DOVER, Del. (AP) -- State environmental officials on Wednesday were investigating an oil spill at a refinery that left a sheen floating on the Delaware River.
The refinery in Delaware City, operated by New Jersey-based PBF Energy Inc., reported the release about 1:30 a.m. Wednesday, about two hours after workers discovered oil in an effluent channel that discharges into the river.
Refinery officials said contractors deployed booms, absorbents and skimmers to contain the sheen.
"They have boomed the spill, which is good," said David Small, deputy secretary of the Department of Natural Resources and Environmental Control. "They have contained what they could see."
Small said the incident involved a leak in a heat exchanger that is part of the refinery's crude oil processing unit, and that a DNREC official was on his way to the refinery Wednesday.
DNRC spokesman Michael Globetti said the leak of what the refinery reported as "gas oil" caused a sheen measuring about 500 feet by 50 feet on the river.
A telephone message left for the refinery shift superintendent was not immediately returned Wednesday.
PBF spokesman Michael Karlovich said Wednesday afternoon that the leak involved less than 20 gallons of partially refined petroleum.
Karlovich said workers at the refinery discovered a problem about 11:10 p.m. Tuesday, and that the heat exchanger was quickly found and isolated as the source of the leak. Workers noticed oil in the effluent channel, which contains equipment to capture oil, about 11:30 p.m., he said.
"We discovered there was an issue in the refinery ... and then we had evidence that it went to the river later on, and that's when we called it in," Karlovich explained.
PBF bought the refinery in 2010 for $220 million after Valero Energy said it would halt operations there and lay off 550 workers.
Gov. Jack Markell's administration provided $20 million in incentives to PBF to restart the refinery and has supported the new crude oil transfer operation.
But state environmental groups have recently raised concerns about the potential harm a new crude oil transfer station at the refinery could cause.
However, Delaware's Coastal Zone Industrial Control Board last month dismissed a challenge filed by the Sierra Club and the Delaware Audubon Society to an air quality permit granted to PBF Energy in May.
The permit granted by state environmental secretary Collin O'Mara involves loading unrefined crude oil onto barges at Delaware City for shipment to another PBF refinery in Paulsboro, N.J. The barge loading operation is part of a larger transfer operation in which PBF brings crude oil by train from various sources, including tar sands oil from Canada, to a new rail loop it built near the refinery.
PBF has spent millions of dollars on the new rail facility and has said the crude oil transfer operation is critical to its long-term business strategy.
Last month, O'Mara issued more than half a million dollars in penalties against the Delaware City refinery for air pollution violations.
The order covers more than a dozen air quality violations since the 2011 restart of the refinery through January of this year.