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Geological Technics fix. '•� Page 2 Additional Site Characterization Work Plan Project No.724.2 March 15,2005 • 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 SimulProbea 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. The results of this endeavor suggested that the contamination extended to a depth of 128 feet below grade surface (bgs). This depth was the target of a SimulProbe°sampling effort and the soil sample from this elevation contained detectable TPH-G. • Seven quarterly monitoring events have been completed since the installation of deep well MW-201. This well was completed with a screened interval of 148 — 150.5 feet bgs. The amount of contamination in this well has attenuated to trace levels suggesting that it was a drilling artifact. • 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, 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 was performed on July 26—31, 2004. • The results of the dual phase extraction pilot test were detailed in GTI's November 5, 2004"Dual Phase Pilot Test"report and submitted to the SJC/EHD.