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'1r I Ily. i{_til Wm. I Hunter & Associates �r,#� 2220 Loma Vista Dr Registered Geologists �, , Sacramento, CA 95825 Petroleum &Mineral Appraisers ` , ' I PP) 2 17 (916) 972-7941 FAX (916) 972-1683 December 31, 1997 Steven Sasson, Sr REHS San Joaquin County PHS ✓ Environmental Health Division P O Box 388 Stockton, CA 95201-0388 RE: Fourth quarter 1997 groundwater monitoring report for Valley Wholesale Drug Co., 1401 W. Fremont St., Stockton - Site Code 1782 We are enclosing a report covering the results of the sixth sampling event at the above site It includes the field log, laboratory results, and maps showing the hydraulic gradient& lines of equal concentration of benzene, ethylbenzene, toluene, xylene, and TPHg based on the latest data The field work was performed on October 23, 1997 by Del-Tech Geotechnical as directed by our office The site had not been sampled since November, 1996, pending receipt of a letter of comm ttment from the Cleanup Fund, which has recently been issued PLATE I shows the hydraulic gradient based on the latest work It continues to be to the north/northwest at about 009'/ft The water table was measured at an average depth of 8 19' msl datum, a rise of 0 39' since the November, 1996 sampling The groundwater surface continues to be below the tops of the screens in the 3 monitoring wells -they are at 5' bgl The results of the analyses of water samples from the three monitoring wells since start of the project are summarized on TABLE I. Levels of all tested compounds are significantly lower than the November, 1996 results MW-1 continues to record the highest levels, but concentrations have dropped steadily since the March, 1996 sampling MW-2 has been ND since the March, 1996 sampling Concentrations recorded from MW-3 have been erratic, but have shown a general reduction in all compounds since the March, 1996 event MTBE was analyzed after the March& July, 1996 sampling, it was ND in all wells It was analyzed again after this latest event, and was ND again The other oxygenates, TBA, ETBE, DIPE, & TAME, were also analyzed, all were below detection levels PLATES H through VI are maps showing the approximate lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, and TPH as gasoline based upon this latest ampltng event They reveal that the limits of groundwater contamination have been well defined to the east and south, but have not been located to the north and west The hydraulic gradient (refer to PLATE I) has been quite stable to the north/northwest,but the plume appears to be oriented more to the west The reason for this is not known, but further work should clarify the matter 1