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R604 :UPDATE 13 11-24--1.992 <br /> A portable ambient air PID-GC (Photovac 10550 packed column) is <br /> used at the site to sample for breakthrough of the carbon scrubs, <br /> ° the influent and effluent of the system, and the influent from the <br /> various vapor extraction wells Prior to sampling the wells or <br /> the system, a calibrant prepared from fresh gasoline is infected <br /> into the GC-PID The resulting chromatogram has numerous <br /> responses The microprocessor of the GC-PID computes the area per <br /> response in volt seconds, and assigns a peak number and retention <br /> time The sum of all the responses are then used to obtain a mg/L <br /> per volt second calibrant factor, which is used to calculate mg/L <br /> as gasoline vapor from each analysis produced Pounds per day <br /> can be computed using these mg/L values produced from the analysis <br /> of the different vapor recovery wells, the pressure differential <br /> created at the orifice to determine flow rates for each well, and <br /> the influent values The pounds per day values for each well and <br /> the influent are then averaged to the preceding site visit' s pound <br /> per day value and then multiplied by the number of days the system <br /> operated between visits to estimate the total pounds each well and <br /> the total system have removed for that time period. This poundage <br /> is then added to the accumulated poundage of the previous visit to <br /> update the total pounds removed to date, see Table 3 and Appendix <br /> B <br /> Sampling Vapor Streams <br /> The vapor samples are obtained by attaching a dedicated air tight <br /> 60 cc syringe and soft polytubzng to a sample port on the well <br /> side of the orifice plate on the vapor recovery manifold. The <br /> sample port is then opened and the syringe is purged by pulling <br /> and pushing the syringe plunger several times filling and <br /> depleting the syringe of that particular wells vapor stream Then <br /> the syringe is filled, the sample valve closed and forceps are <br /> used to clamp onto the soft polytubing to create an air tight seal <br /> for the syringe before removing the syringe from the sample port . <br /> Once the 60 cc syringe is removed, the plunger is pushed into the <br /> syringe to create pressure within the syringe and released to <br /> allow the vapors that have been captured to reach equilibrium. A <br /> small dedicated needle attached to a dedicated 1 cc syringe is <br /> then inserted into the 60 cc syringe via the soft tubing. Again <br /> the 1cc syringe is purged numerous times prior to filling it with <br /> the sample All but 0 5 cc of the sample is e3ected into the air <br /> prior to zn3ecting the remaining 0 5 cc syringe sample into the <br /> GC-PID (the calibrant infection is 0 5 cc) Once the ghromatogram <br /> has been recorded, an instrument blank is run prior to the next <br /> sample . The instrument blank will indicate if residual peaks are <br /> being carried onto the next analysis <br /> While the GC-PID analysis is running for a particular sample (25 <br /> minutes per sample run) , vacuum influent readings are obtained <br /> from the wells by attaching a manometer calibrated in mm water to <br /> sample ports at the well heads These readings show the mm water <br /> pressure or vacuum that is being created at each well <br /> page 5 <br />