An oil sheen that coated 8 miles of the Potomac River at its peak and killed 21 birds has been linked to a coolant leak at a Dominion Virginia Power facility, officials said on Friday.

U.S. Coast Guard Petty Officer David Marin said a lab confirmed that samples of the sheen taken in Roaches Run off the Potomac matched samples from an oil leak at Dominion’s Crystal City Substation located near a storm drain.'

Dominion spokesman Rob Richardson confirmed last week that 13,000 gallons of mineral oil spilled Jan. 24 from a transformer at a power substation in Crystal City, not far from Roaches Run. He said at the time that there was “no evidence” that that spill was related to the sheen in the Potomac.

On Friday, after initially saying Dominion would accept responsibliity if its own testing confirmed the Coast Guard findings, Richardson later emailed: We concur with their findings that the substance was transformer mineral oil and we accept responsibility.....We will move with all due haste to work with the agencies to ensure the remaining cleanup work is done."

The Coast Guard initially identified the various samples it collected in Roaches Run and the Potomac as “moderately weathered intermediate petroleum oil.” But further lab tests found the samples all came from a “common source,” a spokesman said, and matched the oil that had spilled at Dominion’s substation. Mineral oil, a distillate of petroleum, is used as a coolant for the company’s transformers.

Richardson said the company responded immediately to its Jan. 24 spill. The contractor that Dominion hired cleaned up “90 percent” of the oil and removed 200 tons of tainted soil surrounding the substation, the spokesman said.

Dominion also promptly notified the Virginia Department of Environmental Quality, according to the company spokesman. State inspectors monitored the cleanup and checked several outfalls afterward, Richardson said.

First reported Feb. 3, the oily sheen continued to ooze from an outfall into the Roaches Run Waterfowl Sanctuary as late as Sunday. Officials say that leak has now stopped, and no additional oil has been spotted in the last 24 hours. The rainbow-colored coating on the Potomac also continues to dissipate.

The sheen appeared as the snow that had blanketed the Washington, DC, region in late January began to melt. Officials initially suggested it could be oily runoff from streets and parking lots.

But Potomac Riverkeeper Dean Naujoks said he received a tip linking the oil sheen to a spill at the Dominion facility. The Potomac Conservancy’s president, Hedrick Belin, also criticized the government agencies’ response as “tepid” and complained about a “lack of communication” over efforts to identify the source of the oil.

In addition to the 21 birds of three different species that have died from contact with the oil sheen, another 32 birds are being treated and cleaned by a nonprofit wildlife rehabilitation service, Tri-State Bird Rescue & Research of Newark, DE. The surviving birds are expected to be returned to the wild within a week, Marin said.

The Virginia Department of Environmental Quality and the Environmental Protection Agency will take over the spill response, Marin said, including any actions that might be taken against the source. The cleanup was funded by the Coast Guard’s National Pollution Funds Center and has so far cost less than the $250,000 that was authorized from that fund. Marin said the responsible party will have to reimburse that fund for the money spent in response to the sheen.