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—Emayation Backfilling The excavations will be backfilled immediately after the confirmation sampling and analysts have been completed As noted earlier, any clean material that is excavated will be stockpiled for reuse as backfill ' The remaining area of the excavations will be backfilled with clean, certified backfill An estimated 500 to 1000 cubic yards (cyds) of backfill will be delivered to the site and stockpiled in the vicinity of the proposed excavation areas prior to the start of the excavation The excavations will be backfilled in 6 to 8-inch lifts, and compacted with a small steam roller3 The soil will be compacted to 90% to prevent excessive settling The soil compaction will be verified with a nuclear density gauge during the backfilling operations Soil Aclation The proposed aeration treatment area is shown on Figure 5-1 This area has been selected because it will minimize the impact on traffic flow around the property The area is covered with asphalt pavement The asphalt will serve as the impermeable layer to separate the affected soil from underlying clean soils The pavement will be inspected prior to the start of the excavation/aeration activities to ensure that it is in good repair If not, the proposed area may be relocated to another portion of the site, and/or may be lined with HDPE to create an impermeable layer The excavated soil will be transported to the proposed area as it is being excavated, and spread out in a layer approximately 8 inches deep The perimeter of the excavated soil will be secured with straw bales The aeration area will be fenced in with a portable fence, and posted against unauthorized entry The average concentration of volatile organic constituents, including ' gasoline, is estimated to be less than 500 mg/kg (ppm) This estimate will be confirmed with the excavation confirmation sampling data Therefore, consistent with APCD requirements4, 120 cyds of soil will be ' added daily to the soil actively being aerated Based on the expected volume of affected soil, the total mass of affected soil would therefore be subject to active aeration within five to ten days of the start of the 1 aeration process Once the total mass of affected soil is being aerated, the soil will be turned continuously for eight hours per day, five days 3 Because of the small area of the proposed excavations, conventional equipment would be too large 4 For concentrations between 101 and 500 ppm,the APCD allows aeration of 120 cyds per day 5-5