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SJC Page 2 <br /> The discussion which questions the source of hydrocarbons is not substantiated. The <br /> migration and subsequent disposition of contamination detected in MW2 and MW3 has <br /> likely increased the extent of soil contamination providing a secondary source of <br /> contamination to groundwater. The supposition that soil contamination would not be <br /> encountered during the 1991 drilling of off site monitoring wells, MW4, MWS, MW6, <br /> MW7, and MW8, is not supported by analytical data. Additional investigation of residual <br /> soil contamination will be required. In order to better characterize subsurface lithology, <br /> at least one soil boring should be included which is drilled and sampled continuously. <br /> Please submit a work plan to define the extent of soil and/or groundwater contamination <br /> by November 17, 1992. <br /> The detection limits used during the investigation have been erratic. Please summarize <br /> all soil samples which exceed acceptable detection limits as outlined in the LUFT field <br /> manual. Please also provide a map locating all soil samples summarized. Include the <br /> summary and map in the next quarterly report due August 17, 1992. <br /> The groundwater gradient of the site has not been determined. For purposes of <br /> confirmation and clarification, immediately initiate monthly groundwater elevation <br /> measurements, for at least one quarter. Please attempt to schedule monitoring when the <br /> tide is in relatively the same position. Include results of monthly monitoring and copies <br /> of local tide tables within the next quarterly monitoring report due August 17, 1992. <br /> Please contact Mary Meays, REHS, of my staff at (209) 468-0337 if you have any <br /> questions or to schedule the next quarterly sampling event by July 10, 1992. <br /> Jogi Khanna, M.D., M.P.H. <br /> Health Officer <br /> Laurie A. Cotulla, R S, Program Manager <br /> Environmental Health Division <br /> LAC/MM:lb <br /> c: Elizabeth Thayer, CVRWQCB <br /> c: Mel Wingett, San Joaquin County Administrator <br /> c: John Cheadle, San Joaquin County Counsel <br />