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carbon traps and adsorbs the hydrocarbon gases until the sample is analyzed at the <br /> laboratory by desorption with carbon disulfide followed by gas chromatographic <br /> analysis of the solution The volume of the of the sample is determined by multiplying <br /> the flow rate of the sampling pump by the duration of the sampling event to obtain <br /> liters of air sampled A typical SKC carbon tube sample is obtained by sampling the <br /> blower exhaust at one liter per minute for three to five minutes to obtain a three to five <br />' liter sample In this manner the vapor composition of the extracted well vapors can be <br /> determined for specific compounds such as benzene, toluene, ethylbenzene, total <br /> xylenes, or total petroleum hydrocarbons (TPH) as gasoline Appendix 11 presents the <br /> Ianalytical laboratory reports obtained from the SKC Tube analyses <br /> I <br /> The OVA 128-GC cannot directly measure vapor concentrations of hydrocarbons <br /> greater than 1 000 m as methane However, the instrument can be effective) <br /> 9 � pp � Y used <br /> Ito monitor vapor concentrations above 1,000 ppm as methane if a volumetric dilution <br /> of the vapor stream is performed This is accomplished by using a 1 liter tedlar bag <br /> filled with zero gas air at atmospheric pressure and injecting a 5 or 10 mL gas sample <br /> to the bag which then provides a 200 1 or 100 1 diluted sample which can then be <br /> used to analyze samples of up to 200,000 ppm as methane The contents are allowed <br /> to mix and are then are analyzed with the OVA to obtain a vapor concentration of the <br /> Idiluted sample Correction for the dilution is made by multiplying by the dilution factor <br /> VAPOR EXTRACTION TECHNOLOGY, INC <br />