NYC Sewer Question for Story

April 13, 2008 12:03 PM

How far below street level are the NYC Sewers? And by sewers, I mean the large tunnels that you see on TV and in the movies. What might be the minimum distance below someone's basement or cellar? Anyone have any ideas?
posted by vVCHAZVv to grab bag (18 comments total)

I don't have any NYC-specific knowledge but it must vary by quite a bit from one place to another, as they need to have a slope so that the direction in which the contents should flow is always downhill.
posted by winston at 12:06 PM on April 13, 2008

It varies, but there's usually a good amount of earth on top of any underground pipe/tunnel, so that the weight of stuff on the ground gets distributed through the dirt, and doesn't overload the pipe.

But, in almost all circumstances, the tunnels wouldn't run beneath anybody's house. Typically, there would be much smaller feeder lines that dump into the huge trunk lines that run underneath the streets.
posted by hwyengr at 12:13 PM on April 13, 2008

Thanks, Winston. I'm sure you're correct on that one. I should explain a little more here...

I'm working on a story and would like to include a sewer gag (no pun intended). I'm just looking for a reasonable minimum distance that a character can cite, without being completely wrong. Something to the effect of, "In some places in this city, the sewer tunnels are just X feet below your basement."

That kind of thing.
posted by vVCHAZVv at 12:15 PM on April 13, 2008

Thanks hwyengr. Would that include businesses? Say, perhaps, older buildings built around the turn of the century?
posted by vVCHAZVv at 12:16 PM on April 13, 2008

I'd assume so. It's a pretty rare instance for any building to erected on top of a utility like that. If it broke, or had to be replaced, it would be nearly impossible to repair.

The only exception could be if they were tunneling, like in subway constructing, but in that case they'd probably be 40-50' beneath. I don't know exactly how the NYC sewers were built or laid out, but pretty much if there's a grid street network on the surface, there's a grid sewer system underneath.
posted by hwyengr at 12:26 PM on April 13, 2008

1865 Sewer Map of Manhattan
posted by hwyengr at 12:29 PM on April 13, 2008 [1 favorite has favorites]

What if you could change it so that the character said something along the lines of "In some places in this city, the sewer is five feet out your front door, and three feet down" or something along those lines? Cos then all you'd have to do is find out the minimum of all sewers, not those under houses.

There's got to be a way of making that gag. And I want to read it when you're done. :)
posted by brina at 12:42 PM on April 13, 2008

According to this link, somewhere in the range between 30 to 200 ft? You can click the image for a scaled version.
posted by Teh Bean at 12:50 PM on April 13, 2008 [1 favorite has favorites]

The gargantuan Water Tunnel No. 3 is not a sewer, but it is an enormous water-filled tunnel underground. In places it is 800 ft underground. Strictly speaking, this does not answer your question as you are looking for a minimum, but it might be helpful for your story.
posted by grouse at 1:34 PM on April 13, 2008

According to Kate Ascher's "The Works: Anatomy of a City", sewer pipes in NYC are "generally buried more than 10 feet underground -- below the level of clean water pipes, so as to avoid any possible contamination if they leak".

The clean water pipes she refers to are the pipes used for distribution to buildings, not the giant tunnels used to carry water from upstate New York.
posted by plastic_animals at 1:51 PM on April 13, 2008

As mentioned above, the sewers in any municipality are in the street or nearly so. First, this makes it possible to work without destroying the building; secondly, this makes easement laws easier.

In St. Louis, a good rule of thumb is that the sewer in the street is gonna be deep enough that the crap can flow from the far end of the building adjoining it. So if the the far end of the building is say 120 feet away (40 feet from pipe to to building, and a big building can be 80 feet in length, easily), at 1/8" per foot slope (the code-approved minimum) and starting a foot below basement level, you've got (8 foot deep basement + 1 foot below basement floor + 15 feet of slope) 24 feet deep. That is a pretty good napkin figure; I regularly have to have my trenching crew dig 20 feet deep to connect to pipes.
posted by notsnot at 2:21 PM on April 13, 2008 [1 favorite has favorites]

I imagine this book would be right up your alley^H^H^Htunnel.
posted by namewithoutwords at 2:46 PM on April 13, 2008

In large sewer systems, you're actually going to have pumping stations where the 'flow' coming downhill is pumped back up to a higher level, so that gravity can continue its work without the pipes ending up hundreds of feet below ground. It's probably safe to say that most lines are only about 20-30 feet down, as mentioned above. Also, while those giant caverns you see in the movies do exist in a few places, most sewage lines are not big enough to drive a dump truck through.

I must say this question caused me to pull out my copy of Flushed: How the Plumber Saved Civilization. Great read!
posted by pupdog at 6:20 PM on April 13, 2008

Do you mean like the tunnels in Ghostbusters? No clue. They may not even actually exist.

I was in NYC on vacation a year or two back, and down near Wall Street they were doing some utility work. They had the street dug up to expose all the pipes and conduits below. It was fascinating- seemingly unending mass of infrastructure as far as I could see going down. It started about a foot and a half below grade.
posted by gjc at 7:28 PM on April 13, 2008

David MacCauley's book "Underground" might answer this.
posted by zippy at 7:43 PM on April 13, 2008

By "the large tunnels" I suspect you're thinking of the tunnels in, for instance, Die Hard 3 -- the Water Tunnel No. 3 mentioned above, which is a potable water feeder sourced from upstate and deep beneath the surface, where it is brought up under pressure by various pumping stations. Once it is activated, it is not accessible; in fact they're trying to figure out how to fix one of these feeders that's upstate, because draining it could lead to a collapse.

As for the sewers, that's going to vary considerably. Keep in mind that at the edges of Manhattan (and most of the edges of the other boroughs), you have water at essentially sea level. The World Trade Center basement is a big hollow concrete basin they labeled "the bathtub". If not continually pumped dry, it would flood. That's the reality not far under most of New York. Most of the old pier districts on both sides of Lower Manhattan, and especially the area around Battery Park, is unstable fill. By contrast, up in Washington Heights/Inwood, you have a subway station 140 feet straight down an elevator through bedrock.

On the other hand, not even Manhattan is remotely all flat. There's quite a bit of topography. The sewer map linked above should give you an idea of some of the rills and creekbeds that define the island. Those creeks no longer exist -- above ground. But they remain drainage channels for groundwater, and cause no end of trouble for all the underground infrastructure.

Anyway, I suspect the answer to your question is "just about as deep or shallow as you need for story purposes" ....
posted by dhartung at 11:05 PM on April 13, 2008

Yeah, that NYC aqueduct system is amazing.

Here in Chicago, they needed to fix a similar thing. It was an underwater tunnel/pipe (made of brick 100+ years ago) that went out on the bottom of the lake to suck in cleaner water for drinking. They made a big ass deal about what they were going to do to repair the thing, how scientific it all was, etc. Then they proceeded to pump out all the water and instantly crushed the tunnel.
posted by gjc at 7:59 AM on April 14, 2008

I remember in the book "Rats: Observations on the History and Habitat of the City's Most Unwanted Inhabitants," the author mentions that there are actually three layers of sewers underneath the city.
posted by blim8183 at 12:39 PM on April 29, 2008