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1 ISite Background Information SUTTER OFFICE CENTER ' 242 North Sutter Street, Stockton, California ' PREVIOUS SITE ASSESSMENTS Ten soil borings have been advanced and three ground water monitoring wells have been installed ' at the site to assess the vertical and lateral extent of impacted soil and ground water The following is a summary of milestone events at the site ' On 22 May 2000, a total of seven on-site soil borings were established by Hydra-Geo Consultants, Inc with a Geoprobe sampling rig Borings A,B, and C were established on the northeast corner of the site and borings D through G were established on the west and southern edge of the former service station location,to a depth of 45 feet below surface grade(bsg) Based on laboratory analysis • Total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d) were ' detected in soil samples collected during boring operations at concentrations as high as 300 milligrams per kilogram (mg/kg) and 2,400 mg/kg, respectively, in the sample from ' boring A at 30 feet bsg BTEX compounds were detected in the soil samples at maximum concentrations of 0 5 mg/kg(toluene), 1 5 mg/kg(ethylbenzene),and 30 mg/kg(xylenes)in the sample from boring A at 40 feet bsg • TPR-g and TPH-d were detected in grab ground water samples collected during the soil boring operations at concentrations as high as 470,000 micrograms per liter (µg/1) and 230,000 }rg/l, respectively, in the sample from boring A Dissolved BTEX compounds were detected at maximum concentrations of 1,900 gg/l benzene, 4,100 gg/I toluene, and 3,600 pg/l ethylbenzene in sample A, and 35,000 µg/1 xylenes in sample B ' On 31 January 2002,three additional soil probe borings were advanced,two borings were advanced on-site to a depth of 90 feet bsg (I and J), while boring H was established off-site across California ' Street to a depth of 50 feet bsg Laboratory analysis indicated • TPH-g and TPH-d were detected in grab ground water samples collected during the soil ' boring operations at concentrations as high as 120,000 }ig/I and 190 µg/l,respectively,in the sample from boring J at a depth of between 46 and 50 feet bsg Dissolved BTEX compounds were detected at maximum concentrations of 650 µg11 benzene in sample I at a depth of ' between 46 and 50 feet bsg, and 9,000 µg/1 toluene,2,900µg/1 ethylbenzene, and 9,000 Ag/l xylenes in sample J at a depth of between 46 and 50 feet bsg ' On 02 August 2001, three ground water monitoring wells (MW-1, MW-2, and MW-3), screened between 20 and 40 feet bsg, were installed at the site (Figure 2) Well MW-1 was installed at the Inortheast corner of the site and wells MW-2 and MW-3 were installed at the southern edge of the • dissolved plume area Eight ground water monitoring events have occurred to date, the last one in July 2004 1 Advanced GeaEnvironmental,Inc