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LSA ASSOCIATES, INC. INITIAL STUDY/MITIGATED NEGATIVE DECLARATION JULY 2010 FIRST STREET BRIDGE REPLACEMENT PROJECT CITY OF SANTA ANA Less than significant impact with mitigation. Refer to VIILA., above. The site is currently developed; the proposed project does not result in greater water quality impacts other than existing uses. Vehicles using the existing site are already generating some pollutants which settle down on the street surface. The proposed project does not increase traffic volumes and therefore, will not result in substantial increase of the pollutants on site. Due to the high percentage of impervious surfaces already existing on site, no aspect of the proposed project could result in a substantial degradation of water quality because of the small amount of infiltration. No excessive runoff or discharge is anticipated to occur as a result of the project. Less than significant impacts are anticipated with the implementation of Mitigation Measures WQ-1 and WQ-2. G. Place housing within a 100 -year floodplain, as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map? No impact. The proposed project does not involve housing development and would not place housing within a 100 -year floodplain. Therefore, no impacts are anticipated and no mitigation is required. H. Place within a 100 -year floodplain structures which would impede or redirect flood flows? Less than significant impact. According to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) No. 06059CO256J (December 3, 2009), the Santa Ana River 100 - year floodplain within the project area is designated as Zone A, with the 1 percent annual chance flood discharge contained in the channel. The portions of the project area outside of the Santa Ana River are designated as Zone X, which is an area determined to be outside of the 100 -year and 500 - year floodplains. Construction activities would be required within the Santa Ana River 100 -year floodplain in order to replace the bridge piers and nosing. All construction activities in the channel would be conducted during the dry season (April 15 to October 15). Therefore, construction activities associated with replacement of the bridge within the 100 -year floodplain is not expected to impede or redirect flood flows. Four existing bridge piers and nosing, totaling 0.024 ac, would be permanently removed from the Santa Ana River channel and be replaced with two bridge piers and nosings totaling 0.015 ac resulting in a net decrease of 0.009 ac of structures within the 100 -year floodplain. Replacing the bridge piers would result in a minimal decrease in flood flow elevations, which would continue to be contained within the Santa Ana River 100 -year floodplain. Replacement of the bridge piers would not substantially impede or redirect flood flows; therefore impacts related to flood flows would be less than significant. No mitigation is required. L Expose people or structures to a significant risk of loss, injury or death involving flooding, including flooding as a result of failure of a levee or dam? Less than significant impact. According to the Santa Ana General Plan, Safety Element, Santa Ana River has a normally dry river bed and broad engineered channel banked by high earthen levees. Although the likelihood of significant flood hazard is low, Santa Ana River has a history of 07/25/10 «P:\DMJ0701\MND\4.0 Environmental Analysis.doe. 20A-75 4-24