Managing Stormwater Runoff

National Pollutant Discharge Elimination System (NPDES) 

A National Pollutant Discharge Elimination System (NPDES) and State Waste Discharge Permit (Permit) has been issued by the State of Washington Department of Ecology (Ecology) to Pierce County authorizing discharges of stormwater runoff to surface waters and to groundwaters of the state from the county’s municipal separate storm sewer system (MS4).

A new permit took effect on Aug. 1, 2019 and covers the County’s stormwater discharges through July 31, 2024. A copy of the permit can be found on the Department of Ecology website here.


NPDES Permit Requirements

Pierce County, like most other Washington counties and cities, has been covered under an NPDES Municipal Phase I Stormwater Permit since 1995. The current Phase I permit requires the use of stormwater best management practices (BMPs) to reduce the discharge of pollutants to the maximum extent practicable to protect water quality.


The Municipal Phase I Permit contains comprehensive and wide-ranging requirements, including but not limited to the following elements:

  • Stormwater system mapping and documentation
  • Interdepartmental coordination and intragovernmental mechanisms
  • Public involvement and participation
  • Prevention and control of stormwater runoff impacts from new development, redevelopment and construction activities
  • Watershed-scale stormwater planning
  • Structural stormwater controls program to prevent or reduce impacts to waters of the state by discharges from the stormwater system
  • Source control program for existing development
  • An ongoing program to address illicit connections and illicit discharges into the stormwater system
  • Operations and maintenance program
  • Education and outreach program
Stormwater Management Program Plan (SWMP) 

The Permit requires the implementation of a Stormwater Management Program Plan (SWMP Plan). The SWMP Plan is a detailed document with a set of actions organized according to the program components. It is designed as a means to inform the public of the planned activities for the upcoming calendar year. It is updated each year and submitted with the county’s annual report to Ecology.


Annual Report

No later than March 31 of each year (beginning in 2015), the county submits an annual report to Ecology. Annual reports are comprised of electronically-submitted documents and answers to approximately 100 individual questions. Information contained within an annual report includes, but is not limited to: a copy of the SWMP Plan; summaries, descriptions, reports and other information as required; a notification of any annexations, incorporations or jurisdictional boundary changes; and certification and signature of authorized county official.



NPDES Permit Document Library

Important reference documents related to Pierce County’s Municipal Phase I Stormwater permit are archived in the NPDES Permit Document Library. This archive houses electronic files including: Annual Reports, SWMP Plans and more.


Get Involved

The 2023 Stormwater Management Program Plan (SWMP) is now available. Pierce County wants to hear from you! Click here to review the document, then contact staff with any questions or comments.



Contact Us


Surface Water Management
 (253) 798-2725
[email protected]

Monday–Friday

7:30 a.m.–4:00 p.m.

Mailing Address:

2702 S 42nd St, Ste 109

Tacoma, WA 98409-7322