SAN FRANCISCO (CBS SF) — The smell of rotten eggs that has perplexed residents in San Francisco and Richmond over the last two days could have come from a sulfur release during flaring incidents at the Chevron refinery in Richmond, according to the Bay Area Air Quality Management District.

The air district has gathered data at monitors surrounding the Chevron refinery indicating that there was sulfur released during a flaring incident on Monday.

However, air district investigators have not concluded it was the source of the smell and are looking into other possible factors, such as ships, landfills or wastewater treatment facilities.

PG&E has ruled out the possibility that the nearly 70 reports of sulfur smells received in San Francisco over the last two days were caused by a gas leak.

The utility advised residents to call them if they smell sulfur or rotten eggs because it might indicate a gas leak and received 54 reports of the odor on Wednesday morning and 15 more Thursday, PG&E spokeswoman Teresa Jimenez said.

The air district is continuing to gather data from monitoring stations and weather data to try to determine the smell’s source. In a statement, air district executive officer Jack Broadbent said the district will pursue any available enforcement actions once the source has been determined.

Despite the smell turning out to be non-hazardous so far, anyone who detects a similar odor is still encouraged to call 911 or report the odor to PG&E for investigation.

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