Hoping to better understand the scope of the problem, the state Department of Environmental Services has asked the town to complete a supplemental site investigation (SSI) of current and former fire station facilities where high concentrations of per- and poly-fluoroalkyl substances (PFAS) have contaminated the soil.

In response, the town has contracted an engineering firm to complete the investigation, which is likely due to start in early April.

“They won’t be starting any testing or field work until the week of April 8,” Sullivan said in an email.

A final report is due later this fall.

Last year, the town partnered with Nobis Group Inc. to complete the initial site investigation of a former fire station at 3 North Lowell Road, and the current town fire station and fire training area at 3 Fellows Road.

A final report was submitted in November, with revised tables prepared by Jan. 2.

The source of the contamination is believed to be the historic and frequent use of Class B firefighting foam at the sites.

On Jan. 16, DES sent a letter to the town saying it needed more information about the scope of the contamination, outlining six specific steps it wanted the town to take to delineate the issue. Officials posted that letter to the town website on March 18.

Meanwhile, development projects such as the proposed Library Hill site, a 55-and-older senior living development behind town hall offices, and another mixed-use development by E.G. Holdings between town buildings and Enterprise Bank, are in a holding pattern until the water situation can be figured out, according to Town Planner Dick Gregory.

“They were all going to use the well across the street,” Gregory said.

The problem with that, Gregory said, is that environmental officials have warned that doing so could draw the PFAS plume in the groundwater in that direction.

Alternatively, he said, new wells could potentially be drilled on the development projects’ side of the street, but that could present other challenges related to septic radius regulations.

The $27 million project funded by the MTBE Settlement Fund and the New Hampshire Drinking Water and Groundwater Trust Fund will continue the existing pipeline from Derry down Bypass 28. In Windham, that will include a leg that extends from Bypass 28 to the McDonald’s and the Gateway Park project currently under development.

Water is expected to start flowing to Salem by May of 2020.

Gregory hopes it will be possible to construct an additional section of water line from the McDonald’s to Ledge Road, which would service the area affected by PFAS chemicals. He hopes to partially fund that initiative — estimated at $9.5 million — with the state Groundwater Trust Fund, other grants and some buy-in from developers.

That would provide a clean water source to the developments on hold, but he guessed it would likely take until about 2024 to get built.

Joseph Maynard from Benchmark Engineering, representing the Library Hill project, requested an extension at the March 6 planning board meeting, saying no state permits can be received until a clean water source is found.

“I can’t do any permitting with state agencies until we come to a solution about water,” Maynard said during the meeting.