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16. coologica[Teclutkslnc Page 4 Dual Phase Extraction Pilot Test Report Project No.723.2 y November 5,2004 2.3 Extraction Well Survey On August 4, 2004, the three new wells were surveyed in accordance with Geotracker r.. requirements by Thompson-Hysell Engineering of Modesto, CA. L- 3.0 PILOT TESTS 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. GTI utilized the services of Mako Industries (Mako) of Pleasanton, California to provide equipment for the extraction test. Mako provided a portable trailer comprised of a vacuum blower, a liquid ring pump to separate water/soil vapors, a thermal oxidizer to treat extracted vapors, and manifolds to distribute vacuum among various extraction hoses. A Mako subcontractor provided a propane tank for fuel to operate the thermal oxidizer and American Valley provided a trailer for use as an extracted groundwater holding tank. The general process for the dual phase extraction was as follows: _.� ■ Remove vapors and groundwater from the extraction well(s) using the vacuum pump capable of producing >21 inches of mercury vacuum. The vapors and water were drawn out of the well(s) through a stinger set at the desired depth for extraction. �.. ■ The influent vapors and water were separated in a portable vacuum tank. • The contaminated vapors were then extracted through a liquid ring pump and oxidized in a thermal oxidizer. �- ■ Collect data for vacuum flow and contaminant concentrations and temperature. ■ The captured contaminated groundwater was transferred to a storage tank via a high vacuum pump. The storage tank was emptied periodically by a licensed hauler (American Valley) for transportation to a waste disposal facility. GTI installed the extraction wells in their locations for purposes specific to this dual phase test. The location of EW-1 was selected to provide maximum mass removal in the location of the former dispenser island that contains the highest levels of soil contamination. Wells VEW-1 & VEW-2 were necessary because the groundwater elevation has exceeded the screened intervals of all eight of the site's existing monitoring wells for the quarterly events completed since 1998. This required the installation of new extraction wells to measure vacuum influence above the water table. GTI installed the two wells with screened intervals similar to the construction of well EW-1 so they can be used as monitoring points during the pilot tests and can also be used as future soil vapor/groundwater extraction wells. A pre-test depth to water measurement was conducted in well VEW-1 on the morning of July 26, 2004. The test was then started with vapor extraction only from well EW-1 to determine