EPA ID# WAD980638910
EPA Region 10
King County

9th Congressional District

Other Names: Midway Disposal Site, City of Seattle Midway Landfill
Last Update: August, 2012

Hide details for Site DescriptionSite Description

The Midway Landfill, located in Kent, Washington, is a 60 acre former gravel quarry that operated as a muncipal solid waste landfill from 1966 to 1983. About 3 million cubic yards of waste were deposited in the unlined landfill. The Midway Landfill was created primarily to accept demolition materials, wood waste, and other slowly decomposing materials, but other industrial wastes were also put in the landfill, including paint sludges, oily waste water and sludges, alkaline waste, and coolant. In 1983, the landfill was covered with silt and fine sands. In l985, combustible gas was detected in structures around the landfill. Contaminated groundwater was also found beyond the landfill boundary. Approximately 8,200 people live near the affected area. Two elementary schools and a community village are located within mile of the site.

Site Responsibility: This site is being addressed through municipal actions, with oversight by the Washington Department of Ecology (Ecology). In September 2000, EPA prepared a CERCLA Record of Decision that was issued by Ecology and EPA. Ecology will continue to oversee the cleanup.

NPL Listing HistoryDates
Proposed Date:10/15/1984
Removed Date:
Withdrawal Date:
Final Date:06/10/1986
Deleted Date:

Hide details for Threats and ContaminantsThreats and Contaminants

Media Affected: Groundwater, Air
Groundwater was contaminated with heavy metals, and volatile organic compounds (VOCs) including benzene and vinyl chloride. Risks associated with heavy metals are now under control at the site and VOC concentrations have greatly decreased in groundwater downgradient of the landfill.

Gases emanating from the landfill also contained VOCs. This problem was also addressed. People could have been exposed to contaminants by inhaling landfill gas or ingesting or coming into direct contact with contaminated groundwater.

Hide details for Cleanup ProgressCleanup Progress

The city of Seattle completed a Remedial Investigation/Feasibility Study (RI/FS) pursuant to a consent order with the State, signed in May 1990. In November 1992, the city of Seattle constructed interim remedial measures: a final cap over the site; refined landfill gas control; and a stormwater and drainage control system.

The remedial work performed by the City of Seattle at Midway Landfill since 1985 has greatly improved the environmental conditions at the site. Potentially explosive gas has not left the property since 1990. The groundwater beneath and down gradient of the landfill is much cleaner than it was in 1985.

EPA designated this site as "construction complete" in September 2000. Groundwater monitoring is ongoing. Ecology completed the first Five Year Review report in September 2005 and concluded that the remedy continues to be protective.

Hide details for Regional ContactsRegional Contacts

SITE MANAGER(S):Ching Pi Wang (Ecology contact)
E-MAIL ADDRESS:cwan461@ecy.wa.gov
PHONE NUMBER:425-649-7134

Tim Brincefield (EPA contact)
Information pertaining to this site is housed at the following location(s):
Seattle Public Utilities Office (Administrative Record - Ecology-lead work)
Solid Waste Field Operations
710 2nd Avenue, 11D
Seattle, WA 98104