2018-09-04_PERMIT FILE - C1980007A (44)

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West Elk Mine 4. Barrett stated that, `2~lowhere 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 lazge, 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 insigrrificant amounts of subsurface water." The drill logs validate his memory on this point. (The October field investigation noted several small wet areas on the surface of the slide). This lack of subsurface water bears on the interpretation of potential hydrologic impact as well as indicating less likelihood that the slides will reactivate. 6. The CDOT maps indicate the road embankment was constructed directly over the Oliver No. 2 Mine main portal. The fan portal is immediately north of the embankment and a third portal is 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 lazge amounts of methane. A consultant was even hired to advise CDOT on handling the methane. Surface equipment was designed to trap the methane at the top of the drilling 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 `PTO 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 indicates that the closest edge of the landslide activity would be 600 feet from the neazest mining acfivity (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 would be 600 feet from any projected subsidence effect. Even at the conservative 21 degree angle of draw (the maximum observed at West Elk Mine), the neazest landslide activity would be 500 feet from the closest projected subsidence effect. These data indicate 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, aze 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 fast 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 azea. 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 pernut area. 1.04-41 Revised November 2004 PRI G