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David Wang <br /> Page 3 <br /> based standards, not a predetermined numbers. Guidance on <br /> establishing cleanup levels can be derived from the U. S. <br /> Environmental Protection Agency's Public Evaluation Health <br /> Manual and DHS's Site Mitigation Decision Tree. <br /> 4) DHS is very concerned with the lack of detail regarding <br /> the characterization of the subsurface geology in the remedial <br /> investigation at Defense Depot Tracy. Geologic units should <br /> be described and logged in detail. From this information, the <br /> location of monitoring wells and piezometers can be chosen. <br /> Currently, DHS considers that little is known about the <br /> Depots' subsurface geology, little is known about the Depots' <br /> groundwater hydrology, and little is known to explain why <br /> contaminant distribution values in the groundwater are so <br /> unpredictable. The above stated concepts on geology, <br /> hydrology, and contaminant distribution values are all <br /> inter-related. A thorough understanding of the subsurface <br /> geology and groundwater hydrology would lead to an <br /> understanding of the contamination distribution. <br /> DHS considers the practice of logging boreholes from cuttings <br /> samples to be a very poor method for obtaining accurate, <br /> representative samples of the subsurface. Specifically: <br /> Section 3 . 4 . 5, Task 37 - Groundwater Monitoring Wells page <br /> 3-26, paragraph 3 . 4 . 5. 2 , lines 3 through 6: <br /> The RI report states: <br /> "Cuttings were collected at approximately every 10 feet <br /> from the cyclone cuttings discharge and were used to <br /> construct the stratigraphic section (lithologic borehole <br /> log) for each well (Appendix D-1) . " <br /> Cuttings collected continuously from the cyclone discharge <br /> would have provided greater detail. <br /> In summary, the goal of a hydrogeologic investigation for <br /> characterizing hazardous waste sites is to determine the <br /> contaminant pathways and hydraulic parameters of the <br /> hydrostatigraphic units of concern. To date DHS considers that <br /> this investigation has been very deficient regarding these <br /> concerns. <br /> 5) Section 3 .4 . 1, Groundwater Movement, page 3-16, paragraph <br /> 3 .4 . 2 . 2 , lines 6, 7 , and 8: <br /> The RI report states: <br /> "The contours on Figure 3 . 4-2 represent groundwater <br />