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• <br /> MEMORANDUM <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road Phone: (916) 361-5600 <br /> Sacramento, CA 95827-3098 ATSS: 8-495-5600 <br /> TO: ANTONIA K. J. VORS FROM: ROBERT L. NIBLACK <br /> Senior Engineer Engineering Geologist <br /> DATE: 19 October 1987 SIGNATURE:F,,Z <br /> SUBJECT: DEFENSE DEPOT TRACY WORKPLAN, SAN JOAQUIN COUNTY <br /> We have received a reply to our workplan comments dated 5 October <br /> 1987 from the Army Corps of Engineers, Huntsville Division. I have <br /> discussed this reply with Jim Pinasco of the Department of Health <br /> Services, and he feels, as I do, that the proposal for <br /> characterization of off-site contamination in "Area 2" is deficient. <br /> This is especially critical considering the proposal to model "Area <br /> 3" contamination based on "Area 2" characterization. My specific <br /> comments follow. <br /> 1. The objective of well placement in this investigation is to <br /> surround the plume laterally and vertically with wells that show <br /> non-detectable levels of contaminants, while characterizing the <br /> plume sufficiently to develop remedial measures. The contract <br /> deadline for completion of the Remedial <br /> Investigation/Feasibility Study (RI/FS) will be over soon, and <br /> this has not been accomplished or proposed. <br /> 2. Additional characterization is needed in the following areas, at <br /> a minimum. More characterization may be necessary based on the <br /> results of sampling from the wells once they are constructed: <br /> a. Aquifer intervals above and below those in which well <br /> . construction is now proposed at the location of IM53 <br /> and LM54 . The lack of a proposal to sample the <br /> shallow interval is especially puzzling considering <br /> the results of analyses done on samples from LM30, <br /> LM49, and LM50. <br /> b. Upper aquifer intervals in the cluster consisting of <br /> LM55, LM56, and LM57 . <br /> 3. LM57 is proposed for the 180 to 200 foot interval in a cluster <br /> which should bound the lateral edge of the plume. The need for <br /> this deep well shou ' 1 be decided based on the results of <br /> sampling from LM56 , in the 120 to 140 foot interval . If LM56 is <br /> constructed as the first well in this next round of well <br /> construction, sample results should be available before the <br /> entire round of drilling is completed. Then LM57 could be <br /> drilled to sample the 180 to 200 foot interval , or it could be <br /> used to better define the extent of contamination in another <br /> area. <br />