Here is the Department of Energy's official statement on the incident [PDF].
Snip: "DOE emphasizes there is no danger to human health or the environment. WIPP’s system of air monitors and protective filtration system continue to function as designed. The source of the airborne radiation is still being investigated."
A spokesman said the incident "looked like the first real alarm since the plant opened in 1999." At the Waste Isolation Pilot Plant (WIPP), federal officials are testing for radiation in air samples at the site "where radioactive waste, such as plutonium used in defense research and nuclear weapon making, is dumped half a mile below ground in an ancient salt formation." [Reuters].
Local coverage at the Carlsbad Current-Argus.