EPA Superfund Site

ANACONDA ALUMINUM CO COLUMBIA FALLS REDUCTION PLANT

MT | EPA ID MTD057561763

About this site’s exposure pathways: As of September 2025, the Anaconda Aluminum Co Columbia Falls Reduction Plant Superfund site is considered Current Human Exposure Not Under Control (HENC). A byproduct of the aluminum reduction process is spent pot liner (SPL), which is known to contain cyanide and fluoride. SPL was disposed of onsite in several landfills between 1955-1990. An Administrative Order on Consent for the Remedial Investigation (RI) and Feasibility Study (FS) was signed in late 2015. The RI Report was finalized on February 21, 2020, and the FS Report was finalized on June 16, 2021 and the ROD was signed in January 2025.
The findings from the RI indicate that polycyclic aromatic hydrocarbons (PAHs) (soil and sediment), cyanide (groundwater), and fluoride (groundwater) are the Contaminants of Concern (COCs) that are the primary risk drivers at the Site. The results of the RI indicate that groundwater is the primary migration pathway for the potential transport of COCs from the various source areas. In addition, results indicate that cyanide and fluoride are the primary COCs from a contaminant migration⁄fate and transport perspective. The exposure pathways are considered unacceptable based on EPA risk-based criteria because they contribute to risk estimates that exceed acceptable levels for potential human health risk (i.e., excess lifetime cancer risk of 1E-06 for carcinogens; or hazard index of 1 for non-carcinogens) or pose moderate or higher risk from the ecological perspective (i.e., lowest observed adverse effect level Hazard Quotient values greater than 1 for at least one receptor).
To date, the planned activities to address this pathway are identified and detailed in EPAs proposed plan and Record of Decision (ROD). The proposed plan was released in June 2023 and the ROD was signed January 2025. EPA currently anticipates that human exposure will be under control by September 2031. In addition, the Potentially Responsible Party (PRP) implemented a time critical removal action in Fall 2020⁄Spring 2021 at the South Percolation Ponds. The South Percolation Ponds were the only feature within the River Area Decision Unit (DU) that contained sediments with COCs at concentrations exceeding preliminary remediation goals. This work was implemented in advance of FS completion to prevent erosion and transport of contaminated sediments by the Flathead River and was performed in accordance with the EPA-approved Removal Work Plan. The EPA estimates the human exposure will be under control in September 2031, when the remedial actions have been completed.
The PRP, in consultation with the EPA and state partners, provides the community with information to reduce exposures to potentially contaminated sources. The PRP has implemented a robust community involvement program to communicate risk about the site and sponsors a bi-annual well water sampling program for residents of Aluminum City. The PRP has been proactive in coordinating community involvement support with EPA. EPA’s site profile page (https://www.epa.gov/superfund/columbia-falls) is regularly updated with information on the status of the project. EPA provides periodic project updates to the community and holds update meetings for the community.