CORNISH — Students and employees at Cornish Elementary School were allowed to resume drinking the school’s well water this month, bringing an end to a nearly four-year period of bottled water deliveries.

Water from a new “whole school filtration system” installed in November at the source where water enters the school underwent testing to ensure that the levels of PFAS, or polyfluoroalkyl, were well below state and federal levels before the school community resumed drinking the well water, Cornish Superintendent Sydney Leggett said last week.

“We tested it three times and we gave the all clear when everyone came back from the holiday break,” Leggett said. “We are good to go and everyone is really excited about that.”

PFAS was first detected in the school’s drinking water in the summer of 2021, and since then the school has provided bottled water as school officials sought the source of contamination and also investigated drilling a new well. The contaminant is typically found in a variety of products including clothing, carpets, upholstery, food packaging, paints and cleaning products and has been linked to a variety of health effects, including cancer, liver damage and weakening of the immune system.

The full cost of the filtration system, including installation, was paid with a $150,000 New Hampshire Department of Environmental Services grant, Leggett said. The system had been recommended by Aries Engineering of Concord.

The school district will be responsible for annual maintenance costs of about $25,000, Leggett said.

The school opted for the filtration system after a search for a location for a new well was unsuccessful. Two spots recommended by a geologist failed to produce sufficient flow, Leggett said. She said if the board chooses to look further it would have to explore sites off school property.

The source of the contamination remains unclear, but engineering reports point to the material used to clean, strip and wax the school’s floors, Leggett said. Wastewater was poured down school drains and entered the septic system. It later leached into groundwater and contaminated the dug well, which also is used by the nearby town hall. The town hall continues to use bottled water.

“To date, school floor waxing maintenance operations have been indicated to be the primary source of PFAS impact to site groundwater,” according to an August 2024 report by Aries Engineering of Concord.

The report also pointed to “the potential for multiple PFAS sources at the site,” which prevented the firm from concluding that the floor waxing operations were the only source of the contaminant.

“Use of other PFAS containing products, such as car wash and waxes, cleaning detergents, etc. may also contribute in part to the observed PFAS distribution,” according to the Aries report.

Because of this uncertainty, school officials are continuing to look for all the potential sources of contamination, Leggett said.

The school now deposits the flooring stripping wastewater into barrels which are then picked up and removed off site.

In its August letter, Aries recommended more groundwater, drinking water and surface water samples for possible PFAS and also the sampling of wells within 1,000 feet of the school property.

DES has concluded that “discharges of PFAS-containing substances at CES have impacted groundwater, surface water, and drinking water supplies,” Amy Gibney, of the Hazardous Waste Remediation Bureau of DES, wrote to the town in a Dec. 24 letter.

DES supports Aries’ recommendation to test all water supply wells within 1,000 feet of the school, Gibney wrote.

Contacted earlier this month, Gibney said she could not comment because the “investigation is still active.” Her letter gives the school 60 days to arrange for the additional testing, with the possibility of extending that to 120 days.

Patrick O’Grady can be reached at pogclmt@gmail.com.