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1 <br /> 5 3 7 Excavation to 1 000 mg/kg and Off-Site Disposal - Option 6b <br /> Option 6b was developed to demonstrate the relative cost-effectiveness of ex-situ options <br /> compared to in-situ options with a similar cleanup goal This option is considered comparable <br /> in terms of contaminant mass reduction to Option 5, and consists of excavation of impacted soils <br /> and off-site disposal with a final cleanup goal of 1,000 mg/kg Based on site investigation data, <br /> it is estimated that approximately 4,900 cubic yards (6,400 tons) of soil contain concentrations <br /> of hydrocarbons in excess of 1,000 mg/kg Based on the spatial distribution of the impacts, it <br /> is estimated that the total excavated volume would be on the order of 37,000 cubic yards (48,000 <br /> tons), assuming excavation to 35 feet bgs and no shoring Again, shoring is assumed to be cost- <br /> prohibitive, and the location of the clean soil stockpile has not been considered Significant <br /> amounts of dust could be generated by the estimated 325 haul truck trips in and out of the site <br /> As with Option 6a, clean soils would be separated from impacted soils during excavation <br /> based on visual assessment and/or field screening Impacted soil would be loaded onto trucks, <br /> sampled for waste characterization purposes, and hauled to an off-site disposal/recycling facility <br /> (assumed to be the Forward, Inc facility in Stockton, California) <br /> Confirmation soil samples would be obtained f$rrm�the sidewalls and bottom of the <br /> excavation for analytical testing to determine whether the cleanup level has been achieved Once <br /> excavation is complete, the clean soil would be systematically replaced in lifts and compacted <br /> Clean import material would be brought from off-site as needed until the entire excavation is <br /> filled <br /> Option 6b also includes quarterly monitoring of groundwater elevations in on-site <br /> monitoring wells (including the new well to be constructed in 1994), annual groundwater <br /> sampling and analysis of the five wells, and preparation and submittal of annual monitoring <br /> reports to the PHS/EHD and RWQCB for a penod of five years following soil remediation <br /> Analytical testing of groundwater samples would include TPH/D and BTEX <br /> 5 3 8 Excavation to Back round Concentration and On-Site Thermal Treatment - <br /> Option 7a <br /> Option 7a consists of excavation of impacted soils and on-site thermal treatment to <br /> remove and destroy the hydrocarbons The assigned cleanup level for this option is non-detect <br /> SAC127 10 18 <br /> DAMns & MooRE <br />