ARCHIVED REPORTS XR0008192 - Laserfiche WebLink

Home Browse Search

RG04 UPDATE 20 7-16-1993 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 zs corrected for the negative vacuum head (potentzometric head) . Vapor Recovery System and Monitoring- As stated in the Update Status Report #11, SB3, SB5, SB9 and SB11 were converted into vapor extraction wells on July 22, 1992 (VSB3 , VSB5, VSB9 and VSB11) Along with MW5, these wells are manifolded to a vapor extraction system with individual valved orifices for flow control and measurement from the individual wells . The individual 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 individual 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, 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 1OS50 packed column) was 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 or the system, a calibrant made from fresh gasoline is infected 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 retention time The sum of all the responses are then used to obtain a mg/L per volt second calibrant factor This factor is used to calculate mg/L as gasoline vapor from each analysis Pounds per da can be computed using these mg/L values, and the pressure differential created at the orifice (flow rate) for each well, and total influent . Since September 25, 1992 , tedlar bag samples are obtained and brought back to be analyzed in the WEGE portable laboratory. This is necessary due to long eluting time (analysis time increased from 10 minutes per sample to 30 minutes per sample) needed per analysis using the 10s50 (all early eluding compounds have been removed by vapor extraction) The pounds per day values for each well and the influent are then averaged to page 7