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Chevron Products Company 2 Former Chevron Service Station#9-6258,Stockton,CA October 28,1998 The Mark Group performed a preliminary subsurface investigation involving the drilling of six soil borings. The Mark Group reported residual concentrations of hydrocarbons in the former UST excavation backfill. Groundwater was not encountered and was reported to be in excess of 50 feet below the ground surface(bgs). In June 1996, NorCal Geophysical Consultants, Inc. (NorCal) performed a geophysical survey at the site. NorCal identified five anomalies associated with the waste oil tank, sump drain line, two corners of the former building where utilities entered the building, one location adjacent to the former pump islands; and one location where the former product lines and utility lines crossed. Subsequent excavation in these areas revealed debris within approximately 2 feet of the surface, including asphalt, both clay and metal piping, and wires. In September and October 1996, Pacific Environmental Group, Inc. (PACIFIC) observed excavation of the waste oil tank and former product lines, excavation of debris from the former gasoline UST pit, and limited over-excavation of the former gasoline UST pit. No detectable concentrations of hydrocarbons were reported in soil samples collected in the areas of the former waste oil UST and product lines. Gasoline hydrocarbon concentrations of up to 4,000 parts per million (ppm) were reported in the southeast corner of the former UST pit. After limited over-excavation of approximately 380 cubic yards of impacted soil and 200 cubic yards of concrete debris from the former gasoline UST pit, perimeter soil samples collected from the excavation were reported nondetectable to 2,300 ppm TPH-g. In May 1997, one boring (B-7) was drilled within the southeast portion of the footprint of the former gasoline UST pit. Groundwater was encountered in Boring B-7 at a depth of approximately 58 feet bgs. A groundwater"grab" sample collected from B-7 was reported to contain 32,000 parts per billion (ppb) TPH-g and nondetectable concentrations of benzene. PROPOSED SCOPE OF WORK The scope of work for this site assessment will include the drilling of three soil borings and installation of three groundwater monitoring wells in the areas of the former USTs and product islands. Two borings will be drilled north and west of the former gasoline USTs and one boring will be drilled southeast of the former UST pit and south of the former product island. Based on data from the drilling of Boring B-7, groundwater is expected to be encountered at a depth of approximately 60 bgs. As required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), SECOR will prepare a Site-Specific Health and Safety Plan prior to the commencement of fieldwork. The Site-Specific Health and Safety Plan will be reviewed by the field staff and contractors before beginning field operations at the site. 76007-018-01/WPLAN.DOC