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However, if an earthquake were to occur during construction, workers at this site would not be expected to be exposed to elevated risks relative to any common construction site or urban location. Particular aspects of the project site may reduce the hazards associated with ground shaking relative to a typical urban location. The open nature of the site, with no multi-story buildings or overhead structures, would reduce the potential for injury associated with falling debris. Therefore, potential impacts associated with construction-period seismic hazards are not further discussed. Similarly, under current conditions and once the project is completed, the project site would likely be a relatively low-risk location during a moderate to large earthquake. The subsurface geologic materials may experience violent seismic shaking, but the lack of topography and overhead structures that could generate falling debris would reduce hazards to users of the trail relative to people in most urban settings. The bridge could experience shaking and ground acceleration that could cause significant damage and/or settlement. The site-specific geotechnical studies include seismic design parameters that should, if properly incorporated into the final design, reduce the potential for seismic shaking-related impacts to a less than significant level. A mitigation measure has been included below to address this issue. Regional hazard mapping indicates that the liquefaction susceptibility at the site is ''very high" (ABAG, 2004). Liquefaction is the rapid transformation of saturated, loose, fine-grained sediment to a fluid-like state because of ground shaking during earthquakes. Seismic shaking raises the pore- water pressure so that sediment grains are momentarily forced apart. Liquefaction-induced ground failure can occur on level ground if the liquefied material is unevenly loaded. Liquefaction has resulted in substantial loss of life, injury, and damage to property. However, the results ofa site-specific field investigation indicate that the existing fills are generally above the groundwater level; therefore, the risk of liquefaction of fill at the site is considered to .be low. The clayey sand layer below the Younger Bay Mud has low liquefaction potential in a major earthquake event due to the abundance of fines in the sandy units (AGS, 2002b). Excavation, grading, and construction activities associated with building the trail and bridge abutments could result in discharge of sediment and/or sediment-laden runoff into wetland areas behind the existing levees and potentially to the Bay, temporarily causing elevated turbidity levels locally. This potential impact is further discussed, and mitigation provided, in Section vrn, Hydrology and Water Quality, of this document. Impact V-I: Potential impacts associated with seismic hazards Mitigation Measure V-l: The final bridge design shall incorporate the seismic design parameters recommended in the site-specific geotechnical reports. The bridge shall be designed and constructed to withstand the expected seismic shaking and acceleration associated with the maximum expected earthquake on the Hayward Fault. A qualified geotechnical professional shall inspect thefoundation construction activitiesfor the trail and bridge abutments, including predril/ing and pile drivingfor the bridge piers. If any unexpected Y 4204IS.OO693.doc - 415107 -22-