Duke Energy is scrambling to contain another major river spill—this time, of about 5,000 gallons of diesel.

The company on Tuesday reported that the discharge of diesel oil #2 into the Ohio River inadvertently occurred at about 11:15 p.m. during a routine transfer of fuel oil used for boiler ignition sources at the W.C. Beckjord Station in Ohio. The release was stopped by 11:30 p.m.

Duke Energy spokesperson Sally Thelen told POWERnews that the company has initiated an investigation to determine why the spill occurred. The spill happened on the banks of river as crews were transferring the fuel oil from larger holding tanks to smaller tanks.That is daily process, Thelen said. No incidents to that scale have been recorded onsite before, she confirmed.

The incident prompted the U.S. Coast Guard to close a 15-mile stretch of the Ohio River, a 981-mile-long waterway that streams westward from Pennsylvania to Illinois. The river was reopened to vessel traffic on Wednesday. Drinking water intakes have also been reopened in the Greater Cincinnati area and Northern Kentucky.

The company reportedly quickly mobilized resources to respond to the spill, including three vessels on the river deploying about 2,000 feet of oil-containment booms, skimmers, and vacuums to help contain and collect the oil. The Coast Guard, the Ohio Environmental Protection Agency, the Kentucky Department of Environmental Protection, and Piece Township (Ohio) are also engaged in cleanup efforts.

According to the U.S. Environmental Protection Agency (EPA), heavy rains on Tuesday washed oil from the river banks into six collection points along the river between New Richmond, Ohio, and the Interstate 471 bridge. As of Wednesday (Aug. 20), about 1,000 gallons of diesel and contaminated water have been recovered.  “Most of the sheen between New Richmond and Cincinnati has dissipated, but sheen is still visible on the Cincinnati side of the river,” the agency reported. It also said that wildlife has been minimally impacted by the spill.

The 60-year-old Beckjord Station in Clermont County has six coal-fired units (all which will have been retired as of Jan. 2015) and four combustion turbine units that burn the #2 fuel oil. According to Duke Energy, the combustion turbines are used mostly for generating power during periods of high demand or emergency situations.

Duke Energy wholly owns Units 1 through 5 (Units 1 through 4 have already been retired) and 37.5% of Unit 6. The remainder is owned by Dayton Power and Light (50%) and American Electric Power (12.5%).

Duke Energy continues to clean up a coal ash spill in the Dan River that occurred six months ago at a power plant near Eden, N.C.

On Wednesday, acting on concerns about the safety of 32 other coal ash ponds across the state, North Carolina became the first U.S. state to pass a comprehensive coal ash bill.

The bill gives Duke Energy 15 years to remove coal ash at four coal-fired power plants. It also calls for the establishment of a new commission to determine how Duke should be required to deal with its remaining coal ash facilities.

Sonal Patel, associate editor (@POWERmagazine, @sonalcpatel)

Update (Aug. 22): Adds details on how spill occurred