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Wm. J. Hunter & Associates <br /> f f „ ,�,'� � � 2220 Loma Vista Dr <br /> Registered Geologists Sacramento. CA 95825 <br /> Petroleum &Mineral Appraisers (916) 972-74 41 <br /> �. '3 FAX (916) 972-1683 <br /> August 19, 1997 <br /> Steven Sasson, Sr. REHS <br /> San Joaquin County Health Department <br /> Environmental Health Division <br /> P O Box 388 <br /> Stockton, CA 95201-0388 <br /> Ref Fourteenth Quarterly Groundwater Monitoring Report for 814 <br /> E Charter Way, Stockton, Site Code 1061 <br /> We are enclosing a copy of the field report, laboratory analyses, <br /> and maps showing groundwater gradients and lanes of equal concen- <br /> trations of benzene, toluene, ethylbenzene, xylene, & TPHg. The <br /> field work was performed on June 20, 1997, by DelTech Geotech- <br /> nical Support Services as directed by our office . <br /> The attached EXHIBIT A shows the potentiometric surface as of <br /> June 20, 1997; the gradient continues to be to the east at about <br /> . 004 ' /ft <br /> EXHIBIT B summarizes the fifteen (15) hydraulic gradients <br /> measured to date on the property Except for the July 1995 <br /> sampling, all of the data indicate a rather stable gradient to <br /> the east/northeast The reason for the reversal in the potentio- <br /> metric surface in July, 1995 cannot be explained based upon <br /> available data <br /> EXHIBIT C shows lines of equal concentration of benzene from the <br /> June, 1997 sampling event MW-1 continues to be below detection <br /> limits, the only event that revealed any benzene was in February, <br /> 1994 Levels in MW-2 increased from 45 ug/L in January, 1996 , to <br /> 1320 ug/L an June, 1997 The reason for this large increase, <br /> (the highest since monitoring began, ) is not known. Levels of <br /> benzene in MW-3 dropped from 36 ug/L in January to 1 0 ug/L in <br /> June <br /> PLATE D shows isoconcentrataon lines for Toluene from the 6/97 <br /> sampling The levels have dropped significantly since January <br /> (see Table I ) PLATES E & F show lanes of equal concentration of <br /> ethylbenzene & xylene based on the 6/97 sampling. <br /> PLATE G shows lanes of equal concentration of THPG from the <br /> January, 1997 sampling Levels an MW-1 decreased from 199 ug/L <br /> in January, 1997 to 111 ug/L in June Levels in MW-2 increased <br /> from 147 ug/L in January, 1997 to 4810 ug/L an June MW-3 showed <br /> a decrease from 847 ug/L to 103 ug/L <br /> 1 <br />