Hartford Business Journal

www.HartfordBusiness.com November 2, 2015 • Hartford Business Journal 3 Continued I M A G E S | T H E M E T R O P O L I T A N D I S T R I C T $500M tunnel project aims to preserve CT River By John Stearns jstearns@HartfordBusiness.com C onstruction is expected to begin next year on a tunnel about four miles long, 18 feet in diameter and 200 feet deep underground that will carry stormwater and sewer overflows to the Hartford sewage facil- ity and help keep untreated water out of the Connecticut River. The $500 million South Hartford Convey- ance and Storage Tunnel will run from West Hartford to the Hartford Water Pollution Con- trol Facility on Brainard Road, and is a key piece of The Metropolitan District's 20-year Clean Water Project that aims to safeguard the future of the Connecticut River by clean- ing up discharges to streams and reducing oxygen-depleting nitrogen in the river, which ultimately flows to Long Island Sound. The tunnel's designer, Rocky Hill-based AECOM, called the project one of North America's largest wastewater storage and conveyance projects after it was awarded the design contract in 2011. "There's nothing else like it in Connecti- cut," said Nick Salemi, a spokesman at MDC. MDC has prequalified eight construction firms to bid on the project, Salemi said. A tunnel-boring machine will chew through shale, siltstone and basalt and travel through several inactive fault zones 175 to 250 feet below ground, according to MDC and a report on the project in Water Practice & Technology from IWA Publishing Online. As it moves along, the machine will simulta- neously lay sections of pipe to line the tun- nel while moving extracted material out of the tunnel via a conveyor belt. It's up to the contractor to determine where the excavated material will be trucked, Salemi said. The tunnel-boring machine will start at the Hartford treatment plant and cut slightly uphill to allow gravity to move the wastewater to the plant. The tunnel will end in a private West Hartford industrial area off Talcott Road, between Quaker Lane and New Park Avenue. MDC hopes to issue bids for the project soon and award the contract in the first quarter of 2016, with work beginning shortly thereafter. According to MDC's website, firms prequalified to bid on the project are: J.F. Shea Construction Inc. of Walnut, Calif.; Kenny Construction Co., Northbrook, Ill.; Kiewit Infrastructure Co., Omaha, Neb.; Obayashi Corp., Burlingame, Calif.; S.A. Healy Co., Henderson, Nev.; Salini Impregilo S.p.A., Henderson, Nev.; Skanska USA Civil Northeast Inc., Queens, N.Y.; and Traylor Bros. Inc., Alexandria, Va. Separate from the $500 million tunnel is a "wet weather expansion project" at the Hartford Water Pollution Control Facility. Already under way, that project will increase the plant's capacity to 200 million gallons per day, up from its current daily capacity of 130 million gallons to process the additional inflow from the tunnel, Salemi said. Wet weather threats Wet weather is a major driver of the tun- nel project. Areas of south Hartford have only one pipe that carries a combination of sewage and stormwater. So, with as little as 0.25 inches of rain, those singular pipes can become overwhelmed as stormwater surges in, resulting in "combined sewer overflows," or CSOs, into streets and homes, and dis- charges into streams and the Connecticut River. Those untreated discharges can hap- pen about 50 times a year, depending on weather, Salemi said. About 1 billion gallons of CSOs flow into the river annually, according to MDC. One pipe was fine for carrying sewage and stormwater when Hartford's population was much smaller, Salemi said. "Now, with a bigger population, when there's a big rain event, even not that big of a rain event, the stormwater takes up the capacity in the pipe," he said. "The combined stormwater and sewage — that's how you get backups or overflows." The massive tunnel will collect those CSOs from south Hartford and sanitary sew- age overflows, or SSOs, from West Hartford and Newington. Those towns have separate pipes for stormwater and sewage, but still experience capacity issues due to ground- water and stormwater infiltration into leaky pipes and from sump pumps and downspouts illegally connected into residential sewer lines that overwhelm the system during storms, Salemi said. In areas prone to overflows, consolidation conduits will collect the CSOs and serve as (Above top left) A tunnel-boring machine is expected to be used to dig the four-mile-long, roughly 200-foot-deep South Hartford Conveyance and Storage Tunnel. (Above bottom left) This graphic shows how the tunnel-boring machine will convey extracted rock (top of machine) on a conveyor out of the tunnel and also shows the pipe the machine will place behind it to line the tunnel. (Above right) This graphic shows the geology the tunnel-boring machine will encounter on its dig under south Hartford and West Hartford. The machine will bore through basalt, shale and siltstone and several inactive faults. ▶ ▶ The tunnel's designer, Rocky Hill-based AECOM, called the project one of North America's largest wastewater storage and conveyance projects. GREEN SOLUTIONS…ONE SOURCE Only one company can build, power, protect, and maintain the critical systems in virtually every type of facility. Our clients trust us to provide sustainable, more productive, greener facilities. 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