Work began Friday to connect Westhampton Beach homes near Francis S. Gabreski Air National Guard Base that have contaminated wells to the municipal water system, with all costs covered by the state and federal governments, state officials announced.

Fifty-seven homes with wells threatened by contamination with the chemical PFOS, or perfluorooctanesulfonic acid, will be joined to the municipal system, the state Department of Environmental Conservation said.

The U.S. Department of Defense, under a separate agreement, will cover the costs of connecting nine additional homes with well contamination that meets or exceeds federal Environmental Protection Agency health advisory levels for PFOS.

The chemical can potentially cause blood, immune system, thyroid and fetal growth issues.

The work started Friday and is expected to be complete in December. The total connection estimate is $2.5 million, the DEC said, and the Suffolk County Water Authority will be reimbursed for costs associated with the work by the state and federal governments.

The Air National Guard base was declared a New York Superfund site in September.

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“DEC is working aggressively to protect the public and the environment whenever and wherever contamination is found and to hold polluters accountable for their actions,” DEC Commissioner Basil Seggos said in a statement.

In July, the DEC identified the Air National Guard base, including the former fire training area at the airport, as a potential Superfund site because of past use of firefighting foam containing PFOS.

The state agency initiated an investigation and took groundwater and soil samples at the base, and testing confirmed the site is a significant source of PFOS contamination in the area, officials said.

In late July, Suffolk County collected samples from 66 private drinking water wells in Westhampton Beach and found that several were contaminated. Of the wells sampled, those of nine homes were found to have PFOS contamination that met or exceeded the EPA’s threshold of 70 parts per trillion. Samples from three wells detected levels of PFOS below the EPA threshold.

The cleanup effort includes approximately 57 residents with private wells that currently do not exceed the contamination threshold but are threatened in the future.

DEC officials said the state has worked closely with Suffolk County and the Suffolk County Water Authority to inform residents and ensure they have access to bottled water and that they are quickly connected to the municipal water supply.

Discovery of the groundwater contamination near Gabreski Airport came after the state’s Water Quality Rapid Response Team, created by Gov. Andrew M. Cuomo, analyzed data from the EPA’s Unregulated Contaminant Monitoring Rule program to identify potential areas of contamination statewide.

The DEC in April added PFOS to the state’s list of hazardous substances, meaning that state Superfund money could be used to address such contamination.

When the agency formally declared Gabreski Air National Guard Base a Class 2 Superfund Site in September, the designation identified the Defense Department, which oversees the site’s operations, as the potentially responsible party for PFOS contamination detected in nearby groundwater supplies.

“We look forward to connecting residents impacted by PFOS with public water from SCWA that is constantly tested and meets health standards,” said Jeffrey W. Szabo, CEO of the Suffolk County Water Authority.