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903808-S54 LUN-iy <br /> 4.3.5.4.7 The distribution of PCE in the Upper Horizon is similar to <br /> that of TCE, although PCE is more restricted. Like TCE, PCE is present in <br /> relatively high concentrations in the vicinity of both Contaminant Areas 1 <br /> and 2, and 3 and 4; however, unlike TCE, PCE concentration data are <br /> sufficient to define the lateral and downgradient extent of <br /> contamination. The extent of contamination is defined by concentrations <br /> below the MCL (5 ug/1) in Wells LM 1, LM 15, LM 71,_'LM 66, LM-83, LM 68, LM <br /> 72, LM 76, LM 74, and LM 23. <br /> 4.3.5.4.8 In detail , there are uncertainties in the distribution of <br /> both TCE and PCE in the interior of the plumes in the Upper Horizon. As <br /> drawn (Figure 4.3-1 and 4.3-2) , relatively high concentrations of both TCE <br /> and PCE are shown to be present between Contaminant Areas 1 and 2. This is <br /> a conservative interpretation. Available data would also permit the <br /> interpretation that relatively low concentrations are present between <br /> Contaminant Areas 1 and 2. <br /> 4.3.5.4.9 Similar uncertainty is present in the vicinity of <br /> Contaminant Areas 3 and 4. Well LM 17, located in Contaminant Area 4, <br /> shows TCE and PCE concentrations of 25 and 39 ug/1 , respectively (Figures <br /> 4.3-1 and 4.3-2) . The downgradient extent of this contamination is poorly <br /> defined. Because Wells LM 34 and LM 59, screened in the Upper Horizon in <br /> or just downgradient of Contaminant Area 3, both show TCE and PCE <br /> concentrations which are below the action limit, concentrations in excess <br /> of 20 ug/1 are not interpreted to extend from Contaminant Area 4 to <br /> Contaminant Area 3. <br /> 4.3.5.4.10 Concentrations of PCE in the western part of Contaminant <br /> Area 1 permits the interpretation that the distribution of contamination <br /> results from a groundwater high associated with the Stormdrain Holding Pond <br /> and the Sanitary Settling Ponds. Well LM 24, located near the west edge of <br /> Contaminant Area 1, has been sampled four times. It showed 760 ug/l PCE in <br /> 1986, 250 ug/l in 1987, 20 ug/l in 1988, and 15 ug/l in 1989. Well LM 1, <br /> located to the west of LM 24 and outside of Contaminant Area 1, has shown a <br /> 4-183 <br />