Earlier this month, crews working more than 500 feet beneath New York’s streets broke through the final inches of rock for Water Tunnel No. 3, an 8.5-mile-long section of what is considered the biggest public works project in the city’s history.

The project, encompassing nearly 60 miles of storage and delivery tunnels, and costing an estimated $6 billion, was first authorized in 1954. Construction of stage one-a 13-mile-long tunnel that travels west from the Bronx into Upper Manhattan and into Central Park-began in 1970 and was completed in 1998. Water Tunnel No. 3 is part of stage two, connecting Midtown and Lower Manhattan to the earlier work under Central Park, which is scheduled to be completed in 2012.

According to city officials, completion of the entire project will nearly double the capacity of New York’s water supply, which is currently 1.2 billion gallons per day.