Vashon Island Landfill

King County Solid Waste Division finalized the Remedial Investigation Report for the Vashon Island Closed Landfill on November 6, 2020.

• Final Remedial Investigation Report​

The final Remedial Investigation Report updates the draft Remedial Investigation Report (October 2018) to address additional investigation activities, including:

• Updated sampling results.
• Statistical evaluation of groundwater monitoring data (Section 6.1.3).
• Updated South Slope Area Influence Testing Results (Section 6.3.4) for the interim action.
• A beneficial use survey (Section 7) evaluates groundwater use in the vicinity of the closed landfill.
• A terrestrial ecology survey (Section 8) evaluates the risk to ecological receptors near the west hillslope, where groundwater seeps from the hillside. No adverse ecological impacts are posed by the groundwater seeps.
• The following data gaps will be addressed in the subsequent Feasibility Study:
  • Evaluate seasonal groundwater seepage into gas extraction well GW-11 in the South Slope Area, which inhibited the interim action.
  • Determine the extent of vinyl chloride along the southern property boundary.
    

The report cover letter, Final Remedial Investigation Volume I Report (including text, tables, and figures) and Volume II (including appendices) are available in the electronic documents link on the right side of this webpage; a hard copy will be available once the Vashon Island Library reopens.

King County Solid Waste Division operates the Vashon Island Closed Landfill at 18900 Westside Highway Southwest on Vashon Island, Washington. The 52.5-acre property is located west of the Island Center Forest King County Park, and bisected by Westside Highway Southwest. Solid waste facilities are located east of the highway, including a 10.3-acre closed landfill, leachate and landfill gas control facilities, stormwater ponds and controls, and the recycling & transfer station. The remainder of the property is undeveloped woodlands.

History of activities at the facility:

• Solid waste has been disposed at the site since the early 1900s.
• King County Solid Waste Division assumed operations in the 1950s. 
• Environmental investigations have been conducted since 1983.
• The northwest portion of the Vashon Island Landfill was closed in 1988.
• The facility accepted solid waste for placement in the south portion of the landfill until 1999.
• Final closure was completed in accordance with state regulations between 1999 and 2002.
• King County Solid Waste Division initiated an independent cleanup action under the Model Toxics Control Act in August 2010 to address vinyl chloride contamination in the Cc2 aquifer within the pre-Fraser glacial deposits and in hillside seeps on the west side of the property.

Ecology’s Solid Waste Management Program oversees corrective action at the closed landfill in accordance with the state Model Toxics Control Act (MTCA) regulation (Chapter 70.105D of the Revised Code of Washington and Chapter 173-340 of the WAC.).

Ecology develops regulations and guidelines and provides assistance to Public Health-Seattle & King County and Puget Sound Clean Air Agency. Public Health - Seattle & King County regulates post-closure care at the closed municipal solid waste landfill (Chapter 173-351 WAC).

Puget Sound Clean Air Agency regulates landfill gas emissions from the closed landfill.

Ecology Websites

• Washington State Department of Ecology -Solid Waste Department  

King County Solid Waste Department Websites

• King County Closed landfills  
• Vashon - Maury Island environment  
• King County recycling & transfer stations, drop box facilities   
• Vashon Recycling & Transfer Station   

 Public Health – Seattle & King County Website

• King County Public Health  
• King County -Toxics, air quality and solid waste   

Puget Sound Clean Air Agency

• Puget Sound Clean Air Agency  
  

Washington State Department of Fish and Wildlife Conservation 15

•  Washington Department of Fish and Wildlife Conservation 15  

To report an environmental problem or concern, any time, day or night.

Ecology is committed to providing people with disabilities access to information and services. To request an ADA accommodation, contact Ecology by phone at 360-407-6831 or email at ecyadacoordinator@ecy.wa.gov. For Washington Relay Service or TTY call 711 or 877-833-6341.  Visit Ecology’s website for more information.

​If you speak a non-English language, free language services are available.