2009-10-06_PERMIT FILE - C1980005 (2)

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Introduction • Sediment Pond 008 was constructed in 1987. The pond is located in the NW/4, Section 7, Township 5 North, Range 86 West (see Exhibit 13-2A, Postmining Topography and Permanent Features) in the Bond Creek drainage, which is tributary to Fish Creek. Pond 008 was constructed as an earthen fill embankment pond (see Exhibit 7- 17A, Sediment Pond 008 As-Built). The original spillway was a 6-inch diameter orifice cut into a 24-inch diameter drop inlet pipe. In 1992, a trapezoidal emergency spillway channel was cut into the embankment to increase the capacity of the pond. Certified as-built reports for each construction phase are included as Appendix 7-6f.1, Pond 008 1987 As-Built Report and Appendix 7-6f.2, Pond 008 Emergency Spillway As-Built Report. Certified as-built drawings for each construction phase are included as Exhibits 7-17A and 7-17C, Sediment Pond 008 As-Built. During the April 2005 inspection following snow and ice melt, Seneca Coal Company (SCC) representatives noted that the "existing" principal spillway was no longer functioning as designed and constructed. The 24-inch CMP riser pipe had significantly deteriorated below the 6-inch inlet orifice • and was not retaining the design volume of water. SCC submitted a technical revision (TR-39) which presented the design and replacement plan for a new principal spillway pipe in June 2005. The replacement principal spillway construction was initiated and completed during August 2005. The new principal spillway is an 8-inch diameter plastic corrugated straight pipe set at an invert elevation of 7,015.3 feet. A screened cage is fitted to the inflow end to prevent trash and debris clogging the spillway pipe. The redesign did not affect or include the pond embankment configuration (except to abandon the old pipe and install the new pipe) or the existing emergency spillway channel. The existing 24-inch CMP straight pipe was abandoned as follows: the pipe was uncovered for approximately 15 feet at the downstream end; the exposed pipe was crimped; concrete was pumped into the straight pipe until the barrel through the embankment was filled; and, the exposed pipe was backfilled at both the downstream end and the riser. The pond embankment has a top width of approximately 15 feet, with upstream and downstream slopes of approximately 3H:1V, respectively. The existing emergency spillway is a trapezoidal open channel with a bottom width of 20 • feet and 3H:1V side slopes. The crest is vegetated, while the outslope channel has a riprap lining with a D50 of 6-inches. TR-51 1 Revised 09/09