The Delaware Department of Natural Resources and Environmental Control reported the release of 4,000 pounds of sulfur dioxide at Delaware City Refining Co.
The release was reported at 5:28 p.m. at the refinery on Wrangle Hill Road, Delaware City.
Sulfer dioxide, a byproduct of the refining process, is considered to be hazardous by the EPA.
A compressor issue led to flaring, a procedure used to relieve pressure. Refinery workers repaired and restarted the compressor.
Delaware City Refining Co. is owned by New Jersey-based PBF Energy.