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903806-SS4 CON-38 <br /> TCE PCE <br /> Well Contaminant Concentration Concentration <br /> Number Area (ug/1) (ug/1) <br /> LM 5 3 1.5 NO <br /> LM 31 3 NO NO <br /> LM 32 3 67 100 <br /> LM 33 3 1.2 NO <br /> LM 17 4 25 39 <br /> LM 26 4 NO 0.8 <br /> The downgradient extent of the contamination from Contaminant Areas 1 <br /> through 4 is shown on Figures 4.3-1 through 4.3-6. These figures show the <br /> horizontal distribution of TCE and PCE contamination at each of the three <br /> horizons. Figures 4.3-1 and 4.3-2 show TCE and PCE concentrations in the <br /> Upper Horizon. <br /> 4.3.5.4.6 A TCE concentration of 470 ug/l was detected in Well LM 25 <br /> in the southeastern part of Contaminant Area 1. TCE contours shown on <br /> Figure 4.3-1 do not exceed 30 ug/1 . At the map scale and the chosen <br /> contour interval it was not possible to show all the concentration contours <br /> associated with Contaminant Area 1. It is expected, however, that high <br /> values of TCE are present in and to the north of Well LM 24. TCE <br /> concentrations are greatest in the vicinity of Contaminant Areas 1 and 2 <br /> and also in the vicinity of Contaminant Areas 3 and 4, thus defining two <br /> groundwater contaminant plumes which are separated by an area of relatively <br /> low concentrations. The lateral and downgradient extent of contamination <br /> in the Upper Horizon is controlled by concentrations of less than the <br /> MCL (5 ug/1) in Wells LM 24, LM 15, LM 71, LM 83, LM 63, LM-77, LM 80, <br /> LM 74, and LM 23. Upgradient extent is assumed to be coincident with the <br /> upgradient edge of the Contaminant Area (defined by soil gas sampling <br /> data) . Existing wells are sufficient to define the extent of contamination <br /> except at the eastern edge of the plume. Well LM 76 (located at the <br /> eastern edge of the plume associated with Contaminant Areas 3 and 4) showed <br /> a concentration of 12 ug/l TCE - a value which exceeds the MCL. <br /> 4-178 <br />