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GROUNDWATER REMEDIATION FEASIBILITY STUDY VALLEY MOTORS 800 East Main Street Stockton, California INTRODUCTION Investigation of soil and groundwater contamination at 800 East Main Street(Figure 1) began in 1994.. By the end of 2003,the investigation phase was largely complete,and a Problem Assessment Report and Soil Remediation Plan was prepared. Soil remediation began in 2005 and continued through 2006,and although soil vapor concentrations of gasoline-range hydrocarbons were reduced,quarterly groundwater monitoring showed no evidence of improvement in groundwater quality. Therefore,the San Joaquin County Environmental Health Department(SJCEHD)directed Valley Motors to evaluate additional remedial methods to address the groundwater contaminationproblem. A pilot test of air sparging was conducted in 2007,and the results indicated that this technology would not be successful at the site. In the subsequent report,Upgradient Environmental Consultants listed five options for SJCEHD to consider,and the regulatory agency directed Valley Motors to prepare a feasibility study that evaluates at least two remedial methods. The two methods that Upgradient Environmental has chosen to evaluate are groundwater extraction and in-well air stripping. As directed by SJCEHD,the methods are compared in terms of their cost and effectiveness. GENERAL DESCRIPTION OF THE TWO METHODS Groundwater extraction utilizes pumps placed in specially designed wells to pump contaminated groundwater to the surface,where it is treated in som, type of treatment unit and then discharged to the sanitary sewer or storm drain under permit.Canisters or larger vessels containing a filter material, such as granulated activated carbon(GAC), are commonly used as the treatment unit if hydrocarbon concentrations are fairly low, but GAC can become expensive if concentrations are high and the GAC must be frequently replaced. In such cases,other,more complicated methods, such as above-ground air stripping towers, are used for treatment. These towers disperse the water into a fine mist, where it passes through a series of"trays"that separate out the hydrocarbons from the water droplets. The hydrocarbons,then in vapor phase,are vented to the atmosphere if the concentration are within Air Quality district standards or are piped through a second treatment unit that burns or absorbs the vapors. The cleaned water is then discharged to the sewer or storm drain. In-well air stripping utilizes some of the same principles as above-ground air stripping, but in this method the stripping unit is a small device that can be fitted down a.special well. A small pump is placed below the stripping device to pump groundwater upward, 1