be triangular, at least 3 feet in depth with 2H:1 V or flatter <br />side slopes, and with bottom slope of 1% to 2 %. <br />The maximum area to be diverted by any such ditch will be about 30 acres of disturbed <br />land, with CN at 85. Such a watershed will produce runoff flows from a 10 year 24 hour <br />storm (1.8 inches) of 13 to 22 cfs, depending on watershed slope. This flow can be <br />conveyed by the above described triangular v -ditch at depths less than 2 feet. In short <br />sections of less than 100 feet, the ditch can exceed this slope provided that erosion <br />protection measures are utilized where needed. <br />The ditches called out as "Temporary Ditches" on Fig. Exh. 7- 14R -7, were constructed <br />after all 2009 East Pit Reclamation activities were completed. Most of these were <br />removed during initial rough grading of the spoil areas in 2010. To prevent runoff and <br />sheet flow from the haul truck access road being released to recently competed <br />reclamation, these temporary ditches will be re- constructed using a D6 dozer immediately <br />following the 2010 East Pit reclamation, more or less at their previous locations, but in <br />accordance with design parameters as described above. Each will eventually be <br />permanently eliminated as final reclamation activities proceed from east to west. As <br />shown on Fig. Exh. 7- 14R -7, which is based on the reclamation progression as described <br />on Map 29, the two easternmost temporary ditches will be permanently removed in 2010, <br />and the two westernmost ditches will be removed in 2012. The ditch running along the <br />power line corridor will more or less remain in tact and will double as an access road for <br />power line inspections in this particular area. The corresponding gradual increase in <br />watershed tributary to Prospect Pond and its permanent ditch system, as discussed earlier <br />in this section, takes this progression into account. <br />Exh. 7 -14R -4 <br />Revision Date: 11/3/10 <br />Revision No. TR -87 <br />