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Wm. I Hunter & Associates 2220 Loma Vista Dr <br /> Registered Geologists Sacramento, CA 95825 <br /> *etroleum& Mineral Appraisers (916) 972-7941 <br /> FAX (916) 972-1683 <br /> October 5, 1995 <br /> Steven Sasson, Sr REHS <br /> San Joaquin County Health Department <br /> Environmental Health Division - - <br /> 445 North San Joaquin Street <br /> Stockton, Ca 95202 <br /> Ref • Ninth Quarterly Groundwater Monitoring Report for 814 E. <br /> Charter Way, Stockton; Site Code 1061. <br /> Dear Mr. Sasson, <br /> We am enclosing a copy of the field report, water analysis, and <br /> maps showing groundwater gradients and lines of equal concentra- <br /> tions of Benzene & TPHG The field work was performed on July 10, <br /> 1995 by Del-Tech Geotechnical Support Services as directed by our <br /> office. <br /> The attached EXHIBIT A, shows the contours on the top of the <br /> water table taken July 10 ; the gradient is to the northwest at <br /> • about 13 ' /mile . EXHIBIT B summarizes the ten (10) hydraulic <br /> gradients measured to date on the property. Except for the <br /> latest measurement, all of the data indicate a rather stable <br /> gradient to the northeast The northeast gradient is consistent <br /> with both regional data and that measured at the Darpetro site in <br /> January, 1995 to the northwest of the Morita property. The <br /> reason for the reversal in the potentiometric surface cannot be <br /> explained based on the data available at time this report was <br /> prepared. <br /> EXHIBIT C shows the approximate contours based on lanes of equal <br /> concentration of benzene from the July 10, 1995 sampling event . <br /> They show that MW-2 recorded the highest levels, (also the case <br /> in the March, 1995 sampling, ) and that MW-1 was ND, (also in <br /> March, 1995 ) Although the shape of the contours agrees closely <br /> with those mapped in March, 1995, the concentrations measured in <br /> both MW-2 & MW-3 are much higher in the July event . <br /> i <br /> EXHIBIT D shows lanes of equal concentration of THPG from the <br /> July, 1995 sampling It does not agree with the March, 1995 <br /> data, (see prior report for details . ) Data from the 3/95 event <br /> showed that MW-2 had the highest levels of gasoline, with a <br /> decrease in concentration in a westerly direction. The July, <br /> 1995 data shows MW-3 to have the highest levels, with a decrease <br /> in concentration towards the southeast <br />• As mentioned in previous reports, a mayor soil & groundwater <br /> 1 ' <br /> s <br />