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i 1 ` ' 27 October 2004 AGE-NC Project No 96-0254 ' Page 2 of 10 ' and San Joaquin Valleys Based on the General Soil Map from the San Joaquin County Soil Survey,published by the United States Department of Agriculture Soil Conservation Service in 1992, the site is situated within an area of Capay clay soil Capay clay is located in mterfan basin or alluvial fan areas, and generally consists of very deep,moderately well-drained grayish brown and dark grayish brown clay The soil formed in alluvium derived from mixed rock sources 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) This basin is drained primarily by the San Joaquin River ' 2 2 LOCAL GROUND WATER SETTING ' The nearest surface water feature in the vicinity of the property is the Stanislaus River approximately five miles south of the site Ground water at the site is currently encountered at a depth of 20 feet r below surface grade(bsg), and has a northern flow direction The ground water gradient map, along t • with a flow direction frequency chart is depicted on Figure 3 The depth to ground water has been measured a high as 14 feet bsg and as low as the current depth of n20 feet bsg Ground water occurs in a generally silty sand extending from surface grade to approximately 25 feet bsg over all but the ' southern portion of the site, where it only extends to approximately 15 feet bsg Ground water elevation data is presented in Table I 2 3 UNDERGROUND STORAGE TANK REMOVAL AND OVER-EXCAVATION ' Four USTs, including two 3,000-gallon gasoline USTs, one 4,000-gallon gasoline UST and one 12,000-gallon diesel UST, had been in operation at the site for approximately twenty years The ' USTs,along with two dispenser islands and associated product lines(Figure 2),were removed from the site on 10 September 1998 During the removal of the USTs and fueling system,AGE performed interim soil remediation by removing approximately 350 cubic yards of soil from two UST ' excavations and four dispenser excavations On 15 September 1998,interim soil remediation continued with removal of an additional 100 cubic ' yards of significantly diesel-impacted soil from the bottom of the diesel UST excavation The soil was excavated from the diesel UST excavation at the central area of the site to a depth of 20 feet below surface grade(bsg) One grab water sample was collected from the northern edge of the diesel ' UST over-excavation The soil left in place was impacted by low to moderate concentrations of total petroleum hydrocarbons as diesel (TPH-d) Analytical results of the soil samples collected are , ' Advanced Geo Environmental,Inc