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4 Geological Technics Inc. Page 2 Additional Site Characterization Work Plan Project No. 723.2 December 10,2007 • In September and October 1997 five Strataprobe soil borings (SP-1, SP-4 SP-5, SP-5A & SP-6) were installed at the site. Groundwater samples collected from these borings indicated the presence of low to moderate levels of TPH-G to a depth of 60 feet bgs. • In August 1999, one deep screened monitoring well (MW-101) and one soil boring (SB- 201) were installed at the site. The purpose of these borings was to define the vertical extent of the groundwater plume. Soil samples collected by use of the SimulProbe® Maxitool from the soil borings tested positive for BTEX and TPH-G compounds to a depth of 111 feet. Pore water samples, also collected with the SimulProbe, revealed the presence of BTEX and TPH-G to a depth of 111 feet bgs. • An abandoned domestic well located at an adjacent residence was destroyed in accordance with SJC/EHD directives on April 20, 2001. • A discretely screened deep well (MW-201)was installed in October 2001. • On November 20 — 26, 2003, GTI supervised the installation of three continuous multi- chambered tubing (CMTTM) wells (MW-7, MW-8 and MW-9, respectively). Each CMTTM well was constructed with three discretely screened intervals with the bottom cap comprising an integral fourth screen at the terminal depth. The MW-7 CMTTM well borehole was installed across E. Castle Street approximately 120 feet northwest of the location of the former dispenser island. The MW-8 CMTTM well borehole was placed across N. El Dorado approximately 140 feet east of the location of the former dispenser island in the predominant down gradient groundwater direction. The MW-9 CMTTM well borehole was placed in an up gradient location on W. Adams Street approximately 220 feet from the former dispenser island. • In our September 8, 2003 work plan, Geological Technics Inc. (GTI)proposed a pilot test to evaluate the use of dual phase extraction technology to clean up the soil and groundwater plumes. Dual phase extraction involves the use of both soil vapor extraction and groundwater extraction technologies simultaneously from one well. Extracting groundwater induces a cone of depression that exposes more impacted soil to vapor extraction. The SJC/EHD approved the work plan in their November 15, 2003 letter correspondence. Three new extraction wells (EW-1, VEW-1 and VEW-2) were installed at the site on July 7, 2004 and the pilot test was performed on July 26—31, 2004. • A remediation system was installed at the site and operations commenced in June 2007. The system consists of dual phase extraction (DPE - soil vapor and groundwater) from shallow wells EW-1, VEW-2 and VEW-2 with groundwater extraction from well EW-2 via a dedicated submersible pump. The extracted vapors are treated with a thermal oxidizer and then discharged to ambient air under permit from the San Joaquin Valley Air Pollution Control District (SJVAPCD). The extracted water is treated by an air stripper, polished in carbon vessels and is then discharged to the municipal sewer system under permit from the City of Stockton.