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4.0 ANALYTICAL RESULTS 4.1 SOIL Parsons was retained by PG&E to assess further the lateral and vertical extent of impacted soil in response to DTSC's recommendations to the April 2008 Workplan (Parsons, 2008) and the Final Technical Memorandum (Parsons, 2009). As identified in Section 2.5.3, MGP Site operations generate residues and byproducts which may be categorized as COPCs. In particular, PAHs tend to be the most common of those chemicals encountered on-site due to historic oil-gas plant operations. Localized MGP contamination was identified during the course of this RI/SSI. Notable Site contaminants included: PAHs, TPH (diesel and motor oil), and various metals. Select analytical data for soil is shown in Figure 11, while tabulated soil analytical data for the constituents of concern and non-analytical data (i.e. geotechnical data) are presented in Tables 12 through 21. Laboratory analytical reports for soil samples are available in Appendix L I. 4.1.1 Polycyclic Aromatic Hydrocarbons A total of 83 soil samples were analyzed for PAHs using EPA Method 8310. This method analyzes for 16 PAHs. Eight of these PAH compounds are considered to be non-carcinogenic. The other eight PAH compounds are evaluated as carcinogens. With the exception of naphthalene, measured concentrations of the carcinogenic PAHs (CPAHs) were converted to benzo(a)pyrene [B(a)P] equivalents using the California Environmental Protection Agency (Cal/EPA) potency equivalency factors listed in Table 12. The B(a)P values were then summed to obtain the total B(a)P value for each soil sample. The CPAHs used to convert concentrations to B(a)P equivalents include: benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, and indeno(1,2,3- cd)pyrene. Naphthalene is evaluated separately from the other CPAHs because it has toxicity values that are not dependent upon B(a)P. The eight PAHs that are traditionally referred to as non-carcinogenic PAHs (NPAH) include: acenaphthene, acenaphthylene, anthracene, benzo(g,h,i)perylene, fluoranthene, fluorene, phenanthrene, and pyrene. A summary of PAH analytical results for soil from the Site investigation are presented in Table 13. A total of 28 soil samples (including duplicates) at the Site contained CPAHs above laboratory method detection limits (MDL). These samples were confined almost entirely to depths shallower than three feet bgs. Samples collected in quadrants Bl, E2, and E3 exhibited the highest CPAH concentrations. Sample B1-1-1 had the highest CPAH concentration; 15,000 ug/kg of chrysene and a B(a)P equivalent concentration of 18.746 mg/kg. Additionally, in the B1 quadrant, Boring 131-2 had elevated benzo(a)pyrene and indeno(1,2,3-cd)pyrene at one foot bgs, each was detected at 1,500 ug/kg. The corresponding B(a)P equivalent concentration for this location was approximately 1.90 mg/kg. Soil gas boring A3-SG3 had an elevated chrysene concentration of 15,000 ug/kg and a B(a)P equivalent concentration of approximately 10.41 mg/kg at one foot bgs. Slightly elevated CPAH detections in close proximity to the B 1 quadrant were observed in samples collected at Al-1; however impacts at B1 were generally isolated. Sample E2-2-1 had a CPAH high detection of 4,600 ug/kg of indeno(1,2,3-cd)pyrene, with an expressed B(a)P equivalent concentration of approximately 5.91 mg/kg. At quadrant E3, sample PARSONS 32 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010