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James T. Allen, Ph.D Page 2 July 31 , 1987 The following paragraphs discuss comments that have not been addressed or have been addressed in a manner that differs from the DHS/RWQCB comments. Comment 6 : McCormick & Baxter believes that the collection of continuous soil cores , while providing additional data, is neither cost effective, nor necessary to obtain a geo- logic understanding of subsurface conditions. CH2M HILL believes, based on their experience working in similar geo- logic environments , that given the highly discontinuous na- ture of the alluvial beds, the beds will probably not be horizontally correlatable even with continuous cores. All wells will be carefully logged during drilling and down-hole geophysical logs will be conducted. This should provide the necessary and sufficient data needed for the feasibility studies . The additional costs associated with continuous coring in a 250-foot well are, at a minimum, $5 ,000 per well and it is believed that the additional increments of data would not justify these costs . It appears that the addi- tional costs for coring would be better applied toward more beneficial activities. If, after implementation of tasks 18 and 19 , it is determined by McCormick & Baxter' s consultant, CH2M HILL, that continuous coring is necessary to support feasibility studies; this coring will be completed during the stages of the investiga- tion. The revised workplan contains provisions for such additional work as data needs are defined. Comment 7 : McCormick & Baxter agrees to add a well or piezo- meter into the "A-zone" at site OS-1 and the workplan has been revised accordingly. Although it is understood that D-zone wells ultimately will be necessary, it is not appro- priate to commit to the precise locations of these wells at this time. Following the first phase of well installations , a determination of data gaps will be completed and additional D-zone wells will be drilled in the locations that appear to be most appropriate to define the extent of groundwater con- tamination. The revised workplan more clearly states the approach and rationale for the offsite investigation. Comment 9 : McCormick & Baxter has stated in the workplan that the extent of groundwater contamination will be defined in order to support feasibility studies and mitigation. This applies to all boundaries of the facility. Therefore, if the extent of contamination needs to be defined north of