Required Actions

Snohomish County must implement a variety of actions that limit or prevent pollution from entering and leaving the County’s storm drainage system. The County’s storm drainage system is the network of ditches, pipes, and catch basins that convey stormwater in county roadways and on county-owned property such as road maintenance facilities, the fairgrounds in Monroe, and Paine Field airport.


Each year, the County produces a SWMP document that describes these actions in more detail. The County also submits annual reports to the Department of Ecology. Each annual report is due on March 31 and covers the previous calendar year.


The permit refers to the set of required actions as a Stormwater Management Program (SWMP). The requirements of the SWMP include:

  • Having adequate codes, contracts, interlocal agreements, or similar means to control discharges to and from the county’s storm drainage system
  • Mapping the storm drainage system
  • Coordinating permit actions, both within Snohomish County government and with other cities and counties
  • Involving the public in developing and implementing the SWMP
  • Controlling runoff from new development
  • Constructing stormwater treatment facilities to clean up pollution from existing development
  • Requiring pollution prevention measures through county code and proactively inspecting businesses to ensure code compliance
  • Inspecting the county’s storm drainage system to find pollution, locate the source, and take measures to stop the pollution
  • Maintaining the county’s storm drainage system according to established standards, and ensuring inspection and maintenance of private systems
  • Educating county staff and the public about stormwater pollution and how to prevent it

The County is also required to monitor stormwater discharges, treatment systems, and the effectiveness of pollution control programs.