(Reuters) - New Mexico has given its approval to resume operations at the nation’s only permanent nuclear waste disposal site after state inspectors found the facility safe to reopen for the first time since a radiation leak there nearly three years ago, officials said on Thursday.

However, it remained unclear how much longer it would take the U.S. Energy Department to complete its checklist of corrective actions inspectors have identified as necessary to resume waste burial at the site near the town of Carlsbad.

The Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico has been shut down indefinitely since February 2014, when a barrel of plutonium-contaminated debris entombed half a mile beneath the desert floor ruptured, spewing radiation that leaked to the surface.

The accident, in which 22 workers were exposed, ranked as the facility’s worst mishap since it opened in 1999.

The site, privately operated under contract for the U.S. Department of Energy, was built for the disposal of radioactive refuse generated for decades by the DOE’s network of nuclear weapons laboratories and development facilities.

Winning the state’s consent to resume operations at the facility was a key hurdle in efforts to reopen the site.

The New Mexico Environment Department’s resource protection division director, Kathryn Roberts, said in a letter to federal authorities last Friday her agency was “approving the resumption of normal operating status at WIPP.”

The state said its inspections took place over several visits to the site from August 2014 through this month.

Department of Energy inspectors have identified 21 issues that need to be resolved before the site can reopen. Once those corrections are made and validated, officials can set a date for resuming operations there, the department said.

Federal inspectors cited chronic lapses in safety procedures they said led to chemically incompatible materials, including organic kitty litter used as an absorbent, being packaged together in one of the waste drums sent to the disposal site from the Los Alamos National Laboratory near Santa Fe.

The mix of organic material and nitrate salts inside the barrel sparked a chemical reaction, causing a buildup of heat and gases that breached the container, DOE concluded in its report on the accident.

The U.S. Energy Department agreed in April 2015 to pay New Mexico $73 million as compensation for safety violations at the plant.