3400 RIVERFRONT BLVD BASE FILE 2020-07-15

Stormwater Pollution Prevention Plan Storm Drain Inlet Projection will be installed on the one existing catch basin on 36th Street which is downstream of the project site. Silt fence will be installed on the north and east edges of the project site to keep sediment from leaving the site in surface runoff. Alternate sediment 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. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed,to minimize tracking of sediments on vehicle tires away from the site and to minimize washoff of sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas (BMP C240 paragraph 5,page 4-102). In some cases, sediment discharge in concentrated runoff can be controlled using permanent stormwater BMPs(e.g., infiltration swales,ponds,trenches). Sediment loads can limit the effectiveness of some permanent stormwater BMPs, such as those used for infiltration or biofiltration; however,those BMPs designed to remove solids by settling(wet ponds or detention ponds) can be used during the construction phase. When permanent stormwater BMPs will be used to control sediment discharge during construction, the structure will be protected from excessive sedimentation with adequate erosion and sediment control BMPs. Any accumulated sediment shall be removed after construction is complete and the permanent stormwater BMP will be restabilized with vegetation per applicable design requirements once the remainder of the site has been stabilized. The following BMPs will be implemented as end-of-pipe sediment controls as required to meet permitted turbidity limits in the site discharge(s). Prior to the implementation of these technologies, sediment sources and erosion control and soil stabilization BMP efforts will be maximized to reduce the need for end-of-pipe sedimentation controls. • Temporary Sediment Pond (BMP C241) • Construction Stormwater Filtration(BMP C251) • Construction Stormwater Chemical Treatment(BMP C 250) (implemented only with prior written approval from Ecology). 7