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Section 780.18 (b) Continued. <br /> <br />sufficient size to allow for safe working conditlons within the <br />pit. In this case, where the maximum economic pit depth is 265 <br />feet, the working face (where overburden and coal are being re- <br />mpved) moat be no steeper than 10 percent to be within the safety <br />limits of the scrapers and haul trucks. Therefore, as shown on <br />Figure 33, Typical Steady State Pit, the length of the working face <br />from natural ground level to the pit bottom is approximately 2,650 <br />linear feet. Por the same reasons as above, the backfill face <br />(where removed overburden is being replaced) must be no steeper <br />than 10 percent or also 2,650 linear feet. A 300 linear foot <br />buffer zone is provided in the pit bottom (between the working face <br />and the backfill faEe) to assure that recoverable coal is not <br />covered by backfilling operations, and to allow enough room to <br />safely maneuver equipment in the pit bottom. Given the above <br />constraints, the required pit length will be approximately 5,600 <br />linear feet. <br />The highwalls on either side of the pits have been designed by CTL <br />Thompson, Inc. (See Exhibit 43, Analysis of Pit Wall Stability) to <br />provide the optimum combination of safety and coal recovery. In <br />Figure 32, Typical Pit Cross-Section, two 25 foot wide benches are <br />provided on the west pit wall to catch any material which might <br />slough off the highwall, and to prevent any sloughed material from <br />collecting and thus contaminating the coal. The east highwall has <br />a series o£ 40 foot wide benches which serve to stabilize the high- <br />wall, to catch slough material, and to provide haulage ways far <br />overburden haulage between the working and active faces. The pit <br />width varies slightly with an average width of approximately 750 <br />feet. <br />The constraints of open pit mining of the type described above and <br />as visually depicted on Figure 33, Typical Steady State Pit, and <br />Figure 32, Typical Pit Cross Section, dictate that the area of open <br />pit be at Least 100 acres at any •given time. The volume of over- <br />780-61 <br />