Tunnel Will Hold Waste from 17 Sewer Overflow Points

By Elijah Polance
UConn Journalism

Reducing com­bined sewer over­flows is a time-con­sum­ing and expen­sive endeav­or for the agency that man­ages Hartford’s sewage treat­ment. The Metropolitan District Commission set­tled on a solu­tion not used any­where else in Connecticut: stor­ing untreat­ed waste inside a giant tun­nel.

In 2016, the MDC signed a con­tract autho­riz­ing the cre­ation of this tun­nel, called the South Hartford Conveyance and Storage Tunnel. The tun­nel will help the MDC com­ply with the con­sent order with Connecticut’s Department of Energy and Environmental Protection, requir­ing it to cor­rect pol­lu­tion dat­ing to the mid-1990s. The tun­nel was planned to begin hold­ing back waste oper­ate in 2023, but delays have pushed that to 2026.

The tun­nel will store excess stormwa­ter and waste­water that ends up in com­bined sewer sys­tems dur­ing heavy rain­fall. The pre­cip­i­ta­tion over­loads these sys­tems, caus­ing untreat­ed sewage to drain into pub­lic water­ways and back­flow into res­i­dents’ homes.

Specifications from the MDC state the tun­nel is four miles long and 200 feet below the ground. It has a diam­e­ter of 18 feet and can store 41.5 mil­lion gal­lons of water.

“A foot­ball field is 360 feet long, 160 feet wide,” said Susan Negrelli, the MDC’s direc­tor of engi­neer­ing and plan­ning. “So pic­ture that with about 100 feet of water on it. That’s 42 mil­lion gal­lons.”

The buried stor­age tun­nel begins in West Hartford, by Talcott Road, and ends in the South Meadows area of Hartford, across Brainard Road from the Hartford Water Pollution Control Facility.

The tun­nel will main­ly elim­i­nate com­bined sewer over­flows in south­ern Hartford, espe­cial­ly 10 of the CSOs that over­flow into the South Branch of the Park River and seven oth­ers that flow into Folly Brook and then into Wethersfield Cove. The tun­nel will also take in water from sur­round­ing towns includ­ing West Hartford, Newington and Wethersfield, said Nick Salemi, spokesper­son for the MDC.

Negrelli said the MDC decid­ed to build the tun­nel in south­ern Hartford because of the con­sent order require­ment to elim­i­nate CSOs to near­by bod­ies of water, CSO issues in West Hartford, and the prox­im­i­ty to the Hartford WPCF. She called it the “log­i­cal start­ing point.”

“This is where the plant is too, so the tun­nel ends at the plant,” Negrelli said. “So any­thing you’re going to build onto that, you can go fur­ther into the sys­tem as you may.”

According to Negrelli, the tun­nel project involved five con­struc­tion con­tracts that includ­ed relo­cat­ing util­i­ties, bor­ing under­ground to build the main tun­nel and shafts, build­ing a sta­tion to pump the waste to the sewage treat­ment plant, and cre­at­ing con­duits for more waste from the east and west.

The drilling for the tun­nel began in 2019 and was car­ried out with a “hard rock tun­nel bor­ing machine” built in Germany and known as ISIS. The drilling took three years, fin­ish­ing in 2022.

The pump sta­tion will pump the stored waste to the Hartford WPCF. Because the tun­nel runs slight­ly down­hill from West Hartford to this point, grav­i­ty will Negrelli said the pump sta­tion relies on grav­i­ty to get the water mov­ing up 200 feet to get treat­ed.

The con­duits are a series of pipes that will allow water to descend 200 feet from sewer sys­tems to the tun­nel with­out let­ting too much water pres­sure build.

Salemi said that the tun­nel will not become less use­ful as the MDC sep­a­rates com­bined sewer sys­tems through­out Hartford. He said that because the process will take a long time, and because excess rain­fall can be an issue regard­less of the sewer sys­tem, it will remain valu­able.

“It’s help­ful to deal with the storms, it’s not going to be we build it and then ‘Why did we build this, we don’t need it any­more,’” Salemi said. “It’s part of the sys­tem as the way to deal with it.”

Graham Stevens, Chief of the Bureau of Water Protection and Land Reuse at DEEP, believes the tun­nel is a valu­able short-term solu­tion, but does not solve the root of the prob­lem.

“Tunnels get real­ly com­pli­cat­ed, real­ly expen­sive, and ulti­mate­ly, although it’s a solu­tion to CSOs, you’re still not get­ting to the core issue, which is the fact that you’ve got one pipe,” Stevens said.

According to MDC tun­nel plans, the need to sep­a­rate sys­tems was taken into account while plan­ning CSO elim­i­na­tion in Hartford.

In the past, there were pro­pos­als for addi­tion­al tun­nel projects to help north­ern Hartford. But the MDC opted for sep­a­ra­tion instead, because a tun­nel would be logis­ti­cal­ly chal­leng­ing because of the dis­tance to the Hartford WPCF, would not refur­nish the out­dat­ed sewer sys­tems that still need replac­ing and could end up cost­ing more.

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TOP IMAGE: This illus­tra­tion from the Metropolitan District Commission’s plan­ning brochure shows the route of the waste tun­nel under­neath bedrock, head­ing slight­ly down­hill for 4 miles from West Hartford to near the sewage treat­ment plant in the South Meadows area of Hartford.