2022-02-22_PERMIT FILE - C1980007 (5)

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West Elk Mine 2.04-41 Rev. 11/04- PR10, 04/06- PR10, 09/07- PR12, 10/08- PR14; 01/22- MR459 4. Barrett stated that, “Nowhere did any drill holes detect more than 30 feet of thickness of slide material.” This information is quite significant because even if future mining were to reactivate slide movement, it would be fairly limited with little to no likelihood of impacting the highway. If it were one large, deep rotational slide, any reactivation, even at the head of the slide, could materially impact the highway below. 5. “Even though the surface of the slide was wet and muddy, the drill holes and two attempted horizontal drain holes found none or very insignificant amounts of subsurface water.” The drill logs validated his memory on this point. (The October field investigation noted several small wet areas on the surface of the slide). The lack of subsurface water bears on the interpretation of potential hydrologic impact as well as indicating less likelihood that the slides would reactivate. 6. The CDOT maps indicated the road embankment was constructed directly over the Oliver No. 2 Mine main portal. The fan portal was immediately north of the embankment and a third portal was immediately south of the embankment. 7. Because there were seeps and springs below the mine portals, the road embankment crossing of the unnamed drainage west of Box Canyon was “constructed on a cobble and geotechnical fabric drain to enable surface water to drain beneath and through the embankment.” 8. Several of the drill holes encountered large amounts of methane. A consultant was hired to advise CDOT on handling the methane. Surface equipment was designed to trap the methane at the top of the drill hole and direct it away from the personnel and drill rig. Drill logs obtained of holes drilled along the alignment prior to construction indicate considerable methane. Logs of holes at a later date and at higher elevations and presumed to be up on the landslide, noted “No Gas.” Careful review of 1994 detailed color aerial photos at a 1:12,000 scale and a detailed topographic map at a scale of 1 inch equals 500 feet indicated that the closest edge of the landslide activity was 600 feet from the nearest mining activity (the barrier pillar) and 800 feet from the edge of the northernmost longwall panel. Assuming a 16 degree angle of draw (the most common at West Elk Mine), the landslides were 600 feet from any projected subsidence effect. Even at the conservative 21 degree angle of draw (the maximum observed at West Elk Mine), the nearest landslide activity was 500 feet from the closest projected subsidence effect. These data indicated that it would be highly unlikely that mining would have any influence relative to possible reactivation of these slides or any adverse impact on SH-133. The conditions, which reactivated the prominent slides, are distinctly different from those expected in the foreseeable future within the permit area. The old Minnesota Reservoir slide occurred over geologic time from a series of unique geological circumstances. The Jumbo Mountain slide first occurred many hundreds or possibly thousands of years ago when climatic and topographic conditions were considerably different from today. Deep excavations reactivated the highway slides along SH-133 during highway construction. Such excavation is not foreseen anywhere in the permit area. Under the current or proposed mining plans, even deep slides would not be deep enough to reach or adversely affect mining or cause a hazard in the permit area.