SITE INFORMATION AND CORRESPONDENCE_1988-1991

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Jim Pinasco Page 3 July 5, 1989 system is affecting ground water levels as planned. It is suggested that monitoring wells be placed down-gradient of the proposed extraction wells to monitor whether contamination is escaping capture. It is also suggested that some monitoring wells be installed up-gradient of the extraction wells to determine if the pumping is influencing the ground water levels as predicted. Comment 7 : The subsurface geology at the site has been very poorly characterized. The basis of this poor characterization is poor borehole logs. The lithology of many of the past boreholes were described using substandard logging techniques. Poor techniques used include descriptions of auger cuttings, lithologic interpretations from the drilling rate when auger cuttings were not returning up the borehole, and samples taken every 10 feet from a cyclone separator. DHS advocates continuous cores and borehole geophysical logs for subsurface characterization. Comment 8 : TSSU has little confidence that the subsurface geology is accurately depicted by the geologic cross-sections. The most recent geologic cross-sections in the Draft RI/FS are not consistent with geologic cross-sections in previous reports. Previous reports submitted to DHS from DDTC presented cross-sections with gravelly sand, sandy gravel, and silty clay units. The cross-sections in the Draft RI/FS have many portions where sand is indicated that had been depicted as silty clay in previous reports. Clarification is requested as to how the most recent interpretations were obtained. The following comments refer to the Pumping Test report: Comment 9 : The results presented on Table 6-3 , page 6-5 should be supported with the calculations and constants used. Comment 10: The match points used and their coordinates should be presented on Figures E-5 and E-6 for review.