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STOCKPOND ST-1 <br />PERMANENT POND DEMONSTRATION <br />• SCC has constructed a stock pond in the south reclaimed area at the Yoast Mine and, along with the land owner, <br />believes that the pond should remain permanent. The location of this stock pond ST-1 is shown on Exhibit 20-2, <br />Postmining Topography Map. The purpose of this evaluation is to demonstrate that Stock Pond ST-1 meets the <br />design criteria spedfied in Rule 4.05.9 for permanent impoundments. <br />Water Quality <br />This stock pond is located in the upper reaches of the watershed and contains water that originates from surface <br />runoff from the Yoast reclamation area. There is no indication that neither the spoil nor the replaced topsoil <br />contains potentially acid or toxic forming material that could adversely impact surface water quality. Therefore the <br />water is suitable for the approved post mine land use that includes livestock grazing and wildlife habitat. <br />Water Persistence <br />It is expected that this stock pond will hold water from the spring runoff through early summer at a minimum. <br />Accessibility <br />This pond is easily accessible to livestock and wildlife. There are no drop offs or excessively steep slopes around the <br />edges of this pond. <br />Ca aci <br />The water storage capacity for ST-1 is 1.2 ac. ft. Since the capacity is under the 2 ac. ft. limit, the State Engineer's <br />office does not need to review the permanenry request and the pond should not have any significant effect on down <br />stream users. Attached is a general stability analysis based on the construction methods and material characteristics. <br />A Factor of Safety greater than 1.3 was calculated by this analysis. <br />Pond Dimensions <br />The dimensions and capacity for this stock pond are shown in the PAP on Exhibit 13-12.8, Stock Pond ST-1 As- <br />Built. As shown on the as-built drawing, the embankment does not exceed 5 feet in height as measured from the <br />upstream toe of the embankment to the invert of the spillway. The combined slope of all the embankments do not <br />exceed SV:1H with no slopes greater than 2H:1V. <br />Postmine Land Use <br />The approved land use for the Yoast reclamation area is livestock grazing and wildlife habitat. This stock pond will <br />enhance the postmine land use in this area. <br />Snillw~ Capacity <br />The peak discharge, spillway capacity and armoring requirements were determined using SEDCAD4 (see attached <br />SEDCAD demonstration). The peak discharge was determined using the methodology outlined in this permit. The <br />spillway capacity was determined using SEDCAD4 and was constructed with a 10 foot bottom width and a <br />minimum depth of 1.3 feet. <br /> <br />TR-37 1 08/08 <br />