ARCHIVED REPORTS_SEPARATE PHASE HYDROCARBON INVESTIGATION UNOCAL EXTRACTION WELL PILOT STUDY 2011

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Stantec Report of Findings for the Waterfront Towers Separate Phase Hydrocarbon Investigation and Unocal Extraction Well Pilot Study Waterfront Towers Parking Lot March 4, 2011 Based on the above data, SPH was consistently observed in two sandy layer zones between 30 and 35 feet and 40 and 45 feet near the center of the Waterfront Towers parking facility and varied vertically as the investigation moved outward in all directions. 3.6 UVOST MODELS BY DAKOTA TECHNOLOGIES Based on the UVOST models by Dakota Technologies (Dakota) the hydrocarbon smear zone appears to be most prominent around DP-24 and extending north and east into the area of DP- 29 and DP-28 (see Appendix G-Figures 1A through 1D). There appears to be two separate smear zones, one identified at approximately 35 feet bgs and a second at approximately 45 feet bgs. The hydrocarbon impacts appear to dissipate in these zones moving further east and south. 3.7 SPH ASSESSMENT CONCLUSIONS The following conclusions were developed based on the interpretation of the field observations and analytical results of DP-22, UVOST and CPT data gathered during this investigation, and • the UVOST modeling. Soil analytical results collected from direct push boring DP-22 suggested that the observed hydrocarbons in soil are a combination of middle distillate hydrocarbons (TPHg) to higher end hydrocarbons (TPHd), primarily consisting of the TPHd which is defined in two smear zones; one around 31 feet bgs and another around 43 feet bgs; this is consistent with additional observations made throughout the investigation with CPT/UVOST data collected from adjacent boreholes. CPT and UVOST data suggest that there is considerable hydrocarbon mass remaining in subsurface strata, particularly in sandy and silty soil layers around 35 and 45 feet bgs in the western and southwestern portions of the Waterfront Towers parking facility. The highest %RE, indicating hydrocarbon impacts, were observed in borings DP-24, DP-28, and DP-29 and were generally in the 35 and 45 foot bgs zones. Based on the data collected from the UVOST investigation, there is no indication of deeper hydrocarbon smear zone impacts to the northeast, east, and southeast of the Waterfront Towers Parking facilities. Stantec did not perform further step-out borings to fully determine the extent of hydrocarbon impacts north and west of the assessment area for a number of reasons. As a preliminary matter, it was Stantec's opinion that the data that was collected would be sufficient to determine an appropriate next step in the ongoing remediation at the site. In addition, there were practical impediments to further step-out borings; the Stockton Deep Channel is directly to the north, Native American burials were discovered to the west during previous excavation activities, and the negotiated access agreement with WOTOA limiting additional drilling. 3.3