The sewer separation project aims to reduce flooding and waterway pollution in the Winter Hill and Ten Hills areas.

By The Times Staff

The city is upgrading infrastructure to separate a combined sewer system into separate stormwater and wastewater pipes in an effort to mitigate flooding and reduce waterway pollution in Winter Hill and Ten Hills.

The Mystic River Outfall and Sewer Separation (MROSS) project will separate stormwater from sanitary sewage and include a “trunk drain” or collector pipe to convey stormwater from neighborhood streets to the outfall on the Mystic River at Blessing of the Bay Park near the pedestrian footpath that runs under the Route 28 bridge.

“Not only is this going to bring some much-needed relief, but this is part of the larger plan for the city to reduce its combined sewer water outfall discharges,” said Ward 4 Councilor Jesse Clingan.

At the third virtual community meeting held on November 12, Project Manager Gina Cortese said this project is a priority for the city.

The team is at a 30 percent design milestone, and there is roughly one year to go in additional field investigations.

“As climate change progresses on, there will be more intense and more frequent rain events,” said Cortese. “With this project, a lot of that flooding goes away, close to 95 percent.”

The data is based on a 2030 storm event model. Cortese says there will be substantial improvements on the streets around Foss Park.

In order to alleviate flooding in homes and streets, big pipes will be utilized to accommodate the water surges.

The project will include roughly 1.7 miles of new storm drain pipe ranging from 15 to 36 inches in diameter. The trunk drain will be a larger 78-inch concrete pipe.

Stormwater pipes will be added in Winter Hill, while Ten Hills already has “partially separated” pipes that converge, explained Cortese.

The trunk drain will go under Wheatland Street, cross under Mystic Avenue and I-93, run parallel to Fellsway, and turn left on Shore Drive to the proposed outfall location.

Another significant project purpose is the reduction of combined sewer outflows (CSOs) in the Mystic River.

In a combined sewer system like we have now, we have a capacity issue when it rains,” said Cortese.

Stormwater has nowhere to go, and that causes neighborhood floods.

“Once the project is completed, we’ve modeled those combined overflows to decrease by approximately 50 million gallons in a year,” said Cortese.

This would result in a 55 percent reduction in CSO discharges into the Mystic River, based on “baseline” conditions in a 2050 typical year. Calculations could change as the design progresses.

In addition, the team initially identified 35 sites that are suitable for green stormwater infrastructure and prioritized 15 of those sites that will be most effective in removing pollutants.

GSI systems mimic natural processes to manage stormwater, utilizing plant and soil volume to slow stormwater and remove pollutants with bioretention basins and subsurface infiltration trenches.

“Green stormwater infrastructure is a hot topic, and it’s something that we as a city are increasingly committed to,” said Cortese.