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APPE M BST _CLOSURE EVALUATION REPORT Beacon Station No.696 2448 West Kettleman Lane Lodi,California ' Delta Project No.D093-916 Page 2 2.2 Site History and Site Activities ' Prior to acquisition of the site by Ultramar in July 1990, the site was owned and operated by Conoco, Inc. The presence of petroleum hydrocarbons in soil and ground water beneath the site was initially detected in early 1985. ' Since that time numerous investigations have been conducted at the site. There have been 37 ground water monitoring or soil vapor extraction (SVE) wells installed at the site and on the adjacent properties. A total of 21 of ' these wells, and an on-site domestic water supply, have been destroyed. Three single-walled underground fuel storage tanks were removed from the site in March 1989 and were replaced by the three existing double-walled tanks. ' Remedial activities have included installation of a ground water pump and treat system which was in operation from January 1986 until approximately late 1988, installation of a SVE treatment system which operated from ' December 1989 through April 1994, and the excavation and removal of soil from the tank pit and product line locations. 1 2.3 Site fill The site is located in the Northern San Joaquin Valley Basin which is an asymmetric synclinal trough containing Jurassic to Holocene sedimentary rocks and sediments. These sediments reach a maximum thickness of ' approximately 33,000 feet in the San Joaquin Valley(Repenning, 1960). ' The soil impacted with petroleum hydrocarbons are units of the Victor Formation. According to the State of California Department of Water Resources(DWR), (1967)the Victor Formation is of Quaternary age, up to 150 feet ' thick, and consists of recent alluvium and, alluvial fan and flood plain deposits. The Victor Formation is heterogeneous with no extensive clay layers to act as confining layers. The Victor Formation consists of sand and ' gravel deposits in the fan areas, while clay, silt, and sand occur in the interfan areas. The material is derived from volcanic, granitic, and metamorphic sources in the Sierra Nevada range to the east. The proceeding description is ' consistent with the descriptions of soil encountered in the borings drilled at the site. 1 2.4 Site ffydrogeoloa The following bodies of surface water are located near the site: the Mokelumne River, approximately 2.5 miles to the north; South Main Canal and percolation basins, located 1 mile to the northeast; and Pixley Slough, located approximately 3.5 miles to the south. RPT001.916