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ERI 205505 R02 Tosco Service Station 5886,Stockton,California September 25 2001 <br /> 43 Periodic PurgIng of Impacted Groundwater <br /> Since second quarter 2000, Phillips has been purging groundwater from the UST cavity well and <br /> groundwater monitoring well MW3 To date, 201,000 gallons of groundwater have been purged from <br /> beneath the site and transported to the Phillips refinery in Rodeo, California, for disposal The volume <br /> of hydrocarbon mass removed during purging has not been calculated However, dissolved MTBE <br /> concentrations have decrease in groundwater samples collected from well MW3 since groundwater <br /> j� purging was initiated (Appendix C) While groundwater purging has successfully removed impacted <br /> groundwater from the vicinity of the UST cavity, it does not address hydrocarbon-impacted <br /> I� groundwater that may be migrating downgradient In addition, remediation goals could be reached in a <br /> timelier manner using a more aggressive remediation approach <br /> 44 Ozone Micros ar in <br /> Ozone microsparging is a remedial technology that has demonstrated encouraging results in removing <br /> volatile organic compounds (VOCs) (including MTBE) from groundwater Microsparging is a process <br /> ozone and air are injected into the groundwater through very fine porous plastic sparge <br /> by which 1 <br /> points The very fine ozone and air bubbles diffuse into the formation and strip VOCs from <br /> groundwater by rapid oxidation as they rise through the groundwater column In addition, the ozone <br /> not consumed in the oxidation process decomposes to oxygen, which benefits natural biological <br /> ' degradation Based on the distribution of dissolved MTBE in groundwater in the vicinity of the UST <br /> cavity and the ROI of SVE demonstrated during the ASISVE feasibility study, ERI concludes that <br /> ozone microsparging is an effective remediation alternative for this site <br /> 5 0 RECOMMENDED CORRECTIVE ACTION <br /> ERI recommends the installation of an ozone microsparging groundwater remediation system for the <br /> site The proposed remediation system is intended to provide treatment of hydrocarbon-impacted <br /> groundwater beneath the site in the vicinity of and downgradient of the UST cavity, in a timely and <br /> cost-effective manner ERI recommends operation of the ozone microspargmgs system until dissolved <br /> hydrocarbon and MTBE concentrations decrease to asymptotic levels At that time, ERI will evaluate <br /> the site for case closure <br /> i <br /> 1 <br />