Latest PFAS Numbers Down, Source Remains Unknown

By: Alan Pollock

Topics: Drinking Water , Health

Tap water

CHATHAM The latest round of water tests show a decline in the concentration of PFAS contaminants in a public supply well off Training Field Road, but officials aren’t celebrating yet.

“There’s more questions in these numbers than answers, unfortunately,” Chatham Health and Natural Resources Director Robert Duncanson said Tuesday.

In April, town officials shut down a well off Training Field Road after PFAS levels were recorded at 28.7 parts per trillion, over the 20 ppt threshold set by state regulators. Subsequent tests showed the contaminant present at 40.7 and 56.6 ppt. But on June 24, two samples were taken of untreated water from the well, Well 5, showing PFAS readings of 9.58 and 8.93.

To try and put the sudden drop in context, the town ordered two more tests of treated water from the well five days later, which came back at 7.56 and 7.25 ppt.

“That has dropped down significantly, considering that back in May we had a sample of 56,” Duncanson said.

Known as “forever chemicals” because they do not break down in the environment, per- and polyfluoroalkyl substances (PFAS) are being investigated for possible links to cancer and other serious diseases.

Duncanson said it’s hard to say whether the drop in concentration is a sign that the contamination is migrating, or if it’s a simple fluctuation related to the minuscule amounts of PFAS being detected.

“I don’t think we have enough data yet to really know,” he said. While test results would be expected to be variable given the extremely low levels being detected, “we did have significantly higher counts at Well 5 at the beginning of this,” he said. “Could it possibly be because the well’s been shut down, so we’re not drawing water from as widespread a region?”

Left undisturbed, contaminants in the groundwater flow in a predictable direction on Cape Cod, generally toward the coast from the direction of the Mid-Cape Highway. But pumps can actually draw contaminants against the flow of groundwater within the “zone of capture” around the well head. The result is that, when a well is operating, it is difficult to tell which direction any contaminants might be coming from.

“We’re getting a fair number of comments from public pointing the finger at the airport, but we don’t have any indication yet where the source may be,” Duncanson said.

PFAS are present in high concentrations in certain firefighting foams, but can also be found in a variety of household products, including treated fabrics and nonstick cookware.

Well 5 remains offline, but town officials are considering a plan to blend its water with water from adjacent Well 8 to yield usable water below the 20 ppt threshold. The latest results at Well 8 showed PFAS concentrations of between 6.27 and 6.75 ppt, and a test of blended water from the two wells on June 29 yielded numbers of 7.88 and 7.81 ppt, Duncanson said.

Town officials will likely make a decision within a couple of weeks about whether to allow the blended water from the two wells to be added to the town water system.

“We probably want to see some more data before we pull the trigger,” Duncanson said.

One factor guiding that decision will be the demand for water. While water use peaks in the summertime, the system is still able to meet the demand even with Well 5 offline, for the time being.

“Luckily, the cool, rainy weather over the holiday weekend actually helped,” Duncanson said. But the next spate of hot, dry weather might put the system under strain again, and for that reason, the town’s water operator continues to install equipment needed to bring the old Indian Hill well back online. Shuttered in the 1990s because of contamination by the solvent tetrachloroethylene, that well now shows no signs of that pollution and could be brought online by the end of the month, Duncanson said. The town is also working on a longer-term plan to complete two wells near Mill Pond to help meet the demand for water.

Later this month, the town will conduct quarterly sampling of all the town’s public water supply wells.