Boring, A Tunnel

It kind of sucks that the largest, most expensive public works project in New York City history is unseen by most of us:

It is the biggest public works project in New York City’s history: a $6 billion water tunnel that has claimed 24 lives, endured under six mayors and survived three city fiscal crises, along with the falling and rising fortunes of the metropolis above it.

Yesterday, the city’s Water Tunnel No. 3 reached a major milestone, as workers completed the excavation of an 8.5-mile section that connects Midtown and Lower Manhattan to an earlier section under Central Park. The tunnel is a multi-decade effort spanning four stages; yesterday’s announcement signifies the end of excavation for the second of those stages.

It was a major step forward for the tunnel, which was authorized in 1954, begun in 1970 and then halted several times for lack of money. The completion of the second stage will nearly double the capacity of the city’s water supply, currently 1.2 billion gallons a day, and provide a backup to two other aging water tunnels, allowing them to be closed, inspected and repaired for the first time since they opened, in 1917 and 1936.

“Future generations of New Yorkers will have the clean and reliable supply of drinking water essential for our growing city,” Mayor Michael R. Bloomberg said, before he descended 550 feet into the city’s lower bedrock and sat at the controls of a 70-foot-long tunnel-boring machine, as it excavated the last eight inches of quartz, granite and silica.

Since 2003, the giant excavating machine’s 27 rotating steel cutters, each weighing 350 pounds, have chipped through the bedrock at a rate of 55 to 100 feet a day, more than double the 25 to 40 feet that could be excavated each day under the old drill-and-blast method.

For further discussion: “Tunnel Vision” (Popular Mechanics, April 2005).