The Alaska District Court ruled in favour in October of the US Environmental Protection Agency's request to remand and vacate its 2019 withdrawal of a 2014 proposed CWA determination. 

The Obama-era decision had effectively vetoed Pebble, with the 2019 withdrawal seeing the project make progress, however the project has since been set back by a negative record of decision from the US Army Corp of Engineers 12 months ago and the EPA's recent move.

The EPA was required to make a recommended determination within 30 days of a public hearing but said last month it was able to extend the timeline to May 31, 2022, to consider "the substantial volume of new information" since the 2014 decision.

"Today's announcement underscores EPA's commitment to making science-based decisions to protect our natural environment, prevent pollution, and protect a sustainable future for all Americans," EPA Region 10 acting regional administrator Michelle Pirzadeh said at the time.

Northern Dynasty president and CEO Ron Thiessen said the company was pleased the EPA had established a timetable, suggesting they intended to comply with regulations and not attempt to "regulate by inaction".

"While it is not yet known what action, if any, the EPA will finally take, we are cautiously optimistic about their commitment to consider new information that has become available since the 2014 Proposed Determination and to make science-based decisions," he said.

The company released a preliminary economic assessment for the large-scale polymetallic project in September, which put a US$6 billion price tag on a 20-year mine and outlined three expansion scenarios which could take mine life to 101 years.

"We echo recent comments from BHP and others that the global markets will need double the amount of copper in the next 30 years than it did in the past 30 years to facilitate a decarbonised economy," Thiessen said.

"The US has significant copper resources within its borders, all it needs to do is develop them."

Northern Dynasty shares (TSX: NDM) had spiked to C$1.45 in February but are now similar to 12 months ago at 49c, valuing it at $258 million (US$201 million).