Town beats shortage with treated pond water

With the addition of a dual water treatment system, Stonington, Maine, has expanded its water supply. The project, which took four months to complete, has alleviated water shortages, particularly during the summer.

Travel brochures call the remote coastal town of Stonington “down-east Maine at its best.” Situated on Deer Isle, the century-old fishing community is a haven for tourists, and it is that very attraction that threatened the drinking water supply.

During the peak tourist months and at the height of lobster season, Stonington’s drinking water supply was severely depleted. Local wells did not yield enough water to meet the demand, and, although the town had a pond, the water was badly discolored.

“Deer Isle is a poorly fractured granite island, which means that water does not naturally pool to form wells,” explains Roger Stone, superintendent of Stonington Water. “What limited water resources we have cannot adequately provide the potable water the town needs. This affects not only Stonington residents, but the island’s economy as well. We simply needed to expand our water resources.”

Encompassing 21 acres, Burntland Pond appeared to be the most feasible resource for expanding the water supply. However, in addition to having an amber color caused by high organics, the pond contained TOC levels of approximately 12 to 17 milligrams per liter, and it suffered from low turbidity and low alkalinity. Treating it would not be a simple task.

The town evaluated conventional water treatment methods, which depend on chemical coagulation using a metal coagulant, such as iron or aluminum. However, it did not want to deal with chemical sludge handling and disposal.

Instead, officials chose to build a facility incorporating ozonation, ultrafiltration (UF) and nanofiltration (NF). The town hired Watertown, Mass.-based Ionics to design, engineer, install and operate the plant.

The new system, which went online last August, is situated near the pond and treats 4,000 gallons of pond water per day. For color removal, it employs ozone micro-flocculation followed by UF membrane filtration. By adding ozone to the high TOC water source, organic material and biological contaminants are reduced significantly. To achieve the drinking water standard of 15 CoPt units, the plant filters the water through a loose NF membrane after UF.

“By using ozone, UF and NF, the desired level of water quality is achieved without the production of waste sludge materials associated with other water treatment technologies,” Stone says. “Due to Stonington’s remote location, sludge removal would have been extremely difficult.”

In addition to purifying the pond water, the filtration system treats water from Stonington’s network of wells. The wells are close to the pond, and the pond water can affect the quality of the well water, Stone explains. “When the pond system is off, well water is treated by the same UF that the pond water goes through,” he says.

With the filtration system in place, Stonington now is meeting its water demands year-round. The project was funded with money from a Community Development Block Grant.