More than 550 people were affected by the release, most of whom lived in the Swinomish Reservation and La Conner.
Hundreds reported symptoms of eye, throat and lung irritation, nausea, and fatigue, and 12 people sought medical attention.
Shell employees had deviated from procedures during maintenance which allowed for 700 pounds of pollutants to enter the air, according to the EPA.
Shell has also paid $420,000 fines to the Northwest Clean Air Agency and Washington Safety and Health Agency for violations of environmental and worker safety laws.
“We are glad to see the EPA take action to hold Shell Oil accountable for its violations of air pollution laws,” Swinomish Tribal Chairman Steve Edwards said in a press release.
Andrea E. Petrich, a spokesperson for the refinery, said in a prepared statement that “Shell has cooperated fully with the EPA on this matter and has addressed the issues identified by the EPA within this Consent Agreement. Shell puts the safety of our workers and the surrounding community first, and we are committed to learning from all incidents, and continuously improving.”
— This report was updated to include a statement from Shell.