Region 8
Superfund Program
National Information
Regional Information
Site Information
National Priorities List (NPL) History
Proposed Date
4/9/2009
Final Date
9/23/2009
Flat Creek IMM
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Site Type: Final NPL |
What's New?
Updated October 2011
A public hearing will be held October 12, 2011 at the Ambulance Service Facility, 1202 5th Avenue East Street in Superior, to present the proposed plan for Operable Unit 1 (OU1) of the Flat Creek IMM Superfund Site. EPA issuance of this proposed plan is part of its public participation responsibilities under Section 300.430(f)(2) of the National Oil and Hazardous Substances Pollution Contingency Plan (NCP).
The proposed plan summarizes information that can be found in greater detail in the Remedial Investigation and Feasibility Study reports and other documents contained in the Administrative Record for this site. The plan provides an overview of site history, contamination and risk; summarizes the remedial alternatives EPA is considering; and provides details of EPA's preferred remedial alternative and supporting rationale.
Issuance of the proposed plan denotes the start of a 30-day public comment period (October 3 to November 3, 2011). At the end of that period, EPA will review and consider all comments provided. EPA will then either move forward with the preferred alternative, modify it or select another of the alternatives presented in the plan
September 20, 2011 - Remedial Investigation (RI) report and Feasibility Study (FS) finalized. Key findings from the RI are presented below under Cleanup Progress.
September 19, 2011 - Construction began on the joint permanent repository at Wood Gulch, located approximately 3.5 miles north of town. Contaminated soil generated from the cleanup will be placed at the repository.
Looking north: road contruction activities at the Wood Gulch repository
Looking west: repository construction activities at Wood Gulch
Site Description
The Iron Mountain Mine and Mill (IMM) is the primary source for 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 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 has also been 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. Wastes were stockpiled in a repository at the local airport. The preliminary assessment was updated in 2007 in preparation for potential listing on EPA’s National Priorities List (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 subsequent time-critical removal action was conducted in 2010 on the basis of the initial results obtained from the 2009 field events.
Site Risk
| Media Affected | Contaminants | Source of Contamination |
| soils, surface water, groundwater | lead, arsenic, antimony | 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 (OU1) used a drinking-water well (groundwater) two miles downstream from the Iron Mountain Mine and Mill. 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.
Cleanup Progress
A time-critical removal action initiated in 2010 by EPA’s Emergency Response and Removal section is ongoing at the site. The removal action was initiated to address 33 properties with highly contaminated soils (concentrations greater than 3,000 ppm lead and 400 ppm arsenic). Removals have been completed at 29 properties (25 residential and four non-residential). The remaining four properties (three residential and one non-residential) are expected to be completed in October 2011.
Emergency removals have significantly reduced the overall concentrations of contaminants at the site. However, moderate to high concentrations remain. These remaining properties are the subject of this current site investigation.
Three Operable Units (OUs) are currently planned for the site:
- 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
The source of excess concentrations of lead, arsenic, antimony and manganese is believed to be mine waste from the Iron Mountain Mine 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.
Migration routes considered at OU1 include soil and wind erosion. Migration of contaminants of concern (COCs) into surface water and groundwater is possible and will be addressed under OU2. Ecological risk will also be addressed under OU2.
Current potential human receptors at OU1 include area residents and visitors. The routes of exposure for those receptors are:
- Incidental Ingestion of Outdoor Soil. Residents (especially children) may ingest soil that sticks to their hands during outdoor work or play. Contact is primarily with surface soil.
- Ingestion of Indoor Dust. Outdoor soil may be tracked inside or may enter by deposition of dust, and ingestion of dust can occur.
- Inhalation of Airborne Soil Particulates. Particles of exposed contaminated soil may be suspended in air by wind or mechanical disturbance and be inhaled. This is generally minor compared to ingestion.
Additional pathways that were considered but not evaluated further in the Human Health Risk Assessment (HHRA, see Section 7 of the Remedial Investigation report) because of low potential for risk are: dermal (skin) contact with soil and ingestion of homegrown produce.
The HHRA showed that there was significant hazard to receptors, particularly children, from concentrations of COCs in shallow soils. The most highly contaminated properties have been addressed through emergency removals conducted by EPA. However, elevated concentrations resulting in unacceptable long-term risk remain and will be addressed.
