WASHINGTON — US officials knew of the potential for a catastrophic blowout of toxic waste water from an inactive gold mine, yet appeared to have only a cursory plan to deal with such an event in place when government contractors triggered a 3-million-gallon spill, according to internal documents released by the Environmental Protection Agency.
EPA released the documents after prodding from Associated Press and other media organizations. EPA and contract workers accidentally unleashed 3 million gallons of contaminated waste water Aug. 5 as they inspected the idled Gold King Mine near Silverton, Colo.
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. ‘‘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 subsequent action plan drafted in May also notes the potential for a blowout at the mine.
It was not clear what additional precautions were taken to prepare for such a release, and the EPA did not immediately respond to questions on the issue.
A 71-page safety plan for the site produced by Environmental Restoration included only a few lines describing steps to be taken in the event of a spill: Locate the source and stop the flow if it could be done safely, begin containment and recovery of the spilled materials, and alert downstream sanitary districts and drinking water systems as needed.
There are at least three ongoing inquiries into exactly how EPA triggered the disaster, which tainted rivers in Colorado, New Mexico, and Utah with lead, arsenic and other contaminants. The toxic plume traveled roughly 300 miles to Lake Powell on the Arizona-Utah border.
EPA says its water testing has shown that contamination levels have since been returning to pre-spill levels, though experts warn that the heavy metals have likely sunk and mixed with bottom sediments,, and could someday be stirred back up.
The documents do not include any account of what happened immediately before or after the spill.
The waste water flowed into a tributary of the Animas and San Juan rivers, turning them a sickly yellow-orange color.
Elected officials in affected states and elsewhere have been highly critical of the EPA’s initial response. Among the unanswered questions is why it took the agency nearly a day to inform local officials in downstream communities that rely on the rivers for drinking water.
Communication problems have persisted in the spill’s aftermath, according to US Representative Lamar Smith, a Texas Republican who chairs the House Science, Space, and Technology Committee.
‘‘Weeks after the spill, families and businesses who depend on the Animas River continue to deal with uncertainty and limited information,’’ Smith said Friday, as he called for the EPA’s administrator, Gina McCarthy, to appear before his committee at a hearing scheduled next month.
‘‘The EPA has an obligation to be forthcoming about what went wrong.’’
Much of the text in the documents released Friday was redacted by EPA officials.
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.
In the wake of the spill, it has typically taken days to get any detailed response from the agency, if at all.
Melissa Harrison, an EPA spokesman, said Saturday that the agency has been inundated with media inquiries and ‘‘worked diligently to respond to them.’’
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.’’
The St. Louis-based company bills itself as the largest provider of emergency services for the EPA and is the agency’s prime contractor across most of the nation.
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 spill’s aftermath has cost the EPA $3.7 million through Thursday, according to information provided by the agency.
To deal with the toxic water from the mine, which continues to flow out of the site, the EPA built a series of containment ponds so that contaminated sediments can settle out before the water enters a nearby creek that feeds into the Animas River.
The agency said more work was needed to make sure there are no additional reserves of tainted water inside Gold King that could lead to another surge of contamination. Those efforts will include the removal of any blockages inside the mine that are holding back water, according to the EPA.
That work is ongoing and no timetable has been provided for its completion.