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<br />Revised 04/20/90 <br /> <br />Section 780.11(a) Continued <br />The proposed mine plan calls for a northward extension of the <br />existing Marr Mine operations as shown on Map 1, Kerr Mine Area Mine <br />Plan. Designed to maximize coal recovery while minimizing surface <br />disturbance, the pit configuration and sequence of operations is <br />similar to the existing Marr Mine operation. (See: Figure 32, Typical <br />Pit Cross $ectiort.) Overburden removal will be accomplished <br />primarily with Caterpillar 988 front-end loaders and Dart 50 ton end <br />dump trucks. Overburden will be fragmented for loading by ripping <br />with three Caterpillar D-9 dozers and one Fiat-Allis 41 dozer. Some <br />overburden zones (thin beds of hard sandstone) will be drilled with <br />an air track drill for blasting. Since the sandstone beds are thin, <br />typically one row of 14 foot deep drill holes, spaced eight feet <br />apart will be sufficient to handle the explosives necessary to break <br />the rock. All drill holes will be loaded with ANFO, stemmed with <br />drill cuttings, and blasted according to the detailed description <br />given in Section 780.13. In this regard, blasting procedures will <br />comply with MSHA and OSM requirements. <br />Open pit mining by its nature requires that a large amount of <br />overburden be removed and stored outside the active mining area to <br />create an opening of sufficient size to allow for safe working <br />conditions within the pit. In this case, where the maximum economic <br />pit depth is 265 feet, the working face (where overburden and coal <br />are being removed) must be no steeper than 10 percent to be within <br />the safety limits of the scrapers and haul trucks. Therefore, as <br />shown on Figure 33, Typical Steady State Pit, the length of the <br />working face from natural ground level to the pit bottom is <br />approximately 2,650 linear feet. For the same reasons as above, the <br />backfill face (where removed overburden is being replaced) must <br /> <br />as <br />