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S E C 0 R Third Quarter 2004, Groundwater Monitoring Report November 10, 2004 Page 3 Attachment B. ARCO's laboratory analytical results, chain-of-custody documents, and field data sheets are provided as Attachment C. REMEDIAL RESULTS SUMMARY (CHEVRON) Operation of the soil vapor extraction (SVE) and air sparge (AS) systems were initiated at the site in April 1997. The SVE system has been disabled and the AS continues to operate. A brief description and performance evaluation of the remedial system between March 05, 2004 and Mune 11, 2004 are presented below. The inactive SVE system is comprised of ten SVE wells (VW-1 and GM-1 through GM-9), underground mechanical piping, a 5-horsepower (hp) positive displacement blower, and 100-cubic feet per minute (cfm) catalytic oxidizer (Figure 2). During 3Q04, the SVE system did not operate due to high groundwater levels. The SVE system has not operated since February 1998. On September 21, 2004, depth to water in the monitoring wells at the site ranged from 11.60 to 13.25 feet below ground surface (bgs). The screened intervals in the SVE wells range from 10 to 17 feet bgs; therefore water levels are currently too high for effective operation of the SVE system. The AS system is comprised of nine AS wells (GM-1 and GM-9), underground mechanical piping, and a 1.5-hp rotary vane air compressor. During 3004, the AS system was operational for 98% of the reporting period at an average flow rate of 15.2 standard cubic feet per minute (scfm) and an average injection pressure of 5.5 pounds per square inch gauge(psig). CHEVRON's AS system operational data is presented in detail as Attachment D. 3 REMEDIAL RESULTS SUMMARY (ARCO) Cumulative FP Recovered to Date: 642 lbs Cumulative TPHg Removed by GWE: 3,980 lbs Total Groundwater Extracted: 32,000,000 gal TPHg Removed by SVE this quarter: None Cumulative TPHg Removed by SVE: 4,897 lbs MtBE Removed this Quarter: None Cumulative MtBE Removed: 4.5 lbs Approximate Depth to Groundwater: 8.63—9.48 ft ARCO's historical SVE data and recent AS system operational data are presented in detail in Attachment E. CONCLUSIONS AND RECOMMENDATIONS With the exception of a significant decreasing MtBE concentration trend observed in Chevron well MW-1 over the last three consecutive quarters since the fourth quarter 2003, groundwater flow direction, hydraulic gradient, groundwater concentrations reported during 3Q04 are consistent with historical data. Due to the site's commingled plume status, SECOR will take over the responsibility of conducting groundwater monitoring and sampling activities at both the CHEVRON and ARCO sites during the I:%Chevron1942751Peri0dic Monitoring\Q M R1200413Q04.d0c