Result came from a groundwater monitoring well, but Suffolk County plans to offer testing of private drinking water wells at 107 nearby homes.

A monitoring well drilled near a former landfill in East Quogue has detected a perfluorinated compound in a concentration more than 150 times the level at which federal officials say exposure in drinking water can cause health problems, including impaired fetal growth, certain cancers and immune system conditions.

State Department of Environmental Conservation officials said the result — the highest concentration detected on Long Island of the compound, used in some firefighting foams — came from groundwater samples, not a drinking-water well.

Nevertheless, Southampton Town began delivering bottled water Wednesday afternoon to 107 homes in the surrounding area with private wells. Suffolk County will offer free testing of those wells starting Monday.

“People who are on private wells in the area of concern should not be drinking the water,” Southampton Town Supervisor Jay Schneiderman said. “Hopefully the test results will show no contamination.”

If test results are above a federal health advisory level, the state will decide whether a home should have a treatment system installed or be hooked up to public-water supplies, which, unlike private wells, must comply with drinking water standards.

“We can’t tell the exposure [in drinking water] just from detections in the monitoring well,” a DEC official said.

Suffolk County Water Authority supply wells near the former landfill have not detected perfluorinated compounds, authority CEO Jeffrey Szabo said in a statement.

The DEC monitoring well was one of three drilled near the 10.6-acre site off Damascus Road in January as part of a broader state investigation into how pollution from closed landfills affects groundwater. The site also was used for firefighter training.

Tests in February at the well, drilled south of the landfill, revealed levels of the compound — perfluorooctanesulfonic acid, or PFOS — at 11,200 parts per trillion.

The compound is not regulated in drinking water, but the U.S. Environmental Protection Agency has a health advisory level of 70 parts per trillion for PFOS alone or in combination with a related compound, perfluorooctanoic acid, or PFOA.

The landfill site was once slated to be a park with tennis courts and a softball field but when digging began, crews discovered old cars, trucks and other spoils, said Al Algieri, president of the Civic Association of the Hamlet of East Quogue Inc.

“Our water has been poisoned time and time again,” Algieri said. “They keep telling us not to worry about it . . . every week there’s another area with bad water.”

This finding is the latest discovery of what some officials say is becoming ubiquitous in local groundwater.

Gabreski Air National Guard Base in Westhampton Beach and the Suffolk County Fire Academy in Yaphank were added to the state Superfund list in 2016 and 2017, respectively, because of PFOS or PFOA contamination, though at far lower concentrations than what was detected in East Quogue.

In both cases, homes were connected to public water supplies.

MacArthur Airport in Ronkonkoma was listed as a possible Superfund site in January, as was East Hampton Airport, where detections have been found in private wells in Wainscott. A Hampton Bays Fire District parcel also is listed as a possible site. DEC officials said they were considering adding the East Quogue parcel as a possible Superfund site.

Earlier this week, Assemb. Fred Thiele (I-Sag Harbor) and state Sen. Kenneth LaValle (R-Port Jefferson) called on the DEC and Department of Health to use some of the state’s $2.5 billion Clean Water Infrastructure Act funds to address the problem.

“There needs to be a comprehensive plan put together for extending public water on the East End,” Thiele said Wednesday. “We can’t be addressing this on an ad hoc basis one site at a time.”

Last year, a state Drinking Water Quality Council was charged with recommending a safe level of the compounds to the health commissioner to help in crafting a state drinking-water standard. A meeting in March to discuss that final recommendation was postponed and has not been publicly announced.

For homes with private wells