819 N BROADWAY WASHINGTON STATE UNIVERSITY 2018-05-11

Stormwater Pollution Prevention Plan 3.1.3 Element#3—Control Flow Rates In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. The specific BMPs for flow control that can be used on this project include: • Project Scheduling (BMP C162) • Interceptor Ditch(BMP C200) • Check Dams (BMP C207) I • Silt Fence (BMP C233) or Straw Wattles (BMP C235) • Portable Water Storage Tanks (e.g. Baker Tanks) for Sedimentation Excessive stormwater discharge from the site to the combined sewer could create a combined sewer overflow condition downstream of the project site. The contractor should not allow discharge above the existing 2-year rate for the site (see Section 2.2) during a storm event. Stormwater captured on site should be retained as necessary in a sedimentation tank or pond and slowly released to avoid surcharging the combined sewer during peak flow events. Alternate flow control BMPs are included in Appendix C as a quick reference tool for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit(Appendix D). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit(as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix C after the first sign that existing BMPs are ineffective or failing. The project site is located west of the Cascade Mountain Crest. As such, the project must comply with Minimum Requirement 7 (Ecology 2005). In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements (e.g. discharge to combined sewer systems). 3.1.4 Element#4—Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged to an infiltration facility. The specific BMPs to be used for controlling sediment on this project include: • Silt Fence (BMP C233) or Straw Wattles (BMP C235) 6 1