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0 • <br /> less soluble than TCE and thus more likely to migrate <br /> downward more rapidly. <br /> 19. In correlating this round of analytical results with those <br /> obtained through earlier rounds, a steady decrease was noted <br /> in the level of PCE in LM-24 from the first level noted in <br /> 12/85 of 780 gg/l (Radian, 1986) to the August 1991 level of <br /> 11. 1 µg/1. Placement of a middle horizon monitoring well in <br /> an area just downgradient of LM-24 would increase the <br /> possibility of intercepting the plume in that area and <br /> interpreting the path of downward migration of the plume. <br /> 20. A review of historical data compared to current data shows a <br /> general decrease in several wells, until the August 1991 <br /> round of sampling, when a marked increase is noted as shown <br /> in the following Table 2 . <br /> TABLE 2 : SUMMARY OF HISTORICAL RESULTS FOR VOC'S - LM-25, <br /> LM-28 , LM-29, LM-30 AND LM-32 <br /> :WELL NO. PARA- 12/85 1/87 ;5/88 6/91 9/91 <br /> METER ("9/1) W/1) W/1) (-8/1) GB/1) <br /> LM-25 PCE NR <50 <20 1.4 <0.3 <br /> TCE 350 500 560 470 130 <br /> LM-30 PCE 430 410 340 340 470 <br /> TCE 38 43 38 31 50.7 <br /> LM-32 PCE 320 110 100 85 215 <br /> TCE 210 75 67 41 111 <br /> LM-88 PCE - - - ND 6.18 <br /> TCE - - - _J ND <05 <br /> LM-25 has shown a fairly steady level of TCE since 1985 <br /> until the August 1991 sampling round when we see a 72% <br /> decrease in TCE, along with an approximate 78% decrease in <br /> PCE. <br /> LM-30 has shown an increase in concentration of PCE since <br /> December 1985 of 9%, while since the June 1991 sampling <br /> round LM-3O 's PCE concentration has increased by 38%. The <br /> TCE concentration in LM-30 showed an increase from December <br /> 1985 to August 1991 of 33%, while the increase in TCE <br /> concentration from June 1991 to August 1991 was 53%. <br /> LM-32 showed a decrease in concentration of PCE from <br /> 6 of 7 <br />