SITE INFORMATION AND CORRESPONDENCE

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. V 1419 Charter, Stockton January, 2006 Page 2 Although an estimated 383.7 gallons of gasoline have been removed by the SVE system, a significant mass of dissolved contamination remains in the groundwater. Based on the QMR, no distinct trend of reduction in the concentrations.of the contamination in " groundwater appears to be taken place, even though an ozone injection system.has come into operation in 2005 (i.e. 200,000 to 210,000 ug/l of TPH-g and 2,500 to 3,000 ug/l of benzene in MW-2. EHD could not evaluate the effectiveness of the ozone injection system since no information on the system's operational status, a record of its on-line and off-line, as well as the level of dissolved oxygen (DO) and oxygen reduction potential (ORP) in the groundwater of the monitoring wells have been'included in any of the quarterly reports of 2005 to date. A record of the DO and ORP.-is an important indicator of the efficiency of the ozone injection system. , Submit a report on the operation and monitoring results of the ozone injection system since ' it came on line,including its operational schedule, the amount of ozone generated, and the DO and ORP record to EHD. EHD also directs you to submit a calculation of the discovered contaminant mass existing immediately before the start up of the ozone injection system. EHD also directs you to submit an estimate with assumptions and calculations of the period of operation of the ozone system required in order to meet the clean up goals as stated in the QMR. Submit this information to EHD by January 31,2006. EHD approves AGE'S recommendation to reduce quarterly sampling of MW-4 to MW-7 to biannually. Donna Heran, REHS, Director k Environmental Health Department Jeffrey Wong, Senior REHS Nuel C. Henderson Jr., PG LOP/Site Mitigation Unit LOP/Site Mitigation Unit C: CVRWQCB —James L. L. Barton, PG c: Advanced GeoEnvironmental, Inc. —Anna W. Behrens , k