FINAL SEPA DETERMINATION
OF N...
FINAL SEPA DETERMINATION
OF N...
FINAL SEPA DETERMINATION
OF NON-SIGNIFICANCE (DNS) OF
PROPOSED ACTION
Seattle-Tacoma International Airport (SEA)
Flight Corridor Management Program
The Port of Seattle (Port) has completed an environmental analysis, including review of pertinent and available environmental information and preparation of a State Environmental Policy Act (SEPA) Checklist for the Flight Corridor Management Program.
Description of Proposed Project Action: The Flight Corridor Management Program (Program) identifies and manages obstructions to the flight corridor at SEA, which are typically trees. Maintenance of the flight corridors is a requirement and priority for the FAA, State of Washington, and the Port of Seattle. The Port is required to ensure there are no obstacles or obstructions on or around SEA that could affect the flight corridors. 1 The Program, implemented on a regular basis (i.e., approximately every 5 years), ensures obstructions (e.g., trees) are identified and removed. The Program also requires ongoing site management and monitoring to support healthy ecological communities as a result of obstruction removal. Tree removal and replacement requirements are identified based on the jurisdiction and/or property they are located. The Port will coordinate directly with commercial and private property owners and affected jurisdictions. Information about each implementation cycle, including the number and location of trees identified for removal, tree replacement requirements and commitments, and best management practices (BMPs), is available on the Port of Seattle's website, www.portseattle.org.
Location of Proposed Action: To complete this environmental review of the Program, the area where tree removals may occur in the future has been estimated. The area is based on the Runway Protection Zones for SEA's east and west runways (34R/16L and 34L/16R), extending 1,500 feet east and west, and 3,500 feet north and south beyond the outer limits of these zones. This area covers the location of obstructions identified during past data collection in 2014, 2019, and 2024. The Program Area includes Port-owned properties; public properties (owned by the Washington State Department of Transportation [WSDOT], Highline School District and the cities of SeaTac, Burien and Des Moines; and commercial and privately-owned lands in the cities of Burien, SeaTac, and Des Moines.
Lead Agency: Port of Seattle (SEPA File Number 2025-05)
Determination: The Port of Seattle completed an environmental evaluation including review of pertinent environmental information, following the provisions of the Washington State Environmental Policy Act (SEPA) under Chapter 43.21C, Revised Code of Washington (RCW), Chapter 197-11, Washington Administrative Code (WAC), and Port of Seattle Commission Resolution No. 3650, and Port of Seattle SEPA Policies and Procedures. The Port of Seattle's SEPA determination concludes that environmental impacts of the proposal are not significant.
Supporting Information: Information used to reach this determination is available upon request. Flight Corridor Management Program Determination of Non-significance (POS SEPA File No. 2025-05), Environmental Checklist, and supporting documents are available online at https://www.portseattle. org/environment/sepa-nepa.
Public and Agency Comment: The DNS and Environmental Checklist for the Flight Corridor Management Program was published on August 27, 2025. During the 15-day public comment period the Port received 48 comments, including 3 from public agencies (City of Des Moines, Washington State Department of Ecology, and Washington State Department of Fish and Wildlife) which were carefully reviewed and considered. It is noted that the majority of public comments are on the merits of and justifications for the Port's Program requiring tree removal, particularly in public spaces. In consideration of public comment, the Port issued a document on its website answering frequently asked questions, published a revised Environmental Checklist, and is now issuing a Final DNS, affirming that no potential for significant impacts were identified, and no additional environmental review under SEPA is needed. Please refer any questions relating to this determination or to the proposed actions to Steve Rybolt, Port of Seattle, Aviation Environment and Sustainability Department, P.O. Box 68727, Seattle, Washington 98168. Telephone 206.787.5527. Email SEPA@portseattle.org. Include your mailing address when submitting comments to the electronic Internet address.
Appeals: The Port's decision on the proposal described above and the Port's issuance of a Final DNS on this proposal constitute the Port's Final SEPA decision. This SEPA DNS determination may be appealed by filing a writ of review in King County Superior Court within twenty-one (21) days of the date of issuance pursuant to Port of Seattle Resolution No. 3650. Any appeal of the SEPA DNS must also satisfy the requirements of RCW 43.21C.075.
SIGNATURE ON FILE
Sarah Cox, Director, Aviation Environment and Sustainability and SEPA Responsible Official
Port of Seattle, Seattle – Tacoma International Airport
1 SEA has three parallel runways, each with instrument- guided, very precise flight procedures and flight paths. The Port is required to follow conditions of Title 49 of the United States Code (49 U.S.C.) Subtitle VII and Title 14 of the Code of Federal Regulations (14 CFR 139), as stipulated in SEA's Airport Operating Certificate issued by the Federal Aviation Administration (FAA).
