75B - PH ADOPT RESO FOR PR NO 15-6827

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L S A FAIRVIEW BRIDGE REPLACEMENT AND STREET IMPROVEMENTS (9TH STREET TO 16TH STREET( PROJECT INITIAL STUDY/MITIGATED NEGATIVE DECLARATION SANTA ANAL CALIFORNIA MAY 2020 For regulatory purposes, the Santa Ana RWQCB designates watershed areas in Hydrologic Units (HUs), which are further divided into Hydrologic Areas (HAs) and Hydrologic Subareas (HSAs). As designated by the Santa Ana RWQCB, the Project area is located within the Santa Ana River HU, the Lower Santa Ana River HA, and East Coast Plain HSA.21 The Santa Ana River extends approximately 96 mi from its headwaters to where it drains into the Pacific Ocean. The headwaters for the Santa Ana River and its tributaries originate in the San Gabriel, San Bernardino, and Santa Ana Mountains. From the San Bernardino and San Gabriel Mountains, the Santa Ana River flows through San Bernardino and Riverside Counties, then through the Prado Basin and a narrow pass in the Santa Ana Mountains. From the Santa Ana Mountains, the Santa Ana River flows southwesterly through Orange County to the Pacific Ocean. The Santa Ana River is divided into six reaches. The Fairview Street bridge crosses Reach 1 of the Santa Ana River, which is defined as the portion of the river between the tidal prism and 17th Street in Santa Ana. The Santa Ana River within the Project area is a concrete -lined, trapezoidal channel and is devoid of vegetation. Intermittent flows within the Santa Ana River can be attributed to storm water runoff, urban runoff, and treated wastewater. 3.10.1.2 Floodplains According to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) No. 0659C0144j,28 the Santa Ana River within the Project area is designated Special Flood Hazard Area Zone A; such areas are subject to inundation by the 1 percent annual chance flood (100-year flood) with no base flood elevations determined. The remainder of the Project area (outside of the Santa Ana River) is designated as Other Areas of Flood Hazard Zone X; such areas have a reduced flood risk due to levee. 3.10.1.3 Groundwater Hydrology The Project area is above the Coastal Plain of Orange County Groundwater Basin, which underlies the Lower Santa Ana River Watershed. The basin is bounded on the north by the Puente and Chino Hills, on the east by the Santa Ana Mountains, on the south by the San Joaquin Hills, on the southwest by the Pacific Ocean, and on the northwest by low topographic divide at approximately the Orange County —Los Angeles County line.29 For regulatory purposes, the Santa Ana RWQCB divides the Coastal Plain of Orange County Groundwater Basin into three Groundwater Management Zones. The Project area is within the Orange County Groundwater Management Zone.30 The Orange County Groundwater Management Zone is bounded to the north by the Chino Hills, to the east by the Santa Ana Mountains, to the 27 Santa Ana Regional Water Quality Control Board. 1995. Water Quality Control Plan, Santa Ana River Basin Updated 2008 and 2011. 28 United States Federal Emergency Management Agency. 2009. Flood Insurance Rate Map (FIRM) No. 0659C0144J. December 3. 29 California Department of Water Resources. 2004. California's Groundwater, Bulletin 118—South Coast Hydrologic Region, Coastal Plain of Orange County Groundwater Basin. February. 30 Santa Ana Regional Water Quality Control Board. 1995. op. cit. 3-54 7 5848ND\Final ISMND\Fairview Street Bridge Final ISMND.docx (OS/26/20)