Federal prosecutors have decided not to bring criminal charges to Environmental Protection Agency employees involved with the 2015 leak of wastewater at an abandoned mine, the agency’s inspector general announced this week.

The EPA’s inspector general previously launched a criminal probe in conjunction with the Justice Department after the work of EPA employees led to a blowout at the Gold King Mine in Colorado, which resulted in 3 million gallons of toxic water spilling into multiple rivers in the region. The IG said an EPA employee may have violated the Clean Water Act and False Statements laws. The U.S. Attorney’s Office, however, has declined to prosecute the employee.

“In lieu of criminal prosecution, the OIG will prepare a Report of Investigation for submission to EPA’s senior management for review,” said Jeffrey Lagda, a spokesman for the IG’s office. He added the agency is required to report any administrative action it takes in response.

The IG will now resume its program evaluation, which it had paused in favor of the criminal investigation.

The spill at the defunct Gold King disaster began after an EPA inspection crew was examining existing leakages. While excavating loose material in the mine, pressurized water burst out of a tunnel and into a creek that fed into the Animas and San Juan rivers. The spill affected populations in Colorado, New Mexico, Arizona and Utah, as well as multiple Indian nations.

In the weeks after the blowout, EPA released its own, internal report that shifted the blame away from the agency. The report acknowledged employees missed some warning signs and failed to take certain precautions to prevent the spill, but ultimately found the blowout was “likely inevitable” due to built up pressurization.

A subsequent report from the Interior Department, however, faulted EPA for not drilling into the mine to determine the level of water in the mine. “Had it been done, the plan to open the mine would have been re­vised and the blo­wout would not have oc­curred,” Interior officials wrote.

In a September hearing, McCarthy promised to fire employees if investigations found individuals at fault.

“They made a judgment that turned out to be wrong,” the administrator said of the inspectors. “We will follow up and they will be held accountable if there were mistakes made, if they could have avoided this, if they forgot to look at something or made a judgment that wasn't based on profound and good engineering and science.”