TagDeicing(7)

The Port of Seattle is proposing upgrades to Seattle-Tacoma International Airport's Industrial Wastewater Treatment Plant (IWTP) to better handle wastewater from aircraft deicing operations, with construction planned from 2026 to 2030. The project involves replacing aging treatment equipment at the existing facility and building a new aerated gravel bed (AGB) treatment system on a 10.6-acre site nearby to process high levels of biochemical oxygen demand (BOD) on-site. These upgrades are required to comply with tightening discharge limits set by King County and state environmental permits.

In 2003, Washington State's Department of Ecology issued a water pollution permit (NPDES No. 002465-1) for Sea-Tac International Airport, which was then challenged by multiple parties including the Port of Seattle and several community groups. The appeals, heard in July 2004, centered largely on concerns about aircraft deicing and anti-icing chemicals being discharged into Puget Sound and nearby waterways, where they can deplete dissolved oxygen levels critical to aquatic life. The Pollution Control Hearings Board reviewed the permit's terms and conditions to determine whether adequate environmental protections were in place.

The Washington State Department of Ecology issued this draft addendum to address shortcomings in the NPDES wastewater discharge permit for Seattle-Tacoma International Airport, following a ruling by the Pollution Control Hearings Board. The document outlines required changes to how the Port of Seattle manages contaminated wastewater from aircraft deicing operations, including stricter pollution limits, improved treatment standards, and enhanced water quality monitoring of nearby waterways such as Miller Creek. The revisions focus on reducing harmful biochemical oxygen demand (BOD) discharges into Puget Sound and ensuring the Port implements all available pollution control measures as quickly as possible.

A 1993 Port of Seattle letter to Des Moines resident Barbara Stuhring explains that airplane deicing at Sea-Tac uses only FAA-approved ethylene or propylene glycol, and that wastewater from deicing drains to the airport's treatment system before being discharged to Puget Sound — not to Miller or Des Moines Creeks. A 1996 Final Environmental Impact Statement (EIS) later addressed public concerns about deicing fluid effects on local waterways, concluding that glycol quantities in stormwater runoff were too small and too diluted to cause lethal impacts on aquatic life in those creeks. Stuhring subsequently wrote to the Port challenging what she saw as a contradictory response in the Final EIS compared to the original 1993 letter.