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• acres of final graded spoil in the Yolf Creek area es shown on Exhibit 92.2, Soil end Spoil <br />Monitoring Mep. Soil was also exported from Sites AA and HH to 24.0 acres of final graded <br />slopes in the Yadge area es shown on Exhibit 92.2. The soil reserve et the remaining 11 <br />stockpiles did not Change. Approximately 401.3 acre-feet of soil was stockpiled as of <br />December 31, 1992. <br />Soil Redistribution Thickness. The mean soil redistribution thickness is calculated by <br />comparing the disturbance area that requires soil replacement as of December 31, 1992 with <br />the soil reserve in stockpiles end soil to be selvaged ahead of mining. The disturbance <br />area was determined from the 1991 Soil Balance Plen (Exhibit 91.3), the October 11, 1992 <br />black and white 1" = 400' scale aerial photograph, end on-site field checks. The <br />disturbance area requiring soil replacement es of December 31, 1992 totals 675.8 acres <br />(Table 92.2). <br />There are 762.6 acres of land that ere ar will be disturbed by mining which will receive <br />replaced soil from January 1, 1993 through 1998 (final reclamation year, Seneca II Mine, <br />Exhibit 13-2, Reclamation Flen). As of December 31, 1992, there was 401.3 acre-feet of <br />• stockpiled soil and 173.9 acre-feet of soil remaining to be selvaged (Table 92.2). By <br />dividing the number of acre-feet available soil (575.2) by the number of acres of projected <br />disturbance (762.6), it is estimated 0.8 feet of suitable soil is available to be replaced. <br />The average thickness of replaced soil is likely to exceed 0.8 feet as the stockpiled soil <br />swells during redistribution. Field studies (1979) from Seneca it Mine indicate fine sandy <br />loam, loam, and silt loam textured soil may shrink (compact) from 21 to 28 percent when <br />atockpi led. Soil replaced from stockpiles et Big Sky Coal Company's Big Sky Mine in <br />southeastern Montana during 1991 swelled 15.2 percent during replacement (BSCC, 1993). The <br />soil replaeement thickness (0.8 feet), determined from the annual soil balance, is similar <br />to previous projected soil replacement thicknesses determined in March 1991 (0.9 feet) and <br />Msrch 1992 (0.8 feet). <br />Soil Reolacement Technique. Soil replacement areas for the 1992 field season are shown on <br />Exhibit 92.2, Soil end Spoil Monitoring Mep. Historical soil replacement areas for the <br />1977 through 1992 field seasons ere shown on Exhibit 92.4, Chronological Soil Replacement <br />Mep. One reclamation block in the upper Yolf Creek eree totalling 11.7 acres was reclaimed <br />during 1992 using direct haul soil. The remaining reclamation blocks, three in the Yolf <br />• Creek eree and five in fhe Yedge eree, were reclaimed using stockpiled soil from Sites AA, <br />EE, MX, and JJ. The soiled areas ere identified on Exhibit 92.2. <br />5 <br />