Paula Wallis, TunnelTalk

A 3 mile bypass tunnel is part of a $2.1 billion upgrade of the Delaware Aqueduct, a vital component of New York City's drinking water supply system.

The Rondout-West Branch Tunnel section of the 85 mile Delaware Aqueduct, claimed as the longest continuous tunnel in the world, is leaking between 15 and 35 million gallons of water each day. The aqueduct was completed in 1944 and supplies about half of New York's drinking water (500 million gallons per day) from four upstate reservoirs. More than eight million people in New York City and one million people in neighboring counties have their water supplied via the aqueduct.

To address the leaking issues, the New York City Department of Environmental Protection (DEP) is proposing a bypass. The tunnel and internal repairs will cost about $1.2 billion, with an additional $900 million going to projects to supplement the City's water supply during construction.

The bypass tunnel will run 600ft to 800ft (183m to 284m) deep, east from a new shaft in the Town of Newburgh in Orange County, under the Hudson River, to a shaft on DEP property in the Town of Wappinger in Dutchess County on the east side of the Hudson (Figs 1 and 2). Preparation is currently under way for the repair work, including the installation of a pumping system and site improvements to support construction; purchase of equipment for the repair; planning and design of the bypass tunnel; and assessments of environmental impacts of the project. The DEP anticipates release of the draft environmental impact statement (EIS) by November 30 this year (2011). To date the City has invested about $493 million in preparation work for the eventual repair of the aqueduct. The Delaware Aqueduct varies in diameter from 13.5ft to 19.5ft (4m-5.9m) and runs as deep as 1,500ft (457m). Constructed by drill+blast, it is lined mostly with unreinforced concrete. In areas where the rock is not as strong, a steel reinforcement liner was added. Designed to last at least a century, the aqueduct's Rondout-West Branch developed leaks a few decades after its completion.

Table 1. Project cost estimate and schedule Phase Cost ($M) Schedule Bypass & Repair Design $40 Aug 2009 - May 2014 Property Acquisition $2 June 2010 - August 2012 Environmental Review Incl. in Design July 2010 - Apr 2012 Break Ground June 2013 Construction Management $84.5 Mar 2013 - Jan 2019 Shaft Construction $511 Mar 2013 - June 2016 Tunnel Repair & Bypass Tunnel Construction $552 Feb 2015 - Jan 2018 Connect Bypass Tunnel Incl. above Oct 2018 - Oct 2019 Wawarsing Tunnel Repair Incl. above Oct 2018 - Feb 2019 Total Cost $1.19B

Inspections have indicated that cracking and leakage is occurring in sections where the aqueduct passes through limestone, a rock more susceptible to weathering than the sandstone, shale, gneiss and granite that hosts the majority of the vital water supply line. The tunnel's concrete lining has cracked and is leaking along a 500ft (152m) section in the Wawaring area and along a 5,000ft (1,524m) stretch in Rosenton.

Groundbreaking on contract to build the bypass tunnel is planned by the DEP in 2013, with connection to the Delaware Aqueduct anticipated in 2019. Between 1,000 and 1,500 jobs are expected to be created by the major repair project.

DEP - Delaware Aqueduct Rondout-West Branch Tunnel Repair

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