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31 March 2000 AGE-NC Project No. 00-0699 Page 2 of 9 2.2. UNDERGROUND STORAGE TANK REMOVAL According to information obtained from the PHS-EHD, via Espana Geotechnical Consulting (Espana) and Pacific Environmental Group, three 8,000-gallon gasoline USTs and associated dispensers were removed from the site in December 1980. The former location of the tank cluster is illustrated on Figure 2. The PHS-EHD had no records of the UST removal nor associated sampling, if performed. 2.3. CALTRANS SITE INVESTIGATION In October 1999,Espana supervised the advancement and sampling of three soil borings within the former UST cluster.The borings were advanced as part of a proposed CalTrans investigation for the expansion of the Highway 99 - Hammer Lane interchange. The three borings, EGC-1, EGC-2 and EGC-3, were advanced to depths of 21.5 feet, 66 feet and 26.5 feet below surface grade(bsg),respectively. A total of nine soil samples and one grab ground water sample were submitted to a laboratory for analysis of total petroleum hydrocarbons quantified as gasoline(TPH-g)and diesel(TPH-d)and volatile aromatics(benzene,toluene,ethyl benzene and xylenes; BTEX). TPH-g and TPH-d were reported in five soil samples at concentrations ranging from 1.70 mg/kg to 2,390 mg/kg.BTEX compounds were reported in three soil samples at concentrations ranging from 0.0249 mg/kg to 239 mg/kg. TPH-d (0.173 gg/L) was the only target analyte reported in the water sample submitted for analysis. 2.4. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING The site is located within the northern 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. 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 is located on unconsolidated and Advanced GeoE nviron mental,Inc.