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E IN Figure 6.2-1 is a plot of selenium data. The text does not indicate that these data have been kriged. ■ Figures 6.3-1 through 6.3-3 are contour plots of kriged arsenic data. Figure 11.0-1 shows the locations of proposed monitoring wells. Comments 1. The large area identified in Figure 6.1.5-2 as a continuous TCE plume in the South Balloon is probably composed of several smaller plumes. The highest concentrations seem to occur in Extraction Well A-8, and along either side of a pine extending from a point southeast of Extraction Well A-10 to Extraction Well A-5. This was approximately the path of groundwater flow in the A zone in January 1988. Extraction wells that are located away from this line, such as A-4, A-6, A-3, & A-1 may have the effect of dispersing this elongated plume. As a result, more pumping may be required to clean up this plume than would be necessary if the wells were located nearer to the high concentration. zone. 2. Wells A-1, A-3 and A-5 do not appear capable of fully capturing the plume. In fact these wells may help to accelerated contaminant transport from the central part of the plume toward the northwest. This effect would not be observed until the plume reached Monitoring Wells 445A or 406A. A piezometer located in the vicinity of PW3-C or downgradient of it and screened in the A zone would help in evaluating the effectiveness of the extraction system in this area. Without this data, how can SHAD be confident that the plume is being captured? 3. Only one monitoring well is located downgradient of the trench burial area west of Monitoring Well 403-A. There is no monitoring well in the B or C zones down - gradient of this area in spite of the fact that an agricultural well (AGWI) may create a downward gradient in this area. How can SHAD be certain that contaminants from this potential source area are not moving off -base in the direction of AGWI, avoiding capture by extraction wells? 15