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 water that escapes the low -flow channel is diverted back to the low -flow channel before reaching the construction area. A staging area would be located along the riverbank. No materials or equipment would be stored within the river channel. Projects that disturb more than 1 ac of soil are subject to the requirements of the CGP. However, projects that disturb between 1 and 5 ac are potentially eligible for a Small Construction Rainfall Erosivity Waiver, which would exempt the project from coverage under the CGP. To obtain a waiver, a project would need to demonstrate that there would be no adverse water quality impacts, because construction activities would only take place when there is a low erosivity potential (i.e., the rainfall erosivity value in the Revised Universal Soil Loss Equation [R factor] for a project is less than 5). Based on a 2-year construction schedule, the R factor for the proposed Project would be approximately 38. Because of the two-year construction schedule, the R factor is well above 5, and the proposed Project would not qualify for a CGP erosivity waiver. Therefore, the proposed Project would be required to obtain coverage under and comply with the requirements of the CGP. Based on the Risk Determination methodology outlined in the CGP, the Project has a low Sediment Risk (the relative amount of sediment that can be discharged, given the Project location and construction schedule—i.e., no work in the river during the wet season) and a low Receiving Water Risk (the risk sediment discharges pose to the receiving waters), which results in a combined Risk Level of 1 (low risk to water quality). Risk Level 1 projects are subject to the BMPs and visual inspection requirements of the CGP. To prevent significant water quality impacts during ground -disturbance activities, the Project would need to prepare and implement a SWPPP that includes construction BMPs that comply with the requirements of the CGP. These requirements are included in Mitigation Measure HYDRO-1. Construction BMPs would include, but not be limited to, Erosion Control and Sediment Control BMPs designed to minimize erosion and retain sediment on site, Good Housekeeping BMPs to prevent spills, leaks, and discharge of construction debris and waste into receiving waters, and Entrance Control BMPs to mitigate any tracking from the Project. Construction BMPs around the work area within the Santa Ana River are anticipated to include a gravel bag or fiber roll perimeter barrier to contain spills and potential runoff, to be installed and maintained year-round. Additional Construction BMPs would be determined during preparation of the SWPPP. When Construction BMPs are properly designed, implemented, and maintained to address pollutants of concern, as required in Mitigation Measure HYDRO-1, pollutants of concern would be retained on site so that they would not reach receiving waters; therefore, the project would not violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or groundwater quality. Impacts would be less than significant with mitigation incorporated. Groundwater dewatering may be required during construction of the bridge piles to ensure that groundwater levels are below the pile cap elevation.35 Release of dewatered groundwater to surface waters can introduce total dissolved solids and other constituents to surface waters. To prevent significant impacts to water quality associated with dewatering during construction, the Project would need to comply with the requirements of the De Minimus Permit. Mitigation Measure HYDRO-2 specifies compliance with this permit for groundwater dewatering. In compliance with this " Earth Mechanics, Inc. 2018. op. cit. 3-56 7611V"0,ND\FiD.1ISMND\FairviewSt,EFtBridgPROMISMND.doC.(05/26/20)