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• <br /> b ♦ 915 Harger Road, Suite 330 <br /> ' Oak Brook, IL 60523 <br /> Phone: (630) 684-9100 <br /> environmental engineers Fax: (630) 684-9120 <br /> and consultants Website: http://huffnhuff.com <br /> \\V L�� <br /> July 21, 2008 JUL 2 v 2008 <br /> Mr. Harlin Knoll, Senior REHS EfV RONNIEN i'HEAL►H <br /> Public Health Services of San Joaquin County PEP,(v111T/SERVICES <br /> Environmental Health Division <br /> 600 Main Street <br /> Stockton, CA 95202 <br /> Re: Vapor Intrusion Evaluation <br /> Continental Grain Co. <br /> Penny Newman Elevator, Site Code 1132 <br /> 1805 Harbor Street <br /> Stockton, CA 95203 <br /> Dear Mr. Knoll: <br /> Continental Grain Company completed additional site investigation activities in March, 2008. <br /> One activity that was scheduled but not completed was the investigation of the vapor intrusion <br /> pathway associated with Total Petroleum Hydrocarbons (TPH) in the groundwater. Continental <br /> Grain Company has completed additional evaluation regarding this potential pathway. This letter <br /> summarizes site history, geological conditions at the site, and site petroleum residual <br /> characteristics. With this information an analysis of the potential for the vapor pathway to be <br /> complete at this site was evaluated,and that evaluation is included in this letter for your review. <br /> 1. Site History <br /> The project site is located in Stockton, California south of the Port of Stockton's Deep Water <br /> Channel (Figure 1). The site is an active grain storage and transportation facility currently <br /> occupied by the Penny-Newman Grain Company. The subsurface material underlying the site <br /> consists primarily of fine grained (e.g., clay and silt) material with zones of sand. The uppermost <br /> fine-grained clay and silt material exists from ground surface to a depth of approximately 15 feet <br /> below ground surface bgs, under which lies a zone composed primarily of sand-sized material to <br /> a depth of approximately 41 feet bgs. An approximately 5-foot thick clay zone is reported to <br /> exist from approximately 41 to 46 feet bgs followed again by sand-sized material to a depth of <br /> approximately 52 feet bgs which is the total depth explored at the site. Measured depth to <br /> groundwater in the area of the former underground storage tank (UST) has ranged from 7.97 to <br /> 14.29 feet(bgs) (off-site ground surface elevations near MW-5 and MW-6 are approximately 4 to <br /> 5 feet lower than the site, and corresponding depth to water measurements vary accordingly). <br /> The direction of the horizontal hydraulic gradient is southeast to the southwest. <br /> In January 1988, a 10,000-gallon UST was removed from the grain elevator under the <br /> supervision of SJCEHD. When this UST was removed, TPH concentrations of 160 mg/kg and <br /> 24 mg/kg were detected at depths of 17 feet beneath the UST. This area was subsequently <br />