2010-04-26_PERMIT FILE - C1980007A (3)

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surface water and facility access. If test values are lower than the minimum values provided for Cases A and B, the updated slope stability model (conducted with the actual refuse material test values) will be used to determine the amount of benching required to establish a stable slope. 2.3 Subsidence The potential for subsidence related to mining activity in the area of the RPE East was examined. Historically, the Oliver Mine exploited the E -Seam near the current elevation of Highway 133 (Elevations 6,130 to 6,300 in the area underneath the proposed RPE East refuse pile). This mine used the room - and - pillar mining technique in which pillars of coal remain after mining is completed to support the roof. This type of mining typically results in very little subsidence observed at the ground surface. Mining was completed in the Oliver Mine decades ago. More recently, the longwall mining method was utilized to mine the B -Seam of the West Elk Mine at approximately elevations 5,940 to 6,050 in the vicinity of the proposed RPE East. Longwall mining typically results in much greater surface manifestation of settlement than room - and - pillar mining. The longwall panels were located directly beneath the Oliver Mine workings and both mine workings are located directly below the proposed RPE East refuse pile as shown in Figure 2 -13. Completion of longwall mining of the B -Seam panels in the area of the proposed RPE East refuse pile occurred in 2006, and it is believed that essentially all of the subsidence due to mining of the 13- foot -thick coal seam was completed within the first year after mining stopped in this area. Therefore, Barr does not anticipate that any appreciable subsidence at the ground surface in the area of the RPE East refuse pile will occur during the life of the refuse pile. PAMpls \06 CO \26 \06261003 MCC Refuse Pile Site Review & Permit \WorkFiles\Pern it Application \Text \2010- 04- 19_RPE East Permit Application.doc 8