PASCO — After decades, work is coming to a close at one of the largest landfill cleanups in Washington state.

The Washington State Department of Ecology this past week celebrated the removal of more than 35,000 drums of industrial waste from the Pasco Sanitary Landfill Superfund site — a significant milestone in the environmental cleanup at the site.

In total, more than 23,500 tons of toxic waste — about the mass of 1,900 school buses — were safely excavated from Zone A, the site’s largest section of cleanup, to out-of-state facilities. Most of the drums contained solvent and paint sludge, cleaners and other hazardous waste buried about 50 years ago.

It’s the last section to be cleaned up at the landfill.

“Bringing this decadeslong cleanup to a close is a pivotal and encouraging moment for the community,” said Jeremy Schmidt, Ecology’s Pasco Landfill site manager, in a news release. “Safe removal of the drums permanently eliminates long-term environmental risk to communities in Franklin County and the City of Pasco.”

But a presence at the site will remain for many more years.

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Groundwater monitoring and landfill-cover maintenance will continue because of leaking materials, and a groundwater-protection area surrounding parts of East Pasco will remain in place until Ecology deems it safe.

There will be continued limitations on how the property can be used. The site will remain fenced up, access limited, and a “final cover system” will be placed over Zone A.

The contaminated soil will also undergo thermal treatment starting next year, and is expected to be finished in about three years.

Located 1.5 miles northeast of Pasco near Highway 12 at the Pasco Kahlotus Road intersection, the landfill collected a mixture of municipal, commercial and industrial waste from 1958 until its closure in 2001.

Zone A is one of five sections at the landfill.

The site in total covers about 200 acres, and is surrounded by agriculture and commercial businesses. The site does not pose a threat to nearby residents, though the city passed an ordinance in 2001 defining a groundwater-protection area because of large-scale contamination.

The land is owned by Pasco Landfill Inc. and the Dietrich family.

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Boeing is one of 30 companies and agencies liable for the waste, known collectively as the Industrial Waste Area Group III, or IWAG. Other companies include 3M, BNSF Railway, Daimler Trucks Northwest, Georgia Pacific, DuPont and Weyerhaeuser, as well as government agencies Franklin County and the U.S. Air Force.

Nick Garson, a remediation project manager with Boeing, said the hope is they’ll be able to bring the Pasco Landfill off the Environmental Protection Agency’s Superfund: National Priorities List before 2052.

Across four zones at the landfill, the companies have collectively spent more than $75 million on cleanup, Garson said.

“This project was a special kind of complicated, requiring years of negotiation, planning and teamwork to safely execute one of the largest cleanup actions in Washington state history,” Schmidt said at last week’s event marking an end to the cleanup.

The sheer size and amount of contaminants has also made it one of the most challenging.

Before cleanup, several chemicals leached from the waste into the soil and groundwater, including dioxins, herbicides, metals, polychlorinated biphenyls, and volatile and semi-volatile organic compounds.

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A plume of contaminants at one time even extended underground from the landfill to the Columbia River, but site cleanup and other mitigation efforts have since reduced the risk of contaminating the river to near zero.

Today, with waste removed, all that remains is a 16-foot pit in the ground at Zone A where the soil will be thermally treated.

“Basically, we’re going to heat up the soil, boil out the contaminants, we’re going to capture them with an extraction system and then we’re going to treat them,” said Garson, who chairs IWAG’s technical committee.

After that, IWAG will continue to sample the groundwater and maintain the site for upward of three decades until the area meets Ecology’s and the EPA’s standards for a recovered site.

Rigorous cleanup

Zone A is the largest of five zones at the Pasco Landfill that have since been closed.

Nearly 5,000 drums of herbicide-manufacturing waste were extracted from Zone B in 2002.

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Residues from about 3 million gallons of plywood resin waste, wood treatment and preservative waste, lime sludge, cutting oils, paint and paint solvent waste, and other bulk liquids were once located in lagoons in Zones C and D.

Zone E contained about 11,000 tons of sludge from paper manufacturing.

And a 45-acre municipal landfill has been covered and closed. A gas-extraction system generates methane that’s burned at a flare as the material underneath breaks down.

“The permanent drum waste removal at Zone A was the largest and one of the final, necessary cleanup actions at the site,” said Schmidt, from Ecology.

The Pasco Landfill originally opened in 1958. Waste burning began in 1971 when the site became a sanitary landfill.

From 1972 to 1975, the site accepted industrial waste drums, which were organized and disposed between two zones.

The site was added to the EPA’s National Priorities List in 1990, and the landfill ultimately closed in 2001. Shortly after, cleanup began in the industrial waste zones and municipal landfill.

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Interim cleanup lasted from 2008 to 2019, when IWAG and the landfill group finalized a cleanup action plan for Zones A and B and monitoring of the remaining municipal solid waste.

In 2017, concerns mounted that the underground material in Zone A was smolder.

“We were at a decision point and at that point we said, ‘It’s time to remove the drums,'” Schmidt said. He added later: “All of the repositories like this across the country, most of them have already all been cleaned up. It wasn’t really believed there were very many left like this one.”

The contractor, Illinois-based Entact, excavated more than 120 sections of Zone A to remove the drums of waste, which were shipped off to disposal facilities in Oregon and Idaho. Workers erected a giant cover over their workspace and tested materials and soils along the way.