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Jim Pinasco <br /> Page 3 <br /> August 1 , 1989 <br /> To remedy the present lack of geologic definition needed to <br /> complete the RI/FS, TSSU proposes that continuously cored <br /> boreholes be installed. These cores should be thoroughly <br /> logged and maintained for the duration of the RI/FS . In <br /> addition, the boreholes should be be geophysically logged by <br /> resistivity, spontaneous potential, and caliper techniques to <br /> properly define subsurface conditions. <br /> Comment 4 <br /> On page 7-4, paragraph 7 . 2 . 1. 0, the Draft RI/FS states the <br /> following: <br /> "Although significant uncertainties exist in <br /> characterizing groundwater flow pathways on a small scale <br /> (as noted in Sections 3 . 4 , 3 . 5, 3 . 6, and 4 . 0) , which is <br /> typical of sites at which groundwater contamination is <br /> present in heterogeneous stratified aquifers, in general <br /> the hydrogeology and extent of contamination have been <br /> sufficiently defined for RI/FS purposes. " <br /> TSSU does not agree with statements presented in the above <br /> quote. To date, the subsurface geology has not been adequately <br /> characterized. Proof of this fact is present in the geologic <br /> cross-sections which are misleading and inaccurate. <br /> Many of these cross-sections inappropriately exhibit geologic <br /> strata abruptly terminating between wells in a given well <br /> cluster. <br /> Cross-section A-A' shows that the formation is predominately <br /> clay from approximately 25 to 75 feet below ground surface <br /> (BGS) . The borehole log for IM 57 indicates that there are <br /> thin layers of sand (two to three feet thick) within a sandy <br /> clay formation in this interval, and that the formation <br /> produced water as drilling proceeded. <br /> Cross-section A-A' also shows that the formation is <br /> predominately clay from 125 to 185 feet BGS. The borehole log <br /> for IM 57 indicates that there is significant gravel (with <br /> clay) in this interval, and that the formation produced water <br /> while drilling proceeded. <br /> Such types of geologic illustrations indicate that site geology <br /> is poorly understood and renders all subsurface data subject to <br /> uncertainty. This level of geologic understanding requires <br /> that additional subsurface investigation is needed to fully <br /> complete the remedial investigation. <br />