WNPR

Tunneling 200 Feet Underneath Connecticut For Cleaner Water, At A Cost

Nov 7, 2017

A giant, miles-long tunnel is about to be drilled hundreds of feet beneath Connecticut’s capital. This subterranean project will take years, cost hundreds of millions of dollars, and the hope is, result in cleaner water for the Connecticut River and Long Island Sound.

The size is impressive. About 200 feet below ground will lie a tunnel, 18 feet in diameter that’s drilled through rock -- and extending about four miles.

Overlooking a giant shaft in Hartford that’s getting deeper and deeper -- Susan Negrelli, director of engineering for the Metropolitan District, which oversees water for the region, said pretty soon, a giant drill will make its way underground -- followed by tons and tons of machines.

“It’s a small city that you put down there in the tunnel. It has to have its own air, its own clean water, its own dirty water,” Negrelli said. “There’s electricity. Hydraulics.”

Negrelli spoke on the construction site for The South Hartford Conveyance and Storage Tunnel. At an estimated cost of $500 million, it’s the biggest project the MDC has ever done.

As we talk, that giant drill sits behind us. Brian McCarthy, project manager for MDC, said its journey will take it west out of Hartford -- burrowing underground beneath highways and roads until it gets to its endpoint one town over.

Attached to the tunnel boring machine will be a "cutter head," which will be instrumental in moving the rock required to make a massive tunnel 200 feet below Hartford's surface.
Credit Patrick Skahill / WNPR

“We think once we get in the ground, and actually start churning, it will probably take around 18 months or so for that journey to happen,” McCarthy said.

The tunnel’s goal? To eliminate sewer overflows.

These overflows happen when there’s a lot of rain. Sewers built as far back as a century ago can get overwhelmed, and rainwater can mix with sewage from toilets and baths.

To avoid that sewage flowing back into homes and businesses, older systems outlet directly into places like the Connecticut River.

That’s a major water pollution concern, one the EPA said plagues hundreds of U.S. cities.

But the Clean Water Act is working to change that. In the decades since becoming law -- it’s forced many cities to reduce or eliminate those sewage overflows.

Negrelli said Hartford’s tunnel, which will be funded by the state and ratepayers, is in direct response to the Clean Water Act. The tunnel will catch problematic storm overflows, treat them, and release the cleaned-up water.

That, she said, will help suburban towns.

“Ultimately, when finished, it will permanently eliminate overflows to the Wethersfield Cove, control other overflows that we have in our sewer system to a one-year level of control, and eliminate some of the sanitary sewer overflows that we have out in the West Hartford, Newington area,” Negrelli said.

Attached to the boring machine will be a train of "trailing machines," which will help move materials into and out of the tunnel and ensure that workers have adequate life support.
Credit Patrick Skahill

“All of our stormwater runoff and all of our sewage is contributing to the problem,” said Anne Jefferson, an associate professor at Kent State University who studies watershed hydrology. “So it’s not as easy as cleaning up industrial operations in one factory. We really are now talking about the urban fabric of the city.”

“These tunnels are expensive. These tunnels are big infrastructure. They’re big engineering. They’re what we call a gray’ approach,” Jefferson said.

She said tunnel projects like Hartford’s can be found up and down the east coast. Old industrial sites, where engineering decisions were made long ago, that need to be fixed today.

The Narragansett Bay Commission’s Jamie Samons, said that was the case in Providence, Rhode Island. Her group completed a tunnel there in 2008.

“Underground construction is always complicated and it can be expensive, but when you’re in a very highly developed urban environment -- sometimes it’s just more convenient,” Samons said.

Still, it cost a lot -- about $360 million. And she said it meant they had to raise sewer rates for their customers.

“In 2001, the annual average single family dwelling paid about $135 a year for their sewer service,” Samons said. “Now they pay $500. So rates have gone up substantially to pay for this project.”

Samons said the tunnel did yield results. She said it kept billions of gallons of dirty water from going into Narragansett Bay. It’s led to fewer beach closures, and restored shellfish beds in the area.

Still, the tunnel idea seems to be up for debate. Samons said her group was planning to dig another one. But right now, it’s not sure it can afford the estimated $750 million price tag.

So they’re open to other ideas.

“Will we receive a larger bang for our buck in water quality if we spend it somewhere else?” Samons said. “Like, on habitat re-establishment, or on nutrient reduction, or stormwater abatement?”

Anne Jefferson from Kent State said each city faces a unique set of sewer problems. But for some, “green” approaches may be the way to go -- doing things like building rain gardens or detention ponds.

“But there is certainly resistance to that. There’s a lot of concerns among engineers and maintenance crews -- are these things going to be harder to maintain?” Jefferson said.

Then there’s the unpredictability of giant tunnels. Jefferson said they’re built for a fixed volume today, which could ignore urbanization or climate change -- that could make more water flow, tomorrow.

Hartford’s tunnel is expected to be online in 2023.