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Geological Technics Inc. <br /> 1101 7`h Street <br /> Modesto,California 95354 <br /> (209)522-4119/Fax#522-4227 <br /> December 10, 2007 <br /> Project No.: 723.2 <br /> Project Name: Valentine (Castle Motors) <br /> Mr. Stephen Valentine <br /> 6232 Hemet Avenue <br /> Stockton, CA 95207 <br /> RE: Work Plan: Soil and Groundwater Investigation <br /> Location: Valentine (Castle Motors), 2315 N. El Dorado Street, Stockton, CA <br /> Dear Mr. Valentine: <br /> In their October 12, 2007 letter correspondence the SJC/EHD directed that a work plan be <br /> submitted for additional site characterization. Geological Technics Inc. (GTI) is pleased to <br /> present the attached Work Plan for additional site characterization. We propose the <br /> following investigative work at the 2315 N. El Dorado Street, Stockton, site: <br /> • Advance one soil boring to define the vertical extent of the soil plume. <br /> • Install four well sets consisting of an intermediate and a deep well to define the lateral <br /> extent of the plume. <br /> • Obtain soil and groundwater samples. <br /> • Update the Site Conceptual Modell <br /> In their letter they also requested an investigation of soil vapor intrusion potential at the site. <br /> Due to the active operation of a soil vapor extraction (SVE) system at the site to address the <br /> soil plume GTI believes it is appropriate to defer this action. At present time the system is <br /> extracting at vacuum levels of 17 — 20 inches of mercury and removing 3 - 10 lbs./day of <br /> contaminants. Performing a soil gas survey would necessitate shutting down vapor <br /> extraction for two weeks or longer to allow the subsurface to reach equilibrium. This action <br /> should be delayed until after the SVE system has reached asymptotic conditions. <br /> Another concern raised in their letter was the sampling of the deepest interval of the multi- <br /> chamber well sets installed at the site- MW-307, MW-308 and MW-309. These well <br /> intervals were sampled during the third and fourth quarter groundwater monitoring events of <br /> 2007 conducted on July 23 and October 22, 2007. The third quarter monitoring report was <br /> submitted on November 7, 2007 and the fourth quarter 2007 report will be submitted by <br />