The Environmental Protection Agency reported a “mine burp” that caused discoloration of the Animas River on Wednesday north of Silverton in the San Juan Mountains.

The discharge was coming from the Frisco Bagley Mine in the Bonita Peak Mining District. It was first reported to the EPA by the Colorado Division of Reclamation, Mining and Safety.

A mine burp is when a sludge dam builds somewhere in the mine and eventually breaks down, releasing acidic mine drainage into the water.

The discharge caused discoloration of the Animas River north of Cinnamon Creek, and possibly farther down, said Athena Jones with the EPA.

“It’s a rust, essentially, and that’s why it has an orange-red color,” Jones said. “It’s really visible and alarming, and can carry other metals.”

Efforts to reach the EPA for updated information Thursday were unsuccessful.

Jones said it was an isolated event and appears to have ended three hours after the EPA was notified. The EPA is conducting visual inspections and sampling the Animas River to determine any potential impacts from the release.

“We’re collecting samples from the areas that we know material has traveled today from the Frisco Bagley Mine,” Jones said. “We’re going to be assessing those samples for total metals and dissolved metals, as well as general water quality parameters.”

Jones said someone will be monitoring the river for signs of discoloration over the next couple of days at the 14th Street Bridge in Silverton.

“We don’t anticipate any lasting impacts,” Jones said.

The Frisco/Bagley Tunnel is part of the Bonita Peak Mining Superfund site north of Silverton. The Superfund was created in response to the 2015 Gold King Mine spill, in which the EPA accidentally pierced an adit that sent about 3 million gallons of acidic mine waste down the Animas River. The yellow plume worked its way through Durango and into the San Juan River in New Mexico.

njohnson@durangoherald.com