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delineate potential impacts identified in TB-26. Previous investigation Borings TB-9, TB-10, TB-28 and TB-33 confirm the lack of impacts at the western property boundary. Borings E2-1 and E3-1 were selected to identify potential impacts at the southern boundary of the Site in areas that were identified as impacted during previous investigations. Boring E2-1 was placed to laterally delineate impact identified in the only PA sample location (identified as "1" in Figure 6) and in previous investigation Boring TB-22. Boring E3-1 was used to delineate the lateral and vertical extent of impacts identified in previous investigation Boring TB-24. Additional boring locations (E3-2 and 131-2) were advanced as part of the SSI to delineate the lateral extent of impacted soil not adequately assessed with the above identified boring locations. The locations of these previous investigation and RI/SSI borings are shown on Figure 9. Where physical evidence (staining and/or odor) and visual/olfactory observations and/or PID readings were observed, additional samples were collected for analysis. After receipt of the initial sample results, the need for additional borings was determined. 3.2.5.1 On-Site Soil Sampling A total of 83 soil samples, including duplicates, were collected from 15 soil borings and eight soil gas borings, where potentially impacted materials were anticipated and/or observed in the field. All 15 of the soil borings were placed in biased areas which were deemed to require further investigation due to impacts identified in previous investigation or as a follow up to the Phase 1 RI conducted at the Site. Boring locations were placed adjacent to following features: a former gasoline UST, a former 50 foot diameter gas holder, and in areas adjacent to previous investigation borings that identified impacts. The soil sampling boring locations are shown on Figure 9. As previously discussed, soil samples were collected at one, three, five, and eight feet bgs (depth of groundwater) in each boring location to accomplish vertical delineation. Samples were collected at additional depth intervals based on the observance of potentially impacted soil in the field. Additionally, in three borings the vertical depth of the boring was extended to: 1) delineate impacts identified in a previous investigation boring (E3-1 and E3-2); and 2) install Monitoring Well TW-5 (Boring A3-2). Borings E3-1 and E3-2 were drilled to a depth of 15 feet bgs and boring A3-2 was drilled to 26 feet bgs to install the monitoring well. A summary of the boring locations, sample depths, and analyses performed is provided in Table 11. A discussion of analytical results for soil samples is provided in Section 4.1. 3.2.5.2 Background Soil Sampling To determine the existing background conditions in shallow soil surrounding the site, five background soil samples (BK-TR-I through BK-TR-5) were collected and analyzed for PAHs, TPH, and Title 22 Metals. The background sample locations were selected based on the Site inspection conducted on December 13, 2007. The locations are in areas that appear to have been undeveloped and/or have been developed as residential property. It should be noted that the selected background locations were placed in areas where access to the public is not restricted; thus, no access agreements were necessary for sampling in these locations. The locations of the background soil samples are provided in Figure 10. Analytical results for background soil samples are provided in Section 4.1.6. PARSONS 28 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010