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|Site Type: Final NPL
Street Address: Adjacent to county airstrip
ZIP Code: 59019
EPA ID: MTD021997689
Site Aliases: Mouat Indust.
Congressional District: At Large
Updated November 2013
EPA has revised the Post Removal Site Control Plan for the Mouat Industries site. The plan was revised to update activities that have occurred since the original plan was written in 2009 and to modify the groundwater monitoring network. The report is available in the Site Documents section below.
The Mouat Industries site is located south of Columbus, Montana. The site lies in the flood-plain of the Yellowstone River, less than 0.6 miles north of the present river channel in the SW ¼ of the NW ¼ of Section 27, T2S, R20E. The site is approximately 4.5 acres. The land is owned by the town of Columbus and was leased to Mouat Industries from 1957 to 1962.
Mouat Industries processed chromite ore mined from the Stillwater Mining Complex in south-central Montana into high-grade sodium dichromate, which was sold as a corrosion inhibitor. The process subsequently generated sodium sulfate process wastes containing sodium chromate and sodium dichromate. These hexavalent chromium-containing compounds leached from the sodium sulfate waste piles into underlying soils and eventually into the site groundwater. Additionally, normal facility operations resulted in sodium dichromate spills. The chromium processing plant was built and operated from 1957 to 1962. Chromium wastes were created during this time, but not after 1962.
EPA conducted a preliminary assessment/site inspection from 1979 to 1980. Various entities also conducted multimedia sampling during the late 1970s and 1980s. These studies led EPA to send a letter to the town in 1984 stating that the analytical numbers from the sampled monitoring wells exceeded the recommended drinking water standards for chromium and recommended that the contaminated groundwater not be used for human and animal consumption. EPA proposed the facility for the National Priorities List (NPL) in Federal Register notice 29 FR 40320 of October 15, 1984. The site received a Hazard Ranking System score of 31.66. The listing was final in 51 FR 21054 of June 10, 1986.
Soils and groundwater were contaminated with hexavalent chromium, a hazardous substance as defined by CERCLA Sec. 101(14) and designated as such under 40 CFR 117 and 40 CFR 302.
|Media Affected||Contaminants||Source of Contamination|
|soil, groundwater||hexavalent chromium (Cr+6)||chromium processing activities|
The contaminated surface and subsurface soils at the Mouat Industries Superfund Site were addressed through two action memorandums, signed in 1990 and 1991, while two other action memorandums, signed in 1996 and 2008, addressed site controls and groundwater. In 1990, EPA issued an action memorandum to initiate a time-critical removal action to (1) secure the site and to mitigate the threat of direct contact to hazardous materials to on-site workers and nearby individuals, and (2) provide run-on, run-off drainage control for the site. EPA erected a chain link fence around the area of contaminated soils. At the request of EPA, the town of Columbus redirected an existing drainage ditch that channeled runoff directly onto contaminated soils at the site.
After additional soil and groundwater samples indicated elevated levels of chromium, it was determined that there was still a threat to public health posed by the site through exposure to hexavalent chromium-contaminated soils, surface water and groundwater through direct contact, inhalation and ingestion pathways. The threats met the removal criteria specified in the National Contingency Plan (NCP) at 40 CFR Section 300.415(b) (2)(i), (ii), (iv), (v). A second action memorandum was issued in 1991 that specified treatment of hexavalent chromium-contaminated soils on-site as the primary removal alternative with off-site disposal of soils as a backup.
In 1991, EPA also issued an Administrative Order on Consent (AOC) to all the identified potentially responsible parties (PRPs) that directed the removal and treatment of on-site contaminated soils. The treatment process included soil screening, chemical addition for chromium reduction, and the addition of Portland cement for soil fixation. The treated soils were formed into 5-foot by 5-foot by 6-foot blocks for curing, testing and placement. Approximately 14,000 cubic yards of chromium-containing soil were treated, creating approximately 7,000 blocks. The treatment process rendered the contaminants as a less toxic and immobile trivalent chromium (Cr+3). Another 19,000 cubic yards of chromium-containing soil were also disposed of off-site to address final site configuration and future land use considerations. Soil treatment and off-site disposal was completed in 1994. Work conducted under the AOC is summarized in the 1995 Response Action Fieldwork Completion Report.
