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R603 UPDATE-20 9/15/93 10 measurements obtained prior to the installation of the heat exchanger. Vacuum applied to the formation was limited to the amount Of 02 supplied to the thermal oxidizer (TO) (needed 18t) . The vapor stream had to be air diluted to maintain an 02 level above 18.16 to prevent flame-out conditions at the TO which limited the amount of vacuum placed on the formation. Figure 4B are measurements obtained two days after operating the system with the heat exchanger which allowed a lower 02 supply to the TO (14$) The manifold setting for the various vapor extraction wells was not adjusted, vacuum was increased to the wells by closing the air dilute system. Figure 4C are measurements obtained prior to shutting the system down due to excess noise . The vacuum was increased at MW10 by partially closing the manifold valves that service MW1, MW2 and MW3 GROUND WATER QUARTERLY SAMPLING Ground water samples were collected on June 14, 1993 , see Table 1 . These samples were collected by a WEGE geologist and "Chain of Custody" delivered on ice to a state certified testing laboratory (SUPERIOR PRECISION ANALYTICAL, INC DHS#1332) for chemical analyses . These samples were analyzed for TPH and BTEX concentrations using EPA Methods 8015 and 602 respectively Since diesel has never shown up in the sample results, the samples obtained on 11/27/90 and later were analyzed using EPA methods 5030 and 602 for Total Fuel Hydrocarbons and BTEX. The next quarterly sampling will occur in September, 1993 . 3 .0 RESULTS GROUND WATER SAMPLE RESULTS Ground water samples were obtained from all of the monitoring wells on June 14, 1993 The latest sample results showed a decline in contaminant levels associated with the ground water at MW1 and MW3 . Of the other wells that have some degree of ground water contamination (MW2 , MW8, MW10 and MW12) showed slight increases, see Table 1 The increase in contaminant concentrations found at MW2 and MW10 is thought to be associated with the vacuum extraction at these wells, concentrating the contaminant from adjacent areas to the source of the vacuum, see Table 1 . The increase in contaminant concentrations found at MW8 and MW12 is associated with the rise in the ground water to near the 50 foot depth This depth is where the highest levels of gasoline range hydrocarbons have been detected in soil samples from the exploration and well borings PAGE 2