Appendix A Water Quality Memo - Laserfiche WebLink

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14 In addition, the proposed Project would improve the hydraulics of the Santa Ana River. As part of the bridge replacement, the proposed Project would replace eight existing pier walls within the Santa Ana River (totaling an area of 0.09 acre) with four new pier walls (totaling an area of 0.05 acre). As detailed in the River Hydraulics Analysis (Civil Works Engineers, Inc. 2019a) prepared for the proposed Project, in the existing condition, a hydraulic jump occurs upstream of the bridge (i.e. flows transition from supercritical to subcritical, which represents a high energy loss with erosive potential). The proposed Project would improve the river hydraulics upstream of the bridge by lowering the water surface elevation and reducing the length of the subcritical flows by approximately 300 ft. Therefore, implementation of the proposed Project would have a beneficial effect on the river hydraulics upstream of the Project area. Additionally, the proposed Project would maintain the overall drainage patterns in the Project area. For these reasons, Project impacts to current, circulation, and drainage patterns would not be adverse. Suspended Particulates (Turbidity) Construction activities disturb and expose soil and increase the potential for soil erosion. Suspended particles, trash, and debris are often discovered on streets and highways. Because the proposed Project would increase impervious surface area, the amount of suspended solids and sediments generated within the Project area could increase. However, the increase in impervious area is minor and construction and operational BMPs would be implemented to reduce pollutants of concern in runoff, including suspended particles. Therefore, impacts related to suspended pollutants would not be adverse. Oil, Grease, and Chemical Pollutants Grading and earthmoving equipment is a source of chemicals, liquid products, and petroleum products if the equipment leaks. Chemicals, liquid products, and petroleum products (such as paints, solvents, and fuels), and concrete-related waste may be spilled or leaked during construction and have the potential to be transported via storm runoff into receiving waters. During operation, oil, grease, and toxic organic compounds are pollutants of concern from transportation facilities. These pollutants of concern can be generated from maintenance activities as well as vehicles operating on the facility. However, the increase in impervious area is minor and construction and operational BMPs would be implemented to reduce pollutants of concern in runoff, including oil, grease, and chemical pollutants. Therefore, impacts related to oil, grease, and chemical pollutants would not be adverse. Temperature, Oxygen Depletion, and Other Parameters The proposed Project is not anticipated to impact the temperature or decrease oxygen in receiving waters. In addition, Reach 1 of the Santa Ana River is not listed as impaired by temperature or low dissolved oxygen. Therefore, the proposed Project does not have a potential to impact receiving water temperature or oxygen levels. Flood Control Functions As discussed previously, the proposed Project would improve the river hydraulics upstream of the bridge by lowering the water surface elevation and reducing the length of the subcritical flows by approximately 300 ft. Therefore, implementation of the proposed Project would have a beneficial effect on the flood control functions of the surface waters upstream of the Project area.