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National Information | ||
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Superfund Program
Gilt Edge Mine
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Site Type: Active NPL City: Ley: Lawrence Street Address: 4 miles SE of Lead Zip Code: 57754 EPA ID#: SDD987673985 Site ID#: 0801688 Site Aliases: Brohm Mining Corp. Congressional District(s): At Large |
Site Status & Updates
NEW: The Record of Decision for the Gilt Edge Mine Superfund Site, Operable Unit 1 (OU1) is now final. The record of decision describes the final cleanup plan for overall contamination at the mine site. EPA, in consultation with the South Dakota Department of Environment and Natural Resources selected Alternative 5, EPA's preferred alternative presented in the proposed cleanup plan issued for public comment in May.
The selected remedy will cost approximately $50 million and will take five to seven years to complete. The selected remedy will cover and/or contain acid-generating waste rock and fills, exposed, acid-generating bedrock, and sludge. It will also collect additional areas of contaminated surface water and groundwater and upgrade the existing water treatment plant. The selected remedy will protect human health and the environment by preventing direct exposure to mine waste with elevated metals concentrations and by preventing a catastrophic release of acid rock drainage from the site. EPA believes that the selected remedy will substantially reduce risks, is feasible, implementable, and has long-term cost-effectiveness.
Attached to the Record of Decision is a Responsiveness Summary, which summarizes
and responds to all significant public comment submitted this summer during
the public comment period on the proposed cleanup plan. To view a copy of the
Record of Decision and Responsiveness Summary, or for further information, please
see the Contacts section below.
EPA is currently offering a Technical Assistance Grant (TAG) to community groups. A TAG provides money for activities that help community groups participate in decision making at eligible Superfund sites. Grant recipients can contract with independent technical advisors to interpret technical information about the site. For more information, contact Linda Armer, U.S. Environmental Protection Agency, Region 8, 1595 Wynkoop Street, Denver, CO 80202 (303) 312-6696, armer.linda@epa.gov.
Site Description
The Gilt Edge Mine, near Deadwood, is located about five miles east of Lead at the headwaters of the cold-water fisheries and municipal water supplies of the northern Black Hills. It is a former 258-acre open pit, cyanide heap-leach gold mine. Nearly a decade ago, the mine operator, Brohm Mining Company (BMC) became insolvent, leaving 150 million gallons of acidic, heavy-metal-laden water in three open pits, as well as millions of cubic yards of acid-generating waste rock that requires cleanup and long-term treatment.Mining operations for gold, copper and tungsten were conducted in this small mining district starting in 1876. About a century ago, a series of small mines began dumping metals-laden mill tailings into Strawberry Creek and Bear Butte Creeks. By 1986, when BMC began conducting larger-scale open-pit mining, off-site waters were already contaminated.
When BMC faced financial problems and informed the State that it could not continue site controls, the Governor of South Dakota requested that EPA Region 8 propose the site for the Superfund National Priorities List (NPL). The site was proposed for the Superfund NPL in May 2000, and final placement of the site on the NPL was announced in the Federal Register in December 2000.
Site Risk
Sulfide waste rock and exposed ore zones (which generate leachates to surface and ground water) contain heavy metals, including arsenic, cadmium, chromium, copper, lead, nickel, silver and zinc. Elevated nitrates and sulfates are also present in heap leach residues. Copper, cadmium and zinc appear to be the metals contaminating the habitats of Strawberry and Bear Butte Creeks. While controlled, the site presents no immediate threat to human health. If uncontrolled, the large volumes of contaminated waters could threaten the well-water supplies of downstream users, including the City of Sturgis.The Baseline Human Health Risk Assessment describes the levels of risk associated with exposure to the variety of contaminants and media (air, soil, surface and groundwater) at the site. It also helps EPA and the South Dakota Department of Environment and Natural Resources (DENR) evaluate remedial strategies that do not preclude reasonable future use(s) of the property.
| Media Affected | Contaminants | Source of Contamination |
| Surface water, liquid waste, leachate, solid waste | Arsenic, cadmium, copper, lead, zinc, nitrates, sulfates | Mining activities and associated heap leach |
Cleanup Progress
The Gilt Edge Mine Site is divided into three Operable Units (OUs): OU1, OU2, and OU3. In 2001, after receiving public input, EPA developed cleanup plans for OU2 and OU3. Cleanup plans for OU1 are presented in the recently finalized Record of Decision for OU1.OU1 addresses the surface contamination for the entire 258 acres of the Gilt Edge Mine site.
EPA finalized the final Remedial Investigation Report for OU1 in early 2008. The report details the nature and extent of the residual mining contamination in the groundwater, surface water, waste rock, and soils at the Gilt Edge Mine site.
EPA issued a Feasibility Study in the spring of 2008. The Feasibility Study analyzes various remedial alternatives that could be used to reduce the amount of acid rock drainage that is generated at the site and to remove or contain contaminated fill materials. The primary objective of all of the alternatives described in the Feasibility Study, including the alternative ultimately selected in the final cleanup decision, is to reduce the amount of acid rock drainage that is generated on site in order to protect human health and the environment. A primary goal of the OU1 cleanup will be to clean up and contain mine wastes at the Gilt Edge Mine Site. This will reduce the amount of contaminated water that is generated on the site and treated in the water treatment plant.
