CO Mine Wastewater Spill Highlights SD Cleanup Plan

Aug 13, 2015

Outside the Gilt Edge Superfund Site in the Northern Black Hills.
Credit Amy Varland

A recent spill of 3 million gallons of mine wastewater from an EPA Superfund Site in the Rocky Mountains turned Colorado’s Animus River orange.

South Dakota and other states across the west are dotted with abandoned mines that are now being cleaned up by government regulators.

Currently the Gilt-Edge Superfund Site in the Northern Black Hills has 68 million gallons of mine wastewater stored in holding ponds.     

But EPA and state officials are undertaking a $50 million project to reduce the annual cost of water treatment.

In the 1990’s the Brohm Mining Company took about 100-thousand ounces of gold out of the Gilt Edge strip mine above Deadwood. The mining company then went bankrupt and abandoned the site, leaving behind millions of tons of waste rock.

When it rains on those exposed mine tailings the water picks up residual contaminants and turns acidic. To stop that acid mine drainage from running into Bear Butte Creek requires constant water treatment and because the mining company left, taxpayers foot most of the on-going water treatment bill.

"We spend about $2 to $2.4 million per year for treatment,” says Joy Jenkins who manages the Gilt Edge Superfund site for the EPA.

Jenkins says state and federal regulators are now undertaking a renovation project at the site that is aimed at saving some of those annual costs. Officials plan to cap some of the waste rock to keep it from generating more acid mine drainage. Jenkins says regardless on-going water treatment is needed at this site for years to come.

“River systems can generally recover from pulses of acid mine drainage, and this has happened in this river system during the mining days. But the constant input of metals and acidity can decrease aquatic life diversity,” Jenkins says.

Jenkins says the project to consolidate and cap exposed mine tailings begins in 2016 and aims to reduce the amount of water treatment needed at the site by about 70-percent.