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330 Land Company, LLC Arroyo Lago <br />9785.004.001 Design-Level Geotechnical Report <br /> <br /> <br /> Page | 11 April 16, 2024 <br />Latest Revision October 31, 2025 <br />3.3.4 Lateral Spreading <br /> <br />Lateral spreading is a failure within weak soil, typically due to liquefaction, which causes a soil <br />mass to move along a free face, such as an open channel or down a gentle slope. The site borders <br />Lake I on the northern side of the property line to the north of the Alameda County Flood Control <br />easement. Lake I generally slopes down from the easement at a 3:1 (horizontal:vertical) slope. <br />The Alameda County Flood Control easement acts as a berm between Lake I and the site. Due <br />to the proximity of Lake I, we evaluated the potential for lateral spreading. <br /> <br />Based on the low risk of liquefaction of the native deposits on site and the depth of hydrostatic <br />groundwater, we consider the potential for lateral spreading at the site to be low. <br /> <br />3.4 COMPRESSIBLE SOIL <br /> <br />Compressible soil is subject to settlement when a new loading scenario is introduced by <br />structures, earthwork, and/or equipment. The amount of settlement is dependent on the <br />magnitude and duration of the applied load, the shape and size of the applied area, and the depth, <br />thickness, and the stress history of the compressible soil. The time required for settlement due to <br />compressible soil is highly dependent on the permeability of the deposit. Consequently, sandy <br />soil will settle almost immediately, whereas clayey soil will settle much more slowly. <br /> <br />During our exploration, we encountered predominantly lean clay fill outside of the Busch Pit Area. <br />Based on our review of historical aerial photographs and documents, the existing fill was placed <br />at least 30 years ago in potentially a mechanically compacted manner. Therefore, we anticipate <br />that settlement due to existing fill loads is essentially complete. <br /> <br />Based on the civil plans prepared by CBG Civil Engineers dated July 2025, we understand that <br />anticipated earthwork of up to 7 feet of fill will be needed to achieve proposed pad elevations. The <br />added fill to be placed above existing grades will result in increased long-term loads. Additionally, <br />the structural loads of the building supported on shallow foundations will impose increased loads. <br />The added grading combined with building structural loads are estimated to result in compression <br />of the fill materials and potentially excessive settlements. We estimate the following total <br />settlement may occur in the area outside of Busch Pit if the fill is left unmitigated: <br /> <br />TABLE 3.4-1: Total Estimated Settlement in Areas outside of Busch Pit <br />ADDITIONAL CIVIL FILL <br />(feet) <br />ESTIMATED SETTLEMENT (inches) <br />LOWER BOUND UPPER BOUND <br />0 1½ 2 <br />1 2 2¾ <br />2 2¾ 3½ <br />3 3½ 4½ <br />4 4¼ 5½ <br />5 4¾ 6¼ <br />6 5½ 7 <br />7 6 8 <br />8 6¾ 8¾ <br /> <br />