OU2 includes the management and treatment of the acid rock drainage that threatens surface water in the area. Discharge of acid rock drainage water without treatment poses a risk to human health and the environment, particularly to surface water quality in Strawberry Creek and Bear Butte Creek. In 2001, after receiving public input on its plans, EPA implemented an interim remedy for OU2 that converted the existing water treatment plant to a lime, high-density sludge system. This provided a cheaper and more efficient means of treating the water onsite. The water treatment plant continuously treats acid rock drainage water that is collected at various facilities around the site. As of July 2007, there were approximately 180 million gallons of acid rock drainage water in storage. Several water diversion structures have been constructed to keep uncontaminated water from entering the treatment plant conveyance system.
The final remedial decision for OU2 will provide for the study, design, and implementation of a water treatment system that produces water in compliance with water quality standards. EPA will issue the final decision, taking public input into consideration, after the Record of Decision is issued for OU1 and the resulting new site conditions are investigated; it is estimated that once the OU1 remedy is implemented, there will be less water onsite to treat, and the chemistry of this water will be altered.
OU3 addresses acid rock drainage coming from the Ruby Gulch Waste Rock Repository. The Ruby Gulch Waste Rock Repository is a large acid rock drainage source on the Gilt Edge Mine Site. Acid rock drainage generated from the sulfide-bearing wastes within the dump, if not reduced and contained, posed a major threat of contamination and release into the Ruby Gulch drainage and Bear Butte Creek. Beginning in 2001, EPA addressed this threat by reducing the volume of contaminated materials exposed, reducing water infiltration that produced large quantities of acid rock drainage, and containing waste materials. EPA constructed a cap for the Ruby Gulch Waste Rock Repository by installing a monitoring system and drainage systems, and a synthetic liner and clean soil cover. At the completion of that work in 2003, EPA began ongoing performance monitoring and operations and maintenance activities at the site.
In 2004 it was noted that outflows from the "Ruby Toe" were higher than anticipated. Tests performed on the diversion ditches indicated that many of the diversion ditches were leaking. Efforts are currently underway to repair the leaking diversion ditches to further reduce run-on from entering the water treatment system.
The remedial action at OU3 will be completed when the final eight acres adjacent to the water treatment plant are capped. This will occur during implementation of the OU1 remedy.
Site Documents
Note: most documents below are Adobe PDF files.Also note: the largest documents found below are in the publicly accessible Gilt Edge ftp site.
Gilt Edge FS Appendix A-H (7 MB PDF)
Gilt Edge FS Text, Tables and Figures (VERY LARGE PDF file: 30.3 MB)
Gilt Edge Proposed Plan, May 19, 2008 (PDF, 11 pp, 2 MB)
Operable Unit 1 Remedial Investigation Fact Sheet, February 2008 (PDF, 7 pp, 236 KB)
Operable Units 2 and 3 Five-Year Review, April 2007 (PDF, 40 pp, 1 MB)
Five-Year Review Update, September 2008 (PDF, 4 pp, 43 KB)
Ruby Gulch Waste-Rock Repository Construction (PDF: 2.0 MB)
Lime-HDS Water Treatment Plant Construction (PDF: 1.5 MB)
The following documents are also available. Please contact Jennifer Chergo at 303-312-6601 for a copy of these documents.
- Operable Unit 1
Remedial Investigation Report, 2008
Community Involvement Plan, Initial Review of Potential Future Land Reuse, 2005
Baseline Ecological and Human Health Risk Assessments
2006 Biomonitoring Report
Operable Unit 2
Interim Record of Decision
Lime-HDS Water Treatment Plant Construction
Operable Unit 3
Interim Record of Decision
Ruby Gulch Waste-Rock Repository Construction
Community Involvement
In 2001, a local community group received a Technical Assistance Grant (TAG) from EPA so they could better participate in the investigation and cleanup at the Gilt Edge Mine Site. EPA met regularly with the TAG group members from that time until summer 2007 when the group dissolved. A new TAG grant is now available to interested and qualified community groups. See the "Site Status and Updates" section of this Webpage for contact information.From 2000- 2002, EPA was in the process of investigating the site and developing the proposed plans for cleanup of OU2 and OU3. During this time, EPA hosted tours of the site for members of the public and elected officials. EPA conducted interviews with members of the community in order to understand public concerns about the site and to develop responsive communications with the community, outlined in a 2000 Community Involvement Plan. EPA hosted public meetings and public comment periods to gather input on the Proposed Plans for cleanup for OU2 and OU3 in 2000 and 2001. EPA mailed a site update to community stakeholders in 2002 and continuously updates its Website in order to provide updated information to the public.
Since that time, EPA has met numerous times with community stakeholders and hosted tours of the Gilt Edge Site. EPA and DENR convened a number of public meetings in 2005 to gather input on the potential future use potential for the Gilt Edge site. The Final Report summarizing these meetings and public comment received is called the Community Involvement Plan, Final Report, Initial Review of Potential Future Land Reuse.
In spring 2008, EPA issued the Remedial Investigation Report for OU1. EPA announced the availability of this report in local newspapers, held meetings with individual stakeholders, and hosted site tours at this time.
In May 2008, EPA issued a Proposed Plan for cleanup for OU1. EPA mailed the plan to community members and agency representatives. EPA held a public comment period on the Proposed Plan, notified the public of its availability in local papers and in emails. EPA hosted a public meeting to take comments from the public on the plan, met with stakeholders to hear their views, and again hosted site tours. The final Record of Decision for OU1 includes public comments received on the Proposed Plan and EPA's responses to those comments.
Contacts
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EPA Jennifer Chergo Victor Ketellapper |
South Dakota Mark Lawrensen, Chief |
| View Documents at:
EPA Superfund Records Center Hearst Public Library |
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