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---------------- � S E C O R CHARACTERIZATION STATUS Contamination in soil beneath and downgradient of the site has been adequately delineated. The extent of the dissolved plume is delineated by historically non- detectable concentrations of petroleum hydrocarbons in well MW-21 to the southwest, and by well MW-12 to the west. The dissolved GRO and BTEX plumes have been delineated across the site. Contamination in groundwater, specifically MtBE, has been delineated to low to non- detectable concentrations in wells MW-22, MW-23, and MW-24 situated south and southeast of the site, in wells MW-11 and MW-12 located west of the site, and in wells MW-13, MW-15, and MW-21 located southwest of the site. Historical analytical data indicates that the highest concentrations of TBA are detected in on-site well MW-3, with less frequent detections of the analyte in on-site well MW-6, upgradient well MW-8, and off-site wells MW-9 and MW-10. REMEDIAL PERFORMANCE SUMMARY An OS system has been operational at the site since December 2002. A summary of the operation of the OS system, and monthly groundwater sampling activities are presented in the following sections. A site plan showing the layout of the OS system is included as Figure 1. Ozone Injection Operation ?t =F The OS system consists of a panel mounted KVA Associates (KVA) C-SpargeTM System that produces 4 grams per hour (0.009 pounds per hour) of ozone. Ozone is injected through 10 solenoids connected to wells SP-1/SP-6, SP-2/SP-7, SP-3/SP-8, SP-4/SP-9, SP-5, and SP-10 through SP-15. During the July 5, 2005 site visit, ozone was programmed to be injected into the following wells: SP-1, SP-3, SP-4, SP-5, SP-7, and SP-10 through SP-14. Following the replacement of the injection lines from the panel to the wells on September 19, 2005 for the purpose of repairing leaks and increasing system efficiency, the OS system was reprogrammed to inject ozone into wells SP-6 through SP-15. The system was restarted on September 20, 2005. During the fourth quarter 2005, ozone was injected into wells SP-6 through SP-15. Cumulatively, the OS system has operated for 10,962 hours, and has injected a total of approximately 99 pounds of ozone into the subsurface. Table 1 presents the operating data for the OS system, and includes operating hours and pressure readings. Remediation system field data sheets are included in Attachment 2. Monthly Groundwater Sampling To monitor the effectiveness of the OS system, groundwater samples are collected monthly from wells MW-3 and MW-10, and are submitted to STL for analysis of GRO, BTEX, and MtBE by EPA Method 82608. During the fourth quarter 2005, groundwater samples were collected from wells MW-3 and MW-10 on October 4, 2005, November 1, 2005, and December 1, 2005. Results of monthly groundwater sampling events are summarized in Table 2. Remediation system certified laboratory analytical reports and chain-of-custody documentation are provided in Attachment 3. [ABP-ARC41111951ReporfslQSR&QRPS 2005/11195 QSR& QRPS 4005.doe