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4D The principal spillway is a 24 -inch straight corrugated metal pipe with an <br />invert elevation of 6,775.50 ft. This invert elevation is similar to the <br />invert elevation of 6,774.9 ft. shown on Exhibit 7 -18. SCC is unable to <br />locate construction records that document the installation of an anti -seep <br />collar around the "new" 24 -inch CMP, and therefore, SCC can not certify <br />that it was installed in accordance with the remedial action plan. <br />However, SCC personnel have never noted signs of seepage through the <br />embankment during any monthly pond inspection. Furthermore, PECOCO was <br />created by leaving a portion of the final West Lenox pit excavation open, <br />and consequently, the majority of the storage capacity is below ground <br />surface. The top of the embankment is about six feet above ground surface, <br />which suggests the embankment extends approximately 1.5 to 2.0 feet below <br />the invert of the principal spillway. If the embankment failed around the <br />principal spillway, the amount of water that would flow from the <br />impoundment would be approximately 2.8 ac -ft. Consequently, SCC believes <br />the presence, or lack thereof, of the anti -seep collar does not impact the <br />safety or operation of the PECOCO Impoundment. <br />The emergency spillway is a trapezoidal open channel 10 -feet in width with <br />an invert elevation of 6;776.6 ft. Side slopes are 2.5H:1V and 5.OH:1V, <br />respectively. As documented by the survey, a trapezoidal channel has <br />replaced the original v- shaped channel. The invert elevation of 6.776.6 ft <br />is similar to the invert elevation of 6,777.0 ft. shown on Exhibit 7 -18. <br />SCC has also installed a fence immediately north of the impoundment to <br />control access to PECOCO. The fence alignment is shown on both Exhibit 7- <br />18A and Exhibit 13 -2A, Postmining Topography and Permanent Features. A <br />gate in the fence adjacent to the northern margin of the embankment allows <br />safe access to the impoundment. <br />SEDCAD4 was used to document that the as -built configuration will meet or <br />exceed the CDMG's performance requirements. The SEDCAD4 modeling indicates <br />that runoff volume and peak inflow for the 10 -year, 24 -hour storm event are <br />0.44 ac -ft and 2.83 cubic feet per second (cfs), respectively, with a <br />calculated peak stage of 6,775.59 feet (see Addendum 7- 6g.lA). The <br />corresponding peak discharge from the 10 -year, 24 -hour storm event was <br />estimated as 0.28 cfs. PECOCO is not a sedimentation structure; the <br />discharge from PECOCO flows to Pond 002 for treatment. Consequently, the <br />TR -37 <br />3 Revised 10/05 <br />