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 4.2 GROUNDWATER EXTRACTION WELLS GWE-1 AND GWE-2 GWE-1 and GWE-2 were installed in order to extract groundwater and soil vapors from the GCT. The base of the trench is approximately 16 feet bgs and generally sloped down, north-to- south. The GCT was previously installed by T&R following excavation activities to the east of the wells. 4.2.1 Borehole Clearance For geological purposes, a licensed professional engineer was engaged to survey and marking of locations GWE-1 and GWE-2. The survey was based on coordinates provided by T&R, who was the Environmental Consultant working for the SRDA at the time of the UOU groundwater collection trench (GCT) construction. In order to minimize the risk of encountering underground utilities, on July 20, 2010, Stantec met with a private utility locator (Cruz) to determine if any subsurface utilities or obstructions were located in the vicinity of the proposed wells. In addition, Stantec marked the boundaries of the • proposed well locations and contacted USA at least 48 hours prior to the initiation of field work to evaluate whether the proposed boring locations were clear of potential subsurface obstructions. On August 5, 2010, the borehole locations were cleared to a depth of approximately eight feet one bgs using an air lance and vacuum truck (air knife rig) prior to commencement of mechanical hollow-stem auger (HSA) drilling. 4.2.2 Drilling, Logging, and Well Installation The advancement of the soil borings and the well completions were performed by a California licensed driller, Water Development Company (WDC), and drilling oversight was performed by a Stantec Professional Geologist. Following borehole clearance, GWE-1 was advanced using an HSA rig to a depth of approximately 19.5 feet bgs using 12-inch augers. Soil samples were recovered for lithologic logging at approximately five-foot intervals. GWE-1 was completed to approximately 17.5 feet bgs with four-inch diameter Schedule 40 polyvinyl chloride (PVC). Pre-manufactured 0.010-inch slotted PVC casing was installed from 17.5 feet bgs to 10 feet bgs. The well annulus was backfilled from 19.5 to 17 feet bgs with Monterey #3 Sand, from 17 to 9.5 feet bgs with 3/-inch pea gravel, and from 9.5 to 7.5 feet bgs with hydrated bentonite chips. Neat cement grout seal was installed from 7.5 feet bgs to ground surface, with a traffic-rated vault installed at the surface. 4.5