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Seaport's Stormwater Program


Stormwater is the flow of water generated by precipitation and runoff from land, pavement, building rooftops and other surfaces. These are called 'impervious surfaces', and they do not allow rainfall to absorb into and filter through the soil. Runoff from these surfaces carries pollutants including oil, grease, metals, and bacteria. Annually, the seaport treats 1.2 billion gallons of stormwater runoff from 1,560 acres of facilities. 

The Phase I Permit requires the port to develop and implement a Stormwater Management Program (SWMP)

The Port also publishes an Annual Report as part of the permit requirements.

What does the Seaport's Stormwater Program Cover?
The management of stormwater is a crucial part of the Port of Seattle's responsibility in protecting the Puget Sound. Covering 1,560 acres, the Seaport's paved surfaces are more than 20 times larger than Seattle Center and almost twice the size of New York's famed Central Park.
These surfaces require the seaport to manage 1.2 billion gallons of runoff annually. 
The Washington State Department of Ecology regulates discharges of stormwater runoff through a permitting process. The port works closely with the agency and our tenants to minimize the impact of stormwater runoff on local waters and their habitat.

Stormwater Regulatory Overview

The Seaport operates under a Phase I National Pollutant Discharge Elimination System (NPDES) General Permit for Municipal Stormwater, issued by the Washington State DOE under the Federal Clean Water Act (CWA). Phase I Permits apply to municipalities with populations of 100,000 or more, and to agencies located within the municipality. The Phase I Permit establishes a framework for controlling pollutants from stormwater runoff to the maximum practical extent. Its goal is restoring and maintaining the chemical, physical and biological integrity of our region's waters including rivers, streams, lakes, wetlands, and marine waters.
Most of the seaport's property is leased to commercial and industrial tenants. Approximately 70 percent of these properties are covered by a General Industrial NPDES stormwater permit rather than the Phase I Permit. 
Regulatory compliance activities: Municipal Stormwater Permit.
Learn more about Seaport Division's Phase 1 Municipal Permit

Stormwater Information

The seaport is a secondary permittee under the NPDES Phase 1 Municipal Stormwater Permit (Phase I Permit) issued by the Department of Ecology. The Phase I Permit regulates discharges to waters of the state from large and medium storm sewer drainage systems. The port is regulated under the Phase I Permit because the stormwater system drains to the Duwamish River, Ship Canal, and Elliot Bay. The port received secondary permittee status because it owns and operates its own storm water system within the incorporated area of the City of Seattle.
The Phase I Permit requires the port to develop and implement a Stormwater Management Program (SWMP). The port's SWMP includes the following components:
Seaport tenants play a crucial role in protecting water quality in Puget Sound. Any polluting activity has direct effects on the Lower Duwamish, Shilshole Bay or Elliot Bay. The port is actively working with current tenants to improve operations and manage stormwater runoff to protect the natural environment. Detailed tenant information can be found here

Stormwater Permit Coverage

The Washington State DOE regulates how the port handles stormwater runoff on all of the its properties. Stormwater regulations are part of the National Pollutant Discharge Elimination System of permits created by EPA. Approximately 70% of port tenants are covered by one of the following permits:

• Industrial Stormwater General Permit
• Boatyard General Permit
• Construction General Permit
• Individual Permit

The 30% of tenants not covered by an Industrial or Boatyard general permit are subject to the conditions of the NPDES Phase I Municipal Stormwater Permit issued to the seaport in 2007. The Municipal Permit requires most other tenants to develop a Stormwater Pollution Prevention Plan that includes structural and operational mechanisms to protect water quality.

View maps indicating what permits properties are subject to - North Extent Map (347 KB, PDF), South Extent Map (366 KB, PDF) If you have additional questions regarding stormwater permit coverage, please refer to your lease or contact your property manager.

State and Local Permit Information












































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