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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 GEOMATRIX <br /> (510) 663-4100 • FAX (510) 663-4141 <br /> June 25, 1999 <br /> Project 5306 <br /> Ms. Katie L. Hower <br /> Chevron Environmental Management Company <br /> 6001 Bollinger Canyon Road <br /> P.O. Box 6012 <br /> San Ramon, CA 94583-0712 <br /> Subject: Proposed Soil Boring Work Plan <br /> Defense Distribution Depot <br /> Tracy, California <br /> Dear Ms Hower: <br /> Geomatrix Consultants, Inc. (Geomatrix)proposes to advance six soil borings to the depth of <br /> first groundwater(approximately 14 feet below ground surface) at the subject site(Figure 1). <br /> The borings will be located in the area of the site where previous investigations identified <br /> petroleum hydrocarbons(Figure 2). <br /> Background <br /> During a bore/jack excavation operation performed by Rust Environment and Infrastructure <br /> (RUST), petroleum hydrocarbon-affected soil was encountered approximately 12 feet below <br /> grade on the Defense Distribution Depot, San Joaquin Tracy Site Annex in Tracy, California <br /> (DDJC-Tracy). A subsequent investigation was performed by RUST on U.S. government <br /> property to assess if site soil and groundwater have been affected by petroleum hydrocarbons. <br /> Following review of laboratory analytical results, RUST determined that the subsurface <br /> petroleum hydrocarbons detected were not associated with DDJC-Tracy. The objective of the <br /> work proposed herein is to determine if the source of the petroleum hydrocarbon-affected soil <br /> is Chevron and/or Texaco's historical crude oil lines (these lines transported crude oil and <br /> Bunker C). If this is confirmed, then the objectives include defining the lateral and vertical <br /> extent of petroleum hydrocarbons in the site subsurface, and determining if groundwater <br /> downgradient of the petroleum hydrocarbon-affected area has been impacted. This scope of <br /> work has been developed using the approach outlined in the Manch 19, 1997 Geomatrix <br /> document"Technical Approach to Site Evaluation and Decision-Making, Old Valley Pipeline <br /> Site—Central Valley"(Consistent Approach), which was approved by the Regional Water <br /> Quality Control Board, Region 5 (RWQCB; see enclosures). <br /> Soil Boring Work Plan <br /> One soil sample will be collected from each soil boring for chemical analyses. Soil samples <br /> will be collected from the area of the core just above the water table, or if petroleum <br /> hydrocarbon-affected soil is observed, from the area of the core most visually affected by <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />