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contamination is contained in the saturated sand unit which occurs at a <br /> depth interval of 17 to 34 feet in the area east of the excavated tank <br /> site (monitor wells MW-1, -2, and -3) , and at a depth interval of 17 to <br /> 24 5 feet in the area southwest of the tank site (monitor wells MW-9 and - <br /> 10) , as shown in Figures 9 and 10 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The site assessment investigations have determined that the lateral extent <br /> of soil contamination at this site terminates between 15 and 35 feet from <br /> the inner excavation boundary in all quadrants Soil contamination begins <br /> at a depth of 7 to 12 feet below ground surface and extends down to <br /> groundwater, at approximately 17 to 18 feet below ground surface <br /> Chemical contamination in groundwater extends laterally from the <br /> excavation area to the southwest a maximum of 100 feet The vertical <br /> extent of groundwater contamination is confined to the shallow groundwater <br /> unit encountered at the site A thick silty clay unit underlies the <br /> shallow groundwater throughout the area of investigation and this unit was <br /> encountered in all borings drilled during the assessment investigation <br /> This silty clay unit is at least 5 feet thick It's physical properties, <br /> including firmness, slight plasticity, and a moisture content from <br /> slightly moist to dry indicate an unsaturated condition Fuel <br /> hydrocarbons would not, therefore, be expected to extend vertically beyond <br /> the shallow groundwater unit at the site In addition, analysis of water <br /> samples from the primary supply well do not indicate groundwater <br /> contamination below the shallow unit, which is currently monitored at this <br /> site Construction information available for the primary supply well <br /> suggests that the upper 40 feet of the supply well is cased and <br /> perforations start below that depth <br /> Results of the site investigations at the Sebastiani Vineyards/Woodbridge <br /> Cellars facility indicate that site remediation would be required to <br /> cleanup soil and groundwater containing chemicals in concentrations which <br /> exceed regulatory standards The specific recommendations for site <br /> remediation will be presented in a Final Remedial Plan This plan will <br /> include an assessment of viable remediation alternatives for both soil and <br /> groundwater Soil venting would be a key element of soil remediation at <br /> this site and in situ bioremediation may be considered Groundwater <br /> extraction and on-site treatment would be utilized for groundwater <br /> remediation <br /> 25 <br />