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INTRODUCTION <br />• I In response to a new mine plan, which increased the disturbance area controlled by Pond 016, SCC <br />proposed and designed a second pond to operate in series to effectively treat runoff from the mining <br />disturbance area. Sediment Pond 016A was constructed in the NE%< SE%<, Section 27, TSN, R87W, <br />6th P.M. just upstream from Pond 016. Construction was initiated in June 2003 and originally <br />completed in July 2003. This As-Built Report is intended to serve as construction certification for Pond <br />016A in accordance with Rules 4.05.6 and 4.05.9. <br />The back slope of the impoundment began to experience slumping during the fall of 2003 and is not <br />depicted on Exhibit 16-9C. The slumping does not currently affect the capacity or operating capability <br />of the pond. However, SCC is evaluating methods of stabilizing this back slope and will initiate <br />corrective action in 2004 <br />EMBANKMENT AND EXCAVATION <br />The embankment is a homogeneous earth filled structure. The top width of the embankment is <br />approximately 15 feet with an upstream slope of 3H:7 V and a downstream slope of The 3H: i V <br />principal spillway consists of a 48-inch CMP riser which drops into a 48-inch discharge CMP. The <br />emergency spillway is a trapezoidal riprapped channel 50 feet wide (see Exhibit 13-9C, Pond 016A As- <br />Builtj. <br />Due to the silty nature of the alluvial subgrade material at the embankment location, a keyway was <br />constructed into impervious materials. The keyway for the embankment was constructed at a minimum <br />• 5 feet deep and 10 feet wide <br />A portion of the pond capacity is a result of excavating topsoil and subgrade material below natural <br />ground level. Suitable materials excavated from the pond area and associated side-slopes were used in <br />the embankment construction. <br />DESIGN ANALYSIS <br />Pond 016A was designed to meet or exceed the design and performance requirements of CDMG while <br />utilizing as much of the existing topography as possible. Sedimentation Pond 016A was designed and <br />constructed to adhere to the following specifications: <br />I. Provide storage and treatment for runoff from the 10-year, 24-hour storm event without <br />experiencing any discharge through the emergency spillway; <br />2. Provide an emergency spillway capable of passing runoff from the 25-year, 24-hour storm event; <br />3. Provide adequate storage, in conjunction with Pond 016, for sediment generated as determined by <br />SEDCAD analysis; <br />4. Provide a nonclogging dewatering device and principal spillway that will provide adequate detention <br />time for the 10-year, 24-hour storm event. <br />• In some instances, mining will cause the drainage area to change during the life of the pond. When the <br />mining into the watershed, the pit intercepts the runoff. In these cases a conservative pit move <br />TR-49 13-51-1 Revised January 2005 <br />