One of the largest and most expensive construction projects under way in New York State can’t be seen, and never will be seen, but it is essential to New York City’s health, well being and continued growth.

Related Links: Schemata of the Delaware Aqueduct Bypass (PDF)

If it were happening in a hospital, it would be called by- pass surgery; but in this case, the life-giving fluid is water and the artery is a 2-1⁄2 mile section of the Delaware Aqueduct running deep beneath the Hudson River.

The two major construction portions of the $1.2-billion bypass operation are being managed by Schiavone Construction Co. with the larger second phase, now ramping up, being done by Kiewit-Shea Constructor, a joint venture of Kiewit Construction Co. and J.F. Shea Co.

The operation’s immense technical challenges add to the pressure on contractors to ensure that the quality and quantity of the city’s renowned water supply remains intact.

The Delaware Aqueduct supplies about 60% of the roughly 1 billion gallons of water that New Yorkers use every day and is the more recent of the two aqueducts that move water down from six reservoirs in the Catskill Mountains about 100 miles northwest of the city. Work on the older aqueduct, the Catskill, began in 1907 with the first drop of water delivered to the city in 1915. The Delaware was built between 1939 and 1944.

The Delaware Aqueduct’s younger age means that it was able to use more modern drill-and-blast technology to create a tunnel that runs 85 miles from the Catskills under the Hudson River and then south through Putnam and Westchester counties before emptying into the Kensico Reservoir and into the Hillview Reservoir in Yonkers on the border with New York City.

The city has been monitoring leakage from the Delaware Aqueduct since the early 1990s. Residents in and around Wawarsing in the vicinity of the western end of the aqueduct complained of flooding basements, but it was difficult to make a direct connection to a leaking water tunnel.

Then in 1990 a utility worker for Central Hudson Gas & Electric noticed water bubbling up in a marshy area in Roseton on the western edge of the Hudson River during low tide. He knew that the aqueduct crossed under the river at that point and called the New York Dept. of Environmental Protection, the agency responsible for the city’s water supply.

At the time, DEP added copper sulfate to control algae growth in the water. When tests for trace amounts of the compound came back positive, the agency began to monitor the area and quickly learned that the most of the leak- age was coming from that section of the aqueduct.

Overall, between 15 million and 30 million gallons of water leaks from the aqueduct every day. On an average day the loss is at the low or middle end of that range, but it is still a lot of water.