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So here's the situation. I've got a water main that is gravity fed from a spring into a cistern in my basement (and from there pumped to a pressure tank and the house). The main, black plastic and presumably either 1" or 1 1/4" HDPE is leaking somewhere very close to the stone foundation wall. I'm guessing that abrasion by movement of the stones over time or even during the initial installation by the previous owner maybe caused this. In any event, it's causing water to slowly seep through that section of the foundation and into my dirt basement.

Would like to avoid digging right near the stone foundation as well as disturbing the foundation in any way. That would be both costly and risky.

I've come up with what I think might be a decent plan - dig out farther away, maybe 20 feet from the foundation, and feed a new narrower pipe (with OD < ID of current pipe through the old one. This has the advantage of using the old one as a protective sleeve to prevent further damage. The disadvantage would be a slight decrease in pressure of the main, but because of the cistern I dont think this is a problem (probably why the cistern was used to begin with).

Here's a schematic main:

My questions are:

  1. good idea of bad idea?
  2. Do I use HDPE or PEX as the replacement material? Depending on the current pipe ID I may be forced to use PEX since it looks like HDPE is hard to find in narrow diameters.
  3. How to i make the best possible connection? I can't quite figure out the best way to join HDPE to PEX... would they both use similarly sized barb fittings and clamp rings? Would compression fittings be better?
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So after much thought I think this is a good idea. I've settled on using 1/2" PEX as the new line and SS cinch fittings on a standard PEX adapter should work. BUT, now I'm wondering... can this be done from the inside the house (without excavating) using some kind of barb that would keep the smaller OD tube fixed 20 feet up the wider tube? I'm thinking something like angioplasty for plumbing :) –  aaron Aug 6 at 2:27
    
Step one (which you haven't done, so far as I can tell) is to verify that "the pipe is leaking" rather than "groundwater is following the pipe though the wall." I'd bet a small sum that the pipe is just fine, if it's PE pipe as described and is at least 100PSI normal well-grade pipe - it takes some serious abuse to put a hole in that... –  Ecnerwal Aug 9 at 0:23
    
YES, that's absolutely true! I have not verified it for certain, but I'm not sure how to do that without excavating right near the foundation - something I am extremely reluctant to do. A couple things to note: 1) there is a 5' porch with roof protecting that entire side of the house with a slight grade away from the house, 2) when I wiggle the end of the pipe the drip increases (although slightly). Do you have any suggestions on how to verify either scenario? –  aaron Aug 9 at 1:31
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Plug the pipe at the spring end, and drain it. Or raise the inlet end above water level at the spring, if it's arranged so you can do that. If the leak stops, it was from the pipe. If the leak persists, it wasn't. I can tell you that you may have serious flow rate issues if you replace 1" pipe with 1/2" pipe - I have some 1/2" pipe I ran for an irrigation project that was a huge mistake (cheap to buy, flows poorly with limited pressure.) –  Ecnerwal Aug 9 at 1:34
    
Duh of course! Thanks for the suggestion. There's a valve at the spring end that I can close that makes this basically easy. –  aaron Aug 9 at 7:34

2 Answers 2

up vote 1 down vote accepted
+50

You should (as per comments) verify that the pipe is even leaking. If it's not, you can do all this work and still have water entering the basement. It may be a lot simpler ("slow leak") to simply arrange a nice ditch ("dirt basement") to direct the water to a convenient exit point.

You should make a serious effort to accurately measure the 2" long stub of this pipe you can see - You have described it as 1" or 1-1/4" and as 1" OD (which is not 1" PE well pipe - that has an ID of 1.049" from most makers.) It may be easier to examine at the spring end, if it's the same type of pipe all the way.

If you do have 1" pipe, you can use 3/4" PEX (0.875" OD), which would be far better than 1/2" PEX, even for 20 feet.

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Ah, that. It's 3/4", which means using 1/2" pex. What is your concern? My understanding was that the pressure drop would be pretty small (only ~5 psi assuming a 5 gym flow rate) and it's being pressurized up to > 40 psi by the jet pump anyway. Am I missing something? –  aaron Aug 9 at 7:51
    
Ah, but this is on the gravity flow section of the system, not the pressure-pipe side of the system. Depending how much or little gravity-provided pressure there is, reducing the pipe size may seriously impact the flow rate into the cistern. When the head differential (elevation of the spring relative to the cistern) is low, pipe size is going to affect flow rate (there being no pressure at the cistern, the "pressure loss" shows up as "dynamic head" impacting the flow rate.) Rather than assuming, measure the flow into the cistern now (use a watch with seconds and a bucket.) –  Ecnerwal Aug 9 at 13:50
    
Looks like it's around 6 gpm. There's still some uncertainty due mostly to my being able to actuate the float valve and stopwatch together quickly enough. It goes through an old gate valve immediately prior to the float valve, FYI. Thoughts? (BTW, I really appreciate the discussion!) –  aaron Aug 10 at 0:16

Overall, your plan to run PEX inside the HDPE and connecting them is acceptable.

However, I would not try to jury-rig fittings together. It sounds like you are trying to find a fitting designed for PEX that just happens to "fit" the HDPE, or vice-versa. This is a recipe for mechanical failure. After putting in all this work, the last thing you will want to do is dig it up again for another repair.

Instead I would find a plumbing supply house (not a big box store) and ask them about the proper fittings that are rated for direct burial, or the right way to bury a proper fitting.

You should seriously consider running PEX the entire way. How far are you from the spring? Running some steel cable down the HDPE first and then pulling the PEX all the way through may be a better fix.

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Thanks for your suggestions. I do plan on purchasing fittings from a real plumbing shop. The spring is a good 1/4 mile away... Which makes the full run difficult and costly. I think the pressure drop from using 1/2" pex would be prohibitive too. –  aaron Aug 6 at 3:03
    
1/4 mile? ya, way too far. But that makes me think of an improvement. If you can fit 2 of the 1/2 PEX lines through the HDPE, then you could use a T fitting: 1 inch HDPE in, 2 x 1/2 inch PEX out. –  longneck Aug 6 at 3:09
    
Hmm... I'm not sure I understand what you mean. Anyway, the hdpe is ~1" OD so there can't be much room inside. BTW, I'm assuming it's black hdpe "poly" pipe. Seems like a reasonable assumption, but is there reason to believe it might be something else? I don't see any distinctive markings on the 2" that are exposed... It couldn't be polybutylene could it? –  aaron Aug 6 at 3:20
    
I've personally never seen black polybutylene, but anything is possible. You're going to have to know for certain to get the right fittings. Can you cut off a piece and take it with you to the plumbing supply house? –  longneck Aug 6 at 14:16
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Like I said before: "After putting in all this work, the last thing you will want to do is dig it up again for another repair." Use fittings and clamps specifically designed to work with the pipes in question. This is not the part of the project to cheap out on. –  longneck Aug 6 at 17:58

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