Stormwater Permit

Overview

Issaquah and other urban areas that collect stormwater runoff in municipal storm sewers and discharge it to surface waters are required to have a permit under the federal Clean Water Act.

This permit — called the National Pollution Discharge Elimination System (NPDES) Phase II Municipal Stormwater Permit — requires Issaquah to submit an annual report, and create and implement a Stormwater Management Program (SWMP) that includes:

  1. Stormwater Planning
  2. Public Education and Outreach
  3. Public Involvement and Participation
  4. MS4 Mapping and Documentation
  5. Illicit Discharge Detection and Elimination (IDDE)
  6. Controlling Runoff from New Development, Redevelopment and Construction Sites
  7. Operations and Maintenance
  8. Source Control Program for existing Development
  9. Total Maximum Daily Load (TMDL)
  10. Monitoring and Assessment

Our Goal

Our goal is to protect water quality by reducing the discharge of pollutants from its system to the maximum extent practicable.

Stormwater Manual

All new development and redevelopment must follow stormwater standards from the 2017 City of Issaquah Addendum to the Washington State Department of Ecology’s most recent Stormwater Management Manual for Western Washington. Note: Use the 2014 amended Department of Ecology document.

The new standards include revised flow control, water quality, temporary erosion and sediment control (TESC), and stormwater Low Impact Development (LID) requirements.

Stormwater Flow Control

The default standard is the Level 2 flow control standard, assuming a historic (forested) pre-development condition. However, exemptions are available.

Refer to the the 2017 City of Issaquah Addendum to the Washington State Department of Ecology’s most recent Stormwater Management Manual for Western Washington for more specific information.

Water Quality

Refer to the 2017 City of Issaquah Addendum to the Washington State Department of Ecology’s most recent Stormwater Management Manual for Western Washington for more specific information.

TESC

Temporary Erosion and Sediment Control (TESC) permit coverage is required for all land disturbing activities (with some exceptions). TESC requirements are addressed in the Public Works permit for the project, typically a clearing and grading permit. For smaller projects that don’t trigger a clearing and grading permit, a separate Public Works permit for TESC will be required.

Plan submittal requirements are revised to follow the 2017 City of Issaquah Addendum. Designated TESC supervisors during land disturbing activities shall be a Certified Erosion and Sediment Control Lead (CESCL).

Note: A separate Department of Ecology Construction Stormwater General Permit is required for sites having 1 acre or more of disturbed area.

Stormwater Low Impact Development (LID)

To the maximum extent feasible, stormwater LID principles, facilities, and best management practices shall be incorporated into all new development and redevelopment.

Refer to the 2017 City of Issaquah Addendum to the Washington State Department of Ecology’s most recent  Stormwater Management Manual for Western Washington for more specific information, including feasibility requirements, soil testing requirements, and design methods.

Issaquah’s LID Review and Revision Summary is also available.

For new development and redevelopment projects located within Central Issaquah, different LID requirements or exemptions may apply.