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Jerry Lile <br /> July 11, 2002 <br /> Page 2 <br /> Tracy, California" both prepared for Chevron by Geomatrix Consultants. <br /> DOCUMENT REVIEWED <br /> We reviewed the December May 9, 2002, "Response to Comments-January 2, 2002 Letter, Pombo <br /> Property, Tracy, California"prepared for Chevron by Geomatrix Consultants located in Oakland, <br /> CA. <br /> SCOPE OF REVIEW <br /> The document was reviewed for technical accuracy and validity with respect to the screening level <br /> risk assessment for releases from the OVP. The screening level risk assessment is not reflective <br /> of the potential risks from any other potential or actual sources of release on the Pombo property; <br /> as a specific example,potential releases from the former gasoline station have not been <br /> thoroughly characterized and included in the screening level risk assessment. Therefore, <br /> DTSC/HERD can only make recommendations regarding the OVP-focused investigation and <br /> screening level risk assessment, and not the site-wide safety to humans. <br /> GENERAL COMMENTS <br /> 1. The responses emphasized the limited scope of the investigation and screening level risk <br /> assessment directed solely to releases from the OVP. <br /> 2. Metals can be natural constituents of crude oil and are used as drilling mud additives. Historical <br /> compositional analysis of crude oil transported through the OVP may contain data on the <br /> concentrations of metals such as arsenic,barium, hexavalent chromium, and copper used during oil <br /> production/extrication activities. HERD advises Site Mitigation Staff to assure that releases from <br /> the OVP did not include metals. <br /> SPECIFIC COMMENTS <br /> 1. Data limitations: <br /> a. Soil sampling for the combined data set was limited to 8.5 to 15 ft below ground surface <br /> (bgs); vertical extents of contamination were based on visual soil staining. <br /> b. The western area of the property that had contained high !levels of THPc and low <br /> concentrations of PAHs, toluene, and xylene has been excavated in the process of <br /> construction a percolation/retention pond for storm water. The excavated soil was used on <br /> an adjacent parcel as fill material beneath an asphalt parking lot. Confirmation samples <br /> collected from the base of the excavation were limited to TPHc. <br />