225-Foot Deep Tunnel Critical to Controlling Flooding in Hartford

Just off Interstate 91 in Hartford is perhaps the biggest single infrastructure project in Connecticut.

“It’s probably one of the largest, if not the largest project going on in Connecticut right now, so it is very exciting for us,” said Susan Negrelli, the director of engineering for the Metropolitan District, the agency responsible for water treatment.

The construction project consists of two tunnels that each require 225-foot holes to be drilled into the ground. One of the holes is for a pump station, while the other is for the construction project itself that will eventually lead to a four-mile tunnel being bored through the South End of Hartford, ending in West Hartford near New Park Avenue.

The South End of Hartford, particularly near Franklin Avenue and Wethersfield Avenue have been prone to flooding for decades.

“This project will provide relief in the southern Hartford area,” Negrelli said. “We will completely eliminate the combined sewer overflows into Wethersfield Cove and in the South Hartford area and so, environmentally, that’s huge.”

The centerpiece of the 18-month long drilling project is the Tunnel Boring Machine, or TBM as it’s known.

The red face consists of dozens of black wheels that act as the teeth. They grind the bedrock down, which then mixes with water and chemicals for disposal, and that material is then routed to a conveyor belt where it will travel four miles.

The TBM will be able to drill more than 70 feet per day when it’s operational, however, geological factors will determine a day’s progress.

“If you’re in solid rock or maybe you’re going through a fault area, if you have groundwater coming in you’ll have to grout ahead so there are different conditions underground that will dictate how fast they can move,” Negrelli said.

This project is part of a seven-year process, but this phase is the most expensive at more than $250 million. The cost was picked up in part by the Connecticut Department of Energy and Environmental Protection, and the rest will be covered by MDC ratepayers.

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