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03/27/02 WED 11:00 FAX 510 663 6350 GEOMATRIX OAKLAND Z003 51 GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company March 26:, 2002 Page 2 Therefore, it is proposed than an additional boring(GMX-1B)be advanced in the area of GMX-1 to a depth where no affected soil is observed(e.g., greater than 50 feet bgs). The proposed 'boring location is shown on the revised.Figure 4 from the work plan. Soil samples will be collected at depths of about 5 and 10 feet bgs for laboratory analyses to evaluate the presence of petroleum constituents in shallow soil. A soil sample will also be collected for laboratory analyses from within the vadose zone where heavily impacted soil is observed and from the terminus of the boring to confirm the vertical extent of petroleum affected soil. The bottom sample will be collected from a depth.where field observations and measurements do not indicate the presence of petroleum constituents. As described in the work plan, the soil samples will be analyzed for total petroleum hydrocarbons quantified as crude oil I;TPHc), for benzene, toluene, ethylbenzene, and xyleiaes(BTEX), and for poly- nuclear aromatic hydrocarbons (PAHs). Since the location of the additional boring is in.an area where chlorinatedvolatile organic compounds have been previously identified in shallow soil, soil samples collected from 5 and 10 feet bgs be analyzed for volatile organic compounds (VOCs) using EPA Method 8260. Soil sample collection and handling and other.field proce- dures will be conducted as previously described in the work plan. Notation of GMX-10 Figure 3 of the December 2001 work plan incorrectly presented boring location GMX-10 to the north of the building located in the northeast area of the site. This boring location is shown adjacent to the rail road right-of-way and Highway 33. This boning was noted on the figure in orror and no boring is proposed in this area. A revised Figure 3 is attached. Geor atri.x will initiate field activities upon agency concurrence with the additional investiga- tive activities and issuance of appropriate permits. Please call either of the undersigned if you have any questions. Sincerely„ GEOMATRTX CONSULTANTS, INC. i Todd N. Loar Matin B. Blocs Staff Geologist Senior Scientist TNI.IMRBlpp 1 [,\Doe_Safc\60C10s\6447.001\Welty Road response W-doc Attachments: Figure 1. — Site Location Map Figure 2—Former Sampling Locations Figure 3 —Historical Groundwater Results (Revised) Figure 4 —Proposed Boring Locations(Revised)