Management's lack of nuclear expertise and an eroded safety culture are to blame for the radiation leak that has contaminated 21 people in the U.S. state of New Mexico two months ago, the Department of Energy said Thursday. A 300-page report of the department listed poor management, ineffective maintenance and a lack of proper training and oversight at the underground dump before the radiation leak at the Waste Isolation Pilot Plant near Carlsbad in southeastern New Mexico in mid-February. The lengthy report also found that much of the operation taken by the management failed to meet standards for a nuclear facility. Investigators found the inadequate filtration system of the plant has allowed a small amount of radiation to seep into the surface after the underground leak happened in the dump. It took the crew 10 hours before taking emergency action such as sheltering employees, investigators said. It's yet unknown what caused the leak. A truck fire was reported at the underground site on Feb. 5 and prompted evacuations, but officials said the fire was in a different part of the site and did not seem related to the leak. Having located suspected source of contamination, officials said robots would be used to search the dump if it's deemed unsafe for humans to continue the recovery work.