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n e r m <br /> Wm. J Hunter & Associates L�� -P'?�' ' ,,€ 2220 Loma Vista Dr <br /> Registered Geologists SSacramento, CA 95825 <br /> Petroleum & Mineral Appraisers l� � (916) 972-7941 <br /> J <br /> • L 1 Atf U:: 32 FAX (916) 972-1683 <br /> ti <br /> July 9, 1996 <br /> I <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 - Second Quarterly 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 April 3 , 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 /> 04/03/1996 sampling event, it is to the northeast . The three <br /> monitoring events to date show that the gradient has remained <br /> quite constant since monitoring began The gradient continues to <br /> be very low, at about .004 ' /ft. <br /> The results of the water analyses taken since monitoring began <br /> are summarized on TABLE I MW-1, although upgradient from the <br /> site of the removed UST, measured the highest levels of BTEX & <br /> TPHg Levels of benzene, ethylbenzene, & toluene were signifi- <br /> cantly lower in MW-2 , which is the closest to, and downgradient <br /> from, the UST site Xylene had increased about twofold, and TPHg <br /> was essentially unchanged Benzene was slightly higher in MW-3 , <br /> but all other substances were lower. MTBE was detected in all <br /> three wells; it had not been analyzed in prior samplings <br /> PLATES II thru VI show lines of equal concentrations of BETX & <br /> TPHg based on the April sampling event Levels of all tested <br /> compounds increase to the south/southwest, opposite from the <br /> hydraulic gradient The reason for this anomalous situation is <br /> not known at this time Perhaps additional monitoring events <br /> will clarify the situation <br /> In November, 1995, we submitted a workplan which proposed the <br /> placing of up to eight soil probes in an attempt to define the <br /> plume. After analyzing the latest sampling event, we do not feel <br /> •�� that additional work should be performed until further data is <br /> analyzed <br /> 1 <br />