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Geo44UITerWatxa Dual Phase Extraction Pilot Test Report Project No. 723.2 Page 2 November 5,2004 F � resenc _ P e of significant levels of BTEX and 'TpH_G. The results also indicated that r the pump-island was a major source of contamination. In September and October 1997 five Strataprobe soil borings 5A & SP-6) were installed at the site. Groundwater samplesScollect d fr P . these borings indicated the presence of low to moderate levels of TPH-G to om these feet bgs. a depth of 60 • 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 th vertical extent of the groundwater plume. Soil samples SimulProbe'MaxitOol from the soil borings tested positive forcBTEX and TPH-G compounds to a depth of 1 i 1 feet. Pore water samples, also collected with the F SimulProbe, revealed the presence of BTEX and TPH-G to a d r epth of 1 I 1 feet bgs. • An abandoned domestic well located at an adjacent residence was destroyed in ' accordance with SJC/EHD directives on April 20, 2001. �I • 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 ^t suggesting that it was a drilling artifact. i + On November 20 -- 26, 2003, GTI supervised the installation of three continuous a ' multi-chambered tubingCMT ( TM) wells (MW-7, MW-$ and MW-9, respectively). Each CMTTm-wellwas constructed with three discretely screened intervals with the r 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 PP y 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 F direction. The MW-9 CMTTM well borehole was placed in an up gradient location on i W. Adams Street approximately 220 feet from the former dispenser island. • In our September 8, 2003 work plan, GTI proposed to evaluate the use of dual phase extraction technology to clean up of the soil and groundwater plumes. Dual phase extraction involves the use of both soil vapor extraction and groundwater extraction Ll technologies simultaneously from one well. Extracting groundwater induces a cone of depression that exposes more impacted soil to vapor extraction. The San Joaquin County Environmental Health Department (SJC/EHD) approved the work plan in their November 15, 2003 letter correspondence. _ The following sections detail the installation of three extraction wells at the site and the subsequent use of the-wells to perform the dual phase extraction pilot test. R