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f Stfi1"}1l4l: lFT�I QE41-111Wrn. J. Hunter & Aswciate's,-� t 3�l 3,,-04��11 2220 Loma Vista Dr Registered Geologists Sacramento, CA 95825 • Petroleum & Mineral Appraisers +1'04 1 33 (916) 972-7941 _ FAX(916) 972-1683 September 10, 1996 Steven Sasson, Sr. REHS San Joaquin County PHS Environmental Health Division P 0. Box 388 Stockton, CA 95201-0388 Ref . Third quarterly groundwater monitoring report for 1401 W. Fremont St . , Stockton; Site Code 1782 We are enclosing a report covering the fourth sampling event at the above site, Valley Wholesale Drug Co. It includes the field logs, laboratory results of water analyses, and maps showing the hydraulic gradient (s) and approximate lines of equal concentra- tions of benzene, ethylbenzene, toluene, xylene, & TPHg based on the latest data. The field work was done on July 5 & 12, 1996, by Del-Tech Geotechnical Support Services as directed by our office. PLATE I shows the hydraulic gradient based upon the July, 1996 . sampling event. It is to the north/northwest at about 006 ' /ft The gradient map included with the June 28, 1996 quarterly report is in error It indicated a southerly gradient, whereas it actually was to the north; the water level data was calculated incorrectly The water table has risen an average of . 81 ' since the March sampling, to an average depth of 7 .89 , bgl . The results of the laboratory analyses of water samples taken from the three monitoring wells since monitoring began are shown on TABLE I . MW-1 was the only well which recorded contamination, both MW-2 & MW-3 were below detection levels for BTEX, MTBE, & TPHg MW-1 revealed a reduction in the amount of all compounds analyzed; benzene decreased from 4700 ug/L to 1600 ug/L since the March sampling event . Ethylbenzene dropped from 1.000 ug/L to 830 ug/L; toluene from 3400 ug/L to 860 ug/L, xylene from 5100 ug/L to 2500 ug/L, and TPHg from 24 mg/L to 7 8 mg/L. MTBE has not been detected in any of the wells during the last two sampling periods We recommend that that test be discontinued. PLATES II through VI show the approximate lines of equal concen- trations of BETX & TPHg based upon the July, 1996 laboratory results . Although data is lacking to the northwest, it appears that: MW-1 is situated upon, or very close to, the center of the plume . SUMMARY & CONCLUS I ONS - • The results of work performed to date on this site can be briefly 1