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' detected at MW-1 following ORC injection have generally been less than those detected prior to ORC injection During the most recent sampling event (29 February 2000),TPH-g and BTEX concentrations have decreased to the lowest concentrations historically observed at this location Table 5 presents the results of all ground water samples collected at MW-1 and ' Figure 7 presents the historical chemical concentration trends detected at MW-1 tOverall, the chemical concentrations at MW-4 (immediately downgradient of the former tank location) have decreased since monitoring began in November 1998 The chemical concentrations detected during the three most recent sampling events (30 November 1999, 6 January 2000, and 29 February 2000) were lower than those reported prior to ORC injection ' Concentrations detected during the three sampling events immediately following ORC injection (30 June, 2 September, and 28 October 1999) were highly variable and generally higher than those detected prior to ORC injection, however, as discussed below, these sampling results are believed to be inaccurate Table 5 presents the results of all ground water samples collected at MW-4 and Figure 8 presents the historical chemical concentrations detected at MW-4 As stated above, it appears that the results of the samples collected during the three sampling events immediately following ORC injection do not accurately represent the ground water conditions at MW-4 Based on the questionable result that was recorded from the ground water sample collected on 28 October 1999, a supplemental sampling event was performed on 30 November 1999 to verify chemical concentrations at this 1 location However, due to the previous inconsistent results in this well, the analytical laboratory (AN/EN of Marina, California) recommended that the samples be centrifuged prior to analysis By centrifuging the samples, any soil particles in the ground water sample are separated from the water so that a true ground water sample can be extracted for analysis ' As shown in Table 5, the results of samples collected during the 30 November 1999, 6 January 2000, and 29 February 2000 sampling event are ' consistent(i e , duplicates result in reproducible sample results) and contain lower chemical concentrations than samples collected prior to ORC injection Based on these results, we believe that the inconsistent and ' higher results obtained during June, September, and October 1999 were due to the presence of chemicals attached to soil particles in ground water ' samples collected during these sampling events, and do not accurately reflect ground water conditions at the site ' ERM 9 HEINZ USA 3374 60.3/27/00