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28 April 1995 <br /> AGE-NC-95-0103 <br /> Pag;,e 5 of 11 <br /> Itest in MNV-3 and MW-4, which are 35 5 and 33 5 feet a»ay from VW-1, respectively No <br /> vacuum or pressure was measured in MW-2 situated approximately 45 feet from VW-1 Vacuum <br /> data is included in Table 3 <br /> 4 5- ANALYTICAL RESULTS OF AIR SAMPLES <br /> Concentrations of TPH in the extracted vapor rang=ed from 11,000 pgA to 23,000 pg/l <br /> Converting these values to parts per million volume (ppmv), concentrations ranged from 3,080 <br /> ppmv to 3,440 ppmv The analytical results are summarized in Table 4 The laboratory report and <br /> charm-of-custody are included in Appendix D Equations for coni ersion of po to ppmv are <br /> Iincluded in Appendix E <br /> 5 0_ REINIEDIATION ALTERNATIVES <br /> 5 1- SOIL VAPOR EXTRACTION <br /> Vapoi extraction is a N%idely accepted inetliod of soil tieatment that has been used at numerous <br /> sites an excellent rate of success The meihod \�ofks best on "olatile h�drocaibons in <br /> permeable soil <br /> 5 1 1 PRINCIPLES <br /> I A vacuum blo\+er is used to volatilize hydrocarbons and draw the vapors into extraction wells, <br /> installed and scieened within the contaminant plume The vapois are dra«n from the wells and <br /> treated in one of seN era] possible treatment units (internal conibustion engines thermal oxidizers, <br /> and catalytic oxidizers) <br /> In an inter nal-combustion system, vapors are drawn into a carburetor s}stem of the engine and <br /> mixed Nvith air before undergoing combustion Exhaust gasses (oxides of carbon and nitrogen) are <br /> further broken down in a catalytic converter before being enutted to the atmosphere These <br /> systems require supplemental fuel, such as propane or natural gas, which can become expensive as <br /> vapor concentrations decrease below levels that are noimally required for combustion Typically, <br /> internal combustion engines work effectively where in-situ hydrocarbon concentrations approach <br /> the 40,000 ppiuv required for peak performance of the engine As concentrations decrease below <br /> 20,000 ppmv, supplemental fuel requirements become burdensome Another disadvantage of <br /> these systems is the noise generated by the engine, however, this can be mitigated by placing the <br /> unit inside an enclosure, such as a building <br /> 1 <br />