The rotten-egg smell that spread across Richmond, San Pablo and nearby towns on Thursday night, Oct. 22, came from the Chevron refinery, the Bay Area Air District said in an incident report released Friday.
Why it matters: Hydrogen sulfide at the district's Richmond 7th Street monitor peaked above 200 parts per billion at 7 p.m., more than six times California's one-hour health guideline of 30 ppb, and the exact source inside the refinery still hasn't been found.
What happened
- The Air District started getting complaints at 6:09 p.m. Thursday and had more than 130 as of its report.
- By about 8:30 p.m., staff traced the odor to the Castro Street and Richmond Parkway area. It was strongest at Vernon Avenue and 7th Street.
- At the 7th Street station, one-hour averages were above the 30 ppb guideline for six of the nine hours between 5 p.m. Thursday and 1 a.m. Friday. Chevron monitors also read above it from North Richmond to Atchison Village.
- Air District staff reached the refinery at 10:45 p.m. and, with Chevron staff, traced the odor to an area just downwind of the refinery flares.
- Levels were back to normal background at all monitors by 4 a.m. Friday.
The four-hour gap
Chevron sent a Level 1 Community Warning System alert at 12:19 a.m. Friday that listed the release time as 12:10 a.m. The Air District said complaints and its own staff observations suggest the release started hours earlier, on Thursday evening.
"I am very concerned about the four-hour gap between when the odors were traced to the refinery and when Chevron's CWS alert went out," Contra Costa County Supervisor John Gioia said, according to SFGATE. He said the release caused nausea for some residents in the greater Richmond area, including El Cerrito, San Pablo and Pinole.
What's next
The Air District says its investigation is ongoing and it will update the incident report. Real-time hydrogen sulfide readings are posted on the Air District website and on Chevron's fenceline monitoring site.