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Work Plan-Soil and Groundwater Remediation CSUS Multi-Campus Regional Center,Stockton,CA March 3,2003 Page 6 of 8 j 4.4 OVER-EXCAVATION PROCEDURES Prior to commencement of fieldwork, a tailgate safety meeting will be held and the existing site-specific Health and Safety Plan will be discussed with, and presented to, all crewmembers for their signatures. The excavation contractor will be responsible for maintaining safe excavation procedures and Occupational Safety and Health Administration (OSHA) compliance during all fieldwork. A Condor representative will continually monitor the progress of the over-excavation. Field personnel will'`screen the excavated soil for organic vapors using a photoionization detector (PID). Other field notations will include geologic descriptions,visual observation of petroleum staining, and odor detection. Laboratory results of soil samples indicate that contamination appears to have moved primarily down from the former tank location with some lateral spreading. Based on the extent of hydrocarbon impacted soil shown in Figures 5 through 7, Appendix A, Condor estimates approximately 3,000 cubic yards of hydrocarbon impacted soil with concentrations of TPH-G above 1.0 mg/kg remains.in place at the site. The estimated lateral extent of hydrocarbon contamination in soil covers a lobate shaped area (Figure 3 and Figure 4, Appendix A) approximately 62 feet in length and 42 feet in width with an average depth of 45 feet. M The over-excavation operation would involve the excavation and removal of approximately 8,000 cubic „ yards of soil that includes approximately 2,500 cubic yards of impacted soil from the vadose zone and j another approximately 500 cubic yards of impacted soil from the saturated zone. The actual volume of j the excavation will vary depending on excavation construction, the observed area of contamination, and ! the stability of the subsurface lithology. The presence of buildings to the east and south, fire hydrants to 'v the south, and other utilities may limit the extent of the excavation. Due to the proposed depth'of the 4 excavation and the proximity of buildings to the proposed excavation, shoring of the excavation sidewalls may be necessary to prevent collapse of the excavation walls; however; shoring would add significant cost and is not initially proposed. During the over-excavation, the soil contaminated with petroleum hydrocarbons and soil observed to be relatively uncontaminated overburden would be segregated. The excavation will be backfilled with clean soil removed during the excavation and with clean imported fill. Soil stockpiles will be sampled to clear soil for backfill. a 4.4.1 Soil Verification Sampling Verification samples will be collected from the excavation when it is appears that the contaminated soil has been removed or when the excavation cannot be expanded because of structural or slope stability issues. The site geologist will collect verification samples from the leading edge of the contaminated zone based on visual references and FID measurements Soil samples will be collected from the sidewalls and floor of the excavation, as follows: { . One sidewall soil sample will be collected for each 20 lineal feet of sidewall. It:is anticipated that a minimum of 35 soil samples will be collected from the excavation sidewalls. A minimum of 15 soil samples will be collected from the excavation floor(based-on a 10-foot grid). The sidewall samples will be collected at various depths within the lower half of the excavation and areas of concern. Additional excavation and verification sampling will be conducted, if needed, to identify remaining hot spots. The soil samples will be collected directly from the sidewalls and floor:,of the iexcavation using a rod-mounted sampling tool or from the excavator bucket, depending on access. The �a CONDOR r -