ANACORTES, Wash. (AP) — The Northwest Clean Air Agency issued Tuesday a violation notice against the Shell Puget Sound Refinery for the release of emissions in August and September.

The refinery, on March Point near Anacortes, may face a financial penalty because of the incidents, which impacted the surrounding community including the Swinomish Indian Tribal Community, the Skagit Valley Herald reported.

The notice said two flaring events exceeded allowable, visible emissions for more than 5 minutes. The first occurred on Aug. 19, and the second on Sept. 29. The air agency received 12 complaints and verified the presence of odors following the Sept. 29 incident, according to a news release.

The refinery has until April 28 to respond to the alleged violations. The air agency will then decide its response, including imposing a penalty.

An investigation of the Sept. 29 incident found the incident was related to the failure of a unit that breaks apart hydrocarbons to make products such as gasoline.

As a result of the equipment failure, sulfur and other materials entered the flare system where they were combusted and released into the air, the agency said. During that time, area residents reported and photographed black smoke emerging from the refinery flare release.

The incident was similar to a Shell refinery flare release in February 2015 that led to hospitalizations for some community members who were exposed to the tainted air. The Northwest Clean Air Agency fined Shell $133,000 for that incident.

The U.S. Environmental Protection Agency also issued a $191,000 fine, in February, for that 2015 incident.