Laserfiche WebLink
1986 Design Analysis <br />• Pond 004 was originally designed to meet or exceed the design and <br />performance requirements of the Regulations of the Colorado Mined Land <br />Reclamation Board for Coal Mining and adhere to the following <br />specifications: <br />1) Provide storage and treatment for the 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 />2) Provide storage for the 10-year, 24-hour storm event without <br />discharging through the emergency spillway in accordance with Rule <br />4.05.9(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 />SCC evaluated the pond design in 1986 as part of RN-01; the design <br />evaluation is presented in Appendix 7-6c. The SEDIMOT II hydrology and <br />sedimentology computer model was used to calculate the 10-year, 24-hour and <br />25-year, 24-hour storm event runoff for sizing the 1986 pond configuration. <br />The evaluation indicated that the principal spillway needed a modification <br />to satisfy the performance requirements. At that time, it was determined <br />is that a 6-inch diameter pipe was the best practical size in order to ' <br />increase detention time and maintain an adequate storage volume above the <br />peak stage for pit pumpage. <br />The certified as-built drawing for the 1986 pond configuration is presented <br />as Exhibit 7-12, Pond #004. <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 design elevation for <br />the new principal spillway is in Appendix 7-6c, while the design drawing <br />for the new principal spillway is presented as Exhibit 7-21, Pond 004 <br />Principal Spillway Redesign. <br />The SEDCAD4 hydrologic computer model was used for the redesign of the <br />principal spillway. Model inputs were based on reclaimed and revegetated <br />conditions; the design pond configuration was based on a survey conducted <br />during June 2005. The 2005 pond design was approved by the Colorado <br />Division of Reclamation, Mining and Safety (CDRMS) as part of TR-39 in July <br />2005; the design was revised as part of TR-42 and approved by CDRMS <br />TR-51 2 Revised 09/09