An Environmental Protection Agency contractor works on the clean up in the aftermath of the blowout at the Gold King mine, which triggered a major spill of toxic wastewater, outside Silverton, Colo., Wednesday, Aug. 12, 2015.

(AP Photo/Brennan Linsley)

The Environmental Protection Agency is considering plans to build a wastewater treatment plant for an inactive Colorado gold mine after the agency inadvertently triggered a 3-million-gallon spill of polluted water there last month.

The EPA released documents Tuesday outlining possible plans to quickly build the plant below the Gold King Mine near Silverton.

"This is an emergency response action," a request for proposal says. 

The document also shows the EPA is working on a tight schedule. It calls for a fully operational system within 21 days of a contract being awarded.

EPA spokeswoman Nancy Grantham told the Denver Post that the agency received six bids but hasn't yet yet decided on one -- or if the plant will ultimately be built.

"The treatment plant is a contingency option," Grantham said. "The agency continues to evaluate data to determine the impacts of the Gold King Mine on water quality currently and going into the winter months."

An EPA-led crew triggered the spill on Aug. 5, tainting rivers in Colorado, New Mexico and Utah. The Senate Environment Committee holds a hearing on the incident Wednesday, one of several planned by Congress.

Wastewater was flowing from the mine before the blowout. The EPA says it's still spilling out at about 600 gallons per minute.

The documents don't say how much the plant will cost, but the Post reported earlier this month it will cost $3 million to build and run for a year. The agency said last week it had spent about $8 million on the cleanup.

Included in Tuesday's release were videos of EPA workers talking about the spill.

Editor's note: The headline has been updated to reflect that the EPA is considering building a plant but hasn't made a final decision.