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f � t R604 :UPDATE 11-JULY, 1992 st ' A portable ambient air PID-GC (Photovac 10550 packed column) is used at the site to sample for breakthrough of the carbon scrubs , the influent and effluent of the system, and the influent from the )� various vapor extraction wells . Prior to sampling the wells or the system, a calibrant prepared from fresh gasoline is in3ected ( into the GC-PTD. The resulting chromatogram has numerous responses . The microprocessor of the GC--PID computes the area, per response, in volt seconds , and assigns a peak number , and � IlI retention time. The sum of all the responses are then used to 4' r ` ; obtain a mg/L per volt second calibrant factor, which is used to calculate mg/L as gasoline vapor from each analysis produced. Using these mg/L values produced from the analysis of the 4 ; different vapor recovery wells , the pressure differential created iat the orifice to determine flow rates for each well , and the s � } linfluent values , pounds per day can be computed. The pounds per x i day values for each well and the influent are then averaged with the pounds per day value from the previous visit and then multiplied by the number of days the system operated between visits to estimate the total pounds each well and the total system have removed for that time period. This poundage is then added to the accumulated poundage of the previous visit to update the total pounds removed to date . I� � kl SAMPLING VAPOR STREAMS ! , I The vapor samples are obtained by attaching a dedicated air tight „ 3 � 60 cc syringe and soft polytubing to a sample port on the well 'I'� ;� 1side of the orifice plate on the vapor recovery manifold. The sample port is then opened and the syringe is purged by pulling and pushing the syringe plunger several times , filling and I` ( I depleting the syringe of that particular wells vapor stream. Then the syringe is filled, the sample valve closed, and forceps are used to clamped onto the soft polytubang to create an air tight seal for the syringe before removing the syringe from the sample ' port. Once the 60 cc syringe is removed, the plunger is pushed into the syringe to create pressure within the syringe and released to allow the vapors that have been captured to reach equilibrium. A small dedicated needle attached to a dedicated 1 cc syringe is then inserted into the 60 cc syringe via the soft tubing. Again the lcc syringe is purged numerous times prior to filling it with the sample . All but 0 .5 cc of the sample is eDected into the air prior to inaecting the remaining 0 .5 cc syringe sample into the GC-PID (the calibrant inDectson is 0 .5 CC) . Once the chromatogram has been recorded an instrument blank is run prior to the next sample. The instrument blank will indicate if residual peaks are being carried onto the next �i analysis . While the GC-PID analysis is running for a particular sample (15 minutes per sample run) , vacuum influence readings are obtained from the wells by attaching a manometer calibrated in mm water to sample ports at the well heads . These readings show the mm water pressure or vacuum that is being created at each well . ' page 5 I I i