The U.S. Department of Energy says more needs to be done to improve ventilation for workers at the federal government's underground nuclear waste dump in southern New Mexico.

The contractor that operates the Waste Isolation Pilot Plant has already acknowledged that air filters used to remove particles following a radiation leak in February have restricted the airflow in the underground working area.

The plant developed a plan for operating diesel equipment below ground, but Department of Energy assessors have determined that plan isn't enough to ensure safe conditions once the use of diesel equipment resumes.

The contractor, Nuclear Waste Partnership, and the Department of Energy's Carlsbad Field Office say they are seeking a consultant to help evaluate the ventilation needs and make recommendations.

They are also implementing an air-sampling program for diesel particulates and other gases.