2019-040 - Mainplace Mall Transformation

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City of Santa Ana Addendum to the MainPlace Mall Transformation Proiect Fashion Square Commercial Center Final EIR to the adjacent Caltrans drainage system; and 4) the southwest parking lot drains to a catch basin that connects to the adjacent Caltrans drainage system. The proposed Project would not change the onsite drainage pattern and the existing storm drain infrastructure on the site would be utilized. The Project would also install catch basins that would be sized to accommodate the 100-year storm, and new inlets would tie into the existing storm drain lines as the site is developed. In addition, the Project includes an approximately 580 linear foot extension of the existing storm drain in Main Place Drive to connect to the existing storm drain. The connection points to the offsite drainage infrastructure would not be changed. In addition, as described by the WQMP prepared for the Project, the flow rate at the confluence points would not exceed the existing 100 year flow rate for each drainage area by more than 5 percent, which is consistent with the hydromodification criteria of the Orange County Technical Guidance Document for Water Quality Management Plans (WQMP 2019). Furthermore, the Specific Plan Design Guidelines include the following provisions related to stormwater quality: DG - 119 Design should incorporate stormwater remediation and other Low Impact Development (LID) techniques into the streetscape where feasible. Overall, the proposed Project would not result in an increase of stormwater and the existing drainage facilities would be adequate to accommodate the Project. The new on - site storm drainage facilities would convey the 85th percentile of a 24-hour storm event flows to catch basins, as required by Section 18-156 of the City's Municipal Code. With implementation of the existing regulations through the City's permitting process, impacts related to hydrology, drainage, and sources of polluted runoff would be reduced to a less than significant level. No new impacts would occur. Conclusion for Hydrology Consistent with the determinations of the 1983 EIR and 1996 Addendum, impacts related to hydrology from implementation of the proposed Project would be less than significant. Thus, no new or substantially greater impacts would occur with implementation of the proposed Project when compared to those identified in the 1983 EIR or 1996 Addendum. Based on the foregoing, none of the conditions identified in CEQA Guidelines section 15162 that trigger the need to prepare a subsequent or supplemental EIR or other environmental document to evaluate Project impacts or mitigation measures exist regarding hydrology. There have not been 1) changes to the Project that require major revisions of the previous adopted EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified effects; 2) substantial changes with respect to the circumstances under which the Project is undertaken that require major revisions of the previous adopted EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified effects; or 3) the availability of new information of substantial importance relating to significant effects or mitigation measures or 59