9900 19TH AVE SE 2018-01-02 MF Import

approximately 47,000 cubic feet, will be provided on top of the dead storage. Additional live storage will also be provided as compensation for live storage eliminated by the filling of the wetland. 1-5 Corridor: The third source of rupctf tributary to the existing wetland is runoff from the Interstate 5 corridor. Approximately 4.1 acres of drainage potentially reaches the existing wetland. Site inspections and WSDOT design plans reveal that drainage is conveyed via a pipeline system and a paved ditch to approximately the north corner of the existing Family Tree apartment complex pond. This system was blocked at one of the manholes at the time of the site visit and no drainage was present at the outfall despite recent rainfall activity. However, the system has been desigm:d to account for this drainage, since WSDOT could provide the maintenance required to unclog the pipes and the existing pond and/or I00th Street South right-of-way would receive the 4 acres of runoff. We propose to rechannel the existing outfall from the paved ditch to ensure that any runoff enters the wetland treatment cell portion of the reconstructed Family Tree apartment complex pond. The system will then provide the same enhanced water quality treatment as described above for the Family Tree apartment complex runoff. Silver Lake Professional Center: The fourth area tributary to the wetland is the Silver Lake Professional Center. This office complex is located immediately south of 100th Street S.E. and contains approximately 4.3 acres of drainage area. This system currently contains no detention or water quality; runoff flows directly into the on -site wetland. A wet vault and a duplex storm drainage pump system will pump storms up to the 25-year design storm event into the reconstructed Family Tree apartment complex pond. Flows exceeding the 25-year design storm event will bypass the family tree detention pond and be conveyed to the on -site outflow conveyance system. The pump system will contain a gravity outflow, as well as emergency generator system to handle extreme events and power outages. Home Base Site: The fifth and final source'of runoff to the existing wetland is the Home Base site and 100th Street S.E. In existing conditions, approximately 9 acres of this site enter the wetland at some point along the boundaries of the wetland. An on -site detention/water quality system consisting of a wet/detention vault and an open wetland treatment cell is proposed for the on -site paved portion of this project. This system will be in accordance with the City of Everett Drainage Standards for the Woods Creek Basin, as well as Washington State Department of Fish & Wildlife standards. An underground detention pipe will be used exclusively for roof drainage from the home Base building. In addition, the controlled release from the Family Tree apartment complex pond will be pumped through the on -site wet/detention pond. This will provide additional water quality treatment for all of the previously mentioned sources of runoff that enter the reconstructed Family Tree apartment complex pond, as well as dead and live storage compensation for the existing on -site wetlands. The pump station will consist of duplex pumps capable of passing the 25-year/24-hour design storm flows. A gravity overflow and an emergency generator system will be provided so extreme storm events and/or power outages do not cause flooding to neighboring properties. 5947.001 (MUJssnml