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' 01 June 1999 AGE-NC Project No 95-0137 Page 7 of 26 vapor extraction, excavation, and in-situ soil bioremediation are the appropriate site remediation technologies with potential to address impacted soil and ground water that should be considered for this CAP Natural attenuation is also evaluated and discussed 5 1 SOIL VAPOR EXTRACTION ' Soil vapor extraction (SVE is a well-accepted method of treatment for hydrocarbon-impacted soil and has been used at numerous sites with an acceptable rate of success The method is most effective ' on volatile hydrocarbons in permeable soil ' 5 1 1 Soil Vapor Extraction Principles ' For most SVE systems, a vacuum blower is used to enhance volatilization of hydrocarbons in the vadose (unsaturated) zone and draw the vapor into extraction wells screened within the contaminant plume Hydrocarbon vapor is drawn from the wells and"treated"in one of several possible treatment units(carbon canisters, internal combustion engines,thermal oxidizers and/or catalytic oxidizers) Air injection wells may be installed outside the contaminant plume to increase air flow to the extraction unit Generally, an induced vacuum potential of at least 0 10 inches of water is required ' to successfully volatilize subsurface hydrocarbons The radius of influence is commonly considered to be the distance from the extraction well at which a vacuum of at least 0 1 inches of water is observed(EPA -A guide for Corrective Action Plan Reviewers) ' Inte al-combustionIC to s draw the vapor stream into a carburetors stem of the internal- . � Y ' combustion engine and mix the vapor with air prior to undergoing combustion Exhaust gasses (oxides of carbon and hydrogen) are further broken down in a catalytic converter before being emitted to the atmosphere These systems require supplemental fuel, such as propane or natural gas, ' which can become expensive as vapor concentrations decrease below levels normally required for combustion Typically, internal combustion engines work effectively where in-situ hydrocarbon concentrations approach the 30,000 to 35,000 parts per million- volume (ppmv) required for peak ' performance of the engine As concentrations decrease below 10,000 ppmv, supplemental fuel requirements become burdensome Another disadvantage of an IC system is the noise generated by the engine,however,this can be mitigated by placing the unit inside an enclosure, such as a building 1 C on-cgnister systems adsorb hydrocarbons from the extracted soil gas routed through activated carbon filters, thereby removing the hydrocarbons This type of system works best for low ' concentrations of hydrocarbons, but becomes expensive when high concentrations of hydrocarbon vapors necessitate frequent canister replacement and disposal of spent carbon Adtianced GeoEn�ironmental,Inc