2013-04-08_PERMIT FILE - C1982057A (2)

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STOCK POND T -27 PERMANENT POND DEMONSTRATION In 2006, SCC has constructed a stock pond in the southern reclamation area at the II -W Mine and, along with the land owner, believes that the pond should remain permanent. The location of this stock pond T -27 is shown on Exhibit 20 -2, Postmining Topography Map. The purpose of this evaluation is to demonstrate that Stock Pond T -27 meets the design criteria specified in Rule 4.05.9 for permanent impoundments. Water Quality This stock pond is located in the upper portion of a watershed in the southern portion of the reclamation area. There is no indication that either the spoil or the replaced topsoil contains potentially acid or toxic forming material that could adversely impact surface water quality. Results of the 2012 water sample analysis are attached. The analysis indicates that the water is suitable for the approved post mine land use that includes livestock grazing and wildlife habitat. Water Persistence It is expected that this stock pond will contain water from the spring runoff through early summer at a minimum. Accessibility This pond is easily accessible to livestock and wildlife. There are no drop offs or excessively steep slopes around the edges of this pond. CLapacily The water storage capacity for T -27 is 1.27 ac. ft. Since the capacity is under the 2 ac. ft. limit, the State Engineer's office does not need to review the permanency request and the pond should not have any significant effect on downstream users. A general stability analysis was conducted for stock ponds based on the construction methods and material characteristics. A predicted Factor of Safety of 1.56 was calculated by this analysis. This stability analysis is contained in Attachment 13 -11 and a summary copy is attached. Pond Dimensions The dimensions and capacity for this stock pond are shown on Exhibit 13- 27.T27, Stock Pond T -27 Survey. As shown on the as-built drawing, the embankment is 9.2 feet in height as measured from the pond bottom to the invert of the spillway; however the pond was excavated to provide fill for the embankment. Therefore the embankment is less than 5 feet in height from the upstream natural toe of the embankment to the invert of the spillway. The combined slope of all the embankments do not exceed 5V: I H with no slopes greater than 2H:1 V.