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• Revised 04/20/90 Section 780.11(a] Continued. be no steeper than 10 percent or also 2,650 linear feet. A 300 linear foot buffer zone is provided in the pit bottom (between the working face and the backfill face) to assure that recoverable coal is not covered by backfilling operations, and to allow enough room to safely maneuver equipment in the pit bottom. Given the above constraints, the required pit length will be approximately 5,600 linear feet. The highwalls on either side of the pits have been designed by CTL Thompson, Inc. (See Exhibit 43, Analysis of Pit Wall Stability) to provide the optimum combination of safety and coal recovery. In Figure 32, Typical Pit Cross-Section, two 25 foot wide benches are • provided on the west pit wall to catch any material which might slough off the highwall, and to prevent any sloughed material from collecting and thus contaminating the coal. The east highwall has a series of 40 foot wide benches which serve to stabilize the highwall, to catch slough material, and to provide haulage ways for overburden haulage between the working and backfill faces. The pit width varies slightly with an average width of approximately 750 feet. The constraints of open pit mining of the type described above and as visually depicted on Figure 33, Typical Steady State Pit, and Figure 32, Typical Pit Cross-Section dictate that the volume of overburden that must be removed and stored or replaced outside of the active mining area to accommodate the open pit is approximately 8,200,000 bank cubic yards. Sample calculations relating to this volume can be found in Exhibit 50, Overburden Volume Calculations. _~ As depicted by Map 33, Kerr Mine Area Overburden Replacement and Grading, all remaining overburden to be removed from Pit 1 rill be direct hauled within the pit and backfilled into the south end of Pit 1.