The nation's only underground nuclear waste repository, located approximately 193 miles from Lubbock, continues its investigation into why a radiation sensor alarm was activated Friday night. Yesterday, an independent monitoring center said  it found radioactive isotopes in an air sensor about a half mile from the southeastern New Mexico plant 26 miles east of Carlsbad.

The Waste Isolation Pilot Plant’s history is relatively short, as it became operational in 1999. The facility is used to store waste left over from nuclear weapons research and testing operations. Project facilities include disposal rooms mined 2,150 feet underground in a 2,000 square foot thick salt formation.

A filter from a monitor northwest of the Waste Isolation Pilot Plant in Carlsbad had trace amounts of americium and plutonium, said Russell Hardy, director of the Carlsbad Environmental Monitoring and Research Center.

The levels are the highest ever detected at or around the site, but are far below those deemed unsafe by the Environmental Protection Agency, he said.

Hardy's readings come on the heels of a radiation alert that closed the plant to all non-essential personnel last weekend after an underground sensor detected airborne radiation.

Department of Energy officials have not released any further information.