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demonstrated that the pond was designed and constructed to meet the requirements of Rule <br />4.05.6. The 1990 design is included in this report as Attachment 2.05.3- E2.D -1. <br />• SCC prepared an as -built report in 2005 as part of TR -37 which certified the pond met the <br />requirements of Rules 4.05.6(3)(a), 4.05.9(2)(b) and 4.05.9(2)(c)(ii). The 2005 as -built <br />report is included in this design report as Attachment 2.05.3- E2.D -2. <br />2.0 Embankment <br />The pond is the result of a portion of the historic Seneca II Mine west Lennox Pit highwall filling <br />with water — the embankment was re- constructed in 1990 as part of the permanent pond <br />demonstration. The impoundment and associated structures are pre - existing. The as -built <br />configuration was prepared under the supervision of others. Mr. Ronald J. Gehrke, a registered <br />engineer in the State of Colorado (P.E. No. 19959) experienced in the design and construction of <br />earthen structures certified the 1990 design. Mr. Robert J Shevling, a registered engineer in the State <br />of Colorado (P.E. No. 37382) experienced in the design and construction of earthen structures <br />certified the TR -37 as -built report. The "original" certified as -built drawing is found in the Seneca II <br />Mine permit as Exhibit 7 -18, PECOCO Impoundment As- Built. <br />The top of the embankment is at an elevation of 6,780.0 feet. The top width is approximately 15 feet <br />with minimum upstream and downstream slopes of 4.5H: IV and 3H: IV, respectively. The water <br />surface of the pond covers approximately 2.1 acres, with a permanent pool elevation of 6,775.65 and <br />a 2005 surveyed storage capacity of 19.7 acre -feet (ac -ft). The permanent pool elevation is <br />maintained by spoil spring seepage, which historic Seneca II Mine records indicate averages about <br />40 gallons per minute (gpm). <br />3.0 2005 As -Built Analysis <br />As noted above, SCC evaluated the configuration and performance in 2005 to demonstrate that <br />PECOCO Pond remedial action items proposed in 1990 were implemented. The 2005 analysis <br />documented how SCC implemented the 1990 design and demonstrated that the pond met the <br />following specifications. <br />• Provide adequate freeboard between the calculated peak flow from the 10 -year, 24 -hour <br />storm event and the invert of the emergency spillway so that no runoff from the 10 -year, 24- <br />hour event passes through the emergency spillway as required by Rule 4.05.9(2)(b). <br />• Provide a spillway system that safely passes runoff from the 25 -year, 24 -hour storm event in <br />accordance with Rule 4.05.9(2)(c)(ii). <br />• PECOCO Pond is not a sedimentation structure. Discharge from PECOCO flows to Pond <br />002 for treatment. Consequently, PECOCO does not need to meet effluent limitations in <br />pond discharge and Rule 4.05.2(7) and Rule 4.05.6(3)(a) are not applicable. <br />• Sage Creek Coal Company has re- evaluated the pond to assure continued compliance with the <br />applicable rules and regulations. <br />2.05.3 -E2.D2 12/09 <br />