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City of Pleasanton—Villages at the Quarry Project Consistency Checklist 15183 Consistency Checklist 148 c) Drainage Leading to Erosion/Siltation, Flooding, Additional Sources of Polluted Runoff, or Impedance of Flood Flows Would the project: 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; Summary of Housing Element Update FEIR The Housing Element Update FEIR indicated that future development consistent with the Housing Element Update would involve construction activities such as stockpiling, grading, excavation, paving, and other earth- disturbing activities. Loose and disturbed soils are more prone to erosion and loss of topsoil by wind and water. This could result in an increase in stormwater runoff and the potential to cause erosion or sedimentation in drainage swales and creeks. The Housing Element Update FEIR concluded that compliance with the NPDES, including the Construction General Permit, and SWPPP requirements and the policies and actions included in the General Plan would ensure impacts related to erosion and siltation would be less than significant. Proposed Project Analysis and Conclusion The proposed project would involve construction activities such as stockpiling, grading, excavation, paving, and other earth-disturbing activities. Loose and disturbed soils are more prone to erosion and loss of topsoil by wind and water. This could result in an increase in stormwater runoff and the potential to cause erosion or sedimentation in drainage swales and creeks. Additionally, the proposed project would include the addition of 1,348,814 square feet of new impervious surface. Construction activities and the addition of impervious surface could increase erosion and siltation at the project site. As discussed above, the proposed project would be subject to the NPDES Construction General Permit (Order WQ 2022-0057-DWQ) because the proposed project would disturb one acre or more of land surface. Also discussed above, the NPDES Construction General Permit requires a SWPPP and associated BMPs, which include erosion and sediment controls, runoff water quality monitoring, proper waste disposal, implementation of approved local plans, control of construction sediment and erosion control