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State Re . <br />2.05.2 1 b1INING OPERATIONS - LIFE-OF-MINE <br />II i <br />th <br />f <br />i <br />l <br />d <br />t S <br />l <br />i • <br />e area <br />n <br />ng emp <br />oye <br />a <br />eneca <br />s <br />The genera <br />type o <br />m <br />surface mining method. This type of mining is utilized in many <br />of the western and midwestern coal fields where the reserves <br />cover relatively extensive areas and the coal stratum lies at a <br />fairly constant depth below the surface of the land. Reserves <br />of this type are generally developed by conventional dragline <br />or shovel methods which are typified by the excavation of a <br />sequence of relatively parallel pits extending several thousand <br />feet in length. The overburden from each successive pit is <br />placed or "spoiled" into the previous pit after the coal has <br />been removed and the operation advances to a limit line known <br />as a recovery line which is determined by property ownership, <br />coal outcrop, coal quality, equipment limitations, prevailing <br />market conditions, or a variety of other interrelated factors. <br />Prior to the overburden removal stage, the mining area is <br />prepared by clearing and removing of suitable upper soils which <br />are either stockpiled for future use or redistributed directly <br /> <br />on graded spoil. After the overburden and coal removal stages, • <br />the resulting spoils are graded to approximate original <br />contour, topsoiled, and seeded. <br />Normally, area surface mining is restricted to coal reserves <br />which lie in a relatively level plane below a level or gently <br />rolling surface terrain. However, at Seneca fI the geologic <br />structure is such that the coal seam outcrops at the top of the <br />mountain and dips at approximately 18 to 25 percent while the <br />overlying surface dips at approximately 18 to 20 percent. This <br />does present a fairly constant overburden thickness ranging <br />from approximately 15 to 140 feet which lends itself to area <br />surface mining. The relatively high angle of dip on the. coal <br />seam and surface requires some modification of what would be <br />considered a conventional area mining pit progression. This <br />modification will be detailed later in this section. <br />2.05.2(1) A general discussion of the engineering techniques utilized in • <br />the development of an area surface mine must begin with the <br />exploratory phase. After the initial discovery of a potential <br />12-2 Revised 8/27/86 <br />