ARCHIVED REPORTS XR0010226 - Laserfiche WebLink

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Former Discovery Chevrolet June 5, 1998 Tracy,California Corrective Action Plan site is generally present between approximately 9 to 11 feet bgs with a flow direction toward the north-northwest. 4.0 EXTENT OF SOIL AND GROUNDWATER CONTAMINATION 4.1.1 Initial Vertical and Horizontal Extent of Hydrocarbon -Impacted Soil Based on the soil data collected at the site between 1993 and 1998, it appears that the areas impacted by gasoline hydrocarbons in the soil were confined to the soil primarily in the areas of the former product pipeline, near the former UST cavity, and in the area to the north of the former UST cavity along the seasonally fluctuating water table. The highest concentrations of gasoline hydrocarbons reported were from soil samples collected from the hand-augered soil boring SK in the vicinity of the former product line adjacent to the southwest comer of the former UST excavation. 4.1.2 Current Vertical and Horizontal Extent of Hydrocarbon- Impacted Soil The current vertical and horizontal extents of hydrocarbon-impacted soil were presented in the Problem Assessment Report (PAR). Cross-sections (Figures 4 and 5) presented in the PAR indicated the presence of silty to sandy clay beginning at surface grade and extending vertically to depths between approximately 12 to 18 feet bsg,. The analytical soil data collected between 1993 and 1998 has indicated that the fine-grained silty to sandy clay soil has contained the highest levels of gasoline hydrocarbons. Concentrations of gasoline hydrocarbons from soil samples collected below the groundwater table, which generally ranges between 9 and 11 feet bsg, in relatively coarser sandy clay to clayey sand soils were nondetectable for TPHg, BTEX, MTBE and other fuel oxygenates. Isoconcentration Maps (Figures 6 and 7) also presented in the PAR show the approximate lateral extent of hydrocarbon-impacted soil. 3001-21.cap 7 HORIZON ENVIRONMENTAL INC.