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27 February 2007 AGE-NC Project No. 07-1514 Page 2 of 6 alluvium. lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977). Rocks cornposing the basement complex of the Province have not been completely defined but are believed to be metamorphic and igneous in origin. The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). The closest surface water feature to the site is the confluence of the Little John Creek and Lone5�ree Creek, located approximately one mile to the north of the site and the San Joaquin River, located approximately live miles to the west of the site. Based upon previous environmental assessments conducted at the site,ground water depth occurs at approximately 38 to 42 feet below surface grade (bsg); ground flow direction at the site has not been determined. 2.2. UST UPGRADES AND SITE ASSESSMENT ACTIVITIES According to the Wright Environmental Services, Inc. (Wright) prepared - Preliminary Soil anct Groundwater Site Assessment dated 21 December 2004,during dispenser upgrades in January 2004. 5.54 tons of hydrocarbon-impacted soil was removed from around the UST fill buckets and dispensers and disposed at Forward Landfill in Manteca, California. In their letter- dated 14 April 2004,EHD directed the assessment of impact to ground water and to delineate the vertical and lateral extent of hydrocarbon-impacted soil. In October 2004, Wright advanced four soil borings at the site and collected soil and ground water samples. Low concentrations of total petroleum hydrocarbons quantified as diesel (TPM-d) were reported in the soil sample collected from boring B-2 at 36 ft bsg at 1.1 milligrams per kilogram. No other constituents of concern was reported in the soil samples collected. TPH-d was reported in the ground water samples collected from borings B-1, B-2 and B-4 at a maximum concentration o1-79 micrograms per liter(pg/1)(B-2). TPfI-gasoline(TPI I-g)was reported in the ground water samples collected from borings B-2 and B-3 at a maximum concentration of 270 µg/1. Additionally, ethanol was reported in the samples collected from borings B-2 and B-3 at a maximum concentration of 43 ftg/l (B-2). Kiff Analytical LLC (Kiff) reported that the TPI1-d and TPI I-g did not demonstrate the typical TPI I-d and TPI -g gas chromatographic patterns for both the soil and ground water analytical results for the samples collected frorn borings B-1 through B-4. Wright recommended Kiff further evaluate the analytical results of the soil and ground water samples collected from borings B-1 through B-4; EHD concurred in their letter dated 16 March 2005 and further requested Kif-freview the results by EPA method 9260. On 17,luly 2006, Kiff issued a supplementary laboratory report and reported: Advanced GeoEnvironmcntal,Inc.