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Former Beacon Station No 12474 June 7,2005 <br /> Stockton California Results of Additional Groundwater Assessment <br /> • gradient of approximately 0 004 as shown on Figure 6 Distributions of TPHg and benzene <br /> in groundwater for first quarter 2005 are shown on Figures 7 and 8 <br /> Source, Nature and Extent of Soil and Groundwater Impacts <br /> Results of site investigations indicate the lateral extent of hydrocarbon-impacted soil is <br /> localized in the area of the eastern dispenser island as indicated by soil analytical data <br /> collected from the vapor extraction well VW-1/2/3 and monitoring well MW-12 borings <br /> Lateral delineation of soil impacts to the north, west, south and east is provided by soil <br /> analytical results from the monitoring well MW-4, MW-8, MW-10 and MW-11 and other <br /> outlying borings as shown on Figure 9 <br /> Vertical and lateral extent of petroleum hydrocarbons in soil is indicated on the geologic <br /> cross sections A-A' and B-B' on Figures 3 and 4 Soil TPHg and benzene concentrations are <br /> shown on the cross sections to illustrate their lateral and vertical distribution The apparent <br /> source of petroleum hydrocarbons in soil and groundwater is the eastern dispenser island in <br /> the northern portion of the site <br /> The highest gasoline constituent concentrations in soil samples were collected from the <br /> vapor well VW-1/2/3 and MW-12 borings located near the north end of the eastern dispenser <br /> island and occur predominantly at depths of 85 feet or less as confirmed by the results of soil <br /> analytical data collected below 90 feet bsg from MW-13 The vertical extent of gasoline <br /> constituents in soil in the dispenser island area is delineated by samples collected from the <br /> vapor well VW-7 and air sparge well AS-1 borings <br /> Quarterly monitoring indicates groundwater impacted with dissolved hydrocarbons generally <br /> extends to the vicinity of the site boundaries The current (first quarter 2005) distribution of <br /> TPHg and benzene in groundwater is shown on Figures 7 and 8 <br /> The highest concentrations of gasoline constituents in groundwater have been regularly <br /> detected in monitoring wells MW-2, MW6 and MW-12, and vapor wells VW-1 and VW-4 <br /> AddtnIGWassinnt <br /> Project No 147415 8 HORIZON ENVIRONMENTAL INC <br />