He’s always been suspicious of the steam he sees billowing from the petroleum manufacturer’s stacks. A tightly regulated soup of chemicals is in that vapor, released into the air from the factory below to keep the right balance of volatile substances Valero uses to manufacture gasoline, diesel and jet fuel. Strict rules are meant to keep pollution levels low.

So when Soto first learned this year that one of Valero’s vents had been releasing unlawful amounts of toxic gases for 16 years without detection — including cancer-causing benzene — his first reaction was: “Wow, these guys got caught.”

Then he got mad.

“My grandkids’ baseball team uniform has a Valero patch on the left arm, yet they’re polluting the air that these kids breathe,” Soto said. “It’s that type of hypocrisy.”

Emissions ‘surprise’

From 2003 to 2019, one of Valero’s hydrogen stacks released an estimated average of 4,000 pounds of hydrocarbons each day — more than 266 times the 15-pound limit, according to the Bay Area Air Quality Management District.

The revelation stirred outrage, not only for Valero but toward the district for failing to detect the problem. Even more, some city leaders and residents are irked by the district’s failure to alert the public when it discovered the extent of the violations in 2019. Instead, the district waited three years.

Valero has described the excessive emissions as “a surprise” in a statement to the air district. A company spokesperson declined to answer questions from The Chronicle and referred a reporter to recordings of public meetings.

The district initially defended its silence, saying it was necessary to protect the investigation and its ability to work with Valero to address a complex problem. Today, agency officials admit it was a mistake and find themselves facing the same credibility challenges as the company they’re tasked with overseeing.

“There’s a fair amount of egg in the face of the air district,” said Vice Mayor Tom Campbell. “That’s their job: to protect us citizens from what’s in the air. And they just totally blew it.”

Mayor Steve Young said the explanation that air district officials gave the city for the agency’s silence is that public disclosure could have made it more difficult for regulators to get the company to quickly agree to fixes.

“I don’t understand the logic there,” said Young, who is leading an effort to revise city campaign laws because of Valero’s outsize spending on local elections. “They failed in their obligation to keep everybody informed.”

The district said the potential impact to people may have been minimal because of favorable weather conditions. Benzene is a carcinogen, and long-term exposure carries risks. The district calculated the risk from Valero’s excess emissions over those 16 years as 3 chances in 1 million for developing cancer.

But the risks may add up. The region around Benicia is home to four of the state’s 14 working oil refineries. They belong to Chevron Corp. in Richmond, PBF Energy Inc. in Martinez, Phillips 66 Co. in Rodeo and Valero, a $38 billion company based in San Antonio. Those facilities can produce more than 660,000 barrels of crude oil each day, which is nearly 40% of all crude oil refined in the state, according to the California Energy Commission.

Damian Breen, the air district’s senior deputy executive officer of operations, said his agency notified Solano County health officials and the U.S. Environmental Protection Agency when it learned of the emissions and was focused on verifying the data and negotiating a response with Valero. He said not alerting the public was a mistake and that going forward the district will immediately bring these types of violations before a public hearing board.

“We should have done better, and we should have done better sooner,” Breen said.

‘How did this happen?’

Some remain skeptical about the explanations officials have provided for how such emissions could go undetected for so long in a state with some of the toughest pollution controls in the country.

“I don’t know how a regulator can see a stack with steam historically over 16 years and not want to know what it’s doing,” said artist Marilyn Bardet, a painter who became an environmental activist after moving to Benicia more than three decades ago. “Valero has been sampling it for impurities, then why didn’t it wonder what the heck might those impurities be?”

Air district staff visit these facilities every day for emissions tests and other analyses. In Benicia, a local residents advisory group and city leaders meet regularly with company officials. The EPA tracks emissions data reported by refineries. The Benicia Fire Department also has air monitoring devices.

Washington, D.C., nonprofit Environmental Integrity Project tracks benzene emissions reports using EPA data taken from pollution monitors affixed to refinery fences. Executive Director Eric Schaeffer said data is imperfect because most stacks soar high above fences.

“If they found out the company knew and was knowingly falsely reporting their emissions, depending on the circumstances, that’s criminal liability,” Schaeffer said.

Valero, which operates 15 petroleum facilities in the U.S., Canada and the United Kingdom, has said it discovered the emissions issue at its Benicia refinery after receiving an inquiry from the air district about hydrogen vents.

The district made the inquiry in 2018 after another local refinery, Phillips 66, came forward to report excess impurities in steam emitted from a hydrogen vent, officials said. The district then sent an enforcement letter to the Bay Area’s three other oil refineries requesting information about hydrogen releases.

Valero provided data to the district in 2019 that revealed samples taken since 2003 contained large amounts of toxic substances potentially harmful to people, including benzene, toluene, ethylbenzene and xylene. The company said it was unaware that type of vent must be monitored under pollution laws, according to its filings with the district. Just one plant can have hundreds of emissions points, including storage tanks and other equipment, that require regular reporting to environmental regulators.

Valero said it embarked on a series of projects to limit releases in 2019. By May 2020, the facility had slashed those emissions by 71%, and today it reports the amount of pollutants have plummeted 98% from the peak.

The amount still exceeds lawful limits, and the air district ratified an agreement this month with Valero to require further reductions over time, a process company officials say could take years to implement because it will require temporarily shutting down the entire facility, which the company does about every five years for maintenance.

Megan Berge, a lawyer for the company, urged members of the district’s hearing board to approve the plan during a virtual March 15 meeting, saying the proposal “achieves compliance, protects the community, holds Valero accountable.” The board approved it.

Both Bardet and Soto spoke up at that meeting to demand the district do more to track air pollution in Benicia. Soto urged the district to impose large fines against Valero “to show them that you can’t get away with excessive pollution of an exponentially dangerous level.”

Just this month, Soto retired after nearly a decade working as an organizer with Communities for a Better Environment in Richmond. The jazz saxophonist is now focusing more on his music, teaching and playing gigs. He compares playing jazz to community organizing. Both require method, strategy and focus.

“People don’t really think it’s a problem until they have a health issue, their kid has asthma or they get cancer or the myriad other diseases,” Soto said. “Then they get focused on dealing with that rather than asking: How did this happen? Where did this start? And who is responsible?”

Breen said the district is not finished investigating Valero’s failures and is still considering what kinds of fines to levy against the company. It has referred the case to the EPA’s enforcement division. The district is planning to install more pollution monitors in Benicia this year.

Valero “had the data, they had the information, they simply didn’t come forward and report it,” Breen said. “And more importantly, they didn’t take care of that emission source.”

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Julie Johnson (she/her) is a San Francisco Chronicle staff writer. Email: julie.johnson@sfchronicle.com Twitter: @juliejohnson