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Geological Tulutics Inc. Page 3 Groundwater Monitoring Report Project No.750.2 February 16,2005 In February 2002 the soil vapor extraction system was initiated and has operated for approximately one year. Contaminant mass estimate calculations show that approximately 50% of the petroleum hydrocarbons contained in the subsurface at this site has been removed. The groundwater at this site is free of petroleum hydrocarbon contamination and possibly as much as 600 gallons of gasoline may remain in the vadose zone. On March 28, 2003, GTI submitted the Work Plan for Additional Site Characterization. The work plan was approved, with reservation,by Lori Duncan in a letter dated April 8, 2003. On June 6, 2003, GTI prepared and submitted the Work Plan— Treatment System Feasibility Study. In a letter dated June 23, 2003, Ms Duncan requested that SCJEHD be notified once a decision was made on the method to be employed at the site. The letter requested that remediation should resume as soon as possible. On September 4 and 5, 2003, GTI and Gregg Drilling & Testing Inc. (Gregg) staff arrived at the site and advanced two soil borings per the March 28, 2003 work plan. Details of the event are discussed in GTI's Interim Soil Investigation Report dated October 2, 2003. GTI obtained Fund approval and an Authority to Construct permit to reinstall and operate the Internal Combustion System (IC) at the COE site. The IC was switched on, inspected by the San Joaquin Valley Air Pollution Control District (SJVAPCD) on December 9, 2003, and operated until January 14, 2004. On February 12, 2004, GTI prepared and submitted the Work Plan — Modified Vapor Extraction Treatment System. The work plan was approved by Ms Duncan in a letter dated February 20, 2004. The IC unit was removed from the site in February 2004. On September 24, 2004, a Soil Vapor Extraction — Granulated Activated Carbon System (SVE) was installed at the site. The new system has been in continuous operation since September 24, 2004, with one exception. The system was shut down between November 30, 2004 and December 16, 2004 for modification of the water knockout system. On November 10, 2004, GTI submitted the 3rd Quarter Groundwater Monitoring Report recommending a modification of the analysis for fuel oxygenates. The recommendation was approved by SJCEHD.in a letter dated December 13, 2004. This report documents the results of analysis by EPA method 8260 for the 4th quarter monitoring event. Analysis by EPA method 8260 will continue on an annual basis during the 4th quarter of each year. u r