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03/27/02 WED 11:00 FAX 510 663 6350 GEOMATRIX OAKLAND 2002-1 2U-1 Floor Ui.lklul 1cl ,.71 1 UJ UL-,':j -11 1-11'3 - FAX [F-51('31 1"11 GEOMATMX March 26, 2002 Project 6447.001 Mr. Robert Mihalovich Chevron]!Environmental Management Company P.O. Box 6012 San Raman, California 94583 Subject: Addendum to December 2001 Soil and Groundwater Sampling Work Plan U.S. Can iWelty Road 35275 Welty Road, Vernalis, California Dear Mr. Mihalovich: Gcomatrix Consultants, Inc. (Geomatrix),has prepared this addendum to the December 13, 2001 Soil and Groundwater Sampling Work Plan for the U.S. Can/Welty Road Property in Vernalis, California(the Site; Figure 1). The December 2001. work plan includes advancing two soil borings to a maximum to delineate the lateral and vertical extent of petroleum hydro- carbon a6ceted soil along with the collection of groundwater samples from the existing on- site and off-site monitoring wells, The December 2001 work plan was submitted to the San Joaquin County Public Health Serv- ices(STC-PHS) and the Regional Water Quality Control Board - Central Valley Region (RWQCEI,). Based on conversations with RWQCB staff, it is our understanding that RWQCB and SIC-PHS staff will approve the proposed work as described in the December 2001 work plan and as modified and amended in this letter. Vertical ]Definition of Soil Affected with Residual Petroleum As described in the work plan,petroleum hydrocarbon-affected soil was identified in two areas along the northern perimeter of the site; 1)within the eastern area of the site adjacent to I building and 2) further west in an area currently used for automobile parking the existing bul Z, (Figure 2). The lateral extent of petroleum(i.e,, crude) affected soil has been delineated within the area adjacent to the existing building through visual observations of soil cores and the results of laboratory analytical data. The vertical extent of petroleum M this area has been defined to a depth of approximately 49 feet below ground surface (bgs) through field observa- tions(i.e., visual inspection and monitoring with field instrumentation) of boring GMX-1; however, no soil sample was collected for laboratory analyses from the teiminus of the boring. It has been requested by RWQCB staff that an additional boring be advanced in the area of GMX-1 and a sample of"clean"soil below the petroleum-affected soil be collected and subtritted for laboratory analyses to better define the vertical extent of petroleum affected soil. Geamzztrix Cansu�tants, Onc. Laioloqinc, ond Envirumyip.jiLad