Region 8
Serving Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming and 27 Tribal Nations
Superfund Program
National Information
Regional Information
Site Information
National Priorities List (NPL) History
Proposed Date
10/15/1984
Final Date
6/10/1986
Construction Completion
9/27/1996
Mouat Industries
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Site Type: Active NPL City: Columbus County: Stillwater Zip code:59019 EPA ID#: MTD021997689 Congressional District: At Large |
What's New
Mouat becomes the first Federal Superfund Site in Montana proposed for deletion from National Priority List.
Read the Federal Register Notices here:
http://regulations.justia.com/view/138783: DOCID:fr24mr09-24
Site Description
The Mouat Industries Site is located south of Columbus, Montana. The Site is located 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 was leased from the Town 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 that was sold as a corrosion inhibitor. The process subsequently generated sodium sulfate process wastes containing sodium chromate and sodium dichromate. These hexavalent chromium (Cr VI) 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 lead EPA to send a letter to the Town in 1984 stating that the analytical numbers from the monitoring wells sampled 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 NPL in 1984, 29 FR 40320 (Oct. 15, 1984). The Site received a Hazard Ranking System score of 31.66. The listing was final in 1986, 51 FR 21054 (June 10, 1986).
Site Risks
Soils and groundwater were contaminated with hexavalent chromium. Hexavalent chromium is a hazardous substance as defined by CERCLA Sec, 101(14), and designated as such under 40 CFR 117 and 40 CFR 302.
Cleanup Progress
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 CrVI contaminated soils, surface water and groundwater through direct contact, inhalation and ingestion pathways. The threats met the removal criteria specified in the NCP at 40 CFR Section 300.415(b) (2)(i), (ii), (iv), (v). A second Action Memorandum was issued in 1991 which specified treatment of CrVI contaminated soils on-Site as the primary removal alternative with off-site disposal of soils as a back up.
In 1991, EPA also issued an Administrative Order on Consent (AOC) to all the identified PRPs which directed the removal and treatment of on-site contaminated soils. The treatment process included soil screening, chemical addition for chromium reduction, and Portland cement addition for soil fixation. The treated soils were formed into 5' x 5' x 6' 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 III). 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 Cr concentrations were above the maximum Contaminant Level (MCL) and Montana Water Quality Bureau (WQB) WQB-7 water 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 Cr concentrations greater than 100 µg/L. That same year, EPA issued an action memorandum to address groundwater problems remaining after the soil removal which chose monitored natural attenuation. Data from leaching tests of the treated soil blocks placed on-Site coupled with the geochemistry of the Site groundwater, supported natural attenuation. 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 for the formation of chromium oxide, Cr2O3, which is a stable, solid form of CrIII that has a 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 noticed 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 twenty-five to twelve network wells. This groundwater monitoring program was designed to track groundwater levels as well as groundwater quality. The purpose of this program was to monitor natural attenuation of chromium and evaluate contaminant migration. Semi-annual groundwater monitoring of MPWN wells began in November 1996. Total Cr 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 Final Closure Report, Mouat Industries NPL Site.
This action addressed all remaining health and environmental issues at the Site making the Site eligible for deletion from the NPL.
Community Involvement
Community involvement is integral to the cleanup process at Superfund sites.
See the Site Documents section below for documents that support actions taken a tthe Site and annual updates.
Land Use Controls
The Town complied with the 1996 UAO by establishing and implementing ICs at the Site. The Town established ICs over land use and groundwater use through a zoning ordinance. Institutional Controls over land use and groundwater use have been established and maintained by the Town as part of its response actions as a responsible party under Superfund. A zoning ordinance was approved by Town Council in March 1995 and created the Superfund Overlay District. The intent of the SOD is to protect public health, safety and welfare while allowing appropriate use of lands within the SOD. This intent is accomplished by:
1. 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;
2. Requiring that any development in 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;
3. Requiring submittal of as built drawings with certification from an architect or engineer that Site development and construction in the block placement area (treated soil repository) was completed in compliance with zoning title and federal Superfund law;
4. Limiting well use and prohibiting drilling of wells (except for monitoring) within the SOD; and
5. 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 (Ordinance 321 (2004); Ordinance 298 (1997)).
Five Year Review
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 (4) purposes:
1. It clarified Points of Compliance for groundwater at the Site. Four wells down-gradient of the source area have been identified as the Point of Compliance for groundwater.
2. It ensured that the restriction on groundwater use in 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 through Ordinance 328 to include provisions that limit groundwater use in the block placement area on February 19, 2008. The second reading was done on March 3, 2008 and Ordinance 328 of the Town Council of the Town of Columbus, Montana, amending Subsection D of Section 17.76.010 and Section 17.76.040 of the Columbus Municipal Code took effect thirty days following.
3. It clarified the 30 year groundwater monitoring requirement identified in the 1996 Action Memorandum.
4. 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 (Cr) 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 DEQ 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 notify the Agencies of any upcoming land use changes that may require a more comprehensive review.
Site Documents
Note: the following documents are Adobe PDF documents (about PDF files)
Technical Documents
Five-Year Review Annual Update, December 2008 (PDF, 5 pp, 51 K)
Five-Year Review Report, March 18, 2008 (PDF,1.7 MB)
Contacts
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EPA Roger Hoogerheide, Remedial Project Manager View Documents at: U.S. Environmental Protection Agency Stillwater Co. Library |
Montana Department of Environmental Quality Daryl Reed, Project Manager |