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GROTON — After more than a year and a half since being told that the water at the Groton Dunstable Regional School District’s new $35 million high school was not safe to drink, students will have to wait another few months before it can be said with certainty that contamination has been eliminated.

And even that possibility, said Craig Young, district director of business and finance, may not come to pass.

Young made the forecast to Groton and Dunstable town and school officials at a meeting of the Joint Budget Task Force.

At the time, Young explained that a solution to the water contamination problem at the high school involving coating the interior of pipes with a “polyphosphate additive” had been shown to have some positive effect. But it was not enough to warrant declaring the water safe to drink.

“We had installed equipment to pump in the chemical to the line pipes and fittings and hoped that by doing that the dissolved carbon dioxide would not react with the metal and create sort of a barrier,” explained Young of the decontamination process. “We went live in December and took some samples and had some improvement, but not sufficient improvement. The lead levels were lowered in some places but we continue to pump in the chemical with hopes that it would eventually coat all the pipes. There will be another round in February.”

Use of the polyphosphate additive was only the latest attempt to identify and solve the contamination problem at the high school. Earlier efforts involved shutting down and flushing out the school’s water distribution system that included a well and pumping station. Isolation and testing of each component of the system narrowed the focus of investigators to the pipes themselves prompting the use of the additive to coat the plumbing and prevent brass fittings in the pipes from reacting with carbon dioxide in the water and leaving behind dangerous levels of copper and lead.

“We continue to update the DEP on our progress and have reviewed the changes with them,” said Young, adding that state officials have found the district’s methods “reasonable.”

But although preliminary testing after introduction of the polyphosphate additive by high school project manager Turner Educational Facilities Group and the school’s water system operator Small Water Systems has indicated a drop in the level of contamination in the water, the problem has not been completely solved.

“We did see some progress but maybe we just need to wait a little longer,” said Young. “I suspect we will know for sure once the tests are done in February, but certainly through March.

And if the results are still negative?

“Nothing else is being discussed yet,” said Young. “We’re taking a wait and see attitude. But another option is some sort of aeration device. But that could be pretty expensive. That would be our last option. The aeration device would allow the carbon dioxide gas to escape from the water but when that happens, it changes the chemical aspect of the water.”

Young said that although the aeration method could solve the main problem of the contaminated water, in doing so, it might necessitate changes in other aspects of the purification process requiring a return to the DEP for approval.

In the end, solving the contamination problem may be one simply of time. At the Joint Budget Task Force meeting, Dunstable Selectman Ted Gaudette told Young that a similar problem elsewhere had to wait years to be solved as contamination levels in the water distribution system gradually fell and eventually disappeared.

“We would hope that it won’t take that long,” commented Young.

In the meantime, the high school’s 813 students will continue to get their drinking water from self-contained water fountains located throughout the building.