NEPA Determination, Simple Categorical Exclusion for the Industrial Wastewater Treatment Plan Expansion Project at Seattle-Tacoma International Airport

The FAA has determined that Seattle-Tacoma International Airport's proposed expansion of its Industrial Wastewater Treatment Plant (IWTP) qualifies for a Simple Categorical Exclusion under the National Environmental Policy Act, meaning the project is not expected to have a significant impact on the environment. The project includes upgrades to the existing treatment plant infrastructure, construction of an aerated gravel bed, and updates to the adjacent Lagoon 3 site. This determination, issued November 14, 2025, clears the way for the required Airport Layout Plan update without the need for further environmental review.

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FAA memorandum dated November 14, 2025, from Laura Sample (Seattle ADO Environmental Protection Specialist) to Steve Rybolt (SEA Senior ENV Program Manager) issuing a Simple Categorical Exclusion (CATEX) under NEPA and FAA Order 1050.1G Paragraph B-2.4.d for the Industrial Wastewater Treatment Plant (IWTP) expansion project at Seattle-Tacoma International Airport (SEA), Seattle, WA. Project components include updating the existing IWTP infrastructure in its current location, constructing an aerated gravel bed, and updating the adjacent Lagoon 3 site. The federal action triggering environmental review is an Airport Layout Plan (ALP) revision. The determination finds no extraordinary circumstances and categorically excludes the project from further environmental review under NPDES/water quality compliance and wildlife hazard provisions of FAA Advisory Circular 150/5200-33.

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