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t Mr. Dave Maxwell - 2 - July 26, 198y F-seam Mine Plan Changes The F-seam mine plan has been modified slightly as follows: a small area, three (3) panels, will be mined immediately inside and to the west of the F-seam portals. This area underlies a portion of the approved Upper Waste Pile, which is yet not built, WECC also plans to cease mining in the 1W6S panel due to decreasing coal thickness. An additional panel (1W3N) may be developed north of and paralleling the 1 West Suomains, if geological conditions allow, This panel replaces a parallel set of small panels previously proposed in this same portion of the mine plan. Tne subsidence implications of one larger panel should be less disruptive than the higher flexure resulting from repetitive barriers remaining after the extraction of the group of smaller panels. WECC is planning to discontinue easterly advance of the 1st East Submain, because of bad roof conditions adjoining Sylvester Gulch. The alternative is to advance a new set of East Sunmain Entries to the east southeast, and then drive a series of nine (9) panels (IEIN through 1E91J) to the east northeast. Waste Disposal A lower waste rocK pile was permitted in 1986 to handle 1,771,924 tons of waste over a 15.7 year period, through the year 2000. At the time of permitting, WECC projected that the mine would produce approximately 110,000 tons of waste per year. Construction of the two ramps and ventilation shaft for the B-seam will produce 54,000 tons of waste. This, coupled with an estimate of 50,000 tons of waste associated with the 1989 mining of the F-seam, will maintain the projected refuse production rate. Underground development waste is projected at 105,000 tons in 1990, 50,000 tons each in 1991 and 1992 and 75,000 tons per year thereafter, resulting in storage in the lower waste pile through 2003. The ramp material is composed of alternating sandstone and shales. It has a neutral pH, low salinity and a low iron content; SARs average 12.74. Recommended quality standards for selinium range from 0.1-2 mg/k; the ramp material averages 0.09 mg/k, at the lower end of the range. The material to oe generated by slope and shaft development in the B-seam is of signer shear strength than the material currently contributed to the pile as a result of F-seam mining, so stability of the pile will not be affected. Subsidence Monitoring and Control Within the angle of draw of the B-seam mine plan area there are no renewable resource lands, structures or geological hazards that require protection or mitigation from subsidence. The predicted extent of subsidence to result from the F-seam was approximately four (4) feet. The extent of subsidence noted during the past five years has been less than two (2) feet. The predicted extent of suosidence to result from mining in the B-seam is four (4) feet for room and pillar mining in Dots the B and F seams. If the B-seam is mined using longwall methods, the predicted cumulative subsidence could reach ten (10) feet.