It was an active dump for 22 years -- and a final resting place for 7 million cubic feet of radioactive waste.

On Thursday, Savannah River Site celebrated the end of an 18-year, $56 million project to formally close the 76-acre area that once served as the site's primary burial ground for low-level nuclear waste.

"Through hard work and cooperation with our regulators, smart solutions were put into action to reduce the risk to the community and the environment," said James Rispoli, the Department of Energy's assistant secretary for environmental management.

Known generically as the "Old Radioactive Waste Burial Ground," the site was used to dump clothing, tools, containers and other low-level wastes contaminated with radioactivity. The area was filled in 1974.

The closure plan completed this month included using grout seals to stabilize 22 underground solvent tanks, each with a capacity of about 25,000 gallons; demolition of three buildings; and the use of soil and impermeable liners to seal the area for good.

The remediation was completed in 2007, but final paperwork certifying the project as complete was transferred this month, Energy Department spokeswoman Fran Poda said, noting that the $56 million cost for the project was below the $75 million estimate.

Also on Thursday, Mr. Rispoli and other guests marked the start of normal operations at the site's interim salt waste processing facilities -- the Actinide Removal Process and the Modular Caustic Side Solvent Extraction Unit.

Removing salt waste, which fills about 90 percent of the tank space in the SRS tank farms, is a major step toward closing the site's 49 high-level waste tanks, which contain 36 million gallons of waste.

The two facilities, designed to decontaminate radioactive salt waste, completed a successful trial run in April and are part of a broader salt-decontamination system scheduled to start up in 2013.