The main water supply for the 8 million-plus people who live in New York City is delivered by two massive underground tunnels, both built in the early 20th century. Neither tunnel has been inspected or repaired since then.
Rather than risk a disastrous interruption of New York's water supply should the tunnels ever break down, city leaders decided to build a third tunnel to provide backup water delivery. That ambitious effort began 40 years ago and has evolved into the largest and most complex public works projects in the western hemisphere.
The tunnel is expected to be fully operational by 2020. A new water filtration plant, the first ever for the city of New York, is linked to the underground system.
City sandhogs blast and dig beneath streets
While life goes on normally above ground on city streets, 40 meters under the Van Cortlandt Park golf course in the Bronx, urban miners are on the job. These are the city sandhogs, the men who build the water, sanitation and transportation tunnels.
As he heads down the narrow mine shaft to work, "Walking Boss" Morgan Curran says crews had to excavate a cavernous staging area, then install an elevator, lay down railroad track, connect power cables and put in a pump to get out the muck as they blast and dig.
"We came through the wall of the pit, and we blasted our way here until we got enough room to make way for these tunnels that you see behind me, and then brought a [rock] boring machine in and did one side and then the other side."
Careful calculations go into drilling
The sandhogs are about halfway through the three-tunnel, four-year job. They work 24 hours a day, every day. Chris Smart is the project engineer and surveyor. He says his many calculations end up with a simple spray-painted cross on the wall.
"The guys drill that, and if they go left and right, each time we slowly adjust them. And we just slowly by slowly keep drilling and shooting [dynamite] until we break into the [connecting] tunnel."
In the end, the water pipes - each three to four meters in diameter - are cemented into place.
Observing the progress, Smart says New Yorkers will know they've done the job right, "when they turn on the tap and water comes out."
But that requires teamwork. A mistake could end up as a multimillion-dollar setback.
"Curran knows how to run the machines and crews. He knows the rock conditions. He knows how to drill and blast."
The tunnels adjoin the filtration plant construction site, an area bigger than two football fields side-by-side and nine stories deep. Trucks loaded with building materials circle the grounds as cranes lower supplies to the teams of workers in the massive pit. When construction is complete, the only structure above ground will be a small entrance building, and the golf course will be restored.
Crews hope history judges work kindly
Steven Lawitts, acting commissioner of the New York City Department of Environmental Protection, is charged with keeping New York's drinking water secure and available to 8 million people. His job also includes managing infrastructure projects like the filtration plant and Water Tunnel No. 3.
"The whole point of constructing Water Tunnel No. 3 and other redundant features is to prevent an unexpected leak and unexpected disaster from occurring," he says
It's his job, Lawitts says, "to ensure that it doesn't happen at all."
Smart says he uses technology that didn't exist 100 years ago. He marvels at the sophistication of work from that earlier era.
"We like the way it was built. I hope that within 100 years, the guys look at the work we've done, they say the same thing," Smart says.
Lawitts also hopes that history treats the project kindly "…[seeing] that was a sound decision to build a third water tunnel, to build a filtration plant, to fix the infrastructure and to clean the New York harbor."