WorldWide Drilling Resource

Taking Back Control of the Stormwater Compiled by Caleb Whitaker, Associate Editor WorldWide Drilling Resource ® The South Hartford Conveyance and Storage Tunnel is a four-mile-long deep rock tunnel being constructed in Connecticut, to convey and temporarily store wastewater from portions of Hartford and West Hartford. During major storms, rainwater overwhelms Hartford's drains and sewage treatment system - some sections of which are more than 150 years old. Stormwater connections like sump pumps, downspouts, and driveway drains, as well as cracks and open joints in the sewer pipes, allow stormwater to enter, where it mixes with raw sewage, filling the pipes beyond their capacity, causing sewer overflows. Contaminated water flows directly into streams and the Connecticut River. When those pollutants reach the Long Island Sound, they spur blooms of algae which create broad areas of oxygen-depleted “dead zones,” while bacteria washed into the Sound often forces beach closures. After nearly two years of blasting through bedrock with dynamite, the Metropolitan District boasted a significant construction mile- stone in the $2 billion Clean Water Project. A 400-foot-long tunnel boring machine was built to dig the 18-foot-diameter tunnel. The construction project consists of two tunnels, each requiring 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. This project will completely eliminate the com- bined sewer overflows into Wethersfield Cove and in the South Hartford area. The tunnel will have the capacity to hold about 42 million gallons of water. Kenny / Obayashi, a joint venture of Granite Construction subsidiaries Kenny Construction and Obayashi Corporation, won the contract for the tunnel project and decided to buy the Herrenknecht AG boring machine. An estimated 70 feet of boring will be completed each day, so the machine’s work should take a year to a year and a half. With the boring so deep underground, people shouldn’t be able to hear or feel the machine as it works. By the time the tunnel is completed in 2023, experts estimate 900,000 tons of tunnel muck will have been excavated. Most of the chipped rock is coming from bedrock 150-200 feet below street level, and is almost certain to be contamination-free. ! " # ! Photos courtesy of the Clean Water Project. C&G 39 WorldWide Drilling Resource ® MARCH 2019