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

Home Browse Search

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 potential and, as a result, less potential for pollutants to reach groundwater. Based on exploratory boreholes, groundwater levels are 25 to 30 ft below ground surface.36 It is not expected that any storm water that may infiltrate during construction or operation would affect groundwater quality because there is not a direct path for pollutants to reach groundwater. Therefore, Project construction and operation would not violate any water quality standards or waste discharge requirements or substantially degrade groundwater quality. In addition, implementation of the proposed treatment BMPs would avoid any potential impacts to water quality before storm water would percolate into the groundwater basin. As such, when operational BMPs are implemented in accordance with NPDES Permit requirements as required by Mitigation Measure HYDRO-3, 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. b. Would the project substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin? Less Than Significant Impact. The Project site is located within the Orange County Groundwater Basin, which is managed by the Orange County Water District. The Orange County Water District works to manage and protect groundwater in three main ways: recharge, monitor, and purify.31 According to the Orange County Water District, the Orange County Groundwater Basin has a capacity of 500,000 acre-feet (af) and currently has 243,769 of remaining in storage." Groundwater dewatering during construction of the proposed Project may be required during construction of the bridge piles to ensure that groundwater levels are below the pile cap.39 However, groundwater dewatering would be temporary, and the volume of groundwater removed would be minimal compared to the size of the groundwater basin. Therefore, Project construction would not substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the Project may impede sustainable groundwater management of the basin, and impacts would be less than significant. The Project would increase impervious surface areas on site, which can decrease infiltration. However, due to the large amount of impervious surface area in the vicinity of the Project area and within the Santa Ana River channel, minimal infiltration would be expected to occur in the existing conditions. Additionally, the increase in impervious surface area of 8,500 sf (approximately 0.2 ac) is minimal compared to the size of the watershed and the amount of existing impervious surface area in the vicinity of the Project area. Therefore, the increase in impervious area would substantially interfere with groundwater recharge. In addition, operation of the proposed Project would not require groundwater extraction. Therefore, the proposed Project would not substantially decrease 36 Earth Mechanics, Inc. 2018. op. cit. 37 Orange County Water District. 2019a. Groundwater Management. Website: https://www.ocwd.com/ what-we-do/groundwater-management/ (accessed October 2019). 31 Orange County Water District. 2019b. Groundwater Storage Level August 2019. Website: https://www ocwd.com/media/8151/groundwater-storage-august-2019.pdf (accessed October 2019). 39 Earth Mechanics, Inc. 2018. op. cit. 3-58 76"2ND\Fina1ISMND\Fairview Street Bridge Final ISMND.d.C.(05/26/20)