Snohomish County Drainage Manual Volume VI Stormwater Facility Maintenance July 2020 Ecology Review DRAFT Snohomish County Drainage Manual Volume IV - Stormwater Facility Maintenance i Contents Introduction ................................................................................................................................................................1 Common Components 1. Catch Basins ............................................................................................................................................................5 2. Conveyance Storm Pipes ..................................................................................................................................... 11 3. Debris Barriers (e.g., Trash Racks) ....................................................................................................................... 13 4. Control Structure/Flow Restrictors ..................................................................................................................... 17 5. Facility Discharge Points ...................................................................................................................................... 24 6. Energy Dissipaters and Outfall Systems .............................................................................................................. 26 Stormwater Flow Control Facilities 7. Detention Ponds .................................................................................................................................................. 32 8. Detention Tanks and Vaults................................................................................................................................. 38 9. Infiltration Facilities ............................................................................................................................................. 46 10. Wetponds .......................................................................................................................................................... 53 11. Wetvaults........................................................................................................................................................... 64 Stormwater Treatment Facilities 12. Bioretention Systems ........................................................................................................................................ 70 13. Basic Biofiltration Swales ................................................................................................................................... 74 14. Wet Biofiltration Swales .................................................................................................................................... 80 15. Compost-Amended Vegetated Filter Strips (CAVFS) ......................................................................................... 84 16. Media Filter Drain .............................................................................................................................................. 87 17. Filter Strips ......................................................................................................................................................... 90 18. Sand Filters (above ground/open) ..................................................................................................................... 93 19. Sand Filters (below ground/enclosed) .............................................................................................................. 97 20. Permeable Pavement ...................................................................................................................................... 102 21. Vegetated Roofs .............................................................................................................................................. 107 22. Media Cartridge Filters .................................................................................................................................... 110 23. Hydrodynamic Separators ............................................................................................................................... 114 24. API Baffle Oil/Water Separators ...................................................................................................................... 116 25. Coalescing Plate Oil/Water Separators ........................................................................................................... 120 26. Catch Basin Inserts .......................................................................................................................................... 124 Facility Access 27. Access Gates and Fencing ................................................................................................................................ 127 Snohomish County Drainage Manual Volume IV - Stormwater Facility Maintenance ii 28. Access Roads.................................................................................................................................................... 131 Appendix A – Copy of Drainage Manual, Volume V, Chapter 4.6 Maintenance Requirements for Stormwater Facilities ............................................................................................................. A-1 Maintenance Standards Tables No. 1 Catch Basins ......................................................................................................................................... 8 No. 2 Conveyance Storm Pipes ................................................................................................................... 12 No. 3 Debris Barriers (e.g., Trash Racks) ..................................................................................................... 16 No. 4 Control Structure/Flow Restrictors ................................................................................................... 22 No. 5 Facility Discharge Points .................................................................................................................... 25 No. 6 Energy Dissipaters ............................................................................................................................. 31 No. 7 Detention Ponds ................................................................................................................................ 35 No. 8 Detention Tanks and Vaults ............................................................................................................... 44 No. 9 Infiltration Facilities ........................................................................................................................... 50 No. 10 Wetponds ......................................................................................................................................... 62 No. 11 Wetvaults ......................................................................................................................................... 68 No. 12 Bioretention Facilities ...................................................................................................................... 72 No. 13 Basic Biofiltration Swales ................................................................................................................. 78 No. 14 Wet Biofiltration Swales .................................................................................................................. 83 No. 15 Compost Amended Vegetated Filter Strip (CAVFS) ......................................................................... 86 No. 16 Media Filter Drain ............................................................................................................................ 89 No. 17 Filter Strips ....................................................................................................................................... 92 No. 18 Sand Filters (above ground/open) ................................................................................................... 95 No. 19 Sand Filters (below ground/enclosed) ............................................................................................. 99 No. 20 Permeable Pavement ..................................................................................................................... 105 No. 21 Vegetated Roofs ............................................................................................................................. 108 No. 22 Media Cartridge Filters .................................................................................................................. 112 No. 23 Hydrodynamic Separators.............................................................................................................. 115 No. 24 API Baffle Oil/Water Separators .................................................................................................... 118 No. 25 Coalescing Plate Oil/Water Separators .......................................................................................... 122 No. 26 Catchbasin Inserts .......................................................................................................................... 126 No. 27 Access Gates and Fencing .............................................................................................................. 129 No. 28 Access Roads .................................................................................................................................. 131 Snohomish