ARCHIVED REPORTS_1ST QUARTER 2008 SITE STATUS REMEDIAL SUMMARY AND GROUNDWATER MONITORING REPORT

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S E COR - W • 3.0 SITE GEOLOGY AND HYDROGEOLOGY The shallow groundwater bearing zone (A-Zone) 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 four to ten 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 42 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 imbedded sand is encountered and extends to a depth of approximately 64 feet bgs, underlain by sands and silty sands of varying moisture extending to a depth of approximately 73 feet bgs. Clay is encountered below the sands to an approximate depth of 84 feet bgs, underlain by a sand/silty sand layer extending to approximately 92 feet bgs. This stratum is a water-bearing zone identified as the C-Zone. Below this sand layer, imbedded clays and silts are encountered to a depth of approximately 115 feet bgs, underlain by a sand/silty sand layer with some imbedded clay to a depth of approximately 130 feet bgs. This stratum is designated as the D-Zone. Clay and silt is encountered below this sand layer to a total depth explored of 140 feet bgs. 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. ,6 • a 1Q08QSSRQRSRQMR.F1na1.doc 8 April 30,2008 77TW.26397.42.1307 y.j;