The origin of the oil spill in the Potomac River has been linked to a common source, the U.S. Coast Guard said at a press conference Friday.

What that source is, however, has yet to be confirmed. Since last week, the Coast Guard has been taking samples of oil from different parts of the spill, including four near Gravelly Point and Roaches Run Waterfowl Sanctuary, just north of Reagan National Airport.

“Each one of those samples originated from the same source,” U.S. Coast Guard Commander Michael Keane said this afternoon.

The samples were taken in proximity to a substation owned by Dominion Virginia Power, where a spill of mineral oil occurred last month.

“Dominion has been cooperative and providing samples,” said Keane, without saying that the power company is at fault. As of Friday evening, there has been no sign of additional oil sheening or affected wildlife in the area for the past 24 hours.

In a statement on Friday afternoon, Dominion said it had yet to review the the Coast Guard’s findings but is already conducting an additional study. “We will accept full responsibility should all test results show that the mineral oil from our substation reached Roaches Run and the Potomac River,” the statement said.

Keane also provided an updated figure on the wildlife affected from the spill. The current count has 21 birds dead and 32 currently in treatment, with plans to release the living animals sometime next week.

Photo by Tri-State Bird Rescue & Research, Inc