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 3.3 SPH ASSESSMENT FINDINGS 3.3.1 Summary of Site Geology and Hydrogeology Soils encountered during this investigation generally consisted of clay and silt to approximately 65 feet bgs with interbedded zones of sand, silty sand, and clayey sand typically between 45 and 50 feet bgs. Field notes, boring logs with PID readings, and lithologic data for exploratory borings DP-22 through DP-30 are included in Appendix D. Based on previous site assessment, there is a shallow groundwater-bearing zone (A-Zone) that primarily extends from the ground surface to depths ranging from approximately 25 feet bgs to 40 feet bgs. Subsurface material in the shallow zone predominantly consists of silts, silty sands, and silty gravels from 4 to 10 feet bgs, and then organic clays, clays, high permeability silts, and lenses of silty sands and poorly graded sands to depths ranging from 25 to 40 feet bgs. The shallow zone is generally underlain by low permeability silts and clays (with an occasional, thin, silty sand or poorly graded sand lens) of highly variable thickness. A deeper groundwater- bearing zone (B-Zone) is encountered at a depth of approximately 35 feet bgs and extends to approximately 50 feet bgs. Subsurface material in the B Zone consists of poorly graded sands and silty sands. Below 50 feet bgs, clay and silt with some interbedded sand is encountered and extends to a depth of approximately 65 feet bgs. The lithology observed during this investigation compared well with historic observations of soil types in this area. Groundwater beneath the Site is influenced by the Stockton Channel to the north and the Mormon Slough to the south. The regional groundwater flow direction for the shallow and deeper groundwater-bearing zones is generally to the east-northeast. 3.3.2 DP-22 Verification Borehole- Continuous Core and CPT Lithology The lithologic description of subsurface soils observed by the Stantec field geologist during the advancement of exploratory boring DP-22 was compared with the CPT computer generated data for adjacent borings. In DP-22, fine clays and silts were observed from approximately ground surface to approximately 36 feet bgs, where a three foot layer of well-graded sand was observed. An additional coarse-grained sandy zone of well graded to poor-graded sand was observed between 43 and 48 feet bgs. Below 48 feet, lithology consisted of fine clays and silts. Similar lithology was observed in DP-23 through DP-30. CPT logs and the DP-22 lithologic log are also included in Appendix G Figure 1 B and Figure 1 D. 3.4 SOIL ANALYTICAL RESULTS Soil data were collected for laboratory analysis in exploratory boring DP-22 only. Eleven soil samples at depths ranging from 11.5 to 60.5 feet bgs were analyzed for TPHg, TPHd, BTEX, One Team. Infinite Solutions. TW Stockton SPH Assessment and UOU Pilot Test Report.FINAL.doc 3.1