Where will all the waste go? King County’s only landfill expected to be completely full by 2040

Where does our everyday garbage go?

In King County, all the waste that is not compostable or recyclable — like used diapers, greasy pizza boxes or CVS receipts — is sent to Cedar Hills Regional Landfill, a 778-feet high, 920-acre piece of land in Maple Valley that is close to being completely filled.

How close? According to the people who are in charge of the landfill, Cedar Hills receives about 1 million tons of waste a year, and it is expected to be sealed off within 15 years, which means that 2040 is the projected completion year of the landfill.

“Basically all garbage that is generated within King County, which is 37 cities and excludes Seattle and excludes the city of Milton — all that garbage that is generated comes here to Cedar Hills Landfill,” said landfill supervisor Joseph Newton.

Right now, all of that waste is suffusing throughout Cell 8 of 9. The previous cell — Cell 7 — was opened in 2010 before being sealed and closed less than a decade later.

While all current waste is being placed in Cell 8, Cell 9 is being used for the landfill’s support buildings and office facilities. And because Cell 8 is due to be filled, facilities on Cell 9 will be de-constructed soon and moved to 3005 Northeast 4th Street in the Renton Highlands, which will include a vehicle maintenance shop, office space and parking for employees, laboratory space and space for tractors, trailers and operations vehicles.

Construction is expected to be completed in mid-2025, and once Cell 8 is filled to a height of 800 feet (with 30 feet sealant of dirt on top), work will begin to fill the last remaining section of Cedar Hills Landfill.

What will become of King County’s waste once Cedar Hills is full?

In September 2024, the Cedar Hills Landfill hosted one if its seasonal tours. The public is encouraged to register and see with their own eyes how the county’s waste management services operate and what happens at the landfill.

After parking, about 20 adults and two small kids stepped out into of their vehicles, expecting rotten and repulsive smells from the landfill, but instead being met with what this reporter compares to the fermented smell that comes from a bokashi composting bin.

Everyone was loaded into a green and yellow Metro bus at around 9 a.m., which made its way toward the summit of the county’s waste of yesteryear. For Kate Schenot of Seattle, she joined the tour with few expectations. “I’m interested in systems and want to see what’s behind my every day experience of trash,” she said.

As the Cedar Hills Landfill has ascended and grown over the decades, a paved road with lanes has been added, allowing cars and trucks to make their way around the perimeter of the artificial mountain. Unlike a regular highway, this one dips in random spots, which the tour guide, Scott Barden (the landfill’s assistant operations manager) said was due to some of the buried waste beneath the earth decomposing and sinking.

While the bus pressed on over each bump and dip, Barden talked about the history of the landfill and explained how the first few cells were sealed so long ago that entire flora and fauna ecosystems have made a home on the hills, including eagles, coyotes, bears and elk — the latter of which the bus came across on the road as a hoard of the wild hooved animals chowed down on the hillside’s vegetation, slowly moving out of the way of the hulking metal beast.

Once the bus made its way to the top of Cell 7, everyone got out to look over Cell 8 as trucks dumped waste and flattened it out. People on the tour took pictures and asked Newton about the site and the future of King County’s waste.

Newton explained that there are many options for what happens once the Cedar Hills location is completed. The two most likely options are putting the waste “on a rail” and having it sent to either Republic, Washington, or Hillsboro, Oregon. When asked about the possibility of the waste being sent out of the country, Newton assured that all of the county’s waste would remain in Washington or Oregon. The exact location is still being considered.

In the meantime, social and government efforts for residents to consume less garbage and to recycle more have slowed the amount of waste that has gone into the landfill. Newton explained that the landfill was projected to be at capacity much sooner, but that recycling has slowed the timeline.

Joe Basile of King County Solid Waste Division explained in an email that Re+ initiative is the county’s recycling program and its “approach to reinventing the region’s waste system to cut greenhouse gases and create a more sustainable economy.”

According to Basile, the county relies on partners to keep the recycling system going.

“After leaving the transfer station or your curbside bin, recyclable materials are taken by a hauler to a material recovery facility, a privately owned plant that separates and prepares single-stream recycling materials to be sold to end buyers,” he said. “Once there, materials are first sorted manually, then by a system of conveyor belts and optical scanners that can detect and separate various material types. From there, the separated materials are baled and sent to local, national, or international processors that make recycled-content products.”

Solid Waste Division workers bring waste to Cell 8 of the landfill, working to flatten out the county’s garbage. Photo by Bailey Jo Josie/Sound Publishing.

Trucks unload waste onto Cell 8. Photo by Bailey Jo Josie/Sound Publishing.

The top of Cell 7 — currently the highest point of the Cedar Hills Regional Landfill — has a landscape similar to the dry areas of eastern Washington. Photo by Bailey Jo Josie/Sound Publishing.

The most current map of the Cedar Hills Regional Landfill in Maple Valley. It is expected to be completely filled by 2040. Image courtesy of Washington State Department of Ecology.