CARLSBAD, N.M. (AP) — State environmental regulators have cleared the way for work to continue on a multimillion-dollar ventilation shaft at the federal government’s underground nuclear waste repository in southern New Mexico.

Ventilation has been an issue since 2014, when a radiation release contaminated parts of the Waste Isolation Pilot Plant and forced an expensive, nearly three-year closure, delayed the federal government’s cleanup program and prompted policy changes at national laboratories and defense-related sites across the U.S.

In the notice of approval, New Mexico Environment Secretary James Kenney said more airflow was needed for the repository to achieve its mission.

Donavan Mager, a spokesman for Nuclear Waste Partnership — the contractor that manages the facility — said it was unclear when construction would resume.

Subcontractor Harrison Western-Shaft Sinkers was awarded a $75 million contract to build the shaft in 2019. When complete, it will reach a depth of about 2,275 feet (693 meters) and will include two access drifts to connect the shaft with the rest of the WIPP underground.

The project saw intense criticism from environmental and government watchdog groups that argued it was part of a larger plan to expand the repository beyond its presently permitted mission, which allows for disposal of 6.2 million cubic feet of waste. Officials have said it would take congressional action to increase the volume of waste permitted at WIPP…

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