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NT <br />TS <br />INITIAL STNDV/MITIGATED NEGATIVE DECLARATION FAIRVIEW BPIOGE REVLACEM REST TO STREET STREET) <br />L S A <br />MAY 2020 (9Tx STREET To ANTx STREET) L, PROJECT <br />SANTA ANAL CALIFOPHIA <br />southeast by SR-55, to the south by the Pacific Ocean, and to the northwest by the Orange County — <br />Los Angeles County line. <br />Recharge to the Coastal Plain or to the Orange County Groundwater Basin occurs from percolation <br />of Santa Ana River flow, infiltration of precipitation, and injection into wells.31 A portion of the flow <br />from the Santa Ana River directly below the Prado Dam is diverted to recharge groundwater.32 <br />Based on exploratory boreholes drilled in 2003 and 2004, groundwater levels are 25 to 30 ft below <br />ground surface.33 <br />3.10.2 Impact Analysis <br />a. Would the project violate any water quality standards or waste discharge requirements or <br />otherwise substantially degrade surface or groundwater quality? <br />Less Than Significant with Mitigation Incorporated. Pollutants of concern during construction <br />include sediments, trash, petroleum products, concrete waste (dry and wet), sanitary waste, and <br />chemicals. Each of these pollutants on its own or in combination with other pollutants can have a <br />detrimental effect on water quality. During construction activities, excavated soil would be exposed, <br />and there would be an increased potential for soil erosion and sedimentation compared to existing <br />conditions. According to the Draft Water Quality Management Plan (WQMP)34 prepared for the <br />proposed Project, the disturbed soil area during construction would be 1.15 ac. However, Project <br />construction may disturb additional area depending on any sound barriers incorporated into the <br />proposed Project. In addition, there is a potential for chemicals, liquid products, petroleum products <br />(such as paints, solvents, and fuels), and concrete -related waste to be spilled or leaked and <br />transported via storm runoff into receiving waters. <br />Construction activities within the Santa Ana River during bridge replacement have the greatest <br />potential to impact water quality. However, construction within the river would not occur during the <br />rainy season. Activities above and within the river are anticipated to include demolition of the <br />existing concrete bridge; saw cutting and removal of the concrete invert (i.e., the channel lining <br />below the bridge); excavation (3 ft deep at the channel bottom and 6 ft deep at the abutments); pile <br />driving; and installation of concrete for the pile caps, columns, and reconstructed invert. A potential <br />temporary bicycle detour route may be constructed within the Santa Ana River channel. This <br />potential detour route would be constructed and deconstructed during dry -season work within the <br />channel. The detour route would have a dirt base with an asphalt surface and would be entirely <br />removed prior to completion of construction. <br />Diversion of flows within the Santa Ana River is not anticipated to be required because construction <br />activities would not take place within the low -flow portion of the channel. However, sandbags or <br />concrete K-rails with plastic sheets may be required upstream of the work area to ensure that any <br />31 California Department of Water Resources. 2004. op. cit. <br />32 Santa Ana Regional Water Quality Control Board. 2004. Watershed Management Initiative. November. <br />33 Earth Mechanics, Inc. 2018. op. cit. <br />34 Civil Works Engineers. 2019b. op. cit. <br />R:\WKE1702\ISMND\Fina1 ISMND\Fairview Street Britlge Final ISMND7c 'MO9 3-55 <br />