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Landfill gas–to–energy project

Facility will convert landfill gas to natural gas and reduce greenhouse gas emissions

Landfill Gas Collection at Cedar Hills

• Proposed Project
• Project Benefits
• Environmental Review Process
• Project Schedule
• Contacts
• Documents

King County's Solid Waste Division has embarked on a new project to generate usable energy from methane gas produced by the decomposition of garbage at Cedar Hills Regional Landfill. King County has contracted with renewable energy company Ingenco—doing business as Bio Energy (Washington), LLC ("Bio Energy")—to convert methane gas produced at the landfill into pipeline quality natural gas for use in the region.

Proposed project

Bio Energy proposes to build a landfill gas processing facility on about 2 acres of land within the Cedar Hills Regional Landfill. The landfill is located on a 920-acre site in unincorporated King County at 16645 228th Avenue SE, Maple Valley, WA 98038 (external map). The gas would be distributed through an existing Williams Northwest Natural Gas Pipeline that runs adjacent to Cedar Hills. The facility will also generate supplementary electricity that will be used to run the proposed landfill gas–to–energy facility.

Project benefits

• The estimated annual reduction in carbon dioxide (CO₂) emissions from converting the landfill gas to natural gas will be roughly equal to the annual CO₂ emissions from 22,000 average passenger cars.
• The project will not increase noise or impact traffic in neighboring communities.
• The conversion of landfill gas to natural gas will reduce green house gas emissions from the landfill by approximately 63%.
• The County will receive revenue from the sale of the gas.

Environmental review process – updated June 23, 2008

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.

An Environmental Checklist (PDF, 4.2 MB, note: this is a very large file and may take several minutes to download), and addenda (PDF, 563 K) was completed that addresses questions about the landfill gas–to–energy project's potential environmental impacts.

The King County Solid Waste Division reviewed the environmental checklist and made a determination that the project does not have adverse impacts on the environment provided several mitigation measures are taken. The Solid Waste Division identified the potential environmental impact areas that must be mitigated. See the Mitigated Determination of Non-Significance (MDNS) (PDF, 150 K).

On June 23, 2008, the Solid Waste Division issued an Addendum to the MDNS (PDF, 54 K). The purpose of the addendum is to provide additional information or analysis that does not substantially change the analysis of significant impacts and alternatives in existing environmental documents (WAC 197-11-600 [4] [c], -706). This Addendum attaches three documents:

Note: for copies of the following documents, please contact the Solid Waste Division.

1. Noise Emissions Modeling Analysis – Preliminary Acoustical Design, dated June 11, 2008 and prepared by Hessler Associates, Inc.
2. Emergency Response Plan, dated June 12, 2008 and prepared by Bio Energy
3. Spill Prevention Control and Countermeasures (SPCC) Plan, dated June 12, 2008 and prepared by Bio Energy

Also on June 23, 2008, the Solid Waste Division issued a Notice of Action (PDF, 110 K) for Bio Energy to proceed with the proposal to build a landfill gas processing facility at the Cedar Hills Regional Landfill site provided they obtain the required permits. This proposal includes all of the mitigation measures described in the MDNS. The Solid Waste Division's authorization to proceed was made after a review of the MDNS, the Addendum to the MDNS, all public comments received during the MDNS comment period, and all associated Solid Waste Division responses to public comments.

The project will not be implemented unless Bio Energy addresses all potential environmental impacts and obtains the required permits or approvals from the regulatory agencies involved in safeguarding environmental standards.

Potential environmental impacts and required mitigation measures

Air emissions

Currently, landfill gas is collected in a series of pipes and then burned in a high–temperature flare. The existing flare system is regularly tested and the air emissions meet or exceed all applicable environmental regulations. The landfill gas-to-energy project proposes to convert the landfill gas into a reusable energy source – enough to supply about 22,800 homes with natural gas – and further reduce air emissions ensuring continued compliance with regulatory standards. The conversion of methane gas to natural gas will reduce green house gas emissions from the landfill by almost 63%. The estimated annual reduction in carbon dioxide (CO₂) emissions from converting the landfill gas to natural gas will be roughly equal to the annual CO₂ emissions from 22,000 average passenger cars. Once the new energy facility is in operation, the current landfill gas flare system will be turned off and kept on "stand by" mode for use during annual maintenance of the energy facility or in the event of an emergency. The equipment used at the new facility will include generators, compressors, and other machines that produce exhaust gas. Project compliance 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), will be required. Before construction on this project can begin, Bio Energy must submit a permit application to PSCAA and issuance of a permit will require that the energy facility meets or exceeds the minimum air quality standards.

Noise

The new facility must meet the King County Code for noise levels at the property boundary. The maximum permissible sound level for this facility will be 49 decibels pursuant to King County Code 12.88.020. (Fifty decibels is equivalent to the sound of conversation at home, a quiet office, or moderate rainfall.) Because the facility will be built on about 2 acres of land within the 920-acre landfill site and away from the site's property boundaries, which includes a 1,000-foot buffer, we expect that the noise will be even less at the property boundary. The equipment in the new facility, including compressors and power generating units will be insulated and contained within an insulated building. The facility will operate 24 hours a day, seven days a week.

Before construction on this project can begin, Bio Energy must obtain a permit from the King County Department of Development and Environmental Services (DDES) that includes an approved noise mitigation plan. Noise levels will be monitored regularly to comply with noise standards. Because most of the facility components will be built off-site and then assembled at Cedar Hills, noise levels when the facility is being built is expected to be at or below the noise generated during normal landfill operations.

Liquid waste

Liquid waste is a by-product of the gas conversion process. The liquid will contain oily water and condensation. A high efficiency oil-water separator will be used to pre-treat the water before it is discharged into the on-site wastewater treatment system. Before construction on this project can begin, Bio Energy must obtain a permit from the King County Department of Development and Environmental Services (DDES) that includes an approved wastewater monitoring program.

Emergency response

There is a low probability of accidental events at the new facility that could cause fire, safety, or other human or environmental hazards. Before the facility can operate, Bio Energy must have an emergency response plan, a spill prevention, control and countermeasure plan, and an environmental management plan approved by King County's DDES. These plans must be consistent with the emergency response plan in place for the Cedar Hills Landfill.

Project public comment period

The comment period on the environmental checklist and the Mitigated Determination of Non-Significance (MDNS) for this project ended on May 22, 2008.

Current handling of landfill gas at Cedar Hills Regional Landfill

Currently, all of the garbage generated in King County – except refuse within the City of Seattle and the City of Milton and commercial loads of construction and demolition debris – ends up at Cedar Hills. That is almost a million tons of garbage per year. As the garbage decomposes, it produces landfill gas, which consists of 50 to 60 percent methane, 40 to 50 percent carbon dioxide and less than one percent hydrogen, oxygen, nitrogen and other trace gases. The gas is collected in a series of pipes and then burned in a high–temperature flare. The existing flare system is regularly tested and the air emissions meet or exceed all applicable environmental regulations.

Project schedule – updated June 23, 2008

Contacts

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

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