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• Groundwater Flow Direction Northwest and Radial Flow(at well MW-5) Groundwater Gradient 0 008 to 0 0038 ft/ft INTERIM REMEDIATION SYSTEM OPERATION AND PERFORMANCE Equipment Inventory Ozone Injection System (Manufactured by KVel _ Operating Mode Operational Reporting Period April 5,2005 through June 29, 2005 Historical Highest GRO Concentration 55,000 pg/L(MW-6, 2002) Historical Highest Benzene Concentration 18,000 pg/L(MW-8, 2001) ^ Historical Highest MTBE Concentration 85,000µg/L(MW-6, 2002) Highest GRO Concentration this Period <25,000 pg/L(MW-8) Highest Benzene Concentration this Period 30 /L MW-4 Highest MTBE Concentration this Period 18,000µgIL(MW-6&MW-8) _ Number of System Shutdowns This Period 0 DISCUSSION At the time of the second quarter 2005 monitoring event, groundwater elevations had increased between 1 34 and 2 39 feet in all wells since the previous sampling event (March 16, 2005) 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 in the vicinity of wells MW-7 and MW-8 was generally to the northwest at an average gradient of 0 008 ft/ft Radial flow at gradients of 0 0033 to 0 0038 ft/ft was also observed centered around a groundwater low near well MW-5 Radial and northeast groundwater flow has been observed at this site during previous quarters REMEDIATION SYSTEM STATUS System Description The C-Sparge"' system, manufactured by KVe, 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-SpargJm 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 this programming, each injection point will have ozone injection in 18 cycles for 4 2 hours every day During the second quarter 2005 (between April 5, 2005 and June 29, 2005), a Stratus technician �i conducted six site visits to collect field and laboratory parameters, and to conduct operation and K\Bp-Arco for URS\5469\Quarterly\2005\Arco_5469_2Q05 docPage 3 of 6 STKATUO