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Introduction <br />This storage capacity demonstration amends the As-Built Report prepared under <br />TR-30 (dated May, 2007); which has been subsequently revised under TR-35 <br />(dated September 2007). This report provides revised SEDCAD demonstrations <br />which incorporate recent (2007) changes to the drainage and sediment control <br />network for the mining area that drains to Pond 010. It is important to note <br />that "the disturbance area has not changed from the approved as-built report. <br />SCC has added a new channel (YPM-22) and slightly changed how runoff is <br />collected and conveyed from the YPM-16 and YPM-20 subwatersheds. In <br />addition, the SEDCAD demonstrations account for the current (postmine) <br />watershed conditions in support of retaining Pond O10 as a permanent, <br />postmine feature. <br />The sediment storage capacity has been recalculated using 'watershed <br />conditions as of September 2007. This is an appropriate approach because it <br />evaluates the most current postmine condition (e.g., mining areas have been <br />backfilled, graded, topsoiled and seeded) to evaluate long-term sediment <br />yield as the mine site transitions into a permanent, postmine landscape. <br />Because the watershed is reclaimed, the amount of storage volume needed to <br />effect compliance with Rule 4.05.2(7) and Rule 4.05.6(3) has greatly <br />decreased. <br />The capacity of Pond 010 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 13-4A, As-Built Pond 010, have been verified by physical <br />surveying. <br />Existing Condition Analysis <br />The TR-37 hydrology and sedimentology evaluation demonstrates that Pond O10 <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 />• Provide storage and treatment for the runoff from the 10-year, 24-hour <br />storm event. without experiencing any discharge through the emergency <br />spillway (Rule 4.05.9(2)(b)); <br />• Provide an emergency spillway capable of passing runoff from the 25- <br />year, 24-hour storm event in accordance with Rule 4.05.9(2)(c)(ii). <br />TR-37 13-3A.1-1 Revised 02/08 <br />