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Former Discovery Chevrolet June 5, 1998 Tracy, California Corrective Action Plan 6.2.1 Description of Remedial Work - Soil Excavation and disposal of the hydrocarbon-impacted soil involves the removal and disposal of soils containing benzene above the TCL of 5 ppm in soil. The excavation operations would involve soil removal, and the options of disposal or aboveground onsite treatment, along with replacement of surface materials, such as asphalt and concrete. As indicated in Figure 4, Horizon estimates that approximately 450 cubic yards of soil will be excavated. Excavated overburden soil will be stockpiled separately from the excavated hydrocarbon-impacted soil at the site. After confirmation laboratory testing, the overburden soil that has not been impacted by hydrocarbons would be utilized as backfill materials. The excavated hydrocarbon-impacted soil would then either be transported from the site for immediate disposal at a selected landfill, or the excavated hydrocarbon-impacted soil would be spread on an impermeable surface, such as asphalt, concrete, or plastic, in thicknesses of approximately 12 to 18 inches to allow removal of hydrocarbons through volatilization. The spread soils would then be periodically turned and mixed by a backhoe or equivalent piece of equipment to maximize surface exposure and aeration to the warm summer air. Naturally occurring microbes present in the soils should also convert both volatile and nonvolatile hydrocarbon components into primarily carbon dioxide (CO2) and water. After field evaluation of the aerated soil indicates concentrations of hydrocarbons have decreased or are no longer present, the collection of soil stockpile composite characterization samples for laboratory analysis will be performed to verify the concentrations of gasoline hydrocarbons remaining in the soil, if present. The composite characterization soil samples will be collected from the stockpiled soil by selecting random locations accessible around the soil pile, removing approximately six inches of soil, and driving a clean brass sleeve into the soil pile at the selected location. The number of samples collected will be based on the r V �ted amount of stockpiled soil. Generally, one composite soil sample is collected per 5.0 or- 0 cubic yards of soil. All samples collected will be prepared and chilled for is< ' transport under Chain-of-Custody protocol, and sent to a State-certified laboratory for the 3001-21.cap 17 HORIZON ENVIRONMENTAL INC.