Environmentalists are questioning the accuracy of data reported by the refineries as the Bay Area Air District prepares to revise its regulations.

The Vallejo Sun, by Gretchen Smail, Oct 23, 2025

BENICIA – Local air monitoring groups are questioning emissions data at local Bay Area refineries and asking the Bay Area Air District to more strictly regulate refineries by revising their rules around how they track and report emissions.

The Benicia Community Air Monitoring Program and the Phillips 66 Fenceline Working Group, which monitors emissions around the Phillips 66 refinery in Rodeo, presented their arguments to the air district during a meeting Tuesday attended by several environmental nonprofits, scientists, and former U.S. Environmental Protection Agency officials.

“Having accurate air monitoring is really important to us,” Maureen Brennan, a member of the Phillips 66 Fenceline Working Group, said at the meeting. “There are risks living near a refinery. We’re living next to a very explosive and fire-driven industry, and we live with daily uncertainty. Is it a big leak today, or just a small, daily oozing of gases? We need to know.”

The groups brought up a number of concerns, including how the refineries are measuring the chemicals and how spikes in emissions are flagged. They noted that community members approached them because they said they don’t trust that the numbers that the refineries are reporting are always accurate.

In Benicia, there’s been good reason to question the accuracy of the refinery’s reporting. Valero was fined $82 million last year for not reporting two decades of excess emissions from their Benicia refinery to the air district.

Gov. Gavin Newsom vetoed a bill last year that would’ve strengthened monitoring at the state level. But the Bay Area air district is set to revisit their rules around this issue, and the environmental groups said they hope to have a seat at the table to draft stricter regulations.

Measuring toxic emissions at refinery fencelines

The  environmental groups argued that refineries should be required to improve fenceline monitoring and reporting. Fenceline monitoring is when oil companies measure the chemicals in the air around the boundary of refineries to see if gases are leaking out into nearby areas called “fenceline communities.”

Reporting requirements vary by districts, but the groups argue that this data should be publicly available as soon as it’s captured.

Companies like Chevron and Phillips have been operating refineries in California since the late 1800s, and fenceline communities — which often skew Black and Latino — have long complained about the smells and health effects of living around those sites.

Before fenceline monitoring, communities were often left in the dark about what they were breathing, as agencies didn’t look into leaks until after residents complained of odors or flaring, when most of the chemicals had already dissipated.

Community activism around this issue has spanned decades. In August 1994, gases leaked for 16 days from the Rodeo refinery. Nearby Crockett residents experienced sore throats, nausea, and headaches. No alert was sent out, and the leaking unit was only shut down when a nearby plant complained their workers were getting sick.

The incident caused an uproar, and led to Crockett and Rodeo residents demanding that the company’s land use permit not be renewed unless it installed an air monitoring system at the refinery’s border.

Despite years of community engagement, the EPA didn’t pass a federal rule for fenceline monitoring until 2015, and it only required oil companies to measure one chemical, benzene.

California strengthened these requirements in 2017 and required refineries to install more comprehensive monitoring systems by 2020. But  regional air districts had to decide what chemicals to monitor, what thresholds to set, and if community notifications were needed.

In the Bay Area, talks to improve these systems happened earlier, due to a 2012 fire at the Chevron refinery in Richmond, which resulted in a five-hour shelter-in-place order and thousands of residents seeking medical treatment.

That led to the air district passing Rule 12-15 in 2016, which required the five refineries in the area to monitor for five hazardous chemicals — benzene, toluene, ethyl benzene, xylenes, and hydrogen sulfide — at the fenceline.

Residents can find all the refinery monitoring pages on the air district’s website.

Eric Stevenson, an advisor for the Benicia Community Air Monitoring Program and the former director of meteorology and measurement at the Bay Area air district, helped write Rule 12-15.

He said they wanted to institute the rule because air monitoring sites used to be stationed far away from refineries in order to track the overall air quality. But that meant that it wasn’t always obvious how bad the air quality was within the fenceline communities.

“The intent of Rule 12-15, specifically to fenceline monitoring, was to give the community an idea of what was crossing the refineries’ fence line and to hopefully have the refineries mitigate those emissions quickly and effectively,” Stevenson said. “The reason that that matters is that the residents living near these refineries were deeply concerned about their health impacts, and they wanted transparency.”

