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ameO <br /> February 1, 2012 <br /> Project 0066280010.00005 <br /> Mr. C. Dean Hubbard <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 1685 E Street <br /> Fresno, California 93706 <br /> Subject: Work Plan for Additional Investigation <br /> 990 Beechnut Avenue Property <br /> Tracy, California <br /> Dear Mr. Hubbard: <br /> AMEC Environment & Infrastructure, Inc., (AMEC) has prepared this work plan on behalf of <br /> Chevron Environmental Management Company (Chevron) for additional investigation at the 990 <br /> Beechnut Avenue property in Tracy, California (the site; Figure 1). The additional investigation is <br /> proposed to address comments in a September 21, 2011 letter from the California Regional <br /> Water Quality Control Board, Central Valley Region (Water Board) pertaining to AMEC's <br /> December 23, 2010 Excavation Completion Report and Updated Screening Level Risk <br /> Assessment(Report and updated SLRA). Below is a brief summary of the site background, a <br /> work plan for additional soil investigation at the site, and a schedule for work plan <br /> implementation. <br /> SITE BACKGROUND <br /> Several investigations have been conducted at the site between 1988 and 2010 by AMEC and <br /> others. Using data from these investigations, AMEC performed a Screening Level Risk <br /> Assessment (SLRA) in 2008.' A summary of these investigations is presented in AMEC's <br /> December 2010 Report. Previous sampling locations are shown on Figure 2. <br /> Based on results of previous investigations and the 2008 SLRA, Chevron completed an <br /> excavation at the site in November 2010 to remove polycyclic aromatic hydrocarbon (PAH) <br /> affected material in the southwest corner of the site. The updated SLRA was completed to <br /> assess site risks following removal of PAH-affected soil. The updated SLRA concluded that the <br /> site was suitable for future commercial/industrial uses, with the exception of one location where <br /> the concentration of ethylbenzene in soil suggested a potential vapor intrusion concern for a <br /> hypothetical future commercial/industrial user. The updated SLRA also noted that there were <br /> locations at the site where chemical concentrations exceed residential screening levels, possibly <br /> limiting potential future unrestricted use of the site. At a meeting between Chevron and the <br /> Water Board on August 24, 2011, stakeholders agreed to conduct further work at the site to <br /> Geomatrix Consultants, Inc., 2008, Updated Screening-Level Risk Assessment, 990 Beechnut Avenue, Tracy, <br /> California, October 21. <br /> AMEC Environment&Infrastructure, Inc. <br /> 2101 Webster Street, 12th Floor <br /> Oakland,California 94612-3066 <br /> USA <br /> Tel (510)663-4100 <br /> Fax (510)663-4141 <br /> amec.com <br />