Operators at a South Burlington wastewater treatment plant first noticed something strange Friday morning. A tank was filling with bubbles, like someone had filled it with laundry detergent.

“It looked like a white bubble bath,” said Bob Fischer, the water quality superintendent for South Burlington. “I could tell it was firefighting foam, but I didn’t know what kind.”

Fischer was right. The night before, 800 gallons of highly concentrated firefighting foam had spilled over the floor of the Vermont Army National Guard aircraft hanger in South Burlington.

It gathered in the landing gear of a Black Hawk military helicopter, before some 150 gallons flowed down a drain and entered the town’s wastewater system, according to National Guard estimates. The material reached a nearby pump station before entering the water treatment plant, which sits next to the Winooski River.

This type of firefighting foam is called aqueous film-forming foam or AFFF. It’s used for fires that involve flammable liquids, like burning jet fuel. The state of Vermont has banned its use because it contains relatively high concentrations of manufactured chemicals known as PFAS, which have been linked to cancer, liver problems and a myriad of other health issues and can be toxic even in tiny doses.

The Vermont National Guard hadn’t released the material for years — it wasn’t even supposed to be used in the case of a fire.

“If the fire suppression system discharged, all it would discharge is just water — we essentially bypassed the AFFF tank,” said Col. Jacob Roy, the construction and facility management officer at the National Guard. “We realized that the risk to the environment was pretty significant, and we did not want a chance having either a purposeful or accidental release.”

Roy suspects the spill Thursday night was a mechanical failure in their containment system. He said there’s been no evidence of a fire.

Since Friday morning, contractors have been out every day cleaning and testing the National Guard facility, the sewer lines, the pump station and the wastewater treatment plant. Roy expects the facility to be open to staff by Wednesday morning.

And test results from the Winooski River should come back within a week.

In the grand scheme of things, a release of around 150 gallons — about the size of a hot tub — is pretty small within the bigger river system, said Matt Chapman, who directs waste management and prevention at Vermont’s Department of Environmental Conservation.

“It’s good for perspective purposes to appreciate that on a normal day in the Winooski River, the river has a flow rate of about 5,000 gallons per second,” he said.

While he’s not overly concerned about contamination in the river, he said what’s less straightforward going forward is how to properly dispose of the 650 gallons of foam that’s been collected. The EPA released interim guidance this year that includes incineration, storage in landfills and underground injection, but none of the options are good.

“I think it’s fair to say there’s no guidance from EPA,” Chapman said.

“One of the reasons why we still have this product over the years onsite, [is] because it is not an easy product to get rid of,” echoed Roy.

He said the disposal method will ultimately depend on the concentration of PFAS found in testing and directed further questions about the disposal process to the National Guard’s waste disposal contractor, Republic Services.

A spokesperson for the company said they operate several hazardous waste landfills across North America, which are engineered to safely and responsibly manage this type of waste.

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