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October 11, 2011 <br />DEFINITIONS <br />Page v <br />Coal PillarA rectangular block of coal left to support the overlying strata in a mine. Pillars <br />may be mined during retreat operations or left unmined permanently for support of other <br />underground or surface structures. <br />Mains —The principal underground route in a district along which mined coal is conveyed to the <br />shafts, generally forming the main intake air course of each district. The mains pillars are <br />typically designed for long -term stability. <br />Sub-Mains—Secondary underground routes for mined coal haulage and ventilation. The sub - <br />mains pillars are also designed for long -term stability. <br />PanelA panel is an area underground that constitutes multiple individual coal pillars. Panels <br />are typically separated by inter -panel barriers. <br />Development -Only Mining— Development mining involves only primary mining of coal pillars, <br />i.e., coal pillars of dimensions that are stable in the long term are developed by mining entries <br />and crosscuts around them. No further mining is performed. <br />Retreat Mining—Retreat mining involves secondary mining of developed coal pillars, where the <br />pillars are extracted in steps using a continuous miner; generally in a direction from the mine <br />boundary towards the mine access shaft or decline. Retreat mining is frequently referred to as <br />pillaring or secondary mining. <br />Multi -seam Mining— Mining of underground workings in multiple seams that overlap <br />horizontally. <br />Retreat Line —The retreat line is the hypothetical line joining the extents of retreat mining. <br />Agapito Associates, Inc. <br />