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Site Background Information ENTERPRISE INVESTMENTS (Former J.B. Murphy Trucking) ' 355 Enterprise Place, Tracy, California j SITE LOCATION AND DESCRIPTION Ac n +)i e R o I The site is located in a commercial/industrial area of north Tracy, California, at an estimated ii elevation of 5 feet above mean sea level. The site is presently occupied by4iffeo Gonstmiatio 1 -Resiling: The site is located on the north side of Enterprise Place. The major portion of the site consists of an unpaved dirt area used as a parking lot for trucks(Figure 2).A two-story office facility and truck garage are presently located on the site. REGIONAL GEOLOGIC 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 A 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 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). STRATIGRAPHY Generally, gray to brown, damp to saturated, silty clay was encountered from surface grade to approximately 15 to 20 feet bsg and 25 to 30 feet bsg.Discontinuous intervals of brown, saturated 1 sandy silt of varying thickness was encountered at 15 to 20 feet bsg and 30 to 35 feet bsg.Pea gravel was encountered in the former UST pit at 5 feet and 10 feet bsg, presumably imported back-fill material i UNDERGROUND STORAGE TANK REMOVAL J i On 12 August 1997, one 10,000-gallon diesel UST was removed from the site by Stockton Service l Advanced GeoEnvironmental,Inc.