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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 specified 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. Results of the <br />2009 water sample analysis are attached. The analysis indicates that the water is suitable for the approved post mine <br />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 />Accessibili <br />ty <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 />capacity <br />• The water capacity for ST-1 is 0.6 ac. ft. Since the capacity is under the 2 ac. ft. limit, the State Engineer's office <br />does not need the review the permanency 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 />The Factor of Safety from this analysis shows 1.3. <br />Pond Dimensions <br />The dimensions and capacity for this stock pond are shown on Exhibit 13-12.8, Stock Pond ST-1 As-Built. As <br />shown on the as-built drawing, the embankment does not exceed 5 feet in height as measured from the upstream <br />toe of the embankment to the invert of the spillway. The combined slope of 9A the embankments do not exceed <br />5V: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 />Spillway Capait. <br />The peak discharge, spillway capacity and armoring requirements were determined using SEDCAD4. The peak <br />discharge was determined using the methodology outlined in this permit. The spillway capacity was determined <br />using SEDCAD4 and was constructed with a 10 foot bottom width and a minimum depth of 1.3 feet. <br />is <br />MR-29 1 Revised 8/09