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Landfill gas pipeline upgrade project at Cedar Hills Regional Landfill

Landfill gas pipeline upgrade project

Completed in 2017

Project background

In 2008, King County Solid Waste Division (SWD) contracted with renewable energy company Bio Energy (Washington) LLC, (BEW) to generate renewable energy from landfill gas produced by decomposing organic material at the Cedar Hills Regional Landfill, and thus reduce greenhouse gas emissions. The BEW gas-to-energy plant separates methane from the other components of the landfill gas, compresses the separated methane gas, and conveys it into a commercial natural gas pipeline as pipeline-quality gas.

At Cedar Hills, landfill gas is captured through a network of pipes and delivered to BEW’s on-site landfill gas-to-energy plant through a conveyance pipeline. The pipeline carries collected landfill gas from a flare station, located at the north end of the landfill property, to the BEW gas-to-energy plant, located at the south end of the landfill property, for processing. Prior to construction of the BEW gas-to-energy plant, all collected landfill gas was disposed of by burning at the flare station. When the BEW gas-to-energy plant was opened, the use of the flare station was reduced.

Project description

In 2017, the Solid Waste Division completed installation of a second conveyance pipeline to carry landfill gas from the North Flare Station to Bio Energy Washington’s (BEW) gas-to-energy plant. This new pipeline provides redundancy in this vital infrastructure, allowing a continuous supply of landfill gas to be produced into renewable energy. The new pipeline is the primary pipeline for carrying landfill gas from the flare station to the BEW gas-to-energy plant for processing. The original pipeline will be used in a back-up capacity. This allows for maintenance and testing to occur at the same time, and still allow landfill gas to be delivered for processing into renewable energy. Thus, less landfill gas will be disposed through the existing flare system.

Below are some of the features of the new pipeline:

  • Constructed of 30-inch diameter high density polyethylene (HDPE) pipe.
  • The pipe is buried underground, except short pipe sections are aboveground where the new pipeline connects to the existing pipeline system at the flare station and the BEW plant.
  • Both the original and new conveyance pipelines operate under a vacuum over their entire length using fans that pull the landfill gas from a network of gas collection pipes buried in closed and active areas of the landfill to the BEW plant. This system creates the vacuum that ensures that landfill gas will not leak from the conveyance pipeline into the atmosphere.
  • The new pipeline was installed within the landfill’s permitted footprint, along the edges of existing roads in the western and southern portions of the landfill and does not impact the landfill property buffer. (see map below)

In accordance with the State Environmental Policy Act (SEPA), the SWD completed a SEPA checklist to identify possible environmental impacts from development of this project. Information provided during the SEPA review process helps agency decision-makers, applicants and the public understand how a proposal will affect the environment. The SEPA checklist addressing this project is available for review and comment under the project documents section of this page.

Gas Pipeline Upgrade vicinity map
Vicinity map
Landfill gas delivery map (PDF)
Landfill gas delivery map

  Project milestones


Purpose / action taken

Jan. 20, 2016

SWD issues a “Determination of Nonsignificance” and issues a SEPA checklist for 14-day public review and comment period.

Feb. 3, 2016

Deadline for submitting comments on the Determination of Nonsignificance

Feb 8, 2016

Deadline for submitting a written appeal of the SEPA determination per King County Public Rule PUT 7-4-1

June 2016 - March 2017

Construction of new pipeline

May 2017

New pipeline operational

Project documents

Project contacts

Project manager
Tien Pham
King County Solid Waste Division
Telephone: 206-477-5232, TTY Relay: 711

King County Solid Waste Division mission: Waste Prevention, Resource Recovery, Waste Disposal

Contact Us

 Call: 206-477-4466

TTY Relay: 711