An aluminum smelter buried toxic waste, and now a $57 million wall must hold it

The U.S. Environmental Protection Agency (EPA) announced on July 7, 2026, that Columbia Falls Aluminum Company (CFAC) agreed to a $57 million cleanup of a former smelter site near Columbia Falls, Montana. The company will pay past response costs and carry out the work under EPA and Montana Department of Environmental Quality (DEQ) oversight.

The site is the Anaconda Aluminum Co. Columbia Falls Reduction Plant, and it ran for 54 years, from 1955 to 2009. The contamination it left is specific and measurable: arsenic, cyanide, and fluoride in the groundwater, plus polycyclic aromatic hydrocarbons in the soil.

For anyone who draws water from a well near a former smelter, gardens in the soil, or lives along the Flathead River, the CFAC agreement matters for one reason. This is not a cleanup that digs up the poison and hauls it away. It is a cleanup that wraps the source in an underground wall and holds it in place. Understanding why containment was chosen, and what it does and does not protect, is the difference between assuming the problem is gone and confirming it at your own tap.

Where the Contamination Came From

The source has a name most people have never heard: spent potliner.

Aluminum smelting runs on huge electrolytic cells called reduction pots, each lined with carbon and refractory material. Over time, that lining absorbs the chemistry of the process and wears out. When it is removed, it becomes spent potliner, a hazardous waste loaded with the byproducts of aluminum reduction.

CFAC stored significant amounts of that spent potliner in unlined landfills near the former smelter building, according to the EPA. The word “unlined” is the entire problem. A lined landfill sits on an engineered barrier that stops waste from leaching into the ground. An unlined one does not. Rain and snowmelt percolate through the waste, dissolve its contaminants, and carry them straight into the soil and groundwater below.

Three contaminants leached out of the potliner into the groundwater: arsenic, cyanide, and fluoride. Other areas of the site were contaminated with PAHs from the aluminum reduction process. The EPA and DEQ selected the cleanup in a Record of Decision signed in January 2025.

Why This Fix Is a Wall, Not a Dig

Earlier cleanups in this series excavated contaminated soil and trucked it off-site. The CFAC plan does something different, and the difference is the point.

The cleanup uses containment. CFAC will place low-permeability caps on the landfills and build a slurry wall to fully encompass the main source of groundwater contaminants, the EPA said. Two structures, two jobs.

A low-permeability cap is a sealed cover placed over a landfill. It keeps rain and snowmelt from soaking into the buried waste, which cuts off the water that would otherwise leach contaminants downward. Stop the water from entering, and you slow the leaching at its start.

A slurry wall is an underground barrier, a trench filled with a low-permeability mixture, sunk into the ground to encircle the contamination. It works like a cup buried around the waste, blocking groundwater from carrying contaminants outward. The EPA says this wall will prevent further contamination of the groundwater, stop the migration of contaminants toward the Flathead River, and bring seeps along the river into ecological compliance.

The reasoning is scale. The main source is a mass of buried potliner too large to excavate practically. Isolating it, sealing the top, walling the sides, contains the plume where digging cannot.

The Three Contaminants and Their Thresholds

Containment is judged against numbers. Each of the three groundwater contaminants carries a measurable limit that tells a household when a well result is a problem.

These three numbers, 10 ppb arsenic, 0.2 mg/L cyanide, 4.0 mg/L fluoride, turn an invisible plume into something a lab report can measure.

The Three Pathways From the Plume to Your Body

In building biology, exposure follows a pathway, a source, a route, and a person at the end of it. A groundwater plume near a smelter reaches people through three routes.

1. Drinking Water

This is the primary pathway for a groundwater problem. Contaminants dissolved in groundwater travel toward wells, and a household drinking, cooking with, and mixing baby formula from that water takes them in with every use. A private well near the site is the highest-priority thing to test, because no one tests it for you.

2. Soil Ingestion

Where contaminated groundwater rises near the surface or where waste sits shallow, soil becomes a route. Children are the highest-risk group: they play on the ground and put hands to mouths, transferring soil, and its arsenic, into the body. Contaminated dust tracked indoors adds to the dose, settling on floors and toys.

