Big Gulch Creek Subbasin 9

Updated August 2025

Snohomish County reported contamination at the Big Gulch Creek Subbasin 9 area (Subbasin 9) to Ecology in October 2022. After reviewing the reported contamination, Ecology listed the Site on its Contaminated Sites List on April 18, 2023. The Site is currently considered an independent cleanup under the Model Toxics Control Act (MTCA). As investigations continue at the Site, Ecology may either provide assistance through the Voluntary Cleanup Program, or manage the Site with the Paine Field Fire Training Pit PFAS site (CSID 16912) located to the northwest in a formal agreement.

The Model Toxics Control Act (MTCA) is Washington’s environmental cleanup law. It provides requirements for contaminated site cleanup and sets standards that protect human health and the environment. Ecology enacts MTCA and oversees cleanups. The MTCA site cleanup process is completed in steps over a variable timeline.

The Subbasin 9 area consists of wetlands and undeveloped stream areas located on the southern end of the main runway at Paine Field near South Everett. Surface water in this area drains to wetlands which eventually discharge to Big Gulch Creek, east of Paine Field.

Wetlands and streams in Subbasin 9 receive stormwater from Boeing’s Everett Modification Center (EMC) and the western side of Aviation Technical Services (ATS) Hangar 1. Aqueous film-forming foam (AFFF) was a common fire suppressant used in the fire systems installed at both these facilities. AFFF is known to contain per- and poly-flouroalkyl substances (PFAS). Some types of PFAS, including those found in AFFF, don’t break down easily. Since PFAS can accumulate in humans and animals, they can increase the risk of negative health impacts.

Based on records and reports, AFFF was released by the fire suppression systems in Boeing’s EMC and ATS Hangar 1 in the 1990s and 2000s. The most recent release of AFFF was at Boeing’s EMC in 2023 due to a malfunction in the fire suppression system. Water and AFFF from this release were observed entering the stormwater system and discharging to wetlands south of the facility.

Studies conducted by Paine Field from 2022 to 2024 identified PFAS in soil and surface water in the wetlands in Big Gulch Creek Subbasin 9. The following PFAS compounds have been identified at the Site:

• Soil: Perflourooctanoic acid (PFOA), perflourooctane sulfonic acid (PFOS), perflourononanoic acid (PFNA) perflourohexane sulfonic acid (PFHxS), and perflourohexanoic acid (PFHxA)


• Surface water: PFOA, PFOS, and PFHxS