Quarterly groundwater monitoring was initiated in June 1992 and continued through August 1995. Total chromium concentrations were above the Maximum Contaminant Level (MCL) and Montana Water Quality Bureau WQB-7 quality standard of 100 micrograms per liter (µg/L) at five of the 16 wells monitored in June 1992. In August 1995, 25 wells were monitored and eight of these wells displayed total chromium concentrations greater than 100 µg/L. That same year, EPA issued an action memorandum selecting monitored natural attenuation to address the groundwater contamination remaining after the soil removal. Data from leaching tests of the treated soil blocks placed on-site, coupled with the geochemistry of the site groundwater, supported monitored natural attenuation as a remedy. The groundwater within the alluvial aquifer is supplied by infiltration of precipitation and thus is of an oxidizing nature, and the pH of the groundwater is neutral to slightly basic. The neutral to basic pH (<8) and oxidizing state of the groundwater combine to create a geochemical environment that is conducive to the formation of chromium oxide, Cr2O3, which is a stable, solid form of trivalent chromium with very low solubility. Consequently, there was no reason to believe that chromium would be released to the aquifer beyond the treated blocks under the range of conditions expected for this site.
In 1996, EPA issued a Unilateral Administrative Order (UAO) to all PRPs notified in the 1991 AOC. The UAO required implementation of a Non-Time Critical Removal Action. Also in 1996, the groundwater monitoring network was reduced from 25 to 12 wells. This groundwater monitoring program was designed to track groundwater levels as well as groundwater quality. The purpose of the program was to monitor natural attenuation of chromium and evaluate contaminant migration. Semiannual groundwater monitoring of site wells began in November 1996. Total chromium concentrations began to be below the MCL and WQB-7 standard starting in December 1999. After three consecutive years of meeting the groundwater performance standard established in the 1996 action memorandum, the October 2002 sampling event finalized the demonstration that the MCL and the WQB-7 standards for chromium in groundwater had not been exceeded for a period of three consecutive years. The results of groundwater sampling are documented in the site's Final Closure Report.
This action addressed all remaining health and environmental issues at the site, making it eligible for deletion from the NPL.
Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, ongoing, 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.
See the Site Documents section below for documents that support actions taken at the site and annual updates. EPA and MDEQ expect to conduct community interviews during the five-year review scheduled for late 2012.
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.
Institutional controls over land use and groundwater use have been established and are maintained by the town. The institutional controls allow for site development and construction in the treated soil repository in compliance with the town’s zoning ordinance and federal Superfund law. The town of Columbus has built its new public works building (shown at right) on top of a portion of the waste repository located on the eastern half of the site. Columbus has provided EPA and DEQ with a complete set of plans and the contract documents/specifications for the building.
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.
The town of Columbus complied with the 1996 UAO by establishing and implementing institutional controls at the site in the form of a zoning ordinance. It has maintained the ICs as part of its response actions as a responsible party under Superfund. The zoning ordinance was approved by town council in March 1995 and created the Superfund Overlay District (SOD). The intent of the SOD is to protect public health, safety and welfare while allowing appropriate use of lands within the district. This intent is accomplished by:
- Assuring that land use in the SOD is compatible with protecting and providing for permanent preservation and maintenance of response actions pursuant to the Superfund law, including soil caps, treated concrete blocks, and other remedial structures.
- Requiring that any development within the block placement area (treated soil repository) of the SOD be preceded by submittal of detailed site and construction plans, prepared by an architect or engineer, for review and approval by the town, EPA and MDEQ as an IC in the context of federal Superfund law.
- Requiring submittal of as-built drawings with certification from an architect or engineer that site development and construction within the block placement area (treated soil repository) was completed in compliance with zoning title and federal Superfund law.
- Limiting well use and prohibiting drilling of wells (except for monitoring wells) within the SOD.
