Updated Thursday, 12:40 p.m.
Could a flaring incident at the Chevron refinery in Richmond on Tuesday be the source of a pungent odor that spread across parts of San Francisco hours later?
After more than 70 complaints of a "rotten egg" smell in San Francisco on Wednesday morning, local air regulators are trying to pinpoint its cause. The flaring incident is now a possible suspect.
"We are investigating the Chevron flaring incident ... to determine if it could be the potential source," said Bay Area Air Quality Management District spokeswoman Lisa Fasano late Wednesday.
Chevron did not initially report the flaring to Contra Costa County, but hours later acknowledged the incident.
On Wednesday, a Chevron representative refuted the idea that the refinery problem could be blamed for the smell on the other side of San Francisco Bay, more than 10 miles away.
"We experienced some minor flaring," Chevron spokeswoman Leah Casey said in an email. "Our initial investigation shows no connection between the flaring incident and the odors recently detected in San Francisco."
For the slim possibility that a chemical-like sulfur dioxide could have traveled in the air for such a long distance, the weather conditions would have to be just right.
The winds Tuesday night were gusting between 5 and 10 mph from the north-northeast to the south-southwest, according to Jan Null, a meteorologist with Golden Gate Weather Services.
"However, the distance is about 11 miles and it would have been very diluted," Null said in an email.
Another night, another incident, more odor complaints
Chevron had another flaring incident at its refinery Wednesday night. There was some sort of "process upset" at 7 p.m., according to a report the company filed with the Governor's Office of Emergency Services.
Chevron's Casey said Thursday morning that company officials and air district representatives were meeting to "understand if there is a connection to the source of the odor."
Hours after the new refinery incident, PG&E received another round of odor complaints in San Francisco. More than a dozen people around the city called the utility between 11 p.m. Wednesday and 1 a.m. Thursday, according to PG&E spokesman J.D. Guidi.
The city's Fire Department responded to seven calls overnight, according to that agency's spokesman, Jonathan Baxter.
The air district is investigating Chevron's second flaring incident, according to agency spokesman Ralph Borrmann.
"We are investigating all possible angles. No conclusions have been reached yet," Borrmann wrote in an email when asked if there might be ties to another round of smell complaints in San Francisco.
On Thursday the district revealed that it received "rotten egg" complaints in Richmond as well.
The agency is also looking into other potential sources that include ships, area landfills and wastewater treatment facilities, agency officials said in a statement.
But, preliminary data gathered from Chevron's fence line ground-level and nearby air quality monitors showed that sulfur was released during Chevron's first flaring incident.
Another odor culprit could be the West Contra Costa Sanitary Landfill, said Randy Sawyer, the county's chief environmental health and hazardous materials officer.
"There have been odor complaints the last few months coming from the landfill," Sawyer said in an email. "They have material that is composting and has turned anaerobic. This becomes very odorous."
Contra Costa County's environmental health department is working with the landfill to get the problem under control, Sawyer said.