JUNEAU (AP) — Federal officials are planning another trip to a reserve on Alaska’s North Slope to plug several old oil wells as winter weather settles in the area.

The Bureau of Land Management oversees the National Petroleum Reserve-Alaska, where it’s responsible for cleaning up 50 wells drilled by the Navy and the U.S. Geological Survey decades ago that could possibly leak. Stacie McIntosh, the BLM’s Arctic Office manager, said the work can only get done during the winter to protect the tundra’s permafrost.

“You have a short window of opportunity to do it and it’s very expensive,” McIntosh told Alaska’s Energy Desk. “For most of (the wells), they’re in a stable condition. A lot of them, though, just have plugs that rely on ice and other things down in the well bore. And as we know, there’s the potential to be deep thaw, etc., associated with climate change.”

Sixteen wells have been cleaned up so far, and the agency is looking to complete up to five more “in the near future,” said Nicole Hayes, BLM’s Legacy Wells project coordinator.

State officials are hoping this winter’s cleanup goes smoother than last winter.

The Alaska Oil and Gas Conservation Commission had sent BLM multiple violation notices for last winter’s cleanup, saying the agency didn’t follow proper procedures.

BLM officials said the incidents did not cause environmental damage.

Commission Chair Cathy Foerster said the state is confident the BLM will have more success plugging the wells this season.

“The AOGCC is optimistic that this season’s legacy well cleanup will go better than last year’s,” Foerster said. “We’re committed to working as cooperatively with the BLM as they will allow us to. We’re hopeful that they’ll be more successful this season in cleaning up the messes out there.”