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FORWARD LANDFILL NON-WATER CORRECTIVE ACTION PLAN 4.1.3 Impacts from Tsunamis A tsunami is an oceanic wave or series of waves produced by an undersea or near-shore earthquake, landslide, or volcanic eruption. The Forward Landfill is located approximately 34 miles from the eastern end of Suisun Bay, the nearest coastline to the site. As a result, impact from a tsunami is considered extremely unlikely, and outside the definition of a "reasonably foreseeable"impact. 4.1.4 Impacts from Dynamic Settlement and Liquefaction Liquefaction and dynamic settlement were evaluated as part of the geotechnical investigation for the proposed northeast and southern expansion areas (GLA, 2008a and 2008b). Several borings and Cone Penetration Tests (CPTs) were advanced to evaluate the subsurface materials. The approximate locations of the borings are presented on Figure 2. Because the geologic conditions within the expansion area are similar to the conditions within the existing,permitted landfill area, conclusions regarding liquefaction and dynamic settlement for the expansion area also apply to the existing landfill footprint. Liquefaction and dynamic settlement of soils can be caused by strong vibratory motions that occur during an earthquake. Liquefaction is typified by a total loss of shear strength in the affected soil layer, thereby causing the soil to flow as a liquid, sometimes causing excessive settlement and sand boils at the ground surface. Both research and historical data indicate that loose, saturated, granular soils are susceptible to liquefaction and dynamic settlement, while the structure of silty clays and clays is not adversely affected by vibratory motion. The results of the analyses indicate that the site soil materials (under the loading of the design MCE horizontal site acceleration) are too dense to liquefy. The calculated factor of safety ranges from 1.4 to more than 8. The minimum required factor of safety against liquefaction is typically taken as 1.1 to 1.3 (based on the criteria presented by the California Division of Mines and Geology, 1997 in Special Publication 117, and SCEC, 1999). The soil profiles were also analyzed for dynamic settlement of these materials under the MCE event. The calculated dynamic settlement was less than 0.2 inches (with differential settlement less than approximately 0.1 inch) indicating a negligible effect on the landfill and its structures. Based on site-specific seismic design parameters and soil strength characteristics, impacts resulting from dynamic settlement and liquefaction are considered negligible, and outside of the definition of a reasonably foreseeable impact. M:\2011-012"WFA REPORT.DOCX 10 Geo-Logic Associates