DIY Underground Leak Detection

[Fowl Play]

I’d definitely rule out everything else before paying for leak detection. Anyway to disconnect the upstream side of the pump to ensure the pump itself doesn’t have internal reverse leakage? Etc.

 

[carlc]

I have an underground water leak somewhere along a 100 yard underground line that's fed via irrigation pump. When the pump is on it continuously cycles because it fails to fully pressurize which is how I knew there was a leak. When I pressurize the line with air it goes from 80 psi to 40 psi in about 20 minutes so it's probably a pin hole size leak.

Anyone have any tips or techniques on how to find the spot to dig without getting a professional (expensive) leak detector service to come out, or having to dig up the entire line until I find it?

There is no sign of water or mushy ground anywhere so the leaked water is staying underground. The only thing the line serves is 2 above ground hydrants. Thanks

I didn't read all of the comments. What is keeping the pressure in the line at the irrigation pump when shut off? I would imagine a check valve near a pressure switch? I've seen the check valves get sediment in them, or some styles the rubber can get brittle and crack. Without an obvious wet or soft spot, it could just be backflowing. Throw a ball valve in on the downstream side of the check valve if possible.