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i Site Background Information Sutter Office Center Page 2 of 7 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 Hydro-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 Ianalysis • 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 I 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 • TPH-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 µg/l,respectively,in the sample from boring A Dissolved BTEX compounds were ' detected at maximum concentrations of 1,900 µg/l benzene, 4,100 µg/l toluene, and 3,600 µg/l ethylbenzene in sample A, and 35,000 �Ig/l xylenes in sample B IOn 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 ' northeast 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 ' 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 µg/1 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/l toluene,2,900 µg/l ethylbenzene, and 9,000 µg/l xyleries in sample J at a depth of between 46 and 50 feet bsg Advanced GeoEnvironmental,Inc I