Skip to main content

Green bonds: Vashon Island Landfill

Vashon Island Landfill – Landfill Gas Control and Leachate Collection System Improvements

King County Green Bonds

Vashon Landfill - leachate pond leak detection
Vashon Landfill - leachate pond leak detection

The 24-acre landfill closed in 1999 with an engineered composite liner, leachate collection (gravity pipes with an aeration pond), and gas collection with activated carbon filters. Storm water drainage and groundwater, surface water, and landfill gas monitoring are in place.

Project goals

  • Identify improvements needed to the leachate collection, cover and landfill gas system to address impacts to groundwater. This project will be completed in 2025 with recommendations for needed improvements;
  • Conclude improvements and provide property for secondary beneficial use. 

Percentage completion

  • Approximately 50% complete.

Key environmental attributes

  • Groundwater quality improvements to meet regulatory compliance that are protective of human health and the environment, through improvements to the environmental control systems;
  • Reduce the potency of GHG emissions to the greatest extent feasible, through the collection and treatment of landfill gases;
  • Achieving the above goals in order to minimize or terminate post-closure activities;
  • Installed 3 LFG extraction wells to LFG capture and minimize LFG to groundwater interaction;
  • Remedial Investigation was completed in 2020.
  • Installed new groundwater monitoring well to define extent of contamination.

Project info

Green Bonds: 2017-Series A

$2.2m Green Bond Proceeds spent

MTCO2e/yr: in progress

5% improvement in key water quality parameter per year

CICERO independently rates King County Green Bonds.
Download Cicero's analysis
Cicero Deep Green

Related information

Related agencies