How do you eliminate a toxin designed to last forever? That is the very question which the Martha’s Vineyard Airport was confronted with four years ago, when they found out that an accumulation of the toxic, so-called “forever chemical” PFAS on their property was infiltrating the Island aquifer. And so, rather than try to destroy the PFAS, a project was initiated to trap it, using advanced material science to turn the aquifer itself into a filter.
Known as PlumeStop, the project, which was completed this fall, seeks to stop the chemicals in their tracks, caging them underground before they reach the aquifer or other wells.
“It’s an innovative technology,” said Ron Myrick, the vice president of Tetra Tech who works with the engineering firm in charge of the project.
In 2018, the Martha’s Vineyard Airport first detected PFAS — which stands for per-and-polyfluoralkyl substances — in nearby residential wells, after it was released at the airfield for several decades.
Speaking with the Gazette recently, Mr. Myrick expounded on the unique properties of the “forever chemicals” with which he has spent much of the last four years. They are unparalleled in durability, and their ability to repel oil and water has made them ubiquitous in everything from raincoats to hygiene products to pizza boxes. Their presence in humans, however, can have unwanted side-effects, including hormone and fertility disruption, high blood pressure and cancer, according to MassDEP.
In the 1960s, the U.S. Navy found another application for PFAS: its repulsion to oils made it excellent at smothering fuel fires. It was in that capacity, as a component of fuel fire specific firefighting foams, that PFAS was introduced to the airport.
“The FAA required any airport with commercial traffic to be set up and able to deploy these foams immediately,” Mr. Myrick said. “Every year they would send a [representative] to say, ‘show us that you can deploy.’”
After years of testing, the Vineyard soil became saturated, although it didn’t raise many eyebrows.
“There really wasn’t a particular health concern about it at that time,” he said.
Mr. Myrick began work with the airport back in 1997, on a project to mitigate dry-cleaning chemical contamination. Having developed some familiarity with Island groundwater, Mr. Myrick approached the airport in 2018 with a proposed project to start PFAS-testing downstream wells, as concerns over it rose nationwide. They found dozens of affected properties, leading the airport to pay to have 50 filters installed on wells exceeding the 20 parts per trillion of water limit set by the state.
With the immediate danger to wells negated, Mr. Myrick and his team began planning a way to cut off the contamination at its source. That is where the PlumeStop came in.
At the core of the technology is a material called colloidal carbon. A colloid is just a very small particle; in this case, each bit of carbon is about two microns in diameter — roughly 60 microns smaller than a strand of hair. Already great at catching particles due to its sponge-like structure, the carbon is ground into colloids, thereby increasing its surface area and its opportunity to snatch up particles.
The process is not, in fact, absorptive, but rather adsorptive; that is, PFAS is not taken up into the body of the carbon material, but rather sticks to the outside via strong, intermolecular forces. Adsorption is far more stable than mere absorption.
“They grab on pretty tightly,” Mr. Myrick said. “It would take a lot to kick them off.”
Every pound of the ground colloidal carbon contains 100 acres of surface area — giving it an excellent chance of trapping PFAS chemicals.
To put this material to work, Tetra Tech engineers surveyed an underground area, just south of the plot next to the airport wastewater plant where PFAS was released. After discovering that nearly all the contaminated water flowed through that area, they injected the material directly into the aquifer’s soil, on the order of 10,000 gallons, 30 feet below the surface. The installation was finished on Dec 9, costing the airport $272,500.
Following installation, the in-aquifer filter is now permanent, Mr. Myrick said. The colloidal carbon sticks to soil particles in the aquifer via the same adsorptive process with which they capture the PFAS. It would take a major event to unstick either.
The PlumeStop has enough capacity to continue filtering PFAS for decades, and more material can be inserted behind the existing area if all the carbon becomes saturated.
“We’re calling this a pilot project. It’s not intended to deal with all the issues,” Mr. Myrick said, though the efficacy of the project has been demonstrated in its use at other airports. He emphasized that monitoring would continue, and that further injections were likely.
Still, as awareness of PFAS dangers grow, other mitigation efforts continue.
“The airport is part of this, but it’s not the whole story,” said West Tisbury health Omar Johnson.
Earlier this year, a state-sponsored well-testing program unveiled several PFAS-contaminated wells in West Tisbury and Chilmark apparently unrelated to the airport, including one well near Great Neck detected at a hazardous level, according to the state DEP. An investigation into the source is still ongoing, a DEP spokesman confirmed.
Municipal water systems are also now required to test for PFAS. According to the most recent reports, Edgartown, Oak Bluffs and Tisbury have all tested for PFAS levels below the state limit.
“We’ve done everything we can to be proactive on this, but PFAS is still a great concern, since there are so many unknowns,” said Edgartown water supervisor Bill Chapman.
For a chemical which lasts forever, caging it underground may be the best short-term solution. But to really solve the PFAS issue long-term, Mr. Myrick suggested cutting out the use of the chemical altogether.
“We’re exposed to these compounds in so many different ways,” he said. “Let’s go back to the source of these products, and get them out, so they don’t go out into the environment in the first place.”
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