The King County Solid Waste Division was allocated seven closed landfills in the 1970’s and has subsequently been maintaining and monitoring the closed landfills that ceased operations between the mid-1960s and 2002. Post-Closure Landfill maintenance funding was originally created in 1995 to support the maintenance activities at the closed landfills for a minimum of a 20 years or 30-year term with the goal of rendering the landfills to an inert state.

At times, the period needed is greater than 20 years depending on the condition of these closed landfills, which is why there is ongoing maintenance costs. Most of the closed landfills have reached the end of their required minimum post-closure periods, but still require ongoing maintenance and monitoring and Solid Waste has created strategies to bring the landfills to a stable state.

Although some of the closed landfill planned post-closure periods have elapsed, regulations and the understanding of closure requirements have changed, requiring ongoing maintenance and monitoring until a stable state is reached. Moreover, Public Health-Seattle & King County and the Washington State Department of Ecology will decide if the division can end post-closure activities by demonstrating  the landfill is stable. The Solid Waste Division has also undertaken capital improvement projects in addition to the maintenance program to identify whether the landfill gas control and treatment systems, the wastewater collection and treatment systems, and landfill cover systems need updating to facilitate the landfills reaching stabilization and reducing or concluding landfill operations.  “Stabilization” is determined by “showing there is little or no settlement, gas production or leachate generation” as defined by Washington state landfill regulations.

Key environmental attributes

1. Groundwater quality improvements to meet regulatory compliance that are protective of human health and the environment, through installation and improvements to the environmental control systems;
2. Reduce the potency of GHG emissions to the greatest extent feasible, through the collection and treatment of landfill gases;
3. Achieving the above goals in order to minimize or terminate post-closure activities.

Project info

Green Bonds: 2017-Series A

$8.1m Green Bond Proceeds allocated

10% reduction in GHG emissions tCO2eq/year at Hobart Closed Landfill

20% reduction in GHG emissions tCO2eq/year at Enumclaw Closed Landfill

20% improvement key water quality parameter/year for Cedar Falls Landfill last two years

20% improvement key water quality parameter/year for Hobart Landfill last two years

5% improvement key water quality parameter/year for Enumclaw Landfill last two years

5% improvement in key water quality parameter per year for Vashon Landfill

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CICERO rates King County Green Bonds Deep Green, their best rating.

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Related information

• Cedar Hills Regional Landfill

Related agencies

• Dept. of Natural Resources and Parks
• Solid Waste Division