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<br />falls onto a face conveyor, consisting of flexible steel pans, which transfers the coal away from the <br />face to the gate conveyor. The roof along the face is supported by hydraulic shields that sit behind <br />' the face conveyor. As the shearer passes across the face, the face conveyor is advanced, and then <br />the shields are advanced up to the conveyor. As the shields are advanced, the roof behind them <br />is allowed to cave. This cycle is then repeated each time the shearer passes across the face for <br />' the entire length of the longwall panel. <br />Because longwall mining usually extracts the entire seam height in a solid block of coal, coal reserve <br />extraction is exUemely high. Extraction rates approaching 100 percent can be achieved with <br />longwall mining within individual longwall panels. Maximizing the resource recovery is an important <br />' factor in mine planning. <br />The productivity of longwall faces in the United States has dramatically improved in recent years due <br />to improved cutters, face conveyors and roof supports and application of electronic technology. <br />While 1000 tons per shift was considered a good figure about 15 years ago, the current productivity <br />figures in the western mines have reached as much as 12,000 tons per shift. The Deserado Mine <br />' coal deposit is suitable for this high recovery, high production technology. Based on experience of <br />the longwall system used in the Deserado mine, the production rate per longwall face will be about <br />' 7,000 tons per shift. <br />Longwall mining has a better safety record than continuous mining. The danger from roof falls has <br />been reduced because the roof supports, which are set in a straight line with skin to skin contact, <br />form a continuous canopy of steel which protects the miners. <br />Because longwall mining has advantages (higher recovery, higher productivity, and better safety <br />record) over room-and-pillar mining with continuous miners, the mine plan has been designed to <br />' maximize the use of longwall mining within the constraints of the property boundaries, resource <br />characteristics and viable equipment specifications. The new longwall equipment that replaced the <br />equipment lost in the Deserado Mine fire has a maximum mining height of 10.5 feet and a minimum <br />mining height of six feet. Coal recovery from areas not suited for longwall mining (areas within the <br />property not susceptible to practical longwall panel layout) will be accomplished with room-and-pillar <br />' mining using continuous miners ii economically and technically feasible. Continuous miners will also <br />be used to drive envies and to develop longwall panels. Figure 4-3 shows a typical longwall retreat <br />panel in the Deserado Mine. <br />' The longwall panels are from 2200 feet to 14,000 feet long and 800 feet wide. <br />' 4.2.4 Mltlyatlon of Subsidence Effect Rio Blanco County Road 65 crosses over the mining <br />area where subsidence is expected. <br />. 22 <br />1 <br /> <br />