Reso PC15-01 PC Reso (3051 ) to Adopt Initial Study-Mitigated Negative Declaration - La Palma

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3.0 Environmental Impact Checklist a) Violate any water quality standards or waste discharge requirements? f) Otherwise substantially degrade water quality? Less-than-Significant Impact with Mitigation Incorporated. Construction of the proposed project may result in potentially significant impacts to water quality. Ground disturbing activities may have the potential to affect water quality through soil erosion and storm water discharge of pollutants and sedimentation. Since the project involves disturbance of greater than 1 acre of soil during the construction process, a SWRCB Construction General Permit is required for the project.The Construction General Permit requires the preparation of a SWPPP. A SWPPP typically documents how erosion would be prevented,how sediment and other construction-related pollutants would be controlled, and how fluids from construction equipment or dust for concrete would be prevented. The SWPPP typically include best management practices(BMPs) to keep construction debris, dirt, or other pollutants from entering drainage systems. Typical BMPs include: erosion controls at the project site; run-on and run-off controls to and from the project site;control of sedimentation and fines on the project site; good site management;and non-stormwater management. To ensure that an adequate SWPPP and an erosion and sediment control plan is prepared if work is to occur during the rainy season, Mitigation Measures HYD-1 and HYD-2 would be implemented.With implementation of the SWPPP and erosion control plan, potentially significant water quality impacts associated with project construction would be reduced to less than significant levels. Mitigation Measure HYD-1:All project grading, construction, and subsequent operations shall comply with the provision of the City of Redwood City's NPDES requirements. A SWPPP outlining construction phase and post-construction phase measures to reduce pollutant discharge from the site shall be submitted for review and approval by the Engineering and Transportation Services prior to the issuance of Grading and Building Permits. Mitigation Measure HYD-2: If the project is constructed during the wet season (October through May), an erosion and sediment control plan, compliant with the City's NPDES (stormwater control)requirements,shall be prepared and implemented,to the satisfaction of Engineering and Transportation Services,prior to the onset of the wet season, and shall be maintained throughout the construction period. Water quality during long-term occupancy of the homes could be impacted by the increase in impervious surface that could facilitate polluted runoff. Provisions of the City's NPDES permit program require that all projects creating and or replacing 10,000 square feet or more of impervious surface incorporate stormwater management facilities. The site currently has 17,177 square feet of impervious areas;the project proposes 30,586 square feet of impervious areas post-construction,resulting in a net change increase of 13,409 square feet of impervious surfaces on the project site. To address water quality impacts and ensure compliance with Provision C.3 of the San Mateo County's Municipal Regional Stormwater Permit(MRSP)requirements, a Stormwater Control Plan(SWCP) would be prepared to detail the permanent stormwater management facilities that would be incorporated into the project to treat stormwater runoff and to control runoff rates and volumes after the construction process.The facilities would La Palma Subdivision Project Final Initial Study/Mitigated Negative Declaration 42