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19 June 2000 <br /> AGE-NC Project No 96-0232 <br /> Page 18 of 35 <br /> 8.0. SOIL REMEDIATION ALTERNATIVES <br /> Four methods for remediation of fuel components-impacted soil for the site were evaluated with <br /> consideration of site-specific factors The methods considered included soil vapor extraction(SVE), <br /> ex-situ treatment, in-situ bioremediation and passive remediation <br /> 8 1 SOIL VAPOR EXTRACTION <br /> SVE is a well accepted method of treatment for hydrocarbon-impacted soil, and has been used at <br /> numerous sites with an excellent rate of success, SVE is most effective on volatile hydrocarbons in <br /> permeable soil <br /> 811 Principles <br /> For most SVE systems, a vacuum blower is used to volatilize hydrocarbons in the vadose <br /> (unsaturated)zone and draw the vapor into extraction wells screened within the contaminant plume <br /> The hydrocarbon vapor is drawn from the wells and "treated" in one of several possible treatment <br /> units(carbon canisters, internal combustion engines,thermal oxidizers and catalytic oxidizers) Air <br /> Injection wells maybe installed outside the contaminant plume to increase air flow to the extraction <br /> unit <br /> An internal-combustion(IC)system draws the vapor stream into the carburetor system of the engine <br /> and mixes the vapor with air prior to combustion Exhaust gasses (oxides of carbon and hydrogen) <br /> are further broken down in a catalytic converter before being emitted to the atmosphere These <br /> systems require supplemental fuel, such as propane or natural gas, which can greatly increase <br /> expenses as vapor concentrations decrease below levels normally required for combustion Typically, <br /> internal combustion engines work effectively where in-situ hydrocarbon concentrations approach <br /> the 40,000 parts per million - volume (ppmv) required for peak performance of the engine As <br /> concentrations decrease below 20,000 ppmv,supplemental fuel requirements,and therefore expenses <br /> may become burdensome Another disadvantage of these systems is the noise generated by the <br /> engine, however, this can be mitigated by placing the unit inside an enclosure, such as a building <br /> A carbon-canister system operates by routing hydrocarbon vapor through activated carbon filters <br /> where adsorption of hydrocarbons onto carbon takes place, removing the hydrocarbons from the <br /> vapor stream This type of system works best for low concentrations of hydrocarbons,but becomes <br /> expensive when high concentrations of hydrocarbon vapor necessitate frequent canister replacement <br /> and disposal of spent carbon <br /> Advanced GeoEn%vonmental,Inc <br />