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Wm. J. Hunter & Associates 2220 Loma Vista Dr. <br /> Registered Geologists .I �;=;i_ �a Sacramento, CA 95825 <br /> etroleum & Mineral Appraisers i (916) 972-7941 <br /> r, % ` j i FAX (916) 972-1683 <br /> _ 42 <br /> April 27, 1998 <br /> } <br /> Jeffrey Wong, EHS, Trainee <br /> f San Joaquin County PHS <br /> Environmental Health Division <br /> LOP/Site Mitigation Unit IV <br /> P.Q. Box 388 <br /> Stockton, CA 95201-0388 <br /> RE: First quarter 1998 groundwater monitoring report for Valley Wholesale Drug <br /> Co., 1401 W. Fremont St., Stockton - Site Code 1782 <br /> We are enclosing a report covering the results of the seventh sampling event at the above <br /> site. It includes the field logs, laboratory results, and maps showing the hydraulic gradient <br /> & lines of equal concentration of benzene, ethylbenzene, toluene, xylene, and TPHg based <br /> on the latest data. The field work was performed on April 1, 1998 by Del-Tech <br /> Geotechnical as directed by our office. <br /> PLATE I shows the hydraulic gradient based on the latest work. It continues to be to the <br /> north/northwest at about .017ft. The water table was measured at an average depth of 6,39' <br /> msl datum, a rise of 2.19' since the October, 1997 sampling. The groundwater surface <br /> continues to be below the tops of the screens in the 3 monitoring wells- they are at 5'bgl. <br /> The results of the analyses of water samples from the three monitoring wells sin <br /> the project are summarized on TABLE I. Levels of BTEX & TPHg measured i= <br /> increased significantly since the October, 1997 sampling. This is likely due to the 2+' nse <br /> 'ftrtfte—`w`aFe_rTaTIe__sin_ce then. Oxygenates continue to be bel w detection levels. MW-2 <br /> has not measured any analytes since December, 1995. - revealed a slight increase in <br /> all compounds compared to the last sampling. This is most likely due tot Terise in <br /> groundwater, which is the highest since monitoring began. Oxygenates continue to be <br /> below detection limits. <br /> PLATES H through VI are maps showing the approximate lines of equal concentrations of <br /> benzene, ethylbenzene, toluene, xylene, and TPH as gasoline.based upon this latest ampling <br /> event. They reveal that the limits of groundwater contamination have been well defined to <br /> the east and south, but have not been located to the north and west. The hydraulic gradient <br /> (refer to PLATE I,) has been quite stable to the north/northwest, but the plume appears to <br /> be oriented more to the west. The reason for this is not known, but further work should <br /> clarify the matter. <br /> RECOMMENDATION: <br /> 1 <br />