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01 March 2004 AGE-NC Project No 99-0645 Page 10 of 11 • TPH-g was only detected In the uppermost soil sample from bonng V W 1 A,at the east edge of the site MTBE was detected In samples from boring B7 from 40 feet to 60 feet bsg The lateral extent of adsorbed MTBE may extend below the eastern boundary of the site Soil vapor extraction on the site will likely effectively mitigate the MTBE off-site • Generally,the highest concentrations of MTBE were detected within a 45 foot thick Interval, generally occurring between 15 feet and 60 feet The vertical extent of the MTBE-Impacted soil was limited to less than 70 feet bsg • MTBE was detected In one of the three water samples collected This concentration does exceed the State of California,Department of Health Services maximum contaminant level for MTBE In drinking water • Based upon effective vacuum potential of 0 1 Inches of water,the calculated effective radius of Influence at the site for vapor wells screened from 15 feet to 40 feet bsg will be approximately 40 feet The calculated effective radius of influence at the site for vapor wells screened from 40 feet to 70 feet bsg or greater will be approximately 30 feet • MTBE was detected In one ground water sample (MW-1) at a concentration of 120 pg/L • TPH-g,TPH-d and BTEX compounds were not detected In the three water samples collected 5.0. RECOMMENDATIONS Based upon data collected from the site, AGE recommends Continued quarterly ground water monitoring, the next quarterly monitoring event should be scheduled for March 2004 Implementation of the Interim Soil Remediation Work Plan, dated 10 June 2002 The design of the soil vapor extraction well network should Include all vapor wells on site, including the monitoring well screen from well MW-1, due to the detections of dissolved MTBE If the detections of dissolved MTBE continue,Installation of an additional ground water monitoring well northeast of the site • Advanced GeoEnviron mental,Inc