The Environmental Protection Agency employee overseeing work at the Gold King Mine was aware of blowout danger at the site before a massive August wastewater spill, according to a report released Thursday.

The revelation, in findings by congressional Republicans, comes in contrast to the EPA’s claims that the risk was underestimated ahead of excavation at the mine’s collapsed opening. That work ultimately led to the disaster.

Hays Griswold, the agency’s on-scene coordinator, wrote in an October e-mail to other EPA officials that he personally knew the blockage “could be holding back a lot of water and I believe the others in the group knew as well.”

“This is why I was approaching (the mine) as if it were full,” he wrote of the day of the Aug. 5 release at the Gold King.

The note provides more indications the EPA probably had knowledge of the potentially looming disaster at the mine long before workers accidentally unleashed 3 million gallons of contaminants. The Oct. 28 e-mail came in response to an independent Bureau of Reclamation report about the spill released six days earlier.

Documents revealed by the EPA in the summer already showed blowout warnings predated the spill by more than a year.

An EPA internal review released three weeks after the spill, however, said operators believed water inside the Gold King was not very high because of draining at the site and based on seep levels above its opening. Those factors, officials said, made checking pressure seem unnecessary, and it was never done.

Griswold’s e-mail appears directly to contradict those findings and statements he made to The Denver Post in the days after the disaster, when he claimed “nobody expected (the acid water backed up in the mine) to be that high.”

The e-mail was provided Thursday to The Post and other news outlets as part of a 73-page investigation released by Republican members of the U.S. House Committee on Natural Resources into the event just outside the town of Silverton.

The wastewater spill sent at least 880,000 pounds of metals into the Animas River and cascading downstream through three states and two American Indian tribes.

“The fatal flaw in the whole plan,” Griswold wrote, was that when workers began removing the dirt and debris blocking the mine’s opening, they were operating too low. That opened up a wall of water that could not be stopped.

Griswold told The Post in August his crew’s main intention the day of the spill was to work on the adjacent Red and Bonita Mine and that they had just gone to investigate the Gold King.

Efforts to reach Griswold on Thursday were unsuccessful.

The Department of Interior’s independent report by its Bureau of Reclamation said the disaster could have been avoided if the EPA and its contractors used a drill to check wastewater levels inside the mine before digging with heavy machinery.

It also found the spill resulted from rushing with inadequate engineering know-how.

Republicans have been heavily critical of the EPA’s internal probe of the spill and the Interior’s report, raising questions about bias. The natural resources committee review came after its chairman, Rep. Rob Bishop, R-Utah, called for an investigation into the incident under his authority.

Bishop, who has long criticized the EPA, said the report by his committee confirms his worries about the previous Gold King inquiries.

“This report peels back one more layer in what many increasingly view as a pattern of deception on the part of EPA and DOI,” he said in a statement Thursday. “We will need heavier efforts to squeeze out the full truth. The agencies continue to withhold information requested by the committee.”

The resources committee report says the Interior, in particular, concealed mistakes by the EPA and has refused to provide key documents from their investigation.

Griswold’s e-mail also calls into question the Interior’s findings. He said specifics in the report about events and actions the day of the spill were inaccurate.

“The (report) implies we were in some kind of hurry to open the (mine),” he wrote. “This is incorrect there was no hurry or urgency involved.”

Taking issue with another part of the report, Griswold wrote: “Perhaps the author would have got these details correct had he not slept through my interview and presentation.”

The EPA and the Interior have pushed back against Republican assertions that their probes were incomplete. An EPA spokeswoman said the agency is reviewing the latest report.

“Reclamation and its technical service center stand behind our peer-reviewed report,” said Dan DuBray, a reclamation bureau spokesman.

“It would be reprehensible if the (EPA) intentionally misled the public, and there should be consequences,” Sen. Michael Bennet said.

Republican members of Colorado’s congressional delegation called the natural resource committee’s findings further proof that the EPA has not provided the whole picture on the Gold King spill.

Sen. Cory Gardner said he will continue to push for answers. Rep. Scott Tipton, who represents southwestern Colorado, called for “severe consequences.”

“The EPA has been caught deliberately deceiving the public in order to cover up the fact that it was aware of the risks at the Gold King Mine and yet did nothing, leading to the disaster,” Tipton said. “This is an outrage that cannot go unpunished.”

Jesse Paul: 303-954-1733, jpaul@denverpost.com or @JesseAPaul

Staff writer Mark K. Matthews contributed to this report.