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VZ1 INC <br /> were reportedly present only in borings MW-1, S131, SB2 and S135 at concentrations <br /> ranging from 47 to 790 mg/kg <br /> These soil boring samples contrast with the soil samples taken from immediately beneath <br /> the former tank location at approximately 17 feet bgs which were reported to contain very <br /> high concentrations of both undifferentiated gasoline hydrocarbons (to 6,900 mg/kg) and <br /> volatile organics (to 1,427 mg/kg) These data strongly suggest that gasoline fuel leaked <br /> from the former underground storage tank at the site and migrated dominantly in the vertical <br /> direction until it reached the water table where it spread horizontally by groundwater <br /> movement <br /> WaterWork (1990) recommended that additional excavation or remediation targeted <br /> specifically for a soil remediation effort was not warranted at the Sebastiani Vineyard site <br /> for the following reasons <br /> 1 Soil boring sample analyses had indicated hydrocarbon levels to be below typical <br /> designated levels for the volatile organics The levels that were reportedly detected <br /> during sampling of the excavation bottom were within the capillary fringe, a saturated <br /> zone in continuity with the unconfined groundwater <br /> 2 All hydrocarbon-contaminated soils located above the historical high groundwater <br /> level in the tank area had been removed If additional excavation of soil were <br /> undertaken the clean backfilled material would have become recontaminated once <br /> water levels return to normal (less than 10 feet below grade based on San Joaquin <br /> County Flood Control and Water Conservation District records from years 1975, 1980, <br /> 1984, 1987) <br /> 3 In situ soil treatment methods, such as soil vapor extraction (SVE), were judged to <br /> potentially not be effective in low permeability soils such as those present at the site <br /> 19150011 005 31 <br />