2008-06-09_REVISION - C1980007 (3)

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• :~ wasting is generally associated with steep slopes, but saturated or near-saturated conditions in the near-surface may facilitate mass movement on lesser slopes. Moderate (40 to 60 percent) and steep (greater than 60 percent) slopes are present in the area as bedrock cliffs and outcrops. These slopes may present a roclcfall hazard, but such slopes are localized and overall, occupy a small percentage of the area (Figure 7}. However, the entire project area appears to have the potential for mass wasting. Areas of known mass wasting and potential. instability are depicted on Figure 8. Geologic hazards are present in the project area in the form of mass wasting features associated with unstable slopes. Areas of instability generally occur on moderate to steep slopes with saturated soil conditions. Land instability is more prevalent on the north and east aspects of drainages on the down-dip side of the strata. This is attributed to the dip of the local geologic strata being to the northeast. Ground water movement through the near surface ground water zone lubricates the slopes, and contributes to the instability. Direct and Indirect Effects Alternative 1 The Deer Creek Shaft and methane drainage wells would not be installed. Without the installation of these safety features, mining of the coal underlying the project area may be conducted a slower rate or cease altogether. All topographic and geologic conditions within the area would remain in their current state. Subsidence features anticipated in the Agapito (2005) study, including a general lowering of the land surface by five to seven feet, tension cracks, and potential aggravation of existing landslides and rockfalls, would not be developed. Natural processes of erosion and mass wasting would continue. Alternative 2 Installation of the Deer Creels Shaft would be conducted using a previously constructed pad and road. Reclamation requirements to return the land surface to approximate original contour would result in no permanent change to the topography. Disturbance from constructing drill pads and staging areas for MDWs would be approximately 120 acres. The drill. pads would each require an adequate amount of grubbing and grading to provide a site level enough for safe drilling operations. Access for the methane drainage wells would result in 90 acres of disturbed area. The methane drainage wells have been located with enough latitude to allow their location on topographically favorable sites in order to minimize disturbance (Table 2-1). Analysis methods used for geology overestimates the amount of disturbance because it incorporates broad road corridors and drill pad windows. This method captures anticipated disturbance which could occur in all geologic conditions within the identified road corridors and MDW buffers. The actual on-the-ground disturbance for a road in the corridor and an MDW in the window will be less than estimated with this method. Therefore, this analysis estimates the potential disturbance by geologic condition and is not representative of the actual acres that would be disturbed by the proposed action. This method allows flexibility to identify and avoid unstable geologic areas in the field to avoid potential landsides and unstable conditions. A review of slopes calculated from the state digital elevation model (Figure 7) shows slopes within the methane drainage well project area from 40 to 60 percent. MDW locations would be selected to avoid steep slopes, however; due to site conditions, some wells could be located on steeper slopes, potentially increasing the well footprint and risk of destabilizing the slope. Deer Creek Ventilation Shaft and E Seam Methane Drainage Wells FEIS 69