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1, <br /> Wm. J. Hunter & Associates " ''`�� ' ; f, 2220 Loma Vista Dr <br /> Registered Geologists ° ' f `, �,4 r - Sacramento, CA 95825 <br /> 6i <br />'Petroleum & Mineral Appraisers (916) 972-7941 <br /> 1 2? FAX (916) 972-1683 <br /> August 19, 1998 <br /> Carol Oz, REHS <br /> San Joaquin Co PHS <br /> Environmental Health Division <br /> P O Box 388 <br /> Stockton, CA 95201-0388 <br /> RE: SECOND QUARTER 1998 GROUNDWATER MONITORING REPORT FOR <br /> 814 E. CHARTER WAY, STOCKTON, CA - SITE CODE 1061 <br /> We have enclosed a copy of the field report, summary of laboratory analyses, <br /> copies of the lab reports & custody chains, and maps showing the potentiometric <br /> surface & inferred lines of equal concentrations of benzene, ethylbenzene, <br /> toluene, xylene, and TPHg The field work was performed on July 1, 1998 by <br /> Del-Tech Geotechnical Support Services as directed by our office <br /> The attached PLATE A shows the inferred potentiometric surface as of July 1, <br /> 1998 The gradient continues to be to the northeast at about 0025'/ft , slightly <br /> flatten than the last measurement PLATE B shows all of the gradient directions <br /> since monitoring began They continue to show a predominant northeast <br /> direction <br /> Groundwater was measured at an average depth of 31 88' below grade, a rise of <br /> 1 81' since March, and the highest level since monitoring began The top of the <br /> screen in each of the wells is at 44' bgl, about 12 feet below the groundwater <br /> surface There has been a steady rise in the water table since monitoring <br /> began The lowest average depth was 54 44' in October, 1992, the highest was <br /> this latest event <br /> PLATE C shows inferred lines of equal concentrations of benzene based upon <br /> the latest event MWA continues to be non-detect, with MW-2 the highest at <br /> 555 ug/L, and MW-3 at 6.0 ug/L Benzene levels increased slightly in MW-2 and <br /> MW-3. <br /> PLATE D shows the inferred lines of equal concentrations of toluene MWA is <br /> non-detect, MW-2 measured 1.0 ug/L, and MW-3 0.3 ug/L <br /> PLATE E, (ethylbenzene) shows that MW -1 was ND, MW-3 was 0.9 ug/L, and <br /> MW-2 measured 65 ug/L, up from 31 ug/L in June, 1997 <br />}i <br /> ` I <br /> 1 <br />