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f <br /> 100 Pine Street, 1 Oth Floor <br /> San Francisco, CA 94111 <br /> C415] 434-9400'• FAX [4157 434-1355 GEOMATRIX <br /> 29 September'1993 <br /> Project 2363 <br /> Ms. Mary Meays <br /> San Joaquin County Public Health Services S 3 0 199 3 <br /> Environmental Health Division ENVIRONMENTAL HEALTH <br /> 445 North San Joaquin Avenue PERMIT/SERVICES <br /> Stockton, California 95201 <br /> Subject: Review Comments - "Human Heath.Risk.Assessment for <br /> Petroleum Hydrocarbons in Soil and Groundwater" <br /> Former.Mobil Oil Bulk Plant <br /> 500 East Grant Line Road <br /> Tracy, California <br /> i <br /> Dear Ms. Meays: <br /> As we discussed in our recent telephone conversation, Geomatrix Consultants, Inc. <br /> (Geomatrix), has completed review of the subject report by Alton Geoscience (Alton). <br /> This letter transmits comments on the report, as well as recommendations for additional <br /> p <br /> investigation at the site. <br /> f <br /> The'comments are divided into two categories. First, general comments regarding the <br /> methods and conclusions of the report are presented. Second, specific comments with <br /> reference to specific statements in the report are presented. <br /> GENERAL COMMENTS <br /> The report title does not indicate that remedial options and a final remedial plan are <br /> discussed in the document. " <br /> It is not clear that the signees of the report have the proper credentials. For example, <br /> although the report discusses site conditions and alternative remedies, none of the <br /> signees is a licensed engineer or geologist in California. <br /> Throughout the document, Alton states that the depth of hydrocarbons in soil was <br /> limited to 10 feet below ground surface. As we have discussed, this statement is <br /> {dearly not accurate. A significant layer of gasoline and diesel is still present under <br /> much of the site below a depth of 10 feet. Alton confirmed this when they recently <br /> drilled three new wells at the property and found very high concentrations of diesel, <br /> gasoline, and benzene below a depth of'10 feet. <br /> Gaomatrix Consultants, Inc. <br /> Engineers,Genlogists,and Environmental Scientists <br />