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Dissolved Oxygen (DO) DO levels in the onsite monitoring wells prior to system start-up, measured using a field instrument on December 11, 2002, were in the range of 0.6 mg/L (MW-6) to 3.3 mg/L (MW-7). The DO levels from the laboratory analysis of groundwater samples collected on December 23, 2003 were in the range of 1.75 mg/L to 4.69 mg/L. The difference in DO observed between the field instrument readings and the laboratory results is probably due to aeration of samples during purging and handling of samples collected for laboratory analysis. The field instrument used to measure DO is a down-hole (in-well) probe and is considered representative of field conditions. After the system start-up, DO levels in observation wells measured using a field instrument were in the range of 0.1 mg/L to 11.6 mg/L. During first quarter 2003, the DO levels increased to more than 10 mg/L in observation wells MW-7 and MW-9 located within 15 feet of injection points and to more than 4 mg/L in observation well MW-5 located within 20 feet of injection point. A significant increase on the order of 200% and 300% in DO levels was observed in monitoring wells MW-5, MW-7, and MW-9. In addition to the field instrument measurements for DO, groundwater samples were collected and forwarded for laboratory analysis. The DO levels in groundwater samples analyzed by laboratory during the first quarter 2003 were in the range of less than 1 mg/L to 12.4 mg/L. Based on DO levels measured both by field instrument and laboratory analysis, it appears that a minimum radius of influence of 18 feet has been established by the ozone injection system. Specific Conductivity The average specific conductivity measured in onsite monitoring wells during ozone injection is either less than, or close to, the levels measured prior to ozone injection. Laboratory Parameters Chemical Oxygen Demand(COD) The COD concentrations varied from less than laboratory detection limits (<30 mg/L) to 60 mg/L in the groundwater samples collected prior to start-up (December 23, 2002) of ozone injection system. Analytical results of groundwater samples collected on January 14 and February 12, 2003 (during operation of C-Sparge System) indicate that the COD concentrations varied from less than laboratory limits to 190 mg/L. A consistent correlation of higher COD concentration at monitoring wells with higher petroleum hydrocarbon concentrations has been observed in data collected from monitoring wells MW-4, MW-5, MW-6, and MW-S. Oxidation Reduction Potential(ORP) ORP in groundwater samples collected from onsite monitoring wells on January 14 and February 12, 2003, were in the range of 310 millivolt (mv) to 630 mv. This range of ORP generally falls in the category of an oxidizing environment. Ferrous Iron The ferrous iron concentration in groundwater samples collected from select monitoring wells on December 23, 2002, were in the range of less than 0.1 mg/L to 3.9 mg/L. The ferrous concentrations in groundwater samples collected on January 14 and February 12, 2003, varied from less than 0.10 mg/L to 0.69 mg/L. P A1Bp-Arco for URS154691Quarterly\20031Arco_5469_1 Q03.doe 5 TRA TU,,5