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Approximate Depth to Groundwater: 42.55 to 43.28 feet below ground surface(bgs) Groundwater Flow Direction: Northeast Groundwater Gradient: 0.0013 ft/ft INTERIM REMEDIATION SYSTEM OPERATION AND PERFORMANCE Equipment Inventory: Ozone Injection System Manufactured by KVA� Operating Mode: Operational Reporting Period: April 5, 2004 through June 28,2004 Historical Highest GRO Concentration: 55,000µg/L(MW-6, 2002) Historical Highest Benzene Concentration: 18,000 pg/L(MW-8, 2001) Historical Highest MTBE Concentration: 85,000 ug/L(MW-6, 2002) Highest GRO Concentration this Period: 8,500 IL MW-4 Highest Benzene Concentration this Period: 1,900 pg/L_(MW-4) Highest MTBE Concentration this Period: 32,000 ugIL(MW-8) Number of System Shutdowns This Period: 0 DISCUSSION: At the time of the second quarter 2004 monitoring event, groundwater elevations had increased between 0.07 and 0.52 feet since the previous sampling event (March 4, 2004). Depth-to-water measurements were corrected to mean sea level (MSL) and used to construct a groundwater elevation contour map (Figure 3). Wells MW-9 and MW-10 are screened in a deeper portion of the water-bearing zone and were not used in contouring. The water level in well MW-5 appeared to be influenced by the remediation system and was not used in contouring. The groundwater flow direction on June 8, 2004, was to the northeast at a gradient of 0.0013 ft/ft, consistent with historical conditions. REMEDIATION SYSTEM STATUS System DescriptiOn The C-SpargeTM system, manufactured by KVA�, consists of a control panel (ozone generator, air compressor, and tubing manifold), and strategically located injection points (IW-1 through IW-5, see Figure 2) used to inject low concentrations of ozone into groundwater. In addition, the control panel also has a programmable timer that limits the amount of ozone injected into each injection point. The system injects a timed pulse of ozone at low flows and low pressures (10-30 psi) to each of the five injection points in a sequence. The ozone dissolved in groundwater is expected to oxidize petroleum hydrocarbons into carbon dioxide and water, and any un-reacted ozone will degrade to dissolved oxygen, which is likely to enhance natural biodegradation of residual petroleum hydrocarbons. System Operation Details The C-SpargeTM system was started on December 26, 2002. The C-SpargeTM control panel was programmed and scheduled to inject ozone cyclically into each injection point for 14 minutes. Based on i this programming, each injection point will have ozone injection in 18 cycles for 4.2 hours every day, During the second quarter 2004 (between April 5, 2004 and June 28, 2004), a Stratus technician conducted five site visits to collect field parameters and laboratory parameters and to conduct operation PABp-Arco for URS\54691Quarterly120041Areo_5469_2Q04.doc 5rRATV5