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2905 West Benjamin Holt Drive, Stockton, California March 16, 1994 <br /> Chevron U.S.A. Products Company Page 12 <br /> and groundwater. Airsparging also improves mixing and ox <br /> ygenation in the saturated zone which <br /> enhances the natural biodegradation of hydrocarbons. In addition, hydrocarbons dissolved in <br /> groundwater are stripped from the water during air sparging. Air sparging is Implemented in conjunction <br /> with soil vapor extraction which captures the hydrocarbon vapors. Lithologic data collected during <br /> preliminary investigation at the site indicates that air sparging is a technically feasible alternative for <br /> remediation of hydrocarbon-impacted material at the site, however, further testing would be required. Air <br /> sparging with soil vapor extraction can be more effective than soil vapor extraction alone, since both <br /> unsaturated and saturated zones are treated directly and mass removal rates tend to be much higher. <br /> In order to implement this corrective action alternative, further assessment and continuation of the <br /> groundwater monitoring and sampling program would be required. Assessment would include the soil <br /> vapor extraction testing mentioned in section 4.4, installation of an air sparge test well, and air sparge <br /> testing. Further definition of hydrocarbon-impacted soil on site would enhance the implementation of <br /> this alternative. <br /> An air sparge test well would be installed in the vicinity of the former UST pit where the highest dissolved <br /> hydrocarbon concentrations have been observed. An air sparge test would be conducted by injecting <br /> air through the well and monitoring induced pressure, depth to water, dissolved oxygen and <br /> hydrocarbon vapor concentration at the surrounding groundwater monitoring wells. Measurements <br /> obtained during testing provide information regarding the attainable radius of influence of air sparging, <br /> optimum injection pressure and flow rates for an air sparge system. The results of air sparge testing <br /> would be compared with those from soil vapor extraction testing to evaluate the synthesis of the two <br /> remediation technologies. <br /> Upon analysis of pilot test results, a work plan detailing the steps required to install and implement a <br /> combined air sparging/soil vapor extraction system at the site would be submitted to SJCPHS and the <br /> CRWQCB-CVR for approval. <br /> 5073PAR,RPT GROUNDWATER <br /> 1 TECtiNOL OGY <br />