A Colorado mine that spewed 3 million gallons of contaminated wastewater into rivers in three Western states was designated a Superfund site Wednesday, clearing the way for a multimillion-dollar federal cleanup.

The U.S. Environmental Protection Agency formally added the inactive Gold King Mine and 47 other nearby mining-related sites to the Superfund list. It also included nine other sites in California, Indiana, Louisiana, Montana, New York, Ohio, Texas and West Virginia and Puerto Rico.

A federal crew inadvertently triggered the Colorado spill during preliminary cleanup work at the gold mine in August 2015, sending out a mustard-yellow plume that tainted rivers in Colorado, New Mexico and Utah.

The EPA estimates that 880,000 pounds of metals flowed into the Animas River in Colorado, including arsenic, cadmium, copper, lead, mercury, nickel and zinc.

The Superfund designation comes after months of negotiations with southwestern Colorado residents, who feared it could dampen the region’s vital tourism industry.

An investigation last year by the Interior Department, which is independent of the EPA, said the cleanup crew could have avoided the spill but rushed its work. But Interior officials said they found no evidence of criminal wrongdoing.

A separate criminal investigation is still underway, along with an internal inquiry. New Mexico has sued both the EPA and Colorado over the spill, while the Navajo Nation sued the federal government.

Congress has conducted multiple hearings on the spill and is considering several bills to address hundreds of old, leaking mines nationwide.