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SAN LEANDRO SHORELINE DEVELOPMENT EIR ADDENDUM PROJECT CITY OF SAN LEANDRO May 2022 Page 41 additional impervious surfaces, would remain in compliance with groundwater related specifications applicable to those for the Original Project. Therefore, operational impacts associated with the Modified Project would not result in a new impact or a substantial increase in the magnitude of the existing impacts towards groundwater diversion. As discussed within the Certified EIR, the Original Project did not involve the alteration of any watercourse, stream, or river. Consistent with the Original Project, construction activities for the Modified Project would involve demolition of existing structures and removal of the 462-slip harbor, grading, excavation, and the construction of buildings, sidewalks, driveways, and parking lows, which could increase the potential for erosion and/or siltation. Implementation of Mitigation Measure HYDRO-1, erosion and sediment control measures as part of the SWPPP, as well as conformance with Chapter 7-12 of the San Leandro Municipal Code requiring project applicants to prepare erosion control and sedimentation control plans for submittal to the City Engineer prior to the start of project construction would reduce impacts from surface runoff resulting in significant erosion or siltation to a less than significant impact. Therefore, the demolition and construction phase associated with the Modified Project, which would not alter drainage patterns on the project site or result in additional impervious surfaces, would not result in a new impact or a substantial increase in the magnitude of the existing impacts to any watercourse, stream, or river. During operation of the Modified Project, erosion and siltation impacts would be avoided through implementation of C.3 requirements and LID measures to address stormwater runoff. Because the Modified Project, as with the Original Project, would replace or create more than 10,000 square feet of impervious surface, post-construction stormwater treatment is required as stated in Chapter 4.8, Hydrology and Water Quality, of the Certified EIR. The General Plan goals and policies relevant to the Original Project would also be implemented to ensure that stormwater runoff is adequately handled and would not contribute to on-site or off-site erosion. In conformity with the less than significant finding for erosion and siltation impacts during the operation phase of the Original Project, the Modified Project, which would not alter drainage patterns on the project site or result in additional impervious surfaces, would implement the same specifications, and would therefore, not result in a new impact or a substantial increase in the magnitude of the existing impacts. As discussed in the Certified EIR, the Original Project required the construction of an adequately sized storm drainage system to convey on-site stormwater runoff to existing storm drain facilities due to the increase in stormwater runoff from the increase in impervious surfaces. On-site systems would require City and ACFCD review for C.3 provision verification and that downstream drainage system capacity would not be exceeded. Furthermore, the City of San Leandro would verify that on-site and off-site drainage facilities can accommodate increased stormwater flows and the applicant would be required to pay for improvements to the storm drain system necessary to accommodate increased flows. Implementation of C.3 provisions, LID design, and General Plan goals and policies would minimize increases in peak flows and encourage development that would not exceed the capacity of existing or proposed storm drain systems. Therefore, because the Modified Project, which would not alter drainage patterns on the project site or result in additional impervious surfaces, would implement those specifications applicable to the Original Project, it would not result in a new impact or a substantial increase in the magnitude of existing impacts to storm drain system capacities.