ALBUQUERQUE, N.M.—The U.S. Department of Energy is planning a town hall Thursday to release more information on its efforts to recover from a radiation leak at the nation's only underground nuclear waste dump.

Questions about what caused the leak at the Waste Isolation Pilot Plant, the extent of the contamination and the future of the federal government's national nuclear cleanup efforts have been swirling for weeks now.

Some of the uncertainty was quelled late Wednesday when officials announced that the level particles being captured by monitoring stations in the Carlsbad area had decreased significantly and were close to normal. Also, further testing on the 13 workers who were at the plant at the time of the leak shows they aren't likely to experience any serious health effects.

Jose Franco, head of the DOE's Carlsbad Field Office, told the community in a letter that progress was being made.

"I want to assure you that we are working diligently to address your questions and concerns," he wrote. "We have not faced this kind of challenge in our 15-year history of waste operations, but I have the utmost confidence in the recovery team."

WIPP stopped taking shipments in early February when a truck hauling salt through the underground mine caught fire. Several workers were treated for smoke inhalation, and the mine was temporarily closed.

Nine days later, sensors alerted to a release of radiation from the underground portion of the mine. Monitors as far as half a mile away later detected elevated levels of plutonium and americium in the air.

The DOE, the U.S. Environmental Protection Agency and WIPP managers have all said there's no public health threat, but watchdog groups have questioned whether officials are holding back information related to the leak.

In hopes of finding out what may have happened underground, Franco said a specially trained team is preparing to enter the mine next week after air monitoring equipment is sent inside to gauge the level of contamination.