In two letters dated Jan. 10, the Environmental Protection Agency issued notices of violation to Royal Dutch Shell (RDS.B) (RDS.A) outlining the corporation's lack of adherence to the Clean Air Act .

Through Shell-submitted data  and government inspections, the EPA determined that two of Shell's ships, the Discoverer and the Kulluk, discharged excessive amounts of nitrogen oxides over the 2012 drilling season .

The notices come just three days after Shell confirmed that the Kulluk, which had previously run aground on New Year's Eve, had reached a safe harbor to undergo a "thorough safety assessment ."

The EPA isn't the only entity eyeing Shell's arctic accidents. On Jan. 8, U.S. Secretary Ken Salazar announced a Department of the Interior expedited assessment of the 2012 arctic offshore drilling program to "review practices and identify challenges ." The review is directly linked to multiple Shell violations, and should be completed within 60 days .