FINAL SEPA DETERMINATION
OF NON-SIGNIFICANCE (DNS) OF
PROPOSED ACTION
Seattle-Tacoma International Airport (SEA)
Flight Corridor Management Program
The Port of Seattle (Port) has completed an environmental analysis, including review of pertinent and available environmental information and preparation of a State Environmental Policy Act (SEPA) Checklist for the Flight Corridor Management Program.
Description of Proposed Project Action: The Flight Corridor Management Program (Program) identifies and manages obstructions to the flight corridor at SEA, which are typically trees. Maintenance of the flight corridors is a requirement and priority for the FAA, State of Washington, and the Port of Seattle. The Port is required to ensure there are no obstacles or obstructions on or around SEA that could affect the flight corridors. 1 The Program, implemented on a regular basis (i.e., approximately every 5 years), ensures obstructions (e.g., trees) are identified and removed. The Program also requires ongoing site management and monitoring to support healthy ecological communities as a result of obstruction removal. Tree removal and replacement requirements are identified based on the jurisdiction and/or property they are located. The Port will coordinate directly with commercial and private property owners and affected jurisdictions. Information about each implementation cycle, including the number and location of trees identified for removal, tree replacement requirements and commitments, and best management practices (BMPs), is available on the Port of Seattle's website, www.portseattle.org.
Location of Proposed Action: To complete this environmental review of the Program, the area where tree removals may occur in the future has been estimated. The area is based on the Runway Protection Zones for SEA's east and west runways (34R/16L and 34L/16R), extending 1,500 feet east and west, and 3,500 feet north and south beyond the outer limits of these zones. This area covers the location of obstructions identified during past data collection in 2014, 2019, and 2024. The Program Area includes Port-owned properties; public properties (owned by the Washington State Department of Transportation [WSDOT], Highline School District and the cities of SeaTac, Burien and Des Moines; and commercial and privately-owned lands in the cities of Burien, SeaTac, and Des Moines.
Lead Agency: Port of Seattle (SEPA File Number 2025-05)
Determination: The Port of Seattle completed an environmental evaluation including review of pertinent environmental information, following the provisions of the Washington State Environmental Policy Act (SEPA) under Chapter 43.21C, Revised Code of Washington (RCW), Chapter 197-11, Washington Administrative Code (WAC), and Port of Seattle Commission Resolution No. 3650, and Port of Seattle SEPA Policies and Procedures. The Port of Seattle's SEPA determination concludes that environmental impacts of the proposal are not significant.
Supporting Information: Information used to reach this determination is available upon request. Flight Corridor Management Program Determination of Non-significance (POS SEPA File No. 2025-05), Environmental Checklist, and supporting documents are available online at https://www.portseattle. org/environment/sepa-nepa.
Public and Agency Comment: The DNS and Environmental Checklist for the Flight Corridor Management Program was published on August 27, 2025. During the 15-day public comment period the Port received 48 comments, including 3 from public agencies (City of Des Moines, Washington State Department of Ecology, and Washington State Department of Fish and Wildlife) which were carefully reviewed and considered. It is noted that the majority of public comments are on the merits of and justifications for the Port's Program requiring tree removal, particularly in public spaces. In consideration of public comment, the Port issued a document on its website answering frequently asked questions, published a revised Environmental Checklist, and is now issuing a Final DNS, affirming that no potential for significant impacts were identified, and no additional environmental review under SEPA is needed. Please refer any questions relating to this determination or to the proposed actions to Steve Rybolt, Port of Seattle, Aviation Environment and Sustainability Department, P.O. Box 68727, Seattle, Washington 98168. Telephone 206.787.5527. Email SEPA@portseattle.org. Include your mailing address when submitting comments to the electronic Internet address.
Appeals: The Port's decision on the proposal described above and the Port's issuance of a Final DNS on this proposal constitute the Port's Final SEPA decision. This SEPA DNS determination may be appealed by filing a writ of review in King County Superior Court within twenty-one (21) days of the date of issuance pursuant to Port of Seattle Resolution No. 3650. Any appeal of the SEPA DNS must also satisfy the requirements of RCW 43.21C.075.
SIGNATURE ON FILE
Sarah Cox, Director, Aviation Environment and Sustainability and SEPA Responsible Official
Port of Seattle, Seattle – Tacoma International Airport
1 SEA has three parallel runways, each with instrument- guided, very precise flight procedures and flight paths. The Port is required to follow conditions of Title 49 of the United States Code (49 U.S.C.) Subtitle VII and Title 14 of the Code of Federal Regulations (14 CFR 139), as stipulated in SEA's Airport Operating Certificate issued by the Federal Aviation Administration (FAA).
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