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F <br /> ine hydrocarbons extends to the groundwater surface (approximately 38 I'm below <br /> surface grade), but is confined to a relatively small area. Excavation of soil from this depth <br /> will require unconventional excavation techniques, including shoring or benching. If f <br /> benching is required, a considerable volume of clean soil will be excavated in addition to <br /> the hydrocarbonous soil. In addition, the station building and the remaining underground <br /> fucl-storage tanks are in close proximity to the affected soil. Excavation of soil near these <br /> features will probably require geotechnical engineering and shoring. These requirements <br /> will substantially increase the cost of excavation. The site is an operating firefighting <br /> facility. Deep excavation at the site could require a significant period of time and interfere <br /> rt with activities at the site. Disruption of normal activities at the station may be unavoidable. <br /> In Situ Vapor Extraction <br /> Soil containing volatile hydrocarbons(including gasoline)is commonly remediated by vapor <br /> extraction. A vapor-extraction system consists of vapor-extraction wells,a mechanical device <br /> that produces a vacuum on the wells and exti—ts vapor from the soil, and an emission <br /> control device that reduces hydrocarbon concentrations in the extracted soil vapor before <br /> discharge to the atmosphere. If hydrocarbon concentrations in the extracted soil vapor are <br /> relatively low, discharge to the atmosphere without emission control may be feasible. <br /> Vapor-extraction systems generally require permits by the local Air Quality Management <br /> ti <br /> District. <br /> 4r <br /> APP11dFd 49e0SYS4947.9 <br />