3. Skin Contact

Gardening, yard work, and contact with contaminated soil or river seeps put skin against the contaminants. Skin contact is a lower-dose route than drinking or swallowing, but it moves soil onto hands and clothing that later reach the mouth and the home.

Each pathway delivers a share of the total dose. Cutting any one of them lowers overall exposure.

What the Cleanup Protects, and What It Does Not

The slurry wall and caps protect the groundwater and the Flathead River by holding the source in place. “This slurry wall will prevent further contamination of the groundwater, stop the migration of contaminants toward the Flathead River, and bring seeps along the Flathead River into ecological compliance,” the EPA said.

That is community-scale source control. But containment differs from removal in a way that matters at home: the waste stays on-site. A wall works only as long as it holds, which is why the plan runs under long-term EPA and DEQ oversight, with the design and implementation stage, the remedial design/remedial action, following court approval of the consent decree.

For a household, that means the regional fix reduces the odds of exposure but does not replace testing your own water. The wall protects the aquifer at large. Your specific well, your specific soil, and your specific tap are measured one address at a time.

Practical Steps You Can Take

You cannot build a slurry wall from your home. You can find out whether the three contaminants have reached your water and soil, and put barriers between them and your family.

Test your private well against the limits

Private wells fall outside federal drinking-water rules, so the testing is your responsibility. Have a certified lab measure arsenic (limit 10 ppb), cyanide (0.2 mg/L), and fluoride (4.0 mg/L). Near a Superfund site, retest periodically, plumes shift.

Filter with reverse osmosis

For arsenic and fluoride in water, a reverse osmosis system certified to NSF/ANSI Standard 58 is the most reliable household reduction. Confirm the certification lists arsenic and fluoride specifically. A standard carbon pitcher is not enough for these.

Test your soil against 0.4 mg/kg for arsenic

If your yard sits near the site, have a certified lab test soil where children play and where you grow food, and compare to the residential screening level.

Wash hands before eating

Handwashing before every meal and snack, and after outdoor play, breaks the soil-ingestion pathway at the point where soil would reach the mouth. It is the single most effective habit for protecting children.

Adopt a shoes-off policy

Removing shoes at the door keeps contaminated soil from becoming indoor dust that settles where children play.

Cover bare soil

Grass, clean mulch, or ground cover blocks direct skin contact and keeps soil from becoming airborne dust.

Stay clear of river seeps

Until the cleanup brings the Flathead River seeps into compliance, keep children and pets away from seep areas, and wash skin after any contact.

Garden in raised beds

If you grow food near the site, use raised beds with clean, tested soil and a barrier at the bottom, and wash all produce thoroughly.

Do not rely on boiling

Boiling does not remove arsenic, cyanide, or fluoride, and by evaporating water it can slightly concentrate them. Filtration, not heat, is the tool.

Comment on the consent decree

The proposed consent decree, filed with the U.S. District Court for the District of Montana, carries a 30-day comment period, a direct point of community input.

Why This Matters Now

The CFAC agreement puts a price and a method on a problem 17 years in the making since the smelter closed. Fifty-four years of aluminum production left spent potliner in unlined pits, and three contaminants, arsenic, cyanide, and fluoride, have been leaching from that waste into the groundwater ever since.

The chosen fix is telling. Rather than dig out a mass of waste too large to excavate, CFAC will seal it under caps and encircle it with a slurry wall, holding the source where it lies. “This consent decree represents a significant milestone on the path to successful cleanup and redevelopment,” EPA Region 8 Regional Administrator Cyrus Western said. Montana DEQ Director Sonja Nowakowski said the work will “protect the Flathead River and Columbia Falls.”

For the household nearby, the response is the one source control always demands: find out whether the contamination has reached you, and cut the pathways if it has. Test the well against 10 ppb arsenic, 0.2 mg/L cyanide, and 4.0 mg/L fluoride; test the soil against 0.4 mg/kg; filter with reverse osmosis; and keep contaminated soil off small hands and out of the house. The wall will contain the source. Whether its contaminants reach your body is a matter of pathways you can measure and control.