Chevron says it has pinpointed what caused the rotten-egg stench that blanketed Richmond and San Pablo two weeks ago: a section of its flare system that had been shut down for maintenance instead leaked a mixture of hydrogen sulfide and ammonia into the air for roughly 42 hours. The company estimates about 33,900 pounds of hydrogen sulfide and 1,620 pounds of ammonia escaped before the release was stopped.
According to the Grandview Independent, the gas reached a part of the flare system that was out of service for scheduled upkeep, and the foul smell began spreading across Richmond and San Pablo the night of Oct. 22. Chevron has said it has since isolated the affected section after halting the release. Contra Costa County Supervisor John Gioia, who represents the area around the refinery, said the chemical release caused serious consequences for the community, including nausea, and that it affected residents across greater Richmond, El Cerrito, San Pablo and Pinole.
Readings Spiked Well Above State Health Guidelines
The Bay Area Air District's monitor on Seventh Street recorded a peak one-hour average above 200 parts per billion of hydrogen sulfide at 8 p.m. on Oct. 22 — nearly seven times the state's one-hour health guideline of 30 parts per billion, the same Grandview Independent report notes. Odor complaints had already begun rolling in to the Air District by 6:09 p.m. that Thursday, hours before Chevron's formal alert went out.
Chevron issued its Community Warning System alert at 12:19 a.m. that Friday, per a separate Grandview Independent report. That alert listed the release as beginning at 12:10 a.m., but the Air District said complaints and staff observations indicated it actually started hours earlier. Gioia criticized the hourslong gap between residents first reporting the smell and Chevron's eventual alert, and said the four-hour gap between odors being traced back to the refinery and the company's notification needed to be examined as part of the full investigation underway.
Fire Officials and Air District Disagreed on Severity
Chevron's alert shortly after midnight classified the incident as a lower-severity Level 1 event, but Contra Costa County fire officials determined it met the criteria for a Level 2 incident, according to Richmondside. The Hazardous Materials Program of the Contra Costa County Fire Protection District also reclassified the incident from Level 1 to Level 2, citing possible offsite health impacts to sensitive individuals, per the Grandview Independent's reporting. County fire officials have since required Chevron to submit a root-cause analysis, provide interim 30-day reports, and allow a county hazardous-materials engineer to take part in the company's own investigation.
Chevron's 72-hour report attributed the leak to hydrogen sulfide and ammonia seeping into a flare-system section that had been shut down and isolated for scheduled maintenance, the site's reporting states. The company said hydrogen sulfide readings returned to typical levels around 4 a.m. that Friday and that the smell had dissipated by Friday morning. The Bay Area Air District issued Chevron a notice of violation for public nuisance on Oct. 26, and both the company's and the Air District's investigations remain ongoing.
A Refinery With a Long Flaring History
The Richmond refinery, which SFGATE describes as Northern California's largest fuel refinery, sits on 2,900 acres along San Francisco Bay. Flaring incidents there are not new: the site's own past reporting, drawn from Bay Area Air District records, found Chevron had reported flaring episodes almost every day for nearly six years. Between 2019 and 2022, the five main Bay Area fuel refineries reported 161 flaring events that exceeded Air District emission limits, with more than half of those logged by Chevron in Richmond, and the outlet calculated that Chevron averaged two sizable flaring events per month over that stretch.
The pattern echoes earlier incidents. A November 2023 flaring episode followed a power failure at the refinery's hydrogen plant and continued past 11 p.m., the same explainer notes. Nearly a decade earlier, a 2017 KQED investigation found that elevated hydrogen sulfide concentrations at Point Richmond preceded mysterious odor reports in San Francisco on two occasions, with one monitor recording 451 parts per billion at 12:45 a.m. after the first incident — and it took Chevron 13 hours to notify local emergency agencies about those readings.
How Residents Can Get Alerts
Contra Costa County residents can opt into Level 1 text alerts from the county's Community Warning System by texting CCHEALTH to 21423, according to Contra Costa Health. The county describes Level 1 alerts as covering non-emergency events, including minor hazardous-materials releases and refinery flaring that lasts more than 20 minutes.
