2018-05-30_PERMIT FILE - C1981022A

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Section - 2.05.6 would be damage of sufFcient magnitude as to render them unsafe for human use. With regard to ~~ the renewable resource lands, the lack of such resources means no subsidence-related impacts will-~S~!,~ f~ oleos. ~' ~~."`~ Predicted Subsidence Related Consequences -Recent subsidence evaluations for longwall mining nnera tinng in the rxistina .Canhnm (~rP°lr Mine and nrn.,ne °fl Fllr ('.°°4 MiAe .,.~.7i.-r ...,,1,.,1.1° an,J worst-case subsidence. While subsidence will vary dependent on cover depth, extraction thickness, and a number of other factors, it is probable that the actual maximum surface subsidence will not exceed ten feet, that any chimney subsidence that may occur will not reach the overlying ground surface, and that the maximum angle of draw will be approximately 25 degrees. Documentation of subsidence evaluations for the Sanbom Creek Mine and the Elk Creek mine is provided in Exhibit 2.05-E8, Subsidence Control and Monitoring. Sanborn Creek Mine The subsidence evaluations confirm that neither State Highway 133 nor the North Fork of the Gunnison River will be affected by mining-related subsidence; that the potential exists for subsidence to progressively drain any accumulated water from abandoned overlying mine workings; and that natural landslide areas should not be adversely impacted by subsidence since subsidence trough features will tend to buttress any existing unstable areas. Structures potentially subject to subsidence damage include a portion of the existing Union Pacific railroad line, a portion of old State Highway 133, Mountain Coal's loadout facility, OMLLC's Substation No. 3 and C-Gulch ventilation installation, a portion of the DMEA powerline and the log cabin. The mining plan for the southern portion of the Sanbom Creek Mine included maintenance of a 200- foot barrier between the southernmost main entries and the old State Highway and the limitation of 50 percent extraction in this area. With a 50 percent extraction limit, 50-foot by 35-foot barrier pillars were left in place resulting in a 2.5 factor of safety (based on a Salamon and Munro pillar strength analysis) relative to protection of surface structures. Since they aze outside of the zone of projected subsidence effects, the railroad line, old State Highway 133, Mountain Coal's rail loadout and the log cabin axe unlikely to, and to date have not been, affected by mining-related subsidence. Given that the calculated factor of safety for ground control in the nearby southern part of the Sanbom Creek Mine area significantly exceeds the factor of safety of 1.5 required for long-term stability, potential adverse subsidence effects on Substation No. 3, the C-Gulch ventilation facihry and the potentially affected portion of the DMEA powerline are not anticipated. Thompson Creek has not been and will not be affected by mining or mining-related subsidence since OMLCC decided not to proceed with plans to mine the Sanbom East Tract due to coal quality considerations. Similarly, development of mine entries under Hubbard Creek for the Somerset Mine in 1984 was conducted to limit extraction to approximately 40 percent. Monitoring of overlying areas has detected no noticeable subsidence. Elk Creek Mine D-Seam longwall subsidence studies contained in Exhibit 2.05-ES confum 1) a maximum, worst case, trough subsidence effect of 10.02 ft. to 14.39 ft; 2) enhanced overall stability of existing landslide mass features and 3) the extremely remote possibility that ephemeral water flowing in the Bear Creek drainage will be captured by longwall subsidence. In acearciranc2 •a^.,I•, tt•,e EIS, nc r;;s„r,g w,1,5 sue cer.,ui,cted in cl•,e EYE Creek ^al;r,e untie: pe:e^„r;rai portions of Hubbard Creek within a zone created by projecting a 25 degree angle of draw (from vertical) from the surface expression of the creek down to the top of the D coal seam (see Figure 2.2 Modred Edk Creek CaalLeare Tract-Alternative D of the EIS). PROS 2.05-103 Revised 2002