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Certification of Sediment Pond 015 <br />Introduction <br />In accordance with Rule 4.05.9(14), impoundments shall be inspected by a qualified registered <br />professional engineer or other qualified professional specialist under the direction of a professional <br />engineer. This certification is for the construction of the new sediment Pond 015 within the New <br />Horizon Mine permit boundary. <br />Design <br />Sediment Pond 015 was designed to contain the 100Yr -24Hr event. The captured runoff water <br />will be retained for a few days so the NPDES water quality parameters can be met. Once <br />acceptable water quality is met then a portable pump will be used to pump off excess water to <br />regain pond capacity. For smaller rainfall events, any inflow water will be allowed to evaporate off <br />or infiltrate. <br />Sediment deposits within the pond will be allowed to accumulate until it reaches the Clean Out <br />stage. Clean out of sediment will occur when sediment reaches elevation of 5561.5. Pond 015 can <br />safely contain three years worth of sediment (0.002 ac -ft) and the water volume of a 100 -yr event <br />(0.508 ac -ft; total = 0.510 ac -ft) within it's capacity (0.935 ac -ft). <br />Excavation <br />Sediment Pond 015 was constructed as a totally incised pond that would safely contain the full <br />runoff from a 100Yr -24Hr precipitation event. The excavation of Pond 015 is native bedrock <br />material and without any fill sections. The natural barrier between Pond 015 and the slope to the <br />south is a minimum of six feet wide. The pond was dug almost entirely out of solid sandstone rock, <br />requiring a Caterpiller D -11 size bulldozer with a ripper attachment to break the rock into large <br />boulders. The boulders where then removed by an excavator and articulating truck, and hauled <br />away from the pond. A small amount of topsoil (1.5' thick and less) existed in some areas on top <br />of the sandstone. The top of the bedrock is at 5570.5' in elevation. <br />There was no fill out slopes since the pond was totally incised. The interior pond slopes ranged <br />from 1 H:1 V in the solid rock portions to a nominal 3H:1 V. There was no Primary or Emergency <br />(June 2011 TR -60) Attachment 2.05.3(3) -24 -1 <br />