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Geological Technics Inc. Page 2 City of Escalon Project No.: 750.2 May 16,2005 On June 12, 2000, GTI and Del-Tech Geo Technical (Del-Tech) performed a vapor extraction pilot test at the site. Laboratory and field test results indicate the site is conducive to remediation by vapor extraction. r On June 12, 2000, Ms. Lori Duncan of San Joaquin County Environmental Health Department (SJCEHD) requested in writing that a work plan be prepared to define the lateral and vertical extent of the groundwater plume at the site. On June 29, 2000, GTI prepared a work plan proposing the installation of two water table monitoring wells and one deep, discretely screened monitoring well. Ms Duncan approved the work plan on July 7, 2000. The work was performed during the week of October 16, 2000. On January 30, 2001, GTI prepared and submitted the Corrective Action Plan (Revised) Vadose Zone Remediation. The CAP discusses GTI's proposed methodology for mitigation of the documented petroleum hydrocarbon contamination at the site by vapor extraction. The CAP also discusses the confirmation testing outlined in this work plan. Ms Duncan approved r the CAP, as submitted, in a letter dated April 02, 2001. In February 2002 the soil vapor extraction (SVE) system was initiated and has operated for approximately one year. On January 21, 2003, GTI submitted the Vapor Extraction Treatment System Monitoring Report. The report indicated that approximately 50% of the petroleum hydrocarbons contained in the subsurface have 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. The report also recommended that the site be r considered for closure. In a letter dated February 18, 2003, SJCEHD requested that the well extraction cycle be r utilized to address lower screen intervals and that GTI may consider switching methods of contaminant destruction, such as changing to carbon canisters to lower operational costs. On March 28, 2003, GTI submitted the Additional Site Characterization—Soil Borings Work Plan. Ms Duncan approved the work plan, with reservation, in a letter dated April 8, 2003. The soil borings were advanced on September 5, 2003 and GTI submitted the resulting Interim Soil Investigation Report on October 2, 2003. As per the April 8, 2003 SJCEHD directive, the SVE system was restarted on December 9, 2003 and ran until January 14, 2004. A new vapor extraction — granulated activated carbon (SVE-GAC) system was installed during the summer of 2004. The SVE-GAC was started on September 24, 2004 and ran until April 12, 2005. The SVE-GAC was not operational, due to repairs, for three weeks between December 2004 and January 2005. r V