Limitations of fenceline monitoring technology

Stevenson explained that Rule 12-15 requires that refineries use open-path technology for monitoring. These systems work by shooting a long, straight beam of light along each side of the perimeter. If a gas crosses that lightpath, the refinery can determine what the chemical is and how much of it crosses the fenceline.

He added that different systems measure different chemicals, so it’s important for the fencelines to have a variety of them installed. “It’s all based on the type of light that’s emitted,” Stevenson said. Ultraviolet light detects chemicals like benzene and toluene, while infrared light looks at chemical families called alkanes, which includes gases like propane and hexane.

If these systems are well-maintained, Stevenson said they work well to detect chemicals. “But if you don’t operate the systems well, and if you don’t take the appropriate actions to ensure that the data is of high quality, then the value of those systems is degraded,” said Stevenson.

The air monitoring groups said during Tuesday’s meeting  that they’re concerned this is the case at several of the refineries.

They highlighted an issue with ozone detection at the Phillips 66 Rodeo refinery.

“Ozone is always present in the air, and it increases in the afternoon because it reacts to sunlight,” said Kathy Kerridge of the Benicia Community Air Monitoring Program.

Kerridge told the Vallejo Sun that the Benicia group moved one of their own air monitors into the backyard of someone who lived near the refinery in order to test for the chemical.

“Ours and the air district’s always showed the increase in ozone in the afternoon, and Phillips 66’s just shows it’s not being detected,” Kerridge said.

Jochen Stutz, a professor at UCLA’s Department of Atmospheric and Oceanic Sciences, works with the South Coast Air Quality Management District in Southern California on their own fenceline monitoring programs. He noted that a refinery in LA is also using UV light to measure ozone, but unlike the Bay Area, their data is consistent with the air district’s.

“This is part of the reason why the residents are very concerned about these systems,” Stutz said. “You should be able to measure ozone with these things, and if you can’t, then can you measure anything else?”

Stevenson also talked about an issue with data collection. The groups noticed that some of the refineries weren’t showing as many alkanes as they expected. So they brought the raw data to an outside expert, and found what’s called “background creep.” The alkanes are measured by comparing results to a “clean air” file, which isn’t supposed to have any traces of those gases in it. But they found the clean air files did have the gases, which threw off the results.

“If you’re saying that background doesn’t have any compound in it, and it actually does, when you take the next measurement and you compare it to that background, you’re not subtracting the actual pollution measurement from a zero,” Stevenson said.

As a result, Stevenson said, the system can begin to “forget” what clean air really is and report no pollution, even when the gases are still present.

Mike Davis, a former EPA regional laboratory director, brought up other concerns about Rule 12-15’s flagging rules. He noted that under the current rules, any reading that fluctuates over a certain amount — like a sudden, catastrophic leak — is held for review until the refinery verifies it.

“When these filters are applied to this real world event, most of the data would not be released to the public in real time,” Davis said.

Ultimately, Kerridge said they’d like the district to require refineries to be more accountable to the community. They asked for more access to raw data, for the refineries to monitor for more pollutants, and that the district set limits for how much pollution is allowed before the community is notified of an exceedance.

For comparison, air districts in the Central Valley and Southern California already require that refineries set pollution limits, publish quarterly data reports, and send out notifications if a threshold level is crossed.

Kerridge noted that all these provisions would have been required under state law if Newsom hadn’t vetoed SB 674.

The environmental groups said they also want the air district to more thoroughly vet the monitoring data from the refineries for accuracy, and continue to hold forums with the community to discuss fenceline data.

Joseph Lapka, the principal air quality specialist at the Bay Area Air District, said at Tuesday’s meeting that the air district is in the process of creating a survey to get community feedback on what matters the most to people when it comes to fenceline monitoring.

“I think that the fact that a facility can do these sort of things within the bounds of Rule 12-15 speaks not only to the current limitations of the rule, but also to the types of technical details and the level of detail that we need to think about when writing the new rule requirements,” he said.

The air district will be discussing fenceline monitoring and revising Rule 12-15 at a technical working group meeting on Oct. 29. The public is invited to attend.  [>> NOTE: The Air District’s recording and materials from the meeting are available in the link above at the bottom of the webpage.]