6 - GPA19-01; AA19-01_651 W SUNFLOWER AVENUE

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Legacy Sunflower Apartments Page 61 Mitigated Negative Declaration – March 14, 2019 The project proposes approximately 0.92 acres (40,075 square feet) of pervious area throughout the site to allow surface water to percolate into the local soil. The project would result in an 8% (12,632 square feet) reduction of pervious area on the site for water percolation and absorption compared to the existing condition. The City has stated it has an adequate water supply to meet the water needs of the project and the reduction in pervious open space for local water percolation would not significantly deplete and impact groundwater supplies. The project would have a less than significant impact on groundwater supplies. c) 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: i. Result in substantial erosion or siltation on- or off-site? Less Than Significant Impact. As discussed in section “X.a)” above, silt could be generated from the site during site demolition, grading and construction of the project, especially if construction occurs during the winter months when rainfall typically occurs. The City would require the project developer to prepare a Storm Water Pollution Prevention Plan (SWPPP) in accordance with California State Water Resources Control Board (State Water Board), Construction General Permit Order 2009-0009-DWQ, National Pollutant Discharge Elimination System (NPDES) General Permit No. CAS618030 (Permit). The SWPPP would require the contractor to implement Best Available Technology Economically Achievable measures to reduce and eliminate storm water pollution from all construction activity through the implementation of Best Management Practices (BMPs). Implementation of the required SWPPP prior to and throughout project construction would reduce and minimize potential siltation impacts. As also discussed in section “X.a)” above, the project developer would be required by the City to have a Water Quality Management Plan (WQMP) approved prior to the start of grading. The WQMP would identify the BMPs that would be used on-site to control anticipated pollutants during the life of the project from entering the storm water runoff from the site. The types of pollutants that are anticipated to be generated during the life of the project include suspended solids, sediment, nutrients, heavy metals, pathogens, pesticides, toxic organic compounds, oil and grease and trash and debris. The State required WQMP identifies the measures that would be included in the project including the use of a retention/detention basin, storm water clarifier, and catch basins with BMPs. The implementation by the developer of the required SWPPP and WQMP would reduce potential erosion or siltation impacts to less than significant. ii Substantially increase the rate or amount of surface runoff in a manner which would result in flooding on-or off-site? Less Than Significant Impact. As discussed in section “IX.c)” above, the project would not alter the existing drainage patterns on the site. The existing drainage patterns on the site would be maintained and project flows would continue to be south to Sunflower Avenue. Maintaining the existing on-site drainage pattern along with the proposed biofiltration systems would prevent flooding impacts on or off the site. iii 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? Less Than Significant Impact. Based on hydrologic calculations in the hydrology report, project generated storm water runoff from the site would increase for the 2-year, 25-year and 100-year storm events. Table 10 shows the increase in surface water runoff from the project compared to the existing condition. As shown, the project would increase the amount of surface water generated 6-83