Underground Temperatures - Very Technical Question

[dfkrug]

I have many hundreds of feet of sched 40 PVC pressure lines, 1", 2", and
4". Most are buried only one foot as backfilling was all manual labor on a
50% slope. I have no doubts that the lines stay cool enough. I have
avoided any exposure of PVC to the air, due to UV deterioration and also
the rare freeze I might get in the winter. My 4" wharf fire hydrant is
reqd to have steel 4" riser, by fire dept requirement. My water system is
all gravity pressure (no pressure tank) and the water storage is 5000
gal concrete with plumbing underneath. I did find out that there are no
22.5-degree elbows made for 4" pipe (only 4" dwv PVC) and gluing up
20' 4" lines is a 2-person job....very tough! All pipes de-burred, cleaned,
primed before gluing.

Finally, if you are subject to inspection, you probably have to do a pressure
test. I had to convince the bldg dept to let me use air, since I could
not fill the pipes with water at the time. It took hours to fill the
pipes with air, but it is important to find/fix leaks BEFORE you backfill.

 

[Westonium]

Me? I went with 2" 200psi poly for my 600ft for a lot of reasons.

One concern you haven't mentioned is thermal shrinkage. I believe the formula is 100' of PVC will shrink (or lengthen) 1 inch for 50 degrees of temperature change. You have 700' of PVC. If the PVC has changed in temperature (cooled) 12.5 degrees, that 700' of PVC wants to be 698' .25". It should be a moot point because there is probably slack that was taken in when you filled the pipes with cold water before you backfilled (right?)

Honestly, I think you'd be hard pressed to make the pipes in your pump house 130 degrees or even 90 degrees. If you are concerned about the pipe temps in the well house, insulate them. I forgot to note your location, but you want to do that anywhere it freezes anyway (and maybe have heat wrap under the insulation). The rolls of fiberglass pipe insulation are dirt cheap. I put 2 good layers on and put both included vapor barrier layers on the outside.