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Gilt Edge Mine
|Site Type: Final NPL
Street Address: 4 miles SE of Lead
Zip Code: 57754
EPA ID: SDD987673985
Site Aliases: Brohm Mining Corp.
Congressional District: At Large
Updated December 2014
The remedial design for operable unit 1 (OU1) has been completed, addressing surface contamination including three open pits, heap leach pad material, and other mine wastes around the site. An Explanation of Significant Differences (ESD) for OU1 was issued in September 2014. The ESD documents changes from the remedy described in the OU1 Record of Decision (ROD), which were determined in the design process to be necessary to further reduce the amount of acid rock drainage (water contaminated with metals and acidity) that is generated at the site. Additional consolidation and covering of acid-generating mine waste materials at the site will result in less acid rock drainage generation, which is caused when rain and snow melt come into contact with the acid-generating mine waste. These measures will facilitate long-term operations of the site and maintain protectiveness. Remedial action (RA) construction planning for OU1 will occur in 2015 with the bulk of construction work beginning in 2016. The OU1 RA construction is anticipated to take eight to ten field seasons to complete. However, the exact schedule and time to completion of the remedy will be dependent on the availability federal funding. Settlement money from responsible parties will be utilized first. Federal funding will be required to complete the project.
Interim remedy water treatment activities continue at the site. In 2013 over 118 million gallons of acid mine drainage water were collected from various seeps and sources around the site, treated for metals removal, and discharged to Strawberry Creek. Acid mine drainage water collection and treatment will continue through the OU1 RA construction to protect aquatic life in the streams and downstream water users.
The Gilt Edge Mine Superfund site is located about 6.5 miles east of Lead, at the headwaters of cold-water fisheries and municipal water supplies of the northern Black Hills in South Dakota. The 360-acre primary mine disturbance area encompasses a former open pit and a cyanide heap-leach gold mine, as well as prior mine exploration activities from various companies. In the late 1990s the most recent mine operator, Brohm Mining Company (BMC), became insolvent. In doing so, they left 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. And a legacy of contamination was left by many of these mining entities. When BMC faced financial problems and informed the state that it would not continue site controls, the governor of South Dakota requested that EPA Region 8 propose the site for the Superfund National Priorities List (NPL). EPA proposed the site on May 11, 2000 and announced the site's final NPL designation in the Federal Register on December 1, 2000. The NPL is a list of sites with environmental contamination, commonly referred to as Superfund sites.
Sulfide waste rock and exposed ore zones contain sulfate and heavy metals, including arsenic, cadmium, chromium, copper, lead, nickel, silver and zinc, which generate acid mine drainage or contaminated leachate when exposed to oxygen and water. Elevated nitrates and cyanide were also present in heap leach residues. Copper, cadmium and zinc previously migrated from the site, contaminating the habitats of Strawberry and Bear Butte Creeks. Currently the transport of contaminants off site is controlled through the use of a high density sludge water treatment plant; the site presents no immediate threat to human health. If left uncontrolled, the large volumes of contaminated waters could threaten aquatic life, the well-water supplies of downstream users, and drinking water sources for the city of Sturgis.
|Media Affected||Contaminants||Source of Contamination|
|surface water, leachate, solid waste||arsenic, cadmium, chromium, copper, lead, nickel, silver, zinc, and sulfates||mining activities and associated heap leach|
The site is divided into three Operable Units: OU1, OU2 and OU3. In 2001, EPA developed interim cleanup plans documented in the interim Records of Decision (RODs) for OU2 and OU3. Cleanup plans for OU1 were also developed and are presented in the ROD for OU1, signed in September 2008. Public input was incorporated into all of the site cleanup plans.
OU1 addresses the surface contamination at the site. EPA finalized the Remedial Investigation (RI) report for OU1 in early 2008. The RI report details the nature and extent of the residual mining contamination in the groundwater, surface water, waste rock, and soils at the site.
EPA issued a Feasibility Study (FS) report in the spring of 2008. The FS report analyzed 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 FS report, including the alternative ultimately selected in the ROD, was to reduce the amount of acid rock drainage that is generated on site and to prevent direct contact with metals-laden materials in order to protect human health and the environment.
