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I'm currently in the process of digging a hole in my front yard to install a flag pole. The dimensions of the hole are 16" deep and 24" in diameter. Once I reached my 16" depth, I discovered my PVC sewer pipe that runs from my house to the street. There is no damage to the sewer pipe thankfully.

Can I pour the concrete over the PVC pipe without damaging it?

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    @jsotola if it were rephrased to "If not, what is the best practice to secure a flag pole without damaging sewer pipes underneath ?" it would definitely on-topic however...
    – zakinster
    Jun 14, 2021 at 8:09
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    Can you? Yes. Should you? No.
    – MonkeyZeus
    Jun 14, 2021 at 13:59
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    Obligatory mention that most major cities (and probably the minor ones) have a hotline to call before any sort of groundwork to have them come out and mark all of the pipe locations for free. It's always a good idea.
    – Sean Duggan
    Jun 14, 2021 at 14:45
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    @SeanDuggan, they will mark the incoming utility lines, but I've never seen them mark drain or sewer lines, at least in my area (Iowa, United States).
    – Milwrdfan
    Jun 14, 2021 at 15:55
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    @Milwrdfan: Hmm... I had one marked in my backyard, but I think that was, in part, because it was part of the neighborhood network. If it were a personal sewage line, you're right, that probably would not be noted. That said, I think it's worth rementioning because I've seen a lot of people start ground projects without checking, and either run into trouble, or narrowly avoid it.
    – Sean Duggan
    Jun 14, 2021 at 16:01

4 Answers 4

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Move the hole.

You know its in a bad place. If you break the pipe with your flag pole you will curse your own stupidity and hate the flag pole and that is how bad things start. If you do get away with it then someday in the future someone will try to remove the flagpole and break the concrete, and they will drive the concrete into the PVC and then track you down in the nursing home and hide your teeth for putting a flagpole on top of a PVC pipe.

No, leave the PVC in peace. Move the hole a ways to the side, clear of the pipe and try again. Be happy you did not dig into the pipe like I did recently planting a new little tree. What a mess.

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    Yes! Someone that knows by experience! Never knowingly place concrete fill and vertical pipe or fence posts of any material over drainage pipe. Even without others blunders later, ground settles, gravity affects weight and that flag pole is just a huge lever waiting to dislodge and break your PVC..
    – user113627
    Jun 14, 2021 at 3:46
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    Also planting invasive trees like willow. My parents did and after a few years its roots wrecked the drains, cracked them open and grew inside to get at the water. I gather grapevines will do this too.
    – RedSonja
    Jun 14, 2021 at 5:51
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    All plants try to get into sewer pipes and those that have deep enough roots invariably do. They crack the pipes open, no matter how innocent and vulnerable the plant looks above the surface and no matter what material the pipes are made of (well, stainless steel will probably stand for a while). Gas/electricity pipes are safe only for a while, a thick root will crack them even without the water stimulus. No trees, no vines and no bushes over the pipes, period.
    – fraxinus
    Jun 14, 2021 at 14:07
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    If you DO decide to move the hole, then it might be useful to leave a note in the old one when you fill it in. Fill it in half way, then put your note in a heavy duty ziplock bag "suspected sewer line 8" below this note" and put that in, then the rest of the soil. It might save the next guy some hassle if he wonders why you didn't put the flag in the 'best spot' and he wants to move it back.
    – Billy left SE for Codidact
    Jun 15, 2021 at 7:47
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    @JimmyJames big roots break plastic pipes just by growing.
    – fraxinus
    Jun 15, 2021 at 18:30
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Never, ever, mess with any pipe underground.

No matter if it is any kind of plastic, steel, brass, copper, ceramic, concrete, whatever.

No matter if it is used for sewer, water, gas, electricity, Internet connection or underground smuggling of rocket parts (it happens!) or vodka (it happens, as well).

Pipes sometimes break after a while even when left alone, just because the ground settles unevenly. A bulk of concrete is known to settle in a different fashion (it sinks as a whole) and to break pipes even not directly in contact with it. 20-40cm separation is probably OK-ish, but aim for a meter (3ft) if possible.

When a pipe breaks, you get a great deal of both annoyance and expenses.

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TL;DR

You shouldn't do that.

If for no other reason then consider this simple fact.

If that pole gets knocked over via wind or a rogue vehicle then the concrete will tilt and puncture a hole in the PVC. Now you have two problems.

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    Wow! We've reached "short attention span theatre" so intensely that we now need a TL;DR for a 3 sentence answer!! ;)
    – RockPaperLz- Mask it or Casket
    Jun 16, 2021 at 15:40
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    @RockPaperLz-MaskitorCasket I was planning to write more but ran out of gas and didn't feel like exerting additional effort to remove the TL;DR =D
    – MonkeyZeus
    Jun 16, 2021 at 15:42
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    You just earned yourself an upvote just for adding a smile to my face. :)
    – RockPaperLz- Mask it or Casket
    Jun 16, 2021 at 15:43
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I would move the flagpole to a different location so you do not disturb that PVC pipe. Also, I would contact the sewer company and ask how deep their piping is since most sewer piping is much deeper than 16". That PVC pipe may be for something else.

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    Where I live, incoming water pipes need to be under the freeze limit but sewer pipes not - they are not prone to freeze. On the other hand, they need the right slope. Some of my pipes are almost at the surface.
    – Peter Tölgyesi
    Jun 14, 2021 at 11:50
  • Depends on the sloping. I have seen some PVC drain lines that shallow because there was a slow drop to the street lines
    – Machavity
    Jun 14, 2021 at 17:01
  • I doubt there is a standard for septic lines, since they are designed to not run full and always drain. Although, good to check now that the pipe is exposed.
    – dougp
    Jun 16, 2021 at 23:41

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