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`low, N"ar CitofogluI Tecluucs fisc. Page 6 Interim Remedial Action Plan Project No.723.2 March 7,2005 3.1.2 Treatment System—Dual Phase High Vacuum Extraction Soil vapor and groundwater extraction are two proven technologies for the remediation of gasoline impacted sites. Dual phase extraction involves the use of both technologies simultaneously from one well - extracting groundwater induces a cone of depression that exposes more impacted soil to vapor extraction. This technology was utilized during a pilot test on the site during July 26 — 31, 2004. GTI proposes to use similar equipment to perform soil vapor and groti a beneath the soil dispenser area. The 4" diameter extraction wells will belfitted with 1" PVC' Ming that will be plumbed via underground conveyance piping to a treatment compound on the central portion of the site. Vapors and groundwater will be removed from the extraction well using the vacuum pump capable of producing >21 inches of mercury vacuum. The stingers will be adjusted to a depth that promotes maximum groundwater extraction rates without "deadheading" (i.e.- losing vacuum in) the piping. During the pilot test an optimum level of 47 feet was discovered for well EW-1 that produced a consistent 3 gallons per minute (gpm). An optimal stinger depth will be determined for both VEW-1 and VEW-2 as well to produce maximum extraction rates without losing vacuum to one or more of the three wells. Once the vapor/groundwater is extracted it will be separated in a liquid ring pump with the vapor phase treated by thermal oxidizer and the liquid phase treated by air stripping/carbon filtration. 3.1.2.1 Vapor Treatment—Thermal Oxidation A thermal oxidizer will be used to treat the extracted vapors (this is standard equipment and further elaboration is not necessary here) prior to discharge to the atmosphere. A permit will be obtained from the San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD) for the operation of the unit. 3.1.2.2 Groundwater Treatment &Air Stripper Effluent- GAC The extracted groundwater is stored in a tank after separation in the liquid ring pump. The water will be pumped to an appropriately sized air stripper (this is standard equipment and further elaboration is not necessary here) to remove volatile organic compounds. The vapor and water streams from the air stripper unit will both be treated by granular activated carbon (GAC) filtrati&. The vapor treatment by carbon filtration will require a second permit from the SJVUAPCD. The water will be plumbed from the carbon units for discharge to the City of Stockton publicly owned treatment works (POTVA This will require a permit from the OMI Thames Water organization, a third party that manages discharges to the City of Stockton Municipal Utilities Department, Regional Wastewater Control Facility. System Design A tentative schematic illustrating the likely layout of the treatment system components is included as Figure 6. The layout is subject to changes or modifications due to line/plumbing requirements for PG&E gas, electric, sewer discharge and underground utilities. Since the USTCFP requires that three bids be evaluated - the size, the locations and components of the