Key findings from the Remedial Investigation:
- There are no principal threat wastes at the site. Principal threat wastes are source materials considered to be highly toxic or highly mobile that generally cannot be reliably contained or would present a significant risk to human health or the environment should exposure occur.
- The contaminants of concern in soils from OU1 identified in the human health risk assessment are lead, arsenic, antimony and manganese.
- Most properties (88 percent) in Superior are in the low concentration category: less than 400 ppm of lead, 100 ppm of arsenic or 130 ppm of antimony.
- A total of 29 properties (5 percent) (22 residential and seven non-residential) had moderate concentrations of arsenic (100 to 400 ppm) or lead (400 to 1,200 ppm) in one or more of the three depth intervals sampled.
- A total of 42 properties (7 percent) (30 residential and 12 non-residential) had concentrations in the high category for arsenic (greater than 400 ppm) or lead (greater than 1,200 ppm) in one or more of the three depth intervals sampled.
- Elevated antimony concentrations generally ranged from 130 to 3,490 ppm, and were seen in properties that also had elevated concentrations of arsenic and/or lead.
- Contamination is scattered, rather than clustered in specific areas, confirming reports that waste was imported on a yard-by-yard basis as fill in driveways or other small areas. Mine waste was also used in municipal road construction and on municipal properties such as the school track and the fairgrounds.
- Emergency removals were conducted on 29 properties (25 residential and four non-residential) in 2010, addressing concentrations greater than 3,000 ppm of lead or 400 ppm of arsenic.
- Emergency removals significantly reduced the overall concentrations of contaminants at the site. However, moderate to high concentrations remain. These concentrations do not present an immediate, unacceptable risk but are likely to be addressed in the risk management decisions made for the site.
Please see the Remedial Investigation report for more information.
Community Involvement
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 will be conducting a public meeting on October 12th as well as a 30-day public comment period (October 3 to November 3, 2011) on the proposed plan. The community is encouraged to attend the public meeting and to read and comment on the proposed plan.
Reuse
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.
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 institutional controls are developed as needed during the RI/FS process and selected in the Record of Decision as a part of the remedy.
Five-Year Reviews
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.
Site Documents
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Proposed Plan for OU1, October 2011 (PDF, 14 pp, 557K)
Remedial Investigation Report (text only), September 15, 2011 (PDF, 106 pp, 3MB)
- Tables (40 pp, 208K)
- Figures (16 pp, 18.9MB)
- Appendix A (255 pp, 10.4MB)
- Appendix B (714 pp, 373MB)
- Appendix C (128 pp, 671K)
- Appendix D (473 pp, 1.4MB)
- Appendices E-G (53 pp, 265K)
Feasibility Study Report (text only), September 9, 2011 (PDF, 97 pp, 3MB)
- Tables (PDF, 19 pp, 322K)
- Figures (PDF, 10 pp, 15MB)
- Appendices (PDF, 191 pp, 1.2MB)
Contacts
EPA
Kristine Edwards
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
Montana Office
Federal Building
10 West 15th Street, Suite 3200
Helena, MT 59626
406-457-5021
866-457-2690 (toll free)
edwards.kristine@epa.gov
MDEQ
Daryl Reed
State Project Officer
Montana Department of Environmental Quality
P.O. Box 200901
Helena, MT 59620-0901
406-841-5041
dreed@mt.gov
View Documents at:
Mineral County Courthouse
Environmental Health and Planning
300 River Street
Superior, MT 59872
406-822-3577
EPA Montana Office
Superfund Records Center
Federal Building
10 West 15th Street, Suite 3200
Helena, MT 59626
406-457-5046
Monday-Friday 8 a.m.–4 p.m.
Photo/Video Gallery
Click on a thumbnail below to view the enlarged image.
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Removing the sod cap is the first step at each location
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Sampling in typical compacted gravel driveway
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Collecting subsurface sample after grass cap and shallow interval are removed
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Mine waste in sample excavation
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Flag identifying sampling area location (property RY086, sampling area “D”)
Links
Montana Department of Environmental Quality, Remediation Division
Mineral County Government, Mineral County, Montana