State blocks use of chemical for lake

A proposal to use chemicals to kill invasive weeds in popular Lake Cochituate has been rejected by state environmental regulators, who agreed with the town of Natick that the chemicals could threaten local drinking water.

The Department of Environmental Protection ruled that the town made the right call when its Conservation Commission rejected a request to use chemicals in the lake.

In an order dated Nov. 2, the agency ruled that using herbicides to root out varieties of milfoil and pondweed growing in the lake could threaten the town's water supply in violation of the goals of the Wetlands Protection Act.

The Department of Conservation and Recreation, which is responsible for the lake, proposed the use of chemicals. Supporters of using herbicides in the 614-acre lake, which borders Natick, Framingham, and Wayland, say that managing invasive weeds is essential to ensuring its continued recreational use and that chemical treatment is the most effective method.

The town, however, has sided with Protect Our Water Resources, a group of area residents concerned that the chemicals could seep into the town's drinking supply through nearby wells.

The state's ruling, signed by Richard Tomczyk, section chief in the wetlands program of the department's Northeast Regional Office, affirmed the Conservation Commission's order of conditions, which rejected the request to use chemicals.

The ruling acknowledges that chemical treatment could improve the lake's viability as a fisheries habitat.

"Of great concern to MassDEP, however, is the use of herbicides in this particular case where there is a high probability of introducing these herbicides (in particular, fluridone ) into the public drinking water system of Natick," Tomczyk wrote in the ruling. "Once in the ground water, the herbicides cannot be removed in the existing water treatment system and are not naturally degraded."

Save our Shores, a group of residents from Wayland and Natick who want to preserve the lake's recreational use and see herbicides as the answer, could now appeal to an administrative law judge, said Bob Bois, Natick's environmental compliance officer.

Bois said the local commission "was very confident based on the facts presented during the hearing process that they arrived at the right decision."

While the debate over the best method continues, the state parks agency has moved ahead with an alternative weed-control method at the lake. The agency installed new solar-powered water circulator devices, manufactured by SolarBee, in the lake last month. The mechanical devices are part of a one-year study, conducted by Tufts University, to determine their effectiveness in controlling invasive weeds.

Bois said the town has approved other weed-control methods as well, including introducing weed-eating weevils to the lake, laying down mats on the pond floor in some areas, and hand-pulling. The use of four specific herbicides, Reward, Aquathol K, Renovate, and Sonar, was rejected.

"We denied that [permit] based on the potential impact on ground water and the town's drinking water source," Bois said.

According to a 2003 survey, there were moderate to high densities of milfoil in about 26 percent of the lake's South Pond and about 12 percent of the lake's Middle Pond, including Carling Pond. Water milfoil can grow into a dense blanket of vegetation on the surface of a lake, disrupting recreation and interfering with the water's natural ecosystem.

Controlling the pesky weed has confounded communities across the country that run recreational lakes, and many have turned to herbicides.

However, the Department of Environmental Protection found that fluridone, an ingredient of Sonar, may not break down before it is absorbed into sediment. Over time, the fluridone could re enter the ground water and enter the town's water supply.

The substance would not be removed by current water treatment measures, Tomczyk wrote.

Carole Berkowitz, a member of Protect Our Water Resources, welcomed the state ruling.

"We did recognize the invasive weeds are an issue, but we just wanted to not use chemicals to deal with it," she said.