The U.S. Attorney in Denver will not prosecute an Environmental Protection Agency employee involved in the Gold King Mine disaster, leaving it to the agency to determine administrative action against the employee.

A decision made Oct. 6 was based on information submitted by the EPA’s Office of Inspector General to federal prosecutors after a year-long internal probe.

Instead of a criminal prosecution, the EPA’s internal investigators “will submit a report of an investigation to the agency that details the findings of our investigation,” OIG spokesman Jeff Lagda said in response to queries.

“The agency, not the OIG, will then determine what administrative action they may take against the employee based on that report,” Lagda said. “The EPA will have to report to the OIG what administrative action the EPA will undertake.”

The EPA’s quasi-independent OIG launched an investigation into the Gold King disaster more than a year ago. Federal officials later, driven by members of Congress, began a criminal probe.

The Aug. 5, 2015, blowout at the Gold King Mine above Silverton in southwestern Colorado — accidentally triggered by an EPA-run team led by on-scene coordinator Hays Griswold — fouled waterways in three states and on American Indian lands. An estimated 3 million gallons of acid mine drainage containing heavy metals including arsenic, cadmium, lead, and mercury spilled into Animas River headwaters and turned the Animas mustard-yellow.

The OIG is part of the EPA and investigates agency activities.

The OIG investigators “presented facts to the U.S. Attorney’s Office” in Denver “about whether an EPA employee may have violated” the Clean Water Act and the statute prohibiting false statements, according to a statement Lagda issued Wednesday afternoon.

Acting U.S. Attorney Bob Troyer could not be reached, and spokesman Jeff Dorschner declined to comment.

“It has been a long-standing policy that the U.S. Attorney’s Office does not discuss declinations,” Dorschner said.

EPA investigators now will return to completing work requested by Congress related to the Gold King Mine spill, Lagda said.

Sens. John McCain of Arizona and John Barrasso of Wyoming, members of the Senate Committee on Indian Affairs, in May sent a letter to Attorney General Loretta Lynch urging a criminal probe.

Other federal agencies also have reviewed EPA conduct linked to the Gold King Mine. An Interior Department report issued last fall deemed the Gold King disaster preventable, the result of errors over many years in handling toxic discharges from inactive mines.

House Republicans on Wednesday bristled and demanded a briefing before Oct. 26 by the Justice Department explaining the decision not to prosecute.

“By not taking up the case, the Department of Justice looks like it is going easy on its colleagues in EPA,” said a letter from members of the House Committee on Natural Resources.

Justice officials’ actions “give the appearance of hypocrisy, and seem to indicate that there is one set of rules for private citizens and another for the federal government,” the letter said. “The EPA disaster deserves the same level of accountability to which private citizens are held.”