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<br />Principal Spillway Replacement <br />The 36-inch CMP pipe was removed and replaced with an 8-inch plastic <br />corrugated pipe set at an invert elevation o£ 6,998.2 feet. Bedding <br />material was backfilled in the trench to the appropriate elevation, and <br />after the pipe was installed, the trench material was compacted back around <br />the pipe. Exhibit 7-12A, Pond 004 Principal Spillway Replacement As-Built, <br />presents the as-built configuration following the replacement of the <br />principal spillway. It should be noted that the replacement o£ the <br />principal spillway did not affect or include the existing emergency <br />spillway. <br /> An as-built survey was completed in September 2005. Using the as-built <br /> survey data, SEDCAD4 was used to check the as-built configuration with the <br /> new principal spillway and shows that the pond will meet or ex ceed the <br /> CDMG's performance requirements. The survey indicates a perman ent pool <br /> elevation of 6,946.2 ft, with a storage capacity of 7.2 acre-feet (ac-ft). <br /> The SEDCAD9 modeling indicates that runoff volume and peak inflow for the <br /> 10-year, 24-hour storm event (see Addendum 7-6c.lA) are 2'.63 ac-ft and 9.27 <br /> cubic feet per second (cfs), respectively, with a calculated peak stage of <br /> 6,949.0 feet. The corresponding peak discharge from the 10-year, 24-hour <br /> storm event was estimated as 0.73 cfs. The SEDCAD4 results also indicate <br /> the average discharge settleable solids concentration during the peak 29- <br /> hour period will be 0.0 milliliters per liter (ml/1) , The Water Quality <br /> Control Commission (WQCC) settleable solids effluent concentration limit is <br /> 0.5 ml/1. The SEDCAD9 modeling demonstrate there is sufficient storage <br /> capacity available, and that the settleable solids effluent concentration <br /> is less than the applicable water quality standard. Therefore, Pon d 009 as <br /> constructed and operated meets the intentions of Rule 4.05.6(3)(a). <br />The calculated peak stage from the 10-year, 24-hour storm event is 6,999.0 <br />feet. This elevation is 1.2 feet below the emergency spillway invert <br />elevation (6,950.2 feet). This demonstrates that no flow will pass through <br />the emergency spillway during the 10-year, 24-hour storm event. Therefore, <br />the pond as constructed and opeza ted meets the intentions of Rule <br />9.D5.9 (2)(b). <br />The modeled 25-year, 29-hour storm event peak inflow is 28.99 cfs, while <br />the calculated peak discharge is 8.15 cfs with a corresponding peak stage <br />TR-37 3 Revised 10/05 <br />