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Wm. J. Hunter & Associates - ;, ,{ 2218 Loma Vista Drive Registered Geologists Sacramento, CA 95825-0363 Petroleum & Mineral Appraisers (916) 972-7941 FAX (916) 972-1683 February 14, 2000 Margaret Lagorio, Lead Sr. REHS San Joaquin County PHS Environmental Health Division LOP/Site Mitigation Unit IV P.O. Box 388 Stockton, CA 95201-0388 RE: Fourth 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 tenth 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 December 17, 1999 by Del-Tech GeoTechnical 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 .0057ft. The water table was measured at an average depth of 9.12' msl datum, a drop of 98' 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 230 ug/L to 95 ug/L. Ethylbenzene increased slightly from 100 ug/L to 110 ug/L;toluene remained at 11 ug/L; and xylene decreased from 190 ug/L to 62 ug/L. TPH as gasoline decreased from 3.7 mg/L to 2.7 mg/L. MW-2 has not measured any analytes since December, 1995. Levels of benzene in MW-3 increased slightly from 1.3 to 1.4 ug/L; ethylbenzene increased from 2.4 ug/L to 3.9 ug/L; toluene decreased from 8.2 ug/L to ND; xylene decreased from 6.1 ug/L to 1.2 ug/L; and TPH as gasoline increased slightly from.20 mg/L to .25 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 low Ievels of soil and groundwater contamination exist beneath the building, and may continue a short distance 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