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- <br /> s a r slam <br /> the contamination at the site is comprised primarily of gasoline-range <br /> hydrocarbons, soil venting is considered the most appropriate soil <br /> remediation alternative. A discussion of site suitability for in-situ <br /> soil venting and a proposed vapor extraction system design are presented <br /> below. <br /> Evaluation of Site Suitability for In-Situ Soil Venting <br /> Tn order to evaluate the applicability of soil venting for cleanup of <br /> petroleum hydrocarbon contaminated soil at the Sebastiani Vineyards site, <br /> the lithologic and soil quality data generated by the site assessment <br /> investigation were reviewed. McLaren Engineering has completed soil <br /> borings in the vicinity of the former underground tank to define the <br /> subsurface geology and the extent of contamination. Lithologic logs from <br /> these borings were used to construct generalized geologic cross sections <br /> in the vicinity of the tank site. Figure 4 shows the location of the two <br /> cross sections that are presented on Figures 5 and 6. These cross <br /> sections show the lithologic units encountered beneath the site and depict <br /> the estimated vertical extent of petroleum hydrocarbon and volatile <br /> organic compound (VOC) contamination in both soil and groundwater. <br /> The lithology above the water table in the vicinity bf the tanks is of <br /> interest in evaluating site suitability for soil venting because it is the <br /> area where hydrocarbons have adsorbed onto the soil particles, i.e. , the <br /> area of soil contamination. As can be seen on Figures 5 and 6, the <br /> lithologic units .in the area of interest range from silty sand to silty <br /> clay. The groundwater table at this site is at a depth of approximately. <br /> 16 feet. <br /> Soil venting is an effective method of removing petroleum hydrocarbons and <br /> related volatile organic compounds from soils. Due to the lithologic <br /> variability of materials underlying the site, selective screening of the <br /> silty sand and silty clay units is proposed to maximize soil venting <br /> effectiveness. The selective screening approach to soil venting at the <br /> site is discussed in detail in the vapor extraction system design section <br /> which follows. <br /> Vapor Extraction System Design <br /> The area of soil with chemicals requiring cleanup is illustrated on <br /> Figure 3. Based on the relative .permeabilities of the lithologic units. <br /> encountered at the site and the mechanicalpropertiesof the proposed <br /> vacuum. device which will be used for vapor extraction, the vadose zone <br /> vapor extraction wells are expected to have a 20-foot radius of influence. <br /> Therefore, five soil venting wells (SVW) would be required for remediation <br /> e <br /> of the area of identified soil contamination, as shown on Figure 7. <br /> ---_-...- -soil.__venting_well_design....shown-on...Figure-8--Presents-....------.-.-..----------- ------------ ----- <br /> a dual completion approach to vapor.extraction. The two completion zones <br /> allow for vapor collection from the two sediment types encountered from <br /> ground surface to approximately 30 feet below ground surface at the <br /> subject site. The upper completion zone is designed to extract VOCs and <br /> 10 <br />