2008-03-21_PERMIT FILE - C1980007 (5)

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Affected Environment and Environmental Consequences Creek lies in the near-surface zone of the overburden deformation scheme. Dispersed tension cracks may form on the land surface in this zone, however, as stated previously, cracks that form in unconsolidated deposits do not persist through time and seal naturally. Given the nature of the stream channel and unconsolidated materials present, P is not likely that cracks would form that would intercept or divert water from the stream chanrsel. The physical change in the land surface may impart some minor channel adjustments, although it is believed that given the high energy and dynamic nature of Deep Creek, that these adjustments would not be discernible from the naturally-occurring channel changes. Overall, it is believed that the risk to damaging Deep Creek is low. " Field reconnaissance in September 2004 along this portion of Deep Creek's streambed and surrounding valley floor revealed no visually discernable evidence of subsidence, even though up to seven feet of vertical ground movement is estimated to have occurred in the area. At the time of the visit, undermining had occurred 18 months earlier, therefore subsidence was complete or "mature." No obvious vegetation damage, tension cracks, or compression ridges were found. This is partially attributed to the pliant topsoil cover and limit°d bedrock exposure in the drainage area. Surface conditions such as those found in the Deep Creek valley are generally conducive to self-healing of subsidence related fractures. Any changes in stream gradient were not obvious by visual inspection (Agapito 2005, see Appendix B). No apparent changes in Deep Creek flow resulted from this subsidence. The 2001 EA accurately portrayed the potential effects. Bowie Resources, LLC Bowie No. 2 Mine The Bowie No. 2 is located across Highway 133 approximately 9 miles northwest of the Dry Fork LBA. Ongoing longwall mining of the D Seam has been monitored for subsidence effects on surface resources. Pertinent findings in the Annual Hydrology, Subsidence, and Mine Inflow Report provided by the Forest Service (Stover 2003) are summarized below: "Survey data from various points over extracted longwall panels indicated 3.5 to 6.5 feet (!f Chapter 3 subsidence has occurred, with 1.5 feet of subsidence observed over abutment chain pillars. These values correspond to a subsidence factor of 0.35 to 0.65 over supercritical longwall panels and 0.15 over rigid chain pillars for an assumed mining height of 10 feet. According to the subsidence report, this measured subsidence is consistently less than the predicted subsidence. In addition, hydrologic monitoring has shown no adverse impacts from mining induced subsidence to ponds, streams, springs, or ditches. " Oxbow Mining, LLC- Sanborn Creek and Elk Creek Mines Oxbow Mining LLC operates the Sanborn Creek and Elk Creek Mines, located across Highway 133 approximately 6 miles north of the Dry Fork LBA. Current operations are in the Elk Creek Mine in the D Seam, and the geologic column is similar to the West Elk Mine. The Elk Creek Mine map shows a similar mining plan to that assumed in the RFMP. A site reconnaissance to the Elk Creek Mine by the Forest Service, MCC, BLM, Maxim Technologies, and Agapito and Associates, Inc. personnel was conducted on September 9, 2004 to observe post- subsidence conditions in the Bear Creek (ephemeral drainage). Findings are presented below. "Although no subsidence measurements were available through Oxbow, maximum subsidence in the drainage is expected to have reached 8 feet or more. On the hillside, where zip to three seams were mined, subsidence is expected to have exceeded 15 feet. Observed surface impacts included tension cracks in sandstone outcrop and boulders. Tension cracks were confined to exposed sandstone and did not extend into surrounding soil.. The earthen roadway that passes over the anticipated tensile and compression zones showed no signs of cracks, compression ridges, tilting, or slumping. No fractures or other obvious forms of disturbance were observed in the mostly colluvial streambed of Bear Creek. " There are seven springs inventoried for the LBA tract area (MCC Spring and Stock Pond Locations 2003). All of the perennial springs are located in the bottom of the main Deep Creek drainage or in bottoms of two smaller Deep Creek tributary drainages, ranging in elevation from 7,550 to 8,200 • • 3-22 Dry Fork Lease-By-Application FEIS