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1) Provide storage and treatment for the runoff from the 10-year, 29- • <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 />9.05.9(2)(b). <br />3) Provide an emergency spillway capable of passing runoff from the 25- <br />year, 29-hour storm event in accordance with Rule 9.05.9(2)(c)(ii). <br />SCC evaluated the pond design in 1986 as part of RN-O1; 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, 29-hour and <br />25-year, 29-hour storm event runoff for sizing the 1986 pond configuration. <br />The evaluation indicated that the principal spillway needed a modification <br />to satisfy CDMG performance requirements. At that time, it was determined <br />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 009 <br />Principal Spillway Redesign. <br />The SEDCAD9 hydrologic computer model was used for the redesign of the <br />principal spillway. Model inputs were based on current (i.e., reclaimed <br />and re vegetated) conditions; the design pond configuration was based on a <br />survey conducted during June 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 7-6c. <br />• <br />TR-37 2 Revised 10/05 <br />