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' approximately 1,350 yd3; the maximum excavation volume is anticipated to be approximately 1,350 yd3, so the soil mound is of an adequate volume for backfill of the proposed excavation. The soil mound was sampled in previous investigations. A total of 5 soil samples were collected from 3 boring locations by AMEC (GMX-07, GMX-21, and GMX-22; collected in 2001 ' and 2003), and two soil samples were collected from one boring location by Dames & Moore (B-1; collected in 1988). The five AMEC soil samples were found to have concentrations of COCs less than both the residential and commercial/industrial ESLs based on direct contact ' (Table 4). The two Dames & Moore samples were only analyzed for TPH as oil and grease (TPHog), with one sample being non-detect, and one sample having a low detection of 65 milligrams per kilogram (mg/kg) of TPHog. According to the Department of Toxics and rSubstances Control's "Information Advisory—Clean Imported Fill Material" (August 2001), the number of samples and analytical testing methods collected from the soil mound are sufficiently adequate to characterize soil for re-use as backfill. Backfill material will be placed in loose lifts less than eight inches thick and compacted to at least 90 percent of the maximum dry density as determined by ASTM D 698. An AMEC staff engineer will observe placement and compaction of the backfill material and perform density tests at representative locations to confirm that adequate compaction is obtained. The Site will be graded to maintain current ' drainage. Figure 7 shows the potential post-excavation and grading site topography, assuming the maximum excavation is required. 5.2.4 Dust Monitoring During remediation activities, dust control measures will be implemented. These measures include covering soil stockpiles, watering construction areas, and street sweeping. Windscreens will be utilized on the Site perimeter fence in the vicinity of the excavation (in the southwest portion of the Site). Additionally, the contractor will continuously monitor airborne dust at the upwind and downwind site perimeters during all potential dust-generating activities (i.e., operation of heavy equipment, excavation, stockpiling, and loading) using direct-reading instruments (e.g., Mini-Ram pDR 1000TM) for measurement of total suspended particulate matter. Electronic data logs of real-time measurements will be used to determine the maximum and average dust concentrations at the upwind and downwind perimeter monitoring locations. If the daily average from any day exceeds 50 micrograms per cubic meter(pg/m3)1 above upwind concentrations, corrective actions will be taken to increase dust control. No permits or dust control plans are required by the San Joaquin Valley Air Pollution Control District (SJVAPCD), due to the relatively small size of the excavation and grading (<5 acres). ' In accordance with SJVAPCD Rule 8021 — Construction, Demolition, Excavation, Extraction, ' AMEC Geomatrix Inc I:\Doc_Safe\6000s\6628.001\3000 REPORTS\Excavation Work Plan-8.12.08\1 Text,cover and slips\Text.doc 8