Durango, Colo. • The U.S. Environmental Protection agency wants a mining company to pay for a potentially costly investigation of underground water flows at a southwestern Colorado Superfund site to help the agency devise a cleanup plan.

The EPA on Thursday ordered Sunnyside Gold Corp. to study part of the Bonita Peak Mining District. The district includes the Gold King Mine, where agency workers inadvertently triggered the release of 3 million gallons of wastewater tainted with heavy metals in 2015.

The spill tainted rivers in Colorado, New Mexico, Utah and on Native American lands.

Sunnyside doesn't own the Gold King but has other mining property within the Superfund site.

The EPA has said previous work at one of Sunnyside's mines may have redirected wastewater to other openings, where it escaped into tributaries of the Animas River.

Sunnyside spokesman Kevin Roach said the company is not the cause of the water quality problems in the Animas.

Sunnyside spent $30 million over 30 years on reclamation in the area and without that work, pollution would have been worse, Roach said.

Roach said Sunnyside wants to puts its resources into improving water quality "rather than pointless studies or litigation."

He said the company is reviewing the order. It has until next week to ask the EPA for a meeting to discuss it.

Rebecca Thomas, the EPA's project manager for the Superfund site, told The Durango Herald the agency needs a better understanding of the area before it can start cleanup work.

"Until we can understand how water flows through that system, it will be difficult to put forward a plan to address contamination," she said.

Thomas said the agency decided Sunnyside was liable for conducting and paying for the investigation based on its past ownership and operations in the area.

The Bonita Peak Mining District Superfund site includes 48 mining-related sites and was designated in 2016, a year after the Gold King spill.