Duwamish Waterway Park

Last Updated: September 2025

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Blog | "Cleaning Up: Fieldwork starting in the Duwamish Waterway Park” (Oct. 28, 2024)

Cleanup moves forward with Remedial Investigation fieldwork
Before a cleanup at the park occurs, it is important to first understand what and where the contaminants are, as well as how they might affect human health, plants, and wildlife. Ecology is currently overseeing the remedial investigation of the park.

In August 2024, Ecology and the City of Seattle (City) finalized the plans for how the investigation would be performed. In January 2025 fieldwork activities began, and the work will continue at least through 2025. You may have noticed the City's work on the Site already. Environmental staff have collected soil, sediment, groundwater and surface water samples; however, more sampling work remains to be completed before the investigation ends. Ecology and the City are currently reviewing the field sampling data collected since January, to determine where additional sampling must occur for the remedial investigation.

During this period of fieldwork, impacts to the park have been minimal and the park remains open to the public. There are small areas of the Site around the eastern shoreline of the waterway where the City placed fencing to restrict access by the public. The fences are intended to prevent people from accessing areas of the Site where investigation is still underway and where chemicals have been detected in surface soils above MTCA cleanup
levels.

Once fieldwork is completed the information will be compiled into a report titled Remedial Investigation, and the report will be shared with the public for review before it is finalized. The finalized Remedial Investigation report will then be used by Ecology and the City to evaluate possible options for cleaning up the Site (also referred to as the Feasibility Study). The Remedial Investigation report and the Feasibility Study will both then be used to develop the Cleanup Action Plan for the Site.

We expect the Remedial Investigation fieldwork to be completed and the report to be drafted and ready for public review in 2026.

​What is going on with the fenced portion of the park?
During this period of fieldwork, impacts to the park have been minimal and the park remains open to the public. There are small areas of the Site around the eastern shoreline of the waterway where the City placed fencing to restrict access by the public. The fences are intended to prevent people from accessing areas of the Site where investigation is still underway and where chemicals have been detected in surface soils above MTCA cleanup
levels.

The Duwamish Waterway Park site is adjacent to the Lower Duwamish Waterway Superfund Site, which includes a 5-mile stretch of the Duwamish River. The U.S. Environmental Protection Agency (EPA) added the LDW Superfund Site to the Superfund National Priorities List in 2001. Ecology is working to stop or reduce sources of contamination to the LDW Superfund Site, an effort known as “source control,” so that the EPA can proceed with the cleanup of the river sediment.


Remedial actions (2014–2022) — contaminants confirmed in site soils:

• Arsenic, lead, mercury, and other metals
• Polychlorinated biphenyls (PCBs)
• Carcinogenic Polycyclic Aromatic Hydrocarbons (cPAHs)
• Dioxins and furans
• Petroleum and phthalates
• Other organic contaminants

Additional contamination is suspected in other media at the Site, such as in groundwater, surface water, and sediments.

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.

The City will proceed with the Remedial Investigation, Feasibility Study, and then create a Draft Cleanup Action Plan for public review.

Each of those steps will require a public comment period. The graphic above shows these different stages of cleanup. Sometimes multiple stages occur in one public comment period.

A Public Participation Plan (PPP) was finalized in 2023 that provides information about the Site and also provides information and opportunities for public participation with the cleanup project. 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. We will continue to evaluate the community’s use of our adjusted LDW site outreach planning for future comment periods and will amend the PPP, as needed, based on community engagement. 

As the cleanup process continues at the park, Ecology will make the future Remedial Investigation Report, Feasibility Study, and Cleanup Action Plan available for public review and comment. 

Location
The Duwamish Waterway Park is on the west side of the Lower Duwamish Waterway (LDW) in the South Park neighborhood of Seattle. The site is approximately 1.7 acres and includes a play area, picnic area, a beach with river access, and the property to the east (known as the Park Addition property). The City of Seattle Parks and Recreation owns and manages the park and leases the Park Addition property to the current tenant, United Site Services.

Site discovery and Initial Investigation
Preliminary soil investigations occurred at the site in 2014 and 2019, documenting soil contamination of lead and arsenic. Ecology was notified of the discovery of contamination in spring of 2019, and an Initial Investigation was completed in January 2020. As part of the Initial Investigation, Ecology evaluated environmental conditions at the property and reviewed all available data. The goal of the Investigation was to determine if the release may pose a threat to human health or the environment, and if further cleanup actions are needed.

Ecology’s Confirmed and Suspected Contaminated Sites List
Following the Initial Investigation process the site was listed on the Contaminated Sites List in February 2020.  

The Voluntary Cleanup Program (VCP) enables owners of contaminated sites to meet state cleanup standards under MTCA independently and to receive technical guidance from Ecology during the process.  The VCP enables owners to work on a contractual basis rather than under an Ecology legal order.  Participants in the VCP pay fees to Ecology to cover the department’s costs for guidance and review.  VCP sites must meet the same cleanup standards as properties formally managed by Ecology under MTCA.

In July 2020 City of Seattle Parks and Recreation (SRP) entered into the VCP (VCP Project Number NW3279) and requested a review and opinion on a Remedial Investigation (RI) of the Duwamish Waterway Park in July 2020.  Ecology requested additional information from SRP in August 2020 to draft our opinion letter.  SRP started renovation work at the site in October 2020.  Ecology received a revised RI in August 2021 which included additional information on interim actions.  Interim actions at the site included selective soil excavation, removal, and replacement with clean fill; construction of concrete pathways, placement of vegetation and laying of sod material, and installation of various capping technologies throughout the park.   

In October 2021, Ecology’s issued an opinion letter to the City for the independent interim cleanup actions performed. The opinion letter documented several concerns and information gaps related to the remedial activities performed. Based upon the growing complexity of the Site cleanup, Ecology terminated the VCP project in September 2022 and initiated legal negotiations with the City for an Agreed Order. The Agreed Order cleanup process was pursued by Ecology to ensure that future remedial actions at the Site would be under Ecology’s technical and regulatory oversight.

In November 2023, Ecology entered into an Agreed Order with the City for the Site. The Agreed Order requires the City to address contamination at the Site by conducting a Remedial Investigation and Feasibility Study and drafting a Cleanup Action Plan. 

Currently the Remedial Investigation is underway, and field sampling is expected to last at least through 2025. Based on current Site knowledge, the Remedial Investigation Report is expected to be drafted for public review in 2026.