Two refinery components — a processing unit called a fluid coker, which heats up and "cracks" the thickest and heaviest components of crude oil, and a flue gas scrubber, which is supposed to remove fine particles before they're released from the facility's smokestacks — are under scrutiny in Solano County's probe.
They began malfunctioning on March 11, resulting in the release of sooty smoke from the refinery. The releases intensified two weeks later when the facility belched out a large amount of black soot, leading to elevated levels of particulate matter.
The smoke prompted county officials to issue a health advisory for those with respiratory problems. Refinery managers shut down the facility.
Valero's SEC filing came as the Benicia refinery began a gradual process of restarting after being offline for more than 40 days.
The resumption of operations at the facility coincided with a slow and very small drop in gas prices, after two months of increases. On March 24, the day Valero shutdown, the average cost of a gallon of unleaded gasoline in California was $3.49, according to AAA.
On May 7, as the Benicia refinery gradually got back online, the the average price was $4.10. On Tuesday, it had dipped slightly to $4.07.
Energy experts have said Valero's shutdown, coupled with other refinery problems in California and the high cost of crude oil globally, led to the state's recent gas price hikes, which are currently the subject of a state Energy Commission investigation.