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Flat Creek IMM
Site Type: Final NPL
Updated December 2013
Cleanup of contaminated mining waste has been completed within the town of Superior (Operable Unit 1). The cleanup began on September 8, 2013 and was completed in November 2013. As part of this project, mining waste containing heavy metals including antimony, lead and arsenic that exceeded human health thresholds was removed from 38 residential properties and the Mineral County airport and placed at a repository in Wood Gulch.
During the course of the 2013 cleanup, EPA removed approximately 4,000 cubic yards of contaminated soils from yards and driveways and more than 23,000 cubic yards of contaminated soils from a temporary repository at the Mineral County airport. The cost of this remedial action was approximately $1.5 million.
EPA will monitor the results of the cleanup to ensure the safety of the area before the State of Montana assumes long-term responsibility for maintenance of the cleanup and the Wood Gulch repository in Operable Unit 3. Mineral County will also maintain an electronic filing system which will facilitate access to cleanup and sampling records and assist in future property transactions.
The Iron Mountain Mine and Mill (IMM) is the primary source of contamination at the site. It operated from 1909 to 1930 and again from 1947 to 1953 producing silver, gold, lead, copper and zinc ores. The now-abandoned property includes tunnels, tailings, a discharging adit, and the remnants of a mill and other mine buildings. The tailings from the mine contain elevated concentrations of metals. While the mine was in operation, tailings were disposed of along Flat Creek using gravity drainage. Those tailings have been distributed along Flat Creek as far as its confluence with the Clark Fork River.
Although wastes still exist on the IMM site, most of the tailings were washed down onto the Flat Creek floodplain. Mine waste was also imported into Superior by the local government and various individuals for use as fill material in yards, roadways, and other locations, such as the school track.
EPA conducted a preliminary assessment/site inspection at the site in 2001, at the request of local government and Montana Department of Environmental Quality (DEQ). As a result, additional sampling and a time-critical removal action were conducted in 2002 in the town of Superior by EPA’s Emergency Response Unit. Wastes were temporarily stockpiled in a repository at the local airport and have now been moved to a repository in Wood Gulch. The preliminary assessment was updated in 2007 in preparation for potential listing on EPA’s NPL. The listing occurred in 2009, which is when the Remedial Investigation began. Prior to being listed, the site was known as the Superior Waste Rock site. A second time-critical removal action was conducted in 2010 and a third in 2011, on the basis of the initial results obtained from the 2009 field events. The costs of the three removal actions totalled approximately $2.7 million.
|Media Affected||Contaminants||Source of Contamination|
|soils, surface water, groundwater||lead, arsenic, antimony, manganese||historic mining activities|
Tailings piles in the Flat Creek watershed were found to have levels of arsenic, antimony, lead and manganese that could pose long-term risks to public health and the environment. In the past, the town of Superior used a drinking-water well (groundwater) two miles downstream from the IMM. That well is no longer in use because sampling showed levels of antimony above the drinking water standard (the Safe Drinking Water Act Maximum Contaminant Level or MCL). The municipal water currently provided to residents is safe and is regularly sampled to ensure it is within drinking water standards. Contaminated soil cleanup has been completed in the town of Superior (Operable Unit 1).
The Flat Creek IMM site has been divided into three operable units or OUs:
- OU1 – Town of Superior. Limited to the shallow soils at residential and other properties in Superior.
- OU2 – Flat Creek Watershed. Includes the mine site where the contamination originated, the stream corridor down-gradient of the mine, and the overall site groundwater and surface water issues.
- OU3 – Wood Gulch Mine Waste Repository. Consists of the mine-waste repository that is being constructed specifically to accept wastes from OU1 and OU2
OU1 – Town of Superior
The source of excess concentrations of lead, arsenic, antimony and manganese in the town of Superior is believed to be mine waste from the IMM that was imported to individual properties, generally for use as fill in driveways and under structures. The material was free, easy to transport and had characteristics that made it desirable for these uses. Mine waste was also used in municipal road construction, and on municipal properties such as the school track and fairgrounds.
Migration routes considered at OU1 included soil and wind erosion. Historical migration of contaminants of concern (COCs) into surface water and groundwater was possible and will be addressed under OU2. Ecological risk will also be addressed under OU2.
Three time-critical removal actions have been performed by EPA in the town of Superior, during which mine waste was removed from 33 properties, the school track and the fairgrounds. These emergency removals have significantly reduced the overall concentrations of contaminants at the site. However, moderate to high concentrations remained in certain portions of 38 properties that were not addressed by these removal actions. These concentrations do not present an immediate unacceptable human health risk, and they will be removed during the remedial action, or controlled through land use controls or other institutional controls if removal of these soils is not practical (i.e., infrastructure such as buildings or utilities prevents removal), to mitigate potential future human health risk.
