The federal Superfund site at Pasco could soon have the worst of its remaining waste removed.
The Washington state Department of Ecology has called the Pasco Sanitary Landfill one of the state’s most challenging contaminated sites.
The landfill, which is not associated with the city of Pasco, operated from 1958 to 1993 on nearly 200 acres at the intersection of Kahlotus Road and Highway 12 just east of Pasco city limits
Most of the hazardous waste was put in the landfill from 1972 through 1975, when industrial wastes were accepted.
In an area called Zone A, 35,000 drums were buried. The 55-gallon drums contained solvents, paint sludges, cleaners and other hazardous industrial waste.
Groundwater contamination appears to show that previously intact drums there may be leaking. Sampling done in June 2017 found a 3-inch-thick layer of petroleum hydrocarbons, solvents and polycholrinated biphenyls, or PCBs, floating on the groundwater.
In addition, underground fire has been a problem.
A borehole was used to bring up charred waste in 2017 after elevated temperatures were noticed.
The proposed landfill cleanup plan focuses chiefly on Zone A, with the 30 agencies and companies that used or operated the landfill responsible for the work.
Fire precautions proposed
Ecology proposes digging up the drums — plus waste that likely came from a drum — and larger pieces of potentially combustible waste.
The waste would be sent offsite to another disposal area.
Zone A already has a soil vapor extraction system that would be used to capture and treat volatile organic compound vapors during the excavation. A high temperature treatment unit would be used to treat the contaminated vapors.
A temporary structure would be placed over the area to contain any hazardous emissions during the work.
Gases will be monitored, including for indications of continuing fire.
The underground temperatures in Zone A have dropped over the past six to nine months, said Erika Beresovoy of the Department of Ecology. But there are still some soil gas levels that may indicate pockets of smoldering fire, or they could remain from previous burning.
Intact drums will be placed in overpack drums to minimize hazardous vapors, which could be flammable. Foam suppressant may be used on drums that are breached.
Removal of the drum is expected to take about 15 months, if the plan is approved.
Some waste that is not considered contaminated and is not expected to impact groundwater could be reburied in Zone A with fill material. A high heat treatment is planned for the zone to destroy organic compounds.
If tests show the treatment is effective, a new cover would be installed.
Pasco meeting planned
The household and commercial waste buried elsewhere at the landfill from 1958 to 1993 would be left in place.
Gases from decomposing waste would continue to be collected and burned off by a flare.
Groundwater monitoring would continue across the landfill, and protective covers to keep animals and precipitation from reaching the waste would be maintained or improved.
Those responsible for the landfill work include such companies as 3M Co., BNSF Railway, Daimler Trucks Northwest, Georgia Pacific, DuPont , Weyerhauser and Boeing and such government agencies as Franklin County, the U.S. Air Force and the Bureau of Reclamation.
The landfill also had 5,000 drums of herbicide manufacturing waste buried there in the 1970s, in Zone B.
Those drums were dug up and sent offsite for incineration and disposal in 2002.
Bayer CropScience Inc, the company primarily responsible for that waste, will clean it up under a separate plan to be presented later.
A public meeting to discuss the proposed plan for the landfill is set for 6:30 p.m. Sept. 17 at Virgie Robinson Elementary School, 125 S. Wehe Ave., Pasco.
Public comments may be submitted through Oct. 3 to Charles.firstname.lastname@example.org or Charles Gruenenfelder, Department of Ecology, 4601 N. Monroe, Spokane, WA 99205.