Hazardous levels of PFAS have been found in a private well in West Tisbury following a testing program offered to the town through the Massachusetts Department of Environmental Protection this past winter.

Speaking to the Gazette by phone this week, West Tisbury health agent Omar Johnson confirmed the results, which have been compiled by the DEP. “There has been a recent detect at a level of concern to the DEP,” Mr. Johnson said.

Located on the Road to Great Neck, the private well was found to have PFAS levels of 102 parts per trillion. Levels above 90 parts per trillion constitute an imminent health hazard, DEP spokesman Edmund Colletta told the Gazette in an email Wednesday.

West Tisbury, Chilmark and Aquinnah all participated in the state program that offered PFAS tests to 85 towns in Massachusetts, all of them largely served by private wells.

PFAS (which stands for per and polyfluoroalkyl substances) are a large group of manmade substances, dubbed “forever chemicals” for their strong resistance to decomposition.

The free, voluntary testing program began last winter. Private homes that were tested were chosen either at random or by their proximity to potential contaminants, Mr. Colletta said.

In West Tisbury 37 wells were tested, while Aquinnah and Chilmark each tested seven wells, according to state data. PFAS levels above 20 parts per trillion, the state public drinking water standard, were found in four wells in West Tisbury. PFAS levels below that threshold were found in four more West Tisbury wells, and two in Chilmark. No levels of PFAS were detected in wells tested in Aquinnah.

The West Tisbury well found to have hazardous levels of PFAS triggered further testing conducted by the DEP earlier this week.

“I reached out to neighbors informing them,” Mr. Johnson said. “They should look into getting their wells tested.”

Mr. Johnson said environmental analysts tested six nearby homes following the initial result on Road to Great Neck, adding that the scope of contamination will remain unclear until further results come about two weeks from now.

“Until then, it’s difficult to speak on it,” he said. “It could be an isolated incident.”

Mr. Johnson said the DEP has provided bottled water and will work to install filters at the residence where the high PFAS counts turned up, and he has encouraged any concerned neighbors to avoid tap water.

“If you’re concerned, drink bottled water until you have your well tested,” the health agent said.

Mr. Johnson noted that while the DEP testing program in West Tisbury concluded a few weeks ago, those who weren’t able to get their wells tested can still do so through private means.

“Everyone who requested to be tested is not necessarily tested,” Mr. Johnson said. “If you’re not selected, you’re encouraged to go through an independent testing agency.”

A list of independent testing laboratories that are approved by the state can be found on the DEP website.