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6425 Pacific Avenue <br /> Page 3 <br /> Unfortunately, due to the continued migration of the groundwater petroleum hydrocarbon <br /> plume it may be necessary to install an additional off site well between MW 11 and MW 12. <br /> Once this evaluation period is completed, PHS/EHD will review site conditions to determine <br /> the necessity of an additional off site monitoring well. <br /> PHS/EHD concurs that retrofitting of MW2 for air sparging should provide an adequate <br /> upgradient source of oxygen to enhance the biological degradation of petroleum hydrocarbons <br /> that continue to impact the groundwater. Since MW2 is a part of the vapor extraction <br /> system, it will be modified so that while the well is being sparged, it will not undergo vapor <br /> extraction. Also, WEGE indicated that approximately one week prior to the groundwater <br /> sampling event, that the sparging will be stopped and vapor extraction started to remove any <br /> pressure and vapors that may have accummulated in the well. Please expand the scope of the <br /> dissolved oxygen monitoring that has been proposed in association with the addition of ORC <br /> socks into MW12. <br /> Through December 19, 1995, approximately 12,046 gallons of gasoline range hydrocarbons <br /> have been removed from the soil and groundwater beneath the site. Gasoline range <br /> hydrocarbons were removed through free product and condensate recovery, through vapor <br /> extraction, and through bioventing. As remediation should be entering into the final stages, <br /> consideration should be given to the initiation of confirmation soil sampling. <br /> Please contact Mary Meays at (209) 468-0337, if you have any questions, comments, or wish <br /> to schedule a site inspection. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> Mary Meays, Senior REHS Margarets agorio, REHS <br /> Site Mitigation Unit Lead Senior <br /> MM\6425PACI <br /> c: Elizabeth Thayer, CVRWQCB <br /> c: Wendy Cohen, CVRWQCB <br /> c: George Converse, WEGE <br /> c: Wilbur Smith, Lincoln Properties <br />