- Placing a notice to purchasers on any deed, contract for sale or other instrument of conveyance before any lot or parcel in the SOD is conveyed (Ordinances 321 (2004) and 298 (1997)).
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 2008 five-year review recommended revisiting institutional controls. Due to residual groundwater contamination levels above MCLs within the block placement area, it was determined that groundwater use restrictions should be maintained within this area. A fourth action memorandum was issued in 2008, based on this and other recommendations from the five-year review, and had four purposes:
- It clarified points of compliance for groundwater at the site. Four wells down-gradient of the source area have been identified as the points of compliance for groundwater.
- It ensured that the restriction on groundwater use within the block placement area would be maintained as long as institutional controls are necessary. This revision to groundwater restrictions was identified as a necessary remedy element in order to ensure that the actual or threatened releases of hazardous substances from this site do not occur. Chapter 17.76.040 of the Columbus Municipal Code was amended on February 19, 2008 through Ordinance 328 to include provisions that limit groundwater use within the block placement area. The second reading was done on March 3, 2008 and Ordinance 328 of the Columbus Town Council, amending Subsection D of Section 17.76.010 and Section 17.76.040 of the Columbus Municipal Code, took effect 30 days later.
- It clarified the 30-year groundwater monitoring requirement identified in the 1996 action memorandum.
- It required MDEQ and EPA to prepare a Post Removal Site Control Plan pursuant to Section 300.415(l) (3) of the NCP. This plan identifies background, down-gradient and source area monitoring points, sampling frequency and duration, as well as analytical and statistical methods that will be employed to review collected data. It also establishes contingency trigger levels for chromium concentrations in groundwater that, if realized, may require additional monitoring of groundwater and statistical procedures that will modify or maintain sampling frequency.
To ensure compliance with the federal Superfund law as provided in the SOD, the town also agrees to notify EPA and MDEQ of any proposed land use change and/or development of the site that would affect the block placement area or remedial structures such as vegetative caps, drainage facilities or fences. Such notification will be given in writing sufficiently in advance of any action by the town to approve such changes to allow EPA and MDEQ to determine whether the proposed changes could adversely affect the maintenance or protectiveness of the Superfund remedial measures at the site. Such notice will include any information required in the ordinance, such as detailed site and construction plans, and other information necessary to determine the potential impact of the proposed changes on the Superfund remedial measures.
Currently, EPA and MDEQ agree that the treated soil is "waste left in place" above levels that allow for unlimited use and unrestricted exposure. Policy five-year reviews will continue. As part of the future work to be performed at the site, the town agrees to provide access to the site and to enforce ICs. MDEQ and EPA agree to meet with the town at least once every five years to discuss the site land use and groundwater use restrictions. These meetings are designed to provide better understanding of the issues associated with these restrictions as well as to notify the agencies of any upcoming land use changes that may require a more comprehensive review.
On August 31, 2012, EPA and MDEQ kicked off the second five-year review with a site visit. EPA has procured the Army Corps of Engineers to conduct the review of the remedy. A draft report is expected to be available by end of year and a final report will be issued by March 2013.
Post Removal Site Control Plan, October 2013
Second Five-Year Review Report, April 2013
2011 Groundwater Monitoring Results Final Report, March 2012
Final Closure Report, November 2004
Response Action Fieldwork Completion Report, March 16, 1995
Action Memorandum: Request for…Funding for a Removal Restart, August 12, 1991
Action Memorandum: Request for Removal Action Approval, March 26, 1990
Remedial Project Manager
U.S. Environmental Protection Agency
Region 8, Montana Office
10 West 15th Street, Suite 3200
Helena, MT 59626
866-457-2690 (toll free)
Montana Department of Environmental Quality
1100 North Last Chance Gulch
P.O. Box 200901
Helena, MT 59620-0901
800-246-8198 (toll free in-state only)
View Documents at:
Stillwater County Library
27 North 4th Street
Columbus, MT 59019-0266
U.S. Environmental Protection Agency
Region 8, Montana Office
10 West 15th Street, Suite 3200
Helena, MT 59626
866-457-2690 (toll free)
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