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ARROYO LAGO RESIDENTIAL PROJECT ADDENDUM 138 FCS Https://adecinnovations.sharepoint.com/sites/PublicationsSite/Shared Documents/Publications/Client (PN-JN)/2148/21480036/Addendum/21480036 Arroyo Lago Residential Project Addendum.docx flooding are prevented or minimized to the maximum extent feasible during construction. Therefore, the Prior FEIR concluded that impacts would be less than significant. From an operational standpoint, stormwater on the project site would be captured in two bioretention areas designed in accordance with all applicable standards with adequate capacity to accommodate stormwater flows at the project site. Because stormwater would be treated through bioretention areas to ensure that there would be no net increase in off-site stormwater flow, the County Project would not result in an exceedance of storm drain capacity. Therefore, the Prior FEIR concluded that impacts would be less than significant. (Draft EIR, pp. 3.9-28, 6-16). Proposed Project Analysis and Conclusion Similar to the County Project, the proposed project could result in erosion or siltation, as well as increased risk of flooding and additional sources of polluted runoff during construction. However, the proposed project would be required to comply with the regulations of its NPDES permit. Additionally, the proposed project would be required to comply with construction-phase BMPs and requirements for erosion and sedimentation control plans. The proposed project would be required to design and implement a SWPPP to ensure that erosion, siltation, and flooding are prevented or minimized to the maximum extent feasible during construction. Similar to the County Project, stormwater runoff from the project site during operation would be drained by storm gutters located on the sides of the proposed internal streets. Stormwater would flow into 18-inch to 24-inch pipes located under the streets and then be drained off the project site using two proposed pipes. The first pipe would be a 24-inch diameter pipe that would be constructed to connect to an existing City-owned 54-inch diameter storm drainpipe in Mohr Avenue. The proposed 24-inch storm drainpipe would follow the same alignment as the proposed water line, extending from the northwest corner of the project site, following the existing utility road, to Mohr Avenue (Exhibit 9c). The second pipe would be constructed to extend from the intersection of Street A and Loop A, across the adjacent vacant land to the east of the project site, to a proposed bioretention area and detention basin approximately 0.45 mile east of the project site, adjacent to El Charro Road (Exhibit 9b). The bioretention area would meet all applicable regulatory requirements and would include a treatment area of approximately 1 acre, a discharge pump, and a detention basin, with layers of bioretention soil mix and permeable rock, protected by an approximately 8-foot berm. The stormwater improvements would be designed and constructed to applicable City of Pleasanton Standard Specifications and Details. As discussed in the Prior FEIR, the proposed bioretention area and detention basin would have sufficient capacity to serve the project site pursuant to applicable regulatory standards, which would further ensure that the proposed project would not result in a net increase of off-site stormwater flow, or a significant impact related to flooding or exceedance of the capacity of the City’s existing stormwater infrastructure. As such, impacts related to erosion or siltation, flooding, and runoff would be less than significant, consistent with the impact conclusions in the Prior FEIR. Therefore, the proposed project would not introduce new significant impacts or create substantially more severe significant impacts than those previously identified in the Prior FEIR. No additional analysis is required.