Appendix A Water Quality Memo - Laserfiche WebLink

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15 Storm, Wave, and Erosion Buffers The Project area is approximately 9.5 miles from the coast and would have no impact on storm, wave, or erosion buffers. Erosion and Accretion Patterns The increase in impervious area would increase the volume of stormwater runoff from the Project area into the Santa Ana River. However, the Santa Ana River is a stabilized concrete channel and is not susceptible to hydromodification (County of Orange 2012). Therefore, increasing flow to this channel would not change sediment transport or increase downstream erosion and accretion. Aquifer Recharge/Groundwater Groundwater dewatering during construction may be required during construction of the bridge piles to ensure groundwater levels are below the pile cap elevation (Earth Mechanics, Inc., 2018). 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 change groundwater levels in the groundwater basin. 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 8,500 square feet (approximately 0.2 acre) is minimal compared to the size of the watershed and the amount of existing impervious surface area in the vicinity of the Project area. In addition, operation of the proposed Project would not require groundwater extraction. Therefore, the proposed Project would not substantially deplete groundwater supplies or interfere with groundwater recharge. Baseflow Baseflow is streamflow that results from precipitation that infiltrates the soil and eventually moves through the soil to the stream channel. This is also referred to as groundwater flow or dry-weather flow. The Santa Ana River is concrete lined, so there is no baseflow in the Project area. Therefore, the proposed Project would not impact baseflow. 4.2 Anticipated Changes to the Biological Characteristics of the Aquatic Environment Special Aquatic Sites According to the Natural Environment Study (Minimal Impacts) (NES[MI]; LSA 2018a) prepared for the proposed Project, there are no wetlands or riparian areas present in the Project area. There are no ASBSs within or downstream of the Project area. However, the Santa Ana River is subject to USACE, California Department of Fish and Wildlife, and Santa Ana RWQCB jurisdiction. Although an increase in pollutant loading from construction activities and the increase in impervious surface area can impact the water quality in the Santa Ana River, the disturbance area and increase in impervious area is minimal and construction and operational BMPs would be implemented to reduce pollutants of concern in runoff. Therefore, the proposed Project would not have an adverse effect water-quality related impact on special aquatic sites.