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Wm. J. Hunter & Associates '4`,Fr�f #- ' 2220 Loma Vista Dr <br /> Registered Geologists Sacramento, CA 95825 <br />. Petroleum & Mineral Appraiserst.J+f I4f $ (916) 972-7941 <br /> FAX (916) 972-1683 <br /> November 15, 1996 <br /> Ron Rowe, Sr REHS <br /> San Joaquin County PHS <br /> Envrironmental Health Division <br /> P.O Box 388 <br /> Stockton, CA 95201-0388 <br /> Ref : Third Quarter 1996 Groundwater Monitoring report for 1211 <br /> South Turnpike Road, Stockton, Site Code 1788 <br /> We are enclosing a copy of the field report, laboratory results <br /> of water analyses, and maps showing the hydraulic gradient and <br /> . lines of equal concentrations of benzene, ethylbenzene, toluene, <br /> xylene, and TPHg based on the latest data The field work was <br /> conducted on September 16, 1996 by Del-Tech Geotechnical Support <br /> Services as directed by our office <br /> The attached PLATE I shows the hydraulic gradient based on the <br /> 09/16/1996 sampling event ; it continues to be to the northeast <br /> The four monitoring events to date show that the gradient has <br /> remained quite constant since monitoring began. The gradient <br /> continues to be very low, at about 003 ' /ft <br /> The results of the water analyses taken since monitoring began <br /> are summarized on TABLE I Levels of benzene, toluene, xylene, & <br /> TPHg were highest in MW-1, and in fact had increased in concen- <br /> tration since the last measurement Ethylbenzene levels were the <br /> same as the April sampling Levels of benzene, toluene & TPHg <br /> decreased in MW-2 , but ethylbenzene & xylene increased All <br /> . tested compounds had higher concentrations in MW-3 compared to <br /> the April event MTBE, which had been detected in all three <br /> wells during the April sampling, were below detection levels <br /> during the latest work The reason for this change is not known <br /> PLATES II thru VI show lines of equal concentrations of BETX & <br /> TPHg based on the September sampling event . Levels of all tested <br /> compounds continue to increase in an upgradient direction, which <br /> suggests either- (1) another ma3or source to the south of the <br /> removed UST; or (2) the hydraulic gradient has been to the south <br /> in prior years . <br /> Quarterly monitoring will continue until further notice; the next <br /> sag ent is due in December <br /> i� <br /> cc CB <br /> , <br /> Pump J NlILI R"I J <br /> 1 NO 8�O <br /> s�q� <br /> OFC <br />