by Tom Benoit | Sept 3, 2024 | The MetroWest Daily News

MARLBOROUGH — An idyllic pond located on the Marlborough-Framingham line has all the makings of a classic New England scene: local plants, geese, a nice breeze.

But with that occasional breeze comes the distinct smell of rotten eggs that’s caused by the damming of the pond, according to a local environmental advocacy group.

Concord-based OARS, an environmental nonprofit focused on the Sudbury, Assabet and Concord Rivers, is calling for the Hager Pond Dam to be removed. The group said it has begun working with Marlborough city officials to get this done; however, OARS staff said they plan to also work with stakeholders, including the dam’s owner, on the best possible option.

The group alleges the dam’s presence is causing significant hazardous conditions to the pond. OARS Ecological Restoration Coordinator Heather Conkerton and Director of Communications Sarah Kwan hosted a Daily News reporter and photographer during a recent tour of the dam and pond.

Conkerton said the group plans to work with the city, local groups and the dam’s owner toward the best possible option, whether it be removal or reconstruction. She said removal of the dam is the best way to restore the pond, which is marred by harmful algal blooms, a distinctively unpleasant odor and ecological damage.

“Water quality issues are common for run of the river dams, whatever goes in goes out. We worry about water quality,” Conkerton said. “Our water quality scientist says it’s the worst he’s seen it.”

Expert says Hager Pond is experiencing excessive plant, algal growth

During the tour, OARS staff showed the remnants of a large algal bloom that spread miles downstream. Due to recent rains, the algal bloom had diluted.

Conkerton said Hager Pond is experiencing what’s called “eutrophication” — excessive plant and algal growth due to the increased availability of nutrients, such as phosphorus. She attributed the increased phosphorus to legacy pollution before the 2015 upgrades to the Marlborough Easterly wastewater treatment plant. The excessive plant growth has caused oxygen saturation in the pond, reaching a threshold considered harmful to aquatic life.

Conkerton explained that legacy pollutants get stuck in the sediment behind the dam. Anytime extra nutrients come into the pond, the trapped nutrients causes plant overgrowth. When the overgrowth dies, it causes the rotten egg smell.

“The proliferation of plants shades everything else out and the dieback causes bacteria to pump pure carbon dioxide into the water,” Conkerton explained. “If the fish cannot get away from it, they’ll just die.”

In addition, the dam is considered “high hazard” by the state’s Office of Dam Safety.

“Because it’s a high-hazard dam, if it were to fail it could cause economic destruction and potentially loss of life,” Conkerton explained. Downstream properties include the historic Longfellow’s Wayside Inn in Sudbury.

Hager Pond Dam dilemma: Reconstruction or removal?

OARS is working with local municipalities and elected officials in order to remediate the Hager Pond Dam.

City Engineer Thomas DiPersio Jr. referred questions to the mayor’s office. In an email, Marlborough Mayor Christian Dumais‘ chief of staff, Ryan Egan, said the Hager Dam issue preceded Dumais’ tenure, which started this year.

State Rep. Danielle Gregoire, D-Marlborough, told the Daily News her office, along with other state representatives such as Carmen Gentile, D-Sudbury, have met to discuss the dam. She said they’re looking for the best solution for the dam going forward.

“The city of Marlborough is very concerned about the integrity of the dam,” Gregoire told the Daily News. “Another one of the major concerns is that Raytheon (now RTX Corp.), which is right out there, has right of usage over the water contained by the dam, so we’ve been trying to include Raytheon in the conversations as well.”

“(We) have been working closely with the owners of the dam, state/federal agencies, the legislative delegation, and third parties to come up with a solution for the dam, whether that be reconstruction or removal,” Egan said in his email.

There are no current plans for either reconstruction or removal. The dam is apparently owned by at least one of two entities; however, Gregoire said each is denying ownership.

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