75C - PH - BRISTOL EIR FROM WARNER TO ST. ANDREW

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relief feature than is currently found. The effect of such berms will be primarily visual and a positive aesthetic effect. Mitigation Measures No significant landform impacts will occur with the preferred alternative; therefore, no mitigation measures are needed. B. SEISMIC HAZARDS I ' As discussed in Section III-A.2 of this report, although unlikely, seismic hazards that could affect the project area involve the potential for subsidence and liquefaction. Figure 10 graphically illustrates the location of those portions of the project area that could be affected by such hazards. Since subsidence and liquefaction phenomenon involve soil settlement and loss of soil cohesion, damage to buildings and structures, especially habitable and .- critical structures such as hospitals, reservoirs, schools, etc., are of most concern during such events. The proposed project involves no building construction. The Santiago Creek Bridge lies within an area considered to ., have a high potential for subsidence. At this time, it is not known whether the bridge supports were designed and constructed to withstand such an event. r The potential for subsidence induced damage to this bridge therefore exists. ., Displacement of utility poles, street lights and traffic signal devices may occur within the potential subsidence and liquefaction hazard areas. These activities could occur with the preferred street widening alternative. If not anchored properly, such structures could become loose and wobbly and may collapse during subsidence and liquefaction events. Street pavement, curb, gutter, and sidewalk could buckle and crack if a strong seismic event stimulated subsidence and liquefaction in the project area. Loose utility poles, traffic signals and street lights, along with cracked and buckled pavement, curb and sidewalks could result in safety hazards to pedestrians, bicyclists, and vehicular commuters in the areas. Although the potential for subsidence or liquefaction events in Santa Ana is considered low, such consequences as described above .. could occur with the preferred alternative. Typically, utility poles, street light poles, traffic signal devices, etc. are not t designed to withstand such seismic events. This is due to the fact that such structures are not considered critical, as compared to a hospital, school, etc. It is also due to the extraordinarily higher costs of removing and replacing subsurface materials with subsidence /liquefaction characteristics or with constructing extensive footings that reach down to stable subsurface material. IV -2 75C -137 r