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R603 UPDATE-21 10/15/93 <br /> Figure 4A, are measurements obtained prior to shutting off the <br /> vacuum extraction system for equipment check on August 23, 1993 . <br /> This figure shows a substantial low potentiomentric cone <br /> developed at MW10 and extending towards MW3 , two of the wells <br /> used for vapor extraction at that time . The vacuum system was <br /> turned off that day. <br /> Figure 4B, September 15, 1993 (554 hours after turning the vacuum <br /> system off) shows a reverse in the potentiomentric surface . A <br /> mound or dome is found at MW10 and extends out to MW2 and MW3 . <br /> This dome as most likely the result of lower hydraulic <br /> conductivity at MW2 and MW10 and the effect of using these wells <br /> for vapor extraction and pulling the ground water to them <br /> Figure 4C, September 29, 1993 , represents the potentiometric <br /> surface 883 hours after the vacuum extraction system had been <br /> shut off and dust prior to restarting the vacuum system. Figure <br /> 4C shows a ground water gradient the trends to the east with a <br /> minor discharge area at MW1 . <br /> Figure 4D, September 29, 1993 , represents the potentionmetric <br /> ground water surface approximately two hours after restarting the <br /> vacuum extraction system and indicates a depression developing at <br /> MW1, MW2 and MW10 (wells used for vapor extraction) <br /> GROUND WATER QUARTERLY SAMPLING <br /> Ground water samples were collected on September 29, 1993, see <br /> Table 1 These samples were collected by a WEGE geologist and <br /> "Chain of Custody" delivered on ice to a state certified testing <br /> laboratory (SUPERIOR PRECISION ANALYTICAL, INC DHS#1332) for <br /> chemical analyses These samples were analyzed for TPH and BTEX <br /> concentrations using EPA Methods 8015 and 602 respectively <br /> Since diesel has never shown up in the sample results, the <br /> samples obtained on 11/27/90 and later were analyzed using EPA <br /> methods 5030 and 602 for Total Fuel Hydrocarbons and BTEX. The <br /> next quarterly sampling will occur in December, 1993 . <br /> 3 . 0 RESULTS <br /> GROUND WATER SAMPLE RESULTS <br /> Ground water samples were obtained from all of the monitoring <br /> wells on September 29, 1993 . <br /> The latest sample results showed a decline in contaminant levels <br /> associated with the ground water at MW1, MW2 , and MW10 . Of the <br /> other wells that have some degree of ground water contamination <br /> (MW3, MW8, and MW12) showed slight increases, see Table 1 . <br /> The increase in contaminant concentrations found at MW3 , MW8 and <br /> MW12 is thought to be associated with the vacuum extraction <br /> system operating only 161; of the time due to equipment <br /> modifications (heat exchanger addition) and equipment check <br /> (increase noise from compressor) , see Tables 1 and 3 . <br /> PAGE 2 <br />