The Delaware Department of Natural Resources and Environmental Control reported the release on Monday morning of more than 100 pounds of sulfur dioxide from the Delaware City Refining Co. site of PBF Energy.
The release took place during a flaring event. Flaring typically occurs when the refinery system needs to reduce pressures, due to an equipment failure or some other cause.
The incident follows a similar incident less than a week earlier.
The refinery had a power failure during the late January blizzard that led to toxic releases. No injuries were reported.
The temporary shutdown caused by the power failure and current market conditions led PBF to move up a scheduled maintenance turnaround of the refinery.
The region and nation are seeing large inventories of crude oil and refined products. That has driven down prices and led some refineries to cut production.
