RODEO -- County health workers continued to pump nitrogen and water into a ruptured tank at the ConocoPhillips refinery in Rodeo, and health concerns were easing.
The tank released an unknown amount of hydrogen sulfide Friday morning at the refinery located at 1380 San Pablo Ave., said Randy Sawyer, the county's chief environmental health and hazardous materials officer. Hydrodgen sulfide is not dangerous in low concentrations, but its offensive rotten-egg smell is strong and easily noticed, and can cause dizziness and nausea, Sawyer said.
The evening commute on Interstate 80 passed directly through the refinery, but the California Highway Patrol said there were no incidents.
The tank holds 1.5 million gallons of processed water.
The threshold for the gas becoming a health hazard is 30 parts per million, and the highest measurement in the area surrounding the crude-oil refinery was 1 part per million, recorded around noon, Sawyer said.
The county health agency said late Friday that the measurement was still between 5 and 10 parts per billion, with the higher levels located in the higher elevations of Crockett. The total was expected to remain the same into Saturday morning.
That total was down from the 17 parts per billion measurement taken about an hour after the leak.
Sawyer said the county monitored whether the smell was at a hazardous level throughout the commute, saying the odor can "smell bad, but that's it." If exposed to it too long, a person can become nauseous, he said.
The refinery also pumped diesel into the tank as a way to coat the top of the water and act as a cap preventing any more odors from escaping, Sawyer said.
The incident began about 7 a.m. when the tank ruptured. ConocoPhillips spokesman Rich Johnson said Friday afternoon that the cause of the rupture was still unknown, and that the investigation likely won't be finished for weeks.
County officials said they were notified about 45 minutes after the rupture and began testing throughout the nearby area for gas levels. They warned people with asthma or any other respiratory sensitivity to avoid the area.
Though emissions remained at what the county considers safe levels, the gas apparently caused people nearby to suffer burning eyes and nausea Friday morning.
Marie Shalz, of Hercules, said her children, ages 6 and 9, were swimming Friday morning at Crockett Pool when they first noticed the smell.
She said the children, swim coaches and mothers at the pool all began suffering burning eyes, dizziness and nausea.
"One mom had gone out for a walk," Shalz said, "and she came right back and said, 'My chest hurts, so I couldn't walk any more.'"
A coach at the pool then told everyone the county had declared a shelter-in-place -- about which she would have been mistaken -- and Shalz drove her children home, she said.
"Now we're out of that area, and I think my kids should be fine," she said. "But I want to know, should I take my kids to their doctor? Should we be worried about this? They seem fine to me but I don't know what they've been exposed to."
County officials said there is no reason to panic, but that anybody concerned about their health after smelling the gas should consult their physician.