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R504 :UPDATE16 2-23-1993 used. From these gradient lines; data points representing the1 . contact for the proposed contours are plotted : along each [ individual line. Once the data points have been plotted between all the wells, the data points representing a given gradient elevation (--45 foot; contour, for example) are connected with site ; specific factors, " .e. " incorporating conditions caused by local ! geology, hydrogeology, utility trenches, etc . These are used toy control the contour between data points . This site is presently ' being influenced by' vapor extraction at MW5, VSB3 , :VSB5, VSB9 and , VSB11 . A vacuum ;fat these wells and surrounding wells will. influence the shape of the ground water surface and subsequent : flow directions of; the ground water. To obtain representative measurements that show the influence by the vacuum.extraction at,� this site, a vacuum measurement is obtained at the well head', before removing the cap and the subsequent depth. to waterk measurement is corrected for the negative ,vacuum head; (potentiometric head) . ,I Vapor Recovery System and Monitoring: As stated in the Update Status Report #11, SB3 , SBS,_ SB9 and SB11 � f were converted into vapor extraction wells on July 22 , 1992p (VSB3 , VSB5, VSB9and VSB11) . Along with MWS, these wells are ; manifolded to a vapor extraction system with individual valvedf orifices for flow control and measurement from the individual 11 wells . The individual wells are fitted with a PVC tee head with a locking air tight cap, for well access . The tee lateral (21I inch) is fitted with a 1/4 inch pipe to tubing ; fitting ford obtaining vacuum/pressure and temperature readings . A pipeto.' hose 2 inch union is placed between the tee and the 2 inch PVC flex hose that connects the well to the extraction manifold. At' j the manifold the individual wells are connected- to their own 2 inch PVC riser (Kinch in height) with an orifice ;plate and a' gate valve at the top of the riser. Vacuum/pressure ports are'; located on either side of the orifice plate. Each orifice (well) ,[ has its own manometer (calibrated in millimeters : (mm) water) ' which are connected to the ports for continuous measurement of. flow from a particular well . All the extraction wells are; manifolded togetherabove the gate valve to a set of two orifice risers that are in parallel before the vacuum pumps . After the vapor stream leave's the. manifold', it flows through a moisture, drop out drum (55 gallon 17E) and then is pulled into the pumps; } (two Rotron DR505 placed in series) before entering a secon&, moisture drop outidrum and then into activated charcoal vapor; scrubs . If breakthrough occurs through the lst ' -carbon, this'¢ carbon is removed from the system. The #2 carbon is then placed' at the #1 position and a new carbon placed on the exhaust as the, #2 carbon. R A portable ambient air PID-GC (Photovac 10550 packed column) wase 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 . Before sampling the wells orf the system, a calibrant made from fresh gasoline isfinjected into` the GC-PID. The resulting chromatogram has numerous responses.'[ The microprocessor, of the GC-PID computes the area'per response. I� page 4 11