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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. This AOI is bound to the north by Boring TB-17; bound to the east by Boring TB-19; bound to the south by Borings TB-20 and TB-22; and bound to the west by Boring TB-31. The maximum B(a)P equivalent concentration (estimated at 0.15 mg/kg) associated with these borings was found in Boring TB-22 at a depth of 2.5 feet. As such, no further lateral delineation is necessary. In addition to the lateral delineation achieved with the borings identified above, this AOI is vertically delineated through analysis of samples collected at depths of 3 feet in Boring E2-2 where B(a)P equivalent concentrations were non-detect and at approximately 4.5 feet in Boring TB-21 where Total PAH concentrations are below 0.9 mg/kg; therefore, the B(a)P equivalent concentration would not exceed 0.9 mg/kg. As a note, there are minor detections of TPH in the samples collected from boring E2-2 that are co-located with the PAH impacts identified above. If excavation of the PAH impacts is the selected remedial alternative, the low level TPH impacts will be removed with the PAH impacts. 4.4.3 AOI 3 The third AOI (AOI 3) is characterized by shallow soil (— 0-2 feet bgs) impacted with B(a)P equivalent concentrations greater than 0.9 mg/kg and deeper soil (— 10-15 feet bgs) impacted with elevated TPH concentrations. This AOI is located in the southwest corner of the Site in quadrant E3 and is associated with Borings TB-24 and E3-1. AOI 3 is bound to the north by E3- SG1; bound to the east by Well TW-1; bound to the south by Boring E3-2 and drainage ditch at the property boundary; and bound to the west by natural gas meter and regulator station, where no sampling could occur due to underground utilities. All B(a)P equivalent concentrations in borings that bound that AOI were non-detect. Additionally, results for Boring E3-2 showed no detectable concentrations of TPH; thus, this AOI is delineated in the lateral plane. Based on shallow soil B(a)P equivalent results and relatively deep soil TPH results from these two borings (E3-1 and TB-24), impacts extend to depths up to 15 feet bgs, where TPH results were non- detect in Boring E3-1; thus bounding the impacts in the vertical plane. Based on RI results in Boring E3-1, DTSC requested that a grab groundwater sample be collected from Boring E3-2, which was installed as part of the SSI to laterally delineate impacts identified in Boring E3-1. The grab groundwater sample (E3-2GW) was collected in Boring E3- 2 to determine if impacts in soil had solubilized into groundwater. Based on the results of the grab groundwater sample (non-detect for all TPH constituents and a 2.5 ug/L detection of acenaphthene), soil at this location has not impacted groundwater. Additionally, sampling at TW-1 (crossgradient from Boring E3-2) showed no detectable concentrations of TPH and/or PAHs. Metals concentrations in groundwater at TW-I are consistent with other wells sampled at the site during the RI/SSI and are assumed to be at background levels. 4.4.4 AOI 4 The fourth AOI is located in the northwest corner of the Site in the area where the former gasoline UST was located. AOI 4 is characterized by elevated concentrations of PAHs, TPH and VOCs in soil, soil gas and/or groundwater. Soil impacts are bound to the north by Boring TB-1, to the south by Boring A3-1, to the west by Boring TB-32 and to the east by Boring TB-8. The maximum B(a)P equivalent concentration (0.007 mg/kg) and TPH concentration (44.0 mg/kg of TPH-mo) identified in the borings that bound this AOI were encountered in Sample A3-1-1. PARSONS 39 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010