Reports describing the extent of the hazards at the CFAC site are found on EPA’s website. They form the basis for remedial cleanup planning. The reports are also quite long and complex with lots of data and analysis. Unfortunately they are difficult for the average citizen to follow. Here, we hope to simplify the key technical and regulatory issues for a general audience. Note that this is our interpretation of the official reports – we hope we have maintained accuracy in the interest of simplicity. Please refer to the official EPA documents for the most complete and accurate picture.
What are the actual hazards? Contaminants, location, and movement.
Short answer -> Cyanide, fluoride, and arsenic. Mostly located in the central landfill area, and gradually migrating south in the ground water toward river. Polycyclic aromatic hydrocarbons are also present in soils and landfills and they are not found in groundwater.
More -> The Remedial Investigations conducted in 2016-19 looked at potential sources of contamination:
- landfills
- percolation ponds
- plant drainage systems
- the former drum storage area
- underground and above ground storage tanks
- waste and raw materials storage and handling areas
The study looked at the four potential ways people and the environment could be exposed to contamination:
- groundwater
- surface water and sediments
- porewater
- soil
The contaminants that have been identified on the site that have the potential to impact human and ecological health are cyanide (CN), fluoride (F), arsenic (As), and polycyclic aromatic hydrocarbons (PAHs). The first three have a high solubility in water and thus can migrate in groundwater from the site. Exposure to polyaromatic hydrocarbons is limited as they tend to stay in place in landfills and soils where they can be more easily managed. Cyanide and fluoride are not considered to be human carcinogens, while arsenic and PAHs are.
In the remedial investigations which ended in 2018, sampling of the landfill, soils, and surface/ground water in and around the CFAC site has yielded a picture of where the contaminants are located. The water soluble contaminants, cyanide and fluoride, have indeed begun migrating via ground water beneath the Site and have formed a “plume” which is well-defined and is effectively represented in the following figures from the 2018 sampling results.
Cyanide plume in ground water (2018).
Fluoride plume in groundwater (2018).
Arsenic observations in groundwater. Purple symbols indicate values above the human health standard (2018).
In addition:
- PAHs are found in shallow soils at the North Percolation Ponds, Effluent Ditch, and Main Plant Area.
- Metals are in shallow soils at the North Percolation Ponds, Main Plant Area, and all landfills.
New data gathering has been performed in late 2025 to determine how the picture has changed since the last sampling in 2018. Those results will guide final remedial designs prior to construction work. We will share the report findings when issued in mid-2026.
Concern for Human and Ecological Health. What are the risks from contaminants?
Human health. Note that the standards set by the EPA and Montana DEQ for safe levels of these contaminants for human health in drinking water are 200 micrograms per liter (µg/L) CN, 4000 µg/L F, and 10 µg/L As. The outer (blue) edges of the cyanide and fluoride plumes in the figures above from 2018 testing are defined by the DEQ standards. That is, anything within the outer blue lines is above the safe levels (i.e., unsafe) for human health. It is important to note that groundwater beneath the Site is not used for and is currently restricted from use for drinking water and therefore does not pose a risk to human health. Recent and future testing of groundwater is intended to monitor the locations and concentrations of these contaminants and ensure remedial actions do indeed maintain concentrations at safe levels where exposure can occur. Also note that the plume shape is determined by the ground water flow, moving generally from north to south towards the Flathead River.
Safety standards for concentrations of the contaminants is different for human and ecological health.
Ecological effects. Exposure conditions in two aquatic areas (see map below) indicate the potential for adverse ecological effects due to direct contact pathways. In addition, sediments in the former South Percolation Ponds that had potential for adverse ecological effects were removed during the remedial action completed in 2021.
1. Flathead River – Backwater Seep Sampling Area: The evaluation of Flathead River sediment, sediment porewater, and surface water data indicate that the greatest potential for ecological exposure to Site-related contaminants is associated with direct contact exposure within the Backwater Seep Sampling Area, and areas where groundwater containing cyanide and fluoride discharges to surface water. Dilution of surface water concentrations to below both chronic and acute standards occurs rapidly with increasing distance from the Backwater Seep Sampling Area, particularly during periods of elevated discharge within the Flathead River. Outside of the sampling locations within the Backwater Seep Sampling Area and stations along the shoreline immediately downstream of the Backwater Seep Sampling Area, cyanide concentrations were typically “nondetect”; and did not exceed chronic benchmarks, respectively, in multiple rounds of surface water sampling events. This finding indicates:
- The potential area of exposure to aquatic receptors at concentrations exceeding benchmarks is spatially-limited to a groundwater-surface water mixing zone along the shoreline within and immediately adjacent to the Backwater Seep Sampling Area.
- Potential risks associated with direct and incidental wildlife ingestion pathways are considered by EPA to be minimal in the Backwater Seep Sampling Area.
Seep area.
2. Flathead River Riparian Area Channel: The evaluation of sediment and surface water data in this area (see map above) indicate the potential for adverse effects associated with direct contact exposure of aquatic receptors to cyanide, fluoride, and metals in surface water. Surface water data indicate potential exposure to contaminants may be influenced by groundwater discharge similar to the Backwater Seep Sampling Area.