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Wm. J. Hunter & Associates 2220 Loma vista or Registered Geologists Sacramento, CA 95825 . Petroleum & Mineral Appraisers (916) 972-7941 FAX (916) 972-1683 March 15, 1996 Steven Sasson, Sr REHS San Joaquin County Health Department Environmental Health Division P. 0. Sox 388 Stockton, CA 95201-0388 Ref : Eleventh Quarterly Groundwater Monitoring Report for 814 E Charter Way, Stockton; Site Code 1061 Dear Mr Sasson; We am enclosing a copy of the field report, laboratory analyses, and maps showing groundwater gradients and lines of equal concen- trations of benzene, toluene, ethylbenzene, xylene, & TPHg The field work was performed on February 8, 1996 by Del-Tech Geotech- nical Support Services as directed by our office The attached EXHIBIT A, shows the contours on the top of the water table on February 8, 1996; the gradient is to the east/northeast at about . 331 /100 ' EXHIBIT B summarizes the twelve (12) hydraulic gradients measured to date on the property Except for the July 1995 sampling, all of the data indicate a rather stable gradient to the east/northeast The reason for the reversal in the potentiometric surface in July, 1995 cannot be explained based on the data available at the time this report was prepared. we have not received any data concerning activities at the Darpetro property since January, 1995 EXHIBIT C shows the approximate contours based on lines of equal concentration of benzene from the February 8, 1996 sampling event . They reveal that there has been a decrease in the levels in MW-2 since the October, 1995 sampling, and a slight increase in MW-3 MW-1 continues to be below detection levels . EXHIBITS D, E, & F show lines of equal concentration of toluene, ethylbenzene, & xylene based on the 8/96 sampling. All of the maps show an increase in levels of those components to the east/ northeast, which as the predominant direction of ground water flow. EXHIBIT G shows lines of equal concentration of THPG from the October, 1995 sampling. The direction of increased concentra- tions is to the northeast, whereas in October, 1995, it was essentially due east The amount measured measured in MW-1, 275 ug/L, is the highest level recorded in that well since monitoring . began Concentrations in MW-2 decreased from 1000 ug/L to 645 1 '