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1r • REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING ' The site is located within the southern San Joaquin Valley which comprises part of the Great Valley geomorphic province of California The San Joaquin Valley is formed by the Great Valley geosyncline, which is a large, elongate, northwest-trending asymmetrical structural trough(basin) ' It 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 This trough 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 with the older deposits being primarily marine in origin and the younger deposits being primarily continental Contmental-derived sediments were primarily ' deposited in lacustrine, fluvial,and alluvial environments with sediment sources being the mountain ranges surrounding the valley(Olmsted and Davis, 196 1) The site is located on unconsolidated and ' semi-consolidated alluvium,lake,playa and terrace deposits of Quaternary age(California Division of Mines and Geology, 1977) ' 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) Based on information obtained during drilling, ground water depth ' beneath the site is approximately 25 to 30 feet below surface grade (bsg) Based on information obtained from a nearby site(706 North El Dorado Street)the prevailing ground water flow direction in the vicinity of the site is inferred to be toward the northeast However, flow direction may be both ' locally and seasonably variable ' SITE ASSESSMENT ACTIVITIES On 04 January 2002, four soil borings were advanced by Advanced GeoEnvironmental, Inc (AGE) ' at the site as part of the assessment related to the former USTs Soil probe borings B 1 through B4 were advanced vertically to depths of 40 feet bsg ' TPH-g, TPH-d and TPH-mo were detected in the soil samples collected from borings B 1 through B4 at concentrations ranging from 0 38 (milligrams per kilogram) mg/kg to 8,100 mg/kg TPH-g, 400 mg/kg to 5,500 mg/kg TPH-d and 200 mg/kg to 9,200 mg/kg TPH-mo TRPH was detected in the soil samples collected from borings B1 through B4 at concentrations as high as 36,000 mg/kg (134-30) One or more BTEX compounds were detected in the samples collected from borings B 1 through B4,with the exception of the 15-foot soil sample from B3, at concentrations as high as 45 mg/kg benzene,630 mg/kg toluene, 150 mg/kg ethylbenzene and 760 mg/kg total xylenes (B4-30) Seven additional volatile organic compounds were detected in the soil samples at concentrations ranging from 0 010 mg/kg to 440 mg/kg Fuel additives were not detected at or above laboratory reporting limits in the soil samples TPH-g and TPH-d were detected in the ground water samples collected from borings B 1 through B4 at concentrations as high as 5,400,000 micrograms per liter (µg/1) and 390,000 µg/l, respectively TPH-mo was detected in the ground water sample collected from boring B2 at a concentration of ' Advanced GeoEnvironmental,Inc