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C20-SAI-POMBO-01-04614 Science Applications International Corporation An Employee-Owned Company RD)IE FU ��I��.�� January 27, 2004 FEB 0 5 2004 Mr. M. Scott Mansholt Chevron Environmental Management Company ENVIRONMENT HEALTH 6001 Bollinger Canyon Road, RM K2050 PERMIT/SERVICES San Ramon, California 94583 Subject: Additional Soil and Groundwater Investigation Borings Pombo Property 1755 West 11th Street Tracy, San Joaquin, California. Dear Mr.Mansholt: At the request of Chevron Environmental Management Company(ChevronTexaco), Science Applications r International Corporation (SAIC)presents this letter for the soil and groundwater sampling conducted at the subject site in November 2003. Soil and groundwater sampling was conducted in accordance with the Pombo Property-Soil and Groundwater Investigation Work Plan dated July 31, 2003 and California Regional Water Quality Control Board, Central Valley Region(RWQCB)recommendations presented in a RWQCB letter dated August 21, 2003. The planned soil and groundwater sample was intended to delineate the lateral extent of affected soil and groundwater east and west of previous investigations conducted on the West Side Irrigation District(WSID) easement located immediately north of the subject site, and to delineate the downgradient extent of affected soil and groundwater in the housing development located north of the subject site. Based on the results of the November 2003 soil and groundwater investigation, it appears several areas of the subject property have not been fully characterized and that additional soil and groundwater sampling is required in the vicinity of the areas listed as follows(Figure 1): • West of boring SB-3 located in the WSID easement; • East of boring SB-6 located in the WSID easement; and • North,east, and west of borings SB-1 and SB-2 located in the residential area north of the subject r site. The purpose of this letter is to provide ChevronTexaco a general work scope for the next phase of site investigation, locations of proposed borings, and depths. SCOPE OF WORK SAIC will obtain appropriate permits as required by the City of Tracy and San Joaquin County,notify Underground Service Alert(USA), and contract a private utility locator to clear proposed boring locations of subsurface utilities. SAIC will conduct the soil and groundwater investigation in accordance with the Second Draft Consistent Technical Approach(CTA)' applied to ChevronTexaco's historic pipeline sites. Borings will be advanced in accordance with the July 2003 work plan. Target sample depths of borings vary from approximately 8 to 12 feet depending on historical soil sample results from past investigations. Geomatrix Consultants,Inc.,2002,Second Draft Revised Technical Approach to Site Evaluation and Decision Making,Old Valley Pipeline Sites—Central Valley Region,December. v 3800 Watt Avenue, Suite 210, Sacramento, CA 95821 • (916)974-8800•FAX:(916)974-8830 �"er SAIC Offices:Albuquerque,Colorado Springs,Dayton,Falls Church,Huntsville,Las Vegas,Los Altos,Los Angeles,McLean,Oak Ridge,Orlando,San Diego,Santa Barbara,Seattle,Tucson and Sacramento