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' Page 7,CAP,ARCO ruuii m in As noted in section 2 4, the vapor extraction test conducted in 1993 indicated that this site is ' amenable to vapor extraction Although a silt layer is present from the surface to a depth of approximately 15 feet, little contamination has been detected in this interval Any hydrocarbons that cannot be removed by vapor extraction will likely remain relatively immobile and pose little ' threat to groundwater Most of the contamination is restricted to the sand layer between 20 and 35 or 40 feet, which has sufficient porosity and permeability for effective vapor extraction ' Although vapor extraction will not remove diesel, diesel has not been detected in the vadose zone at this site 1 ' 5.4 REMEDIATION PLAN ' The high vapor concentrations and substantial flow rates obtained during the vapor extraction test indicate that either a thermal oxidizer or an internal combustion engine would be the most appropriate destruction unit for this site Due to the site's location at a busy intersection near the University of Pacific campus, the lower noise level and somewhat lower maintenance requirements of a thermal oxidizer make it preferable to an IC engine Initially, extraction will be from well VW-1 only Flow rates in the 75-150 cfm range are anticipated Additional extraction wells will probably be added to the system after several months of operation, so the capacity of the oxidizer should be sufficient to allow vapor ' withdrawal from three to five wells simultaneously The unit will not be equipped with an air sparging blower, although one may be added at a later date if groundwater remediation is deemed necessary The unit will be located on the southwestern part of the property, west of the tank cavity ' Depending on its size, it could be located either east or west of the concrete-block retaining wall It will be secured with safety fencing ' Well VW-1 will be connected to the extraction unit with 2-inch diameter PVC piping, which will be located in a shallow trench in the asphalt surface VW-1 will be equipped with a vacuum gauge and a sampling port to allow monitoring of vapor concentrations Monitoring will be performed weekly, and inlet and exhaust vapor samples will be collected at the beginning of the extraction period and at least once quarterly thereafter Vapor samples will be analyzed for total ' petroleum hydrocarbons (TPH-g) and volatile aromatic hydrocarbons (BTE&X) and compared to PID readings collected weekly Remedial activities will be reported quarterly to EF ID