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Wm. J. Hunter & Associates 2220 Lorna Vista Dr. Registered Geologists Sacramento, CA 95825 Petroleum & Mineral Appraisers (916) 972-7941 FAX (916) 972-1683 January 26, 1998 Steven Sasson, Sr. REHS San Joaquin County PHS Environmental Health Division Site Mitigation Unit RO. Box 388 Stockton, CA 95201-0388 RE: Fourth Quarter 1997 Groundwater Monitoring Report - 913 W. Fremont St., Stockton, CA. Site Code 1114 Dear Mr. Sasson; We have enclosed a copy of the field report, laboratory analyses, a groundwater gradient map, and maps showing inferred lines of equal concentration of benzene, toluene, ethyl- benzene, xylene, and TPHg. The field work was performed by Del-Tech Geotechnical Support Services on December 5, 1997 as directed by the County EHD. The attached PLATE I shows the potentiometric surface based upon this latest sampling event, along with the 12 measurements taken since monitoring began. The gradient continues to be to the north at about .005'/ft. Groundwater was measured at an average depth of 8.98' msl datum; a drop of 0.30' since the last event. TABLE I summarizes the results of the laboratory analyses of water samples from MW-1 since monitoring began. Except for the suspect samples collected in December, 1995, all components have been below detection levels. TABLE U shows the results of water samples from MW-2, which is located down gradient from the removed UST. BTEX& TPHg have been measured at varying concentrations from the first sampling. Natural attenuation does not appear to be occurring. TABLE III summarizes lab results from MW-3. Minor amounts of BTEX & TPHg were recorded from the March, 1997 sampling, and benzene, ethylbenzene, & xylene were detected in June, 1997. All compounds were below detection levels from the December, 1997 sampling. 1