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i <br /> APPENDIX B <br /> Former Stefano's Gas <br /> VAPOR PHASE CARBON (3 1,000-1b Vessels) <br /> VS <br /> CATALYTIC DESTRUCTION (ELECTRIC) <br /> Rental of the system will be appropriate, since the SVE unit is unlikely to operate more than 6 <br /> months(interim basis) The Carbon-based system would initially be less expensive if purchase was <br /> the preferred option, however, long-term media change-outs could increase the cost significantly <br /> In general, the rule of thumb is for highest vapor concentration sites (greater than 10,000 ppb), the <br /> use of a thermal destruction unit (thermal oxidizer) is most efficient, for sites with concentrations <br /> in the range of 2,000 to 10,000 ppb, a catalytic oxidizer is more efficient, and for lower <br /> concentrations, the use of vapor-phase carbon is most effective (sometime referred to as <br /> "polishing") Also, it is not atypical to utilize two or more destruction methods at a site, depending <br /> upon the concentrations For instance, at a site with very high concentrations, it may be practicable <br /> to begin operation with a thermal oxidizer,then after several months,change the system to a catalytic <br /> oxidizer Once the concentrations have decreased to 1,000 to 2,000 parts per billion,it is appropriate <br /> to utilize carbon <br /> The following are estimated costs for operation of several vapor extraction systems utilized by AGE <br /> The systems are based upon a maximum volume of 250-cfm and vapor concentrations in the range <br /> of 5,000 to 10,000 ppb (TPH-gasoline) <br />