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West Elk Mine account). These ponds, which are located in clay-rich (Wasatch clay) material in order to minimize leakage, occur in overburden that ranges in depth from about 800 feet in Horse Gulch to 2,200 feet in the stock pond P23-4 above the eastern end of mined longwall pane122. Strea»ts and Ditches The primary streams in the South of Divide mining azea are Dry Fork of Minnesota Creek, Deer Creek, Poison Creek, and Lick Creek. The primary source of water to Minnesota Reservoir comes from the Deep Creek Ditch, wherein water is diverted from the upper drainage of Deep Creek and transmitted to Dry Fork. The Deep Creek ditch was constructed in debris flows or colluvium and alluvium derived from the debris flow, as described above, this debris flow material is not expected to be impacted by longwall mining. As discussed in Section 5.3.2 of Exhibit 60B, no cracks were observed in the alluvium and colluvium of Sylvester Gulch and Deep Creek during periodic field observations in the Apache Rocks and Box Canyon mining areas. The near-surface alluvial material consists of primarily sand, silt, clay, and soil that range in estimated thickness of approximately 25 to 150 feet. In the two areas mentioned the drainages were located above rigid pillars and panel boundaries where the overburden depth ranges from 800 to 1,050 feet. The alluvium and colluvium in Dry Fork and Lick Creek, which has an estimated thickness range of approximately 25 to 75 feet, contains more clay than does the Deep Creek alluvium. Therefore, it is even less likely that cracks will occur in colluvium and alluvium in the stream valleys of the South of Divide mining azea despite the shallow overburden. • In the South of Divide mining area the overburden depth to the E Seam ranges from approximately 375 feet above the western edge of longwall panel E2, to 1,300 feet above the eastern limit of longwall panels E6 and E7. However, based on observations made by Mr. Dunrud above the Somerset Mine in the Bear Creek azea, subsidence cracks are not expected to occur in the Dry Fork alluvium where the overburden depth ranges from 375 to 800 feet. No cracks, and no change in stream flow, were observed in the Bear Creek alluvium (estimated to be 10 to 15 feet thick) when coal was extracted by room-and-pillaz methods at depths ranging from 220 to 300 feet beneath Bear Creek (Bureau of Land Management, et al., 2002). The probable reason for the lack of cracking in alluvium is that the fine sand- to clay-sized material and overlying soil yields without cracking or bulging as it deforms as a discrete unit, or as discrete units, in the subsidence process. This same reasoning also applies to the colluvium in the area. Although subsidence cracks were locally observed in colluvium less than one foot to a few feet thick, no cracks were observed in cllluvium more than about ten feet thick. No cracks have been observed in alluvium above mined longwall panels in the Apache Rocks and Box Canyon mining areas. Surface-water monitoring in the Dry Fork and Lick Creek drainages will continue in order to compare the historic information derived from annual subsidence observations in the West Elk Mine azea with field observations in selected azeas of the South of Divide mining area. Subsidence depressions, slope changes, and strain aze projected to occur in above longwall panels E2 through E8 in Dry Fork and its tributaries and in Lick Creek when the panels aze mined. 2.05-/51 Revised June 1005 PRIO, Rev. March 1006; May 1006 PRIO