DENVER (AP) – A $7 billion, decade-long cleanup has been completed at the Rocky Flats nuclear weapons plant, shut down in 1992 amid safety concerns and shifting defense priorities, the contractor running the effort declared Thursday.

Kaiser-Hill Co. said it was proud of finishing the removal of plutonium-tainted buildings and soil – “the largest, most complex environmental cleanup project in United States history.”

However, it could be months before parts of the site northwest of Denver are opened to the public as a wildlife refuge, because federal regulators must still certify it as safe.

The Energy Department has 90 days to formally accept the project and can ask Kaiser-Hill to address concerns.

After that, the Environmental Protection Agency and state officials must verify that the work meets various guidelines.

Rocky Flats made plutonium triggers for nuclear weapons until it was shut down after the end of the Cold War. The core plant, covering nearly 400 acres inside a 6,000-acre buffer zone, once contained 800 buildings with 3.5 million square feet of space.

More than 2,000 truckloads of waste from Rocky Flats was shipped to the Waste Isolation Pilot Plant near Carlsbad, N.M., and at least 1,900 containers of plutonium was shipped to the Savannah River Site in South Carolina, another nuclear facility.

Rep. Mark Udall, a Colorado Democrat, toured the Rocky Flats site Wednesday and said nothing is left. He said he was confident the site will be safe, but he acknowledged environmental groups and others have questioned how thorough the cleanup was. He said the site will be monitored for decades under Energy Department oversight.

“We are in sum much safer than we were, and I say that as someone who lives just three miles from the site,” he said.

Sen. Wayne Allard, a Republican, praised the project, calling Rocky Flats “the best example of a nuclear cleanup success story ever.”

“Eight years ago, when we began this journey, I was one of only a few individuals who believed it would be possible to accomplish so much so fast, and stay within budget as well,” he said in a statement.

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