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. Ozone Microsparge System Pilot Test Status Report,Former Unocal Service Station No.0187, Stockton,CA November 19,2003 Depth to water in the wells ranged from 28.23 to 48.23 feet below top of casing (btoc), and overall groundwater flow was to the east at gradients ranging from 0.01 to 0.006,which is consistent with recent historical data. Since August 1994, groundwater beneath the site has risen steadily from a depth of approximately 48 feet btoc to its present level. OZONE MICROSPARGE SYSTEM PILOT TEST System Installation As a remedial action measure, GR installed an ozone microsparge (C-Sparge) system. Ozone microsparging is a process where ozone is entrained in air and introduced into the groundwater at low flow rates (2-6 cubic feet per minute) through specially designed sparge points to create small "microbubbles." As these microbubbles rise within the column of water, they strip volatile organic compounds (VOCs) from the groundwater. Upon entering the microbubbles, the VOCs are rapidly oxidized. The system installed at this site was considered a pilot test to evaluate the effectiveness of the C-Sparge system. The system was operated continuously except for brief down times due to faulty electrical wiring and tubing failures. In November 2000,eight on-site ozone microsparge wells(SP-IA, SP-1B, SP-2A, SP-2B, SP-3A, SP-3B, SP-4A, and SP4B)were installed at the site. The ozone microsparge wells were installed in four sets of two wells each,with each set consisting of wells set at 75 and 120 feet bgs. Eight additional ozone microsparge wells(SP-1C, SP-3C, SP-5A,B,C and SP-6A, B, C)were installed at the Unocal site on February 11 through 19, 2002 (GR report#240042.11-1,Monitoring Well and Sparge Point Installation Report, dated July 15, 2002).. Based on the manufacturer's recommendations, an approximate zone of influence of 20 feet for each point was used as minimum radius of influence. Two of the points were placed at a depth of approximately 40 feet bgs, two points were placed at a depth of approximately 45 feet bgs, two points were placed at a depth of approximately 65 feet bgs,and two points were placed at a depth of 110 feet bgs. The sparge point depths and locations were chosen to introduce ozone into the areas of highest petroleum concentrations. The point locations are shown on Figure 2. The second system was placed into operation on April 26, 2002. The C-SpargeTM panels include an ozone generator, air compressor,and a programmable timer/controller. Sparge points are connected to the panel by LDPE tubing. Each sparge point has a dedicated line. The tubing was run through Schedule 40 PVC conveyance piping for added protection. System Operation The system cycles ozone/air injection between sixteen specially designed micro-sparge points. The schedule was initially set to cycle through-each point 18 times per day, for nine minutes per point per cycle. There is an eight-minute rest period between cycles. This schedule was varied over the course of the test as part of the system evaluation process to provide more treatment to some areas. • 240042.11-3 3