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.-ntroduction <br />This postmine storage capacity demonstration amends the As-Built Report <br />prepared under TR-26, dated September 2004. This amendment provides updated <br />SEDCAD4 hydrology and sedimentology demonstrations which incorporate recent <br />(2007) changes to the drainage and sediment control network that drains to <br />Pond 013. In addition, the SEDCAD4 demonstrations evaluate the current <br />watershed condition in support of retaining Pond 013 as a permanent postmine <br />feature. <br />The sediment storage capacity has been recalculated using watershed <br />conditions as of September 2007. This is an appropriate approach because the <br />previous SEDCAD modeling demonstration (TR-26) evaluated sediment delivery to <br />the pond based on worst-case disturbance conditions. The worst-case <br />disturbance approach resulted in a much higher amount of sediment delivery <br />than the amount delivered in the current (reclaimed) condition. <br />Consequently, the amount of storage volume needed to effect compliance with <br />Rule 4.05.2(7) and Rule 4.05.6(3) has greatly decreased. Therefore the top <br />of sediment elevation can be increased and the pond cleaned less frequently <br />than calculated in the original as-built report. <br />The capacity of Pond 013 is attributed partially to the embankment and <br />partially to the pond excavation. The embankment design, construction and <br />resulting stability analyses were previously certified and have not changed. <br />Structure elevations input into the modeling conducted for this evaluation, <br />and shown on Exhibit 13-7, As-Built Pond 013, have been verified by physical <br />surveying. <br />As-Built Analysis <br />SCC constructed a new postmining drainage channel in the Pond 013 watershed <br />during 2007. This channel is incorporated into the SEDCAD4 demonstration <br />attached to this report. The channel network that drains to Pond 013 is <br />shown on Exhibit 13-12.1A, Permanent Channels and Ponds, and Exhibit 20-2, <br />Postmining Topography Map. Channel designs are presented in Attachment 13- <br />12.3. <br />The TR-37 hydrology and sedimentology evaluation demonstrates that Pond 013 <br />meets or exceeds the design and performance requirements of the Regulations <br />of the Colorado Mined Land Reclamation Board for Coal Mining. Specifically, <br />the as-built configuration adheres to the following requirements: <br />• Provide adequate storage and treatment for runoff from the 10-year, 24- <br />hour storm event to assure compliance with receiving water quality <br />standards in accordance with Rule 4.05.6(3)(a); <br />TR-37 13-20.1-1 Revised 02/08 <br />