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SEQUDIINALYTICAL <br /> 1900 Bates Avenue • Suite LIM • Concord,California 94520 <br /> (510) 686-9600 • FAX (510) 686-9689 <br /> January 8, 1993 <br /> San Joaquin County <br /> Public Health Services <br /> P.O. Box 2009 <br /> R E C 671 <br /> Stockton, CA 95201 JAW 13 1993 <br /> Attention: MaryMeays ENVIRONMENTAL HEALTH <br /> Dear Mary: <br /> This letter is in regards to the Mobil Oil Corporation site located at 500 E. Grantline Rd. <br /> IG in Tracy, which is being monitored by Alton Geoscience. I have been asked by Stephan Rosen of <br /> Alton Geoscience to give you my opinion, based on the chromatograms, of what is causing <br /> positive results in the tests for TPH as diesel (EPA 8015) on several of the wells. <br /> The wells in question are AW-1 thru AW-8 (except for AW-3, which does appear to <br /> contain diesel), which were sampled on 11126191, and also AW-5, which was again sampled on <br /> 10121192. After looking closely at the chromatograms in question, I have concluded that none of <br /> the above mentioned samples from these wells appears to contain diesel above the stated <br /> detection limit of 50 pg/L. In each case, the positive result is caused by a series of isolated <br /> peaks. These peaks do not appear to form any other kind of common fuel pattern that I am <br /> familiar with (Le. gasoline, kerosene, stoddard solvent,jet fuel, or paint thinner), and cannot be <br /> identified by any of the analyses that have already been run on the samples. <br /> Comparing the chromatograms for AW-5 from both sampling events, it is possible that the <br />` positve results are caused by the same unidentifiable peaks in both cases. However, a comparison <br /> of these peaks by retenti6n tunes (time the peak elutes from the column) is impossible because <br /> two completely different columns were used to analyze these samples.Y <br />�4 <br /> If you have any questions, or would like to discuss this further, please feel free to call me. <br /> Very truly yours, <br /> SEQUOIA ANALYTICAL <br /> i <br /> AA.. effo <br /> �/ <br /> Project Manager <br /> cc: Stephan Rosen - Alton Geoscience <br /> Steve Pao - Mobil Oil Corporation <br />