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ATTACHMENT 1 <br /> EPA COMMENTS ON <br /> DEFENSE DISTRIBUTION REGION WEST - TRACY, CALIFORNIA <br /> PRE-DESIGN TECHNICAL SUMMARY FOR OU-1 <br /> November 1993 <br /> GENERAL COMMENTS <br /> 1. Both the RD Technical Summary and the RD Work Plan repeatedly refer to various <br /> stages of design (e.g., 10%, 30%, 60% 95% and 100%) and to associated meetings and <br /> document reviews at each stage (see also Table 2-1 of the Remedial Design Work <br /> Plan). A number of these documents/reviews are not named in the FFA RD/RA <br /> schedule for OU-1. EPA believes that such an intensive level of document <br /> preparation/review may be unnecessary given that this remedial action is based on the <br /> most commonly selected technology for groundwater treatment. [Note that the text is <br /> silent on the regulatory review periods for these additional documents. In the absence <br /> of concurrence on review periods, time lines outlined in the FFA apply.] EPA is very <br /> interested in streamlining the number of reviews for this RD/RA if such action would <br /> enable DDRW-Tracy to expedite the remedial action schedule. <br /> 2. Monitoring well(s) in the Lower Tulare should be used to provide data to verify the <br /> effectiveness of the Corcoran Clay as an aquiclude, and confirm the vertical limit of <br /> contaminants. Monitoring of water levels in the Lower Tulare should be performed <br /> during the planned pumping tests in the Lower Horizon of the Upper Tulare. <br /> Monitoring of ground-water quality in the Lower Tulare should be performed <br /> immediately down gradient of the plume in the Lower Horizon of the Upper Tulare. <br /> From the OU-1 ROD, it is not clear that the vertical limit of contaminants has been <br /> defined by the site data, only assumed based on the purported effectiveness in the <br /> literature of the Corcoran Clay as an aquiclude. Even the vertical extent of the Upper <br /> Tulare, and therefore, the contaminant extent, is reportedly not defined by the <br /> monitoring well borings (Section 1.3.3.3). <br /> - Please clarify whether the site-wide RI/FS program will verify the vertical limit <br /> of the contaminants. <br /> - Please clarify whether the pre-design pumping tests, or site-wide RDFS, will <br /> verify the effectiveness of the Corcoran Clay as an aquiclude. <br /> - Please indicate whether the vertical gradient across the Corcoran clay is <br /> upward, downward, or unknown. <br /> - Although monitoring of the Lower Tulare `will be considered during the <br /> EPAAIIAN94 1/6 <br />