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s Wm. J. Hunter & Associates , . 2220 Loma Vista Dr. Registered Geologists , Sacramento, CA 95825 Petrol*um &Mineral Appraisers (916) 972-7941 P:, ) FAX {916} 972-1683 March 15, 1999 Jeffrey Wong, REHS San Joaquin County PHS Environmental Health Division LOP/Site Mitigation Unit IV P.O. Box 388 Stockton, CA 95201-0388 i RE: First 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 eighth 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 February 1, 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 .0009'/ft. The water table was measured at an average depth of 7.91'ms] datum, a drop of.62' since the July, 1998 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& H. Levels of benzene in MW-1 increased slightly since July; from 462 ug/L to 510 ug/L. Ethylbenzene decreased from 301 ug/L to 280 ug/L; toluene from 99 ug/L to 80 ug/L; and xylene from 550 ug/L to 260 ugA.. TPH as gasoline decreased from 6.03 mg/L to 2.9 mg/L. MW-2 has not measured any analytes since December, 1995. Levels of benzene in MW-3 increased slightly from ND to 0.57 ug/L; ethylbenzene dropped from 10 ug/L to 2.4 ug/L; toluene from 0.4 to ND; xylene from 5.0 ug/L to 0.63 ug/L; and TPH as gasoline from .341 mg/L to .16 mg/L. MTBE was measured in MW-3 at 7.2 ug/L, but was not confirmed. We will do so at the next sampling event. PLATES H 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 property. Refer to that WJH report titled 1