DNRP > SWD > Facilities > Landfills > Landfill gas–to–energy facility

Landfill gas–to–energy facility at Cedar Hills Regional Landfill

Facility to convert landfill gas to pipeline quality natural gas and reduce greenhouse gas emissions nears completion

Landfill gas-to-energy facility (enlarge image)

• Project description
• Current status of project
• Project benefits
• Environmental review and status of required mitigation measures
• Project schedule
• Contacts
• Documents

Project description

In 2008, the King County Solid Waste Division contracted with renewable energy company INGENCO (external) – doing business as Bio Energy (Washington) LLC, (BEW) (external) to generate usable energy from methane gas produced by decomposing garbage at Cedar Hills Regional Landfill.

BEW designed and built a landfill gas processing facility on about 2 acres of land leased from King County at the 920-acre Cedar Hills Regional Landfill located in Maple Valley. BEW owns and operates the gas-to-energy facility, which includes a quarter-mile pipeline for transporting the processed landfill gas to Williams Northwest Pipeline and on to Puget Sound Energy's natural gas-fired power plants. The facility, which will operate 24 hours a day, seven days a week, will also generate supplementary electricity for use at the plant.

Current project status - June 2009

BEW completed major construction of the facility in March 2009. Since then, BEW has been testing the facility's equipment and operating systems. Testing includes evaluating the facility's noise levels, making adjustments to meet permit requirements, and delivering gas at a limited rate to the pipeline. At full capacity, BEW expects the plant to deliver about 5.5 million cubic feet of gas per day, which is enough to power about 24,000 homes. The plant is expected to be fully operational in late 2009.

Project benefits

• Before the BEW plant was constructed, landfill gas collected through a network of pipes, was burned off through the landfill gas flare system. Now, instead of being wasted, the gas is being used to generate power.
• Once the facility is fully operational, it will not add to noise or traffic in neighboring communities.
• Because the converted methane gas from the landfill replaces an equal amount of nonrenewable natural gas, the landfill gas-to-energy project will result in a 63% overall reduction of emissions, including greenhouse-gas emissions.
• Revenue from the sale of the gas will help keep solid waste disposal rates low. What had formally been an expense to manage will become a significant revenue source - projected to provide approximately $1 million annually – for the county's Solid Waste Division.

Environmental review and status of required mitigation measures

The State Environmental Policy Act (SEPA) requires state and local agencies to consider the likely environmental consequences of a proposal before approving or denying the proposal.

The environmental review process for this project occurred between January and June 2008. The King County Solid Waste Division issued a mitigated determination of non-significance (MDNS), which identified several measures that must be taken in order to mitigate potential environmental impacts.

BEW is responsible for implementing the mitigation measures described in the MDNS (and below) and for obtaining the required permits or approvals from the regulatory agencies involved in safeguarding environmental standards.

Air emissions

The landfill gas processing facility must comply with state and local regulations, including but not limited to the air quality standards established and enforced by the Puget Sound Clean Air Agency (PSCAA). BEW obtained an air permit from PSCAA and issuance of that permit requires the facility to meet or exceed the minimum air quality standards.

Noise

The landfill gas processing facility, which will operate 24 hours a day, seven days a week, must meet the King County Code regulatory requirements for noise levels at the property boundary. The maximum permissible sound level for this facility is 49 decibels (daytime) and 39 decibels (nighttime) pursuant to King County Code 12.88.020. For comparison, 50 decibels is equivalent to the sound of conversation at home, a quiet office, or moderate rainfall.

The Solid Waste Division reviewed BEW's noise mitigation plan and determined that it was consistent with the mitigation measures required in the MDNS. The Solid Waste Division recommended to the King County Department of Development and Environmental Services (DDES) that BEW conduct noise level monitoring prior to, during start-up and periodically during operation of the facility at the facility boundary and at the landfill's nearest property boundary to ensure code compliance. BEW's noise mitigation plan was included in the building permit issued to BEW by DDES.

BEW is evaluating noise levels during the facility start-up phase and making adjustments in order to meet the requirements of the King County Code and the building permit.

Liquid waste

Liquid waste is a by-product of the gas conversion process. The liquid contains oily water from the compression system and other byproducts. A high efficiency oil-water separator is used to pre-treat the water before it is discharged into the Cedar Hills landfill leachate collection system and ultimately is sent to the County's South Wastewater Treatment Plant for further treatment. BEW is required to monitor the facility's wastewater to ensure adherence to the terms and conditions of the approved existing wastewater discharge permit for the landfill site.

Emergency response

There is a low probability of an accident at the facility that could cause fire, safety, or other human or environmental hazards. The Solid Waste Division approved BEW's June 2008 emergency response plan, and spill prevention, control and countermeasure plan. These plans are consistent with the emergency response plan in place for the Cedar Hills Landfill.

Project schedule – updated June 2009

Contacts

Bio Energy Washington
If you have any questions about the landfill gas processing facility or its operation, please contact Bio Energy (Washington) LLC (BEW) (external).

King County Solid Waste Division
Telephone: 206-296-4466 | TTY Relay: 711
If you have questions or would like to provide comments to the King County Solid Waste Division on this project, please use our comment form to ensure a timely response.

Documents

• State Environmental Policy Act (SEPA) Environmental Checklist (PDF, 4.2 MB)
  (note: this is a very large file and may take several minutes to download)
• SEPA Notice of Action (PDF, 110 K)
• Air permit application (PDF, 621 K) submitted to Puget Sound Clean Air Agency
• Mitigated Determination of Non-Significance (MDNS) (PDF, 150 K)
• Addendum to the MDNS (PDF, 54 K)
• Notice of Action (PDF, 110 K)
• Addenda (PDF, 558 K), including:
  1. Bio Energy Addendum on Original Checklist
  2. Bio Energy Solid Waste Plan
  3. Addendum on Thermal Radiation Issue

top of page