UPDATE 1-U.S. EPA to block Pebble Mine copper/gold mine project in Alaska

(Adds details)

Jan 30 (Reuters) -

The U.S. Environmental Protection Agency plans to take steps on Tuesday to block Northern Dynasty Minerals Ltd's proposed Pebble copper and gold mining project in Alaska by preventing the company from storing mine waste in the state's vast watershed.

The move, which had been expected, would be the second in less than a week by President Joe Biden's administration against a proposed domestic source of copper, with officials increasingly calling for the protection of sensitive ecologies even if they contain metals needed for the green energy transition.

The proposed Pebble mine, which would tap one of the world's largest copper and gold deposits, would have "unacceptable and adverse effects on certain salmon fishery areas" in Alaska's Bristol Bay, the agency plans to announce on Tuesday in a step known as a final determination under the U.S. Clean Water Act.

Vancouver, British Colombia-based Northern Dynasty said it will comment after it has seen the EPA's final determination.

The EPA's move also would prevent future development of the Pebble deposit if this would cause the same or more harm to the environment as the existing mine plan.

The project has been through a roller coaster of regulations for the past 15 years. Former U.S. President

Barack Obama

opposed the project, and his successor

Donald Trump

ultimately did, too, after deciding it was too risky. Biden has long opposed the project and took steps upon

taking office

in 2021 to permanently protect Bristol Bay.

Environmentalists cheered the news. "We're thrilled to see the EPA fulfill it's commitment to the people of Alaska and to provide enduring protection for Bristol Bay, its economy, its salmon and its people from the dangerous and destructive Pebble Mine," said Bonnie Gestring of Earthworks, a conservation group.

Shares of Northern Dynasty fell 1.5% to close at C$0.32 ($0.2391) in Toronto.

($1 = 1.3384 Canadian dollars) (Reporting by Ernest Scheyder, Valerie Volcovici and Nichola Groom; Editing by Jonathan Oatis and David Gregorio)