State Builds 3-D Underground Map To Track The Movement Of PFOA

Sep 13, 2016

A state geologist is gathering data to help build a 3-D map of the ground underneath Bennington to try understand how the chemical PFOA may be moving through groundwater.

Since the discovery of PFOA, a suspected carcinogen, in private wells around Bennington, there have been many of questions about how the dangerous chemical got into the ground, and how it moves through the water table.

Jon Kim, a geologist with the Department of Environmental Conservation, has been talking with people in Bennington to gain access to their properties so he can take a look at the geological formations there to better understand what's happening beneath the ground.

He's been traveling around the area, taking compass measurements of rock above the ground to get an idea of what the underground geology might look like.

"We are trying to connect the dots," he says as he bends down to a measure a limestone outcropping. "We are trying to get a pattern on the map, and data for each station to see how it connects to the neighboring stations or not."

To help connect those dots, Kim is working with other scientists who can look inside the wells to measure where the water is flowing from and to, and at what rates.

Kim says measurements can be taken of the water's temperature, mineral content and salinity that give scientists an idea of how the water is flowing underground.

A geologic map shows the Chemfab plant in North Bennington. The Department of Environmental Conservation wants to use a 3-D map of the bedrock aquifer beneath Bennington to better understand the movement of the chemical PFOA.
Credit Howard Weiss-Tisman / VPR

When they're done, Kim says the Department of Environmental Conservation will have a 3-D map of the bedrock aquifer beneath Bennington.

More than 250 private wells around Bennington have unsafe levels of PFOA, a chemical that can affect the immune system and that's been linked to certain cancers.

PFOA was used at the Chemfab plant in North Bennington, but the factory closed in 2002.

Scientists want to know how the chemical stuck around all these years, polluting the wells — some of them more than 2 miles away from the plant. They're perplexed about why some abutting property owners have wildly different levels of PFOA in their water.

"We're trying to understand why certain neighbors have it, and why certain don't." - Jon Kim, Department of Environmental Conservation geologist

By taking thousands of these readings, at hundreds of locations around Bennington, Kim hopes to be able to get some answers.

"We're trying to understand  why certain neighbors have it, and why certain don't," Kim says. "And we're trying to put together enough information so that we can understand that."

It's a big project. To demonstrate what he and his colleagues are dealing with, Kim drove out to a blasted outcrop out along the Bennington bypass.

The rock wall is streaked with lines of limestone, marble and dolomite that bend and fold — telling a story, Kim says, of millions of years of geologic formation.

"This is a microcosm of what underground Bennington looks like," he says, standing in front of a 300-yard view of the inside of the earth.

State geologist Jon Kim talks about a blasted outcrop along the Bennington bypass. The folds and lines on the outcrop show how water moves in the bedrock.
Credit Howard Weiss-Tisman / VPR

The folds and cracks and cleavage show just how hard it is to predict how the PFOA is moving underground as the state tries to prevent more contamination.

"Our goal is to be able to determine which way, or ways, groundwater is flowing," he says. "We want to find out how the water is carrying the contaminant, and hopefully find out roughly what the rates might be. And perhaps where you might consider monitoring further over a longer period of time."

PFOA is a particularly nasty chemical, with a number of potential health threats.

And if Kim could blast down into every backyard he's walked across, to expose the bedrock like it's showing here, we'd know a lot more about where the chemical might end up in 10, or 50, or 100 years.

But that can't happen. So Kim will keep hammering away.