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FP Recovered This Quarter NIA Cumulative FP Recovered to Date NIA Approximate Depth to Groundwater 43 67 to 44 47 feet below ground surface (bgs) Groundwater Flow Direction Northeast Groundwater Gradient 0 002 ft/ft INTERIM REMEDIATION SYSTEM OPERATION AND PERFORMANCE Equipment Inventory _ Ozone Injection System(Manufactured by KVAa Operating Mode Operational Reporting Period October 6,2003 through December 22, 2003 Historical Highest TPHG Concentration 55,000 4g/L(MW-6,2002) Historical Highest Benzene Concentration _18,000 4q/L(MW-8,2001) Historical Highest MTBE Concentration 85,000 gg/L(MW-6,2002) Highest TPHG Concentration this Penod 25,000 /L MW-6 Highest Benzene Concentration this Period 3,400lig/L(MW-4) Highest MTBE Concentration this Period 46,000 ug/L(MW-6) Number of System Shutdowns This Period 1 DISCUSSION Groundwater elevations have decreased approximately 0 6 to 1 02 feet since the previous sampling event (September 9, 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 December 10, 2003, was northeast at a gradient of approximately 0 002 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 fourth 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 the 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-Sparge m 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 P 1Bp-Arca for URS\5469\Quarteriy\2003\Arco_5469_4Q03 doc 5TRATUS