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City of San Leandro 311 MacArthur Boulevard Residential Project 60 quality and low impact development features. The project includes three bio-retention areas constructed consistent with Alameda County Clean Water Program Publication C.3 Stormwater Technical Guidance (City of San Leandro 2017). Therefore, the project would have no impacts beyond those previously identified in the General Plan EIR. LESS THAN SIGNIFICANT OR LESS THAN SIGNIFICANT WITH MITIGATION INCORPORATED c.(iii) Would the project substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner that would create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff? The General Plan EIR found less than significant impacts to the quality of stormwater runoff, as policies and actions in the 2035 General Plan and regulatory provisions limit the amount of pollutants in runoff from new development sites (City of San Leandro 2016a). While project implementation would alter the existing drainage pattern of the site by increasing impervious surfaces, it would not alter the course of a stream or river; it would be required to comply with all applicable 2035 General Plan policies, and to implement stormwater quality improvement measures per Provision C.3 and the required NPDES Permit. Features such as permeable pavements, bioretention, and integrated management practices would be used to control stormwater. As described under criteria a and f and in the Project Description, runoff detention would be provided via three bio-retention basins located within the project site (refer to Figure 3). The General Plan EIR states that new development in the city would be required to ensure provision of adequate stormwater service, in accordance with the General Plan EIR requirements, to ensure a less than significant impact to water quality. There would be no impact beyond that identified in the General Plan EIR. LESS THAN SIGNIFICANT OR LESS THAN SIGNIFICANT WITH MITIGATION INCORPORATED c.(iv) Would the project substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner which would impede or redirect flood flows? The General Plan EIR found less than significant impacts regarding flood flows, as new developments would be required to comply with Federal Emergency Management Agency (FEMA) and City regulatory requirements regarding construction of structures (City of San Leandro 2016a). The project site is located within Zone X, defined as an area of minimal flood hazard (FEMA 2009). The project would result in 484 square feet less of impervious surface area than under current conditions. The project would provide three on-site bio-retention basins and would not otherwise redirect flood flows. There would be no impact beyond that identified in the General Plan EIR. LESS THAN SIGNIFICANT OR LESS THAN SIGNIFICANT WITH MITIGATION INCORPORATED d. In flood hazard, tsunami, or seiche zones, would the project risk release of pollutants due to project inundation? The project site is not located in a tsunami inundation area (California Emergency Management Agency 2009), nor is there a water body near enough to the project site capable of a seiche that would affect the site. Based on the topography of the project site and surrounding area, there is no risk of mudflow in the project vicinity. There would be no impact.