South Park Landfill

Updated March 2023

The City of Seattle is in the preliminary engineering phase for the cleanup action at their property. This work is designed to reduce the chance of human contact with contaminants, control landfill gas, and further reduce stormwater and groundwater contamination at the site. The PLPs for this site are working with Ecology on updates to the legal agreements for this Site. These documents are expected to be ready for public review and comment in late 2023.

To view site reports and fact sheets, click on
the "View Documents" link to the left. 

The landfill and its associated contamination (including methane) could pose risks to human health and the environment in surrounding areas. This site is also part of Ecology’s Lower Duwamish Waterway source control efforts, because it is located near the Lower Duwamish Waterway (LDW) Superfund Site. 

The US Environmental Protection Agency (EPA) put the lower 5 miles of the Duwamish River on its Superfund National Priorities List in 2001. EPA leads cleanup of the river sediments. The sediments contain a wide range of contaminants due to decades of industrial activity and urban runoff. 

Ecology is leading efforts to control sources of contamination from the land area surrounding the LDW. Contaminants in the soil and groundwater around the river can find their way into the river through storm runoff and other pathways. The long‐term goal is to reduce recontamination of the sediments and restore water quality in the river. For more information, visit our Source Control page.

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.

Site location

The South Park Landfill is a closed solid waste landfill located on an approximately 40-acre area between Highway 99 and Highway 509 in Seattle's South Park neighborhood. It is located about 1,600 feet southwest of the Lower Duwamish Waterway. 

The site is bordered to the north by Seattle Public Utilities’ South Transfer Station (across South Kenyon Street), to the west by Occidental Avenue South, to the south by South Sullivan Street, and to the east by Highway 99 and Fifth Avenue South. It is surrounded to the south and east by the residential neighborhood of South Park.

The Lower Duwamish Waterway drainage basin is divided into source control areas. This site is located within the 1st Ave S Storm Drain (river mile 2.1) source control area along the west bank of the river. Current data indicate the landfill is not affecting the LDW, but monitoring will continue in order to confirm this.

Site history

The South Park Landfill property was originally owned by King County and used as a landfill as early as the 1930s. Open refuse burning was a common practice at the site until 1961.  The landfill was closed according to existing laws in 1966. Part of the landfill was also formerly used as an auto wrecking yard from the 1950s - 1970s. By 1970, several facilities had been built on top of the former landfill, including several industrial-use warehouse facilities and the City of Seattle-built South Recycling and Disposal Station (SRDS). From 1984 to 1996, King County leased portions of the site for storage, mostly consisting of truck storage.

Several different parties now own portions of
the former landfill property:

• CenterPoint South Park LLC owns a 21-acre parcel which is currently used for vehicle parking. This parcel was formerly owned by South Park Property Development, LLC (SPPD) and is still referred to as the SPPD parcel.

• The City of Seattle owns 10.55 acres which is used by Seattle Public Utilities to support
operations and as a household hazardous waste collection facility.

• Schnitzer Properties, LLC owns the 6.49-acre parcel in the northwest portion of the former landfill. This area is referred to as the Kenyon Industrial Park (KIP) Area.

• 7901 2nd Ave S LLC owns a smaller 0.72-acre parcel on the north side of the landfill. 

Contamination

The contaminants of potential concern for soil, groundwater and air at the site include:

Soil:

• Arsenic and lead
• Diesel and oil range petroleum hydrocarbons

Groundwater:

• Arsenic, iron, and manganese
• Vinyl chloride
• Benzene and cis-1,2-dichloroethene

Air:

• Landfill gas (methane and carbon dioxide)

Previous cleanup work

Site investigations began in the mid-1980s.  In 2009, Ecology entered into a legal agreement (Agreed Order) with the City of Seattle and SPPD for additional cleanup
investigation and evaluation of cleanup options. The Agreed Order was previously amended in 2013 and 2016. Two interim cleanup actions were conducted at the site under the Agreed Order, one between 2014 and 2015 by SPPD and another between 2018 and 2021 by the City of Seattle.

In 2019, Ecology entered into a legal agreement (Consent Decree) with the City of Seattle and SPPD. The Consent Decree covered the City of Seattle and SPPD portions of the South Park Landfill. The Consent Decree included a Cleanup Action Plan (CAP) which
required the following actions:

• Constructing or maintaining a landfill cap to prevent human contact with the landfill, and to keep rain and stormwater from encountering landfill waste.

• Installing landfill gas and surface water control systems to control the release of landfill gas emissions from the site and move rainwater away from the site.

• Restricting future land use activities to minimize potential exposure to contamination and maintain the effectiveness of cleanup actions.

• Establishing groundwater and landfill gas monitoring to evaluate the performance and effectiveness of the interim cleanup actions.