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Landfills

Cedar Hills Regional Landfill Cross-Section Larger landfill cross-section (PDF, 333 K) has more detailed information about the landfill.

Cedar Hills Regional Landfill is the only operating landfill in King County. The City of Seattle and neighboring counties are already exporting garbage by rail to distant landfills. Nearly all of the solid waste generated by King County residents living outside of Seattle is disposed at the Cedar Hills Regional Landfill. Solid waste is taken to the landfill by county transfer trucks and by the large commercial hauling companies that provide curbside garbage collection services throughout the county. The landfill is not open to the general public for disposal of garbage. The landfill is a 920-acre facility located in Maple Valley, about 20 miles southeast of Seattle. It is owned by King County and operated by SWD.

When the first permits were granted for Cedar Hills Regional landfill back in 1960, few regulations were in place to govern the design and operation of a landfill. Since that time, sweeping environmental changes have been enacted for solid waste management facilities all over the country. New laws set stringent requirements for landfill management, including the use of landfill liners and daily cover, and environmental monitoring, among others.

The Cedar Hills Regional landfill has evolved into a state-of-the-art facility, meeting the highest standards for protecting public and environmental health. In the last 10 years, the landfill has received national recognition for its advanced operations. The cross-sectional view above shows some of the features of the Cedar Hills Regional landfill.

Transfer trucks hauling 18-ton trailers on average deliver loads of garbage to the active area of the landfill. More than 2,500 tons of garbage is added to the landfill each day. The garbage is tamped down and then covered at the end of the day with a layer of compacted soil. Rain that filters through the landfill produces leachate. The leachate is collected in pipes and treated before it's sent to the main water treatment plant. As the cross section above shows, a plastic liner and clay barrier prevent any seepage from the landfill into the soil or groundwater below the landfill floor. The other byproduct of the natural decomposition of garbage is landfill gas - consisting primarily of methane. The gas is currently collected in a series of underground pipes that carry it to an above-ground flare station where the gas is burned.

The landfill receives nearly one million tons of solid waste a year. Under current projections, it is expected to reach capacity and close between 2012 and 2014. At that time, the County will begin to export solid waste by rail lines or barge to an out-of-county landfill. SWD is currently looking at various methods for implementing waste export.

Waste export is the long-haul transport of solid waste for disposal. A schematic (pdf, 685k) shows how the transfer and disposal system currently works and how a typical waste export model might function. There are still many decisions to make before waste export is implemented in the county, such as where and how the waste is compacted into more dense loads before being carted onto trucks, trains, or barges for export.

In addition to the transfer stations, drop boxes, and Cedar Hills Regional landfill, the division has responsibility for maintaining 10 closed landfills. Landfills undergo routine monitoring of groundwater, surface water, wastewater and landfill gas as needed. They are closed to the public, except at select sites where some public activities are permitted because the sites are determined to be environmentally safe by Public Health - Seattle & King County and the Washington State Department of Ecology.

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