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GEORGE DEUKMEJIAN,Governor <br /> STATE OF CALIFORNIA <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br /> CENTRAL VALLEY REGION <br /> 3443 ROLITIER ROAD j <br /> SACRAMENTO,CA 95827-3098 <br /> 4 January 1990 JAPE 5 <br /> PERM IT/,SLqv' <br /> Ms. Diane Hinson <br /> Supervising REHS <br /> Environmental Health Division <br /> San Joaquin County Department of Public Health Services <br /> P.O. Box 2009 <br /> Stockton CA 95201 <br /> SOUTHLAND CORPORATION, 7-ELEVEN STORE, 9110 THORNTON ROAD, STOCKTON - NOVEMBER <br /> QUARTERLY UPDATE, AND WORK PLAN FOR UPGRADING EXISTING VAPOR EXTRACTION SYSTEM <br /> We have reviewed the 2 November 1989 Quarterly Update Report, and the proposed <br /> Work Plan for Installation and Operation of Vapor Extraction System prepared <br /> by Ground Water Technology, Inc. , for this site. <br /> Ground water elevations in the Stockton area have continued to decline during <br /> the reporting period. Many of the existing monitoring wells are now dry or <br /> contain too little water for obtaining representative ground water samples. <br /> Although the on-site ground water extraction system is still in operation, <br /> production has diminished and the contaminant concentrations in the recovery <br /> well are very low. Based on the analytical results from sampling the shallow <br /> and deep on-site wells, hydrocarbons do not appear to have migrated to the <br /> deeper aquifer zones. Therefore, it does not appear practical to install <br /> deeper extraction wells. Expansion of the vapor extraction system appears to <br /> be the most effective remedial alternative available at this time. <br /> We recommend the proposed work plan for expanding the vapor extraction system <br /> be approved. Once the expanded system is in operation, the operator should <br /> provide monthly progress reports documenting the performance of the system. <br /> If you have any questions, please call me at (916) 361-5731 . <br /> THOMAS D. PELTIER <br /> Engineering Geologist <br /> TDP/tdp <br />