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Wm, J. Hunter & Associates , ; 2220 Loma Vista Dr <br /> Registered Geologists } >>,3,1 Sacramento, CA 95825 <br /> Petroleum& Mineral Appraisers (916) 972-7941 <br /> FAX (916) 972-1683 <br /> i <br /> March 21, 1995 <br /> Steven Sasson, Sr. REHS <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> P O Box 388 <br /> Stockton, CA 0388 <br /> Ref : Second Quarterly Groundwater Monitoring Report for 2315 No. <br /> Eldorado Street, Stockton <br /> Dear Mr Sasson; <br /> We have enclosed a copy of the field report, water analysis <br /> results, a gradient map, and maps showing lines of equal concen- <br /> trations of benzene, ethylbenzene, toluene, xylene, & TPHg for <br /> the above site The work was performed on February 2 , 1996 , by <br /> Del-Tech Geotechnical Support Services as directed by our office <br /> PLATE I shows the potent-lometric surface based upon the 2/02/96 <br /> sampling event . The gradient is towards the southeast at about <br /> • . 551 /100 ' The slope is almost identical to the 10/95 sampling <br /> but the direction has shifted about 36-degrees to the southeast . <br /> This puts MW-3 in a downgradi.ent position from the site of the <br /> removed UST' s, which is the most likely reason for the high <br /> levels of BTEX & TPHg measured in that well from the February <br /> sampling Those levels were the highest since monitoring began <br /> Refer to TABLE I for a summary of those results <br /> The water table was measured at an average depth of 43 19 ' bgl , a <br /> rise of about 3 . 74 ' since the October sampling event, and the <br /> highest since monitoring began. <br /> TABLE 1 summarizes the results of all water analyses taken since <br /> monitoring began, which shows that MW-3 has the highest levels, <br /> with MW-2 second, and MW-1 the lowest A review of that table <br /> shows that MW-1 recorded the lowest levels of all contaminants <br /> since sampling began The drop of levels may be partly due to <br /> the rise in the water table, but is most likely a result of the <br /> fact that the well as parallel too, and slightly upgradient from <br /> the direction of groundwater flow. <br /> PLATES II, III, IV, V, & VI show lines of equal concentration of <br /> benzene, ethylbenzene, toluene, xylene, & TPHg based upon the <br /> 2/2/1996 sampling event They reveal that the levels of all <br /> tested compounds increase towards the southeast, (MW-3 , ) in the <br /> general direction of the hydraulic gradient The significant <br /> . increase in the levels in MW-3 since the October sampling event <br /> 1 <br />