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Alternative d; Given that no forested lands exist within the subject area, there would be no impact. No impact. Signature of specialist: Lynn Lewis GEOLOGY AND MINERALS Affected Environment: The proposed coal lease modification area lies on the eastern edge of the Somerset Coal District, which is part of the Paonia Coal Field. The recoverable coal deposits in this area occur in the Upper Cretaceous Mesa Verde Formation in association with a sedimentary sequence of shales, silts ones, claystones, sandstones, and conglomera[es which dip to the north-northeast at approximately 3.5 degrees. The B Coal Seam reserves, which are the objec[ive of the proposed leasing action, are part of the Bowie or Lower Coal Member, occutTing in sequence with interbedded silts[ones, shales, and fine-grain sandstones. While the B. C, D, E, and F coal seams all occur in the proposed lease modification area. only the B-Seam is considered to be economically recoverable. The other coal seams are either [oo [hin to be mined economically or include numerous spli[s or partings which render conventional underground mining methods opera[ionally infeasible. The B Coal Seam is a high volatile bituminous coal averaging L8 feet in thickness, although ground control and equipmen[ considerations limi[ effective mining height to approximately 10 feet in the proposed lease modification area. Longwell mining will result in coal recoveries on tfte order of 70 to 85 percent within the mineable seam thickness or 35 to 50 percent for the overall coal seam thickness. The average overburden depth wi[hin the lease modification area is approximately 2,500 feet. Geologic hazards, including surficial landslides, mudflows, rockfalls, actual or potentially unstable slopes, and expansive soils are common features of surface topography in this area. Environmental Consequences & Mitigation: Proposed ti :The Proposed Action would potentially result in removal and recovery of approximately 806,400 cons of coal. This increase in available coal reserves for the ongoing Sanbom Creek mining operations would not result in any increase in coal production or shipment rates but would extend the life of the Sanbom Creek mining operations by approximately 3 to 4 months. It would also avoid bypass of these coal reserves which could not likely be economically recovered in the future from either a new surface access point or through rehabilitation of old mine workings. Surface subsidence effects could activate existing natural minor surficial instabilities but would more likely increase the stability of these natural features by reducing slope gradients and creating subsidence trench features that would tend to key surficial masses into the hillslopes. The potential for any surface subsidence effects is low given an average depth of cover in this azea of approximately 2,500 feet and based on previous subsidence evaluations. Any resulting impacts would not represent an environmental or public health and 1 safety hazard given the remote location of the lease modification area relative [o drainages, existing surface l structures, and human activities. Impacts would be limited to removal and recovery of approximately 806,400 tons of coal (positive impact} and any minor subsidence-induced impacts on existing unstable su~cial features. Alternative ~ Under the No-Action Alternative, the subject coal reserves would not be leased, developed, or recovered, resulting in the probable bypass and loss of approximately 806,400 tons of coal reserves as an available energy resource. Since no additional surface or underground disturbance would occur, there would be no surface subsidence effects and no related potential for activation of existing surficial geologic hazards. Impact would be the bypass and loss of approximately 806,400 tons of recoverable coal reserves. Signature ojspeciaiist: Lynn Lewis -I a-