2005-099 - Overriding Considerations for the Alton Avenue Overcrossing at the SR-55 Freeway Project

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Draft Findings of Fact and Mitigation Monitoring Reporting Program (applies to CEQA only) 7.0 SIGNIFICANT EFFECTS, MITIGATION MEASURES, AND FINDINGS The Draft EIR/EA identified ten environmental categories that may result in significant or potentially significant environmental impacts. All of these significant impacts can be avoided through the adoption of feasible mitigation measures. This section presents in greater detail the City's Findings with respect to the significant and potentially significant environmental effects of the proposed project. It also summarizes the evidence relied upon by the City in making these findings. This evidence is drawn from the Notice of Preparation, the Final EIR/EA, the comments and responses to comments on the Draft EIRIEA, and other evidence presented to the City, including all other information in the administrative record. 7.1 GEOLOGY, SOILS, SEISMICITY PotentiaUy Significant Effects Permanent Impacts . The proposed project area is subject to groundshaking from fault activity. Ground motion could result in structural damage and potential traffic delays. Fault activity is not considered to be a major constraint to roadway construction in the region. . Possible consequences to roadway features from soil liquefaction are settlement and spreading of embankments and cracking of the pavement and structure surface. . Subsidence, a general lowering of the ground surface, has occurred within various parts of Santa Ana. This is generally attributed to a lowering of groundwater levels. Groundwater extraction is regulated by the Orange County Water District to ensure that groundwater resources are not depleted or that levels are not substantially lowered to cause land subsidence. The proposed improvements would not be exposed to substantial impacts from subsidence of the land due to groundwater extraction. . Soils with a moderate to high expansion potential are found in and near the project area. The use of highly expansive soils would be unsuitable for use as backfill material around roadway and freeway structures, as it can result in uplift or result in cracking of the foundation or other rigid structures. . Implementation of the Preferred Alternative would result in an increase in impermeable surfaces in the form of additional street paving and expanded freeway structures. This increase in paved surfaces has the potential to increase the volume of water runoff possibly resulting in erosion of adjacent soil surfaces. Temporary Impacts (Construction) . Grading activities may result in earth surfaces being exposed to erosive forces. . Temporary structures used during construction have the potential to be affected by seismic events. ResolU~R~~lbQ,ll.llng al SR-55 Page 20 of 49 K.8 April July 2005