A tour last month of the 2,150-foot-deep mines carved in solid salt at the Energy Department’s Waste Isolation Pilot Plant near Carlsbad, N.M. Credit Michael Stravato for The New York Times
Almost two weeks after an unexplained puff of radioactive materials forced the closing of a salt mine in New Mexico that is used to bury nuclear bomb wastes, managers of the mine are planning to send workers back in and are telling nearby residents that their health is safe.
The Waste Isolation Pilot Plant, 28 miles east of Carlsbad, has been in operation for 15 years, burying wastes in an ancient salt bed deep beneath the desert, mostly without incident, and some experts have said that the site should be considered for additional kinds of nuclear waste.
But late on Feb. 14, at an hour when no one was in the mine, an air monitor indicated the presence of radioactive contamination. An automated system cut off most of the ventilation and routed the exhaust through filters that are supposed to capture 99.97 percent of all contamination, turning off fans and changing the air flow, in less than one minute.
This most likely minimized the contamination that reached the surface, according to the mine’s monitors, who were on hand to reassure anxious Carlsbad residents at a town-hall-style meeting Monday night. The monitors told the residents that there had been no health risk at all and that the radiation levels detected near the mine’s surface — far from town — were well below concern.
“For someone living in town, I would say the dose was probably zero,” Russell Hardy, director of the Carlsbad Environmental Monitoring and Research Center, an independent monitoring organization that is part of New Mexico State University, said in a telephone interview Tuesday. He said that the event would not add to background levels of radiation — including bomb fallout — any more than an eyedropper full of water would contribute to the rise in the level of the Pacific Ocean.
There was some small release of radiation, however. The Carlsbad research center registered the materials — plutonium and americium — on filter materials installed on air monitors in the surrounding desert. These filters must be collected and then dissolved in acid so the material they trapped can be analyzed. They can detect amounts far smaller than the device that registered the initial alarm, but the process takes many hours.
The materials registered on the surface are consistent with the material buried at the plant, but the quantities released are far below the levels at which the Environmental Protection Agency would recommend any action, officials said.
Even in the desert, the danger to humans was small, the mine’s operators said. The highest reading from the monitors indicated that a person could have inhaled radioactive material that would emit a dose, over the person’s lifetime, of 3.4 millirem, an amount roughly equal to three days of natural background radiation. But to get the dose, the person would have had to stand for hours in the desert, on the downwind side of the plant.
“The numbers are so low, we need really sensitive pieces of equipment that can detect these low numbers,” said Farok Sharif, the president and project manager for the contracting firm that operates the mine, the Nuclear Waste Partnership.
But the incident, whose cause will not be known until technicians can re-enter the area, has marred a close-to-perfect safety record at the plant, known by its acronym, WIPP. And it came a few days after a truck in the mine caught fire, although the events were said to be unrelated.
The Energy Department, which owns the repository, caught some criticism for the way it communicated the problems. “Information gaps can exacerbate fears and erode trust,” said Steven M. Becker, a professor in the College of Health Sciences at Old Dominion University, in Norfolk, Va., and an expert on communicating radiation risk. Managers have not said when technicians will re-enter the mine.
The plant accepts shipments from Energy Department laboratories and factories involved in nuclear weapons production. Some manufacturing plants from the Cold War era have been able to close because the repository accepted their waste. Officials have not said which sites packaged and shipped the materials that leaked.