EPA issued a proposed plan for public comment in the spring of 2008. This proposed plan presented all of the alternatives offered in the FS and described in detail EPA's preferred alternative. In September 2008, EPA issued a ROD for OU1, identifying EPA's final cleanup decision that will address the surface contamination at the site, including the open pits, heap leach pad material, and other mine wastes around the site.
The remedial design has been completed, addressing surface contamination including three open pits, heap leach pad material, and other mine wastes around the site. An Explanation of Significant Differences (ESD) for OU1 was issued in September 2014. The ESD documents changes from the remedy described in the OU1 Record of Decision (ROD), which were determined in the design process to be necessary to further reduce the amount of acid rock drainage (water contaminated with metals and acidity) that is generated at the site. Additional consolidation and covering of acid-generating mine waste materials at the site will result in less acid rock drainage generation, which is caused when rain and snow melt come into contact with the acid-generating mine waste. These measures will facilitate long-term operations of the site and maintain protectiveness. Remedial action (RA) construction planning for OU1 will occur in 2015 with the bulk of construction work beginning in 2016. The OU1 RA construction is anticipated to take eight to ten field seasons to complete. However, the exact schedule and time to completion of the remedy will be dependent on the availability federal funding. Settlement money from responsible parties will be utilized first. Federal funding will be required to complete the project.
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. Several water diversion structures have been constructed to keep uncontaminated water from becoming contaminated, thereby reducing the volume of water that is required for treatment.
It is estimated that once the OU1 remedy is implemented, there will be less contaminated water generated onsite and the chemistry of this water will be different than the current conditions. The final remedial decision for OU2 will provide for the design and implementation of a water treatment approach that may be different than the current water treatment plant. After the OU1 Record of Decision is implemented, EPA will complete an RI/FS process to investigate the resulting new site conditions and develop a final remedy decision, taking public input into consideration.
OU3 addresses the Ruby Gulch Waste Rock Pile. The Ruby Gulch Waste Rock Pile was created by Brohm Mining Corp. This gulch received waste rock from mine pit excavations that generates acid mine drainage upon contact with rain and snow melt. Acid rock drainage generated from the sulfide-bearing wastes 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 grading and capping the pile, creating a repository to contain the waste rock and reduce water infiltration that produced large quantities of acid rock drainage. EPA constructed a cap for the Ruby Gulch Waste Rock Repository, which included a monitoring system, run-off and run-on diversion ditch control structures, an impermeable geomenbrane, and a clean soil vegetated cover. A toe drain was also installed to collect the residual acid mine drainage water generated due to base groundwater flows that could not be prevented. At the completion of that work in 2003, EPA began ongoing performance monitoring and operations and maintenance activities.
In 2004 it was noted that outflows from the Ruby Repository toe drain were higher than anticipated. Tests performed on the diversion ditches, which were intended to transport water around and away from the repository and reduce infiltration and subsequent acid rock drainage, indicated that many of the diversion ditches were leaking into the repository and creating additional acid mine drainage.
EPA, in consultation with the South Dakota Department of Environment and Natural Resources (DENR), decided to minimize the leakage from the diversion ditches by pressure grouting or lining the stretches that had been shown to be leaking surface water into the ground.
In 2009, the Gilt Edge Mine site received $3.5 million in American Recovery and Reinvestment Act (ARRA) funds to implement the ditch grouting and lining work. In 2009, approximately 1,000 linear feet of the ditches were cleaned of rock, riprap, and other loose debris and drilled to an average depth of 20 feet for pressurized grout injection to seal joints, cracks and fractures. In 2010 and 2011, drilling and pressure grouting continued and some ditches were also lined with an impermeable geomembrane to aid in reducing infiltration. Approximately 3,200 linear feet of ditch were grouted and approximately 660 linear feet of ditch were lined with geomembrane to reduce or eliminate surface water infiltration into the Ruby Repository. These activities are anticipated to reduce the potential for mobilization of residual heavy metal constituents from the waste rock to surface water.
A final ROD for OU3 will be developed in the future and will include any additional repairs required and the capping of the final eight acres of the dump that are adjacent to the water treatment plant. For efficiency in construction, this final capping is currently planned to be accomplished during the OU1 RA construction.
Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, on-going, meaningful community involvement. The goals of the Superfund community involvement program are to:
- Keep communities affected by sites informed throughout the cleanup process.
- Provide opportunities for communities to comment and offer their input about site cleanup plans.
