Puget Sound Olympia

Municipal Stormwater

Permits and Permittees

Municipal Stormwater General Permits

  • The Phase I permit regulates discharges from municipal separate storm sewers owned or operated by Clark, King, Pierce and Snohomish Counties; and the cities of Seattle and Tacoma.

  • The Phase II Municipal Stormwater Permit rule extends the coverage of the National Pollutant Discharge Elimination System (NPDES) program to certain "small" municipal separate stormwater sewer systems (MS4s). The Department of Ecology used maps of the census urbanized areas and jurisdictional boundaries to identify Phase II jurisdictions. Ecology issued two Phase II permits: one for Eastern Washington and one for Western Washington.

Permit Information


1990-1999: MS4 Permit Program Begins

1995 - Phase I Municipal Stormwater Permits Issued
1999 - Phase I Permit Issued to Clark County
1999 - Phase II of EPA's Stormwater NPDES

2000-2010: Refinement and Expansion

2003 - Municipal Stormwater Working Groups
2007 - Municipal Stormwater Permits Issued: Phase I and Phase II
2007 - Permits Appealed
2009 - Phase I and Phase II Modification
2010 - Phase I Modification

2011-Present: Continuing Refinement

2012 - Interim Permits Issued
2012 - Five-Year Permits Issued
2012 - Permit Appeal
2014 - Western Washington Modification
2016 - Phase I Modification

Contacts and Listserv Information