National Pollutant Discharge Elimination System (NPDES)

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Where stormwater is managed by a jurisdiction as a system, they are required to maintain a NPDES permit. That permit defines requirements for discharging pollution, as well as steps that need to be taken to minimize that discharge. Washington State Department of Ecology manages the program, under the authority of Environmental Protection Agency's Clean Water Act authorities.


  • Ecology permit writers are assigned by geography.
  • NPDES permits include a range of requirements and standards for local jurisdictions, including education and outreach systems. These community development requirements (for example Thurston County Stream Team) may have multiple functions locally.
  • Phase 1 and Phase 2 - large municipalities and counties (Jurisdictions) with resources for natural resources management have been designated as Phase 1 permittees, while smaller jurisdictions are designated as Phase 2. The process of updating permitting standards, through dialog between jurisdictions and state and federal regulators is born by Phase 1 permittees, who develop standards that can be efficiently adopted by phase 2 jurisdictions.
  • Ecology manages the Permitting and Reporting Information System Database (PARIS) which is searchable for NPDES permits.
  • "MS4" is short for "Municipal Separate Stormwater Sewer System" and describes the network of ditches, culverts, and pipes maintained by local jurisdictions, but separate from wastewater treatment systems, and thus discharge directly to wetlands, streams, and the nearshore. These concentrated flows thereby circumvent Riparian Buffer Functions.
  • Not all MS4 systems are permitted. An un-permitted release of hazardous substances that has an effect on natural resources could be subject to a Natural Resource Damage Assessment claim under the Oil Pollution Act.