Managers at the Environmental Protection Agency were aware of the possible risk for a catastrophic “blowout” at an abandoned mine that could release “large volumes” of wastewater laced with toxic metals, according to internal documents released late Friday.

EPA released the documents following weeks of prodding from news organizations like The Associated Press. EPA and contract workers accidentally unleashed 3 million gallons of contaminated wastewater on Aug. 5 as they inspected the idled Gold King Mine near Silverton, Colorado.

Among the documents is a June 2014 work order for a planned cleanup that noted that the old mine had not been accessible since 1995, when the entrance partially collapsed. The plan appears to have been produced by Environmental Restoration, a private contractor working for EPA.

"This condition has likely caused impounding of water behind the collapse," the report says. "ln addition, other collapses within the workings may have occurred creating additional water impounding conditions. Conditions may exist that could result in a blowout of the blockages and cause a release of large volumes of contaminated mine waters and sediment from inside the mine, which contain concentrated heavy metals."

A May 2015 action plane for the mine also notes the potential for a blowout. There are at least three current investigations into exactly how EPA triggered the environmental disaster, which tainted rivers in Colorado, New Mexico and Utah with lead, arsenic and other contaminants. Water tests have shown the contamination levels have since fallen back to pre-spill levels. However, experts warn the heavy metals have likely sunk and mixed with bottom sediments that could someday stirred back up.

Officials in the affected states and elsewhere have slammed the agency’s initial response. Among the unanswered questions is why it took the EPA nearly a day to inform local officials in downstream communities that rely on the rivers for drinking water.

Much of the text in the documents released Friday was redacted by EPA officials, according to The Associated Press. Among the items blacked out is the line in a 2013 safety plan for the Gold King job that specifies whether workers were required to have phones that could work at the remote site, which is more than 11,000 feet up a mountain.

On its website, contractor Environmental Restoration posted a brief statement last week confirming its employees were present at the mine when the spill occurred. The company declined to provide more detail, saying that to do so would violate "contractual confidentiality obligations."

EPA spokeswoman Melissa Harrison said the agency has been inundated with media inquiries and worked diligently to respond to them. All information must go through a legal review, she added.

"I do not want people to think we put something out late at night to hide something," she said.

U.S. Rep. Lamar Smith, a Texas Republican who chairs the House Science Committee, said the EPA "has an obligation to be more forthcoming." He called for McCarthy to appear before his committee next month.

U.S. Sen. Cory Gardner, R-Colo., said it was unacceptable that the EPA did not prevent the accident when it knew of the massive quantities of contaminated water inside the mine.

The EPA has not yet provided a copy of its contact with the firm. On the March 2015 cost estimate for the work released Friday, the agency blacked out all the dollar figures.

The Associated Press contributed to this report.