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h w M Ozone Microsparge System First Semi-Annual Status Report—76 Branded(Former BP)Facility leo. 11195,Lathrop,California September 2 2003 i The system is designed to cycle the ozone/oxygen injection between the 15-points (Figure 2). Five of the sparge points (SP-11 through SP-15) are currently operated at all times. The remaining ten sparge points are alternated on a monthly basis so that five sparge points are in operation one month j and the next month the other five points are operated. The schedule is currently set to cycle through f each point 16 times per day, for between 5 and 15 minutes per point per cycle. The schedule can be varied as part of the system evaluation process The sparge wells are constructed with 2-inch diameter ozone sparge points attached to Y4-inch blank Schedule 80 PVC casing. The ozone sparge points are composed of 30-inch long microporous plastic. Lonestar#2116 sand is placed in the annular space from the bottom of the boring (ranging from 30 to 37 feet below ground surface) to 1.5 feet above the top of each sparge point. The two feet of annular space above the sand is filled with bentonite, hydrated by the groundwater in the boring, and the remainder of the annular space in each boring is sealed with neat cement. The ozone microsparge control panel is mounted along a trash enclosure near the southwestern edge of the property. The panel includes an ozone generator, air compressor, the added oxygen generator and a programmable timer/controller. Sparge points are connected to the panel by 3/8" HDPE tubing. Each sparge point has a dedicated line. The tubing was pulled through Schedule 80 PVC conveyance piping for added protection. The process flow diagram is presented on Figure 3. 3 Groundwater Sampling In order to evaluate system effectiveness, periodic sampling of selected groundwater monitoring wells has been performed at the site. Wells MW-3 and MW-10 were selected for sampling and have been sampled on.a monthly basis starting in March of 2003. Well MW-3 is adjacent to the underground storage tanks (USTs) and MW-10 is downgradient of the site. Each well is within the treatment area and the zone of influence of one or more sparge points. These wells are approximately 180 feet apart. Both wells MW-3 and MW-10 have extensive historical sampling data prior to the system activation. These wells were installed in 1992 and 1998, respectively, and have been sampled quarterly since that time. A historical sampling data table for the monitoring well network is attached as Appendix A. Groundwater samples from MW-3 and MW-10 were analyzed for TPHg, benzene, toluene, ethylbenzene, and total xylenes (BTEX) and MtBE by EPA Method 8260. Groundwater analytical results for the two wells are presented in Table 1. The complete laboratory analytical reports and chain of custody records for the monthly groundwater sampling are attached in Appendix B. 140193.16 2