ARCHIVED REPORTS_REPORT OF ADDITIONAL SOIL AND GROUNDWATER INVESTIGATION

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Ms. Dink Mather March 8, 2000 Page 2 Document Reviewed HERD reviewed "Soil and Groundwater Investigation and Screening Health Risk Assessment of the Old Valley Pipeline Right-of-Way" Burns Property (APN 232-170-05), Tracy, California. This document, dated January 2000, was prepared by Geomatrix Consultants, 2101 Webster Street, 12" Floor, Oakland, California 94612, contractors to Chevron Environmental Management Com- pany. Scope of Review The Soil and Groundwater Investigation and Screen Health Risk Assessment of the Old Valley Pipeline Right-of-Way was reviewed for scientific content and sufficiency to support a risk-based clean closure of the site under the Voluntary Cleanup Program. Sampling details, analytical methodology, and technical approach were evaluated. General Comments A total of 7 soil samples and 1 grab groundwater sample were taken to define the vertical and horizontal extent of petroleum hydrocarbon affected soil and groundwater. Soil sample depth began at 8.5 feet bgs and advanced downward to 13- to 19 feet bgs. Surface soils were not affected and, presumably, the former pipeline was located approximately 5 feet below grade. The extent of petroleum hydrocarbon contamination in the soils and groundwater adjacent to the former pipeline right-of-way is limited vertically and horizontally. Levels of petroleum-related hydrocarbons ranged from ND to 14,000 mg/kg for TPH crude and from ND to 5,600 mg/kg for TPH diesel in soils. The PAHs acenaphthene and fluorene were detected in shallow ground- water at 0.1 and 0.3 µg/L respectively. BTEX constituents were less than the detection level in soils. Low levels of PAHs (commonly associated with crude oils, fuel oils, and diesel) were de- tected up to 6.8 mg/kg for naphthalene, up to 5.7 mg/kg for phenanthrene, and up to 3.7 mg/kg for fluorene. Two PAHs, benz(a)anthrancene and chrysene (more notably associated with crude oil) were the only PAHs detected at the site that were potential carcinogens (0.13 and 1.0 mg/kg respectively). None of the constituents identified above were from surface soil samples. Based on the levels of petroleum-related constituents identified at the site, the soils were not completed saturated with product and the product was only identified in the depth profile of from ' 8.5 to 11 feet bgs. The constituents of concern identified on the property included eight PAHs (acenaphthene, ' benz(a)anthracene, chrysene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene). The maximum concentrations of these constituents were used as source terms to estimate chronic daily and lifetime doses of constituents for estimating potential excess cancer risk and noncancer threshold effects. Specific Comments 1. Friedman and Bruya, Inc. of Seattle Washington identified the probable source of the contami- nation as crude oil. The results of the analysis soils and one grab groundwater sample indi- cated the BTEX were not detected. Soil and groundwater samples contained low levels of PAH compounds. The correct spelling of B(a)A is benz(a)anthracene; not benzo(a)anthracene. •