2008-03-21_GENERAL DOCUMENTS - C1980007 (3)

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on this detailed subsurface information, the Division previously found that MCC's proposed undermining of the portion of the perennial portion of Sylvester Gulch will not cause material damage to the main channel or east fork of Sylvester Gulch. (4.20.4). Flow in Deep Creek in the Dry Fork lease area is perennial. Two of the operator's B seam panels previously undermined the segment of Deep Creek that is downstream from the Dry Fork lease area. Detailed underground information provided in the PR-12 submittal and in the existing permit application (workings maps, depth of mining, height of mining, and the lithologic description of overburden) indicates subsidence may cause localized temporary pooling and temporary accelerated erosion in the channel. Exhibit 55 B contains a prediction that undermining of Deep Creek in the Dry Fork lease area by panels 3 and 4 will tilt the 7.3%pre-mining slope of the stream by 1.9%, an amount too small to significantly change the hydraulic characteristics of the stream. Exhibit 55 B (p. 35) predicts mining effects on Deep Creek in the Dry Fork lease area will be the same as the previously undermined section of Deep Creek which had no detectable impacts, indicating the depth to mining in the Dry Fork lease area (which is similar to depths downstream) is sufficient to prevent subsidence fractures from capturing significant volumes of stream flows. Based on this information, mining in the Dry Fork lease area does not appear to have the potential to cause material damage to Deep Creek. 3. Until 1999, subsidence monitoring at the West Elk Mine was accomplished using conventional survey methods of a monument grid. The monitoring of MCC's subsidence grid established the amount of subsidence that occurs over a longwall panel, when and where it occurs, and when it is complete. MCC was approved to replace the monument survey with a visual inspection of the ground over areas that have been undermined for documenting any disturbance: A survey is done prior to mining and in order to areas where effects of subsidence were previously noted in order to monitor the healing of cracks. Given the heavy snow cover and inaccessibility of most of the affected area, MCC conducts the surveys during the summer of each year and reports the results by the end of September. Any mechanical response detected during these surveys that is not consistent with previous observations will be reported to the Division within ten working days of the survey. Due to the steep topography and dense vegetative cover of the West Flatiron area, MCC has proposed a subsidence monitoring program, in accordance with Rule 2.05.6(6)(c), designed to concentrate on the landslide areas nearest Highway 133. MCC will drive steel rods vertically into the old landslide body and monitor these rods to assess any movement. Section 2.05.6(6) of the permit application specifies proposed subsidence monitoring locations, frequencies, and methods for the South of Divide area and the perennial portion of Sylvester Gulch. Methods include surveying monuments, aerial photography, surface water flow measurements, piezometer water level 51