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Former Discovery Chevrolet March 20, 1998 <br /> Tracy.California Problem Assessment Repo <br /> 7.0 REMEDIATION ALTERNATIVES <br /> 7.1 Soil <br /> The following soil remediation alternatives are discussed in this section: <br /> • Passive Remediation <br /> • In-Situ Vapor Extraction <br /> • Excavation and Disposal <br /> • Excavation and Aboveground Treatment <br /> 7.1.1 Passive Remediation <br /> Passive remediation involves allowing the petroleum hydrocarbons to remain in the <br /> subsurface soil while leaving the site surface unaltered. Natural volatilization and <br /> degradation can be expected to reduce petroleum hydrocarbon concentrations through time. <br /> 7.1.2 _In-Situ Soil Vapor Extraction <br /> In-situ soil vapor extraction utilizes soil vent wells to remove organic vapors from the <br /> subsurface. The air streams drawn from soil vent wells contain petroleum hydrocarbons that <br /> may be either removed and treated or discharged directly to the atmosphere, depending on <br /> local air pollution control district requirements. Rates of extraction vary with moisture <br /> content, permeability, and consistency of subsurface soils. The soil type that is present <br /> beneath this site (silty clay and clay) in which the gasoline hydrocarbons are present is <br /> usually not conducive to vapor extraction. <br /> 7.1.3 Excavation and Disposal <br /> This alternative involves the removal and disposal of all soils containing petroleum <br /> hydrocarbons above acceptable concentrations. Excavation would involve removal, <br /> disposal, and replacement of site surface material consisting of asphalt and concrete. <br /> Excavated soils would be manifested and transported by a licensed contractor to a Class I or <br /> II landfill, or possibly for thermal destruction. Clean imported material would be used to <br /> backfill the excavation. <br /> 1 <br /> 3001-12.par 12 HORIZON ENVIRONMENTAL INC. <br />