Seattle Public Utilities Midway Landfill

 

On January 27, 2020, Ecology started a 30-day comment period on documents that would allow for development actions at the Midway Landfill Site (Site). 

Ecology also hosted a public meeting and hearing on February 11, 2020 at Des Moines Elementary. (Download a copy of the presentation and the hearing transcript.)

Ecology reviewed and considered all public comments received on the Consent Decree Amendment, Prospective Purchaser Consent Decree, Cleanup Action Plan Amendment, and Public Participation Plan. Based on Ecology’s evaluation of the comments, no changes were necessary in the documents, and they were finalized.

Seattle Public Utilities (City of Seattle) owns and operates the Site and completed cleanup actions in 1992. New transportation development actions would include construction of Sound Transit light rail facilities and Washington State Department of Transportation (WSDOT) highway widening adjacent to Interstate 5 (I-5) on the eastern boundary of the Site. (See figure below.) Ecology requires that these actions protect human health and the environment during and after development.

The following documents were available for review:

• Consent Decree Amendment #2:  update to the 2006 legal agreement between the City of Seattle and Ecology.
• Prospective Purchaser Consent Decree:  new legal agreement between Sound Transit and Ecology.
• Cleanup Action Plan Amendment #1:  describes actions required by Ecology to maintain the integrity of remedial elements during and after proposed development at the Site.
• Public Participation Plan: document that explains how people can participate in the cleanup process.

Two upcoming WSDOT and Sound Transit I-5 Corridor transportation projects adjoin the Midway Landfill.  Only smaller portions of these projects will occur at the Site. See figure to the left and webpage links below for project details. 

• Sound Transit Federal Way Link Extension (FWLE) will extend light rail from the existing Angle Lake Station at S 200th Street to the Federal Way Transit Center.
• WSDOT State Route (SR) 509 Completion Project will add additional lanes to I-5

The two projects are adjacent to the Site, and the FWLE will be constructed in the WSDOT I-5 right-of-way (ROW) on the east edge of the Site. 

The Model Toxics Control Act (MTCA; Chapter 70.105D RCW 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 of Seattle completed cleanup actions at the Midway Landfill site in 1992.

 

Current Midway Landfill 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.

Site location and background
The Site occupies 60 acres in Kent, Washington, between I-5 and Highway 99, and between S. 252nd Street and S. 246th Street. The Site is owned and maintained by the City of Seattle – Seattle Public Utilities. A gravel pit operated at the Site from 1945 to 1966; the City of Seattle used it as a landfill until 1983. Remediation of the Site was completed in 1992. 

Land use in the vicinity consists primarily of residential areas and commercial activities. Light industry and manufacturing facilities border Highway 99 in the area.

Contamination and completed cleanup actions
Due to historic landfill use, the site contains municipal solid waste and associated landfill gas. Contaminants of concern found in the landfill originally included:

• Metals
• Semivolatile organic compounds
• Polychlorinated biphenyls (PCBs) 

In 1983, gas and groundwater testing revealed potentially combustible methane gas and contaminated groundwater traveling from the closed landfill. As a result, cleanup work began in 1985 under the direction of Ecology. 

In May 1986, the Site was listed by the U.S. Environmental Protection Agency (EPA) as a National Superfund site. 

In September 1988, the City of Seattle and Ecology prepared a Remedial Investigation and Feasibility Study to describe contamination found at the Site, evaluate cleanup alternatives, and identify a preferred cleanup alternative. 

In 1990, the City of Seattle and Ecology entered into a Consent Decree defining remedial actions that would lead to protection of public health and the environment. 

 In 1992, the City of Seattle completed these remedial actions:

• Covered the landfill with an engineered, multilayered waterproof cap with a top layer of grass.
• Installed a gas extraction system to control methane.
• Controlled surface water.
• Fenced the landfill to limit access to the Site. 

The City of Seattle maintains these protective features and monitors groundwater quality and landfill gas at the Site. 

Future land ownership
Following completion of the FWLE Midway Project, the City of Seattle, Sound Transit, and WSDOT will make some changes in property ownership. The Sound Transit FWLE rail alignment property currently owned by WSDOT will become owned by Sound Transit. 

The new Prospective Purchaser Consent Decree between Ecology and Sound Transit defines requirements for Sound Transit’s long-term maintenance of their portion of the Site to ensure continued environmental protection.

The Consent Decree Amendment between Ecology and the City of Seattle and the new Prospective Purchaser Consent Decree between Ecology and Sound Transit will all ensure implementation of the required actions defined in the Cleanup Action Plan Amendment.

For a complete list of documents please see "View Electronic Documents" on the right.

• Consent Decree: May 1990
• Fact Sheet: September 2005
• First Periodic Review: September 2005
• Second Periodic Review: September 2015