The City Under the City - Subterranean Network Underneath NYC
Millions of humans (and 600,000 dogs) walk the streets of New York City each day, oblivious to the massive subterranean network beneath their feet. This hidden infrastructure moves the city’s electricity, water, internet, wastewater, steam, and natural gas. Each element of the network is managed—and often owned—by a different city agency or private company. No single map of all of these interconnecting systems exists. And yet repairs that require streets to be opened are made an average of 550 times a day, a potentially dangerous situation if workers are missing data about what is below them.
The city is currently working toward a full map of the underground infrastructure using the Geographic Information System (GIS), a computer system used for organizing information related to the locations on the earth’s surface. New York City already has a base layer map, and various agencies and companies can create layers of data based on that map. A similar map for above-ground infrastructure can be explored here, and the city’s Open Data Labs have also created a detailed street-related map, but the subterranean infrastructure version will likely never be public due to security concerns.
While we can’t know exactly what’s below us at any given spot in the city, we can explore subterranean New York City from the deepest layer to the concrete and asphalt just below the soles of our shoes.
Deep under NYC lies bedrock, the solid rock below soil and sand that extends inward towards the earth’s core. Between one billion and 300 million years ago, tectonic plates collided, and volcanic ridges erupted, near what would become New York City, forming many of the distinctive rock formations and ridges of Manhattan and the Bronx. In many areas, this bedrock is visible or very near the surface, which is important as modern skyscrapers are anchored to the bedrock, and digging deep for bedrock is difficult and expensive.
Between 90,000 and 70,000 years ago the Wisconsin Glacier extended south over the city, and as it retreated it left a terminal moraine, a belt of rocks, silt, and debris, over the city, but particularly across Brooklyn and Queens. Indeed, the boroughs on Long Island would be underwater if not for the sediment left by the glacier, as their bedrock lies below sea level.
While all this may give you high school earth science flashbacks, it’s important for engineers to know and track as they build and maintain the city’s subterranean world. Information about both soil types and water levels is planned for the final subterranean infrastructure map.
The Water Tunnels and Water System
The deepest human-made element of the vast infrastructure below the city is the water tunnels, which carry the 981 million gallons of water used every day in New York City from the city’s 2,000 square mile watershed. The tunnels—the first of which was completed in 1917, the second in 1936, and the third of which is nearing completion in 2022—run through the bedrock between 1,110 feet and 520 feet below sea level. The force of gravity moves water through the tunnels, and the pressure from the constant flow creates enough upward pressure to send water up into ducts, 200 feet below the surface, and from there into the vertical shafts up to 35 feet in diameter which feed water mains, iron and steel pipes up to 7 feet in diameter that supply water to the service lines that run to individual homes and businesses. These are buried at a depth of only about three feet. The city has almost 7,000 miles of water mains, and they run under nearly every street.
Just about 100 feet below New York streets lies 7,000 feet of sewer lines. There are two types of water in NYC sewers: wastewater, which is anything put down the drain or flushed down the toilet, and stormwater, which is rain and melting snow. About 60% of city sewers are combined sewer systems, meaning the pipes carry both storm and wastewater directly to one of the 95 wastewater treatment plants. The look and structure of sewer pipes aren’t consistent across the system. In 2011, Luis Baerga, a long-serving sewer inspector, told The New York Times, “It depends on how it was built. Some of it was built elliptical. Some of it looks like pipe. Some of it is square. I remember one time…it looked like a catacomb.”
New York City’s subway features around 450 miles of electrified underground track and 275 fully-underground train stations, as well as 2000 track switches. The deepest station, at 180 feet below ground level, is the 191st Street stop on the 1 train—though many are much closer to the surface. The subway’s proximity to both sewer and water mains makes it vulnerable to breaks, which can cause flooding and shut down train service for the duration of the fix.
There are 6,302 miles of natural gas pipe underground in New York City, typically buried at a depth of fewer than thirty feet. Natural gas arrives in the city via interstate pipelines. It then goes into one of six “city gates” or metering stations, from which it’s piped through 400,000 service pipes to either a generating station or an “area gas regulating station,” where the pressure is reduced for delivery to homes and businesses. Approximately 65% of heating and cooking in the city is powered by natural gas, as is 98% of electricity produced by in-city power plants.
New York City is home to the world’s largest and oldest steam system, which dates to 1882. Today, many buildings in Manhattan are heated or cooled by steam, and steam is also used to make hot water. Hospitals use steam for disinfection, and museums use it to regulate humidity. There are 105 miles of steam pipes running underground from the city’s steam-generation plant in the Financial District to 96th Street on the Upper West Side and 89th Street on the Upper East Side. The pipes lie at depths between 10 and 30 feet below street level.
New York City’s internet, old-school telephone, and cable television arrive in homes and businesses via a network of over 50,000 miles of cabling just beneath the surface of New York Streets and sidewalks. Much of this cable—whether fiber, coaxial or lead-encased copper telephone cable—runs through conduit or disused pipes left in place.
86% of New York City’s electricity is distributed via the underground grid. About 130,000 miles of electrical lines run under the city, connecting the 16 lines that import electricity from outside the city to 24 transmission substations, 50 area substations, and then to residences and businesses. Occupying the same sub-street strata as cable and fiber, power is near the surface.
So the next time you and your pup head out for a walk, take a minute to pause and envision everything below you, from near the surface to deep in the bedrock: electrical lines, cable and fiber, steam pipes, gas pipes, the subway, sewer lines, water mains, water tunnels, and all the sedimentary rocks and soil deposited by the retreating glacier. The next time you light the stove, plug in your phone or take a shower, know that each of those resources—natural gas, electricity, and water—arrive in your apartment via a vast and complex system that both makes the city what it is and extends beyond the borders of the city, making our daily conveniences dependent on distant places.