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relatively minor and are silty or clayey and fine-grained. <br /> 1 <br /> Bedding is absent or nondistinct but appears to be essentially <br /> horizontal . owing to a moderate to high silt and/or fine- <br /> grained sand content, <br /> the clays are not highly plastic. <br /> Permeability of the clays and silts is low whereas the sands <br /> exhibit somewhat higher permeability. <br /> The Modesto Formation is known to be underlain by older <br /> Pleistocene and Tertiary strata whish in turn rest on <br /> crystalline basement. However, these formations are of no <br /> significance to this present study because of their depth. <br /> No faulting or fracturing as evident on or near this site. <br />• <br /> Vadose Zone <br /> The logs of the six wells indicate the unsaturated zone consists <br /> predominatly of silts and clays. A zone of sand is located <br /> between 20 and 30 feet below the surface. Another thicker <br /> sand layer begins at about 45 to 50 feet below the surface. <br /> The water table is presently located at 48 feet below grade <br /> within this sand layer. <br /> There is good correlation between the basic soil units except for <br /> the zone between 20 and 35 feet below the surface. This zone <br /> consists of lenses of sand and clay. The two units are not well <br /> defined across the site, however, because of the clay units this <br /> zone will have some effect on the vertical migration of the fuel. <br /> There are no clay units were found in this zone in wells BM-5 and <br /> * BM-8. Enclosed is a cross-section between BM-7 and BM-8, Fig. 3. <br /> Other cross-sections shown in our report of April 30, 1992 show <br /> this same zone. <br /> In order to understand the probable vertical migration, we <br /> • <br /> enclose Fig. 4 which shows the TPH gasoline concentrations found <br /> • Page 5 <br /> • <br />