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. Private companies and separate agencies control each element of the network. No single map of all of these interconnecting systems exists. Yet street workers will open and repair the streets at least 550 times a day. This is a potentially dangerous situation if workers don’t know what resides below.
The city is currently working toward a full map of the underground infrastructure using the Geographic Information System (GIS). The GIS is a computer system 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. There’s already a similar map for above-ground infrastructure, and the city’s Open Data Labs also produced a detailed street-related map. However, the city likely will not release the subterranean infrastructure version 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.
Bedrock
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.
This may give you high school earth science flashbacks. However, 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. They 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. Pressure from the constant flow creates enough upward pressure to send water up into ducts. They ducts rest 200 feet below the surface, and water then moves through vertical shafts up to 35 feet in diameter. Then, water goes to iron and steel pipes up to 7 feet in diameter that supply water to the service lines that run to individual homes and businesses. The water main sit three feet below the street. The city has almost 7,000 miles of water mains, and they run under nearly every street.
Sewer Lines
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, consisting of anything that goes down drain the toilet, and stormwater, which is rain and melting snow. About 60% of city sewers are combined sewer systems. 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… I remember one time…it looked like a catacomb.”
The Subway
New York City’s subway features around 450 miles of electrified underground track and 275 fully-underground train stations. It also includes 2000 track switches. The deepest station, at 180 feet below ground level, is the 191st Street stop on the 1 train. 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.
Gas Pipes
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. Then, it moves through 400,000 service pipes to either a generating station or an “area gas regulating station.” The stations reduce pressure for delivery to homes and businesses. Natural gas accounts for approximately 65% of the city’s heating and cooling.
Steam Pipes
New York City is home to the world’s largest and oldest steam system, which dates to 1882. Today, steam heats and cools many buildings in Manhattan. It also heats hot water for residents. 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.
Cable/Fiber
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.
Power
86% of New York City’s electricity comes via the subterranean 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 subterranean. Think about everything from near the surface to deep in the bedrock. There are 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. They make the city what it is and extend beyond the borders of the city. These complex systems make our daily conveniences dependent on distant places.
Editor’s Note: We updated this article to enhance readability.
