Cedar Hills Regional Landfill

About the Cedar Hills Regional Landfill

The Cedar Hills Regional Landfill is the only active landfill in the county. Located on a 920-acre site in Maple Valley, Cedar Hills has been in operation since 1965. It provides safe and efficient waste disposal for all of King County, except for the cities of Seattle and Milton.

Over 800,000 tons of waste goes to Cedar Hills each year. Most of that waste comes from King County businesses and households. Commercial companies or self-haulers collects and transports waste to a King County transfer station or rural drop box. From these locations, we consolidate the waste for efficiency, then truck it to Cedar Hills for final disposal.

Operations and monitoring

Visit Cedar Hills Regional Landfill Monitoring to read our most recent annual reports and environmental monitoring reports.

Air monitoring during continuous flaring

In 2023, the Solid Waste Division reached out to PSCAA in response to increased landfill gas flaring with the desire to ensure appropriate steps were being taken to maintain compliance with the Air Operating Permit for Cedar Hills. In November of 2023, in response to the Division’s request, PSCAA issued an Administrative Order on requiring evaluation of potential airborne arsenic emissions. 

In January 2024, the Solid Waste Division submitted a modeling protocol and preliminary emissions assessment to PSCAA, including a request for time extension to May 21, 2024, to complete that work. Stack testing for flare emissions and landfill gas composition was undertaken by the Solid Waste Division and completed in January, followed by site-specific testing of the landfill gas in February, and the start of ambient air sampling near the leachate lagoons in March. 

On May 21, 2024, the Solid Waste Division submitted the Toxic Air Pollutant modeling report and best available control technology (BACT) analysis to PSCAA. In July 2024, the Division completed ambient air sampling at lagoons and the fence line and began review of the draft results report. 

In August 2024, the Solid Waste Division received notification of incomplete information and deadline for submittal from PSCAA. A response to the incomplete information notification was submitted to the agency from the Solid Waste Division on September 30.

Landfill gas-to-energy facility

When waste is buried in the landfill it decomposes and produces landfill gas. At Cedar Hills, a network of pipes captures that gas and routes it to an onsite gas-to-energy facility operated by Bio Energy Washington (BEW). The BEW plant processes the gas into pipeline-quality biogas and electric power.

If you have questions or comments on BEW’s landfill gas processing facility, call the BEW comment line at 425-392-3918 or visit BEW’s website.