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Wm. J. HunterAss & Associates 2218 Loma Vista Drive Registered Geologists Sacramento, CA 95825-0363 Petroleum & Mineral Appraisers r 916 972-7941 PP l 1 FAX (916) 972-1683 March 15, 2001 Jeffrey Wong, REHS San Joaqluin County Public Health Service Environmental Health Division Site Mitigation Unit 304 E. Weber St, 3rd. Floor Stockton, CA 95202 Re: First Quarter 2001 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 fourteenth sampling event at the above site. It includes the field logs, laboratory results, and maps showing the hydraulic gradient & lines of equal concentration of benzene, ethylbenzene, toluene, xylene, TPHg, & MTBE based on the latest data. The field work was performed on January 17, 2001 by Del-Tech GeoTechnical as directed by our office. PLATE I shows the hydraulic gradient based on the latest work. It has shifted slightly • from northwest to almost due north. The hydraulic gradient is about .004'/ft. near the southeast corner of the building, flattening slightly to .0048/ft. at the north end of the property. The water table was measured at an average depth of 8.24' msl datum, down slightly since the July 2000 sampling. The groundwater surface continues to be below the tops of the screens in the 6 monitoring wells - they are at 5' bgl. TABLE A summarizes the measured depths to water since monitoring began. i in The results of the analyses of water samples from the six monitoring g w ll e s since start of the project are summarized on TABLES I, II, III & IV. Levels of benzene in July in MW-1 (TABLE I) decreased from 51 ug/L to 34 ug/L. Ethylbenzene increased slightly from 49 ug/L to 76 ug/L; toluene decreased from 4 ug/L to 3 ug/L; xylene decreased from 64 ug/L to 24 ug/L. TPH as gasoline decreased from 1670 ug/L to 575 ug/L. MTBE decreased from 8 ug/L (not confirmed), to non-detect. MW-2 (TABLE II) has not measured any analytes since December, 1995. Levels of benzene & ethylbenzene in MW-3 (TABLE III) were ND in July 2000 and January 2001. Toluene decreased from 0.5 ug/L to ND; xylene decreased from 3.0 ug/L to ND; and TPH as gasoline decreased 264 ug/L to ND. MTBE was below detection limits. TABLE IV lists the three new wells placed in August, 2000. MW-4 measured a increase in benzene from 0.6 ug/L to 14 ug/L. Ethylbenzene levels increased from 2.0 to 3.0 ug/L, but toluene decreased slightly from 0.8 to 0.7 u9/L. Xylenes increased from 16 to 33 ug/L, and TPHg increased from 224 to 372 ug/L. MTBE, which was measured at 49 ug/L in August, dropped to 27 ug/L in January. 1