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Ll • 30 to 45 feet — Well graded and silty sand, including few gravels and varying amounts of silts. Localized areas of clayey silts also noted within this layer near the southern boundary of the site. 45 to 58 feet — Poorly graded sand consisting of dense, medium -grained particles and trace sub -rounded gravels. • 58 to 62 feet — Poorly to well graded sand, interspersed with discontinuous silty clay and silty sand lenses. Clay and silt particles are common. • 62 to 74 feet — Silt with trace gravels and few sands, interbedded with localized silty sand at approximately 68 feet bgs. • 74 to 80 feet — Gravelly sand and sandy silt. Trace amounts of caliche, oxidized wood fragments and roots up to 0.04 inch (1 mm) diameter were also noted in direct push boring DP -9 from 60 to 70 feet. 2.2.2 Hydrogeology Groundwater at the site is included within the Eastern San Joaquin basin, a subset within the San Joaquin River Hydrologic Region. Water -bearing formations of significance in the Eastern San Joaquin basin consist of the Alluvium and Modesto/Riverbank Formations, the Flood Basin Deposits, the Laguna Formation, and the Mehrten Formation (Department of Water Resources [DWR], 2006). It is likely that the Flood Basin Deposits and the Laguna Formation are represented at the site. The Flood Basin Deposits formation consists of Pliocene to Recent aged fine-grained forms of the Laguna, Riverbank and Modesto Formations. These sediments are generally much finer grained with a higher percentage of fine sand and clays. Occasional gravel beds occur along the present waterways. Groundwater in this unit occurs under unconfined and confined conditions. The unit, in general, has low permeabilities and may create semi -confined to confined conditions when interfingered with the Alluvium and Modesto/Riverbank Formations (DWR, 2006). The Laguna Formation is Plio-Pleistocene in age and consists of discontinuous lenses of stream laid sand and silt with lesser amounts of clay and gravel. There are no regionally significant fine-grained intervals that could cause water pressure conditions, although the heterogeneous nature of the sediments can cause local confinement. Groundwater occurs under unconfined to locally semi -confined conditions (DWR, 2006). Within the last five years, the depth to water has varied between 19 to 27 feet bgs in site wells (IT Corporation, 2002; and Shaw 2006a, 2007). Fluctuation in water levels may be attributed to not only seasonal rainfall, but also the operation of the Port of Stockton and the pumping of groundwater supply wells in the Stockton vicinity. Groundwater elevations in the deeper wells FS_Onsite Petroleum Hydrocarbon Remediation.doc 2-2 Shaw Environmental, Inc.