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Multi-Phase Extraction Pilot Test Report& Remedial Design Thrifty station No 171 Stockton,California Page 6 November 30,2010 The significant concentrations of hydrocarbon constituents observed during the pilot test indicated that continued use of a multiphase extraction system to be an appropriate remedial option for the site. The addition of a groundwater treatment system, allowing discharge to the Iocal sewer system, will be necessary to accommodate increased groundwater production and will be more economically feasible then the previous method of offsite disposal of extracted groundwater. 2.4 Waste Management Fuel-hydrocarbon soil vapor recovered during the pilot test was thermally combusted onsite and exhausted to the atmosphere in compliance with air permit requirements. Extracted groundwater was held in an onsite storage tank, tested for compliance with the discharge permit from the City of Stockton, then discharged to the sanitary sewer after onsite City inspection and analytical results of treated groundwater confirmed compliance with discharge permit limits. 3.0 REMEDIAITON SYSTEM MODIFICATION Multi-phase pilot testing indicates multi-phase extraction to be an effective option for the remediation of hydrocarbons from subsurface soil and groundwater. In order to maximize hydrocarbon removal from the site, Environ Strategy recommends modifying the existing remediation system with an onsite groundwater treatment system for the treatment of extracted groundwater from wells EW-5D,EW-5S,and TB-7, and discharge to the sanitary sewer system. In order to add a groundwater treatment system component to the existing remediation system without building a larger remediation compound, it is recommended that two carbon treatment vessels, one 2,000 pound vessel, and one 1,000 pound vessel, be installed in the existing remediation compound along with a holding tank, transfer pump, and control panel. Three thousand pounds of carbon treatment is proposed to reduce influent groundwater hydrocarbon constituents to levels required by City discharge permit limits. The groundwater treatment system component would include the addition of • One 2,000 pound liquid phase carbon vessel. • One 1,000 pound liquid phase carbon vessel. • One 300 gallon holding tank with high/high,Iow/high and low/low water level sensors. • One 3/a hp transfer pump to transfer extracted groundwater from the holding tank through the carbon vessels and to the sanitary sewer discharge line. • One control panel for the control of the transfer pump. environ strategy consultants, inc.