Under the National Pollutant Discharge Elimination System (NPDES) municipal stormwater permit, Snohomish County must carry out a variety of actions that limit or prevent pollution from entering and leaving the county’s storm drainage system. The storm drainage system is the network of ditches, pipes and catch basins that convey stormwater on county roadways and county-owned property such as road maintenance facilities, the fairgrounds in Monroe and Paine Field airport.

Required Actions

The NPDES permit refers to all required actions, taken together, as a Stormwater Management Program (SWMP). The SWMP must 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
  • Considering stormwater in planning processes, and an area-specific Stormwater Management Action Plan
  • 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 participate in stormwater monitoring, either directly or by paying into a regional monitoring program funded by the Washington State Department of Ecology.

Required Documents

Each year, by March 31, the county must prepare two documents and submit them to the Washington State Department of Ecology. One is the Stormwater Management Program (SWMP) Plan, which describes how the county intends to implement required actions during current and future years. The other is an annual report, which describes how the county carried out required actions during the previous calendar year.