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• The important factors and conditions that may influence the stability of the outcrop barrier pillar are not well defined. The coal outcrop is well defined; it is further known that at most locations along the outcrop, the D-coal seam is burnt out. At some locations, such as the Orchard Valley Mine portal entries, the coal burn was not identified. The depth of the coal burn in the horizontal direction is much less defined; we understand that based on the mining experience in the area, the width of the burnt- out zone has been assumed to reach up to 300 feet. According to this assumption, the projected burn line, which r_oincides with the southern mine limit, was estimated. The thickness (or [he width) of the outcrop barrier pillar is thus equal to 300 feet for design purposes. The design burn line may be modified during mining if intact coal is found at this line; mining may then proceed farther to the south in such a case. Mining limits in areas adjoining the outcrop barrier pillar are sometimes dictated by the occurrence of oxidized (weathered) coal close to the outcrop. Such coal is weaker than the fresh coal and it is not mined. The presen^e of the burnt-out coal close to its outcrop brings about an additional factor that might be of importance for potential subsidence or stability problems in • the the vicinity of the outcrop barrier pillar. The old coal fires, when reaching to significant depths into the mountain, created a void space; the overburden lost its support and subsided. Distinct fractures may have developed above such subsidence features as described by Dunrud (1976) in the Somerset - Paonia area. Such fractures have not been observed or documented on the southern rim of the proposed coal lease area. It is evident that potential subsidence or stability problems in the vicinity of the outcrop barrier pillars cannot be ruled out. Landslides of a significant extent have developed close to the coal outcrop at the old Farmers Mine; it cannot be ruled out that they are related to the collapse (crushing or sliding) of the outcrop barrier pillar as the mining proceeded too close to the outcrop. GEO-HYDRO Consulting, Inc. (1983) provides guidelines for a necessary width of an outcrop barrier pillar in different geologic and hydrologic conditions. According to their evaluation, a pillar width of some 50 feet should be sufficient in most conditions of the Orchard Valley Kline to prevent crushing or sliding of the outcrop barrier pillar. • - 40 -