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May 11, 2011 <br />DEFINITIONS <br />Page iv <br />Coal Pillar —A 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 />Panel —A panel is an area underground that constitutes of multiple individual coal pillars. <br />Panels 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 />Agapito Associates, Inc. <br />