For 27 days between 2005 and 2009, the refinery improperly monitored certain gasses that were being sent to the plant's flares, air district spokesman Ralph Borrmann said.
Flares are a safety mechanism designed to release pressure in the refinery to prevent a possible explosion. The flares burn up hydrocarbons to reduce the amount of harmful pollution being released into the air.
Refineries are required to maintain flare minimization plans and to monitor the gasses being sent to the flares, Borrmann said.
During Chevron's 27 days of violations, certain gas lines were bypassing the monitoring equipment and material was being sent directly to the flare, Borrmann said.
Refinery spokeswoman Melissa Hollander said the violation, which was discovered in August 2009, was made inadvertently.
As soon as they knew about the violation, Chevron officials took the involved units out of operation and fixed the problem, Hollander said.
Borrmann confirmed that the refinery has reconfigured its equipment to comply with air district regulations.
As part of the regulatory process, Chevron videotapes all of the refinery's flaring activity. By analyzing the flares, scientists were able to determine that about 219 pounds of unmonitored sulfur dioxide was sent to the flares, which is below amounts that the refinery is required to report to regulatory agencies, Hollander said.
Although a $170,000 fine may not be much for a company that, according to recent reports, had a second quarter profit of $7.73 billion, 30.1 percent higher than the same quarter last year, Borrman said the enforcement process does not rely solely on fines to discourage air quality violations.
The air district has an inspector at the refinery every day and state law requires the refinery to monitor and report its emissions.
Hollander said the refinery is committed to reducing flaring at the plant. In 2010, she said, the refinery reduced its flaring by 96 percent compared to flaring activities between 2004 and 2007, and currently has the lowest flaring rate of any refinery in the Bay Area.