2010-05-07_PERMIT FILE - C2009087 (34)

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1.0 Introduction • The PECOCO Pond was created in 1979 as a result of the final mine excavations of the Seneca H Mine west Lennox Pit. The embankment, a homogeneous earthen fill structure, was constructed in 1987 to control the impoundment water level and discharge. The pond is located in the NW /4 NW /4 Section 2, Township 5 North, Range 87 West. The spillway will be an open - channel trapezoidal combination spillway in accordance with Rule 4.05.9(2)(a). The spillway is designed with a bottom width of ten (10) feet, a left side slope of 5H:1V and a right side slope of 2.5H:1V. Both the spillway crest and the outslope channel with be protected with rock riprap sized for the 25 -year, 24- hour storm event. The pond was approved as a permanent, postmine structure by the Colorado Division of Reclamation, Mining and Safety ( CDRMS) as part of Technical Revision No. 42 (TR -42) for the Seneca II Mine permit (C -80 -003) on September 12, 2007. Sage Creek Coal Company has re- evaluated the pond design and storage capacity for this mine permit application because the watershed area has been expanded as a result of the Peabody Sage Creek Mine operations. Approximately 875 acres of area that were mined during Seneca II Mine operations, which have since been reclaimed and revegetated ( CDRMS approved Phase I bond release [SL -01, December 27, 2006] for this acreage) are being re- routed away from the South Surface Facilities Area and into the PECOCO Pond watershed. While the watershed area has been significantly expanded from the original Seneca 11 Mine design, the watershed has remained relatively undisturbed. The Seneca II Mine design and as -built demonstrations evaluated watershed areas that were 89.5 acres and 48.1 acres, respectively. With the re- routed acreage, the revised watershed drainage is 927 acres. Of the 927 acres, approximately 13.1 acres will be disturbed: the disturbed areas include Road "E" and "E1" and the new channel (SCM -1) that will be used to convey runoff flows from the 875 acre area to PECOCO. Of the remaining 914 acres, approximately 8.1 acres were never disturbed by mining operations and the other 906 acres have been successfully reclaimed and revegetated. The contributing watershed area, including the re- routed acreage, is shown on Map 2.05.3 M4, Drainage and Sediment Control Plan. As of the date of the Peabody Sage Creek Mine PAP submittal, the reclaimed and revegetated lands associated with the Seneca II Mine surface operations have been approved for Phase I Bond Release (SL -01, December 27, 2006). Most of these reclaimed and revegetated lands have either received Phase 11 Bond Release (SL -03 was submitted to CDRMS on September 22, 2007), or are awaiting Phase lI Bond Release. As noted above, the pond was originally constructed in 1979 by Seneca Coal Company (SCC) the Seneca II Mine operator and permittee under Coal Mine Permit C -80 -003. To assure design continuity, the design and construction information for the PECOCO Pond previously approved have been included as part of this design report. Following is a summary of the design and construction history. • The pond design was evaluated by SCC in 1990 as part of a re -design of the spillway system completed as part of the permanent pond demonstration. The 1990 design evaluation 2.05.3 -E2.D1 12/09