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Wm. J. Hunter & Associates E1*A'.RG,`t}4fH hL 19CA T11 2220 Loma Vista Dr <br /> Registered Geologists P'_:R T ERVIC Sacramento, CA 95825 <br /> Petroleum& Mineral Appraisers (916) 972-7941 <br /> 0 93 AUG 16 PM 1: 56 FAX (916) 972-1683 <br /> August 13, 1993 <br /> Michael Collins, REHS <br /> San Joaquin County Health Department <br /> Environmental Health Division <br /> 445 North San Joaquin Street <br /> Stockton, Ca 95202 <br /> ``f-ftef: Quarterly Groundwater Monitoring Report for 814 E. Charter <br /> Wap, Stockton -- Site Code 1061 <br /> Dear Michael; <br /> I am enclosing a copy of the field report, water analysis, and <br /> gradient map for the above property. The work was performed on <br /> June 24, 1993 by Del-Tech Geotechnical Support Services as <br /> directed by my office. <br /> The attached map shows the gradients as measured in October, <br /> 1992, (the first one taken after the monitoring wells were <br /> placed, ) plus the two taken since then in March & June, 1993. <br /> All three measurements indicate a rather eonsistant northeasterly <br /> gradient. <br /> It is interesting to note the differences in levels of contami- <br /> nation measured in the 3 wells between last October and the <br /> current work; they are summarized below for your information. <br /> SU$STANCE HK-1-1 MSI- <br /> Results 10/92 3/93 6/93 10/92 3/93 6/93 10/92 3/93 6/93 <br /> in ug/L <br /> Benzene ND ND ND T.0 3.0 ND 19.0 17.0 13. 0 <br /> Toluene ND ND 0. 9 1. 6 1. 9 0. 7 ND T.4 7.0 <br /> Ethy1B ND ND ND ND 0. 3 ND ND 0. 7 0. 7 <br /> Xylene ND ND 0.4 ND 1.0 0.4 ND 1. 3 1. 3 <br /> TPH-G 60 200 ND 470 500 ND 550 1200 110 <br /> The hydraulic gradient has remained quite stable since first mea- <br /> surements were taken last October - to the northeast. Based on <br /> that data, monitoring well #2 is downgradient from both the site <br /> of the removed UST's and the pump island. Monitor wells #1 & #3 <br /> are essentially on strike, (parallel, ) and a considerable dis- <br /> tance from the UST site. Therefore, if the source of the ground- <br /> water contamination Were the UST' s on the property, MW #2 should <br /> be measuring the highest levels of pollutants. A glance at the <br /> above chart shows that is not the case. Well #3 has con- <br /> sistently recorded higher levels of all components than either <br /> wells #1 or 02. As discussed in the previous quarterly report, ' <br /> the laboratory data strongly supports the belief that the source <br />