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Mr.Nuel Henderson,R.G January 31, 2003 Installation of Ozone Injection System and Remediation Status Report Page 4 The complete oxidation of petroleum hydrocarbons should result in the formation of carbon dioxide and water, which may result in the formation of bicarbonates (Cookson, 1995). Bicarbonates contribute to alkalinity, resulting in high pH. Prior to the C-SpargeTM system start-up, pH measured in onsite monitoring wells (MW-1 through MW-10) on December 11, 2002, was in the range of 6.20 (MW-10) to 7.4 (MW-2). After the system start-up, pH measurements in the onsite monitoring wells were in the range of 6.33 (MW-3 and MW-4) to 9.88 (MW-10) on January 9, 2003, and 6.43 (MW-4) to 9.97 (MW-10) on January 14, 2003. Dissolved Oxygen (DO) The half-life period of dissolved ozone is approximately twenty minutes (How Ozone Works, Rebecca Amato) and then it degrades to oxygen. The radius of influence for C-SpargeTM wells will be evaluated based on the DO levels in the monitoring levels. 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). Groundwater samples collected from select monitoring wells on December 23, 2002, were analyzed for DO by the laboratory. The DO levels from the laboratory analysis were in the range of 1.75 mg/L to 4.69 mg/L. The difference in the field instrument measurement and the laboratory results can be 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 onsite monitoring wells were in the range of 0.4 mg/L (MW-8) to 7.3 mg/L (MW-9), and 0.2 mg/L (MW-6) to 7.4 mg/L (MW-9) for field measurements made on January 9 and 14, 2003, respectively. An increase in DO was observed in monitoring wells MW-3, MW-5, MW-7, MW-9, and MW-10. DO levels at monitoring well MW-9, located approximately 13 feet from injection well IW-5, have increased from 1.8 mg/L (December 11, 2002) to 7.4 mg/L (January 14, 2003) with approximately 15 days of ozone injection. Stratus will continue to monitor for DO levels in onsite monitoring wells on a weekly basis using a field instrument, and samples will be collected from these wells on a quarterly basis for laboratory analysis. PABp-Arco for URS154691Reports\Arco 5469 Remediation Status Report.doc STRATUS