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The Valero refinery in Benicia, CA.

The Valero refinery in Benicia, CA, released more than 74,000 pounds of sulfur dioxide during 14 days of flaring after a power outage in May, according to a new report the company filed with the state.

“A huge amount of sulfur dioxide was emitted,” said Anthony Wexler, director of the Air Quality Research Center at UC Davis, who reviewed the Valero report.

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The data were submitted to the California Office of Emergency Services last week. They will be a part of at least one of the three investigations into the refinery malfunction that led to an increase in the state’s gasoline prices and has prompted Benicia city leaders to consider increasing their oversight of the refinery and improve how they communicate with residents about emergencies.

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Nearly half of the sulfur dioxide the refinery released — 31,000 pounds — was emitted on May 5, the day the plant went offline and began flaring after the outage. That was also the day authorities imposed shelter-in-place and evacuation orders for parts of the city and at least a dozen people sought medical treatment for breathing difficulties.

“The fact that it was emitted over a short period of time in some ways makes it worse,” Wexler said. “That would have a much larger health impact.”

The Valero refinery released nearly 25,000 pounds of sulfur dioxide on May 6 and 7, the company’s report said. On May 14, it released close to 8,000 pounds of the gas, the company’s report said.

To put those numbers in perspective, air district statistics show the Valero refinery released an estimated total of 13,800 pounds of sulfur dioxide in 2016 and 15,400 pounds in 2015 through flaring. From 2004 through 2016, flaring releases have ranged from a low of 13,400 in 2009 to a high of 277,000 pounds in 2008. The facility’s average annual sulfur dioxide flaring release during the period was 76,000 pounds.

In its report, Valero said the refinery also emitted 350 pounds of carbonyl sulfide, a highly toxic and extremely flammable gas, between May 12 and May 15.

Valero’s report said its monitoring did not show an increase in ambient sulfur dioxide levels outside the refinery site, a sprawling facility at the northern end of the Benicia-Martinez Bridge. The company said exposure to the gas was limited to “persons solely within the site or sites on which the facility is located.”

The document did not give details about the hour-to-hour release of sulfur dioxide or the concentration of the gas at the refinery during the episode. The report also did not indicate whether workers at the facility were treated for exposure.

The report covers the refinery’s releases through May 18, but the facility had trouble restarting even after that.

At the end of May, local air regulators opened a new investigation into the facility after it sent another round of black smoke and toxic gas into the air.

The last releases took place on June 1, according to reports posted on a hazardous materials database managed by the California Office of Emergency Services.

Last week, a Valero official said the refinery had finally restarted and for the first time explained what was behind the weeks-long flaring.

“Due to the abrupt nature of the emergency shutdown, the refinery was unable to go through the systematic process we follow for planned shutdowns that allows the refinery to minimize emissions during shutdown and restart,” company spokeswoman Lillian Riojas said in an email on Thursday.

The oil company continues to blame PG&E for the outage.

The San Francisco-based utility has said the electrical failure was triggered by an “inadvertent operation” to protect power circuits. PG&E has hired a third party engineering firm, Exponent, to review the cause.

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