Gas Works Park

Last Updated: October 2026

Back in July 2023, Ecology approved the cleanup action plan at Gas Works Park. The plan includes digging up and covering contaminated soil along the shoreline, treating polluted groundwater near the shoreline, dredging and capping dirty sediment in the water, doing ongoing monitoring, and putting rules in place for how the area can be used in the future. This cleanup plan is part of a legal agreement (called a consent decree) between Ecology, the City of Seattle (City), and Puget Sound Energy (PSE). That agreement became final in January 2024. It requires the City and PSE to design and build the cleanup as described in the plan.

In early 2024, Ecology approved a work plan to gather more information to better define where contamination is and to help design the cleanup. From March to October 2024, investigations were carried out on land, along the shoreline, and in the water. In March 2025, the U.S. Army Corps of Engineers approved a permit giving permission for sampling work in the water, which wrapped up at the end of 2025. Ecology is still reviewing all the data collected during that phase.

In August 2026, Ecology approved a separate work plan to clean up groundwater in one specific area of the site (called GWMA‑1).That cleanup is expected to start in late 2026 and continue through 2028.

What happens next?

2026 through 2028: Clean up groundwater in GWMA-1.

2026 through 2029: Engineers will keep working on the design and permitting for the cleanup work that will happen in the water. This includes doing more studies to better understand the contamination and finalize how the cleanup should be built.

2029/2030: Begin construction of the in-water cleanup work.

The Gas Works Park site consists of two units, a 21-acre Upland Unit and a 56-acre in-water Sediment Unit.  Multiple previous cleanup actions have addressed contamination in the Upland Unit, except for bank soil and arsenic-contaminated groundwater along the shoreline.

Sediment throughout the Sediment Unit is contaminated.  

Contaminants present are from former upland industrial operations and include polycyclic aromatic hydrocarbons, arsenic, nickel, carbazole and dibenzofuran.  Additional contaminants associated with other sources in Lake Union are also present in sediment.

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 the MTCA and oversees cleanups. The MTCA site cleanup process is completed in steps (see graphic below) over a variable timeline.

• June 20 - July 20, 2023:  Public comment period
• June 28, 2023:  Online public meeting (Download presentation PDF)
• Fall 2023: Public comments addressed, and cleanup action plan finalized
• 2023 to 2027: Engineering design and permitting, including additional investigations and evaluations to refine the cleanup action and enable detailed design work
• 2027: Begin construction

Current Gas Works Park cleanup site Public Participation Plan

This plan includes information for the public regarding opportunities to get involved in the Site cleanup process. The outreach activities and mechanisms presented reflect Ecology’s current plans for keeping the public informed and for receiving information and comments from the public.

Background
Formerly territory occupied by three indigenous communities (the Duwamish, Hachooabsh, and Shilsholes), the area surrounding the northern portion of Lake Union was settled by non-natives in the mid- to late 1800s. In 1907, construction of a manufactured gas plant was completed on the upland area of the Gas Works Park site to supply fuel for the growing population of Seattle. The plant operated until 1956.  Other industries (e.g., tar refining, bulk fuel storage, shipbuilding) also historically operated in the upland area.  These past industrial activities resulted in contamination of soil, groundwater and sediment.
Contamination in the upland area has been largely addressed through multiple cleanup actions completed between 1971 and 2020.  

Location
The Gas Works Park site is located at 2101 N Northlake Way, Seattle, Washington on Lake Union. It consists of approximately 21 upland acres (Upland Unit) and approximately 56 in-water acres (Sediment Unit). 

The City of Seattle owns the majority of the Upland Unit and the State of Washington owns the majority of the Sediment Unit.