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UPDATE 28 8-02-94 produced an anomalous high when used From these gradient lines, • data points representing the 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, "i e . " incorporating conditions caused by local geology, hydrogeology, utility trenches, etc These are used to control the contour between data points This site is presently being influenced by vapor extraction at MWS, VSB3 , VSB5, VSB9 and VSB11 A vacuum at 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 water measurement is corrected for the negative vacuum head (potentiometric head) Vapor Recovery System and Monitoring During the latest confirmation soil sample drilling which occurred on February 2 , 1994 , SB13 , SB14 and SB15 were converted into vapor extraction wells These wells along with P3 , VSB5, VSB9, VSB11 and MW5 are presently be utilized for vapor extraction, see Figure 3A These wells have been manifolded into the laterals of the above listed wells that are manifolded to a vapor extraction system with individual valved orifices for flow control and measurement . The wells are fitted with a PVC tee head with a locking air tight cap, for well access The tee lateral (2 inch) is fitted with a 1/4 inch pipe to tubing fitting for obtaining vacuum/pressure and temperature readings A pipe to 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 the manifold the wells are connected to their own 2 inch PVC riser (36 inch 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 together above the gate valve to a set of two orifice risers that are in parallel before the vacuum pumps After the vapor stream leaves the manifold, it is pulled into the pumps (two Rotron DR505 placed in series) and then into activated charcoal vapor scrubs If breakthrough occurs through the 1st carbon (5 pounds per day or greater release of gasoline range hydrocarbons) , 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 A portable ambient air PID-GC (Photovac 10550 packed column) was used at the site to sample, the influent and effluent of the system, and the influent from the various vapor extraction wells , for breakthrough of the carbon scrubs Before sampling the wells or the system, a calibrant made from fresh gasoline is in3ected page8