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. Cumulative FP Recovered to Date: NIA Approximate Depth to Groundwater: 43.01 to 43.69 feet below ground surface(b9s) Groundwater Flow Direction: Northeast Groundwater Gradient: 0.001 ft/ft INTERIM REMEDIATION SYSTEM OPERATION AND PERFORMANCE Equipment Inventory: Ozone Injection System (Manufactured by KVA�') Operating Molle: Operational Reporting Period: June 23, 2003 through September 29, 2003 Historical Highest TPHG Concentration: 55,000µg1L(MW-6, 2002) Historical Highest Benzene Concentration: 18,000µg/L(MW-8, 2001) Historical Highest MTBE Concentration: 85,000µg/L(MW-6, 2002) Highest TPHG Concentration this Period: 9,300µg/l_(MW-4) Highest Benzene Concentration this Period: 1,700µg/l_(MW-4) Highest MTBE Concentration this Period: 49,000µg/L(MW-6) Number of System Shutdowns This Period: 1 DISCUSSION: Groundwater elevations have decreased approximately 1.43 to 1.55 feet since the previous sampling event (May 19, 2003). 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 groundwater flow direction on September 9, 2003, was northeast at a gradient of approximately 0.001 ft/ft. Groundwater flow directions have predominantly been toward the northeast and east during previous monitoring events. In addition to quarterly groundwater sampling, additional groundwater samples were collected during the third quarter 2003 sampling event to evaluate and optimize the performance of ozone injection system. Tabulated results of groundwater elevation and analytical summary of groundwater samples collected under ozone injection monitoring plan and quarterly monitoring program are presented in Tables 1 and 2. A discussion on the results of petroleum hydrocarbon concentrations is presented later in the remediation system status section of this report. 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. R\Bp-Arco for URS154691Quarterly12003\Arco_5469_3Q03.doe 5TRA TU5