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4.4.6 AOI 6 AOI 6 is associated with the soil impacts encountered in Boring A3-SG3. Results for soil at this location (inside the open bay warehouse) showed elevated concentrations of B(a)P equivalents (10.4143 mg/kg) and TPH (TPH-d at 1,100 mg/kg and TPH-mo at 1,900 mg/kg) at a depth of 1 foot bgs. Based on visual/olfactory/PID information gathered during the logging of the A3-SG3 boring, impacts extend to approximately 2.5 feet bgs; thereafter, all observations show that soil is not impacted. Additionally, the soil gas sample collected from this location (A3-SG3) showed only minor detections of acetone (7.50 ug/m3) and carbon disulfide (24.0 ug/m). All other VOC constituents were non-detect. As such, soil gas at this location is not anticipated to be an issue. Metals results for this location appear to be within the range of concentrations observed across the Site. This location is bound to the west by boring A3-SG2, to the southwest by boring A3- SG4, to the north by boring TB-8, and to the northeast by boring A2-1. The highest B(a)P equivalent concentration (0.033 mg/kg) and TPH concentration (95.0 mg/kg for TPH-mo) in the borings that bound this AOI were found in Sample A2-1-1. The southwestern extent of this area is located within the warehouse building, access to which is limited and additional sampling would involve drilling within the operational portion of the building. Due to the fact that soils are capped by the concrete foundation of the warehouse/operations building, a soil exposure pathway is non existent; therefore, it is unlikely that the known releases pose a significant threat to public health or the environment. The extent of these impacts will be further delineated during the remediation of this AOI, if deemed necessary based on potential human health exposure risk. 4.5 SPCC CONTAINMENT STRUCTURE EXCAVATION During the preparation of this Report and between the RI and SSI sampling events at the Site, a spill containment structure was constructed at the PG&E Tracy Service Center (Formerly the Tracy MGP Site), to provide an area for hazardous materials storage for ongoing service center operations. A Workplan for the Oversight of Excavation Operations for the Installation of a Spill Prevention Control and Countermeasure (SPCC) Containment Structure at the PG&E Tracy Service Center (Formerly the Tracy Manufactured Gas Plant (MGP) Site, Tracy, California (hereafter referred to as the "SPCC Workplan") was approved by DTSC on October 6, 2008. The SPCC Workplan provided documentation for the removal of soil potentially impacted by MGP residues in the area where the SPCC Containment Structure was to be constructed. PAHs and/or TPH had been detected in soils during previous sampling in this area. The SPCC Workplan outlined the measures and environmental controls necessary to sample and characterize a small area (93 feet by 20 feet) at the southeastern portion of the Site in which the SPCC Containment Structure is now located. Additionally, the SPCC Workplan provided the procedures necessary to complete the excavation/characterization of this material. Finally, after the excavation work was complete, confirmation samples were collected in the sidewalls and bottom of the excavation to show that any MGP impacted material had been removed. A total of 18 confirmation samples, including two duplicate samples, were collected from the excavation area. Sidewall confirmation samples were collected approximately every 20 linear feet around the boundary of the excavation for a total of 12 sidewall samples (including one duplicate). PARSONS 41 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010