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UPDATE 30 11-11-94 <br /> • riser (36 inch in height) with an orifice plate and a gate valve <br /> at the top of the riser vacuum/pressure ports are located on <br /> either side of the orifice plate Each orifice (well) has its <br /> own manometer, calibrated in millimeters (mm) water, which are <br /> connected to the ports for continuous measurement of flow from a <br /> particular well All the extraction wells are manifolded <br /> together above the gate valve to a set of two orifice risers that <br /> are in parallel before the vacuum pumps After the vapor stream <br /> leaves the manifold, it is pulled into the pumps (two Rotron <br /> DR505 placed in series) and then into activated charcoal vapor <br /> scrubs If breakthrough occurs through the lst carbon (5 pounds <br /> per day or greater release of gasoline range hydrocarbons) , this <br /> carbon is removed from the system The #2 carbon is then placed <br /> at the 41 position and a new carbon placed on the exhaust as the <br /> #2 carbon <br /> A portable ambient air PID-GC (Photovac 1OS50 packed column) was <br /> used at the site to sample, the influent and effluent of the <br /> system, and the influent from the various vapor extraction wells, <br /> for breakthrough of the carbon scrubs Before sampling the wells <br /> or the system, a calibrant made from fresh gasoline is in3ected <br /> into the GC-PID The resulting chromatogram has numerous <br /> responses The microprocessor of the GC-PID computes the area <br /> per response in volt seconds, and assigns a peak number and <br /> retention time The sum of all the responses are then used to <br /> obtain a mg/L per volt second calibrant factor This factor is <br /> used to calculate mg/L as gasoline vapor from each analysis <br /> Pounds per day can be computed using these mg/L values, and the <br /> pressure differential created at the orifice (flow rate) for each <br /> well Since September 25 , 1992, tedlar bag samples are obtained <br /> and brought back to be analyzed in the WEGE portable laboratory <br /> This is necessary due to long eluting time (analysis time <br /> increased from 10 minutes per sample to 30 minutes per sample) <br /> needed per analysis using the 10s50 (all early eluting compounds <br /> have been removed by vapor extraction) The pounds per day <br /> values for each well are then averaged to the corresponding <br /> values from the preceding site visit and then multiplied by the <br /> number of days the system operated between visits to determine <br /> the total pounds removed for each well and for the total system <br /> for that time period This poundage is then added to the <br /> accumulated poundage of the previous visit to update the total <br /> pounds removed to date, see Table 3 <br /> Sampling Vapor Streams. <br /> The vapor samples are obtained by attaching a dedicated air tight <br /> soft polytube to a sample port on the well side of the orifice <br /> plate on the vapor recovery manifold The tubing is then <br /> connected to a tedlar bag placed inside a vacuum sampler. The <br /> sample port is then opened. A vacuum placed on the outside of <br /> the tedlar bag from the sample vessel allows the tedlar bag to <br /> fill with the vapor stream from that particular sample port <br /> Once the tedlar bag is full the valve is closed and the vacuum <br /> removed from the sample vessel The tedlar bag contains an air <br /> tight locking septum valve which is then closed and locked to <br /> pagel2 <br />