WASHINGTON – The Obama administration has removed another hurdle for Shell to drill in Alaska’s Arctic waters — the second in as many days — changing the company’s air pollution limits so its drill ship can operate in the Chukchi Sea.

Shell told the Environmental Protection Agency in June that the company was able to meet overall air quality standards. But it said a set of generators on the drilling rig Noble Discoverer fell short of the specific requirements for nitrous oxide and ammonia emissions.

The EPA now has agreed to allow the drill ship to go ahead and operate in Arctic waters while the agency decides how to handle Shell’s request for a revised permit.

Shell praised the decision Friday as a reasonable accommodation that will let it get to work while still limiting its emissions.

The company said its exploratory drilling could begin within days. Shell is the first oil company attempting offshore drilling in the Alaska Arctic in two decades, and it’s hugely controversial.

Opponents warn of degradation to the relatively pristine environment and argue the company won’t be able to clean up a spill in water with floating ice. Shell sees huge potential for oil and has spent more than $4.5 billion on the effort.

The air pollution issue was the second defeat in a row for opponents of Shell’s plans. The Obama administration Thursday agreed to let Shell start drilling in the Arctic waters even though its oil spill containment barge isn’t ready to go, although the drilling can’t go so deep as to hit oil until the barge is certified.

Alaska Wilderness League executive director Cindy Shogan said Friday the EPA’s decision on the air pollution permit rewards Shell for failing to follow the rules.

“Today’s announcement that the Environmental Protection Agency has given Shell Oil an exemption to pollute in America’s Arctic Ocean is yet another sign from the Obama administration that they are putting the whims of a corporate giant over the future of one of our nation’s most valued natural treasures,” she said.

Environmental groups have sued over the EPA air quality permit, saying Shell’s fleet needs to be stopped from pumping thousands of tons of pollution into the Arctic skies. 

Shell has agreed to use the best available technology to minimize the impact. Shell spokesman Smith said Friday that despite the company’s best efforts at modifications the generators were “slightly over the allowable limits” for nitrous oxide and ammonia. 

“There was a consensus between Shell and the EPA that the best available control technology in the world does not exist to meet this specific emissions standard,” he said. 

EPA spokesman David Bloomgren said Friday that the agency plans to put out a compliance order with a new set of temporary air pollution emission limits for Shell. 

The order “ensures that Shell’s operations will meet congressionally mandated air quality standards under the Clean Air Act until the agency completes a full review of Shell’s application to revise the permit,” he said. “In fact, EPA expects the Discoverer’s overall emissions for this drilling season to be lower under the compliance order than the original permit allowed.” 

Bloomgren would not say how the EPA plans to change the nitrous oxide and ammonia emission requirements for Shell, nor would he provide any details on what EPA is planning. 

He said details will be available soon when the EPA issues the order to Shell.