Workers at the Department of Energy’s underground storage site for plutonium-contaminated waste have been cleared to return to work in portions of the mine shut down in February after high levels of non-nuclear airborne contamination were found in the facility’s northwestern and southern edges.

DOE announced the end of the safety pause in an online note published Monday. The suspension of operations at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, N.M. went into effect Feb. 22 after personnel with the agency’s prime contractor, Nuclear Waste Partnership, discovered unsafe levels of carbon monoxide and volatile organic compounds at the far edges of the underground transuranic waste facility.

Such stagnant air at WIPP is not unprecedented during the plant’s more than 15 years as an active nuclear-waste storage facility; Nuclear Waste Partnership has often pointed out that its tolerances for the sort of bad air that barred workers from some parts of the facility this year are far tighter than accepted industry standards for mines.

In its statement, DOE said “improvements have been made to procedures and processes to help ensure that workers entering low airflow areas with potential poor air quality continue to be adequately protected. Emphasis on increasing ventilation to low airflow work areas in advance of planned activities will ensure workers entering these areas have sufficient fresh air.”

Also, the notice said, “additional warning signs were placed in these known low airflow areas to reflect where continuous air monitoring and additional ventilation is required for entry.”

WIPP, designed to store contaminated equipment and material from across the DOE weapons complex, has been closed to new waste shipments since 2014 because of a radiation leak and unrelated underground fire. Energy Secretary Ernest Moniz said in congressional testimony last month the safety pause should not affect the agency’s plans to reopen WIPP to transuranic waste shipments in December.