ANCHORAGE, Alaska (AP) — Royal Dutch Shell PLC can begin preparation work at exploratory drilling sites in the Chukchi Sea off Alaska’s northwest coast while it awaits certification for its oil spill response barge, Interior Secretary Ken Salazar announced Thursday.

“We are allowing certain limited preparatory activities that we know can be done in a safe manner,” he said in a teleconference with reporters.

The company was granted permission to starting digging with its drill ship, but only into the layer of the ocean bottom that’s above oil reservoirs. Shell can dig mud-line cellars, which will eventually hold and protect a well’s blowout preventer, down 40 feet into the seabed. The company is also authorized to drill narrow pilot holes down another 1,500 feet.

“These activities are essential safety steps that will allow for the installation and protection of the blowout preventer,” Salazar said.

The limited work will be conducted with Bureau of Safety and Environmental Enforcement safety experts present 24 hours a day, Salazar said. The decision followed exhaustive review of Shell drilling rigs and safety equipment including a capping stack that could be lowered onto a leaking well, Salazar said.

Shell remains prohibited from drilling deeper into petroleum-bearing formations until it meets other requirements, including Coast Guard certification of an oil spill response barge that remains in port in Seattle.

“That’s period, end of story,” Salazar said.

Federal regulators are requiring Shell to suspend drilling in the Chukchi 38 days before ice moves in, to make sure the company has time cope with a spill or a wellhead blowout. That means drilling would have to stop around Sept. 24, but Shell this month asked to extend that deadline for two weeks, saying new data indicates ice will not be a factor until mid-November.

Salazar said a decision on an extension is unnecessary until Shell completes work on its response barge.

Shell hopes to drill exploratory wells in both the Chukchi and Beaufort seas during this year’s open water season, which is rapidly drawing to a close.

“We don’t know what’s going to happen with Shell and whether they’re going to be able to complete a well this year,” Salazar said. “The situation remains dynamic.”

Shell Alaska spokesman Curtis Smith said by email that the company welcomed Salazar’s announcement.

“The administration’s decision to approve initial drilling into non-oil-bearing zones in the Chukchi Sea reflects the national importance of understanding the energy resource offshore Alaska,” he said.

Environment groups condemned the decision. Margaret Williams of World Wildlife Fund said technology does not exist to contain a spill in the extreme Arctic Ocean environment.

“This is one of the most productive marine areas in the world, supporting hundreds of species and thousands of people who depend on the sea’s bounty,” she said by email. “To drill in our Arctic Ocean is to gamble with its future.”