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Chevron Products Company 8 Former Chevron Service Station #9-5775, 301 West Kettleman Lane, Lodi, California June 5, 2001 2 3 5 Stratigraphic Setting Based on observations reported during drilling activities, the site vicinity is underlain by sandy silts, clayey silts, silty sands, clayey sands, and sands of varying amounts Numerous water - bearing zones consisting primarily of sands and silty to clayey sands appear from first encountered water (approximately 58 feet bgs) to a depth of approximately 220 feet bgs Low permeability zones were encountered at various depths and locations, but due to the presence of water at varying locations in these zones, they do not appear to act as confining layers A cross section location map and geologic cross section A -A' are presented as Figures 12A and 12B, respectively A cross section location map and geologic cross section for B -B' are presented as Figures 13A and 13B, respectively A geologic cross section for the site from C -C' to a maximum depth of 217 feet bgs is presented as Figure 14 Depth discrete and groundwater monitoring well analytical data are also presented on the cross sections 3.0 EXTENT OF PETROLEUM HYDROCARBON IMPACTS 3.1 Petroleum Hydrocarbons Adsorbed in Soil During UST removal and over -excavation activities in August 1998, soil was found to contain concentrations of TPHg, benzene, and MtBE at 2,300 mg/kg, 41 mg/kg, and 22 mg/kg, respectively, at the bottom of the excavation Historical soil analytical data is included as Attachment C 10 Currently, the maximum concentrations of petroleum hydrocarbons and fuel oxygenates in soil appear to be located in the vicinity of the former USTs, adjacent to extraction well EX -1 and vapor extraction wells VE -1 through VE -4 The vertical extent of TPHg, BTEX, and MtBE in the vicinity of the former USTs extends to approximately 65 feet bgs as indicated by soil analytical results from EX -1, VE -1 through VE -4, and soil borings SB -2 and SB -3. Trace concentrations of benzene and MtBE were detected at a depth of 72 feet bgs in SB -1 • 3.2 Estimated Mass of Petroleum Hydrocarbons in Soil In June of 2000, SECOR performed a calculation to estimate the total mass of TPHg, benzene, and MtBE remaining in soil This mass balance calculation was based on historical soil data, provided in Attachment B For this estimate, the following assumptions were made • The area of impacted soil at the site consists of one contiguous area; • Impacted soil In the area of the former UST extends to a total depth of 55 bgs, and • Soil concentrations in the former UST area are equal to soil data from borings (EX -1, SB -2, SB -3, and VE -1 through VE -4) 11Chevron1957751ParFrpl9-5775PARFRP2 doc