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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 GEOMATFi1X <br /> (51 O) 663-4100 • FAX (51 O) 683-41 41 <br /> May 28,2004 <br /> Project 6628.000 <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: Response to Comments and Work Plan for Additional Investigation <br /> g po 990 Beechnut Property <br /> LkL Tracy, California <br /> Dear Mr. Hubbard: <br /> Geomatrix Consultants, Inc. (Geomatrix)has prepared this letter response and work plan on <br /> behalf of Chevron Environmental Management Company(ChevronTexaco). This letter <br /> addresses comments in a March 2, 2004 letter from the California Regional Water Quality <br /> Control Board, Central Valley Region(RWQCB), and presents a work plan for additional <br /> investigation in the vicinity of the 990 Beechnut property in Tracy, California(the site; <br /> Figure 1). The RWQCB letter contained comments on Geomatrix's January 13, 2004 Soil <br /> Investigation Report. The Geomatrix report recommended conducting additional <br /> investigation of groundwater conditions downgradient of the site; RWQCB concurred with <br /> this recommendation in their March 2, 2004 letter. Below is a brief summary of the site <br /> background, a response to RWQCB comments contained in their March 2, 2004 letter, a <br /> work plan for additional investigation downgradient of the site, and a schedule for work plan <br /> implementation. <br /> SITE BACKGROUND <br /> Several investigations have been conducted at the site between September 1979 and October <br /> 2003 by Geomatrix and others. A summary of these investigations is presented in Geoma- <br /> trix's January 2004 Soil Investigation Report. Previous sampling locations are shown on <br /> Figure 2. <br /> In September and October 2003, Geomatrix advanced two borings, GMX-15 and GMX-16, <br /> approximately 140 feet north of the site boundary within a Union Pacific Railroad (UPRR) <br /> right-of-way. These borings were drilled to assess groundwater quality downgradient(north) <br /> of the site. Stained soil and measurable PID readings were observed in boring GMX-15 from <br /> 9 feet below ground surface(bgs)to the bottom of the boring at 16 feet bgs and in boring <br /> GMX-16 from approximately 16 to 17.25 feet bgs. Because of the presence of petroleum <br /> hydrocarbon affected soil in borings GMX-15 and GMX-16, grab groundwater samples were <br /> not collected from these borings as originally proposed. In our January 2004 report, <br /> Geomatrix recommended further offsite investigation to delineate the extent of affected <br /> groundwater downgradient (north) of the site. <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scient sts <br />