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l <br /> Wm. J. Hunter & Associates - 2220 Loma vista pr. <br /> Registered Geologists !. Sacramento, CA 95825 <br /> Petroleum &Mineral Appraisers (916) 972-7941 <br /> FAX (916) 972-1683 <br /> August 14, 1998 <br /> Jeffry Wong, REHS <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> Site Mitigation Unit <br /> P.O. Box 388 <br /> Stockton, CA 95201-0388 <br /> RE: Second Quarter 1998 Groundwater Monitoring Report - 913 W. Fremont St., <br /> Stockton, CA. Site Code 1114 <br /> We have enclosed a copy of the field report, laboratory analyses, a groundwater gradient <br /> map, and maps showing inferred lines of equal concentration of benzene, toluene, ethyl- <br /> benzene, xylene, and TPHg. The field work was performed by Del-Tech Geotechnical <br /> Support Services on July 17, 1998 as directed by the County EHD. <br /> The attached PLATE I shows the potentiometric surface based upon this latest sampling <br /> event, along with the 13 measurements taken since monitoring began. The gradient <br /> continues to be to the north/northwest at about .0067ft. <br /> Groundwater was measured at an average depth of 8.1 P msl datum; a drop of 1.57' since <br /> April. It is above the well screens in MW-1, MW-2, & MW-3. The top of the well screen <br /> in MW-4,which was installed later, is at 5' bgl, above the water table. <br /> TABLE I summarizes the results of the laboratory analyses of water samples from MW-1 <br /> since monitoring began. Except for the suspect samples collected in December, 1995, all <br /> components have been below detection levels. <br /> TABLE H shows the results of water samples from MW-2, which is located down <br /> gradient from the removed UST. Benzene was measured at 61 ug/L, the lowest level since <br /> the September, 1994 sampling. Toluene increased d slightly from 27 ug/L to 39 ug/L. <br /> Ethylbenzene dropped from 89 to 52 ug/L, and xylene went from 240 to 188 ug/L. TPHg <br /> increased from 2180 to 2220 ug/L. This general reduction in levels is interesting, since <br /> the water table dropped an average of 1.57' since April.. <br /> TABLE III summarizes lab results from MW-3. Toluene was measured at 0.3 ug/L, an <br /> xylene at 0.5 ug/L, all others were ND. The well had tested clean during the last two <br /> samplings, but had recorded some minor"hits" in March& June, 1997. <br /> tie <br /> 1 <br />