EPA’s Selected Remedies for Cleanup
After completion of investigations into the nature and extent of the contamination at the CFAC site, EPA proposed a cleanup plan. Various alternatives were methodically evaluated and the rationale for selection of the preferred methods was described in the Proposed Plan. Following that, the EPA issued its Record of Decision (full doc, 2-page fact sheet) which formally authorized the plan to proceed with remediation (cleanup) of the Site.
So far, the Superfund process has involved identifying the problem and developing solutions. Now, the final design work is in progress, and it is anticipated that by 2027 the bulk of the remediation construction work will begin. However, first the Consent Decree, a legally binding agreement, must be formalized between EPA and CFAC/Glencore. This is expected later in 2026.
There are FOUR focus areas for cleanup, called Decision Units or DUs. Note that DU1, 5, and 6 have been combined. See map below. Following is a summary of EPA’s selected remedies. The documents on EPA’s website contain detailed information on the rationale for selection of each remedy. Final design changes are based on additional testing, including testing completed Fall of 2025.
Decision Units 1-6 at the Site. From EPA’s Proposed Plan for Cleanup (June, 2023).
Landfills DU1/Groundwater DU6/River Area DU5
Containment via Capping, Fully Encompassing Slurry Wall, Interior Extraction, and Monitoring
This combined remedy (landfills, groundwater, river area) includes River Area DU5, because the primary objective of the DU5 monitoring is to evaluate whether decreases in groundwater contamination from DU1/DU6 remedial actions are effective in achieving surface water standards at the DU5 seeps. This joint DU is the critical piece for the site considering the nature of risks, costs (about 80% of total for the Site) and engineering effort.
The wells will be used initially for monitoring and, if the slurry wall is not effective in stopping contaminant migration, they will be used to extract groundwater for treatment. If treatment is determined to be necessary, it would be seasonal and require much less volumes of groundwater to be treated compared to the extraction alternatives which would take place downgradient, i.e., in the plume between the slurry wall and the river area.
The remedy would:
• Construct low‐permeability caps on the Wet Scrubber Sludge Pond and Center Landfill and maintain the West Landfill cap.
• Construct a fully encompassing, low permeability slurry wall around the West Landfill and Wet Scrubber Sludge Pond to depths that key into the underlying low‐permeability, glacial till layer (typically between 100 and 125 feet). If dewatering is needed, that is, if groundwater levels increase within the wall, treat captured groundwater in a treatment plant and return effluent to groundwater via infiltration basins. Brief description of slurry walls.
• Install eight pairs of extraction/monitoring wells (one within and one outside of the slurry wall) downgradient of the Wet Scrubber Sludge Pond, but interior to the slurry wall, with another series of monitoring wells downgradient of the slurry wall.
• Construct a groundwater treatment facility to treat cyanide, fluoride, and arsenic, with infiltration basins for discharge of treated effluent back to groundwater. The facility will be used during construction of the slurry wall for dewatering and will be retained for use after construction is completed. If pumping is needed because groundwater elevations in the interior and downgradient monitoring wells indicate that the slurry wall is not performing as designed, the groundwater extracted from the interior of the slurry wall will be treated and then discharged into infiltration basins (collection areas allowing water to soak into ground).
• Implement groundwater, surface water, and sediment porewater performance monitoring of the groundwater plume using existing and newly installed monitoring wells and at seeps and other floodplain areas within River Area DU5 along the edge of the Flathead River. Pore water is the water found in the small gaps, or “pores,” between sediment, soil, or rock particles, located below the ground surface.
According to EPA this method is consistent with its presumptive strategy for landfill sites as containment remedies are preferred over treatment remedies, while extraction and treatment of groundwater is retained if necessary.
Landfills DU2
Containment via Capping
The components of this remedy are effective and permanent and easily implementable and would have few impacts on the community, according to EPA.
Costs are moderate and represent only about 12% of the total estimated costs for the site.
The remedy would:
• Continue to maintain existing caps on the East Landfill and Sanitary Landfill.
• Install a low‐permeability cap on the Industrial Landfill.
• Improve existing soil covers at the Asbestos Landfills.
Soils DU3
Excavation with On‐Site Consolidation
This remedy was chosen for long‐term effectiveness and permanence while still scoring highly for short‐term effectiveness and implementability.
Costs are the lowest of other alternatives and represent only about 2% of the total estimated costs for the site.
The remedy would:
• Excavate approximately 32,500 cubic yards of impacted soil.
• Consolidate excavated materials with disposal on‐site at the Industrial Landfill or an Agency‐approved new, on‐site engineered repository.
North Percolation Ponds DU4
Excavation with On‐Site Consolidation
This remedy was chosen for long‐term effectiveness and permanence while still scoring highly for short‐term effectiveness and implementability.
Costs are moderate and represent approximately 4% of the total estimated costs for the site.
The remedy would:
• Excavate approximately 35,000 cubic yards of impacted material from the North‐East Percolation Pond, North‐West Percolation Pond, influent ditch, and effluent ditch.
• Consolidate excavated materials with disposal on‐site at the Industrial Landfill or an Agency‐approved new, on‐site engineered repository.