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06 December 1995 <br /> AGE-NC Project No. 95-0100 <br /> Page 6 of 13 <br /> vapor samples are included in Table 3. The laboratory report and chain-of-custody are included in <br /> Appendix E. <br /> 5.0. SOIL REMEDIATION ALTERNATIVES <br /> Data collected from the site during the investigation of the former UST site indicates that <br /> hydrocarbon-impacted soil is present in the vadose zone from approximate depths of 5 to 40 feet bsg. <br /> No ground water investigation was required or performed at the Franklyn Cole site, and ground water <br /> has not been encountered on the site during this or previous investigations. Therefore, only <br /> hydrocarbon-impacted soil remediation alternatives are considered in this CAP. <br /> 5.1 SOIL VAPOR EXTRACTION <br /> Vapor extraction is a commonly proposed method of treatment that has been used at a large number <br /> of sites. The method is most efficient addressing volatile hydrocarbons in permeable soil. <br /> 5.1.1. PRINCIPLES <br /> The soil vapor extraction (SVE) method employs a vacuum blower to volatilize hydrocarbons and <br /> draw the vapors into extraction wells screened within the contaminant plurne. The vapors are drawn <br /> from the wells and treated in one of several possible treatment units (internal combustion engines, <br /> carbon canisters, thermal oxidizers, and catalytic oxidizers). <br /> An internal-combustion(IC) system premixes air, and supplemental fuel if required, with the extracted <br /> hydrocarbon vapors prior to drawing the mixture into an internal combustion engine where the <br /> mixture undergoes combustion. Exhaust gasses (oxides of carbon and nitrogen) are further broken <br /> down in a catalytic converter before being expelled to the atmosphere. These systems generally <br /> require supplemental fuel, such as propane or natural gas, which becomes an increasing expense as <br /> vapor concentrations decrease below levels required to support combustion. Typically, IC engines <br /> work efficiently when in-situ hydrocarbon concentrations approach the 40,000 ppm required for peak <br /> performance of the engine. After concentrations decrease below 20,000 ppm, supplemental fuel must <br /> be added to maintain the IC process. As the hydrocarbon concentrations Fi the extracted soil vapor <br /> continue to decline, the supplemental fuel 'cements can become quite burdensome. An additional <br /> drawback of the IC systems is the noise gt ted by the engine; however, the noise can be mitigated <br /> by placing the unit inside an enclosure, such as a building. <br /> In a carbon-canister system, vapors are drawn into activated carbon filters, where the organic carbon <br /> serves to filter out the hydrocarbons h,., adsorption, removing them from the vapor stream. These <br /> _ systems are most efficient for vapors ­;ith low hydrocarbon concentrations, but are quite expensive <br />