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<br />The pond embankment has a top width of approximately 15 feet, with upstream <br />and downstream slopes of approximately 3H:1V, respectively. The existing <br />emergency spillway is a Crapezoidal open channel with a bottom width of 20 <br />feet and 3H:1V side slopes. The crest is vegetated, while the outslope <br />channel has a riprap lining with a Dso of 6-inches. <br />New Principal Spillway Design Analysis <br />In response to the deteriorated condition of the principal spillway noted <br />in April 2005, SCC prepared a redesign and replacement plan for a new <br />principal spillway in June 2005 as part of TR-39. The pond was designed to <br />meet or exceed the design and performance requirements of the Regulations <br />of the Colorado Mined Land Reclamation Board for Coal Mining and adhere to <br />the following specifications: <br />1) Provide storage and treatment £or the runoff to the pond from a 10- <br />year, 29-hour storm event to assure compliance with receiving water <br />quality standards in accordance with Rule 9.05.6(3)(a). <br />2) Provide storage fox the 10-year, 24-hour storm event without <br />discharging through the emergency spillway in accordance with Rule <br />9.05.9(2)(b). <br />3) 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 />The design elevation for the new principal spillway is found at the front <br />of Appendix 7-6e, while the design drawing fox the replacement principal <br />spillway is presented as Exhibit 7-17D, Pond 008 Principal Spillway <br />Redesign. <br />The SEDCAD4 hydrologic computer model was used for the redesign of the <br />principal spillway. Model inputs were based on current (i .e., reclaimed <br />and revegetate d) conditions; the design pond configuration was based on a <br />survey conducted during Sune 2005. Results of the SEDCAD4 modeling for the <br />2005 pond design are included in the replacement plan found at the front of <br />Appendix 7-6e. <br />Principal Spillway Replacement <br />The new 8-inch plastic corrugated pipe was installed in a trench excavated <br />across the width of the embankment. The invert was set at 7, 015.3 feet, <br />with a barrel slope of one percent. Because of the embankment height (toe <br />TR-92 2 Revised 12/06 <br />