Seattle Public Utilities Midway Landfill

Facility Site ID: 2043 Cleanup Site ID: 4729

Site Status - July 2021

Location of future Sound Transit light rail extension and I-5 land widening
Location of future Sound Transit light rail extension and I-5 land widening

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:

Proposed Development Actions

Aerial view of Federal Way Link Extension (FWLE) Midway Project at the Midway Landfill Site
Aerial view of Federal Way Link Extension (FWLE) Midway Project at the Midway Landfill Site

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. 

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. 

General Cleanup Process

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.

 

Public Participation Plan

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 Information

Midway Landfill and I-5 facing South
Midway Landfill and I-5 facing South

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.

Legal 15
Document Title Document Date Document Type
PPCD, Exhibit E, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
PPCD, Exhibit D, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
PPCD, Exhibit C, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
PPCD, Exhibit B, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
PPCD, Exhibit A, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
PPCD 04-13-2020, Sound Transit, Midway Landfill 4/13/2020 Consent Decree
Exhibit F, CD Amendment 2, Midway Landfill 4/13/2020 Consent Decree - Amendment
Exhibit E, CD Amendment 2, Midway Landfill 4/13/2020 Consent Decree - Amendment
CD Amendment 2, Midway Landfill 4/13/2020 Consent Decree - Amendment
Midway_Draft_PPCD 1/24/2020 Consent Decree
Midway_Draft_CD_Amend2 1/24/2020 Consent Decree - Amendment
Midway Landfill Consent Decree Amendment 1 2/3/2006 Consent Decree - Amendment
Amendment No. 1 to Consent Decree (Midway Landfill Site) 2/3/2006 Consent Decree - Amendment
Midway Landfill Consent Decree 6/29/1990 Consent Decree
Midway Landfill Consent Decree 5/29/1990 Consent Decree
Public Information 9
Technical Reports 14
Document Title Document Date Document Type
Midway Landfill - Ecology Project Coord Change Letter (Sound Transit) 3/22/2021 Site Specific Administrative Document - other (Administrative correspondence)
Midway Landfill - Ecology Project Coord Change Letter (SPU) 3/22/2021 Site Specific Administrative Document - other (Administrative correspondence)
Fourth Five Year Report for Midway Landfill Superfund Site, King County, Washington 8/28/2020 Periodic Review (5 Year)
Midway Landfill 2015-2019 Remedial Action Status Report 7/31/2020 Performance/Confirmational Monitoring Plan or Report
Cleanup Action Plan Amendment No. 1, Midway Landfill Site 3/23/2020 Cleanup Action Plan
Midway_Draft_CAP_Amend_1 1/24/2020 Cleanup Action Plan
Hydrogeologic Assessment for Compliance of 1,4-Dioxane, Midway Landfill 10/31/2019 Site Specific Technical Document - other
Midway Landfill - Second Periodic Review 9/1/2015 Periodic Review (5 Year)
Midway Landfill - Annual Groundwater Monitoring Report 7/22/2011 Groundwater Monitoring Report
Midway Landfill Groundwater Monitoring Data Results May 2010 5/14/2010 Groundwater Monitoring Report
midway landfill groundwater sampling 555-1550-052 annual monitoring round 57 5/3/2010 Groundwater Monitoring Report
midway landfill groundwater monitoring status report 2010-2014 1/1/2010 Groundwater Monitoring Report
Midway Landfill Periodic Review 9/19/2005 Periodic Review (5 Year)
Midway Landfill Remedial Investigation Hydrogeology Technical Memorandum 6/1/1988 Remedial Investigation Report
There may be more documents related to this site. To obtain documents not available electronically, you will need to make a public records request.

Places to see print documents

  • Northwest Regional Office
    15700 Dayton Ave N
    Shoreline, 98133
    Please schedule an appointment to view print documents at this location.
  • Woodmont Public Library
    26809 Pacific Hwy S
    Des Moines, 98198
    This location may only have print documents available during open comment periods.

Contaminants 5

Contaminant Type
Soil
Groundwater
Surface Water
Air
Sediment
Bedrock
Halogenated Organics - Halogenated Organics C
Metals - Metals Priority Pollutants C
Halogenated Organics - Polychlorinated biPhenyls (PCB) C
Other Contaminant - Conventional Contaminants, Organic C
Other Contaminant - Conventional Contaminants, Inorganic C C
S
Suspected
C
Confirmed Above Cleanup Levels
B
Below Cleanup Levels
RA
Remediated-Above
RB
Remediated-Below
R
Remediated
This contaminant list was based on our best information at the time it was entered. It may not reflect current conditions at the site.