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P � 18 July 2008 AGE-NC Project No. 95-0137 Page 2 of 6 MTBE.Twenty soil samples were analyzed for the suite of five fuel additives by EPA Method 8260 Modified. The following is a brief summary of analytical results: • TPH-d was detected in soil samples CBI-20, CB2-20, CB3-20, and CB5-20 at concentrations of 490 mg/kg, 1,300 mg/kg, 610 mg/kg, and 160 mg/kg. r • TPH-g,BTEX compounds,and fuel additives were not detected in the soil samples. Analytes were not detected in deep grab ground water samples CB 1, CB2, CB4 and CB5, collected from the terminal depth of the confirmation soil borings. The hydrocarbon impactappears to have been appropriately mitigated. Site background information, including additional details of previous site assessment work, is presented in Appendix B. 1.3. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The site is situated within the southern portion of the Great Valley Geomorphic Province of California, a large, elongate, northwest trending, asymmetric structural trough; the northern and southern portions of the Province have been designated the Sacramento and San Joaquin Valleys, respectively.The Province is bordered by the Coast Ranges to the west,the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east. The Great Valley has been filled with sediments derived from both marine and continental sources. Thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south central portion of the valley. The sedimentary formations range in age from Jurassic to Recent,with the older deposits being primarily marine in origin and the younger deposits being primarily continental. Continental-derived sediments were primarily deposited in lacustrine, fluvial,and alluvial environments with sediment sources being the mountain ranges surrounding the valley(Olmsted and Davis, 1961);the site itself is located on unconsolidated and semi-consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977).Rocks composing 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 estimated depth to ground water at the site is approximately 25 feet below surface grade(bsg)based on data from the on-site monitoring wells. The ground water flow is generally toward the west to northwest. Advanced GeoEnvironmental,Inc.