- Facilitate the resolution of community issues tied to a site.
The agency 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 information to the public.
In the spring of 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 and mailed the plan to community members and agency representatives. EPA held a public comment period on the proposed plan and 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 ROD for OU1 includes public comments received on the proposed plan and our responses to those comments.
In January 2012, EPA and DENR staff completed community interviews with residents and local officials of Lead, Deadwood, Sturgis and Spearfish to update the community involvement plan. The updated plan is available in Site Documents below.
EPA places a high priority on land reuse as part of its Superfund response program mission. The agency tries to select cleanup options that encourage and support future use of a site. We use two fundamental methods to facilitate reuse of Superfund sites:
- Exploring future uses before the cleanup remedy is implemented, an approach that gives the Agency the best chance of designing cleanup remedies to support the likely future use of a site.
- Working with landowners and communities to remove barriers not considered necessary for the protection of human health or the environment at those sites where remedies are already in place.
EPA and the DENR convened a number of public meetings in 2005 to gather input on the potential future use potential for the 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.
One option for reuse is locating clean and renewable energy projects on contaminated (or formerly contaminated) lands. As part of this effort, EPA is evaluating the potential for energy projects on these properties and working with landowners and communities to identify ways to remove barriers to such projects.
EPA, in consultation with engineers from Department of Energy's National Renewable Energy Lab (NREL), is evaluating whether the Gilt Edge Mine site could be reused as a location for generating renewable energy. Regional wind maps indicate that the wind resource is very good (class 6 or 7). That fact, coupled with the existing electrical transmission lines, makes Gilt Edge a promising candidate site for a commercial wind farm. In May of 2010, EPA and NREL erected a 55-meter meteorological tower at the site to measure wind speeds, in an effort to confirm that the wind resource is as good as the regional maps indicate. The report is pending.
Land use controls are the most common type of institutional control (IC). ICs are administrative or legal controls that help reduce the likelihood for human exposure to contamination. ICs can also help protect the integrity of the remedy. Examples of ICs are:
- Zoning ordinances.
- Environmental covenants.
- Deed notices.
- Well-drilling restrictions.
- Building permits.
- Informational advisories.
Land use controls at the site will be used to minimize risks posed to human receptors from unaddressed contaminant sources, and also to ensure that engineered elements of the remedy (such as covers) are not damaged. They will prevent the unacceptable uses of groundwater that pose human or ecological risk, limit residential and off-road motorized vehicle rider uses, and allow only low intensity recreational site users and commercial workers. The land use controls will consist of a combination of both institutional controls (which may include community awareness programs and land-use restrictions) and engineered controls (which may include posted warnings and fencing).
ICs will be developed during the remedial action phase to protect the integrity of the remedy, since the remedy includes waste left in place.
EPA or the lead agency conducts five-year reviews following the start of a Superfund cleanup when contamination is left on the site. These reviews are repeated every five years. We use these reviews to determine:
- How the remedy is working.
- If the remedy remains protective of human health and the environment.
The second five-year review for Gilt Edge Mine was completed in June 2012. The report is available in Site Documents below.
You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.Note: the larger documents below are located on the publicly accessible Gilt Edge FTP site. Best way to open a very large file: right-click and save it to a folder.
Explanation of Significant Differences, September 2014
Community Involvement Plan, updated April 2012
Gilt Edge OU1 Record of Decision Volume I: Text, September 29, 2008
Gilt Edge OU1 Feasibility Study: Text, Tables and Figures (PDF), May 2008 (216 pp, 30 MB)
Gilt Edge OU1 Feasibility Study: Appendix A-H, May 2008 (PDF, 387 pp, 7MB)
Remedial Investigation Report, February 1, 2008
Remedial Investigation Report: Figures and Tables (PDF), February 1, 2008 (371 pp, 120 MB)
Gilt Edge OU1 Remedial Investigation Fact Sheet, February 2008
Baseline Ecological and Human Health Risk Assessments, November 2003
Lime-HDS Water Treatment Plant Construction, February 2002–September 2003
Gilt Edge OU2 Interim Record of Decision, November 2001
Ruby Gulch Waste-Rock Repository Construction, July 2001–June 2003
Gilt Edge OU3 Interim Record of Decision (PDF), August 30, 2001 (67 pp, 860 K)
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (EPR-SR)
Denver, CO 80202-1129
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