The Bay Area Air Quality Management District has issued four notices of violation to the Martinez Refining Company over a flaring event on Sunday afternoon that MRC initially said was just a grass fire.

At 4:26 p.m. on Dec. 17, air district officials received a Contra Costa County Community Warning System (CWS) Level 1 alert filed by MRC regarding a grass fire.

The district said the alert specifically stated that the smoke was from a grass fire and did not mention flaring directly. The district said on social media that when its staff contacted MRC to discuss the CWS Level 1 alert, MRC they said the grass fire was caused by “the heat of the flare.”

Air district incident response staff contacted MRC at 5:21 p.m. and were told the grass fire started at about 4:20 p.m. and was extinguished at approximately 5:10 p.m. Two district staff members went to Martinez to investigate.

The district said it received five complaints about smoke and/or odor between 4:30 p.m. And 5:07 p.m. It said, based on the smoke plume observed, district staff questioned MRC staff on a grass fire being the sole cause. The district said an MRC representative told staff it was a grass fire.

Personnel from the air district, the Contra Costa County Hazardous Materials division and Contra Costa County Fire Protection District returned to MRC on Monday morning to investigate the previous day’s event.

The district said the investigation is ongoing, but as of Monday afternoon it issued violation notices for public nuisance, visible emissions standard exceeded, federal visible emissions standard exceeded, and illegal fire on a no-burn day.

MRC said on social media Monday that the fire was related to the refinery restarting equipment related to a flaring incident caused by an “operational incident” Friday.

“At approximately 4:30 p.m. On December 17, a ground flare was in operation as part of the re-start process that caused visible black smoke and a brush fire.”

MRC said the brush fire was promptly contained, and extinguished by 5 p.m.

“All appropriate agencies were notified, and we thank our responders for their safe, effective response. We apologize for the concerns we caused the community and will be conducting a root cause analysis of the incident.”

MRC also said there could be more “intermittent flaring to last through most of this week; however, we are working hard to minimize flaring and to maintain clean combustion for any flaring that may occur.”