A temporary engineered cover and 12 more inches of soil have been placed over a fire burning underground at the closed Pasco Sanitary Landfill.
The cover is part of a three-part plan the state Department of Ecology approved after requiring that the fire be put out promptly. It has burned since November.
It could take several weeks to completely extinguish the fire, said Brook Beeler, spokeswoman for the Department of Ecology.
The parties potentially liable for cleanup of the landfill submitted two plans to the state this spring and the state is requiring the more aggressive of the plans to be implemented.
The engineered cap, which includes a heavy plastic layer covered with dirt, should reduce the possibility of oxygen getting through cracks in the ground to feed the fire.
Starting June 23, carbon dioxide will be injected into the ground in low concentrations to displace any oxygen near the burn area, which is a common method of extinguishing underground fires, according to the state. The cap also will help trap the carbon dioxide and keep it underground.
Probes in the ground already are measuring heat in the area of the fire to give three-dimensional information on where it is burning. It has remained at a little more than 25 feet in diameter.
Additional monitoring networks will be added to measure the effectiveness of the temporary cover and carbon dioxide injection. The monitoring network also could provide information on how a vapor extraction system being used to vacuum contaminated air at an adjacent industrial site is influencing the fire.
The operation of the vapor extraction system was modified months ago to make sure gases are not sucked across the burning area to feed the fire.
The second cleanup plan, which was not adopted, called only for placing more soil over the fire and perhaps modifying the vapor extraction system.
The landfill is northeast of Pasco near the intersection of Kahlotus Road and Highway 12. Franklin County is the only local government named as a possible responsible party for the cleanup. Others on the list include businesses and federal government agencies.
The fire is burning in an area of the landfill where bales of household and other municipal waste and construction debris were buried before 1989.
The state is concerned that if the fire is allowed to continue to burn it would pose a potential threat to a part of the landfill where 35,000 drums of solvent and paint sludges, cleaners and other industrial waste are buried.
The closed landfill is a federal Superfund site.
The coalition of responsible parties also is required to install a fire monitoring network and develop a plan to minimize the potential for future underground fires.
-- Annette Cary: 509-582-1533; email@example.com; Twitter: @HanfordNews