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5 – Effects Found Not To Be Significant Draft Environmental Impact Report February 2021 14800 W. Schulte Road Logistics Center 5-12 With respect to groundwater quality, the Project would include BMPs that would allow for stormwater to be collected and treated in biofiltration basins to allow for stormwater flows to infiltrate soils and recharge groundwater. These structural BMPs would treat stormwater flows prior to infiltration, ensuring that flows infiltrating groundwater aquifers do not result in adverse effects to groundwater quality. Moreover, flows entering these biofiltration basins would be typical of runoff collected from a commercial development and would not contain substantial quantities of pollutants that could not be appropriately treated by the proposed BMPs. In summary, Project grading and construction would be completed in accordance with an NPDES-mandated SWPPP, which would include standard BMPs to reduce potential off-site water quality impacts related to erosion and incidental spills of petroleum products and hazardous substances from equipment. Surface water runoff during Project operations would be managed through a mixture of strategies that would be designed to remove pollutants from on-site runoff prior to discharge into the storm drain system to the maximum extent practicable, as required by the SWQCCP. Therefore, impacts associated with water quality standards, waste discharge requirements, and surface water and groundwater quality would be less than significant. Result in Substantial Erosion or Siltation Under existing conditions, the Project site is undeveloped and contains various elevated areas and depressions. The Project would involve grading activities that would bring the Project site to a flat grade and the construction o f new paved surfaces, warehouse buildings, and landscape areas. The Project would also include a new engineered stormwater drainage system that would feature structural BMP s, such as retention facilities, to treat and manage stormwater flows. The Project’s future drainage conditions would be designed to mimic the existing on-site drainage conditions to the maximum extent practicable, but construction activities would inevitably result in changes to the internal drainage patterns of the site. However, the Project’s future storm drain system would be designed to conform with applicable federal, state, and local requirements related to drainage, hydrology, and water quality, including the County’s SWQCCP. Per the requirements of the County’s SWQCCP, Project plans will be required to demonstrate the capacity to capture and treat all on-site stormwater generated by two consecutive 10-year, 24-hour storm events, thereby reducing the potential for the Project to result in stormwater flows off site that could result in erosion on or off site. In addition, the Project’s structural BMPs would be designed such that any potential sediments collected on site would be captured in retention facilities so that they would not be conveyed to downstream waters and result in siltation. As such, alteration of the on-site drainage pattern would be conducted in a manner consistent with all applicable standards related to the collection and treatment of stormwater such that it would not result in substantial erosion or siltation on or off site. Therefore, impacts associated with altering the existing drainage pattern of the Project site and resulting in erosion or siltation would be less than significant. Result in Increased Surface Runoff and Subsequent Flooding The Project would inevitably result in changes to the internal drainage patters of the Project site. However, the Project’s future storm drain system would be designed to conform with applicable federal, state, and local requirements related to drainage, hydrology, and water quality, including the County’s SWQCCP. As such, alteration of the on-site drainage pattern would be conducted in a manner consistent with all applicable standards related to the collection and treatment of stormwater.