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STOCK POND T -20 <br />PERMANENT POND DEMONSTRATION <br />In 2001, SCC constructed a stock pond in the north reclaimed area at the II -W Mine and, along with <br />the land owner, believes that the pond should remain permanent. The location of this stock pond T -20 <br />is shown on Exhibit 20 -2, Postmining Topography Map. The purpose of this evaluation is to <br />demonstrate that Stock Pond T -20 meets the design criteria specified in Rule 4.05.9 for permanent <br />impoundments. <br />Water Quality <br />This stock pond is located at the lower end of the North area reclamation and contains water that <br />originates from surface runoff from the II -W north reclamation area. There is no indication that neither <br />the spoil nor the replaced topsoil contains potentially acid or toxic forming material that could <br />adversely impact surface water quality. Results of the water sample analyses are attached. The <br />analysis indicates that the water is suitable for the approved post mine land use that includes livestock <br />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 <br />minimum. <br />Accessibility <br />This pond is easily accessible to livestock and wildlife. There are no drop offs or excessively steep <br />slopes around the edges of this pond. <br />Capacity <br />The water storage capacity for T -20 is 0.26 ac. ft. Since the capacity is under the 2 ac. ft. limit, the <br />State Engineer's office does not need to review the permanency request and the pond should not have <br />any significant effect on downstream users. A general stability analysis was conducted for stock ponds <br />based on the construction methods and material characteristics. A predicted Factor of Safety of 1.56 <br />was calculated by this analysis. This stability analysis is contained in Attachment 13 -11 and a <br />summary copy is attached. <br />Pond Dimensions <br />The dimensions and capacity for this stock pond are shown in the PAP on Exhibit 13- 27.T20, Stock <br />Pond T -20 Survey. As shown on the as -built drawing, the embankment is 1.0 feet in height as <br />measured from the pond bottom to the invert of the spillway; however the pond was excavated to <br />provide fill for the embankment. Therefore the embankment is less than 5 feet in height from the <br />upstream natural toe of the embankment to the invert of the spillway. The combined slope of all the <br />embankments do not exceed 5V:1H with no slopes greater than 2H:1 V. <br />MR -76 T -20.1 Revised 12/13 <br />