2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis HYDROLOGY AND WATER QUALITY Impact 5.7 -7: Project implementation would introduce development in an area of the City that is within the dam inundation area of Prado Dam. [Threshold HYD -9] ImpactAna7ysis: The project area is in the dam inundation area for Prado Dam. A dam inundation analysis for a proposed charter school at 2840 West 1st Street in Santa Ana, approximately 1,230 feet east of the project area is summarized above in the Seismically Induced Dam Inundation discussion of Section 5.7 -1, Environmental Setting. Flood control improvements to the Santa Ana River channel and to Prado Dam and Seven Oaks Dam, both of which are along the Santa Ana River, are described in the Section 5.7 -1. The US Army Corps of Engineers is planning to update dam inundation maps for Prado Dam by 2020. At that time, the project area will either be out of the dam inundation area for Prado Dam altogether, or the maximum flood depth at the project area from dam inundation will be substantially lower than the four feet shown on the current dam inundation map issued in 1985. Considering the warning time between dam failure and a flood reaching the project site approximately 6.25 hours—people within the project area would be able to evacuate or be evacuated before flooding from dam inundation reached the project area. Additionally, the probability of a catastrophic failure of the Prado Dam during an earthquake or other natural disaster is very low, and emergency evacuation procedures are in place in the event of dam failure. The dam is also required by Division 3 of the California Water Code to be monitored periodically for structural safety. Surveillance measurements of dams in California are the responsibility of the owner and are subject to supervision by the Department of Water Resources, as specified in the California Water Code. Impacts are less than significant. 5.7.4 Cumulative Impacts The area analyzed for water quality impacts is the part of Orange County in the Santa Ana River Watershed, including the Anaheim Bay — Huntington Harbor Watershed. Water Quality Impacts Operation and construction of cumulative development projects in accordance with the City's General Plan (See Section 4.4, AsmVfions Regarding Cumulative Impacts, in Chapter 4) in the Santa Ana River Watershed would each generate pollutants of types varying by land use. However, as with individual development projects that would be accommodated by the Harbor Corridor Plan, cumulative projects would be required to prepare and implement WQMPs covering the design and operation phases of the project, and SWPPPs covering project construction. BMPs implemented by cumulative projects would reduce water quality impacts of those projects to less than significant levels; therefore, significant cumulative water quality impacts are not anticipated, and project water quality impacts would not be cumulatively considerable. Drainage Impacts Cumulative development projects in accordance with the City's General Plan within the Santa Ana River Basin would change amounts of impervious surfaces and thus change amounts of runoff entering storm drainage systems within the watershed. Priority development projects as defined in the MS4 Permit would be required to infiltrate, filter, or treat runoff flow rates or volumes specified in the MS4 Permit. Therefore, October 2014 Page 5.7 -27