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Jim Pinasco <br /> Page 2 <br /> August 1 , 1989 <br /> PRIMARY CONCERNS <br /> Concerns Regarding Subsurface Characterization: <br /> Comment 2 <br /> Page 2-10, paragraph 2 . 3 . 1 states: <br /> "The geologic investigation of the site was carried out by <br /> interpreting published information on the regional <br /> geology, and the lithologic logs from the wells drilled as <br /> part of this investigation. Interpretation of the <br /> lithologic logs was supplemented by the geophysical logs <br /> of most of the wells. " <br /> TSSU has not located borehole geophysical logs in previous <br /> reports from DDTC. Clarification is requested as to which <br /> boreholes were geophysically logged, by what techniques, and <br /> where such information is presented. <br /> Apparently some gamma logs were acquired in the investigation. <br /> Typically, gamma logs are of little value in interpreting <br /> subsurface units in the Central Valley because of false <br /> positive signals from coarse-grained intervals. Borehole <br /> resistivity, spontaneous potential, and caliper logs should <br /> have been obtained. <br /> Comment 3 <br /> On page 3-11, paragraph 3 . 4 . 3 . 1, the Draft RI/FS states that <br /> the abrupt changes in lithology can be explained by <br /> interfingering and cut and fill channels. TSSU interprets that <br /> many of the abrupt changes in lithology shown on the geologic <br /> cross-sections are likely not reflective of the true geologic <br /> character of the subsurface. Many of the lithologic changes <br /> are likely only "apparent" and due to poor borehole logging <br /> techniques that have produced inaccurate logs. <br /> Many of the logs indicate that the lithology was characterized <br /> by drill rig performance and cuttings recovery. This logging <br /> technique is not appropriate for producing accurate data of <br /> subsurface geology. TSSU recommends that the well logs for <br /> LM 40 through LM 46 not be used for geologic interpretation of <br /> the subsurface due to the poor method of borehole logging <br /> utilized. <br /> The logs for LM 47 to LM 52 and LM 63 to LM 74 indicate that <br /> samples were often taken at 10 to 15 foot intervals which is <br /> much too large a spacing to provide for accurate geologic <br /> characterization. <br />