ANCHORAGE, Alaska -- Salvage crews expect to complete work today transferring thousands of gallons of diesel fuel from a tugboat that slammed into the same reef as the Exxon Valdez 20 years ago.

Once the fuel from the 136-foot Pathfinder is transferred to another vessel, the salvage team will have a good idea of how much diesel fuel spilled into Prince William sound.

A mile-long diesel sheen that spread across the sound was found to have escaped from a containment boom and was not the result of a new leak.

The boat is part of the Ship Escort Response Vessel System that was created after the Exxon Valdez ran aground in 1989.

Sen. Mark Begich of Alaska called it troubling that a spill response vessel "managed to run aground on one of the most well-marked and well-known reefs in the Northern Hemisphere."