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Wm. J. Hunter & Associates _ 2220 Loma Vista Dr. <br /> Registered Geologists '": ' ` " '° , . 3, moi-€�= Sacramento, CA 95825 <br /> Petroleum & Mineral Appraisers i(,� (916) 972-7941 <br /> FAX (916) 972-1683 <br /> November 13, 1995 <br /> Steven Sasson, Sr. REHS <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> P.O. Box 388 <br /> Stockton, CA 0388 <br /> Ref : First Quarterly Groundwater Monitoring Report for 2315 No. <br /> Eldorado Street, Stockton <br /> Dear Mr. Sasson; <br /> We have enclosed a copy of the field report, water analysis <br /> results, a gradient map, and maps showing lines of equal <br /> concentration of benzene, ethylbenzene, toluene, xylene, & TPHg <br /> for the above site . The work was performed on October 19, 1995, <br /> by Del-Tech Geotechnical Support Services as directed by our <br /> office . <br /> PLATE I shows the potentiometric surface based upon the 10/19/95 <br /> sampling event . The gradient is towards the northeast at about <br /> .551 /1001 . The direction and slope is almost identical to the <br /> 6/95 sampling, indicating that monitoring well #2 is in a down <br /> gradient position from the site of the removed UST' s . <br /> The water table was measured at an average depth of 46 . 93 ' bgl, a <br /> drop of about 1. 65 ' since the June sampling event . <br /> TABLE 1 summarizes the results of all water analyses taken since <br /> monitoring began, which show that MW-2 & MW -3 have higher <br /> concentrations than MW-1 . This would be expected since those two <br /> wells are downgradient from the site of the removed UST' s . MW-1 <br /> is slightly upgradient from, but closest to, the tank site. The <br /> levels of BTEX & gasoline measured in that well do not indicate a <br /> consistent pattern. <br /> PLATES II, III:, IV, V, & VI are maps showing lines of equal <br /> concentration of benzene, ethylbenzene, toluene, xylene, & TPH as <br /> gasoline based upon the 10/19/1995 sampling event . They reveal <br /> that the levels of all tested compounds increase towards the <br /> southeast, (MW-3, ) about 60 degrees divergent from the indicated <br /> groundwater gradient . The reason for this is not readily <br /> determined based upon data available to date . It is possible <br /> that an additional source or sources of contamination may exist . <br /> MW-3 is close to the location of the dispenser pumps, which may <br /> have contributed to the contamination; a workplan is being <br /> prepared to investigate that possibility. <br /> 1 <br />