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I backfilled with the remaining 150 cubic yards of soil containing less than 100 mg/kg TPH The soil 16 backfill was placed and compacted in 12-inch lifts to an average relative compaction of 95% 1 An asphalt cap was then constructed over the excavation area The old maintenance building pad 1 was cut down to the new subgrade and a four-inch thick layer of asphaltic concrete was placed and compacted The new cap was constructed flush against the old pavement and a one-inch asphalt overlay 1 was applied around the perimeter cap and feathered over the edge of the old pavement 4 2 4 S-Qtl Treatment 1 Approximately 2,500 cubic yards of excavated soils were treated in an aboveground 1 bioremediation treatment facility, constructed on a large paved area approximately 1,000 feet to the north of the excavation The Soil Remediation and Groundwater Monitoring Work Plan (Dames & Moore, April 1990) contains all details of soil amendments, water, and tillage activities which were conducted 1 Soils were treated for approximately 5 months, from mid-June until late November, 1990 to fully utilize the warm summer temperatures to accelerate biological activity and degradation of TPH Following this treatment period, soil chemical analysis met the requirements for disposal at a Class II landfill, and therefore the soil was transferred to the landfill in late November 1990 The details of treatment cell construction, operation and maintenance of the treatment cell, and sampling and analysis of soils during the treatment period are summarized below 1 4 2 4 1 Soil Treatment Cell Construction The soil treatment facility was constructed as described in the Soil Remediation and Groundwater Monitoring Workplan (Dames & Moore, April 1990) The original dimensions described in the work plan (230 feet by 195 feet) were modified slightly to the as-built dimension of 175 feet by 215 feet with a capacity of 2090 cubic yards when filled with soil to a depth of 18 inches An additional 77 feet by ' 78 feet expansion cell with a capacity of 467 cubic yards was added to the cell, to accept additional soil Construction of the biotreatment cell was concurrent with excavation activities to allow impacted soil to be excavated, tested and immediately transferred into the biotreatment cell In order to prepare the surface, the asphalt pavement was repaired and patched as necessary to provide a firm, impermeable ' base for the treatment cell Hay bails laid end to end and stacked two bails high formed the perimeter of the treatment cell Geotextile fabric was laid onto the asphalt and then covered with a 10-mil thick high density polyethylene (HPDE) liner which was secured by the hay bales All edges of the liner, and ' any holes or tearing of the liner was sealed using the adhesives and techniques recommended by the SAC36 OM 18 i