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

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Legacy Sunflower Apartments Page 60 Mitigated Negative Declaration – March 14, 2019 Available Technology Economically Achievable measures to reduce and eliminate storm water pollution from all construction activity through the implementation of Best Management Practices (BMPs). The purpose of the SWPPP is to identify pollutant sources that may affect the quality of the storm water that would be discharged from the site during all construction activity. The SWPPP would require the contractor to identify, construct, and implement the storm water pollution prevention measures and BMPs that are necessary to reduce pollutants that are present in the storm water that is discharged from the site during construction. The SWPPP would include specific BMPs that must be installed and implemented prior to the start of construction. The installation and maintenance of all required BMPs by the contractor during construction would reduce potential water quality impacts to less than significant. The project developer would be required by the City to have a WQMP approved prior to the start of grading. As noted above, the project applicant has prepared a preliminary WQMP (Appendix D) that identifies the Best Management Practices (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 WQMP proposes to install a Modular Wetlands Biofiltration System near the southwest corner of the project site. The Modular Wetlands structure would pre-treat all of the surface water runoff of the project, including all parking runoff, on-site streets, building roofs, etc. The Modular Wetlands structure would treat the 85th percentile 24-hr storm event runoff. Once treated, the runoff would be directed by a proposed on-site storm drain collection system to an existing off-site storm drain catch basin in Sunflower Avenue and to the County of Orange Santa Ana – Delhi Channel that extends along the west project boundary and eventually drains into the ocean. The City must review and approve the WQMP for compliance with State law prior to the issuance of a building permit. The installation of and the regular maintenance of a required SWPPP and WQMP would reduce storm water runoff pollutants generated from the project site during both project construction and the life of the project to less than significant. b) Substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin? Less Than Significant Impact. The project would require the use of water for dust suppression during project demolition, grading and construction in compliance with SCAQMD Rule 403 Fugitive Dust. The amount of water that would be required to control dust during grading and construction would be minimal and not significantly impact existing groundwater supplies. Once completed, the project would require potable water to serve the project residents, landscape irrigation and provide fire flow. The project site currently has open space available for water percolation. Currently approximately 34% (1.21 acres) of the site is pervious and allows water percolation and the remaining 66% (2.38 acres) of the site is impervious due to the existing church, surface parking lot and other hardscape improvements. Once constructed, the project would be approximately 74% impervious and 26% pervious for continued water percolation. 6-82