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t t • 0 Figure 3. A more detailed description of the varying lithologic layers and approximate depths is as follows: • 0 to 30 feet — Clayey silt to silty clay with discontinuous lenses, less than 5 feet thick, of poorly to well -graded sand existing at depths of 15 to 18 feet below ground surface (bgs). • 30 to 45 feet — Well -graded and silty sand, including some gravel and varying amounts of silt. Localized areas of clayey silt 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 gravel. • 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 gravel and sand, 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 Hydrogeo%gy 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 sediments that are generally much finer grained with a higher percentage of fine sand and clay. 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. Groundwater occurs under unconfined to locally semi -confined conditions (DWR, 2006). I Biospatge Pilot Test Final doc 2-2 Shaw Environmental, Inc.