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Soil Redistribution Thickness. The mean soil redistribution thickness is calculated by • comparing the disturbance area that requires soil replacement as of December 31, 1990 with the soil reserve in stockpiles and soil to be salvaged ahead of mining. The disturbance area was determined from the 1989 Topsoil Balance Plan Mep (PCC, 1990), the 1990 Annual Reclamation Report (Exhibit 90.1), the December 11, 1990 black end white 1"=400' scale aerial photograph, end on-site f ield checks. The disturbance area requiring soil replacement es of December 31, 1990 totals 659.4 acres (Table 1). There are 772.2 acres of land that is or will 6e disturbed by mining which will receive replaced topsoil from January 1, 1991 through 1998 (final reclamation year, Seneca fI Mine, Exhibit 13-2, Reclamation Plan). As of December 31, 1990, there was 492.8 acre- feet of stockpiled topsoil and 237.1 ecr a-feet of soil remaining to be salvaged (Table 1). By dividing the number of acre-feet available topsoil (729.9) by the number of acres of projected disturbance (772.2), it is estimated that 0.9 feet of suitable topsoil will be replaced. The average thickness of replaced soil is likely to exceed 0.9 feet as the stockpiled soil swells during redistribution. Previous field studies from Seneca II Mine indicate fine sandy loam, loam, and silty loam textured soil may shrink (compact) from 21 to 28 percent when stockpiled. The soil replacement depth (0.9 feet), determined from the • annual soil balance, is slightly less than previous projected soil replacement depths determined in July 1984 (1.0 feet), August 1986 (1.0 feet), January 1988 (1.1 feet), Aprit 1989 (1.1 feet), and April 1990 (1.0 feet). Soil Reolacement Technique. Soil replacement areas for the 1990 field season are shown on Exhibit 90.1, 1990 Annual Reclamation Report. Historical soil replacement areas for the 1977 through 1989 field seasons ere included with two previous Topsoil end Spoil Nonitoring Reports for Seneca II Mine (PLC, 1989 end PCC, 1990). Stockpiled soil, hauled from Sites P and 2, was used to reclaim 85.6 acres of final graded spoil during this report period. An additional 30.7 acres were reclaimed using direct haul topsoil. The topsoiled areas are identified on Exhibit 90.1. Summary. The soil replacement thickness for the remaining permit terms was projected to be 1.0 feet (Permit L•80-005, Tab 9, Attachment 9-4). The balance completed above shows that et least 0.9 feet of soil will be available to be replaced. Peabody suspects the ~- mean soil replacement depth for 1990 exceeded 1.0 feet and caused the existing • infinitesimal difference between pre-disturbance projected and post-disturbance actual soil redistribution thickness. This assumption will be verified during the 1991 field 3 1990 AP~~