Work has begun to start digging new water tunnel 600 feet under the Hudson River near Marlboro. The work was begun by New York City as it attempts to repair its aging system.

According to a report in the Times Herald Record, work begins Friday by New York City’s Department of Environmental Protection Agency. They are starting to work on a 2.5-mile bypass tunnel under the river. This tunnel is part of a project to fix leaks in the 85-mile-long Delaware Aqueduct. That aqueduct delivers about 500 million gallons of water a day to residents of New York City. The water comes from four different reservoirs in the Catskill Mountains.

This bypass will replace the leakiest portion of the current tunnel. How do crews dig a tunnel like that? They use a 470-foot-long tunnel boring machine that checks in at 2.7 million pounds. Teams have spent years digging two vertical shafts on either side of the river, which is located in Middle hope.