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Brennan Linsley, Associated Press
File--In this Wednesday, Aug. 12, 2015, file photograph, water flows through a series of retention ponds after a spill at the Gold King mine near Silverton, Colo. On Friday, Feb. 5, 2016, the Environmental Protection Agency said that the three million gallon spill from the gold mine may have dumped more than 880,000 pounds of metals into the Animas River.

DENVER — A probe of a mine waste accident in Colorado that fouled rivers in three states with arsenic, lead and other toxic substances has found further evidence that government workers knew a spill from the gold mine was possible, according to documents released Thursday by a U.S. House committee.

Hays Griswold, a U.S. Environmental Protection agency official in charge of the Gold King mine at the time of the August accident, said in an email that he "personally knew" the plugged, inactive mine could contain large volumes of water.

The email was sent Oct. 28 to other EPA officials and provided Thursday to The Associated Press by the House Natural Resources Committee as it released the findings of its Republican-led probe.

An EPA cleanup crew triggered the spill during excavation work at the mine's entrance, unleashing a 3-million-gallon deluge that contaminated rivers in Colorado, New Mexico and Utah.

The release dumped more than 880,000 pounds of heavy metals into Colorado's Animas River, forcing the closure of downstream public water systems until the plume passed and raising concerns about long-term environmental impacts.

"I personally knew it could be holding back a lot of water, and I believe the others in the group knew as well," Griswold wrote in the email.

EPA officials did not immediately respond to questions from the AP about the email.

The spill occurred when workers for EPA and its contractor, Environmental Restoration LLC, started excavation work that was intended to allow them to safely drain the mine.

An Interior Department investigation pinned responsibility on the EPA for not checking to see if the mine held pressurized water. EPA officials previously said the workers on site determined there was no or low pressure from water backed up inside the mine.

Griswold indicated in the email that the determination of low water pressure was based on mistaken assumptions about the location of the top of the mine's buried entrance, known in mining as the brow.

The excavation work was intended to clear away debris for the entrance before the mine was to be drained at a later date, he wrote.

"We and or I particularly thought we were four or maybe five feet above the brow," Griswold wrote. "However, as it turned out we inadvertently got to probably within a foot or two of the brow. That proved to be too close when rock at the exposed face crumbled out, providing an outlet for the water."

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Brown reported from Billings, Mont.