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Wm. J. Hunter & Associates „ ; . ;?220 Loma Vista Dr. Registered Geologists Sacramento, CA 95825 Petroleum &Mineral Appraisers (916) 972-7941 7 �; l FAX (916) 972-1683 September 2, 1999 Jeffrey Wong, REHS San Joaquin County PHS Environmental Health Division 4e-P�,a LOP/Site Mitigation Unit IV P.O. Box 388 OCL ,K5ec-(�� Stockton, CA 95201-0388 a c"TSS 0 � RE: Second quarter 1999 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 ninth 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, and TPHg based on the latest data. The field work was performed on July 9, 1999 by Del-Tech Geo-Technical as directed by our office. PLATE I shows the hydraulic gradient based on the latest work. It continues to be to the north/northwest at about .00097ft. The water table was measured at an average depth of i8.14'msl datum, a drop of.23' since the last sampling. The groundwater surface continues to be below the tops of the screens in the 3 monitoring wells-they are at 5'bgl. TABLE A summarizes the measured depths to water since monitoring began. The results of the analyses of water samples from the three monitoring wells since start of the project are summarized on TABLES I&II. Levels of benzene in MW-1 decreased from 510 ug/L to 230 ug/L. Ethylbenzene decreased from 280 ug/L to 100 ug/L;toluene from 80 ug/L to 11 ug/L; and xylene from 260 ug/L to 190 ug/L. TPH as gasoline increased from 2.9 mg/L to 3.7 mg/L. MW-2 has not measured any analytes since December, 1995. Levels of benzene in MW-3 increased slightly from 0.57 to 1.3 ug/L; ethylbenzene remained the same at 2.4 ug/L; toluene increased from ND to 8.2 ug/L; xylene increased from .63 ug/L to 6.1 ug/L;and TPH as gasoline increased slightly from.16 mg/L to .20 mg/L. MTBE was below detection limits in all three wells. PLATES II through VI are maps showing the approximate lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, and TPH as gasoline.based upon this latest ampling event. They reveal that the limits of groundwater contamination have been well defined except to the north. The geoprobe work done in August, 1998, confirmed that both soil and groundwater contamination exists beneath the building, and may continue to the north along the driveway on the east side of the building. Refer to that WJH report titled `Interim Report Covering Results of Site Investigation; Placement of Soil Water Probes... " dated Sepember 28, 1998 for complete details of that work. 1