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West.Elk Mine <br />0 Reservoirs and Stock Ponds <br />Map 37 shows the locations of all reservoirs and stock ponds within the current permit and lease <br />areas. A total of 36 stock ponds are located in or near the current permit area, and 1 pond is located <br />in the Box Canyon permit revision area. After SOD is approved, approximately 51 ponds will be <br />located in the permit area. No effects of mining to these ponds have been observed during F Seam <br />retreat mining or from B Seam longwall mining. Within the permit area, the majority of the stock <br />ponds are owned by the U.S. Forest Service (none of which are known to be decreed rights). The <br />stock ponds are used on a seasonal basis. These ponds derive their water from surface flows and <br />they are typically constructed via a low, earthen dam across a defined drainage. There are an <br />additional 14 stock ponds in the South of Divide permit area. The total storage volume of the <br />stock ponds in the South of Divide permit area is estimated to be 7 acre-feet based on an <br />average storage capacity of 0.5 acre-feet. (See section 2.2 of Exhibit 71 for more information.) <br />The probable hydrologic consequences of the longwall mining for stock ponds in the permit area are <br />much the same as they are for streams in the permit area. These ponds are supplied by surface <br />runoff or spring flow. Disruption of the water supply to these ponds by mining is not likely because <br />the minimum overburden thickness between the E Seam and the lowest elevation pond is 500 <br />feet. Given that the combined height of the caved/fractured zone is 280 feet above the E Seam, <br />it is clear that none of the stock ponds will be affected by subsurface cracking. Additional <br />discussions and data on stock ponds can be found in the Annual Hydrology Reports, 1986 to <br />present. <br />There is, however, the potential for surface cracking to either directly or indirectly affect the ponds, <br />via one (or both) of the following mechanisms: <br />1. Streamflows in the area tributary to a stock pond are intercepted by a surface crack and <br />prevented (or reduced) from reaching the pond. <br />2. A surface crack forms directly beneath the pond or the embankment, thereby causing water loss <br />or dam failure. <br />As discussed extensively in Section 2.05.6 (3)(b)(iii & viii) Surface Water Quantity Effects, the <br />probability of encountering cracks in the South of Divide and Dry Fork permit revision areas are <br />extremely low based upon data obtained after mining the 1NW through 8NW longwall panels. <br />When cracks are encountered, they are likely to be over the chain and barrier pillars. Cracks that <br />form in the internal portion of panels will tend to heal themselves quickly (see earlier discussion). <br />Superposition of the stock ponds on the E Seam mine plans indicate that roughly half of the <br />ponds are located on or in close proximity to the chain and barrier pillars. <br />Although the risk of surface cracking to stock ponds is small, there are mitigating factors that should <br />also be considered. First, because ire fonds are located in drainages, cracks will tend to seal <br />themselves through the deposition of sediments conveyed by snowmelt and rainfall-runoff. Second. <br />it will be feasible to monitor the response of the stock ponds to mining and to take ntigating steps <br />(i.e., fill in the crack), if necessary. <br />2.05-206 Revised June 2005 PR10; Rev. March 2006: Rev. Apri12006 PRIO; May 2006 PRIO;Sep. 2007 PR12;Feb 2008 PR12