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WrerINTSIC.C. SACRAMENTO soil will be piled on polyethylene sheeting as it is removed from the excavation. Additional noncontaminated soil will be removed as required to maintain the integrity of the excavation side walls and later used as fill . Adequate shoring of the excavation will be maintained to ensure the integrity of the surrounding structure and the sidewalls of the hole throughout the duration of the excavation phase. The goal of the excavation will be to remove all diesel contaminated soil with concentrations greater than 100 mg/kg TPH. However, if either the facility or a buried underground transmission cable in front of the facility are threatened, a revised cleanup threshold level may need to be applied. The revised cleanup level (i .e. , 500 mg/kg TPH) will be applied to these areas without compromising either the facility or the cable. The excavation cross section is shown in Figure 5-2. Upon completion of the excavation, the pit will be filled. Fill material will consist of imported drain rock and imported soil in addition to the removed noncontaminated soil at the site. The soil will be compacted to 95 percent using a hydraulic compactor. Subsurface lines will be restored and the surface returned to the original grade. 5.4 Remediation Alternatives Upon completion of the excavation phase, two remedial action alternatives are suggested. The first would involve bioremediation of the diesel - contaminated soil on site. The second alternative would entail removal and off-site disposal of the untreated contaminated soil . 5.4.1 Bioremediation Bioremediation entails the use of naturally occurring bacteria to consume 1 the hydrocarbon contamination in the soil , leaving water and carbon dioxide as end products. The following activities would be involved with bioremediation of the diesel contaminated soil using the "land farming" technique. 15 1