Building a Carbon Sandwich

A soft, six-inch layer of granulated carbon is being smoothed out over an existing base of sand, the makings of a "carbon sandwich" that officials hope will resolve ongoing problems with a water contaminant.

The carbon sandwich — a base of 21 to 24 inches of sand, followed by six inches of carbon, topped with eight to 12 inches of sand — will replace what is now known as Filter #3 at the company site.

The carbon filter being installed this week cost $280,000, said David Condrey, general manager of the private utility company.

By the end of October, Condrey said he hopes to have the system online. It will work simply: water drawn through underground pipes from Echo Lake in Hopkinton will be pumped onto the top layer of the filter, and percolate down through the carbon.

The filtered water then will move along in the processing system, for treatment, before being pumped into homes and businesses, Condrey said.

"We're shooting for the end of the month," he said.

will be completed in coming months. The technology, approved by the state Department of Environmental Protection, is based on the experiences of a town in Maine, which had also struggled with elevated levels of Total Trihalomethanes. , formed in the disinfection process for public drinking water, has been found in elevated levels in Milford drinking water

After the carbon layer was installed at the community in Maine, Condrey said, a reduction in TTHMs was immediate. "They've had great results."