The Record of Decision (ROD) for OU1 was signed by the Montana Department of Environmental Quality (DEQ) and EPA, effective July 3, 2012 The selected remedy, called for the removal of the remaining mining-contaminated soils from properties in Superior, and from the temporary repository at the airport, and placement of these soils in a permanent mine waste repository in Wood Gulch.
The cleanup began in September 2013 and was completed in November 2013.
EPA will monitor the results of the cleanup to ensure the safety of the area before the State of Montana assumes long-term responsibility for maintenance of the cleanup and the Wood Gulch repository. Mineral County will also maintain an electronic filing system which will facilitate access to cleanup and sampling records and assist in future property transactions.
OU2 – Flat Creek Watershed
The Flat Creek Watershed, OU2, is comprised of the Flat Creek drainage which includes the IMM property and related mill sites, and the approximately 4.5 mile long stream corridor from the IMM to the confluence of Flat Creek with the Clark Fork River. Approximately 1.5 miles of the lower reach of the Flat Creek corridor is located on National Forest Service lands. The USDA Forest Service Northern Regional Office is developing an Engineering Evaluation and Cost Analysis (EE/CA) in preparation for a removal action under CERCLA for this part of the site.
The remaining three miles of the Flat Creek stream corridor and associated mine and mill sites in the Flat Creek drainage are the subject of ongoing discussions between the Forest Service, the state and EPA. EPA is working with the U.S. Forest Service, the Montana Department of Environmental Quality and the Montana Environmental Trust Group to assure that streamside mine tailings along Flat Creek, and contamination at the Iron Mountain mine and mill site, are cleaned up in a coordinated and timely manner.
OU3 – Wood Gulch Repository
On September 19, 2011, construction began on the permanent joint mine waste repository at Wood Gulch. The repository is located approximately 3.5 miles north of town and will be used to safely store the mine waste and contaminated soil generated from cleanup actions taken by the agencies.
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 Superior Technical Assistance Committee (STAC), consisting of a technical advisor and six members of the local community were organized to assist in accomplishing these tasks. Funding for STAC was accomplished through EPA’s Technical Assistance Grant (TAG). Generally, STAC meets on a monthly basis to discuss site-related issues.
Additionally, two Community Advisory Groups (CAGs) were established for the town of Superior and Mineral County for the purposes of securing technical expertise and resources to review and comment on technical documents generated during the course of the investigation and cleanup and to provide local residents desiring to participate in future cleanup work at the site with requisite OSHA training.
EPA and DEQ met with the Mineral County Commissioners and members of the public on July 25, 2012 to present the ROD and address comments and concerns regarding the planned remedial action. The Forest Service also attended this meeting and the Agencies committed to work together to develop timely and appropriate cleanup actions for the remainder of the site.
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. EPA uses 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.
One option for reuse is the siting of 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.
The reasonably anticipated future land use is determined during the RI/FS process. This information is considered during the development and selection of the remedy for the site. Many properties in Superior are already in continued use as residential or commercial properties. The ROD for OU1 called for, among other things, removal of mining-contaminated waste temporarily stockpiled in a repository at the airport. Removal of this material to the permanent repository in Wood Gulch will facilitate the development and reuse of the airport property in the future.
Land Use Controls and Other Institutional Controls
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.
Options for land use controls and institutional controls are included in the Record of Decision as a part of the remedy. EPA worked with Mineral County to develop a list of properties that were sampled and determined to need no further action, as well as those where mine waste was subsequently removed. The list and map will also identify any properties where waste is left in place due to infrastructure and where institutional controls are needed. Mineral County will maintain an electronic filing system which will facilitate access to cleanup and sampling records and assist in future property transactions.
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.
Five-year reviews are not yet required for this site.
Record of Decision for OU1, July 3, 2012
Action Memorandum Amendment, September 27, 2011
Action Memorandum, June 10, 2010
Action Memorandum, August 2, 2002
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
10 West 15th Street, Suite 3200
Helena, MT 59626
866-457-2690 (toll free)
State Project Officer
Montana Department of Environmental Quality
P.O. Box 200901
Helena, MT 59620-0901
View Documents at:
Mineral County Courthouse
Environmental Health and Planning
300 River Street
Superior, MT 59872
EPA Montana Office
Superfund Records Center
10 West 15th Street, Suite 3200
Helena, MT 59626
Monday-Friday 8 a.m.–4 p.m.
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