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It should be noted that B(a)P equivalent concentrations at the deepest sample collected in each soil boring location were non-detect, which supports that Site impacts are vertically delineated. Additionally, the highest B(a)P equivalent concentration at the boundary of the Site is 1.89 mg/kg at 131-2 where the Site drops off approximately 4 feet in elevation; therefore, off-site sampling is not warranted. The following is a description of the six areas of impact, including their distinct characteristics and delineation: 4.4.1 AOI 1 AOI I is characterized by soil with B(a)P equivalents concentrations greater than 0.9 mg/kg to a depth of approximately 3 feet bgs. AOI 1 is located in the northeast portion of the Site and is associated with Borings B 1-1, B 1-2 and TB-13. Impacts in AOI I were observed to a maximum depth of approximately 3 feet bgs. This AOI is bound to the north by Al-1; bound to the east by Boring B 1-2 and the property boundary where elevation drops by more than 4 feet; bound to the south by TW-2; and bound to the west by TB-12. The highest B(a)P equivalent concentration (1.89 mg/kg) at the boundary of this AOI was observed in Sample BI-2-1 where no additional on-site sampling could be conducted. These borings delineate this AOI in the lateral direction. In addition to the lateral delineation identified above, soil impacts in Borings TB-13, B 1-I and 131-2 have vertical delineation based on result of samples collected from each of these borings. In Boring TB-13, elevated concentrations were observed at a depth of 2 feet bgs; however, results for PAHs in the 3.5 foot sample (Sample TB-13-2) were non-detect. At 131-1, elevated PAH concentrations were encountered at 1 foot bgs but the 3 foot sample collected at this location had concentrations below 0.9 mg/kg for B(a)P equivalents. Finally, at Boring 131-2, the depths of impact observed were similar to the BI-1 location; however, the PAH concentrations were dramatically lower. It should be noted that PAH concentrations in previous investigation borings were reported as total PAHs rather than being speciated by compound; therefore, the B(a)P equivalent concentrations for previous investigation borings are estimated at 10 percent of the total PAH concentration. Other constituents, including naphthalene, lead and arsenic were detected in Borings 131-1, B1-2 and TB-13; however, the detected concentrations were either similar to background concentrations (i.e., the heavy metals) and/or were of a lesser concern because they were not identified in the volatile phase in soil or soil gas samples collected at or near these locations (naphthalene). It should be noted that east of the Site boundary, further delineation of the shallow impacts identified in Boring 131-2 was not possible because of the elevation of the surrounding area is approximately four feet below Site grade; therefore, the delineation of this AOI is complete. 4.4.2 AOI 2 Similar to AOI 1, AOI 2 is characterized by shallow soil (— 0-2 feet bgs) with B(a)P equivalent concentrations greater than 0.9 mg/kg. AOI 2 is located in the southeast portion of the Site and is associated with Borings E2-2 and TB-21. The impacts identified in this AOI were observed above 0.9 mg/kg of B(a)P equivalents to an approximate depth of I foot in Boring E2-2 and a maximum depth of approximately 2 feet in Boring TB-21. It should be noted that PAH concentrations in previous investigation Boring TB-21 were reported as total PAHs rather than PARSONS 38 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010