A sulfur dioxide release was reported at 10:50 a.m. Monday at the Delaware City Refinery.
The Delaware Department of Natural Resources and Environmental Control reported the release of 672 pounds of the byproduct of the refining process.
The sulfur dioxide was released in a flaring incident that often occurs during a mechanical malfunction that forces the release as a way to relieve pressure.
The release remains under investigation. No cause for the flaring was listed.