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' 15 November 1995 � AGE-NC Project No 95-0142 ' Page 7 of 19 ' from 19 to 35 feet, at 10 inches of water the radhus of influence ranges from 13 to 23 feet It is likely that the effective radius of influence at the site is less than 20 feet 5 5 ANALYTICAL RESULTS OF VAPOR SAMPLES ' TPH-g was detected in the air samples at concentrations ranging from 10,000 ppb to 3 1,000 ppb BTE&X were detected in the air samples at concentrations ranging from 70 ppb (ethylbenzene,VS 1) ' to 2,100 ppb (toluene, VS3 and VS4) Analytical results of the vapor samples are included in Table 5 The laboratory report and chain-of-custody form are included in Appendix G ' 6.0. SOIL REMEDIATION ALTERNATIVES ' 61 SOIL VAPOR EXTRACTION Soil vapor extraction(SVE) is a well-accepted method of treatment that has been used successfully at numerous sites with an excellent rate of success The method works best on volatile hydrocarbons in permeable soil I611 PRINCIPLES For most SVE systems, a vacuum blower is used to volatilize hydrocarbons and draw the vapors into extraction wells installed and screened within the contaminant plume The vapors are drawn from the wells and treated in one of several possible treatment units (internal combustion engines, carbon Icanisters, thermal oxidizers and catalytic oxidizers) Air injection wells may be installed outside the contaminant plume to increase air flow to the extraction unit In an internal-combustion(IC) system, vapors are drawn into a carburetor system of the engine and mixed with air before 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 that are normally required for combustion Typically, internal ' combustion engines work effectively where in-situ hydrocarbon concentrations approach the 40,000 ppmv required for peak performance of the engine As concentrations decrease below 20,000 ppmv, supplemental fuel requirements become burdensome Another disadvantage of these systems is the noise generated by the engine,however, this can be mitigated by placing the unit inside an enclosure, • such as a building r IIn a carbon-canister system, hydrocarbon vapors are routed through activated carbon filters, where