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R604 UPDATE 13 11-24-1992 BTEX in Ground Water (EPA method 602) No BTEXs were detected in monitoring wells from the March 5 , and June 2 , 1992 sampling During the previous sampling, December 16 , 1991 only MW1, MW2 , and MWS, had BTEXs in very low concentrations . During this latest sampling round (September 11, 1992) , sample results from MW1 detected only benzene (1 2 ug/L) and MW5 sample results detected only the xylenes (4 . 1 ug/L) Vapor extraction has removed the majority of BTEXs from all of the monitoring wells, see Table 1 Fecal Coliform: From December, 1991 through February, 1992 , monthly fecal coliform samples were being collected from monitor wells MW3 , MW4 , MW5 and MW6 Sampling again occurred in June, 1992, from monitoring wells MW3 , MW4 and MW6 . During the September 11, 1992 sampling, MW3 and MW6 were dry, no fecal coliform samples were obtained Table 2 shows the results of these samples As of June, 1992 all these wells are below detection limits, ¢2 . 2 MPN, for fecal coliform. VAPOR EXTRACTION s 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 "T" head with a locking air tight cap, for well access The "T" lateral (211 ) is fitted with a 1/4" pipe to tubing fitting for obtaining vacuum/pressure and temperature readings A pipe to hose 2 " union is placed between the "T" and the 2 " PVC flex hose that connects the well to the extraction manifold At the manifold the individual wells are connected to their own 2 " PVC riser (36" 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 1n millimeters (mm) water) which are hooked to the ports for continuous measurement of flow from a particular well . All the extraction wells are manafolded together above the gate valve to a set of two orifice risers that are in parallel prior to the vacuum pumps After the vapor stream leaves 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) prior to entering a second moisture drop out drum and then onto activated charcoal vapor scrubs If breakthrough was found to be occurring through the lst carbon, this carbon was removed from the system. The #2 carbon was then placed into the #1 position and a new carbon placed on the exhaust as the #2 carbon. page 4