CARLSBAD, N.M. (AP) — New air testing in the nation’s only underground nuclear repository showed no detectable radioactive contamination from a leak last month, the U.S. Department of Energy said Sunday.

Officials at the Waste Isolation Pilot Plant near Carlsbad said in a statement that the results came in as four more employees tested positive for low levels of radiation. The Energy Department earlier reported that 13 other workers were exposed, but they say all 17 aren’t likely to face any serious health effects and that there appears to be no danger aboveground.