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Wm. J. Hunter & Associates 2220 Loma Vista Dr Registered Geologists Sacramento, CA 95825 ��etroleum & Mineral Appraisers (916) 972-7941 FAX (916) 972-1683 June 18, 1998 Carol Oz, REHS San Joaquin Co PHS Environmental Health Division P O Box 388 Stockton, CA 95201-0388 RE- FIRST QUARTER 1998 GROUNDWATER MONITORING REPORT FOR 814 E. CHARTER WAY, STOCKTON, CA - SITE CODE 1061 We have enclosed a copy of the field report, summary of laboratory analyses, copies of the lab reports & custody chains, and maps showing the potentiometric surface & inferred lines of equal concentrations of benzene, ethylbenzene, toluene, xylene, and TPHg The field work was performed on March 30, 1998 by Dei-Tech Geotechnical Support Services as directed by our office The attached PLATE A shows the inferred potentiometric surface as of March 30, 1998 The gradient is to the northeast at about 0033'Ift , slightly flatter than the last measurement PLATE B shows all of the gradient directions since ` monitoring began They continue to show a predominant northeast direction Groundwater was measured at an average depth of 33 fig' below grade, a rise of about 4 feet since the last sampling event The top of the screen in each of the wells is at 44', about 10 feet below groundwater during this sampling There has been a steady rise In the water table since monitoring began The lowest average depth was 54 44' in October, 1992, the highest was this latest event PLATE C shows inferred lines of equal concentrations of benzene based upon the latest event MWA continues to be non-detect, with MW-2 the highest at 255 ug/L, and MW-3 at 0.6 ug/L Benzene levels dropped significantly in MW-2, from 1320 ug/L to 255 ug/L The eastern edge of the plume has not been determined PLATE D shows the inferred lines of equal concentrations of toluene MWA is non-detect, MW-2 measured 0.6 ug/L, and MW-3 0.6 ug/L These levels are down from 1.0 ug/L in June, 1997 PLATE E, (ethylbenzene) shows that both MW -1 & MW-3 were below detection limits MW-2 measured 31 ug/L, down from 139 ug/L in June, 1997 1