In senate hearings on Tuesday republicans grilled Ken Kopocis, the White House nominee for assistant administrator to the EPA’s water office, over the sum.

The original purpose of the hearing was to consider Kopocis’ appointment which has been held up by senate republicans since he was nominated last year.

Under the Clean Water Act the EPA can prohibit mining operations where they would likely have “unacceptable adverse effects” on the environment, Seeking Alpha reports.

The EPA’s review, which looked at the mine’s potential impact on salmon ecosystems in Bristol Bay found that the Pebble Mine “would result in significant impacts on fish populations in streams surrounding the mine site.”

In a letter sent to Kopocis in June of this year, republican senators questioned the study’s purpose, claiming the “true focus in preparing the Assessment is to predetermine the fate of the Pebble Mine project.”

The letter further enquired as to why the EPA was “dedicating precious and scarce resources to speculation on potential mining impacts.”

The senators also quoted peer reviewers as saying the report contained “unfounded assumptions and faulty analyses.”

At Tuesday’s hearing a Louisiana republican senator called the EPA’s assessment “completely unnecessary,” the Daily Caller writes.

The companies behind the Pebble Partnership – Northern Dynasty Minerals (NYSE:NAK), Anglo American (LON:AAL) and Rio Tinto (NYSE:RIO) – have not yet put forward plans for the mine nor have they applied for a Clean Water Act permit.

The company says it is evaluating design options but some critics claim this has taken too long. Earlier this month Rep. Sen. Lisa Mukrowski, a self-proclaimed strong critic of the EPA, sent a letter to the partnership chastising the companies for drawing out the permitting process for nearly 10 years.

Mukrowski wrote that the delay has “created a vacuum that the EPA has now filled with not one, not two, but three hypothetical mine scenarios.”

If approved, the Pebble Mine would become the largest open pit copper and gold mine in the world. With a $1 billion price tag for annual operating costs, the partnership says the site would bring up to $180 million in annual taxes and royalties to the Alaskan state.