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July 24, 2007 <br /> Mr. Nuel Henderson <br /> San Joaquin County Environmental Health Division <br /> 304 East Weber Avenue, 3rd floor <br /> Stockton, California 95201 <br /> Subject: Soil Vapor Survey Workplan Clarification <br /> Moore Petroleum Bulk Plant <br /> 5491 F Street, Banta, California <br /> Apex Project No. ERA02.004 <br /> Dear Mr. Henderson: <br /> Apex Envirotech, Inc. (Apex) has been authorized by Moore Petroleum (Moore) to provide this <br /> soil vapor survey workplan clarification. This workplan was prepared in response to the San <br /> Joaquin County Environmental Health Division (SJCEHD) letter dated June 25, 2007 (Appendix <br /> A). All fieldwork will be conducted in accordance with the Apex standard operating procedures <br /> (SOP), included as Appendix B. <br /> PROPOSED SOIL VAPOR SURVEY <br /> Apex proposes to conduct a soil vapor survey at the subject site to investigate the presence or <br /> absence of fugitive soil vapors in the vadose zone. The soil vapor survey will include the <br /> installation of 13 soil vapor survey points located on Figure 3. The soil vapor survey will include <br /> 10 vapor probes around the onsite commercial building and 3 vapor probes located at the border <br /> between the site and the closest nearby residence (Rhodes Residence). <br /> SOIL VAPOR POINT FIELD PROCEDURES <br /> Soil vapor sampling will.be conducted using a whole-air active approach. As stated in by the <br /> Rhode Island Department of Environmental Management's Standard Operating Procedure "The <br /> whole-air active approach involves the forced movement of bulk soil atmosphere from the <br /> sampling horizon to a collection device through a probe". The whole-air active approach for soil <br /> vapor collection is described in the Environmental Protection Agencies (EPA) User's Guide for <br /> Evaluating Subsurface Vapor Intrusion into Buildings published June 19, 2003 in section 4.2 <br /> entitled Soil Gas Sampling, which states "active whole-air sampling method is used whereby a <br />