EPA outlines plan for Gilt Edge cleanup

By Journal staff

The federal caretakers of the former Gilt Edge Mine south of Deadwood are seeking public comment on a $58 million plan to treat water and remove or seal pollution sources at the defunct open-pit gold mine.

The Gilt Edge Mine was part of a mining district that bore gold, copper and tungsten as far back as 1876. The area is off U.S. Highway 385 near Galena, at the headwaters of cold-water fisheries and municipal water supplies, according to the federal Environmental Protection Agency.

Brohm Mining Co. began operating a large open-pit mine at the historical Gilt Edge property in 1986. Three open pits were dug, with gold-bearing rock heaped in large mounds treated with diluted cyanide that dissolved the gold. The solution was collected to retrieve the gold, refreshed with cyanide and recycled over the mound to repeat the process. A large waste-rock dump also was created.

Rock at the 258-acre site contains sulfides that, when exposed to air and water from rain and snow, becomes acidic. There were historical mine wastes at the site, and EPA says contaminates existed before open-pit mining began in the 1980s.

The runoff unleashes naturally existing toxics, including arsenic, nitrates and sulfates, that contaminate Strawberry and Bear Butte creeks.

While controlled, the site presents no immediate threat to human health, the EPA said. If uncontrolled, the large volumes of contaminated waters could threaten the well-water supplies of downstream users, including the city of Sturgis.

Although some cleanup was done, Brohm went out of business and was unable to continue site controls. That left pits filled with 150 million gallons of acidic, heavy-metal-laden water and tons of exposed acidic-generating waste rock.

In 2000, the site was proposed for the Superfund National Priorities List, and the EPA developed plans for cleanup and control of contaminants. Measures included covering mountains of waste with synthetic tarps and clean soil to restrict and air and water reaching the acidic rock. Uncontaminated water in the area was diverted from the mine, and contaminated water from the pit and surrounding Ruby Gulch drainage is being cleaned and neutralized before being released to nearby streams.

Surface ponds and historical underground mine workings create a complex plumbing system, making cleanup work slow and tedious. In 2007, EPA estimated toxic water in the holding pits had risen to 180 million gallons.

The EPA is now examining a variety of options that would treat millions of gallons of water each year at the site.

The primary culprit for pollution is the waste-rock pile at the heap pads. EPA officials propose backfilling the pits with the waste rock and covering the trouble-making material. The EPA would like to spend more than $58 million to collect and treat polluted water, upgrade a water-treatment plant on site and deal with the site’s pollution sources.

The EPA also would like to limit public access to the site, allowing only non-motorized use of mine area roads, and no housing or other development that would disturb the surface.

Because of the public comment period and state and federal agency reviews, EPA officials guess the next phase of the Gilt Edge cleanup won’t begin until 2010.

To comment

Anyone wishing to comment on the next phase of the Gilt Edge Mine cleanup can do so until Monday, June 23.

Documents outlining the proposed work are at the Hearst Library, 315 Main St., Lead, or online at epa.gov/region8/superfund/sd/giltedge

For more information, contact Jennifer Chergo at the EPA, 303-312-6601; 800-227-8917 ext. 3126601 or e-mail chergo.jennifer@epa.gov.