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Subsidence predictions were conservative and actual measured subsidence was always less than <br />predicted. Depth increases as the mine progresses to the north. As depth increases, subsidence <br />decreases. As acknowledged by DRMS and OSM, subsidence of archaeological sites over LW -2 <br />was found to cause no significant impacts. The lease COC -51551 sites were predicted to subside <br />less than that over LW -2 and therefore are not expected to be significantly impacted. However, <br />longwall mining under these sites did not occur since this area became inaccessible when part of <br />the D Seam was sealed due to the fire. <br />III.A.8 Mine Ventilation A permanent fan is installed at the D -Portal ventilation slope. This fan <br />operates in a blowing configuration pushing fresh air into the mine from the Ventilation Entries and <br />through the working area. It operates continuously with the exception of scheduled maintenance <br />periods. MSHA approved the detailed plans for the ventilation of the underground working. Two <br />ventilation shafts were constructed in the B -Mains to exhaust return air. Details of the construction <br />are given on Maps 151 and 156. The first raise bore shaft is 210 -feet deep and 12 -feet inside <br />diameter and the second 813 -feet deep and 7 -feet diameter. Another shaft (B -Vent Shaft #2) was <br />attempted but failed near Service Hole SH -2 (Map 155). The shaft openings are fenced off and <br />elevated to control unauthorized access to MSHA standards. The shaft sites are approximately <br />100'x200'. Light use roads about 2410 and 1200 feet long were constructed from the existing haul <br />road to B -Vent Shafts 1 and 3. A 1400 foot long light use road extension from RDH -3 serviced B - <br />Vent Shaft 2. Later, a 2150 foot light -use road was constructed connecting RDH -3, SH -1, SH -2, <br />and B -Vent Shaft 2 to the haul road. A 3 -foot diameter, 362 -foot deep ventilation shaft was drilled <br />to the West Mains in the D -Seam (WMVS-1). <br />Return shafts are constructed to the B -Seam to exhaust return air. All are steel lined. RS -1 and <br />RS -2 are 300 and 308 feet deep and five-foot diameter. RS -3 six-foot diameter and 310 feet deep. <br />The upper and lower 20 feet of the annulus between the liner and the shafts are grout sealed with <br />concrete. The middle zones of the annulus are gravel filled with weep holes drilled in the liner to <br />allow drainage. RS -4, RS -5, and RS -6 are 24" ID, RS -11L, and RS -12L are 26" ID, and 585, 610, <br />600, 658, and 640 -feet deep with the annulus grouted the full length. RS -4 was assisted by an <br />adjacent 11" open borehole. Map 153 shows the details of RS -1 which are typical of the other <br />return shafts and roads. Locations and light -use roads to these shafts are shown on Map 147. All <br />return shafts have been sealed except RS -11 L and RS -12L. <br />During early 1987, gassy conditions were encountered at the Deserado Mine. To relieve those <br />conditions, BME drilled a 12-1/4 inch hole (LW1-1) and six (6) 10-5/8 inch holes (LW1-2 to LW1-7) <br />into the gob created behind the protective shield of the longwall 1. In September, 1988, a vent <br />hole (LW1-8) was drilled to relieve methane gas in the sealed area of the longwall panel #1 to <br />improve ventilation in other working areas of the mine. In January 1990, an additional ten (10) <br />Minor Revision #165 (07/2015) 111-26 <br />